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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
Reflex Arc

What is a 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.

  • 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.


Synapses
Synapses detected by a receptor cell, which sends the message to the CNS via a sensory neurone.

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


Synapses1
Synapses detected by a receptor cell, which sends the message to the CNS via a sensory neurone.

  • 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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