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 Organs which recognise and respond to stimuli., which detect stimuli (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.
- The organ, tissue or cell that produces a response. which bring about responses, and restore optimum levels, such as core body temperature and blood glucose levels. Effectors include muscles and An organ or tissue that makes a substance for release, such as a hormone., 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 Chemical messenger produced in glands and carried by the blood to specific organs in the body. 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 |