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Autonomic Nervous System (CONTROL CENTRES (Hypothalamus - water balance,…

- - - - originates in the brain stem and leaves the brain in cranial nerves
      - vagus nerve: major tract
        
        contains 75% of all parasympathetic fibres
        
        carries parasympathetic output from brain to organs
      - long postganglionic fibers
      - few branches --> localised effect
      - neurons secrete acetlycholine
    - - originates in the thoracic and lumbar regions of the spinal cord
      - short postganglionic fibers
      - axons highly branched --> influences many organs
      - PATHWAY
        
        preganglionic neurons in the thoracolumbar spinal cord send their motor axons through the adjacent ventral root into the spinal nerve... from there, the preganglionic axons follow one of 3 pathways:
        
        synapses with a postganglionic neuron in the sympathetic trunk ganglion at the same level
        
        exits via gray ramus communicant into the spinal nerve at that level
        
        ascends or descends in the sympathetic trunk
        
        synapses in another trunk ganglion
        
        exits the sympathetic trunk via the gray ramus communicant at the level of the synapse
        
        passes through the sympathetic trunk
        
        exits on a splanchnic nerve
        
        synapses in a collateral ganglion
        
        extends to the visceral organ via an autonomic nerve plexus
      - neurons secrete norepinephrine