nervous system

Somatic NS

Voluntary control of external environment

Autonomic NS

Involuntary control of external environment

Stimulus

A change to the environment that can cause a response

Receptors

Cells that detect a stimulus

Effector

Responds to a stimulus

Threshold

The minimum stimulus required to start a nervous impulse

All or nothing law

The size of the stimulus has no effect on the size of the impulse. Either a full message is carried or no message

Refractory period

The length of time needed by a nerve cell to recover before it can pass a second impulse

The synapse

The specialised junction between neurons or a cell

Synaptic cleft

The tiny gap between the two neurons at a synapse

Neurotransmitters

Chemicals released by neurons at a synapse, which transmit signals across a synaptic cleft

Grey matter

Make decisions

White matter

Transport messages

Reflex action

An automated response to a stimulus, which is not controlled by the brain

Reflex arc

The nerve pathway involved in a reflex action

Parkinson’s disease

A progressive neurological disorder that affects the control of voluntary movement