Nervous System 1 (Worksheet)

• Neuroglial cell types

  • Microglia
  • Astrocytes
  • Oligodendrocytes
  • Schwann cells
• Microglia


  Immune system cells (phagocytes – engulf bacteria, viruses, and cell debris)
• Astrocytes


  Provide nutrients for the neurons
• Oligodendrocytes


  Form myelin sheaths in the CNS, which insulate axons of interneurons and speed up signal transduction
• Schwann cells


  Form myelin sheaths in the PNS, which insulate axons of motor and sensory neurons and speed up signal transduction
• Types of Neurons

  • Afferent (Sensory)
  • Efferent (Motor)
  • Interneuron
• Afferent (Sensory) neurons


  Collect sensory information from the body and send it to the CNS
• Afferent (Sensory) neurons

  Cell body located in PNS (Dorsal root ganglion), axon located in PNS
• Efferent (Motor) neurons


  Send "commands" from CNS to muscles and glands
• Efferent (Motor) neurons

  Cell body located in CNS (The grey matter of a spinal cord), axon located in PNS
• Interneurons


  Receive and process sensory inputs, make decision, and send out commands
• Interneurons

  Cell body and axon located in CNS (Brain or spinal cord)
• Resting membrane potential is -70mV
• When the cell is resting, the inside of the axon is more negative compared to the outside
• Once the threshold is reached, voltage gated sodium channels open and sodium ions flow into the cell
• During depolarization, the inside of the cell becomes more positive compared to the outside
• When depolarization reaches +30mV, voltage gated potassium channels open and potassium ions flow out of the cell
• After repolarization, the inside of the cell becomes more negative compared to the outside
• Na+/K+ pump

  Restores ion concentrations by moving 3 Na+ out and 2 K+ into the cell
• Phases of action potential

  1. Resting membrane potential

  2. Initial depolarization

  3. Depolarization

  4. Repolarization

  5. Refractory period

  6. Resting membrane potential

  
• Components of a synapse

  • Axonal terminal of a presynaptic (sending) neuron
  • Synaptic knob
  • Synaptic cleft
  • Receptor for the neurotransmitter on the postsynaptic (receiving) cell
  • Ion channel
  • Postsynaptic membrane
  • Synaptic vesicles filled with a neurotransmitter in the axonal terminal of the presynaptic neuron
• When action potential reaches synaptic knob, calcium ions (Ca2+) enter the presynaptic neuron, triggering the release of a neurotransmitter
• Exocytosis


  Type of transport used to release a neurotransmitter
• Ligand-gated ion channel


  Opens only when ligand (a neurotransmitter) binds to it, allowing ions to flow across the membrane
• The neurotransmitter does not enter the postsynaptic cell, it only binds to the receptor on the postsynaptic membrane
• Once the neurotransmitter binds to its receptor, ions (e.g. Na+) flow into the postsynaptic cell, which can depolarize the membrane and generate an action potential
• Acetylcholine


  A neurotransmitter found in both CNS and PNS, important in neuromuscular junctions
• Myasthenia gravis


  An autoimmune disorder where the immune system targets and destroys acetylcholine receptors (ligand-gated sodium channels) on the postsynaptic membrane in the neuromuscular junction
• In myasthenia gravis, as acetylcholine receptors are destroyed


  Multiple signals from a neuron are needed to get enough sodium ions into the muscle cell to reach the threshold of an action potential, resulting in reduced muscle strength
• If most or all acetylcholine receptors are destroyed in myasthenia gravis

  No action potential can be generated on the muscle cell, resulting in complete loss of muscle strength