Muscle spindles and reflexes

Question 1

Function of stretch receptors?

Answer 1

Monitor muscle length and rate of change of muscle length

Question 2

What monitors muscle length and rate of change of muscle length?

Answer 2

Stretch receptors

Question 3

Are stretch receptors afferent or efferent?

Answer 3

Afferent

Question 4

Meaning
Afferent
Efferent

Answer 4

Afferent- sensory to CNS
Efferent- Info away from CNS

Question 5

What are intrafusal fibres? Innervation?

Answer 5

Modified muscle fibres\
y motor neurons

Question 6

Function y motor neurons?

Answer 6

Keep intrafusal fibres at set length
Optimise muscle stretch detection

Question 7

What are two types stretch receptors?

Answer 7

Nuclear chain fibres- respond how much muscle is
stretched
Nuclear bag fibres- respond both magnitude stretch and
speed it occurs at

Question 8

What stretch receptor responds to how much muscle is stretched?

Answer 8

Nuclear chain fibres

Question 9

What responds to both magnitude of stretch and the speed it occurs at?

Answer 9

Nuclear bag fibres?

Question 10

Which part of muscle spindle are contractile?

Answer 10

2 ends contractile
Centre non-contractile

Question 11

What nerves present in middle third of spindle?

Answer 11

Fast type 1a afferent sensory nerves

Question 12

What nerves present in each end 1/3 of spindle?

Answer 12

Type 2 afferent sensory nerves (slower conducting)

Question 13

Are type 1a or type 2 afferent sensory nerves quicker?

Answer 13

Type 1a

Question 14

What increases rate of receptor firing?

Answer 14

More or faster muscle stretched

Question 15

Effect of AP on stretch receptor?

Answer 15

AP causes contraction of extrafusal fibres
Shortening of muscle removes tension on the spindle
Slows rate of firing in stretch receptor

Question 16

What is function of alpha-gamma coactivation?

Answer 16

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

Question 17

What factors influence tension? (3)

Answer 17

1) Muscle length
2) Load on muscle
3) Degree muscle fatigue

Question 18

What measures tension?

Answer 18

Golgi tendon organs

Question 19

Function golgi tendon organs?

Answer 19

Monitor tension
How much tension contracting motor units are exerting
Force developed by the muscles and any resultant change in length

Question 20

Are golgi tendon organs afferent or efferent?
1a, 1b or 2

Answer 20

Afferent
1b

Question 21

How is golgi tendon organs receptors activated?

Answer 21

1) Muscle stretched
2) Tension exerted on tendon
3) Bundles straighten
4) GTO receptor endings activated

Question 22

What is output produced by golgi tendon organs proportional to?

Answer 22

Muscle tension

Question 23

What motor neurons do GTO stimulate?

Answer 23

Motor neurons on antagonistic muscle

Question 24

Explain inverse stretch reflex?

Answer 24

1) 1b fibres inhibit muscle contraction (via inhibiting alpha motor neurons)
2) Interaction between inhibition and interneurons regulates muscle tension
3) Prevents overload

Question 25

What process controls skeletal muscle tone?

Answer 25

Stretch (myotactic) reflex

Question 26

Define stretch reflex?

Answer 26

Afferent fibres activate excitatory synapses on motor neurons which return to the muscle

Question 27

Explain the knee jerk reflex?

Answer 27

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

Question 28

Function knee kerk reflex?

Answer 28

Maintain posture and balance

Question 29

Explain knee jerk

Answer 29

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

Question 30

What are two different arcs in stretch reflex?

Answer 30

Monosynaptic- straight afferent and efferent Polysynaptic- at least one interneuron between aff and eff

Question 31

What level does knee jerk reflex occur?

Answer 31

Spinal cord Bypass CNS

Question 32

Explain withdrawal reflex?

Answer 32

1) Pain stimulation activates flexor muscles and 2) Inhibits extensor muscles, r 3) Affected limb move away from harmful stimulus

Question 33

What occurs if step on pin?

Answer 33

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