Lecture 20 Control Of Movement 2 Flashcards
Proprioception how we sense ourselves in the 3D world
Body’s ability - sense movement, action, location (understand position in space)
What are the receptors that control movement and the function they monitor ?
Muscle spindle (in muscles) - muscle length & speed in length change (muscle stretch)
Golgi tendon organ - muscle tension (sensing force & prevent damage)
Joint receptors - position & signal joint hyperextension/hyperflexion
Pain receptors
Reflexes
Involuntary, unplanned sequence/ action responding to stimuli.
Reflex arc -> acts on impulse before impulse go to brain
What are three types of reflexes and what do they respond to
Stretch / myotatic reflex [muscle spindles] - proprioception
Reverse myotatic reflex [golgi tendon organ]- proprioception
Flexion (withdrawal) and extension reflex - pain
What are the 5 elements of spinal reflexes
Receptors -> sense input (muscle, joint, skin)
Afferent fibres -> transport info to spinal cord
Central synaptic relays -> relay sensory input to allow appropriate response
Efferent fibres -> transport information to action target
Effectors -> muscles
The stretch reflex & reverse myotatic reflex work together to…
…Preserve correct muscle length and tension
Stretch reflex
- purpose
- receptors, afferent fibres, synaptic relay, efferent fibres, effectors
Important - Sustain appropriate muscle length
Receptors: intrafusal muscle fibers of muscle spindle belly [nuclear bag fibres - speed of stretch, nuclear chain fibres - length change]
Afferent fibres: group Ia (speed, nuclear bag fibres), group II (sustained stretch, nuclear chain fibres) [fibres stretching -> AP ]
Synaptic relay : Ia afferent (to spinal cord by dorsal root ganglion) to alpha MN to muscle
Efferent fibres: alpha motor neurons axons
Effectors: same muscle (extramural fibres)
Reciprocal inhibition (stretch reflex)
- purpose
- process
- ensure the agonist muscles activated, others inhibited
- Ia afférent -> excite interneuron -> inhibit alpha MN stimulating antagonistic muscles
Gamma MNs
- function and purpose
- process
Synapse to muscle spindles
Maintain muscles spindle at acceptable length -> active -> muscle shortening stimulated by alpha MNs
Extrafusal fibres stretched -> activate axon around intramural fibre -> signal to spinal cord -> signal extrafusal to contract by activate alpha MN -> intrafusal maintained at stretched length -> activate gamma MN -> return intrafusal to normal length
Golgi tendon organ
Muscle spindles
What does tension on the tendon result in?
Monitor muscle tension /contraction force
Arranged in series
Monitor muscle length
Parallel arrangement
Afferent AP
Reverse myotatic reflex
- function
- receptors, afférent fibres, synaptic relay, efferent fibres, effectors
- keep muscle tension in normal range, protect muscle from overload in extreme conditions
- ·Receptors: Golgi tendon organs (between bone and muscle)
·Afférent fibres: group Ib
·Synaptic relay: Ib afferents -> inhibitory interneuron -> alpha MN
·Efferent fibres: alpha MN axons
·Effectors : same muscle (stop contraction)
Flexion (Withdrawal) reflex
- function
- receptors, afférent fibres, synaptic relay, efferent fibres, effectors
- stimulate limb to withdraw quickly from nocioceptive stimulus
- somatosensory response not proprioception
- receptors: skin nocioreceptors
Afferent fibres: Type III (Aδ fibres), Type IV (C fibres)
Synaptic relay: excitatory interneurons
Efferent fibres: flexor α MNs axons
Effectors: flexor muscles
Flexion and crossed- extension reflex
- important -> maintain balance
Pain stimuli from nocioceptor connected to cutaneous afferent fibre
Leg exposed to pain stimuli -> α MNs activate -> flexion (excitatory interneuron ) and inhibit extension (inhibitory interneuron )-> withdraw leg.
Opposite leg -> activate excitatory interneuron -> LMN -> activate extensor. Inhibitory interneuron -> flexor inhibitory -> extension of leg for support
Why is important to inhibit antagonistic muscles
To ensure coordinated response to stimuli. Enable withdrawal/ movement away from stimulus
