Aims

• To improve your knowledge of the endocrine system and the nervous system

• To improve your confidence with biology• To give you the background knowledge you need for A2• NOT to teach you psychology!

Organisms need to respond to external stimuli, e.g. temperature, oxygen

concentration and levels of sunlight.

These may be over time, e.g. winter fur to summer fur, or quickly, e.g. changing size

of pupils.

Multicellular organisms need to coordinate different organs, so this requires a good

communication system which will:

• Cover the whole body

• Enable cells to communicate with each other

• Enable specific communication

• Enable rapid communication

• Enable both short and long-term responses.

Responding to our Environment

The Nervous System

CNS PNS

The ‘Fight or Flight’ response

• uses energy

• blood pressure increases

• heart beats faster

• digestion slows down.

The ‘Rest and Digest’ response

• saves energy

• blood pressure can decrease

• pulse rate can slow

• digestion can start.

Synapse

The Endocrine System

Endocrine gland -

a gland that secrets hormones directly into the blood. Endocrine

glands have no ducts.

Exocrine gland -

a gland that secrets molecules directly into a duct that carries the

molecules to where they are used.

Hormone -

a molecule released into the blood which acts as a chemical

messenger

Target tissue -

a group of cells that have receptors embedded in the plasma

membrane that are

complementary in shape to specific hormone molecules. Only

these cells will respond to the specific hormone.

Negative feedback

• The reversing of a change in the internal environment• Change needs to be detected• Change must be signalled to other cells• Response to reverse the change

Negative Feedback

Loops

Stimulus

Receptor

Communication pathway (cell signalling)

Effector

Response

Negative feedback pathway

Positive feedback• Not common

• Increases original change detected by receptors

• Usually harmful

• E.g. body temp falls, enzymes become less active, less heat released, temp continues to fall!

Positive Feedback

loops