• The nervous system enables humans to react to their surroundings and coordinate their behaviour.
• Information from receptors passes along cells (called neurones) in nerves to the brain.
• Nerve impulses are electrical signals that travel along neurones.
• Nerve impulses travel at high speed.
• Receptors detect stimuli which include light, sound, changes in position, chemicals, touch, pressure, pain and temperature.
• Sensory neurones – transmit nerve impulses from the receptors to the CNS when a stimulus is detected.
• Motor neurones – transmit nerve impulses from the CNS to effectors, to bring about a response.
• Effectors are muscles or glands.

In I/GCSE Biology, the nervous system can be defined into 2 areas：

1. Central nervous system (CNS)

Brain and spinal cord

This coordinates the response

2. Peripheral nervous system (PNS)

Consists of nerves connecting the CNS to the rest of the body (eg the optic nerve and the sciatic nerve)

💡Nerves are bundles of motor and sensory neurones.💡

Diagram: The connections between neurones

• When the impulses reaches the end of the axon it causes a chemical to be released.
• They are called neurotransmitters.
• They diffuse across the gap and stimulate the impulse to continue in the next neurone.

• A reflex is a rapid automatic response to a stimulus, which does not involve conscious control.

Functions:

• Protection from dangerous stimuli eg. hand withdrawal from a hot object.
• Maintenance of body processes eg. Heart rate and breathing
• Muscle coordination and postur eg. knee jerk

A reflex arc is the route taken by a nerve impulse from receptor to effector via the central nervous system to bring about a reflex action.

In I/GCSE Biology, this involves:

1. A receptor
2. Sensory neurone
3. Relay neurone – a short connecting neurone in the CNS
4. A motor neurone
5. An effector

💡There is a synapse every time one neurone meets another one!💡

Diagram: The withdrawal reflex

That's the end of the topic!

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Drafted by Joey (Biology)

Reference:

https://getrevising.co.uk/resources/biology_revision_notes4