Neurobiology and behaviour

■ Specialised cells called neurones, such as the motor neurone and others, are assembled to form the nervous system.

■ The mammalian nervous system consists of a brain and spinal cord (central nervous system, CNS) and nerves serving the tissues and organs of the body (peripheral nervous system, PNS).

■ The nervous system links receptors (e.g. sense organs) to effectors (muscles or glands). ■ An impulse or action potential is a temporary reversal of the electrical potential difference that is maintained across the membrane of the nerve fibres. Conduction of an action potential is extremely fast.

■ Action potentials are transmitted between neurones across tiny gaps at synapses. Transmission here is chemical, involving diffusion of a specific transmitter substance. 

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Define sensitivity, stimulus, response and reflex

Sensitivity is the ability to detect change and to respond to it. Changes that are detected and lead to a response are called stimuli (singular, stimulus).

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

A response is the activity of a cell or organism in terms of movement, hormone secretion or enzyme production, for example, as a result of a stimulus.

A reflex is a rapid, unconscious response.     

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Explain the role of receptors, sensory neurons, re

The response of the body to a stimulus involves a receptor organ, neurones of the nervous system, and an effector organ arranged in a functional unit called a reflex arc. In the reflex arc, an impulse generated in a receptor is transmitted via neurones to the effector which brings about a response, in the sequence:

stimulus

↓
 receptor → sensory neurone → CNS → motor neurone → effector

↓

response 

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Note down the three types of neurone found in a re

Each neurone has a cell body and a number of extensions, the nerve fibres.

  • motor neurones

These have many fine dendrites (meaning ‘little trees’) which bring impulses towards the cell body, and a single long nerve fibre called an axon which carries impulses away from the cell body. The structure of a motor neurone was introduced on page 211.

  • sensory neurones

These have a single long nerve fibre, a dendron, which brings impulses towards the cell body, and a single long axon which carries impulses away.

  • relay neurones (also known as interneurones)

These have numerous, short nerve fibres. 

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