Sensory Receptors 2 Flashcards
What are proprioceptors?
Mechanoceptors that signal body or limb position
What do proprioceptor include?
- Muscle spindles
- Golgi tendon organs
- Joint receptors
What do muscle spindles monitor?
Muscle length and rate of change of muscle length and so they control reflexes and voluntary movements
What do Golgi tendon organs monitor?
Tension on tendons
Tension produced by muscle contraction
What do joint receptors monitor?
Joint angle, rate of angular movement and tension on the joint
What do proprioceptors do?
- Send sensory information to the brain to control voluntary movement
- Muscle spindles and Golgi tendon organs provide sensory information for spinal cord reflexes
- Provide sensory information to perceive limb and body position and movement in space= kinaesthesia
What are most contractile skeletal muscle fibres?
Extrafusal muscle fibres
What form a muscle spindle?
A few specialised intrafusal muscle fibres with specialised sensory and motor innervation that are contained within a capsule
How are muscle spindles orientated in muscle fibres?
Lie parallel
What are the 2 kinds of intrafusal fibres?
- Nuclear bag fibres
- Nuclear chain fibres
Describe a nuclear bag fibre.
Bag shaped and nuclei collected together
Describe a nuclear chain fibre.
Nuclei lined up in a chain
What forms annulospiral endings?
Primary ending from Ia afferent nerves spiral round the centre of intrafusal fibres
What forms flower-spray endings?
Secondary endings from type II afferents form
What do the ends of intrafusal fibres contain?
Contractile sarcomeres while the central area has no contractile material
What do gamma motor neurones innervate?
The ends of intrafusal fibres which contract
What innervates the extrafusal muscle fibres?
alpha motorneurones
What stimulates the spindle stretch receptors?
Muscle stretch
If a muscle lengthens from Lo to L1, what happens to spindles?
- Resting AP frequency depends on the length Lo
- During stretch from Lo to L1, increase AP frequency is proportional to velocity of stretch
- Increase in AP frequency at new steady state
How does spindle information contribute to perception of body position and movement?
- Joint movement is organised by groups of muscles working in opposition ie. agonists and antagonists
- When agonist contrasts, antagonist relaxes and the joint moves
What informs the brain about joint position??
Spindles and joint receptors
What would movement of the agonist muscle do to spindle discharge?
- Stretching increases
- Contracting decreases
What does muscle have to do to stretch tendons?
Develop tension
What happens in an isometric twitch?
There is a burst of APs in afferent fibre from GTO
Describe the orientation of muscle spindles and GTO in relation to extrafusal fibres,
- Muscle spindle=in parallel
- GTO=in series
What do isometric muscle contraction do?
Increase tension in GTOs and Ib sensory axons fire. But activated muscles stay the same length so 1a afferents do not fire
What is the relevance of the gamma motor innervation of the muscle spindles?
- If it was not present, then when the muscle contracts, muscle spindle would be floppy and spindle discharges could stop
- The brain would not be informed about muscle length
- Failure of info flowing into the brain about muscle length, could prevent use of that muscle
What is the function of gamma motor neurons?
- a motor neurone fires- extrafusal muscle contracts
- If the spindle becomes slack it would off air and no longer report muscle length
- But y motor neuron activation contracts the poles of the muscle spindle , so it shorten to match the shortening of the muscle. This keeps the spindle active and transmitting info to the brain
What happens if a motor neuron fires without y?
-Muscle contracts and shortens but spindle stays the same length so sensory 1a firing decreases
What happens when both a and y motor neurons fire?
Both the muscle and the muscle spindle shorten. This ensure there is no drop off in 1a firing during contraction
What restores tension and resets sensitivity of the central sensory part of the intrafusal fibres, at a new muscle length?
- a-motor neuroes fire causing extrafusal fibre contraction
- y motor neurones fire causing intrafusal fibre ends to contract and so stretch the central sensory elements
What is the norm for voluntary movements?
a-y coactivation
What is a-y coactivation?
- a motor neurones are activated causing contraction
- y motor neurones are activated in parallel to maintain spindle sensitivity
