Proprioception

Question 1

What are proprioceptors?

Answer 1

Mechanoreceptors that signal body or limb position

Question 2

Give three examples of proprioceptors

Answer 2

Muscle spindles- monitor muscle length and rate of change of muscle length - control reflexes and voluntary movements. “M for Measurement”.

Golgi tendon organs - monitor tension on muscles. “T for tension”.

Joint receptors - Monitor joint angle, rate of angular movement, and tension on the joint.

Question 3

Which proprioceptors are involved with sending sensory information for spinal cord reflexes?

Answer 3

Golgi tendon organs and muscle spindles

Question 4

What is a muscle spindle?

Answer 4

Intrafusal fibres with special sensory and motor innervation contained within a capsule, they lie in parallel with extrafusal muscle fibres

Question 5

What are the two different types of intrafusal fibre?

Answer 5

Nuclear bag fibres - bag shaped, nuclei are all grouped together
Nuclear chain fibres - nuclei are lined up in a chain

Question 6

What is contained at the ends of the muscle spindle?

Answer 6

Sacromeres

Question 7

What do gamma motoneurones innervate?

Answer 7

Innervate ends of intrafusal fibres which contract

Question 8

What do alpha motoneurones innervate?

Answer 8

The extrafusal muscle fibres, they are larger than gamma motoneurones “alpha extra”

Question 9

How are regenerative action potentials in the muscle spindles created?

Answer 9

Muscle stretch stimulates the stretch receptors, stretch sensitive ion channel opens causing local generator potential - causing regenerative action potentials

Question 10

Stretch receptors can monitor the rate of change of muscle length, how is this done

Answer 10

The rate of action potential formation reflects the velocity of change of muscle length

Question 11

How is muscle length determined by the muscle stretch receptors?

Answer 11

The resting rate of action potential formation at one muscle length will be different to the resting rate of action potential formation at another length

Question 12

How can spindle discharge be increased?

Answer 12

Stretching the agonnist

Question 13

Describe the structure of the golgi tendon organ

Answer 13

Nerve endings mingle with tendon bundles at the end of the muscle

Question 14

How are golgi tendon organs activated?

Answer 14

Contraction of the muscle, passive stretch doesn’t affect them much

Question 15

Are GTO’s in series or parallel with the muscle?

Answer 15

Series

Question 16

Which proprioceptors are activated during isometric contraction?

Answer 16

Only GTO’s since tension is increased but length of the muscle is kept constant

Question 17

What is the purpose of gamma motor neurones?

Answer 17

Makes the intrafusal muscle contract in time with the extrafusal muscle, this restores sensitivity of the central part of the intrafusal fibres at a new muscle length - maintains spindle sensitivity