Ganglia: Types and Structure

  • Outside the brain and spinal cord there are aggregations of cell bodies of neurons called ganglia.
  • There are two main types of ganglia. They are sensory and autonomic ganglia.

A) Sensory ganglia

  • These ganglia are present on the dorsal nerve roots of spinal nerves, where they are called dorsal nerve root ganglia or spinal ganglia.
  • They are also present on the 5th, 7th, 8th, 9th and 10th cranial nerves.
  • The neurons in these ganglia are of the unipolar type (except in the case of ganglia associated with the vestibule-cochlear nerve in which they are bipolar).
  • An afferent or sensory fibre of a peripheral nerve is formed by the peripheral process of each neuron.
  • The center process enters the spinal cord or brain stem.


What are ganglia in the nervous system? | Socratic

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Structure of Sensory Ganglia

  • The neurons of sensory ganglia are seen to be large and arranged in groups chiefly at the periphery of the ganglion in haematoxylin and eosin stained sections.
  • Group of myelinated nerve fibres separate the group of cells.
  • A layer of flattened capsular cells or satellite cells surround the cell body of each neuron.
  • There is a layer of delicate connective tissue outside the satellite cells.
  • The processes arising from the neuron are covered with the satellite cells that are continuous with the Schwann cells.
  • The connective tissue covering each neuron is continuous with the endoneurium.
  • The entire ganglion is pervaded by fine connective tissue.
  • The ganglion is covered on the outside by a connective tissue capsule.


13.2 Ganglia and Nerves – Anatomy & Physiology

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B)Autonomic Ganglia

  • These are concerned with the nerve supply of smooth muscle or of glands.
  • The pathway for this supply always consists of two neurons: preganglionic and postganglionic.
  • The cell bodies of preganglionic neurons are located within the spinal cord or brain stem always.
  • Their axons leave the spinal cord or brain stem and terminate by synapsing with postganglionic neurons, the cell bodies of which are located in the autonomic ganglia.
  • Autonomic ganglia are therefore aggregations of the cell bodies of postganglionic neurons. These neurons are multipolar.
  • Their axons leave the ganglia s postganglionic fibres to reach and supply smooth muscle or gland.
  • Autonomic ganglia are subdivided into two major types: sympathetic and parasympathetic.
  • Sympathetic ganglia are located on the right and left sympathetic trunks.
  • Parasympathetic ganglia usually lie close to the viscera supplied through them.



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Structure of Autonomic Ganglia

  • The neurons of autonomic ganglia are smaller in comparison to the sensory ganglia.
  • They are seen to be multipolar with silver impregnation.
  • The neurons are not arranged in definite groups as in sensory ganglia, but are scattered throughout the ganglion.
  • The nerve fibres are non-myelinated and thinner and are therefore much less conspicuous than in sensory ganglia.
  • Satellite cells are present around the neurons of autonomic ganglia but they are not so well defined.
  • The ganglion is permeated by connective tissue that also provides a capsule for it.
  • The Nissl substance of the neurons is much better defined in autonomic ganglia than in sensory ganglia.
  • In sympathetic ganglia the neuronal cytoplasm synthesizes catechol-amines; and in parasympathetic ganglia it synthesizes acetylcholine.
  • These neurotransmitters travel down the axons to be released at nerve terminals.




Ganglia: Types and Structure