Co-ordination and response

• Homeostasis

  The control or regulation of the internal conditions of a cell or organism
• Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function
• Physiological factors controlled by homeostasis in mammals

  • Core body temperature
  • Metabolic waste (eg. carbon dioxide and urea)
  • Blood pH
  • Concentration of glucose in the blood
  • Water potential of the blood
  • Concentration of respiratory gases (carbon dioxide and oxygen) in the blood
• Communication systems in mammals that maintain homeostasis

  • The nervous system
  • The endocrine system
• All control systems that carry out co-ordinated responses

  • A stimulus (a change in the environment)
  • A receptor (receptor cells that detect stimuli)
  • A coordination centre (such as the brain and spinal cord), which receives and processes information from receptors
  • An effector (a muscle or gland), which brings about responses to restore optimum levels
• Phototropism


  A response to light
• Geotropism


  A response to gravity
• How do plants grow towards the light?

  Auxins produced in the tip concentrate on the shaded side, making the cells on that side elongate and grow faster than the cells on the sunny side
• Nervous system vs Endocrine system

  • Nervous system is faster
  • Information in nervous system is sent as electrical impulses
  • Endocrine system lasts longer
• Parts of the human nervous system

  • Central nervous system (CNS) – the brain and spinal cord
  • Peripheral nervous system (PNS) – all of the nerves in the body
• Neurone


  A nerve cell that transmits electrical impulses
• Nerve


  A bundle of neurones
• Adaptations of neurones

  • Some human neurones have axons over a metre in length (but only 1 - 4 micrometres wide)
  • The axon is insulated by a fatty myelin sheath with small uninsulated sections along its length (called nodes)
  • Many extensions called dendrites extend out from the cell body of the neurone and at the far end of the axon
• Types of neurones

  • Sensory neurones
  • Relay neurones
  • Motor neurones
• Pathway of nerve impulses

  1. Stimulus received by sensory (receptor) neurone

  2. Impulses travel along sensory neurone to central nervous system

  3. Impulses passed to relay neurone

  4. Relay neurone links to motor neurone

  5. Impulses travel along motor neurone to effector
• Synapse


  Junction where the dendrites of two neurones meet to make a connection
• Synaptic cleft/gap


  Very small gap between neurones where electrical impulses are briefly converted to chemical signals (neurotransmitters)
• Parts of the eye

  • Sclera
  • Cornea
  • Iris
  • Pupil
  • Retina
  • Optic nerve
  • Fovea
  • Ciliary muscle
  • Suspensory ligaments
• Iris reflex

  In bright light: Circular muscles contract, radial muscles relax, pupil constricts

  In dim light: Circular muscles relax, radial muscles contract, pupil dilates
• Accommodation

  To focus on distant objects: Ciliary muscles relax, suspensory ligaments pulled tight, lens becomes less convex (flattens)

  To focus on nearby objects: Ciliary muscles contract, suspensory ligaments slack, lens becomes more convex (rounded)
• Vasodilation of skin capillaries

  Arterioles relax, allowing more blood to flow through capillaries, increasing heat loss
• Sweating

  Sweat is secreted by sweat glands, cooling the skin by evaporation
• Flattening of hairs

  Hair erector muscles relax, causing hairs to lie flat, allowing air circulation and heat loss
• Vasoconstriction of skin capillaries

  Arterioles contract, reducing blood flow through capillaries, decreasing heat loss
• Shivering

  Muscles contract rapidly to generate heat and raise core body temperature
• Erection of hairs

  Hair erector muscles contract, causing hairs to stand on end, forming an insulating layer
• Adrenaline

  Produced by the adrenal gland, readies the body's fight or flight response, causes increased heart and breathing rate
• Insulin

  Produced by the pancreas, reduces blood glucose levels, causes excess glucose to be taken up by muscles and stored as glycogen
• Testosterone

  Produced in the testes, the main sex hormone in males, causes development of secondary male sexual characteristics
• Progesterone

  Produced in the ovaries, maintains pregnancy, maintains the uterus lining, allows fertilised egg to develop
• Oestrogen

  Produced in the ovaries, the main sex hormone in females, causes development of secondary female sexual characteristics, controls the menstrual cycle
• ADH

  Produced in the pituitary gland, controls the water content of the blood, causes reabsorption of water into the blood
• FSH

  Produced in the pituitary gland, causes the ovary to develop a mature egg cell, stimulates release of oestrogen and development of egg cells
• LH


  Produced in the pituitary gland, causes the ovary to release a mature egg cell, stimulates release of an egg cell from the ovary and the release of progesterone