Muscle receptors and reflex Flashcards
What is proprioception
the sense of the body’s position in space based on information from specialised receptors in muscles and tendons
it is both static (joint position sense) and dynamic (kinaesthesia - sense of limb movement)
need to recognise the length of the muscle (stretched or contracted) and whether it is changing or maintaining its current position.
What is the M1 component of the reflex?
The afferent input involving interneurons and motor neurons
what is the M2 component of the reflex?
the cortical component
conscious perception of the location and movement of parts of the body via the dorsal column system and cerebral cortex
Proprioceptive information and reflexes are integrated with centrally generated motor commands to produce adaptive movements.
note: the cerebellum mediates subconscious movement
What is the Classical Patellar Tendon / knee jerk reflex?
Place one knee over the other, relax (removing descending control), tap with tendon hammer which stretches the quad muscle
That short sharp stretch will recruit muscle spindles which will then fire action potentials which will go back through a dorsal root ganglion neuron into the spinal cord through the afferent pathway
Two effects: directly recruit the homonymous motor neurons, some synergistic motor neurons AND through an inhibitory interneuron which will then inhibit antagonistic muscles
One will contract one will relax so that the leg swings forward
Synergistic muscle contracts with other muscles to produce movement in one direction
what are the key receptors in proprioception?
muscle spindles signal stretch
golgi tendon organs signal tension produced by muscle contraction
Skin mechanoreceptors also signal postural information, speech/facial expression
Muscle spindles and GTO are specific to muscle
What are the joint mechanoreceptors?
Large fibres signal joint position
Smaller A∂ fibres are most active at the extremes of movement and are protective
However proprioception is not noticeably affected by joint replacement, indicating the primacy of muscle receptors
where are muscle spindles found?
in the fleshy part of muscles in parallel with the extrafusal fibres and attached to the muscle connective tissue
each muscle has numerous spindles
where are golgi tendon organs found?
at the ends of muscles in series with the extrafusal fibres
What are the three main components of muscle spindles?
intrafusal fibres - non-contractile centres containing nuclei
sensory nerve fibres/endings - large in diameter and myelinated. They wrap around the non-contractile of the muscle the ends of which are sensitive to stretch of the intrafusal fibre
gamma motor nerve fibres/endings innervate the contractile ends of the intrafusal fibres
what are the two types of intrafusal fibres (structural)
Nuclear chain fibres have nuclei aligned in a single row in the centre of the fibre. variable numbers per spindle.
Nuclear bag fibres’ nuclei are collected in a bundle in the middle of the fibre. 2-3 per spindle.
what are the two types of intrafusal fibres (functional)
static - slow adapting
Measure the length of the spindle at any instant
All nuclear chain fibres are static
Nuclear bag fibres can be static
Dynamic - rapidly adapting
Measure the rate of change of length
Only nuclear bag fibres are dynamic
The contractile ends of the dynamic bag fibres are more viscous, so stretching occurs in the central nuclear part
What are the different sensory nerve types?
Muscle receptors Group 1 (A-alpha): widest diameter, heavily myelinated, very quick conduction velocities. Dynamic movement.
Group 2 (A-beta): fairly wide diameter and slightly less myelinated so have slightly slower conduction. Static movement.
(when talking about skin receptors they are referred to as A-alpha A-beta)
What are the different afferents?
1a afferent:
records from the centre of all fibres
report dynamic rate of change and static information
make excitatory monosynaptic connections with alpha motor neurons to the muscle
type 2 afferents
innvervate only static bag and chain fibres
report spindle/ muscle length
Separate gamma motor nerves supply the dynamic and the static intrafusal fibres to modulate the activity of these fibres
what is the basis of the stretch reflex?
The 1a afferent makes excitatory monosynaptic connections with the alpha motor neurons to the muscles
not an intrinsic property of the muscle but rather required sensory feedback by cutting the dorsal or ventral roots
what latency would you expect for monosynaptic and disynaptic pathways?
monosynaptic <1ms
disynaptic >1ms
