How organisms respond to changes in their environment

An animal’s response to a stimulus is coordinated by their central nervous system (CNS).

Responding to a stimulus

A stimulus is a change in the environment of an organism.

Animals respond to a stimulus in order to keep themselves in favourable conditions.

Examples of this include:

• moving to somewhere warmer if they are too cold
• moving towards food if they are hungry
• moving away from danger to protect themselves

Animals that do not respond to a stimulus do not survive for long.

An animal’s response to a stimulus is coordinated by their central nervous system (CNS). The CNS consists of the brain and the spinal cord. It gathers information about, and responds to, changes in the environment.

Receptors respond to a stimulus and send impulses along sensory neurons to the CNS. The CNS coordinates the information and sends impulses along motor neuronsto the effectors, which bring about a response. The sequence is as follows:

1. Stimulus
2. Receptor
3. Sensory neuron
4. Central nervous system
5. Motor neuron
6. Effector
7. Response

There are light receptors in the eye

Some receptors are found in the skin. Other receptors can form part of complex organs, such as:

• light receptor cells in the retina of the eye
• hormone-secreting cells in hormone glands
• muscle cells
• position receptors in the inner ear
• sound receptors in the ear
• touch, pressure, temperature and pain receptors in skin
• chemical receptors in the nose and tongue

The peripheral nervous system

The peripheral nervous system (PNS) consists of motor and sensory neurons that carry information from the receptors to the CNS, as well as instructions from the CNS to the effectors.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/brain_mind/environmentrev1.shtml

Brain and mind

How organisms respond to changes in their environment - Test

Top of Form

1.

A stimulus can be caused by...

  x a change in the environment.

sensory deprivation.

a constant environment.

2.Which answer best describes why animals respond to a stimulus?

To move away from favourable conditions

To relieve boredom

  x To remain in favourable conditions

3.Which of the following statements about the central nervous system (CNS) and sensory neurons is true?

The CNS sends impulses along sensory neurons to receptors.

  x Sensory neurons carry impulses from receptors to the CNS.

Receptors receive impulses from the sensory neurons through the CNS.

4.Which of the following statements about the central nervous system (CNS) and motor neurons is true?

Effectors send impulses along motor neurons to the CNS.

The CNS carries impulses from the effectors to the motor neurons.

  x Motor neurons carry impulses from the CNS to effectors.

5.Which of the following form part of the central nervous system?

receptors and effectors

sensory and motor neurons

  x brain and spinal cord

6.Which of the following form part of the peripheral nervous system?

receptors and effectors

  x sensory and motor neurons

brain and spinal cord