AQA A2 Biology Notes on Nervous and Hormonal Communications

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Nervous and Hormonal Communications

Responding to their Environment Helps Organisms Survive

-Animals increase their chances of survival by reponding to changes in their EXTERNAL envrionment e.g by avoiding places that are harmful- too hot or cold.

-They also respond to changes in their INTERNAL environment to make sure their conditions are always OPTIMAL for their metabolism.

-Plants increase their chances of survival by responding to changes in their environment.

Any change in the INTERNAL or EXTERNAL environment is called STIMULUS.

Receptors Detect Stimuli and Effectors Produce a Responce

-Receptors DETECT STIMULI- they can be cells or proteins on cell surface membranes (there are lots of different receptors that detect different stimuli)

-Effectors bring about a RESPONCE to a STIMULUS, to produce an EFFECT. They include muscle cells and cells in glands e.g pancreas,

Receptors communicate with effectors via the NERVOUS or HORMONAL SYSTEM

The Nervous System Sends Information as Electrical Impulses

-The nervous system is made up of a COMPLEX NETWORK of NEURONES. There are three main types of neurones:

SENSORY NEURONES- transmit electrical impulses FROM RECEPTORS to the CENTRAL NERVOUS SYSTEM (CNS)

MOTOR NEURONES-transmit electrical impulses from CNS to EFFECTORS

RELAY NEURONES-transmit electrical impluses BETWEEN SENSORY NEURONES and MOTOR NEURONES.

1.)A STIMULUS is DETECTED by RECEPTOR CELLS and an ELECTRICAL IMPULSE is sent along a SENSORY NEURONE

2.)When an ELECTRICAL IMPULSE reaches the end of NEURONE, CHEMICALS take the information to the NEXT NEURONE which then sends an ELECTRICAL IMPULSE.

3.)CNS PROCESSES the information and DECIDES what to do. It SENDS IMPULSES along MOTOR NEURONES to an EFFECTOR.

EXAMPLE

STIMULUS=Friend Waving

RECEPTORS=Light Receptors detect the wave

CNS=Proceses

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