General structure

Central portion is located in:

• Hypothalamus
• Brain stem (medulla oblongata, and ?others)
• Spinal cord

 

Preganglionic neurons have
   -> cell bodies in brain stem or spinal cord

   -> axons are thinly myelinated

Postganglionic neurons have

   -> cell bodies in the autonomic ganglia

   -> axons are unmyelinated

 

Sympathetic ganglia are located close to CNS

   -> short preganglionic fibres, long postganglionic fibres

Parasympathetic ganglia are located close to the effector tissues

   -> long preganglionic fibres, short postganglionic fibres

 

Anatomy

Sympathetic motor neurons

• Located in the intermediolateral horn of the spinal cord from T1 to L2
• Send axons via the ventral root, then white ramus, then either:
  (1) synapse in sympathetic chain at the same or different level,
            OR
  (2) go through sympathetic chain, and exit via splanchnic nerve and synapse in a prevertebral ganglion,
            OR
  (3) go through sympathetic chain and splanchnic nerve, and end directly on modified neuronal cells in adrenal medulla

 

Parasympathetic motor neurons

• Located in discrete brain stem nuclei or in S2-S4
• Axons leave brain stem via cranial nerves III, VII, IX, and X
            OR
  leave sacral spinal cord via pelvic nerves

  

Parasympathetic fibres in CN III innervate

• pupillary sphincters and ciliary muscles of the eye

 

Parasympathetic fibres in CN VII innervate

• lacrimal, nasal, and submandibular glands

 

Parasympathetic fibres in CN IX innervate

• parotid gland

 

Parasympathetic fibres in CN X (vagus nerve) innervate

• heart
• lungs
• oesophagus
• stomach
• small intestines
• colon proximal to splenic flexure
• liver and gallbladder
• pancreas
• upper portion of ureter

 

Sacral parasympathic fibres innervate

• descending colon
• rectum
• bladder
• lower portion of ureter
• external genitalia