hubs 16-23

• Nervous system

  Able to sense the environment and produce a suitable response
• Integration

  Brain assessing a situation
• Coordination

  Making a decision in response to respond
• Anatomical organisation of the nervous system


  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (nerves and ganglia)
• Neurons

  Specialized for transmission of information
• Non-neuronal cells (glia)


  • 4 types in central nervous system
  • 1 type in peripheral nervous system
• Dendrites


  • Receive input and send information to the cell body
  • Include receptors that collect information from the environment
• Cell body

  • Contains nucleus and organelles
  • Sum input and the end of the cell body is the summation zone where inputs are summed
• Axon


  • Carries electrical impulses
  • May or may not be myelinated
  • Can be very long to transmit information over long distances
• Axon terminal

  • End of axon
  • Neurotransmitters are released
• Cells in the central nervous system


  • Group of cell bodies are called nucleus or nuclei
  • Bundle of axons are a tract
  • Group of cell bodies in cerebral cortex or spinal cord is called grey matter
• Cells in the peripheral nervous system


  • Group of cell bodies are called ganglion or ganglia
  • Bundle of axon are nerves
  • Multipolar = multiple processes emanate from cell body
  • Bipolar = two processes emanate
  • Unipolar = one process emanate from cell body
  • Anaxonic neurons have no distinct axon and all processes look alike
• 4 types of glia in central nervous system


  • Astrocytes
  • Microglia
  • Ependymal cells
  • Oligodendrocytes
• Glia in the peripheral nervous system


  Schwann cells - support peripheral nerve fibres and unsheathe them with myelin
• Myelin sheath


  • Lipid/fat wrapped around the axon, made up of oligodendrocytes in CNS and schwann cells in PNS
  • Increases speed and efficiency of conduction velocity - allows for fast communication
• Nodes of Ranvier


  Gaps within myelin sheath
• Synapse


  Junction where communication between neurons occur
• Afferent information


  Information that goes into the brain, also called ascending and sensed from the environment
• Efferent information


  Information that comes out of the brain, also called descending and develops a response with an appropriate action
• Somatic information


  Voluntary information that we are aware of and have control over
• Synaptic transmission


  1. Presynaptic neuron releases neurotransmitter

  2. Neurotransmitter diffuses across synaptic cleft

  3. Neurotransmitter binds to receptors on postsynaptic cell

  4. Opens chemically gated ion channels

  5. Changes membrane potential
• Chemically gated ion channels

  Opened by binding of neurotransmitter
• Voltage gated ion channels

  Opened by membrane depolarization to threshold voltage (-60mV)
• Mechanically gated ion channels

  Opened by deformation of the membrane
• Voltage gated K channels and voltage gated Na channels are both triggered to open at -60mV
• K channels open more slowly than voltage gated Na channels - important for action potential
• Resting membrane potential


  Polarized at -70mV, negative due to negatively charged proteins and Na+/K+ exchange pumps
• Electrochemical gradients


  Maintained by Na+/K+ exchange pump, sodium high outside and potassium high inside the cell
• Local potentials


  Localized changes in membrane potential, can be excitatory (EPSP) or inhibitory (IPSP)
• Inhibitory local potentials (IPSPs)


  Make it less likely that the cell will reach threshold and fire an action potential
• Spatial summation


  Summed input from multiple pre-synaptic neurons
• Temporal summation


  Summed input from repeated firing of one pre-synaptic neuron
• Action potential


  1. Voltage-gated Na+ channels open at -60mV

  2. Rapid depolarization phase

  3. Na+ entry stops, K+ exits causing repolarization phase
• Action potential propagation


  Starts at axon hillock, then moves to initial segment of axon, then propagates along the axon
• In unmyelinated axons, action potential depolarizes the next membrane to threshold, causing it to fire
• Action potential propagation

  1. Action potential happens first at the axon hillock

  2. Moves to the initial segment of the axon

  3. Continues throughout the rest of the segments
• Action potential


  A series of sequential changes in membrane potential
• An action potential happens first at the axon hillock and then moves to the initial segment of the axon
• Action potential happens at the axon hillock because there are no voltage gated channels
• Depolarization


  There is a flood of Na+ in the hillock