Spinal Reflexes

Spinal Reflexes - Spinal Reflexes Spinal reflex...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Spinal Reflexes Spinal reflex – monosynaptic reflex : the most rapid way you can get contraction o Function is to defend from unexpected muscle stretches, maintaining postural against the gravity o Latency of the stretch reflex is about 30 ms to EMG (in extensor muscle) compared to voluntary reaction time o The second most rapid way is by VPR From the muscle spindle, Ia afferent neuron that wraps around the annulospiral sensory receptor sends AP to the spinal cord (CNS) through pre-synaptic axons which release transmitter. o 1) Depolarization of quadriceps (extensor aka. ‘ Anti-gravity muscle ’) alpha-MN occurs ( EPSP ). If EPSP reaches its threshold as it summates, A.P is produced in the quadriceps alpha-MN which will then propagate out to the extrafusal muscle fiber of extensor muscle to contract. Stretch reflex will contract anti-gravity extensor muscles to help stops you from falling down due to gravity o 2) Ia afferent branches across to the inhibitory interneuron (called, Ia inhibitory interneuron). This Ia afferent releases excitatory transmitter and produces A.P into the Ia inhibitory interneuron, which in turn, sends post-synaptic inhibition (or hyperpolarization ) on the flexor alpha-MNs. The flexor MNs are antagonists to the muscle that is being stretched. If quadriceps is extensor muscle, then hamstring muscle (flexor) is antagonist. Thus, there is no A.P going into the flexor (antagonist muscle) through efferent alpha-MNs o This is called Reciprocal Inhibition via post-synaptic inhibition of antagonist alpha motorneurons (prevents muscles from contracting @ the same time) This is true for
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 2

Spinal Reflexes - Spinal Reflexes Spinal reflex...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online