Gross Brain and spinal cord labs

Question 1

1. Locate the central sulcus, precentral and postcentral gyri and paracentral lobules on the surface of the brain. Understand the relationship between these locations and the primary motor cortex and primary somatosensory corticies.
2. Describe the appearance of the internal capsule as visualized on coronal and axial sections of the brain, particularly the relationship to the caudate nucleus, putamen/globus pallidus, and thalamus
3. Describe the anatomy of the lateral corticospinal tract.
4. Describe the difference between an Upper Motor Neuron syndrome and
   an Lower Motor Neuron syndrome
5. Describe the anatomical pathway for relaying discriminative touch, vibration sense, and joint position sense. How does this pathway vary above and below the T6 dermatome?
6. Describe the anatomical pathway for relaying pain and temperature sensation
7. Explain the reason for dissociated sensory loss encountered in a Brown-Sequard syndrome

Answer 1

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Question 2

Describe the location and function of the paracentral lobule

Answer 2

Somatosensory and motor cortices are no longer separated by the central sulcus on the medial face (ie no distinct boundary between them).

Question 3

List the Broadmann’s number associated with the:

Precentral gyrus

Answer 3

Precentral gyrus: 4

Postcentral gyrus: 3, 1, 2 (from anterior to posterior, run the entire length of the gyrus longitudinally).

Question 4

UMN syndrome. What diagnostic maneuver can be used to identify this syndrome?

What differentiates LMN syndrome?

Answer 4

Spinal shock - reflex lost for several days, followed by hyperreflexia. Babinski (extensor plantar response)

LMN - flaccid paresis, hyporeflexia, areflexia, muscle weakness, hypotonia

Question 5

What is important about the anterior corticospinal tract (with regard to a stroke, for example)?

Answer 5

These innervate alpha motor neuron on the ipsilateral side, as well as the contralateral alpha motor neuton, specifically those that innervate core muscles (those responsible for posture), so fine motor control of the hand might be lost, but muscles for posture and breathing will remain intact.

Question 6

What is the DCML. What is its role in sensory perception? What route does it take through the body (from the L5 dermatome)?

Answer 6

DCML = PCML Dorsal (Posterior) Column Medial Leminiscal system. Responsible for proprioception (vibration, joint position, light touch)

Big toe (L5 dermatome)–> 1st axon extends up through DRG w/o synapsing (L5/S1 level) and continues upward in the rootlets of the cauda equina until reaching the L5 region of the spinal column where it continues to ascend in a bundle called the fasciculus gracilis (dorsal/posterior column)–>2nd neuron starts in the nucleus gracilis (brainstem) –>crosses midline and ascends with the medial lemniscus–> 3rd neuron starts in the ventral posteriolateral nucleus (VPL) which is part of the thalamus–>innervates the paracentral lobule of the postcentral gyrus of the cerebrum

Question 7

ALS = Anterior Lateral System. Responsible for pain and touch (aka spinothalamic tract)

Describe pathway in detail, as well as name the syndrome created by the difference between the ALS and DCML.

Answer 7

Pinprick in L5–> axon with cell body in DRG at vertebral L5/S1 carries up to spinal L5 in cauda equina rootlet–> ascend or descend in a white matter band called Lissauer’s Fasciculus–>terminates on bundle of dorsal grey matter called the substantial gelatinosa–>2nd order neuron immediately crosses midline via the ventral white commisure–> ascends in white matter of the anteriolateral portion of the spinal cord–>3rd order neuron is in the VPL of the thalamus.

**the fact that the pain response crosses the midline at a different level than proprioception gives a clinical differential (Brown sequard syndrome)

Question 8

Above what dermatomal level does the switch from the fasciculus cuneatus to the fasciculus gracilis occur (DCML)?

Answer 8

Above the T6 dermatome is the point at which you see the fasciculus cuneatus. Everything below that comes into the fasciculus gracilis. The fasciculus cuneatus is located just lateral to the fasciculus gracilis, still in the dorsal column, and the second order neuron begins in the nucleus cuneatus, just lateral to the fasciculus gracilis in the brainstem. The two pathways meet up in the VPL (ventral posteriolateral nucleus) in the thalamus.

Question 9

What is the structure called that prevents the central sulcus from joining with the lateral sulcus?

What is the structure that forms the medial “roof” of the central sulcus?

Answer 9

The subcentral gyrus.

The paracentral lobule.

Question 10

Biceps reflex

Answer 10

C5, C6

Question 11

Brachioradialis reflex

Answer 11

C6

Question 12

Tricipetal reflex

Answer 12

C7

Question 13

Patellar reflex

Answer 13

L3, L4

Question 14

Achilles reflex

Answer 14

S1

Question 15

Plantar reflex

Answer 15

L5, S1*

*Extensor (Babinski) response can indicate UMN, flexor response is not very localizing.

Question 16

1. Describe the functions and pathways within the spinal cord of the 3 major spinal tracts: Anterolateral system, Dorsal column-medial lemniscus, and Corticospinal tract.
2. Discuss the functional consequence for hemilesions of the cord at different levels (Brown-Sequard syndrome).
3. Describe the general layout of gray matter in the spinal cord in anterior (or ventral) horn, intermediate gray, and the dorsal horn.
4. Recognize where along the length of the spinal cord a section is taken from: sacral/lumbar, thoracic, lower cervical, upper cervical, and discuss why the cord is enlarged in lumbar and lower cervical levels.
5. Describe 1) the flow of information from sensory receptors in the skin and muscle to brain stem and spinal cord, 2) the function of the axon collaterals originating in the dorsal (posterior) root ganglia (PRG) that terminate in spinal cord, and 3) the function of axons originating in the neurons in the PRG that ascend and terminate in brain stem.
6. In representative sections of the spinal cord at different levels, identify the posterior fasciculus and its two subdivisions [fasciculus gracilis (FGr) and fasciculus cuneatus (FCu)] and the information these carry, and discuss the effects of lesions of these structures.
7. In reference to the pathways of the anterolateral system, describe the ascending flow of information from pain and temperature sensory receptors with soma in the PRG and sensory endings in the skin to spinal cord, and subsequently to thalamus.
8. In representative sections of the spinal cord at different levels, identify dorsolateral tract (Lissauer’s tract), the substantia gelatinosa, and the location of the anterolateral tract, and describe the effects of lesions at different levels of this pathway.
9. Describe the symptoms occurring after damage of either upper motor neurons or lower motor neurons.
10. Identify the location of neuron cell bodies for preganglionic parasympathetics.

Answer 16

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Question 17

Corticospinal pathway

Answer 17

Motor innervation traveling from the brain to the periphery.

Corona radiata–>internal capsule–>crus cerebri–>pyramid

The ganglionic eminence is split by the corticospinal tract where it forms the internal capsule. Before it coalesces into the internal capsule, it is called the corona radiata.
Laterally: Putamen and Globus Pallidus
Medially: Caudate

Question 18

What is Brown Sequard syndrome? How does it manifest clinically? What anatomy is responsible?

Answer 18

Caused by a hemisection of the spinal cord, in which proprioception/vibrational sense are lost on one side, and pain/temperature is lost on the other. UMN sydromes would also be expected on the side in which the DCML (proprioception) has been affected.

Question 19

The lenticular nucleus is made up of the:

Answer 19

Putamen + Globus Pallidus

pizza slice

Question 20

The striatum is comprised of the:

Answer 20

Caudate and Putamen

Question 21

Caudate + Putamen =

Answer 21

striatum

Question 22

Putamen + Globus Pallidus =

Answer 22

Lenticular Nucleus

Question 23

Shriveling of the hippocampus will be seen in what conditions?

Answer 23

Alzheimers and dementia.