co-ordination-of-response

Co-ordination of Response

• Organisms must respond to changes in their external and internal environments in order to survive

  • Organisms need to

    • Find favourable external conditions e.g. avoiding locations that are too hot or cold

    • Find food

    • Avoid harm e.g. from predators or high blood glucose

• Changes in the environment, or stimuli (singular stimulus) are detected by specialised receptor cells 

  • Receptor cells are located in the sense organs e.g. the nose and eyes

  • Receptor cells can also be found inside the body e.g. pressure receptors in the blood vessels

• Receptor cells send signals via either the nervous system or the hormonal system to the body’s co-ordination centres in the brain or spinal cord

• Signals are then sent on to the parts of the body which respond, known as the effectors

  • Effectors can be either muscles or glands e.g.

    • An arm muscle would respond to a hot surface by contracting to move the hand away

    • The pancreas responds to high blood sugar by secreting insulin

Receptors are cells that detect stimuli in the internal and external environment

The nervous system

• The human nervous system consists of

  • Central nervous system (CNS) – the brain and spinal cord

  • Peripheral nervous system (PNS) – all of the nerves in the body

• The nervous system allows detection of stimuli in our surroundings and the coordination of the body’s responses to the stimuli

• Information is sent through the nervous system in the form of electrical impulses that pass along nerve cells known as neurones 

  • A bundle of neurones is known as a nerve

  • There are different types of neurones including sensory neurones, relay neurones, and motor neurones

• The nerves connect the receptors in the sense organs with the CNS, and connect the CNS with effectors

  • The CNS acts as a central coordinating centre for the impulses that come in from, and are sent out to, any part of the body

• Nerve impulses pass through the nervous system along the following pathway

stimulus receptor sensory neurone  CNS motor neurone effector

• An example of this nerve pathway in action might be

hot surface pain receptor in skin of hand  sensory neurone <img alt=”rightwards arrow” data-mathml='<math ><semantics><mo>→</mo><annotation encoding=”application/vnd.wiris.mtweb-params+json”>{“language”:”en”,”fontFamily”:”Times New Roman”,”fontSize”:”18″}</annotation></semantics></math>’ height=”19″ role=”math” src=”data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20xmlns%3Awr