neuromuscular reflexes

Question 1

why do we need sensory information from skeletal muscle

Answer 1

postur and control of motor function involve integration of sensory and motor inputs/outputs
e.g. some skeletal muscles contract while others relax to keep us upright
this is achieved by reflexes which are relayed via the spinal cord

Question 2

what are the types of muscle fibres?

Answer 2

extrafusal
intrafusal

Question 3

what are extrafusal muscle fibres

Answer 3

bulk of skeletal muscle fibres - force generation
innervated by ⍺-motor neuron

Question 4

what are intrafusal muscle fibres

Answer 4

remaining specialised fibres - muscle spindles
innervated by 𝛾-motor neuron and sensory afferents

Question 5

what is sensory innervation of the muscle spindles

Answer 5

afferent information - travels upto the spinal cord where it synapses
provided by either the group Ia afferents or the group II afferents

Question 6

what is motor innervation of the muscle spindles

Answer 6

𝛾- motor neuron
generates contraction

Question 7

what happens to muscle spindles when they are in action

Answer 7

sense changes and respond to changes in muscle length to return skeletal muscle to resting state after they have been used

Question 8

muscle spindles e.g. abdominus rectus

Answer 8

contractes to help us stand from sitting
extrafusal and intrafusal fibres shorten
sensory afferents (Ia and II) in the intrafusal fibres relay information to the ⍺-motor neuor in the spinal cord
activation of the ⍺-motor neuron stimulates abdominus rectus to relax
at the same time as the ⍺-motor neuron is stimulated, the 𝛾-motor neuron is activated

Question 9

what does a reflex arc consist of

Answer 9

senspry receptors
sensory afferents (Ia and II)
interneurons in the spinal cord
motor efferents (⍺-motor neurons)

Question 10

what is the stretch (myotatic) reflex

Answer 10

e.g. knee jerk
muscle is stretched and group Ia afferent fibres in the muscle spindle start firing
these synapse on ⍺-motorneurons in the spinal cord (the ⍺-motor neurons innervate the same muscle form which the group Ia afferent relayed the sensory information)
⍺-motor neuron induces contraction of skeletal muscle
muscle returns to resting length and firing frequency of group Ia decreases
= the reflex stimulates in the spinal cord, the motor neurons to the extensor muscle, and, inhibits the motor neurons to the flexor muscle

Question 11

what is the golgi tendon (inverse myotatic) reflex

Answer 11

e.g. clasp knife
muscle contracts and the extrafusal fibres shorten, and this stimulates the golgi tendon organ
group Ib afferents start firing and send sensory information to the inhibitory interneurons they synapse on, in the spinal cord
inhibitory interneurons synapse on the ⍺-motor neurons
muscle returns to resting length an dfiring frequency of group Ib decreases - synergistic muscles also relax and antagonistic muscles contract
= the reflex inhibits in the spinal cord the motor neurons to the extensor muscle, and, stimulates the motor neurons to the flexor muscle

Question 12

what is the flexion-withdrawl reflex

Answer 12

e.g. stubbing toe
when something painful/noxious is detected, there are multiple afferent fibres are activated which then synapse on multiple interneurons in the spinal cord
on the same side as the painful/noxious stimuli, flexors are contracted and extensors are relaxed
on the opposite side as the painful/noxious stimuli, flexors are relaxed and extensors are contracted
= in the leg that feels the pain, the reflex inhibits in the spinal cord the motor neurons to the extensor muscle, and, stimulates the motor neurons to the flexor muscle
= in the opposite leg, the reflex stimulates in the spiinal cord the motor neurons to the extensor muscle, and, inhibits the motor neurons to the flexor muscle