Sensory Receptors- Proprioception

Question 1

What is the role of proprioceptors?

Answer 1

are mechanoreceptors that signal body or limb position

Question 2

What are the types of proprioceptors ?

Answer 2

Muscle spindles – which monitor muscle length and rate of change of muscle length - they control reflexes and voluntary movements.

Golgi tendon organs – which monitor tension on tendons
tension is produced by muscle contraction, so monitoring muscle tension.

Joint receptors – which monitor joint angle, rate of angular movement and tension on the joint.

Question 3

What do proprioceptors do?

Answer 3

1. send sensory information to the spinal cord and on to the brain so that it can control our voluntary movements
2. muscle spindles and Golgi tendon organs provide the sensory information to spinal cord neurones which can generate spinal reflex movements
3. they provide sensory information to perceive limb and body position and movement in space = kinaesthesia.

Question 4

What is most of skeletal muscle made up of?

Answer 4

extrafusal muscle fibres

Question 5

What are intrafusal muscle fibres?

Answer 5

specialised muscle fibres with own sensory and motor innervation

Question 6

Where are intrafusal muscle fibres located?

Answer 6

contained within a connective tissue capsule and called muscle spindles

muscle spindles lie in parallel with muscle fibres

Question 7

What neurons cause motor innervation to extrafusal muscle fibre?

Answer 7

alpha motor neurons

Question 8

What neurons cause motor innervation to interfusal fibre?

Answer 8

gamma motor neurons

Question 9

What happens in centre of interfusal muscle fibres?

Answer 9

have sensory neurons - send info off to CNS
no contractile elements of muscle fibres

Question 10

What are the two kinds of intrafusal fibre?

Answer 10

nuclear bag fibres-bag shaped with nuclei collected together
nuclear chain fibres-nuclei lined up in a chain

Question 11

What are annulospiral endings?

Answer 11

Primary endings from Ia afferent nerves wrap around the centre of intrafusal fibres

Question 12

What are flower spray endings?

Answer 12

Secondary endings from type II afferents form flower-spray endings

Question 13

Where contains contractile sarcomeres?

Answer 13

ends of intrafusal fibres but central area has no contractile elements

Question 14

What happens when muscle is stretched?

Answer 14

Muscle stretch stimulates the spindle stretch receptors
Stretch sensitive ion channels open
create a local receptor potential and causes APs in1a afferents

Question 15

If a muscle lengthens from L0 to L1, what happens to spindle APs?

Answer 15

Resting AP frequency depends on the length Lo
During stretch from L0 to L1, increased AP frequency is proportional to velocity of stretch (the slope of the line)
Increased AP frequency at new steady state ……. and so L1 > L0

Question 16

What does difference between AP frequency 1 and 3 tell us?

Answer 16

muscle length

Question 17

What does AP frequency at 2 tell us?

Answer 17

rate of change of length

Question 18

Describe the mechanism of agonists and antagonists?

Answer 18

when agonist contracts, antagonist relaxes and the joint moves

Question 19

Describe the change in length of agonists and antagonists?

Answer 19

if agonist muscle stretched and then contracts the opposite changes in length happen in antagonist

so stretching agonist increases spindle discharge
contracting agonist reduces spindle discharge

Question 20

What does golgi tendon organ do?

Answer 20

monitors muscle tension
Nerve endings of GTO mingle with the tendon bundles at ends of muscles. They are stretch receptors and monitor stretch of tendon

When muscle changes length it increases or decreases tension on the tendon therefore GTO also measuring muscle tension

Question 21

Describe the delivering of info from GTO to brain?

Answer 21

muscle contraction increases the tension in the tendons
this stretches the nerve endings of the GTO and
initiates APs in the group 1b afferent fibre from the GTO

Question 22

What happens in isometric contraction?

Answer 22

activating extrafusal fibres through alpha motor neuron and will see increase in firing rate of them .
That exerts tension on golgi tension organ so its 1b afferents fire action potentials but because muscle itself hasn’t changed in length- the muscle spindle is not activated and no firing action potentials

Question 23

what is the significance of the gamma motor innervation to the contractile ends of muscle spindles?

Answer 23

when alpha motorneurones fire they cause a muscle to contract and shorten, the muscle spindles would stay same length and they would become floppy and would stop firing APs from the 1a afferent annulospiral endings
so the brain would not be informed correctly or at all about a change in muscle length
this would limit the functional usefulness of that muscle

Question 24

What are the function of gamma motor neurons?

Answer 24

if alpha motor neuron fires extrafusal muscles contract and shorten but with no gamma motor neurone activity, spindle just becomes slack and not detecting change in muscle caused by contraction.
So to prevent this, gamma motor neuron activation also contracts the ends of the muscle spindle in response to contraction of extrafusal fibres, spindle shortens to match the shortening of the muscle.
And as the end sarcomeres contract and the spindle shortens, the central sensory region gets stretched. This keeps the spindle active and “on air” - transmitting information to the brain

Question 25

What does spindle 1a afferents do?

Answer 25

report muscle shortening to the brain