Proprioception

Question 1

Describe the function of muscle spindles.

Answer 1

Monitors muscle length and the rate of change of muscle length.
Controls reflexes and voluntary movements.
Muscle tension is monitored.

Question 2

Describe the function of joint receptors.

Answer 2

Monitors joint angle, rate of angular movement, and joint tension.

Question 3

Describe the function of GTOs.

Answer 3

Monitors tendon tension.

Question 4

Give the functions of mechanoreceptors.

Answer 4

Sends sensory information to control voluntary movements and spinal reflex movements.
Allows kinaesthesia.

Question 5

Describe extrafusal and intrafusal fibres.

Answer 5

E - most contractile skeletal muscle.
I - specialised muscle fibres with their own sensory and motor innervation. Contained in a capsule (muscle spindles) that lie in parallel with muscle fibres.

Question 6

How are intrafusal fibres organised?

Answer 6

Nuclear bag fibres - bag-shaped, nuclei collected together.
Nuclear chain fibres - nuclei lined up in a chain.
Ends contain contractile sarcomeres.
Central area has no contractile elements.

Question 7

Describe how annulospiral and flower-spray endings form.

Answer 7

AS - primary endings from Ia afferent nerves wrap around the centre of intrafusal fibres.
FS - secondary endings from II afferent nerves.

Question 8

What innervates intrafusal fibres?
How does this cause APs?

Answer 8

Gamma motoneurons.
This causes the ends to contract and shorten. It stretches stretch sensitive ion channels open, creating a local GP and APs in Ia afferent fibres.

Question 9

What affects AP frequency?

Answer 9

Depends on the original length.
Proportional to the velocity of stretching.
Increases when a new length occurs.

Question 10

How does joint movement occur?

Answer 10

Groups of muscles work in opposition.
Shortening (contraction) reduces spindle discharge.
Spindle and joint receptor information combine to inform the brain about joint position.

Question 11

What is the function of GTOs?

Answer 11

Nerve endings of GTOs mingle with the tendon bundles at the ends of muscles. They lie in series with muscle fibres.

Question 12

How do GTOs form APs?

Answer 12

Muscles contract to increase tendon tension.
GTO nerve endings stretch.
APs occur in Ib afferent fibres.

Question 13

How does isometric muscle contraction affect GTOs?

Answer 13

Increases GTO tension.
Ia muscle spindle afferents only fire when muscle lengths change.
Ib sensory axons fire APs.

Question 14

How do alpha motoneurons work?

Answer 14

They cause muscles to contract and shorten.

Question 15

How do gamma motoneurons work?

Answer 15

They contract the end sarcomeres and the spindle shortens. The central sensory region gets stretched and transmits information to the brain.

Question 16

How do alpha and gamma motoneurons work together?

Answer 16

The muscle and muscle spindle shorten together. There is no drop off in Ia firing during contraction.

Question 17

What happens if gamma motoneurons stop working?

Answer 17

Muscle spindles stay the same length.
The spindle becomes slack and no APs fire from Ia afferent endings.
Extrafusal muscle contracts, intrafusal muscle stays the same. Ia firing decreases when the muscle shortens.

Question 18

How is tension restored in the spindle?

Answer 18

Alpha neurons fire.

Question 19

How is spindle sensitivity maintained?

Answer 19

Gamma neurons fire.

Question 20

What is the function of proprioceptors?

Answer 20

Informs the brain on movements and position of our body in space.
Acts automatically to control movements via spinal cord reflexes.