THE NERVOUSE SYSTEM + RESPONDING TO STIMULI

What does responding to their environment do for organisms?

It helps organisms survive

How do animals increase their chances of survival?

By responding to changes thin their external environment, e.g. by avoiding places that are too hot or too cold

Why do animals respond to changes in their internal environment?

To make sure conditions are always right for their metabolism

What is metabolism?

All the chemical reactions that go on inside animals

How do plants increase their chances of survival?

By responding to changes in their enviroment

What is a stimulus?

Any change in the internal or external environment

What do receptors do?

Detect stimuli

What do effectors do?

Produce a response to a stimuli

Where are receptors?

In the sense organs (the eyes, ears, nose, tongue ad skin) are groups of cells

What do receptors detect?

Groups of cells that detect external stimuli

e.g. rod and cone cells in the eye detect changes in light

Where are effectors?

They include muscle cells and cells found in glands, e.g. the pancreas

Do all effectors respond in the same way'?

No - they respond in different ways

What do muscle cells do?

Contract

What do glands do?

Secrete hormones

How do receptors communicate with effectors?

Via the nervous system, the hormonal system or sometimes both

What does the central nervous system (CNS) do?

Coordinate information

What is the nervous system made up of?

All the neurones (nerve cells) in your body.

How many main types of neurone are there?

3

What are the main types of neurone?

• sensory neurones

• relay neurones

• motor neurones

What does the CNS consist of

• brain

• spinal cord

What happens when receptors in a sense organ detect a stimulus?

They send an electrical impulse along sensory neurones to the CNS

What does the CNS do after receiving an electrical impulse from a sensory neurone detected by the receptors?

CNS sends electrical impulses to and effector along a motor neurone. The effector then responds accordingly

What is the job of the CNS?

To coordinate the response

What do coordinated responses always need?

• stimulus

• receptor

• effector

Why is the nervous system able to bring about very rapid responses?

Because neurones transmit information using high speed electrical impulses

What do synapses connect?

Neurones

How is the nerve signal transferred?

The nerve signal is transferred by chemicals called neurotransmitters which diffuse across the gap.

What do neurotransmitters cause?

Set off a new electrical signal in the next neurone