Functional Hierarchy of the Motor System

Question 1

what is the final common path?

Answer 1

direct control of muscles via alpha motoneurones in the spinal cord

Question 2

how do reflexes occur?

Answer 2

occur autonomously at different segmental spinal levels

Question 3

what are the higher brain centres?

Answer 3

includes Cerebral cortex (Motor cortex and premotor and supplementary motor areas), basal ganglia and cerebellum

Question 4

what spinal reflexes control posture and balance?

Answer 4

higher order reflexes

Question 5

what are the four systems that control movement?

Answer 5

descending control pathways, basal ganglia, cerebellum

and local spinal cord and brain stem circuits

Question 6

describe lower motor neurones

Answer 6

cranial and spinal levels directly innervate muscles to initiate reflex and voluntary movements

Question 7

describe upper motor neurones

Answer 7

in the brainstem or cortex synapse with multiple lower circuit neurones to regulate alpha motoneurone activity

Question 8

which of the upper motor neurones control complex spatiotemporal skilled movements

Answer 8

Those from cortex

Question 9

what do lesions of the lower motor neurones cause?

Answer 9

flaccid paralysis and muscle atrophy

Question 10

what do lesions of the upper motor neurones cause?

Answer 10

cause spasticity, some paralysis, may be transient.

Question 11

what do corticospinal lesions cause?

Answer 11

weakness (paresis), rather than paralysis.

Question 12

Lesions in many posture-regulating pathways cause what?

Answer 12

spastic paralysis

Question 13

proximal shoulder muscle are mapped to medial or lateral motorneurones?

Answer 13

medial

Question 14

distal finger muscles are mapped to medial or lateral motorneurones?

Answer 14

lateral

Question 15

the spinal cord receives descending input from what?

Answer 15

via brainstem

Question 16

the spinal cord receives direct cortical input from what?

Answer 16

via Corticospinal (Pyramidal) tract

Question 17

what occurs after damage to sensory inputs (at spinal level)?

Answer 17

paralysis as if the motoneurones themselves had been damaged.
(they no longer have input)

Question 18

what is the significance of testing for reflexes?

Answer 18

Helps to detect level of spinal cord damage. Can evoke reflexes above but not below level of damage

Question 19

describe flexor (Withdrawal) reflex ?

Answer 19

use information from pain receptors in skin, muscles and joints.
they are polysynaptic and protective

Question 20

how does the flexor reflex work?

Answer 20

Increased sensory APs from pain receptors cause:

• increase activity in the flexor muscles of the affected part
• at same time, the antagonistic extensors are inhibited

Question 21

what is the name of pain receptors?

Answer 21

nociceptors

Question 22

how does the diameter of noiceptive fibres triggered affect the reflex response?

Answer 22

the more powerful the pain stimulus, the greater the spinal spread and the larger the response

Question 23

how does the body prevent falling over when withdrawing a limb from a tack?

Answer 23

contralateral limb extends

this helps to maintain an upright posture by extending the limb to bear the body weight.

Question 24

which of the following fibres has the slowest conduction: nociceptive sensory fibres or muscle spindle afferents

Answer 24

nociceptive sensory fibres have smaller diameter so conduct more slowly

Question 25

what occurs if excessive load is placed on muscle?

Answer 25

golgi tendon reflex activated, causing relaxation thus protecting muscle

Question 26

can reflexes be over-ridden?

Answer 26

yes eg wouldn’t drop child because of GTO reflex

Question 27

how would you override the GTO reflex?

Answer 27

descending voluntary excitation of alpha motoneurones can override the inhibition from the GTOs and maintain contraction.

Question 28

high gamma motoneurone activation of muscle spindle causes what?

Answer 28

muscles to become extremely resistant to stretch and is “spastic”

Question 29

what does activity of gamma motoneurones depend on?

Answer 29

descending pathways

Question 30

what is the spinal spread of a stretch reflex?

Answer 30

spindle input is highly localised and affects only motoneurones of one or two spinal segments

Question 31

what is the spinal spread of a flexor reflex?

Answer 31

pain fibre input is diffuse and spreads through several spinal segments

Question 32

what is it called when the effect of sensory inputs increases?

Answer 32

Facilitation

Question 33

how does the pain fibre input facilitate action of the muscle?

Answer 33

maintain the alpha motoneurones in a more depolarised state.

Question 34

what is the Babinski sign

Answer 34

stroking lateral aspect of the sole causes extension and not flexion, toes fan up and out

Question 35

when is the Babinski sign seen?

Answer 35

damage or disruption to CS tract :

• seen in children < 1 year old motor system not fully developed
• after epileptic seizures - transient cortical function disruption

Question 36

what occurs in spinal shock?

Answer 36

loss of supraspinal excitation and reflexes not evoked for 2-6 weeks - then gradual return of reflexes (often exaggerated)

Question 37

what is clonus?

Answer 37

muscular spasm involving repeated, often rhythmic, contractions