Spinal Reflexes Flashcards
reflex
rapid, involuntary, yet sterotyped and co ordinated response to a sensory stimulus
stereotyped = happens same way every time
reflexes usually involve….
muscle contraction
but can include glandular responses e.g. lactation in response to suckling
can be learned - pavlov
somatic reflexes
aka spinal reflexes as they invlove spinal cord circitary
spinal reflexes:
require stimulation - need sensory input
are quick - few synapses involved
are involuntary and automatic - often aware as they happen and difficult to suppress - suggesting little input from higher centres
stereotyped
patellar reflex
1 - senory stimulant
2 - sensory afferent - dorsal root ganglion directly synapses to motor nerve causing it to fire
3 - motor neruon stimulates extensor = muscle contraction
extensors
muscle causing limb to extend
flexors
muscle causing limb to flex (bend)
myotactic reflex
stretch reflex
tap on knee stretches thigh extensor muscle and associated tendon and sets in motion a process to correct stretching
important for maintainig posture - part of proprioceptive system
stretch reflex pathway
e.g. pouring a drink
1 - sensory fibres sense muscle stretch and send signals to spinal cord
sensory receptor = muscle spindle
2 - direct monosynaptic connection to motor neuron fires action potential which contracts the bicep muscle
3 - simultaneously a distinct connection to an inhibitory interneuron stops firing of motor neuron connected to triceps = relaxing antagonistic muscle = reciprocal inhibition
muscle spindle
among proprioceptors - sense organs that monitor position and movement of body parts
found in most striated muscle and abudnant in muscles involved in fine motor control
innervated by Ia sensory fibres
these provide feedback to motor neurons inverting surrounding muscle (alpha motor neurons) about the amount of muscle that is stretching
muscle spindle has muscles
also innverated by axons from gamma motor neurons
these stimulate intrafusal muscle fibres to adjust tension in spindle as the extrafusal muscle fibres of surrounding muscle contract (so that muscle spindle never slackens)
kinaesthesia
perception of where your body is in space and time
golgi tendon organ
to protect muscles
another proprioceptor
detect muscle tension due to contraction not muscle stretch (thats muscle spindles)
activation of gto sensory afferents leads to activation of inhibitory interneurons which in turn inhibit alpha motor neurons that innverate the same muscle
= GTO is a negative feedback loop that regulates muscle tension and protects from damage when large forces are generated
also regulates contraction to maintain muscle length but also prevents too much contraction
flexor reflex 1
withdrawl reflex
quick contraction of flexor muscles to withdraw a limb from injury
results from activation of nociceptive sensory receptors (pain receptors)
very fast but polysynaptic
activation of multiple excitatory interneurons sustains response = parallel after discharge circuit
parallel after discharge circuit
less synapses = faster
more synapses = initial signal is sustained over extended period
