Spinal Cord: Descending tracts & reflexes

Question 1

The primary motor cortex receives input from which 2 areas which lie anterior to it?

Answer 1

Supplementary motor area. Pre-motor cortex

Question 2

How many neurons are there in descending motor tracts – what are they?

Answer 2

2 – upper motor neuron, lower motor neuron

Question 3

Lower motor neuron lesions can occur in which 4 key areas?

Answer 3

Spinal cord (at level of LMN cell body)
Spinal nerve
Cauda equina
Peripheral nerve damage e.g. radial nerve

Question 4

Damage to an UMN can result in which 5 symptoms?

Answer 4

Spastic paralysis
Hyper-reflexia
No muscle wasting
Clonus
Extensor plantar response

Question 5

Damage to a LMN can result in which 4 symptoms?

Answer 5

Flaccid paralysis
Hypo-reflexia
Muscle wasting (atrophy)
Fasciculations

Question 6

What is a motor unit?

Answer 6

A LMN and the muscle fibres it innervates

Question 7

What are the 2 main types of LMN and what does each innervate?

Answer 7

Alpha motor neurons – innervate motor units of extrafusal fibres

Gamma motor neurons – innervate intrafusal fibres of muscle spindles

Question 8

Which tract and part of the spinal cord are degenerated in ALS?

Answer 8

Corticospinal tract and ventral horn of the spinal cord

Question 9

In ALS, are there UMN or LMN symptoms?

Answer 9

Both (mixed)

Question 10

Polio affects which type of motor neuron?

Answer 10

LMN

Question 11

What are the 3 main descending motor spinal tracts?

Answer 11

Lateral corticospinal tract

Ventral corticospinal tract

Lateral vestibulospinal tract

Question 12

What is the output of the lateral corticospinal tract?

Answer 12

Primary motor cortex
Pre-motor cortex
Supplementary motor area

Question 13

What is the output of the ventral corticospinal tract?

Answer 13

Primary motor cortex

Question 14

What is the output of the lateral vestibulospinal tract?

Answer 14

Vestibular nuclei of pons & medulla

Question 15

What does the lateral corticospinal tract control?

Answer 15

Major voluntary, skilled motor movement

Question 16

What does the ventral corticospinal tract control?

Answer 16

Minor motor movement

Question 17

What does the lateral vestibulospinal tract control?

Answer 17

Extensor muscle control (anti-gravity action)

Question 18

Where do 80-90% of the descending motor fibres decussate? Which tract do they descend as?

Answer 18

Pyramids of medulla – descend as lateral corticospinal tract

Question 19

Where do 10-15% of the descending motor fibres decussate? Which tract do they descend as?

Answer 19

Close to termination (at the level of the LMN synapse) – descend ipsilaterally as the ventral corticospinal tract

Question 20

What is the major motor pathway to the face?

Answer 20

Corticobulbar tract

Question 21

Would UPM or LMN to the muscles in the head / neck be affected in a brainstem lesion?

Answer 21

LMN / LMN signs

Question 22

Would UPM or LMN to the muscles of the body be affected in a brainstem lesion?

Answer 22

UMN / UPM signs

Question 23

Would a brainstem lesion cause ipsilateral or contralateral muscle loss in the face (i.e. if the lesion was on the left side of the brainstem)?

Answer 23

Ipsilateral – LMN loss in left side of face

Question 24

Would a brainstem lesion cause ipsilateral or contralateral muscle loss in the body (i.e. if the lesion was on the left side of the brainstem)?

Answer 24

Contralateral – UPM loss on right side of body

Question 25

Which descending motor tract does not decussate?

Answer 25

Lateral vestibulospinal tract

Question 26

Which condition includes a hemi-section of the spinal cord?

Answer 26

Brown-Sequard Syndrome

Question 27

What is the name of the reflex that is engaged when you touch something hot?

What muscles does it stimulate and inhibit?

Answer 27

Flexor reflex

Stimulates ipsilateral flexors of limb
Inhibits ipsilateral extensors of limb

Question 28

What is the name of the relax that is engaged when you step on a sharp object?

What muscles does is stimulate and inhibit?

Answer 28

Crossed extensor reflex

Ipsilateral flexor withdrawal
Contralateral extensor activation