26/ spinal reflexes Flashcards
(15 cards)
what is a reflex
rapid, involuntary but coordinated to a sensory stimulus
what are spinal reflexes also called
somatic reflexes
outline the patella reflex
- sensory stimulus
- motor neuron stimulates extensor muscle contraction
- primary afferent neuron
- direct synapse to motor neuron
- monosynaptic - only 1 synapse involved
what is the function of the patella/ stretch reflex
- tap on the knee stretches the thigh extensor muscle and associated tendon and sets in motion a process to correct the stretching
- important in maintaining body posture - part of proprioceptive system
how is the stretch/myotactic reflex outlined by pouring a pint
- sensory fibres sense muscle stretch and send signals to spinal cord
- sensory receptor that detects muscle stretch is called the muscle spindle
- direct monosynaptic connection to motor neuron fires action potential which contracts the biceps muscles
- at the same time distinct connection to an inhibitory interneuron inhibits the firing of motor neurons connected to the triceps, thus relaxing antagonistic muscle - reciprocal inhibition
- need to stop triceps and correct their direction but doesn’t counteract desired muscle action
info about the muscle spindle
- spindles innervated by Ia sensory fibres
- provides feedback to alpha motor neurons innervating the surrounding muscle on the amount of stretch thats occurring
- proprioceptor
- found in most striated muscle particularly fine motor control muscles
aside from alpha motor neurons, gamma motor neurons can also innervate muscle spindle. describe
- gamma motor neurons stimulate intrafusal muscle fibres to adjust the tension in the spindle as the extrafusal muscle fibres of the surrounding muscle contract
- so muscle spindle is never slack
- proprioception
golgi tendon organ, what is it, what does it detect, what does activation of sensory afferents lead to, why is that important
- kind of proprioceptor
- detect muscle tension
- activation of sensory (Ib) afferents leads to activation of inhibitory neurons which inhibit alpha motor neurons that innervate the same muscle - golgi tendon reflex
- regulates muscle TENDON to protect muscle from large forces
- also regulates muscle contraction, prevents too much contraction
flexor withdrawal reflex
- quick contraction of flexor muscles to withdraw a limb from dangerous stimulus
- results from activation of nociceptive sensory receptors/nociceptors
- polysynaptic reflex
- like stretch reflex, inhib interneurons also activated - relax extensor muscles
what is a polysynaptic reflex
- activation of many excitory interneurons which sustains the response
- parallel after discharge circuit
- dif synapse routes to same output take dif amounts of time to reach stimulus - longer response
crossed extensor reflex (often involved alongside flexor reflex to balance)
- contralateral signal activates muscle movements to counteract
- signal crosses midline
- flexor reflex: extensor muscles at front relax and flexors at back contract in thigh
- crossed extensor reflex: contralateral extensor muscles contract
ipsilateral and contralateral meaning
- ip: same side
- con: other side
central pattern reflexes (animals walking), individual limb, how do animals move limbs when walking, when does this continue, what does this suggest
- alternation in extensor and flexor activation/ inhibition
- alternation in front to back and side to side limb movements across all limbs
- continues even if links w spinal cord to brain severed
- presence of local circuits that can generate the pattern
key detail from cellular basis of pattern generators
involves inhibition across the midline
what was discovered about proprioception in c elegans
- mutant w loopy swimming - proprioception messed up
- lost a mechanosensor/stretch receptor in the DVA neuron
- dva inhibits motor neurons - allowing alternate muscle contraction
