Edexcel A (SNAB) A Level Biology:复习笔记8.1.1 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 →CNS → motor neurone → arm muscle

    • The muscle in the arm responds by contracting to move the hand away from the hot surface

The nervous system allows the detection of stimuli and the co-ordination of appropriate responses

The hormonal system

  • Hormones are chemical substances produced by endocrine glands and carried by the blood
    • Hormones are sometimes known as chemical messengers
  • Hormones transmit information from one part of an organism to another and bring about change by altering the activity of one or more specific target organs
    • Hormones can leave the blood and bind to specific receptors on the cell surface membranes of target organs
  • Hormones are slower in action than nerve impulses and are therefore used to control functions that do not need instant responses
  • Endocrine glands that produces hormones in animals are known collectively as the endocrine system
    • Endocrine glands secrete hormones directly into the blood
    • Endocrine glands can be stimulated to secrete hormones by the action of another hormone or by the arrival of a nerve impulse
  • The pathway of hormone action is as follows

stimulus → receptor → hormone →effector

  • An example of this pathway in action might be

high blood sugar → cells in the pancreas → insulin → liver cells

    • The liver cells respond to insulin by converting glucose into glycogen

Hormones are secreted into the blood by the endocrine glands


Comparison of Nervous and Hormonal control Table