5.1.3 Spinal Cord Motor System

Question 1

What is the internal capsule?

Answer 1

A bidirectional white matter pathway connecting the cerebral hemisphere with the rest of the CNS

Question 2

What is the anterior limb of the internal capsule responsible for?

Answer 2

Contains axons connecting motor cortex with the cerebellum

Question 3

What is the Genu of the internal capsule responsible for?

Answer 3

Axons of UMNs supplying the face

Question 4

What is the posterior limb of the internal capsule responsible for?

Answer 4

Contains axons of UMNs supply the
Upper limbs
Trunk
Lower limbs
In this order from anterior to posterior

Also contains third order sensory axons connecting the thalamus to postcentral gyrus

Question 5

What is the internal capsule continuous with?

Answer 5

Superiorly- corona radiata
Inferiorly- cerebral peduncle

Question 6

What does the internal capsule contain?

Answer 6

Descending motor neurones mainly
Some third order sensory neurones- connects the thalamus to the post central gyrus

Question 7

What can impaired blood supply to the internal capsule result in?

Answer 7

Lacunar stroke-
Internal capsule is supplied by the deep branches of the middle cerebral artery, the lenticulostriate arteries

Question 8

What does the lateral corticospinal tract do?

Answer 8

Fine motor control in the limbs, primarily distal extremities

Question 9

What happens to UMNs at the medullary pyramids?

Answer 9

85% decussate to contralateral side- forms the lateral corticospinal tract

15% remain ipsilateral, descend in ventral funiculus as the ventral corticospinal tract decussates at the level of their target LMNs

Question 10

What does the ventral corticospinal tract do?

Answer 10

Supplies the proximal muscles and trunk

Question 11

Describe the structure of the spinal cord at the cervical level

Answer 11

Wide
-Presence of the brachial plexus
-Many LMN cell bodies and second order sensory neurone cell bodies at these levels to supply upper limbs

Question 12

Describe the structure of the spinal cord at the thoracic level

Answer 12

Narrow
-Relatively few LMN cell bodies and second order sensory cell bodies due to relatively small dermatomes and myotomes at thoracic levels
-Until L2 these levels have the lateral horn which contains sympathetic preganglionic cell bodies

Question 13

Describe the structure of the spinal cord at the sacral level

Answer 13

Narrow
-Relatively few muscles and small area of skin
-S2-4 contains paraympathetic preganglionic cell bodies as well as LMNs that distribute to the perineum in the pudendal nerve

Question 14

What pattern does white matter follow?

Answer 14

Maximum amount of white matter at the top since it contains UMN axons yet to be distributed as well as the convergence of all sensory axons

As we descend the cord UMN axons distributed to LMNs in cord grey matter, hence UMN axons decreases

Ascending the cord from the bottom sensory axons gradually added

Gradual increase in total white matter as we ascend the cord

Question 15

What are the dorsal and ventral horns?

Answer 15

Cell columns running the length of the cord- not tracts

Columns have subdivisions containing groups of LMN cell bodies

Question 16

Describe the ventral horn column

Answer 16

Laterally-LMNs supplying distal muscles (as they sit closes to lateral CST which supplies distal muscles)

Medially-LMNs supplying proximal muscles (sit closest to anterior/ventral CST which supplies proximal muscles)