Reflex Flashcards
what is a reflex
body’s involuntary, rapid response to stimulus
- helps maintain posture, control visceral activities, safety mechanisms
- can be modified by learning and conscious effort
- happen fast because they don’t travel up to brain
- learn (acquired) reflexes result from practice or repetition
- driving skills becomes second nature after much time and effort.
5 components of reflex arc
receptor- site of stimulus action
sensory neuron- transmits afferent impulses to CNS
integration centre- either monosynaptic or polysynaptic region within CNS
motor neuron- conducts efferent impulses from integration center to effector organ
effector- muscle fibre or gland cell that responds to efferent impulses
reflexes are classified into 2 groups-
- somatic reflexes
- activate skeletal muscle
- autonomic (visceral) reflexes
- activate visceral effectors- smooth and cardiac
monosynaptic versus polysynaptic reflexes
- Monosynaptic- sensory and motor neuron synapse directly
- polysynaptic- sensory and motor synapse with interneurons in the spinal cord
spinal reflexes are somatic reflexes mediated by the spinal cord, what are most commonly assessed reflexes
spinal reflexes occur without direct involvement of higher brain centre
- brain is still advised
- testing of reflexes is clinically useful to assess condiction of nervous system
- abnormal may indicate degeneration/pathology of specific nervous system regions
- most commonly assess reflexes are
- stretch and tendon reflex,
- flexor/crossed-extensor reflex
- superficial reflexes- ocular reflexes
- stretch and tendon reflex,
stretch and tendon reflexes
- function to smoothly coordinate activity of skeletal muscle
- provide the nervous system with important proprioceptive information to regulate joint position and movement
- this includes two types of information- length of movement- sent from muscle spindles- monosynaptic
- amount of tension- force in the muscle- sent from golgi tendon organs- polysynaptic
Anatomy of muscle spindle- length sensors
- functional anatomy of muscle spindles
- 3-10 times skeletal muscle fibres intrafusal muscle fibres within capsule
- two types of afferent endings in muscle spindle send sensory inputs to CNS-
- anulospiral endings- wrap around spindle and stimulated by degree of stretch and rate- flower spray endings- small axons at spindle ends and stimulated by degree of stretch only
- contractile end regions of spindle are innervated by gamma (y) efferent fibers
- help maintain spindle sensitivtity
- extrafusal fibers- contractile muscle fibers are innervated by alpha (a) motor neurons.
- help maintain spindle sensitivtity
stretched muscle spindle initiate a stretch reflex, causing contraction of the stretched muscle and inhibilitation of its antagonist
1) streatch activates muscle spindles, sensory neurons transmit afferent impulses at higher frequency to the spinal cord
2) sensory neurons syapse with alpha motor neurons to excite extrafusal fivers and with interneurons to inhibit motor neurons of antagonistic muscle
3a) efferent impulses of alpha motor neurons cause the stretched muscle to contract, which resists or reverses the stretch
3b) efferent impulses of alpha motor neurons to antagonist muscles are reduced ( reciprocal inhibition)
patella or knee-jerk reflex
- reflex that helps keep your knees from buckling with standing upright, often assessed by clinician
- assesses the nervous tissue between and including the L2 and L4 segments of the spinal cord
the patellar (knee-jerk) - tapping on patellar ligament stretches the quadriceps and excites its muscles spindles
- afferent impulses travel to the spinal cord, where synapses occurs with motor neurons and interneurons
- motor neurons send activating impulses to the quadriceps causing it to contract and extend the knee
tendon reflex
- prevent muscles form tearing due to excessive forces
- initiated by golgi tendon organ- force sensors
- involves only polysynaptic reflexes
- produces muscle relaxation- lengthening in response to tension
- contraction or passive stretch activates tendon reflex
- afferent impulses transmitted to spinal cord
- contracting muscles relaxes- antagonist contracts-
tendon reflex
1) quadriceps strongly contrasts, tendon organs are activated
2) afferent fibers synapse with internursons in the spinal cord.
3a) efferent impulses to antagonist muscle cause it to contract
3b) efferent impulses to muscle with stretched tendom are damped, muscle relaxes, reduces tension.
flexor and crossed-extensor reflexes
- flexor- withdrawal reflex- initiated by painful stimulus
- automatic withdrawal of threatened body part-ipsilateral- reflex happens on same side of body and polysynaptic
- protective and important to survival
crossed extensor reflex
- occures with flexor reflexes in weight bearing limbs to maintain balance
- consists of imsilateral withdrawal reflex and contraclateral extensor reflex
- stimulated side withdrawn- flexed and contralateral side extended
H-reflexes is analogous to stretch reflex
- used by researchers to test sensory and motor function changes with disease, training and age
- short-duration, low intensity electric stimulus is delivered to the tibial nerve
- H-reflex decrease as we age, functional consequence
ocular reflexes
- pupillary light reflex
- controls the diameter of the pupil in response to light on retina
- importnat for adjusting eue to different levels of light, refulaes amount of light
vesibulo-ocular reflex
- controls eye movement when the head moves
- involuntary eye movements equal and opposite to the head so that images can be continuously centred in visual fields
- fastest reflex in human body
pupillary light reflex
