Muscle spindle Flashcards
What is a muscle spindle?
A sensory receptor made of intrafusal fibres with sensory and motor nerve fibres
What do they detect?
Stretch of extrafusal fibres
What does the nuclear bag detect?
Stretch and speed of stretch
What does the nuclear chain detect?
Length of stretch
What happens in the patella tap?
Stimulus (tap), Picked up by muscle spindle, goes through sensory neuron to the spinal cord, to motor neuron output, leg kicks out
1A afferent impulses
Fro the nuclear bag. Respond to phasic stretch. Enter spinal cord via dorsal horn and synapse with interneurons.
IIA afferent impulses
From the nuclear chain. Respond to tonic length. Enter via dorsal horn and synapse with interneurons.
What do the IA and IIA both do?
Inhibit antagonistic muscles so they can’t oppose the shortening of the stretched muscle
Gamma efferents
Stimulate intrafusal fibres to maintain muscle spindles sensitivity and tension
When a muscle is stretched..
It rapidly fires
When a muscle is relaxed..
It fires less
When a muscle is contracted..
It hardly fires
What is alpha gamma co-activaton
If only alpha motor neurons were activated, only the extrafusal fibres would contract.
But alpha gamma co-activation ensures the extrafusal and intrafusal fibres contract at the same time to maintain tension in the muscle spindle.
How does the CNS control the sensitivity of the muscle spindle ?
Via Gamma drive.
Gamma drive causes contraction of bag and chain fibres which stretches the central region where the afferents are located, increasing their sensitivity
So Gamma drive adjusts muscle spindle sensitivity
