A level Biology exam revision resources written by A level Examiners


The simplest example of nerves transmitting information is the reflex. A simple reflex may only involve three nerve cells. The classic example of a reflex is the knee jerk, in this example if a stretch receptor is stimulated on the patella tendon an impulses is passed by one sensory nerve to a relay neurone in the spinal cord. This relay neurone passes the impulse to a motor neurone that connects to a quadriceps muscle. When this muscle is stimulated it causes the lower leg to lift, protecting the stretched tendon. This is shown in the flowchart below.

Figure 2 : The Reflex Arc
The Reflex Arc

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