Functional Hierarchy of the Motor System

Question 1

How are muscles directly controlled in the spinal cord?

Answer 1

Alpha motorneurons

Question 2

What do brainstem nuclei control?

Answer 2

Posture and balance

Question 3

What are the higher brain centres that control brainstem nuclei?

Answer 3

Cerebral cortex
Basal ganglia
Cerebellum

Question 4

What is the result of lesions involving the lower motor neurons?

Answer 4

Flaccid paralysis

Muscle atrophy

Question 5

What is the result of lesions involving the upper motor neurons?

Answer 5

Spasticity

Some paralysis, may be transient

Question 6

What is the result of a corticospinal lesion?

Answer 6

Weakness (paresis)

Question 7

What is the basis of the spatial map of body musculature in the spinal cord?

Answer 7

Proximal areas mapped by medial motorneurones

Distal areas mapped by lateral motorneurones

Question 8

From where does the spinal cord receive descending input?

Answer 8

Brainstem

Question 9

From where does the spinal cord receive direct cortical input?

Answer 9

Corticospinal (Pyramidal) tract

Question 10

Where does sensory input enter the system?

Answer 10

Enters at all levels

Question 11

In what form does sensory input enter the spinal cord?

Answer 11

Proprioceptors
Touch
Pain

Question 12

In what form does sensory input enter the brainstem?

Answer 12

Vestibular system informs about balance

Question 13

In what form does sensory input enter at the level of the cortex?

Answer 13

Visual 
Olfactory 
Auditory 
Emotional 
Intellectual cues

Question 14

What is the result of damage to sensory inputs?

Answer 14

Paralysis (at spinal cord)

Question 15

Where is the stretch reflex found?

Answer 15

Every muscle

Question 16

What is an example of a common stretch reflex?

Answer 16

Patellar tendon (knee jerk reflex)

Question 17

What is the basis of the stretch reflex?

Answer 17

Muscle spindle fibres send impulses to the spinal cord
Synapse in spinal cord
Efferent impulses to alpha motor neurones cause contraction of stretched muscle
Efferent impulses to antagonist muscles are damped

Question 18

What is the significance of the stretch reflex?

Answer 18

Detects level of spinal cord damage

Impaired reflexes indicate areas of nerve damage

Question 19

What type of information does the flexor reflex process?

Answer 19

Information from pain (nociceptors) in skin, muscles and joints

Question 20

How many synapses are involved in the flexor reflex?

Answer 20

Polysynaptic

Question 21

What does the flexor reflex do?

Answer 21

Withdraws body part away from painful stimulus and in towards the body

Question 22

How does the flexor reflex work?

Answer 22

Increased sensory action potentials cause increased activity in flexor muscles via excitatory interneurones
At the same time the antagonistic extensors are inhibited

Question 23

Where are interneurones activated in the flexor reflex?

Answer 23

Several spinal segments

Question 24

How is the body prevented from falling over during the flexor reflex?

Answer 24

Contralateral limb extends:
Excitatory interneurones crossing the spinal cord excite the contralateral extensors
Inhibition of contralateral flexors
Sensory info enters the brain in the contralateral spinothalamic tract

Question 25

Why is the flexor reflex slower than the stretch reflex?

Answer 25

Several interneurones so small synaptic delay | Nociceptive fibres have smaller diameter so conduct more slowly

Question 26

What is the function of the golgi tendon organ at spinal level?

Answer 26

Protective e.g prevents muscle tear due to excess load (can be overridden)

Question 27

How can you continue to hold something that is important, yet heavy, without dropping it?

Answer 27

Descending voluntary excitation of alpha motor neurones can override the inhibition from the golgi tendon organs and maintain contraction

Question 28

How ca the stretch reflex be overridden?

Answer 28

Descending inhibition hyperpolarizes the alpha motor neurones and stretch reflex can not be evoked

Question 29

What is the result of high gamma motor neurones?

Answer 29

Muscles become extremely resistant to stretch (spastic)

Question 30

What area of the spinal cord will stretch reflex affect?

Answer 30

One or two spinal segments (highly localised)

Question 31

What area of the spinal cord will flexor reflex affect?

Answer 31

Spreads through several spinal segments

Question 32

What is the effect of a more powerful pain stimulus?

Answer 32

Greater spinal spread, larger response

Question 33

What is the function of facilitation?

Answer 33

Increases the effect of sensory input

Question 34

What is the Babinski sign?

Answer 34

Extension but not flexion of foot, toes fan yp and out (indicates damage/disruption to corticospinal tract)

Question 35

What are the consequences of spinal shock?

Answer 35

Loss os sensation | Loss of bowel, bladder, sexual regulation

Question 36

What causes spinal shock?

Answer 36

Loss of supraspinal excitation, reflexes not evoked for 2-6 weeks

Question 37

What is clonus?

Answer 37

Oscillatory muscle contraction/relaxation caused by stretch