N14- Descending motor pathways

Question 1

Where is the primary motor cortex found?

Answer 1

anterior to central sulcus

Question 2

what is caused by the crossing of motor fibres across the midline?

Answer 2

the right cortex controls muscles on the left side of the body and vice versa (in almost all cases)

Question 3

How can you tell the difference between a motor and sensory homunculus?

Answer 3

A sensory homunculus has genitalia and a motor one does not

Question 4

How many descending tracts are there?

Answer 4

1 large main one and several small ones

Question 5

What is the main descending tract?

Answer 5

Corticospinal tract

Question 6

What does the corticospinal tract control?

Answer 6

Control of precision and speed of skilled movements, particularly of distal limb muscles (e.g. digits)

Question 7

What do tracts of the corticospinal tract form?

Answer 7

visible ridges referred to as the ‘pyramids’ on the anterior surface of the medulla

Question 8

What are the pyramids on the anterior surface of the medulla called?

Answer 8

pyramidal tract

Question 9

Where do 85% of fibres cross in the corticospinal tract?

Answer 9

in the caudal medulla at the decussation of the pyramids

Question 10

Where does the corticospinal tract project from?

Answer 10

Primary cortex and areas around it to the spinal cord

Question 11

What do the crossed fibres form?

Answer 11

Lateral corticospinal tract

Question 12

what do the uncrossed fibres form?

Answer 12

Ventral corticospinal tract

Question 13

Where do the uncrossed fibres cross?

Answer 13

Segmentally at whatever segment they are terminating in

Question 14

What does the pre central gyrus project?

Answer 14

internal capsule

Question 15

What motor systems are collectively referred to as the extrapyramidal system?

Answer 15

• Tectospinal tract
• Vestibulospinal tract
• Reticulospinal tract

Question 16

What does the tectospinal tract input mostly to?

Answer 16

cervical segments

Question 17

Where do fibres originate in the tectospinal tract?

Answer 17

In the superior colliculus which is in a region of midbrain called the tectum

Question 18

What does the tectospinal tract mediate?

Answer 18

The superior colliculus receives visual information and so this tract is thought to mediate reflex movement due to visual stimuli

Question 19

Where is the crossed tract limited to in the tectospinal tract?

Answer 19

Upper portion of spinal cord

Question 20

Where does the fibres originate in the vestibulospinal tract?

Answer 20

ipsilateral vestibular nuclei of pons and medulla (these in turn receive input from vestibular apparatus and cerebellum

Question 21

Where do fibres from the vestibule nuclei in the vestibulospinal tract project to?

Answer 21

projects ipsilaterally in spinall cord and to antigravity muscles of lower limbs

Question 22

what does the reticular formation form?

Answer 22

central core of the brainstem

Question 23

Where does the reticulospinal tract receives input from?

Answer 23

all parts of the CNS

Question 24

Name one of the functions of the reticulospinal tract.

Answer 24

influencing of voluntary movement

Question 25

where do fibres originate in the reticulospinal tract?

Answer 25

areas of the reticular formation in pons and medulla

Question 26

what do fibres in the reticulospinal tract originating in the pons do?

Answer 26

facilitate extensor movements and inhibit flexor movements

Question 27

what do fibres in the reticulospinal tract originating in the medulla do?

Answer 27

the opposite of the fibres originating in the pons

Question 28

What does it mean that some fibres extend to many spinal levels?

Answer 28

help coordinate movement involving upper and lower limbs