Motor system and Spinal Cord

Question 1

What is the internal capsule?

Answer 1

Bidirectional white matter pathway connecting cerebral hemisphere with the rest of the CNS

Boomerang/tick shaped on both sides of the brain (when cut axially) creating sand timer shape with both hemispheres

Question 2

What is above and below internal capsule? (extensions)

Answer 2

Superiorly continuous with corona radiata
Inferiorly continuous with cerebral peduncle of the midbrain

Question 3

What does internal capsule contain?

Answer 3

Primarily descending motor neurones but there is some third order sensory neurones

Question 4

3 parts of the internal capsule

Answer 4

Anterior limb
Genu
Posterior limb

Question 5

What is contained within the anterior limb of the internal capsule?

Answer 5

Contains axons connecting PMC with cerebellum

Question 6

What is the genu of the internal capsule? What’s in it?

Answer 6

‘Bend’ in capsule
Contains axons of upper motor neurones supplying face

Question 7

What is within the posterior limb of the internal capsule?

Answer 7

Axons of upper motor neurones supplying

(anterior of capsule limb)
Upper limb
Trunk
Lower limb
(posterior of capsule limb)

• mapped out in that order

Question 8

What else (non motor) is within the posterior limb of the internal capsule?

Answer 8

Third order sensory neurones connecting thalamus to post central gyrus

(face, arm, trunk, lower limbs from anterior to posterior)

Question 9

What pathology occurs within the internal capsule that is important?

Answer 9

Lacunar strokes
- internal capsule supplied by lenticulostriate arteries (branches of MCA)

Question 10

What is the function of the lateral corticospinal tract?

Answer 10

Supplies distal muscles

Question 11

What happens at the decussation of pyramids to the UMNs?

Answer 11

85% cross to the contralateral side and form lateral corticospinal tract

15% stay ipsilateral and form ventral corticospinal tract - these then decussate at the level of their target LMN

Question 12

What is the function of the ventral corticospinal tract?

Answer 12

Supplies proximal and trunk muscles

Question 13

What is the spinal cord structure like at the cervical level?

Answer 13

Wide at cervical enlargement
- presence of brachial plexus
- lots of LMN cell bodies and second order sensory neurone cell bodies at this level to supply upper limb

Question 14

What is spinal cord structure like at thoracic spinal level?

Answer 14

Narrow - few LMNs cell bodies and second order sensory neurones due to small myotomes and dermatomes at this level

BUT these levels of cord –> L2 contain lateral horn with sympathetic pre-ganglionic cell bodies

Question 15

Spinal structure between lumbar and sacrum?

Answer 15

Wide at lumbosacral enlargement - lumbosacral plexus present here

Many LMNs and second order sensory neurones to supply lower limbs

Question 16

Structure of spinal cord at sacral region

Answer 16

Narrow- few muscles that need supply here and small area of skin

But S2-S4 contains parasympathetic pre-ganglionic cell bodies and LMNs cell bodies distributing to perineum in pudendal nerve

Question 17

What is white matter like at the top of the cord?

Answer 17

Maximum amount - contains UMN axons waiting to be distributed and convergence of all sensory axons from below

= gradual amount of added white matter as we ascend the cord due to more and more sensory neurones being added

Question 18

What are the dorsal and ventral horns of the cord?

Answer 18

Cell columns running through the cord - they are NOT tracts

Ventral horn contains subdivisions with groups of LMNs cell bodies

Question 19

What is the layout of the ventral horn with regards to LMNs supplying which area of the body

Answer 19

Laterally - lower motor neurones supplying distal muscles (makes sense as they sit closest to the lateral corticospinal tract which supplies distal muscles)

Medially in ventral horns - lower motor neurones supplying proximal muscles (makes sense as they sit closest to anterior/ventral corticospinal tract