The Nervous System

The Nervous System

1. divided into two parts

   • the Peripheral Nervous System (PNS)
     • in vertebrates this is composed of the nerves and ganglia
     • transmits signals to and from the CNS as well as regulating movement and the internal environment
       • afferent neurons transmit signals to the CNS
       • efferent neurons transmit signals away from the CNS
       • cranial nerves originate in the brain and generally terminate in the organs in the head or upper body
       • spinal nerve originate from the spine and extend to parts of the body below the head
     • two functional components of the PNS
       • Motor system
         • is voluntary and controls the movement of skeletal muscles
       • autonomic nervous system
         • is involuntary and regulates the internal environment as well in voluntary muscle contractions such as peristalsis
   • the Central Nervous System (CNS)
     • in vertebrates this is composed of the brain and spinal cord
       • the spinal cord sends signals from the brain to the PNS
         • it also mediates reflex reactions such as the knee jerk reflex
           • reflexes occur independently of the brain
       • the brain and spinal cord are made up of:
         • white matter: consists of myelinated axon bundles
         • grey matter: consists of cells bodies and dendrites
         • the ventricles of the brain and the central canal of the spinal cord are hollow and they both contain cerebrospinal fluid
           • this is filtered from the blood and acts as a cushion for the brain and spinal cord

2. most multicellular organisms have a nervous system

   • except for
     • sponges
     • placozoans
     • mesozoans
   • this can be a diffuse nerve net in the case of radially symmetrical organisms such as:
     • Cnidarians
     • ctenophores
   • most nervous systems consists of:
     • a brain
     • a central nerve cord or two cords running in parallel
     • nerves radiating from the brain and central cord

3. Autonomic Nervous system: split into three divisions

   • sympathetic division
     • fight or flight
     • fight or flight
   • parasympathetic division
     • have antagonistic effects on target organs
       • gas exchange
       • circulation
       • hormone action
     • rest and digest
     • rest and digest
   • enteric division
     • digestive tract
     • pancreas
     • gall bladder
     • pancreas
     • gallbladder

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