Proprioception Flashcards
Describe the function of muscle spindles.
Monitors muscle length and the rate of change of muscle length.
Controls reflexes and voluntary movements.
Muscle tension is monitored.
Describe the function of joint receptors.
Monitors joint angle, rate of angular movement, and joint tension.
Describe the function of GTOs.
Monitors tendon tension.
Give the functions of mechanoreceptors.
Sends sensory information to control voluntary movements and spinal reflex movements.
Allows kinaesthesia.
Describe extrafusal and intrafusal fibres.
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.
How are intrafusal fibres organised?
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.
Describe how annulospiral and flower-spray endings form.
AS - primary endings from Ia afferent nerves wrap around the centre of intrafusal fibres.
FS - secondary endings from II afferent nerves.
What innervates intrafusal fibres?
How does this cause APs?
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.
What affects AP frequency?
Depends on the original length.
Proportional to the velocity of stretching.
Increases when a new length occurs.
How does joint movement occur?
Groups of muscles work in opposition.
Shortening (contraction) reduces spindle discharge.
Spindle and joint receptor information combine to inform the brain about joint position.
What is the function of GTOs?
Nerve endings of GTOs mingle with the tendon bundles at the ends of muscles. They lie in series with muscle fibres.
How do GTOs form APs?
Muscles contract to increase tendon tension.
GTO nerve endings stretch.
APs occur in Ib afferent fibres.
How does isometric muscle contraction affect GTOs?
Increases GTO tension.
Ia muscle spindle afferents only fire when muscle lengths change.
Ib sensory axons fire APs.
How do alpha motoneurons work?
They cause muscles to contract and shorten.
How do gamma motoneurons work?
They contract the end sarcomeres and the spindle shortens. The central sensory region gets stretched and transmits information to the brain.
How do alpha and gamma motoneurons work together?
The muscle and muscle spindle shorten together. There is no drop off in Ia firing during contraction.
What happens if gamma motoneurons stop working?
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.
How is tension restored in the spindle?
Alpha neurons fire.
How is spindle sensitivity maintained?
Gamma neurons fire.
What is the function of proprioceptors?
Informs the brain on movements and position of our body in space.
Acts automatically to control movements via spinal cord reflexes.
