Neuroanat Week 3

8/2/2019 Neuroanat Week 3

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Neuroanatomy Weekend Review 3

Week 3, Lectures 7-10

Describe the receptors, nerve, and pathways for perceiving pain on the face.

Trigeminal divisions V1, V2 and V3 are responsible for cutaneous innervation of the face. The spinal trigeminal tract

extends from C3 to the level of the trigeminal nerve in the midpons (is homologous to the dorsolateral tract of Lissauer) and

receives pain, temp., and light touch input. Pain fibers from the spinal trigeminal tract terminate in the caudal third of thespinal trigeminal nucleus (pars caudalis).

The ventral trigeminothalamic tract serves as pain, temp. and light touch pathway from the face. It receives input from free

nerve endings and Merkels disks. It receives discriminative tactile and pressure input from the contralateralprincipal

sensory nucleus of CN V, which terminates in the ventral posteromedial (VPM) nucleus of the thalamus. It then ascends to

the contralateral sensory cortex via three neurons:

First-order neurons are located in trigeminal ganglion; mediate pain and temp. and give rise to axons that descend in the

spinal trigenimal tract; mediate light touch and give rise to bifurcating axons that ascend and descend in the spinal trigeminaltract; synpase with second-order neurons in the spinal trigeminal nucleus.

Second-order neurons

are located in the spinal trigeminal nucleus; give rise to decussating axons that terminate in thecontralateralVPM of thalamus; project axons to reticular formation and to motor cranial nerve nuclei to mediate reflexes

(corneal reflexes); mediate painful stimuli and are found in the caudal third of the spinal trigeminal nucleus (par caudalis).

Third-order neurons are located in the VPM; project via the posterior limb of the internal capsule to the face area of the

postcentral gyrus (areas 3,1 and 2).

The dorsal trigeminothalamic tract subserves discriminative tactile and pressure sensation from the face (and oral cavity)

via the GSA fibers of CN V. It receives input from Meissners and Pacinian corpuscles. It is an uncrossedtract and is the

rostral equivalent of the dorsal column-medial lemniscus system. It ascends to the sensory cortex via three neurons:

First-order neurons are located in the trigeminal ganglion; synapse in the principal sensory nucleus of CN V.

Second-order neurons are located in the principal sensory nucleus of CN V and project to the ipsilateralVPM of

thalamus.

Third-order neurons are located in the VPM and project via the posterior limb of the internal capsule to the face area of

the postcentral gyrus (areas 3, 1 and 2).

Describe the consequences of a lesion in the upper medulla that interrupts the spinal tract of the trigeminal nerve and the

spinothalamic tract.

The spinal tract of the trigeminal nerve contains primary afferents for pain and temp. from the ipsilateral side of the face.

The nearby spinothalamic tract (ALS) carries pain and temp. for the contralateral side of the body.

Describe the origins of the ventral trigeminothalamic tract and the synaptic destination in thalamus.

The ventral trigeminothalamic tract serves as pain, temp. and light touch pathway from the face. It receives input from free

nerve endings and Merkels disks. It receives discriminative tactile and pressure input from the contralateralprincipal

sensory nucleus of CN V, which terminates in the ventral posteromedial (VPM) nucleus of the thalamus. It then ascends to

the contralateral sensory cortex via three neurons:


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First-order neurons are located in trigeminal ganglion; mediate pain and temp. and give rise to axons that descend in the

spinal trigenimal tract; mediate light touch and give rise to bifurcating axons that ascend and descend in the spinal trigeminal

tract; synpase with second-order neurons in the spinal trigeminal nucleus.

Second-order neurons are located in the spinal trigeminal nucleus; give rise to decussating axons that terminate in thecontralateralVPM of thalamus; project axons to reticular formation and to motor cranial nerve nuclei to mediate reflexes

(corneal reflexes); mediate painful stimuli and are found in the caudal third of the spinal trigeminal nucleus (par caudalis).

Third-order neurons are located in the VPM; project via the posterior limb of the internal capsule to the face area of the

postcentral gyrus (areas 3,1 and 2).

What are the thalamic nuclei identified as sensory relay called? Motor relay nuclei? Describe the efferent projections from

these nuclei to the cerebral cortex.

Thalamic nuclei are defined in relation to the area of cortex with which they connect, and the function of each is principally; sensoryrelay, or motor relay, or association relay, or nonspecific.

A BAKER'S DOZEN OF IMPORTANT THALAMIC NUCLEI

KEY NUCLEUS MAJOR SUBCORTICAL INPUT MAJOR OUTPUT

SENSORY RELAY

1 Ventral posterior lateral Medial lemniscus and ALS Postcentral gyrus

2 Ventral posterior medial Trigeminothalamic tract Postcentral gyrus

3 Lateral geniculate nucleus Optic tract Medial occipital cortex

4 Medial geniculate nucleus Brachium inferior colliculus Transverse temporal gyri

MOTOR RELAY

5 Ventrall lateral nucleus Cerebellum (VLp); basal ganglia (VLa) Precentral & premotor cortex

6 Ventral anterior nucleus Basal ganglia, cerebellum Motor & premotor Cortex

ASSOCIATION RELAY7 Anterior nucleus Mammillothalamic tract Cingulate gyrus (limbic)

8 Lateral dorsal nucleus Limbic forebrain, septal area Cingulate Gyrus & Parahippocampal Gyrus

9 Medial dorsal nucleus Amygdala, septal area, anterior

hypothalamus

Prefrontal Cortex

10 Pulvinar Optic tract & superior colliculus Visual association cortex

INTRALAMINAR NUCLEI ARE NONSPECIFIC

12 Centromedian Found in internal medullary lamina Collaterals to widespread cortical areas (primarily

motor and premotor) & striatum

13 Reticular Found in external medullary lamina Thalamus

What are the nuclei medial to the internal capsule, and what are the major functional components of the posterior limb of the

internal capsule?

The caudate nucleus and thalamus are medial to the internal capsule. The posterior limb of the internal capsule contains

sensory radiations (pain, temp. and touch), corticospinal fibers and the visual and auditory radiations.

The dorsal medial nucleus and Pulvinar are "association nuclei", to what areas of cortex do they project?


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The dorsal medial nucleus is reciprocally connected to the prefrontal cortex; has abundant connections with the

intralaminar nuclei; receives input from the amygdaloid nucleus, the temporal neocortex, and the substantia nigra; is part of

the limbic system and striatal system; when destroyed, causes memory loss (Wernicke-Korsakoff syndrome); plays a role in

the expression of affect, emotion, and behavior (limbic functions).

The pulvinar is the largest thalamic nucleus; has reciprocal connections with the association cortex of the occipital,

parietal, and posterior temporal lobes; receives input from the later and medial geniculate bodies and the superior colliculus;

is concerned with the integration of visual, auditory, and somesthetic (touch, pain, temp.) input; lesions of dominant sidemay result in sensory aphasia (impaired of absent communication by speech, writing, or signs; loss of the capacity for spoken

language).

Describe the neurons in the cerebral cortex that are primarily projection (output) neurons, and the others that are interneurons

The projection neurons of the cerebral cortex are typically pyramidal shaped, and have dendritic trees that are wide spread,

while the axon will project out of that region of the cortex (frequently these use an excitatory transmitter such as glutamate).

The interneurons are typically the granule or stellate shaped cells which have a dense dendritic arborization but in a fairly

restricted area, and their axon will generally end in the same general vicinity (frequently these use inhibitory transimitters

such as GABA or somatostatin).

What are the Brodmann area numbers for the primary sensory areas of cortex and for the primary motor cortex?

Brodman areas 1, 2 and 3 - Primary sensory cortex; Brodman area 4 - Primary motor cortex

Describe a pathway for visual information to get transmitted from occipital lobe to the frontal lobe of a hemisphere.

The association bundles of axons within a hemisphere provide examples of ways that visual information may reach the

frontal lobe, e.g. the superior longitudinal fasciculus.

Contrast the histology and functions of the fovea, optic disc and peripheral retina.

Optic disc is located 3.5mm nasal to the fovea; contains unmyelinated axons from the ganglion cell layer of the retina; is

the blind spot (contains no rods or cones); contains a central cup, a peripheral disk margin, and retinal vessels.

Fovea is located within the macula lutea; contains only cones and is the site of highest visual acuity; is avascular and

receives nutrients by diffusion via the choriocapillaris (the choroid layer behind the retina); subserves color or day (photopicvision; projects to the posterior part of the visual cortex

Peripheral retina (paramacular area) is a large area surrounding the macular area that contains predominately rods;

projects to the visual cortex anterior to the macular representation.

Draw two cups for eyes and an X for the optic nerves, chiasm and tracts. Identify the "left visual field" in relation to both

eyes and indicate which part of the retinas will receive the stimulus. Trace the signal pathways for this stimulus through your

drawing.

Hey, Im not going to go to the trouble of figuring out how to draw this stupid shit on my computer and since there isnt acopy machine anywhere to be found anymore just look this up in the book if you have too. Netter plate 114 is good and there

are diagrams in Nolte and Purves too. Its not that hard of a concept anyway.

Describe the foveal representation on the primary visual (striate or V1) cortex, and contrast it with the non-foveal

representation. What vessel supplies blood to this area of cortex?


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The visual (striate) cortex (area 17) is located on the banks of the calcerine sulcus and receives its blood supply from the

calcarine artery, a branch of the posterior cerebral artery (anastomosis with the middle cerebral artery may be substantial

possible explanation for macular sparing phenomenon). Posterior third of the visual cortex receives macular input (central

vision). Intermediate are of the visual cortex receives paramacular input (peripheral vision). Anterior area of visual cortex

receives monocular input.

LAB IV Study Questions:

1. What structures are seen in a frontal section at the level of the genu of interal capsule?

Column of fornix, foramen of Monro and optic chiasm

2. What relationship does the caudate nucleus have to the lateral ventricle?

Lateral/caudal

3. What arteries supply the arterial blood to :

internal capsule lateral striate aa, anterior choroidal aa

hippocampus anterior choroidal a

occipital lobe posterior cerebral a

corpus callosum anterior cerebral a

4. What is medial to the posterior limb of internal capsule?Thalamus (diencephalon)

5. The thalamic somato-sensory radiations are found in what part of internal capsule?

Posterior limb

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Neuroanat Week 3