Введение
Нейроанатомия – это раздел нейронауки, изучающий структуру и организацию нервной системы. В отличие от животных с радиальной симметрией, нервная система которых состоит из распределённой сети клеток, у животных с двусторонней симметрией нервная система чётко разделена и имеет определённую структуру. Поэтому их нейроанатомия изучена лучше. У позвоночных нервная система разделена на внутреннюю структуру мозга и спинного мозга (вместе называемую центральной нервной системой, или ЦНС) и систему нервов, соединяющих ЦНС с остальным телом (известную как периферическая нервная система, или ПНС). Разделение и идентификация конкретных частей нервной системы были критически важны для понимания принципов её работы. Например, значительная часть знаний нейробиологов получена благодаря наблюдению за тем, как повреждения или "очаги поражения" в определённых областях мозга влияют на поведение или другие нейронные функции. Информацию о строении нервной системы нечеловеческих животных можно найти в статье "Нервная система". Информацию о типичной структуре нервной системы человека (Homo sapiens) можно найти в статьях "Мозг человека" или "Периферическая нервная система". В данной статье рассматриваются сведения, относящиеся к изучению нейроанатомии.
Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems. Their neuroanatomy is therefore better understood. In vertebrates, the nervous system is segregated into the internal structure of the brain and spinal cord (together called the central nervous system, or CNS) and the series of nerves that connect the CNS to the rest of the body (known as the peripheral nervous system, or PNS). Breaking down and identifying specific parts of the nervous system has been crucial for figuring out how it operates. For example, much of what neuroscientists have learned comes from observing how damage or "lesions" to specific brain areas affects behavior or other neural functions. For information about the composition of non human animal nervous systems, see nervous system. For information about the typical structure of the Homo sapiens nervous system, see human brain or peripheral nervous system. This article discusses information pertinent to the study of neuroanatomy.
История
Первым известным письменным свидетельством изучения анатомии человеческого мозга является древнеегипетский документ – папирус Эдвина Смита. В Древней Греции интерес к мозгу зародился с работ Алкмаона, который, судя по всему, проводил вскрытия глаз и установил связь между мозгом и зрением. Он также предположил, что мозг, а не сердце, является органом, управляющим телом (то, что стоики называли гегемониконом), и что чувства зависят от мозга. Дебаты относительно гегемоникона продолжались среди древнегреческих философов и врачей на протяжении долгого времени. Сторонники теории о мозге часто вносили вклад в понимание нейроанатомии. Особенно влиятельными были Герофил и Эрасистрат Александрийский, чьи исследования, включавшие вскрытие человеческих мозгов, подтвердили различие между головным мозгом и мозжечком, а также позволили идентифицировать желудочки и твердую мозговую оболочку. Греческий врач и философ Гален также убедительно доказывал, что мозг отвечает за ощущения и произвольные движения, что подтверждалось его исследованиями нейроанатомии быков, варварских обезьян и других животных. Культурный запрет на вскрытие человеческих тел сохранялся еще несколько сотен лет, что препятствовало значительному прогрессу в понимании анатомии мозга и нервной системы. Однако папа Сикст IV фактически возродил изучение нейроанатомии, изменив папскую политику и разрешив вскрытие человеческих тел. Это привело к всплеску активности среди художников и ученых эпохи Возрождения, таких как Мондино де Луцци, Беренгарио да Карпи и Жак Дюбуа, кульминацией которой стала работа Андреаса Везалия. В 1664 году Томас Уиллис, врач и профессор Оксфордского университета, ввел термин «неврология», опубликовав свой труд «Анатомия мозга», который считается основой современной нейроанатомии. Последующие триста пятьдесят с лишним лет принесли огромное количество документации и исследований нервной системы.
Состав
На уровне тканей нервная система состоит из нейронов, глиальных клеток и внеклеточного матрикса. Как нейроны, так и глиальные клетки представлены множеством типов (см., например, раздел о нервной системе в списке различных типов клеток взрослого организма человека). Нейроны – это клетки, осуществляющие обработку информации в нервной системе: они воспринимают окружающую среду, общаются друг с другом посредством электрических сигналов и химических веществ, называемых нейротрансмиттерами, которые обычно действуют через синапсы (тесные контакты между двумя нейронами или между нейроном и мышечной клеткой; следует отметить, что возможны также экстрасинаптические эффекты, а также высвобождение нейротрансмиттеров в нейронное внеклеточное пространство), и обеспечивают формирование наших воспоминаний, мыслей и движений. Глиальные клетки поддерживают гомеостаз, производят миелин (олигодендроциты, клетки Швана) и обеспечивают поддержку и защиту нейронов мозга. Некоторые глиальные клетки (астроциты) способны даже распространять межклеточные волны кальция на большие расстояния в ответ на стимуляцию и высвобождать глиотрансмиттеры в ответ на изменения концентрации кальция. В мозговых рубцах в основном содержатся астроциты. Внеклеточный матрикс также обеспечивает поддержку клеток мозга на молекулярном уровне, осуществляя транспорт веществ к и от кровеносных сосудов. На уровне органов нервная система состоит из областей мозга, таких как гиппокамп у млекопитающих или грибные тельца у плодовой мухи. Эти области часто имеют модульную структуру и выполняют определенную роль в общих системных путях нервной системы. Например, гиппокамп играет ключевую роль в формировании памяти, взаимодействуя со многими другими областями мозга. Периферическая нервная система также содержит афферентные или эфферентные нервы – это пучки волокон, которые берут начало в головном и спинном мозге или в сенсорных и моторных периферических ганглиях и многократно ветвятся, чтобы иннервировать все части тела. Нервы состоят главным образом из аксонов или дендритов нейронов (аксонов в случае эфферентных моторных волокон и дендритов в случае афферентных сенсорных волокон нервов), а также из различных мембран, которые обертывают их и разделяют на нервные пучки (фасцикулы). Нервная система позвоночных делится на центральную и периферическую. Центральная нервная система (ЦНС) состоит из головного мозга, сетчатки и спинного мозга, а периферическая нервная система (ПНС) – из всех нервов и ганглиев (скоплений периферических нейронов), расположенных за пределами ЦНС и соединяющих ее с остальным телом. ПНС далее подразделяется на соматическую и автономную нервные системы. Соматическая нервная система состоит из "афферентных" нейронов, которые передают сенсорную информацию от соматических органов чувств (тела) в ЦНС, и "эфферентных" нейронов, которые передают двигательные команды к произвольным мышцам тела. Автономная нервная система может функционировать с или без контроля ЦНС (поэтому она называется "автономной"), и также имеет два подразделения – симпатическую и парасимпатическую, которые важны для передачи двигательных команд к основным внутренним органам, контролируя таким образом функции, такие как сердцебиение, дыхание, пищеварение и слюноотделение. Автономные нервы, в отличие от соматических, содержат только эфферентные волокна. Сенсорные сигналы, поступающие от внутренних органов, достигают ЦНС через соматические сенсорные нервы (например, висцеральная боль) или через некоторые черепные нервы (например, хемо- или механосенсорные сигналы).
Ориентация в нейроанатомии
В анатомии в целом и нейроанатомии в частности используется несколько наборов топографических терминов для обозначения ориентации и локализации, которые обычно соотносятся с осью тела или мозга (см. Анатомические термины локализации). Ось ЦНС часто ошибочно представляется более или менее прямой, но на самом деле она всегда демонстрирует два вентральных изгиба (шейный и цефалический изгибы) и один дорсальный изгиб (мостовой изгиб), что обусловлено дифференциальным ростом в процессе эмбриогенеза. Наиболее часто используемые пары терминов в нейроанатомии:
Dorsal and ventral: Dorsal refers more or less to the top or upper side of the brain, which is symbolized by the floor plate, and ventral to the bottom or lower side. These descriptors originally were used for dorsum and ventrum – back and belly – of the body; the belly of most animals is oriented towards the ground; the erect posture of humans places our ventral aspect anteriorly, and the dorsal aspect becomes posterior. The case of the head and the brain is peculiar, since the belly does not properly extend into the head, unless we assume that the mouth represents an extended belly element. Therefore, in common use, those brain parts that lie close to the base of the cranium, and through it to the mouth cavity, are called ventral – i. e., at its bottom or lower side, as defined above – whereas dorsal parts are closer to the enclosing cranial vault. Reference to the roof and floor plates of the brain is less prone to confusion, also allow us to keep an eye on the axial flexures mentioned above. Dorsal and ventral are thus relative terms in the brain, whose exact meaning depends on the specific location. Rostral and caudal: rostral refers in general anatomy to the front of the body (towards the nose, or rostrum in Latin), and caudal refers to the tail end of the body (towards the tail; cauda in Latin). The rostrocaudal dimension of the brain corresponds to its length axis, which runs across the cited flexures from the caudal tip of the spinal cord into a rostral end roughly at the optic chiasma. In the erect Man, the directional terms "superior" and "inferior" essentially refer to this rostrocaudal dimension, because our body and brain axes are roughly oriented vertically in the erect position. However, all vertebrates develop a very marked ventral kink in the neural tube that is still detectable in the adult central nervous system, known as the cephalic flexure. The latter bends the rostral part of the CNS at a 180 degree angle relative to the caudal part, at the transition between the forebrain (axis ending rostrally at the optic chiasma) and the brainstem and spinal cord (axis roughly vertical, but including additional minor kinks at the pontine and cervical flexures) These flexural changes in axial dimension are problematic when trying to describe relative position and sectioning planes in the brain. There is abundant literature that wrongly disregards the axial flexures and assumes a relatively straight brain axis. Medial and lateral: medial refers to being close, or relatively closer, to the midline (the descriptor median means a position precisely at the midline). Lateral is the opposite (a position more or less separated away from the midline). Note that such descriptors (dorsal/ventral, rostral/caudal; medial/lateral) are relative rather than absolute (e. g., a lateral structure may be said to lie medial to something else that lies even more laterally). Commonly used terms for planes of orientation or planes of section in neuroanatomy are "sagittal", "transverse" or "coronal", and "axial" or "horizontal". Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis. Due to the axial brain flexures, no section plane ever achieves a complete section series in a selected plane, because some sections inevitably result cut oblique or even perpendicular to it, as they pass through the flexures. Experience allows to discern the portions that result cut as desired. A mid sagittal plane divides the body and brain into left and right halves; sagittal sections, in general, are parallel to this median plane, moving along the medial lateral dimension (see the image above). The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin). A section plane orthogonal to the axis of any elongated form in principle is held to be transverse (e. g., a transverse section of a finger or of the vertebral column); if there is no length axis, there is no way to define such sections, or there are infinite possibilities. Therefore, transverse body sections in vertebrates are parallel to the ribs, which are orthogonal to the vertebral column, which represents the body axis both in animals and man. The brain also has an intrinsic longitudinal axis – that of the primordial elongated neural tube – which becomes largely vertical with the erect posture of Man, similarly as the body axis, except at its rostral end, as commented above. This explains that transverse spinal cord sections are roughly parallel to our ribs, or to the ground. However, this is only true for the spinal cord and the brainstem, since the forebrain end of the neural axis bends crook like during early morphogenesis into the chiasmatic hypothalamus, where it ends; the orientation of true transverse sections accordingly changes, and is no longer parallel to the ribs and ground, but perpendicular to them; lack of awareness of this morphologic brain peculiarity (present in all vertebrate brains without exceptions) has caused and still causes much erroneous thinking on forebrain brain parts. Acknowledging the singularity of rostral transverse sections, tradition has introduced a different descriptor for them, namely coronal sections. Coronal sections divide the forebrain from rostral (front) to caudal (back), forming a series orthogonal (transverse) to the local bent axis. The concept cannot be applied meaningfully to the brainstem and spinal cord, since there the coronal sections become horizontal to the axial dimension, being parallel to the axis. In any case, the concept of 'coronal' sections is less precise than that of 'transverse', since often coronal section planes are used which are not truly orthogonal to the rostral end of the brain axis. The term is etymologically related to the coronal suture of the craneum and this to the position where crowns are worn (Latin corona means crown). It is not clear what sort of crown was meant originally (maybe just a diadema), and this leads unfortunately to ambiguity in the section plane defined merely as coronal. A coronal plane across the human head and brain is modernly conceived to be parallel to the face (the plane in which a king's crown sits on his head is not exactly parallel to the face, and exportation of the concept to less frontally endowed animals than us is obviously even more conflictive, but there is an implicit reference to the coronal suture of the cranium, which forms between the frontal and temporal/parietal bones, giving a sort of diadema configuration which is roughly parallel to the face). Coronal section planes thus essentially refer only to the head and brain, where a diadema makes sense, and not to the neck and body below. Horizontal sections by definition are aligned (parallel) with the horizon. In swimming, creeping and quadrupedal animals the body axis itself is horizontal, and, thus, horizontal sections run along the length of the spinal cord, separating ventral from dorsal parts. Horizontal sections are orthogonal to both transverse and sagittal sections, and in theory, are parallel to the length axis. Due to the axial bend in the brain (forebrain), true horizontal sections in that region are orthogonal to coronal (transverse) sections (as is the horizon relative to the face). According to these considerations, the three directions of space are represented precisely by the sagittal, transverse and horizontal planes, whereas coronal sections can be transverse, oblique or horizontal, depending on how they relate to the brain axis and its incurvations.
Дорсальный и вентральный: дорсальный относится более или менее к верхней стороне мозга, символизируемой пластинкой пола, а вентральный – к нижней стороне. Изначально эти термины использовались для обозначения спины (дорсум) и живота (вентрум) тела; живот большинства животных ориентирован к земле; прямостоячая поза человека располагает наш вентральный аспект спереди, а дорсальный – сзади. Случай с головой и мозгом своеобразен, поскольку живот не простирается непосредственно в голову, если только мы не предположим, что рот представляет собой продолжение брюшной части. Поэтому в обычном употреблении части мозга, расположенные близко к основанию черепа и через него к полости рта, называют вентральными, то есть на его нижней стороне, как определено выше, в то время как дорсальные части находятся ближе к окружающему черепному своду. Обращение к крыше и пластинке пола мозга менее подвержено путанице и позволяет учитывать упомянутые выше осевые изгибы. Таким образом, дорсальный и вентральный – это относительные термины в мозге, точное значение которых зависит от конкретной локализации.
Dorsal and ventral: Dorsal refers more or less to the top or upper side of the brain, which is symbolized by the floor plate, and ventral to the bottom or lower side. These descriptors originally were used for dorsum and ventrum – back and belly – of the body; the belly of most animals is oriented towards the ground; the erect posture of humans places our ventral aspect anteriorly, and the dorsal aspect becomes posterior. The case of the head and the brain is peculiar, since the belly does not properly extend into the head, unless we assume that the mouth represents an extended belly element. Therefore, in common use, those brain parts that lie close to the base of the cranium, and through it to the mouth cavity, are called ventral – i. e., at its bottom or lower side, as defined above – whereas dorsal parts are closer to the enclosing cranial vault. Reference to the roof and floor plates of the brain is less prone to confusion, also allow us to keep an eye on the axial flexures mentioned above. Dorsal and ventral are thus relative terms in the brain, whose exact meaning depends on the specific location. Rostral and caudal: rostral refers in general anatomy to the front of the body (towards the nose, or rostrum in Latin), and caudal refers to the tail end of the body (towards the tail; cauda in Latin). The rostrocaudal dimension of the brain corresponds to its length axis, which runs across the cited flexures from the caudal tip of the spinal cord into a rostral end roughly at the optic chiasma. In the erect Man, the directional terms "superior" and "inferior" essentially refer to this rostrocaudal dimension, because our body and brain axes are roughly oriented vertically in the erect position. However, all vertebrates develop a very marked ventral kink in the neural tube that is still detectable in the adult central nervous system, known as the cephalic flexure. The latter bends the rostral part of the CNS at a 180 degree angle relative to the caudal part, at the transition between the forebrain (axis ending rostrally at the optic chiasma) and the brainstem and spinal cord (axis roughly vertical, but including additional minor kinks at the pontine and cervical flexures) These flexural changes in axial dimension are problematic when trying to describe relative position and sectioning planes in the brain. There is abundant literature that wrongly disregards the axial flexures and assumes a relatively straight brain axis. Medial and lateral: medial refers to being close, or relatively closer, to the midline (the descriptor median means a position precisely at the midline). Lateral is the opposite (a position more or less separated away from the midline). Note that such descriptors (dorsal/ventral, rostral/caudal; medial/lateral) are relative rather than absolute (e. g., a lateral structure may be said to lie medial to something else that lies even more laterally). Commonly used terms for planes of orientation or planes of section in neuroanatomy are "sagittal", "transverse" or "coronal", and "axial" or "horizontal". Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis. Due to the axial brain flexures, no section plane ever achieves a complete section series in a selected plane, because some sections inevitably result cut oblique or even perpendicular to it, as they pass through the flexures. Experience allows to discern the portions that result cut as desired. A mid sagittal plane divides the body and brain into left and right halves; sagittal sections, in general, are parallel to this median plane, moving along the medial lateral dimension (see the image above). The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin). A section plane orthogonal to the axis of any elongated form in principle is held to be transverse (e. g., a transverse section of a finger or of the vertebral column); if there is no length axis, there is no way to define such sections, or there are infinite possibilities. Therefore, transverse body sections in vertebrates are parallel to the ribs, which are orthogonal to the vertebral column, which represents the body axis both in animals and man. The brain also has an intrinsic longitudinal axis – that of the primordial elongated neural tube – which becomes largely vertical with the erect posture of Man, similarly as the body axis, except at its rostral end, as commented above. This explains that transverse spinal cord sections are roughly parallel to our ribs, or to the ground. However, this is only true for the spinal cord and the brainstem, since the forebrain end of the neural axis bends crook like during early morphogenesis into the chiasmatic hypothalamus, where it ends; the orientation of true transverse sections accordingly changes, and is no longer parallel to the ribs and ground, but perpendicular to them; lack of awareness of this morphologic brain peculiarity (present in all vertebrate brains without exceptions) has caused and still causes much erroneous thinking on forebrain brain parts. Acknowledging the singularity of rostral transverse sections, tradition has introduced a different descriptor for them, namely coronal sections. Coronal sections divide the forebrain from rostral (front) to caudal (back), forming a series orthogonal (transverse) to the local bent axis. The concept cannot be applied meaningfully to the brainstem and spinal cord, since there the coronal sections become horizontal to the axial dimension, being parallel to the axis. In any case, the concept of 'coronal' sections is less precise than that of 'transverse', since often coronal section planes are used which are not truly orthogonal to the rostral end of the brain axis. The term is etymologically related to the coronal suture of the craneum and this to the position where crowns are worn (Latin corona means crown). It is not clear what sort of crown was meant originally (maybe just a diadema), and this leads unfortunately to ambiguity in the section plane defined merely as coronal. A coronal plane across the human head and brain is modernly conceived to be parallel to the face (the plane in which a king's crown sits on his head is not exactly parallel to the face, and exportation of the concept to less frontally endowed animals than us is obviously even more conflictive, but there is an implicit reference to the coronal suture of the cranium, which forms between the frontal and temporal/parietal bones, giving a sort of diadema configuration which is roughly parallel to the face). Coronal section planes thus essentially refer only to the head and brain, where a diadema makes sense, and not to the neck and body below. Horizontal sections by definition are aligned (parallel) with the horizon. In swimming, creeping and quadrupedal animals the body axis itself is horizontal, and, thus, horizontal sections run along the length of the spinal cord, separating ventral from dorsal parts. Horizontal sections are orthogonal to both transverse and sagittal sections, and in theory, are parallel to the length axis. Due to the axial bend in the brain (forebrain), true horizontal sections in that region are orthogonal to coronal (transverse) sections (as is the horizon relative to the face). According to these considerations, the three directions of space are represented precisely by the sagittal, transverse and horizontal planes, whereas coronal sections can be transverse, oblique or horizontal, depending on how they relate to the brain axis and its incurvations.
Ростральный и каудальный: ростральный в общей анатомии относится к передней части тела (к носу или роструму на латыни), а каудальный – к хвостовому концу тела (к хвосту; cauda на латыни). Рострокаудальное измерение мозга соответствует его продольной оси, которая проходит через указанные изгибы от каудального конца спинного мозга к ростральному концу примерно в области зрительного перекреста. У прямоходящего человека направленные термины «верхний» и «нижний» по сути относятся к этому рострокаудальному измерению, поскольку оси нашего тела и мозга ориентированы примерно вертикально в вертикальном положении. Однако у всех позвоночных развивается выраженный вентральный изгиб в нервной трубке, который все еще обнаруживается в центральной нервной системе взрослого человека, известный как цефалический изгиб. Последний изгибает ростральную часть ЦНС под углом 180 градусов относительно каудальной части, на переходе между передним мозгом (ось, заканчивающаяся рострально в области зрительного перекреста) и стволом мозга и спинным мозгом (ось примерно вертикальная, но включающая дополнительные незначительные изгибы в мостовых и шейных изгибах). Эти изгибательные изменения в продольном измерении создают проблемы при попытке описать относительное положение и плоскости сечения в мозге. Существует множество литературы, которая ошибочно игнорирует осевые изгибы и предполагает относительно прямую ось мозга.
Dorsal and ventral: Dorsal refers more or less to the top or upper side of the brain, which is symbolized by the floor plate, and ventral to the bottom or lower side. These descriptors originally were used for dorsum and ventrum – back and belly – of the body; the belly of most animals is oriented towards the ground; the erect posture of humans places our ventral aspect anteriorly, and the dorsal aspect becomes posterior. The case of the head and the brain is peculiar, since the belly does not properly extend into the head, unless we assume that the mouth represents an extended belly element. Therefore, in common use, those brain parts that lie close to the base of the cranium, and through it to the mouth cavity, are called ventral – i. e., at its bottom or lower side, as defined above – whereas dorsal parts are closer to the enclosing cranial vault. Reference to the roof and floor plates of the brain is less prone to confusion, also allow us to keep an eye on the axial flexures mentioned above. Dorsal and ventral are thus relative terms in the brain, whose exact meaning depends on the specific location. Rostral and caudal: rostral refers in general anatomy to the front of the body (towards the nose, or rostrum in Latin), and caudal refers to the tail end of the body (towards the tail; cauda in Latin). The rostrocaudal dimension of the brain corresponds to its length axis, which runs across the cited flexures from the caudal tip of the spinal cord into a rostral end roughly at the optic chiasma. In the erect Man, the directional terms "superior" and "inferior" essentially refer to this rostrocaudal dimension, because our body and brain axes are roughly oriented vertically in the erect position. However, all vertebrates develop a very marked ventral kink in the neural tube that is still detectable in the adult central nervous system, known as the cephalic flexure. The latter bends the rostral part of the CNS at a 180 degree angle relative to the caudal part, at the transition between the forebrain (axis ending rostrally at the optic chiasma) and the brainstem and spinal cord (axis roughly vertical, but including additional minor kinks at the pontine and cervical flexures) These flexural changes in axial dimension are problematic when trying to describe relative position and sectioning planes in the brain. There is abundant literature that wrongly disregards the axial flexures and assumes a relatively straight brain axis. Medial and lateral: medial refers to being close, or relatively closer, to the midline (the descriptor median means a position precisely at the midline). Lateral is the opposite (a position more or less separated away from the midline). Note that such descriptors (dorsal/ventral, rostral/caudal; medial/lateral) are relative rather than absolute (e. g., a lateral structure may be said to lie medial to something else that lies even more laterally). Commonly used terms for planes of orientation or planes of section in neuroanatomy are "sagittal", "transverse" or "coronal", and "axial" or "horizontal". Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis. Due to the axial brain flexures, no section plane ever achieves a complete section series in a selected plane, because some sections inevitably result cut oblique or even perpendicular to it, as they pass through the flexures. Experience allows to discern the portions that result cut as desired. A mid sagittal plane divides the body and brain into left and right halves; sagittal sections, in general, are parallel to this median plane, moving along the medial lateral dimension (see the image above). The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin). A section plane orthogonal to the axis of any elongated form in principle is held to be transverse (e. g., a transverse section of a finger or of the vertebral column); if there is no length axis, there is no way to define such sections, or there are infinite possibilities. Therefore, transverse body sections in vertebrates are parallel to the ribs, which are orthogonal to the vertebral column, which represents the body axis both in animals and man. The brain also has an intrinsic longitudinal axis – that of the primordial elongated neural tube – which becomes largely vertical with the erect posture of Man, similarly as the body axis, except at its rostral end, as commented above. This explains that transverse spinal cord sections are roughly parallel to our ribs, or to the ground. However, this is only true for the spinal cord and the brainstem, since the forebrain end of the neural axis bends crook like during early morphogenesis into the chiasmatic hypothalamus, where it ends; the orientation of true transverse sections accordingly changes, and is no longer parallel to the ribs and ground, but perpendicular to them; lack of awareness of this morphologic brain peculiarity (present in all vertebrate brains without exceptions) has caused and still causes much erroneous thinking on forebrain brain parts. Acknowledging the singularity of rostral transverse sections, tradition has introduced a different descriptor for them, namely coronal sections. Coronal sections divide the forebrain from rostral (front) to caudal (back), forming a series orthogonal (transverse) to the local bent axis. The concept cannot be applied meaningfully to the brainstem and spinal cord, since there the coronal sections become horizontal to the axial dimension, being parallel to the axis. In any case, the concept of 'coronal' sections is less precise than that of 'transverse', since often coronal section planes are used which are not truly orthogonal to the rostral end of the brain axis. The term is etymologically related to the coronal suture of the craneum and this to the position where crowns are worn (Latin corona means crown). It is not clear what sort of crown was meant originally (maybe just a diadema), and this leads unfortunately to ambiguity in the section plane defined merely as coronal. A coronal plane across the human head and brain is modernly conceived to be parallel to the face (the plane in which a king's crown sits on his head is not exactly parallel to the face, and exportation of the concept to less frontally endowed animals than us is obviously even more conflictive, but there is an implicit reference to the coronal suture of the cranium, which forms between the frontal and temporal/parietal bones, giving a sort of diadema configuration which is roughly parallel to the face). Coronal section planes thus essentially refer only to the head and brain, where a diadema makes sense, and not to the neck and body below. Horizontal sections by definition are aligned (parallel) with the horizon. In swimming, creeping and quadrupedal animals the body axis itself is horizontal, and, thus, horizontal sections run along the length of the spinal cord, separating ventral from dorsal parts. Horizontal sections are orthogonal to both transverse and sagittal sections, and in theory, are parallel to the length axis. Due to the axial bend in the brain (forebrain), true horizontal sections in that region are orthogonal to coronal (transverse) sections (as is the horizon relative to the face). According to these considerations, the three directions of space are represented precisely by the sagittal, transverse and horizontal planes, whereas coronal sections can be transverse, oblique or horizontal, depending on how they relate to the brain axis and its incurvations.
Медиальный и латеральный: медиальный относится к близости или относительной близости к срединной линии (термин медиана означает положение точно на срединной линии). Латеральный – это противоположность (положение, более или менее удаленное от срединной линии). Следует отметить, что такие дескрипторы (дорсальный/вентральный, ростральный/каудальный; медиальный/латеральный) являются относительными, а не абсолютными (например, о латеральной структуре можно сказать, что она лежит медиально к чему-то другому, что лежит еще более латерально). Обычно используемые термины для плоскостей ориентации или плоскостей сечения в нейроанатомии – «сагиттальная», «поперечная» или «корональная» и «осевая» или «горизонтальная». И в этом случае ситуация отличается у плавающих, ползающих или четвероногих (прональных) животных, чем у человека или других прямоходящих видов из-за изменения положения оси. Из-за осевых изгибов мозга ни одна плоскость сечения никогда не обеспечивает полную серию сечений в выбранной плоскости, поскольку некоторые сечения неизбежно оказываются скошенными или даже перпендикулярными ей при прохождении через изгибы. Опыт позволяет различать участки, которые в результате разрезаются по желанию.
Dorsal and ventral: Dorsal refers more or less to the top or upper side of the brain, which is symbolized by the floor plate, and ventral to the bottom or lower side. These descriptors originally were used for dorsum and ventrum – back and belly – of the body; the belly of most animals is oriented towards the ground; the erect posture of humans places our ventral aspect anteriorly, and the dorsal aspect becomes posterior. The case of the head and the brain is peculiar, since the belly does not properly extend into the head, unless we assume that the mouth represents an extended belly element. Therefore, in common use, those brain parts that lie close to the base of the cranium, and through it to the mouth cavity, are called ventral – i. e., at its bottom or lower side, as defined above – whereas dorsal parts are closer to the enclosing cranial vault. Reference to the roof and floor plates of the brain is less prone to confusion, also allow us to keep an eye on the axial flexures mentioned above. Dorsal and ventral are thus relative terms in the brain, whose exact meaning depends on the specific location. Rostral and caudal: rostral refers in general anatomy to the front of the body (towards the nose, or rostrum in Latin), and caudal refers to the tail end of the body (towards the tail; cauda in Latin). The rostrocaudal dimension of the brain corresponds to its length axis, which runs across the cited flexures from the caudal tip of the spinal cord into a rostral end roughly at the optic chiasma. In the erect Man, the directional terms "superior" and "inferior" essentially refer to this rostrocaudal dimension, because our body and brain axes are roughly oriented vertically in the erect position. However, all vertebrates develop a very marked ventral kink in the neural tube that is still detectable in the adult central nervous system, known as the cephalic flexure. The latter bends the rostral part of the CNS at a 180 degree angle relative to the caudal part, at the transition between the forebrain (axis ending rostrally at the optic chiasma) and the brainstem and spinal cord (axis roughly vertical, but including additional minor kinks at the pontine and cervical flexures) These flexural changes in axial dimension are problematic when trying to describe relative position and sectioning planes in the brain. There is abundant literature that wrongly disregards the axial flexures and assumes a relatively straight brain axis. Medial and lateral: medial refers to being close, or relatively closer, to the midline (the descriptor median means a position precisely at the midline). Lateral is the opposite (a position more or less separated away from the midline). Note that such descriptors (dorsal/ventral, rostral/caudal; medial/lateral) are relative rather than absolute (e. g., a lateral structure may be said to lie medial to something else that lies even more laterally). Commonly used terms for planes of orientation or planes of section in neuroanatomy are "sagittal", "transverse" or "coronal", and "axial" or "horizontal". Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis. Due to the axial brain flexures, no section plane ever achieves a complete section series in a selected plane, because some sections inevitably result cut oblique or even perpendicular to it, as they pass through the flexures. Experience allows to discern the portions that result cut as desired. A mid sagittal plane divides the body and brain into left and right halves; sagittal sections, in general, are parallel to this median plane, moving along the medial lateral dimension (see the image above). The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin). A section plane orthogonal to the axis of any elongated form in principle is held to be transverse (e. g., a transverse section of a finger or of the vertebral column); if there is no length axis, there is no way to define such sections, or there are infinite possibilities. Therefore, transverse body sections in vertebrates are parallel to the ribs, which are orthogonal to the vertebral column, which represents the body axis both in animals and man. The brain also has an intrinsic longitudinal axis – that of the primordial elongated neural tube – which becomes largely vertical with the erect posture of Man, similarly as the body axis, except at its rostral end, as commented above. This explains that transverse spinal cord sections are roughly parallel to our ribs, or to the ground. However, this is only true for the spinal cord and the brainstem, since the forebrain end of the neural axis bends crook like during early morphogenesis into the chiasmatic hypothalamus, where it ends; the orientation of true transverse sections accordingly changes, and is no longer parallel to the ribs and ground, but perpendicular to them; lack of awareness of this morphologic brain peculiarity (present in all vertebrate brains without exceptions) has caused and still causes much erroneous thinking on forebrain brain parts. Acknowledging the singularity of rostral transverse sections, tradition has introduced a different descriptor for them, namely coronal sections. Coronal sections divide the forebrain from rostral (front) to caudal (back), forming a series orthogonal (transverse) to the local bent axis. The concept cannot be applied meaningfully to the brainstem and spinal cord, since there the coronal sections become horizontal to the axial dimension, being parallel to the axis. In any case, the concept of 'coronal' sections is less precise than that of 'transverse', since often coronal section planes are used which are not truly orthogonal to the rostral end of the brain axis. The term is etymologically related to the coronal suture of the craneum and this to the position where crowns are worn (Latin corona means crown). It is not clear what sort of crown was meant originally (maybe just a diadema), and this leads unfortunately to ambiguity in the section plane defined merely as coronal. A coronal plane across the human head and brain is modernly conceived to be parallel to the face (the plane in which a king's crown sits on his head is not exactly parallel to the face, and exportation of the concept to less frontally endowed animals than us is obviously even more conflictive, but there is an implicit reference to the coronal suture of the cranium, which forms between the frontal and temporal/parietal bones, giving a sort of diadema configuration which is roughly parallel to the face). Coronal section planes thus essentially refer only to the head and brain, where a diadema makes sense, and not to the neck and body below. Horizontal sections by definition are aligned (parallel) with the horizon. In swimming, creeping and quadrupedal animals the body axis itself is horizontal, and, thus, horizontal sections run along the length of the spinal cord, separating ventral from dorsal parts. Horizontal sections are orthogonal to both transverse and sagittal sections, and in theory, are parallel to the length axis. Due to the axial bend in the brain (forebrain), true horizontal sections in that region are orthogonal to coronal (transverse) sections (as is the horizon relative to the face). According to these considerations, the three directions of space are represented precisely by the sagittal, transverse and horizontal planes, whereas coronal sections can be transverse, oblique or horizontal, depending on how they relate to the brain axis and its incurvations.
Средняя сагиттальная плоскость разделяет тело и мозг на левую и правую половины; сагиттальные сечения, как правило, параллельны этой срединной плоскости и проходят вдоль медиолатерального измерения (см. изображение выше). Термин «сагиттальный» этимологически относится к срединному шву между правой и левой теменными костями черепа, классически известному как сагиттальный шов, поскольку он напоминает стрелу своим слиянием с другими швами (sagitta; стрела на латыни). Плоскость сечения, ортогональная оси любой удлиненной формы, в принципе считается поперечной (например, поперечное сечение пальца или позвоночного столба); если нет оси длины, невозможно определить такие сечения или существует бесконечное количество возможностей. Поэтому поперечные сечения тела у позвоночных параллельны ребрам, которые ортогональны позвоночнику, представляющему собой ось тела как у животных, так и у человека. Мозг также имеет собственную продольную ось – ось первичной удлиненной нервной трубки – которая становится в основном вертикальной в вертикальной позе человека, подобно оси тела, за исключением ее рострального конца, как отмечалось выше. Это объясняет, почему поперечные сечения спинного мозга примерно параллельны нашим ребрам или земле. Однако это справедливо только для спинного мозга и ствола мозга, поскольку передний конец оси нервной трубки изгибается, как крюк, во время ранней морфогенеза в перекрест гипоталамуса, где он заканчивается; ориентация истинных поперечных сечений соответственно меняется и больше не параллельна ребрам и земле, а перпендикулярна им; отсутствие осведомленности об этой морфологической особенности мозга (присутствующей во всех мозгах позвоночных без исключения) вызывало и продолжает вызывать множество ошибочных представлений о частях переднего мозга.
Dorsal and ventral: Dorsal refers more or less to the top or upper side of the brain, which is symbolized by the floor plate, and ventral to the bottom or lower side. These descriptors originally were used for dorsum and ventrum – back and belly – of the body; the belly of most animals is oriented towards the ground; the erect posture of humans places our ventral aspect anteriorly, and the dorsal aspect becomes posterior. The case of the head and the brain is peculiar, since the belly does not properly extend into the head, unless we assume that the mouth represents an extended belly element. Therefore, in common use, those brain parts that lie close to the base of the cranium, and through it to the mouth cavity, are called ventral – i. e., at its bottom or lower side, as defined above – whereas dorsal parts are closer to the enclosing cranial vault. Reference to the roof and floor plates of the brain is less prone to confusion, also allow us to keep an eye on the axial flexures mentioned above. Dorsal and ventral are thus relative terms in the brain, whose exact meaning depends on the specific location. Rostral and caudal: rostral refers in general anatomy to the front of the body (towards the nose, or rostrum in Latin), and caudal refers to the tail end of the body (towards the tail; cauda in Latin). The rostrocaudal dimension of the brain corresponds to its length axis, which runs across the cited flexures from the caudal tip of the spinal cord into a rostral end roughly at the optic chiasma. In the erect Man, the directional terms "superior" and "inferior" essentially refer to this rostrocaudal dimension, because our body and brain axes are roughly oriented vertically in the erect position. However, all vertebrates develop a very marked ventral kink in the neural tube that is still detectable in the adult central nervous system, known as the cephalic flexure. The latter bends the rostral part of the CNS at a 180 degree angle relative to the caudal part, at the transition between the forebrain (axis ending rostrally at the optic chiasma) and the brainstem and spinal cord (axis roughly vertical, but including additional minor kinks at the pontine and cervical flexures) These flexural changes in axial dimension are problematic when trying to describe relative position and sectioning planes in the brain. There is abundant literature that wrongly disregards the axial flexures and assumes a relatively straight brain axis. Medial and lateral: medial refers to being close, or relatively closer, to the midline (the descriptor median means a position precisely at the midline). Lateral is the opposite (a position more or less separated away from the midline). Note that such descriptors (dorsal/ventral, rostral/caudal; medial/lateral) are relative rather than absolute (e. g., a lateral structure may be said to lie medial to something else that lies even more laterally). Commonly used terms for planes of orientation or planes of section in neuroanatomy are "sagittal", "transverse" or "coronal", and "axial" or "horizontal". Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis. Due to the axial brain flexures, no section plane ever achieves a complete section series in a selected plane, because some sections inevitably result cut oblique or even perpendicular to it, as they pass through the flexures. Experience allows to discern the portions that result cut as desired. A mid sagittal plane divides the body and brain into left and right halves; sagittal sections, in general, are parallel to this median plane, moving along the medial lateral dimension (see the image above). The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin). A section plane orthogonal to the axis of any elongated form in principle is held to be transverse (e. g., a transverse section of a finger or of the vertebral column); if there is no length axis, there is no way to define such sections, or there are infinite possibilities. Therefore, transverse body sections in vertebrates are parallel to the ribs, which are orthogonal to the vertebral column, which represents the body axis both in animals and man. The brain also has an intrinsic longitudinal axis – that of the primordial elongated neural tube – which becomes largely vertical with the erect posture of Man, similarly as the body axis, except at its rostral end, as commented above. This explains that transverse spinal cord sections are roughly parallel to our ribs, or to the ground. However, this is only true for the spinal cord and the brainstem, since the forebrain end of the neural axis bends crook like during early morphogenesis into the chiasmatic hypothalamus, where it ends; the orientation of true transverse sections accordingly changes, and is no longer parallel to the ribs and ground, but perpendicular to them; lack of awareness of this morphologic brain peculiarity (present in all vertebrate brains without exceptions) has caused and still causes much erroneous thinking on forebrain brain parts. Acknowledging the singularity of rostral transverse sections, tradition has introduced a different descriptor for them, namely coronal sections. Coronal sections divide the forebrain from rostral (front) to caudal (back), forming a series orthogonal (transverse) to the local bent axis. The concept cannot be applied meaningfully to the brainstem and spinal cord, since there the coronal sections become horizontal to the axial dimension, being parallel to the axis. In any case, the concept of 'coronal' sections is less precise than that of 'transverse', since often coronal section planes are used which are not truly orthogonal to the rostral end of the brain axis. The term is etymologically related to the coronal suture of the craneum and this to the position where crowns are worn (Latin corona means crown). It is not clear what sort of crown was meant originally (maybe just a diadema), and this leads unfortunately to ambiguity in the section plane defined merely as coronal. A coronal plane across the human head and brain is modernly conceived to be parallel to the face (the plane in which a king's crown sits on his head is not exactly parallel to the face, and exportation of the concept to less frontally endowed animals than us is obviously even more conflictive, but there is an implicit reference to the coronal suture of the cranium, which forms between the frontal and temporal/parietal bones, giving a sort of diadema configuration which is roughly parallel to the face). Coronal section planes thus essentially refer only to the head and brain, where a diadema makes sense, and not to the neck and body below. Horizontal sections by definition are aligned (parallel) with the horizon. In swimming, creeping and quadrupedal animals the body axis itself is horizontal, and, thus, horizontal sections run along the length of the spinal cord, separating ventral from dorsal parts. Horizontal sections are orthogonal to both transverse and sagittal sections, and in theory, are parallel to the length axis. Due to the axial bend in the brain (forebrain), true horizontal sections in that region are orthogonal to coronal (transverse) sections (as is the horizon relative to the face). According to these considerations, the three directions of space are represented precisely by the sagittal, transverse and horizontal planes, whereas coronal sections can be transverse, oblique or horizontal, depending on how they relate to the brain axis and its incurvations.
Признавая уникальность ростральных поперечных сечений, традиционно был введен другой дескриптор для них, а именно – корональные сечения. Корональные сечения делят передний мозг от рострального (переднего) к каудальному (заднему), образуя серию, ортогональную (поперечную) к локальной изогнутой оси. Эта концепция не может быть осмысленно применена к стволу мозга и спинному мозгу, поскольку там корональные сечения становятся горизонтальными по отношению к продольной оси, будучи параллельными оси. В любом случае, концепция «корональных» сечений менее точна, чем концепция «поперечных», поскольку часто используются корональные плоскости сечения, которые не являются строго ортогональными к ростральному концу оси мозга. Термин этимологически связан с коронарным швом черепа и, следовательно, с местом, где носят короны (corona на латыни означает корона). Неясно, какая именно корона имелась в виду изначально (возможно, просто диадема), и это, к сожалению, приводит к неоднозначности в плоскости сечения, определяемой просто как корональная. Корональная плоскость, проходящая через голову и мозг человека, в настоящее время понимается как параллельная лицу (плоскость, в которой корона короля сидит на его голове, не совсем параллельна лицу, и экстраполяция этой концепции на животных, менее наделенных лобной частью, чем мы, очевидно, еще более конфликтна, но есть неявная ссылка на коронарный шов черепа, который образуется между лобной и височной/теменной костями, создавая своего рода конфигурацию диадемы, которая примерно параллельна лицу). Таким образом, корональные плоскости сечения по сути относятся только к голове и мозгу, где диадема имеет смысл, а не к шее и телу ниже.
Dorsal and ventral: Dorsal refers more or less to the top or upper side of the brain, which is symbolized by the floor plate, and ventral to the bottom or lower side. These descriptors originally were used for dorsum and ventrum – back and belly – of the body; the belly of most animals is oriented towards the ground; the erect posture of humans places our ventral aspect anteriorly, and the dorsal aspect becomes posterior. The case of the head and the brain is peculiar, since the belly does not properly extend into the head, unless we assume that the mouth represents an extended belly element. Therefore, in common use, those brain parts that lie close to the base of the cranium, and through it to the mouth cavity, are called ventral – i. e., at its bottom or lower side, as defined above – whereas dorsal parts are closer to the enclosing cranial vault. Reference to the roof and floor plates of the brain is less prone to confusion, also allow us to keep an eye on the axial flexures mentioned above. Dorsal and ventral are thus relative terms in the brain, whose exact meaning depends on the specific location. Rostral and caudal: rostral refers in general anatomy to the front of the body (towards the nose, or rostrum in Latin), and caudal refers to the tail end of the body (towards the tail; cauda in Latin). The rostrocaudal dimension of the brain corresponds to its length axis, which runs across the cited flexures from the caudal tip of the spinal cord into a rostral end roughly at the optic chiasma. In the erect Man, the directional terms "superior" and "inferior" essentially refer to this rostrocaudal dimension, because our body and brain axes are roughly oriented vertically in the erect position. However, all vertebrates develop a very marked ventral kink in the neural tube that is still detectable in the adult central nervous system, known as the cephalic flexure. The latter bends the rostral part of the CNS at a 180 degree angle relative to the caudal part, at the transition between the forebrain (axis ending rostrally at the optic chiasma) and the brainstem and spinal cord (axis roughly vertical, but including additional minor kinks at the pontine and cervical flexures) These flexural changes in axial dimension are problematic when trying to describe relative position and sectioning planes in the brain. There is abundant literature that wrongly disregards the axial flexures and assumes a relatively straight brain axis. Medial and lateral: medial refers to being close, or relatively closer, to the midline (the descriptor median means a position precisely at the midline). Lateral is the opposite (a position more or less separated away from the midline). Note that such descriptors (dorsal/ventral, rostral/caudal; medial/lateral) are relative rather than absolute (e. g., a lateral structure may be said to lie medial to something else that lies even more laterally). Commonly used terms for planes of orientation or planes of section in neuroanatomy are "sagittal", "transverse" or "coronal", and "axial" or "horizontal". Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis. Due to the axial brain flexures, no section plane ever achieves a complete section series in a selected plane, because some sections inevitably result cut oblique or even perpendicular to it, as they pass through the flexures. Experience allows to discern the portions that result cut as desired. A mid sagittal plane divides the body and brain into left and right halves; sagittal sections, in general, are parallel to this median plane, moving along the medial lateral dimension (see the image above). The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin). A section plane orthogonal to the axis of any elongated form in principle is held to be transverse (e. g., a transverse section of a finger or of the vertebral column); if there is no length axis, there is no way to define such sections, or there are infinite possibilities. Therefore, transverse body sections in vertebrates are parallel to the ribs, which are orthogonal to the vertebral column, which represents the body axis both in animals and man. The brain also has an intrinsic longitudinal axis – that of the primordial elongated neural tube – which becomes largely vertical with the erect posture of Man, similarly as the body axis, except at its rostral end, as commented above. This explains that transverse spinal cord sections are roughly parallel to our ribs, or to the ground. However, this is only true for the spinal cord and the brainstem, since the forebrain end of the neural axis bends crook like during early morphogenesis into the chiasmatic hypothalamus, where it ends; the orientation of true transverse sections accordingly changes, and is no longer parallel to the ribs and ground, but perpendicular to them; lack of awareness of this morphologic brain peculiarity (present in all vertebrate brains without exceptions) has caused and still causes much erroneous thinking on forebrain brain parts. Acknowledging the singularity of rostral transverse sections, tradition has introduced a different descriptor for them, namely coronal sections. Coronal sections divide the forebrain from rostral (front) to caudal (back), forming a series orthogonal (transverse) to the local bent axis. The concept cannot be applied meaningfully to the brainstem and spinal cord, since there the coronal sections become horizontal to the axial dimension, being parallel to the axis. In any case, the concept of 'coronal' sections is less precise than that of 'transverse', since often coronal section planes are used which are not truly orthogonal to the rostral end of the brain axis. The term is etymologically related to the coronal suture of the craneum and this to the position where crowns are worn (Latin corona means crown). It is not clear what sort of crown was meant originally (maybe just a diadema), and this leads unfortunately to ambiguity in the section plane defined merely as coronal. A coronal plane across the human head and brain is modernly conceived to be parallel to the face (the plane in which a king's crown sits on his head is not exactly parallel to the face, and exportation of the concept to less frontally endowed animals than us is obviously even more conflictive, but there is an implicit reference to the coronal suture of the cranium, which forms between the frontal and temporal/parietal bones, giving a sort of diadema configuration which is roughly parallel to the face). Coronal section planes thus essentially refer only to the head and brain, where a diadema makes sense, and not to the neck and body below. Horizontal sections by definition are aligned (parallel) with the horizon. In swimming, creeping and quadrupedal animals the body axis itself is horizontal, and, thus, horizontal sections run along the length of the spinal cord, separating ventral from dorsal parts. Horizontal sections are orthogonal to both transverse and sagittal sections, and in theory, are parallel to the length axis. Due to the axial bend in the brain (forebrain), true horizontal sections in that region are orthogonal to coronal (transverse) sections (as is the horizon relative to the face). According to these considerations, the three directions of space are represented precisely by the sagittal, transverse and horizontal planes, whereas coronal sections can be transverse, oblique or horizontal, depending on how they relate to the brain axis and its incurvations.
Горизонтальные сечения по определению выровнены (параллельны) с горизонтом. У плавающих, ползающих и четвероногих животных сама ось тела горизонтальна, и, следовательно, горизонтальные сечения проходят вдоль длины спинного мозга, разделяя вентральные и дорсальные части. Горизонтальные сечения ортогональны как поперечным, так и сагиттальным сечениям и, теоретически, параллельны оси длины. Из-за осевого изгиба в мозге (переднем мозге) истинные горизонтальные сечения в этой области…
Dorsal and ventral: Dorsal refers more or less to the top or upper side of the brain, which is symbolized by the floor plate, and ventral to the bottom or lower side. These descriptors originally were used for dorsum and ventrum – back and belly – of the body; the belly of most animals is oriented towards the ground; the erect posture of humans places our ventral aspect anteriorly, and the dorsal aspect becomes posterior. The case of the head and the brain is peculiar, since the belly does not properly extend into the head, unless we assume that the mouth represents an extended belly element. Therefore, in common use, those brain parts that lie close to the base of the cranium, and through it to the mouth cavity, are called ventral – i. e., at its bottom or lower side, as defined above – whereas dorsal parts are closer to the enclosing cranial vault. Reference to the roof and floor plates of the brain is less prone to confusion, also allow us to keep an eye on the axial flexures mentioned above. Dorsal and ventral are thus relative terms in the brain, whose exact meaning depends on the specific location. Rostral and caudal: rostral refers in general anatomy to the front of the body (towards the nose, or rostrum in Latin), and caudal refers to the tail end of the body (towards the tail; cauda in Latin). The rostrocaudal dimension of the brain corresponds to its length axis, which runs across the cited flexures from the caudal tip of the spinal cord into a rostral end roughly at the optic chiasma. In the erect Man, the directional terms "superior" and "inferior" essentially refer to this rostrocaudal dimension, because our body and brain axes are roughly oriented vertically in the erect position. However, all vertebrates develop a very marked ventral kink in the neural tube that is still detectable in the adult central nervous system, known as the cephalic flexure. The latter bends the rostral part of the CNS at a 180 degree angle relative to the caudal part, at the transition between the forebrain (axis ending rostrally at the optic chiasma) and the brainstem and spinal cord (axis roughly vertical, but including additional minor kinks at the pontine and cervical flexures) These flexural changes in axial dimension are problematic when trying to describe relative position and sectioning planes in the brain. There is abundant literature that wrongly disregards the axial flexures and assumes a relatively straight brain axis. Medial and lateral: medial refers to being close, or relatively closer, to the midline (the descriptor median means a position precisely at the midline). Lateral is the opposite (a position more or less separated away from the midline). Note that such descriptors (dorsal/ventral, rostral/caudal; medial/lateral) are relative rather than absolute (e. g., a lateral structure may be said to lie medial to something else that lies even more laterally). Commonly used terms for planes of orientation or planes of section in neuroanatomy are "sagittal", "transverse" or "coronal", and "axial" or "horizontal". Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis. Due to the axial brain flexures, no section plane ever achieves a complete section series in a selected plane, because some sections inevitably result cut oblique or even perpendicular to it, as they pass through the flexures. Experience allows to discern the portions that result cut as desired. A mid sagittal plane divides the body and brain into left and right halves; sagittal sections, in general, are parallel to this median plane, moving along the medial lateral dimension (see the image above). The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin). A section plane orthogonal to the axis of any elongated form in principle is held to be transverse (e. g., a transverse section of a finger or of the vertebral column); if there is no length axis, there is no way to define such sections, or there are infinite possibilities. Therefore, transverse body sections in vertebrates are parallel to the ribs, which are orthogonal to the vertebral column, which represents the body axis both in animals and man. The brain also has an intrinsic longitudinal axis – that of the primordial elongated neural tube – which becomes largely vertical with the erect posture of Man, similarly as the body axis, except at its rostral end, as commented above. This explains that transverse spinal cord sections are roughly parallel to our ribs, or to the ground. However, this is only true for the spinal cord and the brainstem, since the forebrain end of the neural axis bends crook like during early morphogenesis into the chiasmatic hypothalamus, where it ends; the orientation of true transverse sections accordingly changes, and is no longer parallel to the ribs and ground, but perpendicular to them; lack of awareness of this morphologic brain peculiarity (present in all vertebrate brains without exceptions) has caused and still causes much erroneous thinking on forebrain brain parts. Acknowledging the singularity of rostral transverse sections, tradition has introduced a different descriptor for them, namely coronal sections. Coronal sections divide the forebrain from rostral (front) to caudal (back), forming a series orthogonal (transverse) to the local bent axis. The concept cannot be applied meaningfully to the brainstem and spinal cord, since there the coronal sections become horizontal to the axial dimension, being parallel to the axis. In any case, the concept of 'coronal' sections is less precise than that of 'transverse', since often coronal section planes are used which are not truly orthogonal to the rostral end of the brain axis. The term is etymologically related to the coronal suture of the craneum and this to the position where crowns are worn (Latin corona means crown). It is not clear what sort of crown was meant originally (maybe just a diadema), and this leads unfortunately to ambiguity in the section plane defined merely as coronal. A coronal plane across the human head and brain is modernly conceived to be parallel to the face (the plane in which a king's crown sits on his head is not exactly parallel to the face, and exportation of the concept to less frontally endowed animals than us is obviously even more conflictive, but there is an implicit reference to the coronal suture of the cranium, which forms between the frontal and temporal/parietal bones, giving a sort of diadema configuration which is roughly parallel to the face). Coronal section planes thus essentially refer only to the head and brain, where a diadema makes sense, and not to the neck and body below. Horizontal sections by definition are aligned (parallel) with the horizon. In swimming, creeping and quadrupedal animals the body axis itself is horizontal, and, thus, horizontal sections run along the length of the spinal cord, separating ventral from dorsal parts. Horizontal sections are orthogonal to both transverse and sagittal sections, and in theory, are parallel to the length axis. Due to the axial bend in the brain (forebrain), true horizontal sections in that region are orthogonal to coronal (transverse) sections (as is the horizon relative to the face). According to these considerations, the three directions of space are represented precisely by the sagittal, transverse and horizontal planes, whereas coronal sections can be transverse, oblique or horizontal, depending on how they relate to the brain axis and its incurvations.
Инструменты
Современные достижения в нейроанатомии напрямую связаны с технологиями, используемыми для проведения исследований. Поэтому необходимо обсудить различные инструменты и методы, которые имеются в распоряжении. Многие гистологические методы, применяемые для изучения других тканей, могут быть использованы и для изучения нервной системы. Однако существуют также методы, разработанные специально для нейроанатомических исследований.
Цветение клеток
В биологических системах окрашивание – это техника, используемая для усиления контраста определенных структур на микроскопических изображениях. Окрашивание по Нисслю использует анилиновые основные красители для интенсивного окрашивания кислых полирибосом в шероховатом эндоплазматическом ретикулуме, который в большом количестве содержится в нейронах. Это позволяет исследователям различать различные типы клеток (например, нейроны и глию), а также формы и размеры нейронов в различных областях цитоархитектуры нервной системы. Классическое окрашивание по Гольджи использует дихромат калия и нитрат серебра для избирательного заполнения небольшого числа нервных клеток (нейронов или глии, хотя в принципе любые клетки могут реагировать аналогично) осаждением хромата серебра. Эта процедура серебряного хроматного пропитывания полностью или частично окрашивает тела клеток и нейриты некоторых нейронов – дендриты, аксоны – в коричневый и черный цвет, позволяя исследователям прослеживать их пути до самых тонких терминальных ветвей в срезе нервной ткани благодаря прозрачности, возникающей из-за отсутствия окрашивания в большинстве окружающих клеток. В настоящее время материал, пропитанный по Гольджи, адаптирован для электронной микроскопической визуализации неокрашенных элементов, окружающих окрашенные процессы и тела клеток, тем самым повышая разрешающую способность.
Гистохимия
Гистохимия использует знания о биохимических свойствах химических компонентов мозга (включая, в частности, ферменты) для применения селективных методов реакций, позволяющих визуализировать их локализацию в мозге и любые функциональные или патологические изменения. Это особенно важно для молекул, связанных с производством и метаболизмом нейротрансмиттеров, но также применимо и во многих других областях, таких как хемоархитектура или химическая нейроанатомия. Иммуноцитохимия является частным случаем гистохимии, использующим селективные антитела к различным химическим эпитопам нервной системы для избирательного окрашивания определенных типов клеток, аксональных пучков, нейропилей, глиальных процессов или кровеносных сосудов, а также специфических внутрицитоплазматических или внутриядерных белков и других иммуногенетических молекул, например, нейротрансмиттеров. Иммунореагирующие белки транскрипционных факторов отражают геномную экспрессию в виде транслированных белков. Это значительно расширяет возможности исследователей по различению различных типов клеток (таких как нейроны и глия) в различных областях нервной системы. In situ гибридизация использует синтетические РНК-зонды, которые селективно связываются (гибридизуются) с комплементарными мРНК-транскриптами ДНК-экзонов в цитоплазме, для визуализации геномной экспрессии, то есть для дифференциации активной экспрессии генов на основе мРНК, а не белка. Это позволяет гистологически (in situ) идентифицировать клетки, участвующие в производстве генетически кодированных молекул, которые часто отражают признаки дифференцировки или функции, а также молекулярные границы, разделяющие различные области мозга или популяции клеток.
Генетически закодированные маркеры
Выражая в мозге переменные количества красного, зеленого и синего флуоресцентных белков, мутантная мышь, известная как "brainbow" (мозговой радугой), позволяет визуализировать комбинации множества различных цветов в нейронах. Это позволяет маркировать нейроны достаточным количеством уникальных цветов, чтобы их часто можно было различить от соседних клеток с помощью флуоресцентной микроскопии, что дает исследователям возможность картировать локальные связи или взаимное расположение (мозаичное расположение) между нейронами. Оптогенетика использует трансгенную конститутивную и сайт-специфическую экспрессию заблокированных маркеров (обычно у мышей), которые могут быть селективно активированы освещением световым лучом. Это позволяет исследователям изучать аксональные связи в нервной системе с высокой степенью различительной способности.
Неинвазивная визуализация мозга
Магнитно-резонансная томография широко используется для неинвазивного исследования структуры и функции мозга у здоровых людей. Важным примером является диффузионно-тензорная визуализация, которая основывается на ограничении диффузии воды в тканях для получения изображений аксонов. В частности, вода перемещается быстрее вдоль направления, совпадающего с аксонами, что позволяет судить об их структуре.
Методы на основе вирусов
Некоторые вирусы способны размножаться в клетках мозга и преодолевать синапсы. Следовательно, вирусы, модифицированные для экспрессии маркеров (например, флуоресцентных белков), могут быть использованы для прослеживания связей между областями мозга через множество синапсов. Два трассировочных вируса, реплицирующихся и распространяющихся транснейронально/транссинаптически, – это вирус простого герпеса 1 типа (ВПГ-1) и рабдовирусы. Вирус простого герпеса использовался для прослеживания связей между мозгом и желудком с целью изучения областей мозга, участвующих в висцеросенсорной обработке. В другом исследовании вирус простого герпеса вводили в глаз, что позволило визуализировать зрительный путь от сетчатки к зрительной системе. Вирус псевдобешенства является примером трассировочного вируса, реплицирующегося от синапса к телу нейрона (соме). Используя вирусы псевдобешенства с различными флуоресцентными репортерами, модели двойного заражения позволяют анализировать сложную синаптическую архитектуру.
Методы на основе красителей
В аксональных методах транспорта используются различные красители (варианты пероксидазы хрена, флуоресцентные или радиоактивные метки, лектины, декстраны), которые в разной степени поглощаются нейронами или их отростками. Эти молекулы избирательно транспортируются антероградно (от тела клетки к аксонным терминалям) или ретроградно (от аксонных терминалей к телу клетки), что позволяет выявлять первичные и коллатеральные связи в мозге. Эти "физиологические" методы (поскольку основаны на свойствах живых, неповрежденных клеток) могут комбинироваться с другими процедурами и практически полностью заменили более ранние методы, изучавшие дегенерацию поврежденных нейронов или аксонов. Детальные синаптические соединения могут быть установлены с помощью корреляционной электронной микроскопии.
Коннектомика
Серийная электронная микроскопия широко развивалась для изучения нервных систем. Например, первое применение сканирующей электронной микроскопии блочного среза было проведено на коре головного мозга грызунов. Реконструкция нейронных цепей по данным, полученным с помощью этого высокопроизводительного метода, представляет собой сложную задачу, и для содействия исследованиям в этой области была разработана научно-популярная игра EyeWire.
Вычислительная нейроанатомия
Это область, использующая различные методы визуализации и вычислительные техники для моделирования и количественной оценки пространственно-временной динамики нейроанатомических структур у здоровых людей и пациентов.
Модельные системы
Помимо человеческого мозга, существует множество других животных, мозг и нервная система которых интенсивно изучались в качестве модельных систем, включая мышей, данио-рерио (рыбок-зебр), дрозофилу и вид круглых червей под названием C. elegans. Каждая из этих моделей имеет свои преимущества и недостатки. Например, нервная система C. elegans чрезвычайно стереотипна у разных особей. Это позволило исследователям с помощью электронной микроскопии составить карту путей и связей всех 302 нейронов этого вида. Дрозофила широко изучается, в частности, благодаря хорошо изученной и легко поддающейся манипулированию генетике. Мышей используют, поскольку, будучи млекопитающими, их мозг структурно больше похож на наш (например, у них есть шестислойная кора), при этом их гены легко модифицируются, а репродуктивный цикл относительно короткий.
Caenorhabditis elegans (острый ракообразный)
Мозг у некоторых видов, таких как нематода, небольшой и простой, поскольку план строения тела у них довольно прост: трубка с полым кишечным пространством, простирающимся от рта до анального отверстия, и нервный шнур с утолщением (ганглием) для каждого сегмента тела, причём особенно крупный ганглий расположен в передней части и называется мозгом. Нематода Caenorhabditis elegans изучается благодаря своей значимости в генетике. В начале 1970-х годов Сидни Бреннер выбрал её в качестве модельной системы для изучения механизмов, посредством которых гены контролируют развитие, включая развитие нейронов. Одним из преимуществ работы с этим червём является то, что нервная система гермафродита состоит ровно из 302 нейронов, которые всегда находятся в одних и тех же местах и формируют идентичные синаптические связи у каждого червя. Команда Бреннера нарезала червей на тысячи ультратонких срезов и фотографировала каждый срез под электронным микроскопом, а затем визуально сопоставляла волокна на разных срезах, чтобы составить карту каждого нейрона и синапса во всём теле, получив полную коннектому нематоды. Ни для какого другого организма нет данных, приближающихся к такому уровню детализации, и эта информация позволила провести множество исследований, которые были бы невозможны без неё.