Muscle spindles

Question 1

What is the myotatic reflex?

Answer 1

When a skeletal muscle is pulled, it pulls back

stretch of muscle spindle –> activation of 1a afferent –> excitatory synaptic transmission –> activation of alpha motor neurone –> contraction of homonymous muscle

Question 2

What does the muscle spindle do?

Answer 2

It registers the length (and rate of change) of the muscle

Question 3

Which type of fibres are in muscle spindles?

Answer 3

Intrafusal (innervated by class 1a fibres)

extrafusal fibres generate muscle force

Question 4

Sensory innervation of muscle spindles?

Answer 4

Ia class, myelinated and fast conducting

Question 5

Which neurotransmitter mediate the myotatic reflex?

Answer 5

Glutamate

Question 6

Supinator (wrist) reflex

Answer 6

C5-C6

Question 7

Biceps (elbow) reflex

Answer 7

C5-C6

Question 8

Triceps (elbow) reflex

Answer 8

C7

Question 9

Quadriceps (knee) reflex

Answer 9

L3-L4

Question 10

Gastrocnemius reflex (ankle)

Answer 10

S1

Question 11

What do alpha motor neurones innervate?

Answer 11

Muscle fibres

Question 12

What do gamma motor neurones innervate?

Answer 12

These innervate the muscle spindles (remember these are the tiny sensory organs IN the muscles)

Stimulation of the gamma motor neurones causes the spindles to contract

Question 13

What do group Ib afferents innervate?

Answer 13

Innervate golgi tendon organs

Question 14

What do golgi tendon organs do?

Answer 14

Act to regulate muscle tension to:

• protect muscle from overloads (e.g. in weight lifting)
• more generally regulate muscle tension to an optimal tension

Question 15

How does the reverse myotatic reflex work?

Answer 15

Ib fibre - spine - motor fibre (this is reverse to the myotatic reflex, it is inhibitory)