Download Sectional Anatomy of the Brain - Dr. Leichnetz

Sectional Anatomy of the Brain
George R. Leichnetz, Ph.D.
In this course the student is primarily responsible for coronal sections of the brain, those cut parallel to
the front of the face, anterior to posterior. A horizontal section is required so the student can observe
the three portions of the internal capsule: anterior limb, genu, and posterior limb.
I.
TELENCEPHALON:
A. Striatum/Anterior Limb of Internal Capsule
Lateral ventricles- anterior horns
Corpus callosum- rostrum, genu, and rostral body of corpus callosum interconnect frontal lobes
Septum pellucidum- vertical membranous partition separating lateral ventricles
Anterior limb, internal capsule- separates the caudate from the putamen
Caudate nucleus- in lateral wall of lateral ventricle; head (its rostralmost portion is large and
located in rostral coronal sections through the frontal lobe
Putamen- lateral to anterior limb of the internal capsule; with caudate nuc. makes up striatum
External Capsule- lateral to putamen
Claustrum- thin sheet of gray matter, lateral to external capsule (between external & extreme
capsules)
Insular Cortex
Lateral sulcus
Temporal lobe/ temporal pole
Noback et al. The Human Nervous System
B. Amygdala/ Globus Pallidus
Caudate nucleus- body, reduced in size, but still in lateral wall of lateral ventricle
Anterior limb of internal capsule
Putamen- with globus pallidus constitutes the lentiform nucleus
Globus pallidus- with putamen makes up lentiform nucleus
Basal forebrain- below lentiform nucleus on base of frontal lobe
Anterior commissure- interconnects temporal lobes
Fornix- columns of fornix are vertical, course through septum, behind anterior commissure;
large principal efferent tract from hippocampus to mammillary bodies
Temporal lobe
Parahippocampal gyrus- ventromedial temporal lobe
Amygdala- complex of subnuclei involved with emotion
Noback et al. The Human Nervous System
II.
DIENCEPHALON:
A. Thalamus/ Hypothalamus
Thalamus- two large egg-shaped masses separated by midline third ventricle, interconnected
through interthalamic adhesion (not a commissure)
Hypothalamus- in walls of ventral part of third ventricle; includes mammillary bodies
Third ventricle- midline space, separating thalami and hypothalamus
Posterior limb of Internal Capsule- separates thalamus from the lentiform nucleus
(putamen/globus pallidus)
Subthalamus- region ventral to the thalamus, lateral to the hypothalamus (medial to internal
capsule)- contains subthalamic nucleus
Hippocampus- in ventromedial temporal lobe within parahippocampal gyrus; medial to
temporal horn of lateral ventricle
Temporal horn of lateral ventricle
Noback et al. The Human Nervous System
B.
Thalamus/ Subthalamus
Thalamus
Third ventricle
Subthalamic nucleus
Lateral geniculate nucleus
Posterior limb of internal capsule
Putamen
External capsule
Claustrum
Extreme capsule
Insular cortex
Noback et al. The Human Nervous System
III.
MIDBRAIN:
A. Rostral Midbrain
Superior colliculus- paired elevations, part of tectum (roof) of midbrain; involved in reflexive
eye and head movements associated with attention
Cerebral aqueduct- channel traverses midbrain, connecting third ventricle to fourth ventricle
Oculomotor complex- origin of oculomotor nerves (C.N. III) in ventral periaqueductal gray
Midbrain tegmentum- region below cerebral aqueduct; between “tectum” and crus cerebri
Red nucleus- large round nucleus in midbrain tegmentum; origin of major tract to spinal cord
Substantia nigra- pigmented (neuromelanin) nucleus above crus cerebri (Parkinson’s disease)
Crus cerebri- large fiber bundles (cerebral peduncles) on the base of the midbrain contain major
efferent tracts descending from cerebrum
Goss, Gray's Anatomy
B. Caudal Midbrain
Inferior colliculus- paired elevations in tectum (roof) of caudal midbrain; related to auditory
reflexes
Trochlear nucleus- in ventral periaqueductal gray
Decussation of superior cerebellar peduncles- containing cerebellar efferents, which cross in
the caudal midbrain tegmentum
Portion of basilar pons- in a typical cross section through the inferior colliculus, the rostral
portion of the basilar pons can be seen ventrally
Goss, Gray's Anatomy
IV.
PONS:
A. Rostral Pons
Trochlear nerve (C.N. IV)- exits through anterior medullary velum; only cranial nerve that
exits dorsally from the brainstem
Anterior medullary velum- membrane forms roof over rostral fourth ventricle, between superior
cerebellar peduncles
Superior cerebellar peduncles- large bundles on the dorsolateral aspect of the rostral pons;
carry cerebellar efferent (output) tracts
Rostral fourth ventricle
Periventricular gray- gray matter surrounding fourth ventricle
Locus ceruleus- small pigmented nucleus in lateral periaqueductal gray; principal source of
norepinephrine
Tegmentum of pons- between floor of fourth ventricle and basilar pons
Medial lemniscus- major sensory tract, forms border between tegmental and basilar pons
Basilar pons- major relay for cortical fibers to cerebellum; see crossing pontocerebellar fibers
running horizontally;
Goss, Gray's Anatomy
B. Caudal Pons
Middle cerebellar peduncles (brachium pontis)- large bundles on lateral aspect of pons; connect
basilar pons to cerebellum (contains pontocerebellars)
Facial colliculus- paired elevations on floor of fourth ventricle, where facial nerve (C.N. VII)
courses over the abducens nucleus
Fourth ventricle- widest at pontomedullary junction (level of lateral recesses)
Deep cerebellar nuclei- nuclei in cerebellar white matter above fourth ventricle; origin of
cerebellar efferents
Tegmentum of pons- between floor of 4th ventricle (rhomboid fossa) and basilar pons; medial
lemnisci are flat sensory tracts that delineate this border
Basilar pons- contains horizontally-oriented pontocerebellar fibers that enter the middle
cerebellar peduncles laterally; pyramidal tracts coursing caudally through basilar pons are
cut in cross section
Goss, Gray's Anatomy
V.
MEDULLA:
A. Rostral Medulla
Inferior cerebellar peduncle (restiform body)- connects medulla to cerebellum
Vestibulocochlear nerves (C.N. VIII)- course over inferior cerebellar peduncles, below lateral
recesses of fourth ventricle to terminate in dorsolateral rostral medulla
Cochlear nuclei- in dorsolateral rostral medulla; first synapse of auditory fibers
Vestibular complex- in dorsolateral pontomedullary junction; first synapse of vestibular fibers
Inferior olivary nucleus- convoluted nuclear complex in ventrolateral medulla; projects to
cerebellum
Pyramidal tracts- in medullary pyramids, descending long parallel voluntary motor tracts on
ventral surface of medulla
Deep cerebellar nuclei- in cerebellar white matter in roof above fourth ventricle
Goss, Gray's Anatomy
B. Caudal Medulla
Obex- caudalmost point of fourth ventricle
Nucleus gracilis- nucleus under gracile tubercle where ascending fibers in fasciculus gracilis
terminate; origin of medial lemniscus
Gracile tubercle (clava)- elevation over nucleus gracilis
Nucleus cuneatus- nucleus under cuneate tubercle where ascending fibers in fasciculus
cuneatus terminate; origin of medial lemniscus
Inferior olivary nucleus- a small portion of this nucleus still present
Pyramidal decussation- crossing of pyramidal (voluntary motor) tracts
Goss, Gray's Anatomy
VI.
HORIZONTAL SECTION: INTERNAL CAPSULE
A horizontal section through this level shows the anterior limb, genu, and posterior limb of the
internal capsule, and how they delineate the thalamus, striatum, and globus pallidus
Genu, Corpus Callosum- interconnects frontal lobes
Splenium, Corpus Callosum- interconnects occipital lobes
Anterior horns, lateral ventricles- in frontal lobes, separated by septum pellucidum
Posterior horns, lateral ventricles- in occipital lobes (optic radiations course in lateral wall)
Caudate nucleus- head of caudate in lateral wall of anterior horn of lateral ventricle
Lentiform nucleus- putamen and globus pallidus
Anterior limb of internal capsule- separates caudate and lentiform nucleus
Posterior limb of internal capsule- separates thalamus and lentiform nucleus
Thalamus- large masses on either side of the third ventricle
Noback et al. The Human Nervous System