Spinal Reflexes Flashcards
(30 cards)
what is a reflex?
a rapid, involuntary, and coordinated response to a sensory stimulus.
what are some factors of spinal reflexes?
they are quick, involuntary, automatic, difficult to supress, stereotyped (occur the same way each time).
what is the Patellar / knee-jerk reflex?
involves a sensory stimulus (tapping the knee),
causes primary afferent sensory neuron to conduct and action potential,
relayed on to the dorsal horn of the spinal cord,
sensory afferent synapses on to motor neurons in the ventral horn.
what type of reflex is the patellar reflex?
monosynaptic – only one synapse is involved.
what happens when the motor neurons in the ventral horn are activated during the Patellar reflex?
the motor neurons fire,
project back on to the muscle,
stimulating the extensor muscle to contract.
what are extensor muscles?
muscles causing limbs to extend.
what are flexor muscles?
muscles causing limbs to flex.
what happens when extensor muscles contract?
the limb pulls away / bends.
what is the Myotatic / stretch reflex?
refers to the contraction of a muscle in response to its passive stretching, such as pouring a drink and the glass getting heavier.
what does the Myotatic / stretch reflex involve?
involves sensory fibres sending signals to the spinal cord,
a monosynaptic connection on to motor neurons,
fires action potential,
causing bicep contraction and the glass is held in place.
explain the reciprocal inhibition that occurs during the Myotatic / stretch reflex:
simultaneously, the sensory fibre also synapses on to an inhibitory interneuron,
inhibits the firing of motor neurons connected to the triceps,
it relaxes the antagonistic muscles.
what does this reciprocal inhibition ensure?
it ensures that the resistance to the stretch is not then further resisted by the tricep.
what is the name of the sensory receptor that detects muscle stretch?
the muscle spindle.
what type of sense organ are muscle spindles?
proprioceptors - monitor the position and movement of body parts.
where are muscles fibres found?
striated muscle.
what does this mean?
the muscle fibres are innervated by Ia sensory fibres.
they provide feedback to the motor neurons innervating the surrounding muscle on the amount of stretch that is occuring.
what are muscle spindles made up of?
intrafusal fibres and extrafusal fibres.
what happens when the extrafusal fibres of muscles contract?
the motor neurons stimulate intrafusal fibres to adjust tension in the spindle.
what is the Ian Waterman, 1972 case?
a viral infection destroyed nerves providing sense of touch and nerves attached to muscles that provided limb perception,
lost the ability to coordinate movement unconsciously.
what is the Golgi tendon organ?
a kind of proprioceptor that detects muscle tension due to muscle contraction.
what does the activation of the Golgi tendon organ sensory Ib afferents lead to?
the activation of inhibitory interneurons that inhibit motor neurons innervating the same muscle.
the Golgi tendon organ reflex is a negative feedback circuit which does what…
regulates muscle tension and protects the muscle and tendons from damage when large forces are generated.
what is the flexor / withdrawal reflex?
a quick contraction of flexor muscles to withdraw a limb from an injurious stimulus.
what sensory receptors does the flexor / withdrawal reflex activate?
nociceptors.
