The nervous system What is the nervous system

The nervous system

What is the nervous system made up of? • The brain • The spinal cord • The nerves (neurones) The central nervous system (or CNS for short) is made up of the brain and the spinal cord.

What is the job of the nervous system? Our survival depends on us being sensitive to our surroundings. We need to be able to detect any changes and be able to respond to them.

What are our sense organs? The sense organs are: These organs sense: • • • The eyes The ears The nose Tongue skin Light Sound and balance Smell Taste Pressure, pain, temperature

How does our nervous system work then? • Our sense organs contain special receptor cells which will detect a change in our surroundings (a stimulus) • The receptor cells will change the stimulus into an electrical impulse which is passed along nerve cells • The message will usually go to the brain which will then process it • The brain then sends a message along nerves to an effector organ (usually a muscle or a gland) • The effector organ will then give a response (e. g. a muscle will move, or a gland will produce a hormone)

Response Stimulus Receptor Effector Sensory neurone Central Nervous system Motor neurone

Synapses • When a nerve ending meets up with another nerve ending we get a microscopic space • This space is called a synapse • The electrical message travelling along a nerve has to cross the synapse as a chemical message • When the chemical (neurotransmitter) reaches the other nerve ending it causes an electrical impulse to travel along the next nerve cell

Reacting without thinking • Sometimes a stimulus requires an immediate response. This is called a reflex action. It is an involuntary response and we do it without thinking. These automatic responses do not have to be learned. They can be very important in preventing injury to ourselves.

A reflex arc The nerve pathway taken in a reflex action is called a reflex arc. The nervous message goes to the spinal cord, then a message passes from the spinal cord directly to an effector to give an immediate response.

A reflex arc

Sometimes called a relay or Connector neurone The knee jerk reflex action

Another reflex action

Examples of responses Voluntary actions Involuntary actions • • • Eating a cake Riding a bicycle Walking Playing the piano Coming to school Your heart beat Breathing Blinking Removing hand from hot object • Choking • Salivating

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