Reflex arc
Five essential component
1. Receptors; site of stimulus action
2. Sensory neuron; afferent sensory neuron transmits impulses to CNS.
3. Integration center; Integration center is always within CNS.
4. Motor neuron; Efferent motor neuron conduct impulses from Integration center to effector organ.
5. Effector; muscle fiber that response to effferent impulses (by contracting
Superficial reflex, which arise from surface of body.
For an example; scrapping of skin
Spinal reflex; simple reflex arc
These consist of three element-
1. Sensory neurons
2. Connector neurons (or interneurons) in spinal cord.
3. Lower motor neurons
A reflex action is an involuntary and immediate motor response to sensory stimulus.
Many connector and motor neurons may stimulated by afferent impulse from small area of skin.
For example, pain impulse initiated by touching a very hot surface with finger are transmitted to spinal cord by sensory fibers in mixed nerves.
These stimulate many connector and lower motor neurons in spinal cord, which results in contraction of many skeletal muscles of hand, arm and shoulder and removal of finger.
Reflection action happens very quickly, infact the motor response may occur simultaneously with perception of pain in cerebrum.
Reflexes of this type are invariably protective but they can occasionally be inhibited.
For an example, if it is a precious plate that is very hot when lifted every effort will be made to overcome pain to prevent dropping it.
Fig ; Event of spinal reflexes
Stretch Reflex
Only two neurons are involved; the cell body of lower motor neuron is stimulated directly sensory neurons, with no connector neuron in between.
For example, knee jerk is an example.
Stretch Reflex prevents injury due to overstretching of muscle.
When stretching agonist muscle contracts, and antagoinst muscle relaxes.
Branches of afferent fibers also synapse with interneurons that inhibit motor neurons controlling antagonistic muscle.
Stretch stimulus causes antagonists to relax.
All strech reflex are monosynaptic, they involve single synapse and ipsilateral (motor activity on same side of body).
Reflex arc that inhibits motor neurons serving antagonistic muscle are polysynaptic.
Tendon reflex
Tendon reflex cause contracting (agonist) muscle to relax and opposing (antagonist) muscle to contact.
Tendon reflex is response to contraction of muscles.
Tendon reflexes are polysynaptic and ipsilateral.
In tendon of agonist muscle, tendon organ receptors are stimulated by contraction.
Sensory impulses excite association neuron in spinal cord, which then excite motor neuron to antagonist muscle.
Sensory neuron also synapse with inhibitory association neuron which sends fewer nerve impulse to contracting muscle.
Innervation provided by tendon reflex causes contracting (agoinst) muscle to relax and the opposing (antagonist) muscle to contract.
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