Lecture 4: Muscle Spindle I

Question 1

Peripheral receptors project where via what?

Answer 1

Project centrally to the spinal cord via 1st order peripheral somatosensory neurons

Question 2

How do peripheral receptors project to more superior structures?

Answer 2

By forming spinal reflex pathways

Question 3

How are afferents labeled?

Answer 3

Based on cross-sectional diameter (size)

Question 4

Afferents are labelled I-IV, meaning?

Answer 4

I- largest
IV- smallest

Question 5

Conduction velocity of sensory afferents depends on _____

Answer 5

Diameter

Question 6

What are muscle spindles?

Answer 6

Fusiform shaped receptors found in most skeletal muscle

Question 7

Muscle spindles provide feedback about:

Answer 7

• Muscle length
• The ROC of muscle length

Question 8

Two major kinds of intrafusal fibers:

Answer 8

Bag or chain

Question 9

3 specific types of intrafusal fibers:

Answer 9

• Bag1 (dynamic bag)
• Bag2 (static bag)
• Nuclear chain (static)

Question 10

Two types of sensory afferent innervation

Answer 10

• Group Ia (primary) afferents
• Group II (secondary) afferents

Question 11

How do Group Ia and Group II afferents differ from each other?

Answer 11

Group Ia spirals around the centre of the equatorial region of all 3 intrafusal fibre types
Group II innervates Bag2 and static fibres, but not Bag1 (dynamic)

Question 12

Sensory afferents wrap around _____ region of muscle fibres:

Answer 12

Equitorial region

Question 13

What part of sensory afferents innervate spindles?

Answer 13

Sensory endings

Question 14

Different spindle afferent response to muscle stretch:

Answer 14

• Ia afferents are sensitive to velocity and length
• II afferents are sensitive to the length change

Question 15

What region of muscle spindles have myofilament contractile components?

Answer 15

Polar region (ends)

Question 16

Muscle spindles without efferent after firing- steps:

Answer 16

1. Alpha motor neuron fires
2. Muscle contracts
3. Stretch of centre of intrafusal fibres is reduced
4. Firing rate of spindle sensory neurons decreases

Question 17

Muscle spindles with efferent after firing- steps:

Answer 17

1. Alpha motor neuron fires and gamma motor neuron fires
2. Muscle contracts
3. Stretch on centres of intrafusal fibres unchanges. Firing rate of afferent neuron remains constant

Question 18

Dynamic gamma motor neurons innervate;

Answer 18

Only Bag 1 fibres

Question 19

Static gamma motor neurons innervate:

Answer 19

Static Bag 2 and static chain fibres