Biology B1a

A stimulus is a change in your environment

Sense organs contain receptors which sense a stimulus

We have 5 sense organs-eyes, ears, nose, tongue, skin

The CNS is where reflexes and actions are coordinated

The CNS is made up of the brain and the spinal cord

Neurones transmit the information as electrical impulses

These instructions are sent to the effectors (muscles and glands)

Sensory neurones carry signals from receptors to the CNS

Motor neurones carry signals to effector muscles or glands

Reflexes help to prevent injury

They are automatic responses to stimuli

e.g. If a bright light is shone in your eye, your pupils get smaller so that you don't damage your eyes

THE PASSAGE OF INFORMATION IN A REFLEX (RECEPTOR TO EFFECTOR) IS CALLED A REFLEX ARC

1) Reflex arc neurones go hrough the spinal cord/ unconscious part of brain

2) When a stimulus is detected by receptors an impulse is sent along a SENSORY NEURONE to the CNS

3) In the CNS the sensory neurone passes the message to the RELAY NEURONE

4) Relay neurones relay the impulse to a MOTOR NEURONE

5) The impulse travels along the motor neurones to the effector

6) The (muscle) contracts and the reflex action occurs (e.g. hand snatched away)

YOU DO NOT HAVE TO THINK ABOUT IT (UNLIKE NORMAL RESPONSES) SO IT IS MUCH QUICKER

A REFLEX ARC-

STIMULUS>RECEPTOR>SENSORY NEURONE>RELAY NEURONE>MOTOR

NEURONE>EFFECTOR>RESPONSE

Synapses Connect Neurones

1) The connection between two neurones is a synapse

2) The nerve signal is transferred by chemicals which diffuse across the gap

3) These chemicals then set off a new electrical signal in the next neurone

DOCTORS CHECK PART OF YUR NERVOUS SYSTEM BY TAPPING YOUR KNEE WITH  A HAMMER AND CHECKING THAT YOU KICK IN A RESPONSE