5.1.2 The Reflex Arc

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A reflex arc is the pathway taken by the nerve impulses that produce a reflex action. Reflex actions are automatic and rapid responses that protect the body from harm.

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Key Stages in the Reflex Arc:

Stimulus Detection: A stimulus (e.g., heat, light) is detected by receptors.
Sensory Neuron Activation: The receptors send an electrical impulse along a sensory neuron to the spinal cord (part of the central nervous system).
Relay Neuron in the CNS: In the spinal cord, the impulse passes to a relay neuron (also known as an interneuron).
Motor Neuron Activation: The relay neuron passes the impulse to a motor neuron.
Effector Response: The motor neuron carries the impulse to an effector (a muscle or gland), causing it to respond (e.g., a muscle contracts to move a hand away from a hot surface).

Importance of Reflex Arcs:

Reflex arcs enable quick responses to potentially harmful stimuli.
These responses occur without involving the conscious part of the brain, which allows them to happen faster, protecting the body from injury.

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Examples include withdrawing a hand from something hot or blinking when something comes close to your eyes.

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