Download NEUROANATOMY NOTES 07/21/99 Profesor: Dr. Martinez

NEUROANATOMY NOTES 07/21/99
Profesor: Dr. Martinez Sandoval
Cerebral Cortex with millions of cells. There are sensory pathways that ascend in order to reach the
thalamus, and the thalamus is the last relay to project to different areas of the cerebral cortex. The efferent
pathway go to the cortex to end at layer 4. However, layer 5, and 6 are the main layers that contribute to
descending axons, or to axons that will connect both cerebral hemispheres. Or, short axons that may
connect between two lobes within one cerebral hemisphere.
So, there are 3 types of axons: short axons, that connect gyri or lobes within same cerebral hemisphere.
For example, we said yesterday, area 22 projects axons to areas 44, 45. So we are talking about projections
between lobes within the same cerebral hemisphere. Area MII and area 6 will be connected also. These are
short axons within same cerebral hemisphere. The corpus callosum is the main commisure, because it
contains axons from one hemisphere to the contralateral area of the other hemisphere. These axons are
commisural. Then you have the long projection axons. They descend through the cerebral hemisphere.
These axons contribute to the formation of all the white matter area known as the oval center. This oval
center is called corona radiata. So the axons from the cerebral cortex will run and then in some point in the
internal structure, they will reach this classical and very popular structure known as internal capsule. So,
before the internal capsule, we have the corona radiata, the point where the axons begin to converge before
entering the interal capsule. The internal capsule, grossly, lies between the thalamus and caudate nucleus,
medially, and the putamen and globus pallidus laterally. The internal capsule is the site where most of the
vascular accidents of the brain will occur. This is the common site for cerebral vascular stroke.
He puts of a slide of the internal capsule. Using superior view, see the internal capsule. Can see the
internal capusle between the head of the caudate and the thalamus which liemedial. The globus pallidus
(pars mediales, pars lateralis) and putamen lie lateral to internal capsule. So, there are anterior and
posterior limbs of the internal capsule, and a medial part. See corticobulbar fibers are found here. This is
the region of the genu, which contains the corticobulbar tract. This occurs in the upper half of the internal
capsule, that measures 5 cms in brain. When the axons descend in order to reach the internal capsule, it
measures 5 cms. Most of the axons from the corticobulbar tract reach the genu, and then descends dorsally.
If you look at slice of brain at level of genu, see corticobulbar tract. But, if you look at a more dorsal
horizontal slice you will see the corticobulbar tract more posterior than when it was at the genu. This tract
controls muscles controlled by cranial nerves. They have somatic and branchial arch origin. The head and
neck somatic origin are oculomotor, abducens, trochlear, and hypoglossal will contain the functional
component known as General Somatic Efferent (GSE). They are from somites. The branchial arch origin:
trigeminal, facial, glossopharyngeal, vagus, spinal accessory, they are Special Visceral Efferent (SVE).
Muscles supplied by only GSE or SVE. Corticobulbar tract nerves control only head and neck. The
extrapyrimadal system with the corticospinal tract controls the remaining group of muscles in body. The
lateral pathway and the ventromedial pathway control the muscles of the neck and below.
There is a very special figure in the book by Young which may appear on the exam. There are two figures,
one at the level of the superior part of the internal capsule, and one of the lower half of the internal capsule.
Corticospinal and rubrospinal tracts are upper motor neurons found in the lateral pathway. They are upper
motor neurons because come from superior centers and suppy nuclei whose axons will exit the CNS through
peripheral nerves. The cell bodies of the peripheral nervous system are from lower motor neurons. The
neurons from the upper motor neurons never leave the CNS, but they connect to new axons which exit the
CNS as peripheral nerves. Both tracts supply flexor muscles. This is the same as when you say they excite
or stimulate flexor muscles. They inhibit the extensors muscles. Both supply all muscles of the body from
the neck down. However, the corticospinal tract supplies specially the distal muscles of the limbs. The
muscles that require fine movements, precision, skill, movments of the human body. That is the
characteristic of the corticospinal tract. And rubrospinal supplies particularly proximal muscles of the
limbs. What do we mean with proximal? Muscles that move the shoulder joints. Muscles that flex the
elbow. Muscles that flex the wrist joint. This is proximal to the axial line of the body. And finally the
distal are the fingers, that's why they belong to the corticospinal. But, don't forget, both tracts supply
muscles from the neck down. So the corticospinal and rubrospinal supply muscles derived from somites.
What was the functional component of the somites? GSE. Origin of the corticospinal is 4, 6, MII. Origin
of the rubrospinal is the red nucleus in the midbrain. This is one of the conspicuous nuclei of the midbrain.
You can identify the substancia nigria is the other conspicuous nuclei. The red nucleus also gives origin to
axons. That is the partial origin of descending axons that will supply another nucleus that lies in the
medulla, known as the inferior olive nucleus. These desceding axons form the central tegmental fasciculus.
lateral ventriculo striated artery, branch of middle cerebral artery, is subject to strokes, and affects the
corticobulbar nerves in the genu. Jugular n. is supplied by the corticobulbar tract. The eye is supplied also
by the coticobulbar, which elevates, adducts, and depresses the eye. The corticobulbar abducts and
depresses and causes intorsion of the eye via the trochlear nerve. And the corticobulbar causes abduction of
the eye from CN VI (abducens n.). But these movements except the abduction of the abducens n., receives
signals from both hemispheres. Number 6 slightly supplied by the contralateral corticobulbar tract.
Corticobulbar supplies bilaterally the trigeminal, means masticatory muscles, and so the affectation of the
corticobulbar affects the contralateral muscles in the lower face.
He shows slide of the brain stem from Heinz Atlas of Anatomy, and the corticbulbar tract. It connects to
the CN III, IV, V, VI, VII. Can see the corticobulbar tract from left hemisphere descending to the nuclei on
the right side. Facial is mainly (95%) contralaterally and 5% dypsilaterally. Abducens is partially
contralaterally. Nucleus ambiguus received bilaterally. Hypoglossal is more or less the same, but slightly
contralateral. Vagus is mainly contralateral. So, in the end, the affectation of any part of the corticobulbar
part of one hemisphere, you will have weakness in the contralateral face, slight deviation of tongue, and
slight medial strabismus because of problem with abducens.
He shows picture of internal capsule superior view again. He shows posterior limb, contains corticospinal
plus all sensory ascending pathways from the GSA, SVA. The posterior limb contains corticospinal,
corticobulbar, and all sensory ascending pathways except olfaction. Posterior limb has special zones. The
lateral geniculate nucleus has axons that loop around, and then goes to visual cortex area 17-19. This is the
retroventricular portion of the internal capsule. It is part of the posterior limb. Now, if you observe the
medial geniculate nucleus, they pass below the internal capsule. That is the sublenticular portion of the
internal capusle, contains auditory pathway. Both are part of the posterior limb of the internal capsule.
He shows general view of the big long tracts of the cerebral hemispheres. For example, the frontal lobe is
connected to the temporal pole by means of the uncinate fasciculus. They work together in terms of
emotional reactions, part of limbic system. This fasciculusis dealt with when have a frontal lobotomy.
Then when you are given opiod drugs, you have no control of pain. For lobotomy, they don't remove all of
frontal lobe, but just destroy the uncinate fasciculus. By cutting this, the connections between the amigdala
that lies in the temporal lobe of the brain is associated with the prefrontal cortex. The patient still feels
pain, but doesn't care about the pain. So the uncinate fascuculus connects the amigdala with the prefrontal
lobe.
Superior longitudinal fasciulus connects frontal, parietal, occipital, and temporal lobe. This lies on the
lateral surface. If you remove the cortex, then slightly remove the axons that enter the cortex, can find very
easily the long tract. Can see similar tract on the medial surface, but its called the cingulate fasciculus. The
inferior longitudinal connects the temporal with the occipital lobe. And then you see the arcuate fasciulus
seen running above the insular cortex, immediately below the inferior longitudinal fasiculus. So these are
only...which of the following are association tracts in the brain? superior, inferior longitudinal, cingulate,
arcuate, and uncinate fasciculi. The cingulate fasciculus is part of the papes circuit.
See picture of coronal slice of brain. See regions of innervation in paracentral lobule for motor innervation
for the leg and foot, plus the anal and urinary voluntary sphincters. This area is supplied by the anterior
cerebral artery, while the other areas supplied by the middle cerebral artery.
Tomorrow we are going to begin to observe the horizontal sections, to try to identiy the horzontal sections,
because we're going to identify the nuclei in these sections.