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The Nervous System


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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.