Responding to changes in environment

Organisms need to detect and respond to changes in their internal and external environment. This is because the conditions inside our body must be carefully controlled for it to function effectively and survive. The control systems that allow organisms to respond to changes are incredibly important.

All control systems include:

Cells called , which detect (changes in the environment).
The coordination centre, such as the brain, spinal cord or pancreas, which receives and processes information from receptors around the body.
which bring about responses, and restore optimum levels, such as core body temperature and blood glucose levels. Effectors include muscles and , and so responses can include muscle contractions or hormone release.

The nervous system

The nervous system allows an organism to respond quickly to changes in the internal or external environment. The responses to the stimuli are short-lasting.

Receptors

Receptors are groups of specialised cells. They detect a change in the environment stimulus. In the nervous system this leads to an electrical impulse being made in response to the stimulus. Sense organs contain groups of receptors that respond to specific stimuli.

Sense organ	Stimuli receptors respond to
Skin	Touch, temperature, pain
Tongue	Chemicals (in food and drink, for example)
Nose	Chemicals (in the air, for example)
Eye	Light
Ear	Sound, position of head

Sense organ	Skin
Stimuli receptors respond to	Touch, temperature, pain

Sense organ	Tongue
Stimuli receptors respond to	Chemicals (in food and drink, for example)

Sense organ	Nose
Stimuli receptors respond to	Chemicals (in the air, for example)

Sense organ	Eye
Stimuli receptors respond to	Light

Sense organ	Ear
Stimuli receptors respond to	Sound, position of head

Effectors

Effectors include muscles and glands - that produce a specific response to a detected stimulus.

For example:

a muscle contracting to move an arm
muscle squeezing saliva from the salivary gland
a gland releasing a into the blood

Receptors are connected to effectors as follows:

Sensory receptors	These detect the changes in the environment (stimulus)
Sensory neurons	Nerve cells that send a signal from the sensory receptors to the CNS
CNS	The central nervous system (CNS), which is the brain and the spinal cord. This coordinates a response and sends a signal down a motor neuron.
Motor neurons	Nerve cells that receive a signal from the CNS and transfer it to the effector
Effectors	The muscles or glands that produce a response to the stimulus

Sensory receptors
These detect the changes in the environment (stimulus)

Sensory neurons
Nerve cells that send a signal from the sensory receptors to the CNS

CNS
The central nervous system (CNS), which is the brain and the spinal cord. This coordinates a response and sends a signal down a motor neuron.

Motor neurons
Nerve cells that receive a signal from the CNS and transfer it to the effector

Effectors
The muscles or glands that produce a response to the stimulus

Diagram showing how receptors connect to effectors

Adaptations of neurons

How does the nervous system help us respond? - OCR 21st CenturyResponding to changes in environment