Option E: Neurobiology & Behaviour

E.1.1. Define the terms stimulus, response and reflex in the context of animal behaviour

A change in the environment (internal or external) that is detected by a receptor and elicits a response.

Reaction to a stimulus

A rapid, unconscious response

E.1.2. Explain the role of receptors, sensory neurons, relay neurons, motor neurons, synapses and effectors in the response of animals to stimuli

Animals can respond to stimuli with a reflex. Receptors receive the stimulus and generate a nerve impulse in the sensory neurons. The sensory neurons carry the impulse towards the spinal cord. 

The axon of the sensory neurone enters the spinal cord in the dorsal root and sends a chemical message across a synapse to a relay neurone.

The relay neurone is located in the grey matter of the spinal cord. The relay neurone synapses with a motor neurone in the grey matter of the spinal cord and transfers the impulse chemically across the synapse. 

The motor neurone is located in the ventral root of the spinal cord. It carries the impulse to an effector. 

An effector is an organ that performs the response. 

The series of actions is caused as the spinal cord nerves carry impulses to the brain. As the brain becomes aware of what is happening, it coordinates the other responses. 

E.1.3. Draw and label a diagram of a reflex arc for a pain withdrawal reflex, including the spinal cord and its spinal nerves, the receptor cell, sensory neuron, relay neuron, motor neuron and effector