Muscle spindles and reflexes Flashcards
Function of stretch receptors?
Monitor muscle length and rate of change of muscle length
What monitors muscle length and rate of change of muscle length?
Stretch receptors
Are stretch receptors afferent or efferent?
Afferent
Meaning
Afferent
Efferent
Afferent- sensory to CNS
Efferent- Info away from CNS
What are intrafusal fibres? Innervation?
Modified muscle fibres\
y motor neurons
Function y motor neurons?
Keep intrafusal fibres at set length
Optimise muscle stretch detection
What are two types stretch receptors?
Nuclear chain fibres- respond how much muscle is
stretched
Nuclear bag fibres- respond both magnitude stretch and
speed it occurs at
What stretch receptor responds to how much muscle is stretched?
Nuclear chain fibres
What responds to both magnitude of stretch and the speed it occurs at?
Nuclear bag fibres?
Which part of muscle spindle are contractile?
2 ends contractile
Centre non-contractile
What nerves present in middle third of spindle?
Fast type 1a afferent sensory nerves
What nerves present in each end 1/3 of spindle?
Type 2 afferent sensory nerves (slower conducting)
Are type 1a or type 2 afferent sensory nerves quicker?
Type 1a
What increases rate of receptor firing?
More or faster muscle stretched
Effect of AP on stretch receptor?
AP causes contraction of extrafusal fibres
Shortening of muscle removes tension on the spindle
Slows rate of firing in stretch receptor
What is function of alpha-gamma coactivation?
Prevents loss of sensory information:
Prevent central region of muscle spindle from going slack during shortening muscle contraction
Ensures information about muscle length will be continuously available
What factors influence tension? (3)
1) Muscle length
2) Load on muscle
3) Degree muscle fatigue
What measures tension?
Golgi tendon organs
Function golgi tendon organs?
Monitor tension
How much tension contracting motor units are exerting
Force developed by the muscles and any resultant change in length
Are golgi tendon organs afferent or efferent?
1a, 1b or 2
Afferent
1b
How is golgi tendon organs receptors activated?
1) Muscle stretched
2) Tension exerted on tendon
3) Bundles straighten
4) GTO receptor endings activated
What is output produced by golgi tendon organs proportional to?
Muscle tension
What motor neurons do GTO stimulate?
Motor neurons on antagonistic muscle
Explain inverse stretch reflex?
1) 1b fibres inhibit muscle contraction (via inhibiting alpha motor neurons)
2) Interaction between inhibition and interneurons regulates muscle tension
3) Prevents overload
What process controls skeletal muscle tone?
Stretch (myotactic) reflex
Define stretch reflex?
Afferent fibres activate excitatory synapses on motor neurons which return to the muscle
Explain the knee jerk reflex?
1) Patellar tendon is tapped
2) Thigh muscles are stretched
3) Stretch receptors activated
4) Burst of action potentials in the afferent nerve fibres
5) Activate excitatory synapses on the motor neurons that control the muscle
6) Stimulations of motor units
7) Contraction of the muscle
8) Extension of lower leg
Function knee kerk reflex?
Maintain posture and balance
Explain knee jerk
1) Patellar tendon of quadraceps muscle tapped
2) Stretch receptors activated
3) Stimulate sensory neurons to spinal cords
4) Synapse with motor neurons
5) Motor neurons cause contraction of quadraceps muscle
6) Sensory neurons travel from muscle spindle stimulate intraneurons that inhibit activity motor neurons that supply opposing muscles (hamstring)
7) Quadraceps unopposed
What are two different arcs in stretch reflex?
Monosynaptic- straight afferent and efferent
Polysynaptic- at least one interneuron between aff and eff
What level does knee jerk reflex occur?
Spinal cord
Bypass CNS
Explain withdrawal reflex?
1) Pain stimulation activates flexor muscles and
2) Inhibits extensor muscles, r
3) Affected limb move away from harmful stimulus
What occurs if step on pin?
Crossed-extensor reflex occurs
1) Motor neurons to contralateral extensors activated 2) Flexors are inhibited
3) Shift in weight when the injured foot is lifted via flexion from the stimulus
