Regulation and Response

• Structure of the nervous system

  The nervous system is made up of the brain and spinal cord (central nervous system, CNS) along with specialised nerves that carry information as impulses into and out of the CNS.
• There are three types of neurone:

  • Sensory neurone - carries impulses from receptors (sense organs) to the CNS
  • Relay neurone - carries impulses from sensory neurones to motor neurones in the CNS.
  • Motor neurone - carries impulses from the CNS to effectors (muscles and glands).
• What is a synapse?

  A small gap between neurones across which a nerve impulse is transmitted via neurotransmitters.
• What is sensitivity?

  The ability to detect changes in the environment. These changes are called stimuli. Being able to respond to these stimuli helps the organism survive. Organisms use two ways to respond, nerves or hormones
• What is CNS?

  Central Nervous system

  • Brain
  • Spinal cord
• What is peripheral nervous system?

  Nerve cells that carry information to or from the CNS
• What are neurons?

  Transmit an impulse electrically
• What are sense organs?

  Our sense organs detect changes in the world around us known as stimuli. The sense organs contain groups of specialised cells called receptor cells which produce electrical impulses in response to specific stimuli.
• The table shows the stimuli which cause receptor cells in the sense organs to produce impulses.

  A) Skin

  B) Tongue

  C) Nose

  D) Eye

  E) Ear

  
• What are effectors?

  Parts of the body, such as muscles and glands, that produce a response to a detected stimulus. For example:

  • a muscle contracting to move an arm
  • a gland releasing a hormone into the blood
• The route followed by a reflex arc involves 5 parts

  1. Receptor - which receives the stimulus e.g. skin receptors
  2. A sensory nerve fibre - which carries impulses from the receptor to deep in the spinal cord
  3. A relay nerve - which passes the impulse across the spine from the sensory nerve to the correct motor nerve. This occurs in the co-ordinator (brain or spine).
  4. A motor nerve fibre - which carries the impulse from the spinal cord to muscle
  5. An Effector - which responds when impulses reach it
• We have 5 sense organs which contain receptor cells. These receptor cells detect external stimuli and send an electrical signal along neurones to the central nervous system (CNS) made up of the brain and spinal cord to coordinate a response.
• Reflex arc

  This is the path taken by an electrical impulse from stimulus to response by an effector (muscle or gland). Withdrawal action reflex is shown where an automatic reaction to the hot pan causes a quick withdrawal from the area.
• Reflex arc - picture

  A) Stimulus = heat

  B) Receptor = skin

  C) Sensory neurone

  D) Relay neurone

  E) Synapse

  F) Co-ordinator = spinal cord

  G) Motor neurone

  H) Effector = muscle

  
• What is negative feedback?

  Any change from the balance in optimal internal conditions results in the body’s hormonal and nervous systems compensating for the change and restoring the balance.
• What is a reflex arc?

  This is a rapid, automatic, protective response to an external stimulus