Functional hierarchy of the motor system

Question 1

What is the direct control of muscles via?

Answer 1

alpha motorneurons in the spinal cord

Question 2

What 2 tracts give descending inputs to incorporate the trunk and limb muscles into reflexes?

Answer 2

vestibulospinal and reticulospinal

Question 3

What are the 3 higher brain centres controlling brainstem nuclei instructing voluntary movement?

Answer 3

cerebral cortex
basal ganglia
cerebellum

Question 4

Lesions of LMN results in?

Answer 4

flaccid paralysis and muscle atrophy

Question 5

How is alpha motor neuron activity regulated?

Answer 5

UMN in brainstem or cortex synapse with multiple lower circuit neurons

Question 6

Lesion in UMN

Answer 6

spasticity, high tone eg Parkinsons

Question 7

Corticospinal tract lesion

Answer 7

weakness rather than paralysis

Question 8

Paresis

Answer 8

muscle weakness

Question 9

How is the body musculature mapped in spinal cord?

Answer 9

medio-laterally

Question 10

If there is damage to sensory inputs what happens?

Answer 10

paralysis as if the motor neurons themselves were damaged

Question 11

In the stretch reflex which muscle is innervated by a monosynaptic synapse and which by a polysynaptic reflex?

Answer 11

the extensor is monosynaptic and the flexor is polysynaptic

Question 12

Name the 4 main stretch reflexes and their cord segment which they align with

Answer 12

biceps - C6
triceps - C7
patellar - L4
Achilles tendon - S1

Question 13

How can reflexes help detect level of spinal cord damage?

Answer 13

reflexes can be evoked above but not below level of damage

Question 14

In diabetes which reflex may be lost?

Answer 14

Achilles tendon - ankle jerk

Question 15

Why must patients be distracted when testing their reflexes?

Answer 15

avoid voluntary interference

Question 16

What are nociceptors?

Answer 16

pain receptors

Question 17

nociceptor - 3 P’s

Answer 17

protective, polysynaptic and pain

Question 18

Do nociceptive fibres have a large or small diameter?

Answer 18

small

Question 19

Flexor reflex - is there contralateral or ipsilateral flexion?

Answer 19

ipsilateral

Question 20

Flexor reflex - is there contralateral or ipsilateral extension?

Answer 20

contralateral

Question 21

Why does the contralateral limb extend?

Answer 21

prevent falling over

Question 22

In the flexor reflex how does sensory information ascend to the brain?

Answer 22

spinothalamic tract

Question 23

This basic circuitry for the flexor withdrawl and contralateral extension is the same for what simple day to day activity?

Answer 23

walking

Question 24

Why is the flexor crossed extensor reflex much slower than the stretch reflex?

Answer 24

several interneurons with synaptic delay

nociceptive fibres have small diameter = slow conduction

Question 25

Excessive load on a muscle activates what to protect the muscle from tearing?

Answer 25

Golgi tendon organ

Question 26

What can override the GTO?

Answer 26

descending voluntary excitation of alpha motor neurons

Question 27

High activity of gamma motor neurons can lead to what?

Answer 27

muscles becoming resistant to stretch –> spastic

Question 28

What Is altered gamma motor neuron discharge to spindles associated with?

Answer 28

neurological disorders

Question 29

What is facilitation of reflexes?

Answer 29

increases effects of sensory inputs

Question 30

Pain fibre input facilitates action of muscle spindles by maintaining alpha motor neurons in which state?

Answer 30

depolarised

Question 31

When the lateral aspect of sole is stroked what should happen?

Answer 31

plantar flexion

Question 32

What is babinski’s sign?

Answer 32

disruption to corticospinal tract causes plantar extension

Question 33

What group of non pathological patients is babinski’s sign found in?

Answer 33

children < 1 years old as their motor system is not fully developed

Question 34

What is spinal shock?

Answer 34

spinal cord injury leading to loss of reflexes for a month which come back gradually and are often exaggerated

Question 35

Clonus

Answer 35

stretch causes oscillatory muscle contraction and relaxation