GCSE Biology (AQA)

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Reflexes

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Homeostasis and Response The Human Nervous System

Reflexes

3:45 Reflexes and Reaction Times
Spec 4.5.1 4.5.2.1
Previous Synapses Next Investigating Reaction Times
  • Reflex action is a quick and automatic response to a stimulus.
  • Common examples include the knee jerk or patella reflex, which is a sudden kicking movement of the lower leg in response to a sharp tap on the tendon below the kneecap.
  • Reflex actions help maintain balance and protect the body from damage.
  • Reflex actions involve a reflex arc, which is the pathway of information from receptor to effector.
  • A reflex arc includes a stimulus, receptor (such as skin cells detecting pain), sensory neuron, relay neuron, motor neuron, and an effector (like a muscle).
  • The sensory neuron detects and sends the impulse, the relay neuron transfers it across the central nervous system, and the motor neuron causes the movement.
  • Neurons have specialized structures such as branched endings for connections, long axons for transmitting messages over distances, and insulating fatty layers to speed up messages.
  • Sensory and motor neurons have insulating fatty layers to facilitate long-distance signal transmission, unlike relay neurons.
  • Reflexes are automatic because they bypass the conscious part of the brain.
  • Some reflexes, like the knee jerk reflex, are coordinated entirely by the spinal cord without brain involvement.

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