Sensory Receptors 2

Question 1

What are proprioceptors?

Answer 1

Mechanoceptors that signal body or limb position

Question 2

What do proprioceptor include?

Answer 2

• Muscle spindles
• Golgi tendon organs
• Joint receptors

Question 3

What do muscle spindles monitor?

Answer 3

Muscle length and rate of change of muscle length and so they control reflexes and voluntary movements

Question 4

What do Golgi tendon organs monitor?

Answer 4

Tension on tendons

Tension produced by muscle contraction

Question 5

What do joint receptors monitor?

Answer 5

Joint angle, rate of angular movement and tension on the joint

Question 6

What do proprioceptors do?

Answer 6

• Send sensory information to the brain to control voluntary movement
• Muscle spindles and Golgi tendon organs provide sensory information for spinal cord reflexes
• Provide sensory information to perceive limb and body position and movement in space= kinaesthesia

Question 7

What are most contractile skeletal muscle fibres?

Answer 7

Extrafusal muscle fibres

Question 8

What form a muscle spindle?

Answer 8

A few specialised intrafusal muscle fibres with specialised sensory and motor innervation that are contained within a capsule

Question 9

How are muscle spindles orientated in muscle fibres?

Answer 9

Lie parallel

Question 10

What are the 2 kinds of intrafusal fibres?

Answer 10

• Nuclear bag fibres

- Nuclear chain fibres

Question 11

Describe a nuclear bag fibre.

Answer 11

Bag shaped and nuclei collected together

Question 12

Describe a nuclear chain fibre.

Answer 12

Nuclei lined up in a chain

Question 13

What forms annulospiral endings?

Answer 13

Primary ending from Ia afferent nerves spiral round the centre of intrafusal fibres

Question 14

What forms flower-spray endings?

Answer 14

Secondary endings from type II afferents form

Question 15

What do the ends of intrafusal fibres contain?

Answer 15

Contractile sarcomeres while the central area has no contractile material

Question 16

What do gamma motor neurones innervate?

Answer 16

The ends of intrafusal fibres which contract

Question 17

What innervates the extrafusal muscle fibres?

Answer 17

alpha motorneurones

Question 18

What stimulates the spindle stretch receptors?

Answer 18

Muscle stretch

Question 19

If a muscle lengthens from Lo to L1, what happens to spindles?

Answer 19

• Resting AP frequency depends on the length Lo
• During stretch from Lo to L1, increase AP frequency is proportional to velocity of stretch
• Increase in AP frequency at new steady state

Question 20

How does spindle information contribute to perception of body position and movement?

Answer 20

• Joint movement is organised by groups of muscles working in opposition ie. agonists and antagonists
• When agonist contrasts, antagonist relaxes and the joint moves

Question 21

What informs the brain about joint position??

Answer 21

Spindles and joint receptors

Question 22

What would movement of the agonist muscle do to spindle discharge?

Answer 22

• Stretching increases

- Contracting decreases

Question 23

What does muscle have to do to stretch tendons?

Answer 23

Develop tension

Question 24

What happens in an isometric twitch?

Answer 24

There is a burst of APs in afferent fibre from GTO

Question 25

Describe the orientation of muscle spindles and GTO in relation to extrafusal fibres,

Answer 25

• Muscle spindle=in parallel

- GTO=in series

Question 26

What do isometric muscle contraction do?

Answer 26

Increase tension in GTOs and Ib sensory axons fire. But activated muscles stay the same length so 1a afferents do not fire

Question 27

What is the relevance of the gamma motor innervation of the muscle spindles?

Answer 27

• If it was not present, then when the muscle contracts, muscle spindle would be floppy and spindle discharges could stop
• The brain would not be informed about muscle length
• Failure of info flowing into the brain about muscle length, could prevent use of that muscle

Question 28

What is the function of gamma motor neurons?

Answer 28

• a motor neurone fires- extrafusal muscle contracts
• If the spindle becomes slack it would off air and no longer report muscle length
• But y motor neuron activation contracts the poles of the muscle spindle , so it shorten to match the shortening of the muscle. This keeps the spindle active and transmitting info to the brain

Question 29

What happens if a motor neuron fires without y?

Answer 29

-Muscle contracts and shortens but spindle stays the same length so sensory 1a firing decreases

Question 30

What happens when both a and y motor neurons fire?

Answer 30

Both the muscle and the muscle spindle shorten. This ensure there is no drop off in 1a firing during contraction

Question 31

What restores tension and resets sensitivity of the central sensory part of the intrafusal fibres, at a new muscle length?

Answer 31

• a-motor neuroes fire causing extrafusal fibre contraction

- y motor neurones fire causing intrafusal fibre ends to contract and so stretch the central sensory elements

Question 32

What is the norm for voluntary movements?

Answer 32

a-y coactivation

Question 33

What is a-y coactivation?

Answer 33

• a motor neurones are activated causing contraction

- y motor neurones are activated in parallel to maintain spindle sensitivity