The Nervous System, Organisation of the Nervous System, Basic Functions of Synapses and Transmitter Substances

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  1. The general design of the Nervous system:
    1. The Nervous system includes both sensory and motor systems interconnected by complex integrative mechanisms
      1. neuron
        1. Soma
        2. several dendrites
        3. single axon
      2. sensory receptors
        1. sensory neuron
        2. motor response
      3. Motor response
        1. memory
  2. Function of the Central Nervous System
    1. This is based upon interactions that occur between neurons at specialised junctions called synapses
      1. synaptic terminals or synaptic boutons
      2. synaptic cleft
      3. synaptic vesicles
      4. neurotransmitter agent
    2. Chemical synapses and electrical synapses are the two most prevalent types of synapses in the brain
      1. chemical synapses
        1. presynaptic element - releases neurotransmitter agent that bind to the
        2. postsynaptic neuron - which is excited or inhibited
      2. electrical synapse
        1. gap junctions
    3. Neurotransmitter Release is Calcium Dependent
      1. voltage gated calcium channels
      2. calcium moves into the terminal
    4. Action of a Neurotransmitter is Determined by its Postsynaptic Receptor
      1. Receptors are 
        1. a binding domain that extends the synaptic cleft
        2. an ionophore that extends through the membrane into the interior of the postsynaptic structure
        3. ligand-gated ion channels
          1. Ligand gated ion channels can be cationic or anionic
          2. sodium channels are excitatory
          3. chloride channels are inhibitory
          4. Second messenger activators are activators are commonly G-proteins
    5. Chemical Substances Function as Neurotransmitters
      1. small molecule neurotransmitters and neuroactive peptides
      2. Small-molecule, rapidly acting transmitters can be synthesized and packaged into synaptic vesicles in the axon terminal
        1. recycled
        2. Acetylcholine
          1. Acetyl coenzym A and choline in the presence of choline acetyl transferase
          2. acetylcholineesterase, in the synaptic cleft
      3. Neuropeptides from second group of transmitter agents, and these substances are typically synthasized in the soma as an integral component of large proteins
        1. colocalized 
    6. Certain Electrical Events are Characteristic of Excitatory Synaptic Interactions
      1. Resting membrane potential
      2. potassium 
      3. ligand gated sodium channels
      4. excitatory postsynaptic potential (EPSP)
      5. threshold
      6. many - summation 
    7. Certain Electrical Events are characteristic of Inhibitory Synaptic Interactions
      1. ligand-gated chloride channels - inhibitory postsynaptic potential (IPSP)
      2. "short-circuiting" or shunting
    8. EPSP and IPSPs are Summated Over Time and Space
      1. Temporal Summation
      2.  Spacial Summation
      3. all the EPSPs and the IPSPs
    9. Dendrites Perform Special Functions in the Excitation and Inhibition of Neurons
      1. not able to propogate
      2. electrotonic conduction
    10. Firing Rate of a Neuron: Related to Its State of Excitation
    11. Synaptic Transmission Exhibits Special Characteristics
      1. fatigued
      2. post-tetanic facilitation
      3. pH - more acidic increase excitability, more alkaline levels decrease synaptic excitability
      4. decrease in supply of Oxygen diminishes synaptic activity
      5. Caffeine increases excitability; 
      6. synaptic delay

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