Lecture 5/6 - reflexes

What is a stretch reflex?

Response that resists the lengthening of a muscle

What is reciprocal inhibition?

Relaxes the antagonist muscle, it requires an inhibitory interneuron

How is reciprocal inhibition involved in the stretch reflex?

Afferent neurons excite motor neurons and inhibitory interneurons that prevent the firing of motor cells in opposing flexor muscles

What is recurrent inhibition?

Self regulating mechanism where active motor neurons inhibit themselves via Renshaw cells to prevent excessive excitation of the muscle

What is a H reflex?

Reflexive response caused by activation of sensory Ia afferent fibres in muscle spindle, bypasses muscle spindle

What is a withdrawal reflex?

Initiated by painful stimulus and produces coordinated excitation of flexors and inhibition of extensorsH

How does withdrawal reflex differ to stretch reflex?

It is slower than the stretch reflex as it can be variable as it depends on which afferents are activated by stimulus

What is crossed extensor reflex?

Important for one leg to maintain balance (contralateral extensor reflex) whilst the other withdraws from the painful stimulus (ipsilateral flexor withdrawal reflex)

What is the muscle spindle?

Sensory receptor in muscle that detects changes in muscle length and rate of change in length

What is the tendon organ?

Sensory receptor in muscle that detects changes in muscle force

Why does the msucel spindle need an efferent innervation?

Efferent nerves (gamma motor neurons) innervate the muscle spindle to keep the sensor active and responsive, sustained tension

What is a group 1a afferent?

Afferent innervation of muscle spindle, wrap around central region of intrafusal fibres, sensitive to stretch

What are group II afferents?

Afferent innervation of muscle spindle, terminate mostly on nuclear chain fibres, sensitive to static length

What is alpha-gamma coactivation?

Alpha motor neurons innervate muscle which contract and shortens, without gamma the muscle spindle will slacken, gamma ensure they remain sensitive to stretch

What are 3 locations within the reflex pathway that can influence reflex excitability?

Alpha motor neurons, interneurons, afferent terminals