CB2

• Central nervous system


  Brain and spinal cord
• Spinal cord


  A long, thin structure composed of neurones that extends from the medulla oblongata down the spine
• Spinal cord


  • Connects the peripheral nervous system (nerves outside of the CNS) to the brain
• Neurones


  Nerve cells adapted to quickly transmit nerve impulses. They are the functional units of the nervous system.
• Function of the nervous system

  Allows an organism to rapidly react to environmental and internal changes
• Cell cycle

  A series of events that take place in a cell involving cell growth, DNA replication and cell division
• Cell cycle

  The lifecycle of a cell
• Stages of the cell cycle

  • Interphase
  • Mitosis
  • Cytokinesis
• Function of the axon

  • Carries impulses away from the cell body
  • Enables the transmission of electrical impulses over long distances
• Interphase


  The longest stage of the cell cycle that involves cell growth, the synthesis of new organelles and DNA replication
• Function of the dendrites and dendrons

  • Carry impulses towards the cell body
  • Dendrites provide a large surface area to receive electrical impulses
• Role of the myelin sheath

  • Electrically insulating layer
  • Surrounds the axon in a fatty layer and increases the speed of electrical impulses
• Chromosome

  A linear DNA molecule tightly coiled around proteins
• Function of a sensory neurone


  Carries impulses from receptors to the central nervous system
• During DNA replication


  The DNA in the 'arm' of each chromosome (chromatid) is replicated
• Structure of a sensory neurone

  • Long dendron carries impulses from receptors to the cell body
  • Cell body is found in the middle of the neurone
  • Short axon carries impulses from the cell body to the CNS
• Mitosis


  A form of cell division that produces two diploid 'daughter' cells, both genetically identical to the parent cell
• Function of a motor neurone


  Carries impulses from the central nervous system to effectors
• Importance of mitosis in organisms

  • Asexual reproduction
  • Growth
  • Repair of damaged cells
  • Cell replacement
• Structure of a motor neurone

  • Short dendrites carry impulses from the CNS to the cell body
  • Cell body found at one end of the neurone
  • Long axon carries impulses from the cell body to the effectors
• Stages of mitosis


  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Function of a relay neurone


  Carries impulses from sensory neurones to motor neurones within the central nervous system
• Prophase


  1. DNA condenses, chromosomes become visible

  2. Nuclear membrane disappears
• Structure of a relay neurone

  • Short dendrites carry impulses from sensory neurones to the cell body
  • Short axon carries impulses from the cell body to motor neurones
• Metaphase


  Chromosomes line up along the cell equator
• How the central nervous system coordinates a response to a stimulus

  1. Stimulus

  2. Sensory receptor detects stimulus

  3. Sensory receptor sends impulses along sensory neurone to CNS

  4. CNS coordinates response

  5. CNS sends information to effector along motor neurone

  6. Effector produces a response to the stimulus
• Anaphase


  1. Spindle fibres attach to each chromosome

  2. 'Arms' of each chromosome pulled to opposite poles

  3. Chromatids separated
• Synapse


  A small gap between neurones across which a nerve impulse is transmitted via neurotransmitters
• Telophase


  1. Nucleus of the cell divides

  2. New membrane forms around each set of chromosomes
• Cytokinesis


  • Division of the cell membrane and cytoplasm
  • Two genetically identical 'daughter' cells produced
• Cancer


  Non-communicable disease

  Uncontrolled cell division (due to damaged DNA) results in the formation of a primary tumour

  Tumour cells break off and spread to other tissues forming secondary tumours
• Percentile charts


  A chart used to monitor growth

  Measurements (e.g. fetal length or head circumference) can be compared to the expected values at a certain age
• How nerve impulses are transmitted across a synapse

  1. Nerve impulse reaches the end of a neurone

  2. This triggers the release of chemicals called neurotransmitters

  3. Neurotransmitters diffuse across the synapse

  4. They bind to receptors on the start of the next neurone

  5. This stimulates an electrical impulse in the next neurone
• Synapses slow down the transmission of nerve impulses because it takes time for the neurotransmitters to diffuse across the synapse and bind to receptors on the postsynaptic neurone.
• 95th percentile


  95% of measurements will be below the value of the 95th percentile
• Reflex


  • Automatic response to a stimulus by the body
  • Involuntary - does not involve conscious part of the brain
  • Protective mechanism e.g. a withdrawal reflex is initiated when a hot object is touched to prevent burns
• Reflex arc


  1. stimulus

  2. sensory receptor

  3. sensory neurone

  4. relay neurone

  5. motor neurone

  6. effector

  7. response
• What can doctors determine from percentile charts?

  • Slower growth than normal (below the bottom line)
  • Faster growth than normal (above the top line)
  • Abnormal growth (irregular growth patterns)
• Growth in animals


  • Cell division occurs in all body cells. It occurs at a slower rate in adults that in younger animals as growth stops and cell division is only required for replacement and repair.

  Most cells differentiate at an early stage and become specialised. Some adult stem cells retain their ability to differentiate.
• Growth in plants


  • Cell division can only occur in meristematic tissue. The rate of cell division remains the same throughout a plant's life.

  Meristematic stem cells can differentiate into any cell type for as long as the plant lives

  Cell elongation occurs in all cells. Cells expand and enlarge enabling growth of the plant.