Week 8 - Motor cortex and motor pathways

Question 1

What are descending pathways?

Answer 1

• Can start from brain and go all the way down the spinal cord to connect with the peripheral nerve
• Other pathways start from the brain and terminate in the brainstem
• Others originate in the brainstem and travel down the spinal cord

Question 2

Where is the motor cortex?

Answer 2

In the pre-central gyrus in the frontal lobe

Question 3

What are the 3 main areas responsible for movement?

Answer 3

Motor cortex/homonculus

Premotor cortex

Supplementary motor area

Question 4

What is the motor homunculus?

Answer 4

A topographic representation of the body parts and it’s correspondents along the pre-central gyrus of the frontal lobe.

-different sizes/representations relative to different body parts e.g. hand represented by different surface area than hip - because of amount of precision needed with movement

→ larger area = higher degree of precision needed

Question 5

What is involved in the corticospinal pathway?

Answer 5

(known as the pyramidal tract)

→ originates in the primary motor and pre-motor cortex
→ control of fine skilled movements on contralateral side of the body
→ in medulla oblongata - pathway decussates and forms “pyramids”
→ MOST fibres cross over, but some don’t

Question 6

How are the fibres in the corticospinal pathway distributed?

Answer 6

75-90% decussate - lateral corticospinal tract
10-25% ipsilateral - anterior corticospinal tract

(may influence post-stroke symptoms)

Question 7

What is the role of the corticospinal pathway?

Answer 7

Main pathway for producing voluntary, skilled movement

Question 8

What is involved in the corticobulbar pathway?

Answer 8

→Pathway originates in cortex and travels to brainstem - HERE THEY SYNAPSE WITH CRANIAL NERVES
→If these pathways continue they become the cortiocospinal pathway (skilled, voluntary movement)
→Only supplies neck and face

Question 9

What are extrapyramidal tracts and examples?

Answer 9

Originate in brainstem, not under our conscious control unlike corticospinal

Examples: vestibulospinal tract, reticulospinal tract

Question 10

What is involved in the vestibulospinal tract?

Answer 10

Has a lateral and medial tract
𝐋𝐚𝐭𝐞𝐫𝐚𝐥
- receives info from places such as inner ear, and cerebellum - received afferent/sensory info
- message from brainstem (vestibular nuclei) travels down but doesn’t cross over and supplies muscles of back and thorax (posture - innervates muscles of spine and trunk)

𝐌𝐞𝐝𝐢𝐚𝐥
- cross over

Question 11

What is an alpha motor neurone?

Answer 11

innervates contractile elements of muscles (actin and myosin)

Question 12

What is a gamma motor neurone?

Answer 12

innervates muscle spindle

Question 13

What is involved in the reticulospinal tract?

Answer 13

Responsible for posture in the head/neck/torso

→ Originate from reticular formation in brainstem
→ Medial and lateral pathways - some info from cerebellum and some from brain
→ 2 pathways influenced by what is happening to us and what environment we are in
→ Influencing body position/ posture/ muscle tone to enable out voluntary movement to be more effective

Question 14

How can voluntary movement be more effective through facilitation and inhibition?

Answer 14

Reticulospinal tract activates gamma neurones to control/modulate sensitivity of the muscle spindle

Question 15

What is the internal capsule and what does it do?

Answer 15

White matter tracts have to squeeze down this to descend

→ it carries info. past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus
→ the internal capsule contains both ascending and descending axons, going to and coming from the cerebral cortex