The nervous system

• Why do synapses slow down the transmission of nerve impulses?

  It takes time for the neurotransmitters to diffuse across the synapse and bind to receptors on the postsynaptic neurone
• How are nerve impulse transmitted across a synapse?

  • Nerve impulses reaches a presynaptic neurone

  • This triggers a release of neurotransmitters

  • Neurotransmitters diffuse across the synapse

  • They bind to receptors on the postsynaptic neurone

  • This stimulates an impulse in the postsynaptic neurone
• How does the CNS coordinate a response to a stimulus?

  • Stimulus

  • Sensory receptor detects stimulus

  • Sensory receptor sends impulses along sensory neurone to CNS

  • CNS coordinates response

  • CNS sends information to effector along motor neurone

  • Effector produces a response to the stimulus
• Function of a relay neurone

  Carries impulses from sensory neurones to motor neurones within the central nervous system
• 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 effectors
• Function of a motor neurone

  Carries impulses from the CNS to effectors
• Structure of a sensory neurone

  • LONG DENDRON -> carries impulses from receptors to the cell body

  • Cell body found part way along the neurone

  • SHORT AXON -> carries impulses from the cell body to the CNS
• Role of the myelin sheath

  • Electrically insulating layer

  • Surrounds the axon and increases the speed of impulses
• Function of dendrites and dendrons

  • Carry impulses towards the cell body

  • Dendrites provide a large surface area to receive impulses
• Why is it difficult to treat damage to the CNS?

  • Damage to neurones is permanent and cannot be repaired as nerve cells don’t divid by mitosis

  • Hard to reach some areas of the brain

  • Risk of further permanent damage to other areas of the CNS during surgery
• Describe how PET scans are useful to investigate brain function

  • Show which areas of the brain are active and which areas are not

  • Comparisons of brain activity in healthy patients and patients with brain damage allow scientists to determine the functions of inactive regions
• What does a PET scan involve?

  • Radioactive substances injected into a patient’s bloodstream and taken up by tissues in the brain

  • Radiation emitted by tissues detected, enabling the identification of active and inactive regions of the brain
• Describe how CT scans are useful to investigate brain function

  • CT scans show damaged regions of the brain e.g. areas of swelling or bleeding

  • Observations of the patient’s symptoms can enable scientists to determine the function of the damaged region