Veterinary Histology and Embryology

GANGLIA

• Ganglia consist of aggregations of neurons situated outside the central nervous system. Each ganglion is surrounded by a connective tissue capsule which is continuous with the epineurium and perineurium of the peripheral nerve.
• Connective trabeculae extend from the capsule into the ganglion to form a framework. Within the ganglion the nerve cells are separated into irregular groups by strands of connective tissue and by bundles of nerve fibres.
• Each ganglion cell is enveloped by a double layer. The outer part of capsule is composed of flat fibroblasts and connective tissue fibre which are continuous with the endoneurium of the associated nerve fibre.
• The inner part consists of a layer fusiform of satellite cells or amphicytes, which derived from the same source as the ganglion cells themselves.
• Cranial and spinal ganglia
• They are made up of pseudo-unipolar or ‘T’ bipolar neurons with prominent nucleolus. Chromophil substance may either be scattered throughout the cytoplasm as diffuse granules or it may form rather small finely granular.
• Nissl bodies which are concentrically arranged around the nucleus. Most of these cells have one Principal myelinated process which at some distance from the cell body, divides into a peripheral nerve and a central branch which enters the CNS as a sensory root fibre.
• Autonomic ganglia
• The majority of the sympathetic and parasympathetic ganglia have a connective tissue framework and multipolar neurons with numerous nerve fibre. The cell bodies vary in size from 20 to 45 microns.
• The nucleolus is relatively large and vesicular round or oval and has one or more well defined nucleoli. The nucleus is often eccentrically situated. Binucleated neurons are not uncommon and multi nucliated neurons have also been seen.
• Chromophil substance or Nissl bodies may be distributed uniformly throughout the cytoplasm or may be confined to the perinuclear zone or to peripheral cytoplasm.
• In large ganglia, stellate cells are present. The dendrites either terminate within the capsule or pass through capsule to form intercellular plexus of fibres depending on their length.
• Often two ganglion cells share a single capsule in smaller terminal ganglia such as those in the intestinal wall, many of the ganglion cells lack capsule parasympathetic ganglion cells are found in almost all visceral structures.