The Nervous System

Sense organs

Organs that detect stimuli that you need to react to, e.g eyes, ears

Stimulus

A change in the environment

Receptors

Groups of cells in sense organs which are sensitive to stimuli, and convet stimulus energy to electrical energy

Effectors

Muscles and glands that carry out the necessary change

Response

The result of the action of the effector (e.g body temperature returning to 37 degrees)

Central Nervous System

The brain and the spinal chord

Neurones

Nerve cells which transmit nerve impulses

Sensory neurones

Carry nerve impulses from the receptors to the CNS. They have long dendrons and short axons

Motor neurones

Carry nerve impulses from the CNS to the effectors. Many short dendrons and one long axon

Relay neurones

Carry nerve impulses inside the CNS from sensory neurones to motor neurones. Short dendrons and axons.

Dendrons

Branches which carry nerve impulses towards the cell body

Dendrites

The tiny branches of dendrons which are connected to cells

Axons

Branches which convey the electrical impulses away from the cell body

Myelin sheath

Insulating envelope that surrounds an axon

Synapse

A small gap where one neurone connects to another

Neurotransmitters

Chemicals that transmit impulses across synapses

Reflexes

Automatic responses to stimuli

Reflex arc

When nerve impulses travel straight from the receptors to the CNS to the effector, bypassing the brain. A reflex reaction.