Coordination and control

• The central nervous system consists of the brain and spinal cord
• Central Nervous System


  Controls and co-ordinates the responses between the receptors and effectors (muscles and glands)
• Hormone System


  Chemical messages produced by special glands which release them into the blood, the hormones can only affect target organs, act more slowly than the nervous system and over a longer period
• Hormones help maintain the hormonal environment of the body in a relatively constant state in response to changes
• Nervous System


  Anything that causes a response is called a stimulus, each type of stimulus affects a receptor in the body
• Receptor stimulation


  1. Receptor is stimulated

  2. May cause a different part of the body, an effector (muscles/glands) to produce a response
• Types of receptors


  • Sight
  • Sound
  • Touch
  • Smell
• Eye


  • Conjunctiva helps prevent microorganisms from entering
  • Cornea allows light into the eye and causes it to bend/refract slightly
  • Pupil allows light into the eye
  • Iris controls the amount of light entering by changing its diameter
  • Aqueous/vitreous humour help maintain the shape of the eye and lens
  • Lens bends light towards the retina
  • Retina contains cells sensitive to different types of light
• Voluntary actions


  What we deliberately choose to do
• Reflex actions


  Don't involve conscious thought
• Neurone


  • Nucleus which controls the activities is surrounded by most of the cell cytoplasm
  • Axon is a long extension of the cytoplasm which can be very long to transmit nerve impulses
  • Myelin sheath is a fatty layer around the axon that acts as an insulator and speeds up nerve impulses
  • Branched ends of the axon allow the neurone to make connections with many other nerve cells
• Synaptic transmission


  1. Electrical impulse reaches end of axon

  2. Axon releases a transmitter substance

  3. Substance diffuses across the gap

  4. If concentration is high enough in the other neurone, it triggers an electrical impulse
• Accommodation


  Adjusting the thickness of the lens to focus light on the retina
• How the lens changes shape

  1. Ciliary muscle relaxes, suspensory ligaments tighten, lens becomes thinner

  2. Ciliary muscle contracts, suspensory ligaments slacken, lens becomes thicker
• Diabetes


  A condition where the blood glucose control mechanism fails, either the pancreas stops producing insulin or the body becomes resistant to insulin
• Types of diabetes


  • Type 1 - pancreas stops producing insulin, requires insulin injections
  • Type 2 - progressive disease linked to lifestyle and obesity, can be controlled by diet and medication
• Symptoms of diabetes include high blood glucose, increased urination, lethargy, and thirst
• Long-term effects of diabetes include eye damage, kidney failure, heart disease and strokes
• Increasing numbers of people getting diabetes is related to lifestyle factors
• Receptor


  • Detects stimuli in the environment and produces nerve impulses
  • Consists of a sensory, association and motor neurone connected by synapses
• Homeostasis


  The maintenance of the constant state of the internal environment of the body
• Examples of homeostasis


  • Controlling the concentration of glucose in the blood
  • Controlling the water content of the body
• Hormones


  Chemical messengers produced by glands and released into the blood which carries them to target organs
• Insulin regulation of blood glucose

  1. Pancreas constantly monitoring blood glucose concentration

  2. Pancreas produces insulin in response to increasing blood glucose

  3. Insulin causes liver and muscles to absorb excess glucose from the blood, lowering the concentration
• Negative feedback


  A mechanism to ensure the concentration of something does not deviate too far from the normal value
• Fall in blood glucose concentration

  Absorbed by liver, converted to glycogen and respired
• Meal rich in carbs

  Increases blood glucose concentration
• Increased blood glucose concentration

  Pancreas produces more insulin
• Excretory system


  • Blood passes into each kidney through the renal artery
  • In the cortex, much of the liquid portion of the blood and many dissolved substances are filtered out
  • In the medulla, water and other substances are reabsorbed back into the blood until normal concentration is reached
  • Excess water and dissolved substances pass into the ureter and bladder, then out through the urethra
• Osmoregulation


  The homeostatic process that controls the water content of the body
• Osmoregulation


  1. Water gained through food, drink and respiration

  2. Water lost through sweating, breathing and urine production

  3. Kidneys filter blood and control reabsorption of water

  4. ADH (anti-diuretic hormone) produced by the brain to regulate water reabsorption in the kidneys
• Low water content


  Brain produces more ADH
• High water content


  Brain produces less ADH
• Plant hormones


  Important in controlling and co-ordinating plant growth and development
• Phototropism


  1. More auxin hormone passes to the shaded side

  2. Auxin causes increased elongation of cells on the shaded side

  3. Results in uneven growth, causing the plant to bend towards the light
• Bending towards the light allows the plant to undergo more photosynthesis and growth