Coordination and respone in man

• Nervous system


  Consists of the central nervous system (brain and spinal cord) and the peripheral nervous system (all nerves in the body)

  
• Nervous system


  • Allows us to make sense of our surroundings and respond to them
  • Coordinates and regulates body functions

  
• Nerve impulses


  Electrical signals that pass along nerve cells called neurones

  
• Nerve


  A bundle of neurones
• Types of neurone

  • Sensory
  • Relay
  • Motor

  
• Sensory neurones


  • Carry impulses from sense organs to the central nervous system

  
• Relay neurones


  • Found inside the central nervous system and connect sensory and motor neurones

  
• Motor neurones


  • Carry impulses from the central nervous system to effectors (muscles or glands)

  
• Neurone structure

  • Long fibre (axon)
  • Axon insulated by fatty sheath with uninsulated sections (nodes)
  • Cell body with many extensions (dendrites)

  
• Voluntary responses start with the brain, involuntary (reflex) responses do not involve the brain

  
• Reflex

  An automatic and rapid response to a stimulus that does not involve the brain

  
• Reflex arc


  1. Stimulus detected by receptor

  2. Sensory neurone sends impulse to spinal cord

  3. Relay neurone passes impulse to motor neurone

  4. Motor neurone carries impulse to effector (muscle)

  
• Synapse


  Junction between two neurones
• Impulse passing across a synapse

  1. Electrical impulse travels along first axon

  2. Presynaptic neurone releases neurotransmitters

  3. Neurotransmitters bind to receptors on postsynaptic neurone

  4. Second neurone generates electrical impulse

  
• Sense organs


  • Skin
  • Tongue
  • Nose
  • Ear
  • Eye
• Sense organs


  Contain receptors that respond to specific stimuli and generate electrical impulses
• Parts of the eye

  • Cornea
  • Iris
  • Lens
  • Retina
  • Optic nerve
  • Pupil

  
• Pupil reflex

  • Pupil dilates in dim light to allow more light
  • Pupil constricts in bright light to prevent damage

  
• Pupil reflex mechanism

  1. Photoreceptors detect change in light

  2. Radial muscles relax/contract

  3. Circular muscles contract/relax

  4. Pupil size changes

  
• Accommodation


  • Lens changes shape to focus light from near and distant objects
• Accommodation mechanism

  1. Ciliary muscles contract/relax

  2. Suspensory ligaments slacken/stretch

  3. Lens becomes fatter/thinner
• Rods and cones

  • Rods sensitive to dim light, cones distinguish colours in bright light
• Fovea has mostly cone cells
• Object far away


  The light is refracted less
• Object close by


  The light is refracted more
• Ciliary muscles

  • Relaxed
  • Contracted
• Suspensory ligaments

  • Pulled tight
  • Slack
• Lens


  • Thinner
  • Fatter
• Rods

  Sensitive to dim light
• Cones


  Distinguish between different colours in bright light
• There are 3 types of cone cells which are sensitive to different colours of light (red, blue and green)
• The fovea is an area on the retina where almost all of the cone cells are found
• Rod cells are found all over the retina, other than the area where the optic nerve attaches to the retina – there are no light-sensitive cells at all in this area, and so it is known as the blind spot
• Hormone


  A chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs
• Endocrine system


  The glands that produce hormones in animals
• Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about the response
• Once a hormone has been used, it is destroyed by the liver
• Major endocrine glands in the body


  • Glands not specified

  
• Hormones only affect cells with target receptors that the hormone can bind to. These are either found on the cell membrane, or inside cells. Receptors have to be complementary to hormones for their to be an effect
• The liver regulates levels of hormones in the blood; transforming or breaking down any that are in excess