Cells of the Nervous System

Neurons
1. are excitable
  1. hey generate and transmit electrical signals
    1. these are called action potentials
2. human brain contains 100,000,000,000 neurons
  1. any given neuron can have upwards of 10,000 synapses
    1. therefore in the brain there are 100,000,000,000 x 10,000 synapses
      1. the number of possible networks is almost infinite
  2. as the incredible ability to :
    1. process information
    2. learn
    3. solve complex tasks
    4. have emotions
3. have four regions
  1. cell body
    1. contains the nucleus and organelles
  2. dendrities
    1. bring information to the cell body
  3. axon
    1. carries information away from the cell body
  4. axon terminals
    1. at the tip of the axon
4. all neurons share some common mechanisms
  1. the plasma membranes of all neurons can generate and conduct action potentials
  2. action potentials can travel at speeds of up to 100 m/sec (360km/hour)
  3. the axon terminal comes extermely close to the membrane of the target cells forming a synapse
  4. electrical synapses allow the action potential to pass directly between two neurons
    1. synapses can either be electrical or chemical
      1. in vertebrates most synapses are chemical
        the arrival of the action potential at the terminal causes it to release neurotransmitter
        neurotransmitters are chemicals which diffuse to the receptors on the target cell
    2. l
Glia
1. modulate neuron activity and provide support
2. outnumber neurons in the human brain
  1. about 10 times more
  2. represent 90% of the cells in the brain and spinal cord
3. have numerous functions
  1. Ependymal cells
    1. promote the circulation of cerebrospinal fluid
    2. modified ependymal cells found in the choroid plexus are responsible for the production of cerebrospinal fluid
      1. there are four choroid plexuses, one in each ventricle of the brain
  2. Microglia
    1. protect the nervous sytem from micro organisms
  3. oligodendrocytes
    1. form the myelin sheaths around axons
  4. Schwann Cells
  5. Astrocytes
    1. provide structural support for neurons
    2. regulate extracellular ions and neurotransmitters
    3. induce the formation of the blood-brain barrier
      1. this regulates the chemical environment of the CNS
    4. store glycogen which can be broken down to supply neurons with fuel
    5. aid repair and regeneration of neurons
    6. make contact with blood vessels and neurons
      1. signal changes in the composition of the blood
    7. their role in plasticity/memory has been discussed recently
    8. it's projections can make contact with more than 100,000 synapses
tripartite synapse
1. the idea that a synapse has pre and porsynaptic neurons as well as connections from astrocytes

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Cells of the Nervous System

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Medienanhänge

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