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Reflex Arc

Reflex Arc. What is a Reflex arc?. Reflex arc. In a simple reflex arc, such as the knee jerk, a stimulus is detected by a receptor cell, which sends the message to the CNS via a sensory neurone.

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Reflex Arc

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  1. Reflex Arc What is a Reflex arc?

  2. Reflex arc

  3. In a simple reflex arc, such as the knee jerk, a stimulus is detected by a receptor cell, which sends the message to the CNS via a sensory neurone. • In the CNS a relay neurone (interneurone) passes the message to a motor neurone, which carries the nerve impulse out to an effector, such as a muscle, which responds by contracting.

  4. Synapses • The CNS is made of many billions of neurones, which have links with all the other neurones through synapses.

  5. Synapses • A synapse is a gap between two nerve cells. • The gap is not crossed by the electrical impulses passing through the neurones, but by chemicals. • Each axon secretes a chemical called neurotransmitter. • The chemical diffuses across the gap and attached to the membrane of the second neurone. • After the neurotransmitter has ‘passed the messge on’ it is broken down by an enzyme.

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