Science biology revision Unit 1 triple science yr 10 part 2

Touch, hear, smell, taste, sight-->sense organs are organs that contain receptors to detect stimuli.

What are the following receptors sensitive to?

Skin: pressure, temperature, textiles, pain.

Eye: Light

Ear: sound waves, equilibrum (balance)-body movement  

Tongue: taste, flavours-->tastebuds, chemical signals-sweet, savoury, salty, sour recognition 

Nose: smell, taste, chemicals in air

The receptors send nerve impulses (messages) along neurons to the CNS as a response to the stimuli/stimulus (i.e-hot surface of pan) from the surroundings. The CNS then sends these messages back to the effectors (i.e finger) which then brings a response (finger is taken away from saucepan)

the effector is: a muscle that causes movement

or

a hormone releasing gland like the thyroid or the pitituary gland 

Nerves or neurones are cells that make up nerves. The 3 main types of nerve cells are the sensory, relay and motor neurones. Neurones have a cytoplasm, nucleus & cell membrane and they are specialized. 

SENSORY: receive messges from the receptors and send them to the CNS.

RELAY: connects the sensory to the motor in CNS.

MOTOR: send messages from the CNS to the effectors which tells them what to do.

Nerve impulses only travel in 1 DIRECTION. They have a fatty sheath which is used for INSULATION and also increases the speed of Nerve Impulses.

What's a synapse? A synapse is a gap in between the neurones. When an impulse reaches the end of an axon, a chemical is discharged which is scattered across the gap. This continues an impulse into the next neurone.

What stops them from functioning properly? Drugs and alcohol can have an affect on the synapses, delaying or even halting them from working.   

There is a reflex response in which the message goes to the spinal cord and back again. this is called the reflex arc. 

If for example, the stimulus is a heated object

The receptor is heat and pain in the skin

The message travels along the SENSORY neurone. 

This impulse passes along a synapse to the RELAY.

It again crosses a synapse to reach the motor neurone.

The impulse passes along a synapse to the muscle effector (in this example, the finger)

This causes response-in this case, the arm moves away. 

simplified version:

stimulus->receptor->Sensory->Relay->Motor->effector->response

What are these actions?

Voluntary actions are things that have to be thought about under conscious control. They usually have to be learned, like talking or reading. 

Reflex actions are abrupt movements and often protect from harm. it does not involve the brain. For example, blinking, breathing and the response to light from the pupils in the eye.

Sometimes, the brain reflexes can override each other. For example, holding a hot mug and a nerve impulse is sent to the motor neuron to keep hold of the mug and not drop it.

Conditioning is a learnt reflex response to a situation. It involves stimuli. A well known example was found by scientist Pavlov who rung a bell at the feeding times of his dogs which triggered the saliva production in the dogs. He used the fact that food makes them salivate.