Autonomic Nervous System

• What is the nervous system split into?

  CNS: brain and spinal chord

  PNS:

                - Somatic: voluntary actions

                - Autonomic: ‘automatic’ actions

    o  Sympathetic

  o  Parasympathetic
• Examples of automatic activities:

  -          Regulation of activity of smooth muscle in blood vessels and viscera

  -          Activity of glands

  -          Regulation of heartbeat

  -          Digestive tract activity

  -          Inputs that are feedback (e.g. bp)

  Voluntary (somatic) actions:

  -          Movement of skeletal muscle

  -          Sensory inputs (e.g. touch, temperature, pain)
• The autonomic nervous system:


  • Composed of sympathetic and parasympathetic
  • Regulates operation of internal organs
  • Organs receive innervation from both divisions
• Gross organisation of autonomic nervous system?


  To get from CNS to organs there is a 2 neurone chain

  This has a preganglionic neurone arising from the CNS

  A synapse within an autonomic ganglion between the preganglionic and post ganglionic neurones

  A postganglionic neurone that then innervates the target organ

  Sympathetic nerves have a short preganglionic neurone and a long postganglionic neurone. Opposite in parasympathetic.

  Neurones innervating adrenal medulla are anomaly. Adrenal medulla acts like a postganglionic neurone. Releases neurotransmitter directly into the blood.

  
• Autonomic ganglia?


  -Ganglia are swellings on peripheral nerves that contain neuronal cell bodies.

  -Contain synapse between pre and post ganglionic neurone

  -Preganglionic nerves are myelinated and are called ‘white rami’

  -Postganglionic nerves are unmyelinated and are called ‘grey rami’
• Sympathetic and Parasympathetic nervous system organisation?

  Sympathetic:

  • Has a thoracic-lumbar origin in CNS
  • Generally higher nerves innervate higher organs

  Parasympathetic:

  • Has a cranio-sacral origin in CNS
  • Outputs are arranged viscerotopically (top neurones affect top organs etc..)
  • The thoracic and abdominal viscera are innervated by the vagus nerve

  A) sympathetic

  B) parasympathetic

  C) parasympathetic

  
• sympathetic pre and post ganglionic neurones?

  Preganglionic:

  • Found in the thoracic and upper lumbar levels of spinal chord
  • Preganglionic neurones are found in the lateral horn
  • Preganglionic neurones project out from spinal cord via ventral root and connect to the sympathetic ganglia via the white ramus

  Postganglionic:

  • Project from sympathetic ganglia to their targets
  • Targets any be smooth muscle, cardiac muscle or glands
  • These projections have extensive branching to allow multiple points of contact with their target

  A) lateral horn

  
• Sympathetic and parasympathetic ganglia?

  Sympathetic:

  -          Located close to the spinal cord

  -          Found in 2 main sites:

  o   The paravertebral chain (sympathetic chain): runs alongside vertebral column

  o   The prevertebral ganglia (abdominal/collateral ganglia): found in front of the abdominal aorta

  Parasympathetic:

  • Located close to or embedded in target organ (e.g. embedded in heart or lung

  A) paravertebral

  B) prevertebral

  
• The adrenal gland?


  It is considered a modified sympathetic ganglion. It is directly innervated by sympathetic preganglionic neurones. Cells in the adrenal medulla are neurone-like and release adrenaline and noradrenaline into the bloodstream
• parasympathetic pre and postganglionic neurones?


  Pre:

  • Found in specific cranial nerve nuclei and in lateral horns of the sacral spinal cord
  • Project outward towards their targets through the cranial nerves or through dedicated parasympathetic nerves coming from the sacral spinal cord
  • Preganglionic neurones display a lot of branching to reach their targets. Especially those in the vagus nerve.

  Post:

  • Project from parasympathetic ganglia to their targets
  • Targets may be moth muscle, cardiac muscle or glands
  • These projections have very short axons and minimal branching
• what are some major neurotransmitters?

  -        Neurones with cell bodies in the spinal cord release Ach

  -        Post ganglionic parasympathetic neurones also release Ach

  -        Sympathetic post ganglionic neurones are more diverse

  -        Sometimes other transmitters such as NO, ATP can be co-released with the main transmitter

  A) Ach

  B) NE

  C) Ach

  D) Epi

  E) Ach

  F) sweat glands

  
• What is the role of the autonomic nervous system in homeostasis?


  The sympathetic and parasympathetic divisions have opposing actions on most organs. Altering the balance of civility between the two allows fine control of organ function (as opposed to on/off)
• What is the role of the enteric nervous system?


  Embedded in the gut, it regulates the activity of the intestines (peristalsis), local blood flow and glands. It’s called the second brain as it has more neurones than the CNS. Could be important for neurological disorders e.g. first symptoms of Parkinson’s might be bowel disorder.