Control of movement 2: Muscle reflexes

Question 1

Whats important in the formation of planned movement?

Answer 1

Sensory information inputs into motor movement.

Question 2

Whats the final common pathway?

Answer 2

Alpha motor neurons are the final common pathway, which receive multiple inputs.

Question 3

What are the inputs of the final common pathway?

Answer 3

1) Descending tracts i.e corticospinal, reticulospinal
2) Spinal (Segmental) interneurons i.e 1a inhibitory interneurons
3) Propriospinal neurons (co-ordinate movements of upper and lower limbs)

Question 4

Which are the main receptors which control movement?

Answer 4

• Muscle spindles (monitor dL/dt)
• Golgi tendon organs (monitor muscle tension)
• Nocioceptive receptors
• Joint receptors

Question 5

How do receptors influence movement?

Answer 5

Initiates reflex or inhibits movement.

Question 6

What are the five elements of spinal reflexes?

Answer 6

1) Receptors
2) Afferent (sensory) fibres
3) Central synaptic relays
4) Efferent (motor) fibres
5) Effectors (i.e muscles)

Question 7

What are some names for the stretch reflex?

Answer 7

Stretch or tendon/myotatic reflex.

Question 8

What is unique about the stretch reflex?

Answer 8

Only monosynaptic reflex in body

Question 9

What is the stretch reflex?

Answer 9

Muscle spindles detect stretch or vibration in the muscle.

Question 10

Describe the stretch reflex using the five elements?

Answer 10

1) Receptors; Muscle spindles
2) Afferents; 1a afferents (100ms, fastest)
3) Synaptic relay (glutamatergic excitatory on alpha)
4) Efferents (axons of AMNs)
5) Effectors; Homonymous or synergistic muscle
6) Latency of the knee jerk reflex

Question 11

What is reciprocal inhibition?

Answer 11

Between flexors and extensors.

Additional synaptic relay, collaterals of 1a afferents make synapses on 1b inhibitory interneurons. These inhibit motor neurons innervating antagonistic muscles.

Question 12

What are 3 commonly tested stretch reflexes?

Answer 12

Brachioradialis; C5,6
Knee jerk; L3,4
Ankle jerk; S1

Question 13

What is the role of gamma motor neurons?

Answer 13

Precedes AMN activation but not in isolation. (alpha gamma coactivation)

Gamma motoneurons activates intrafusal muscle fibres maintains the stretch receptors during muscle contraction.

Question 14

What is the reflex evoked from the golgi tendon organs?

Answer 14

• Adjusts tension among muscles among muscles during a motor task.
• Inhibition of stretched muscles and excitation of antagonistic muscle.

Question 15

What are the additional features of golgi tendon organs?

Answer 15

• Protects muscles from overloading and compensation for the muscle fatigue (when muscle tension decreases)

Threshold higher in diseased upper motoneurons

Question 16

Describe the flexor withdrawl reflex;

Answer 16

• Nocioceptors
• Afferents; Type 3 and 4 fibres
• Synaptic relays; Excitatory interneurons to flexors and inhibitory interneurons to extensors.
• Efferents (AMNs)
• Effectors, flexor muscles.