relfex pathways Flashcards
what is a reflex?
involuntary, stereotyped pattern of response brought about by a sensory stimulus
what is the myotatic relfex?
stretch- is a muscle with intact innervation is stretched it responds by contracting and this is the myotatic reflex
it is only mediated by two neurons- one efferent and one afferent which form a monosynaptic reflex arc
helps maintain muscle tone and postural stability, prevent overstretching
mechanisms of monosynaptic myotatic reflex
- intrafusal muscle spindle (sensory receptor in muscle) detects stretch
- this stretches the muscle spindle which activates its sensory fibres (type Ia afferent fibres)
- sensory fibres enter dorsal horn
- synapse with extrafusal motor neuron in the ventral horn which sends an efferent signal for same muscle to contract
polysynaptic myotatic reflex
involves one or more interneurons which involve agonist (muscle performing the action) and antagonist (muscle opposing the action) muscles
mechanisms of polysynaptic myotatic relfex
- sensory afferent neuron synapses with interneurons in spinal cord
- interneurons can facilitate or inhibit motor responses contributing to reciprocal inhibition
- e.g interneurons activate flexor muscles to contract from painful stimulus and inhibit antagonistic from resisting movement
what is reciprocal inhibition?
involves the inhibition of the antagonistic muscle (the muscle that opposes the movement)
examples of monosynaptic and polysynaptic myotatic reflexes
mono= patellar (knee jerk)
poly= flexore withdrawal and crossed extensor reflex
primary (Ia) afferents
sensory neuron important for muscle spindle funcion
detect changes in muscle length and rate of change in muscle length
secondary (II) afferents
transmit information from muscle spindles about static length and to a lesser extent rate of change
main differences between Ia and II afferents
Ia in middle of spindle, II at polar end
Ia detect dynamic change, II detect static muscle length
Ia has wider axon diameter for faster conduction
what are golgi tendon organs?
specialised sensory receptors located between muscles and tendons
monitor change in muscle tension
inhibit further muscle contraction
structure of golgi tendon organs
enclosed in funnel-like capsule containing collagen fibre bundle and nerve fibres
Ib afferent fibres
loctaed on each end of a muscle
golgi tendon reflex mechanism
disynaptic reflex
when a muscle contracts and generates tension, the golgi tendon organ is stretched
if the tension is too high, the GTOs trigger an inhibitory response (stop alpha innervating muscle) to reduce muscle contraction
this protects the musce from producing too much tension and tearing ir breaking tendons
what is the opposite reflex of the golgi tendon?
myotatic
each alpha motor neuron receives input from 3 different sources:
sensory input from muscles involuntary
reflex movement
input from upper motor neurons initiates and controls voluntary movement
spinal interneurons (excitatory or inhibitory) produce coordinated movement
