Ganglion

File:Ganglion high mag.jpg

High magnification image of a ganglion showing connective tissue structures

File:DRG Chicken e7.jpg

Developing dorsal root ganglion in a chicken embryo (day 7)

Ganglion (plural: ganglia) is a structure containing a collection of neuron cell bodies located in the peripheral nervous system (PNS). Ganglia serve as relay points and processing stations for neural signals and are distinct from nuclei, which are clusters of neuron cell bodies located within the central nervous system (CNS).

Overview

In the peripheral nervous system, ganglia are classified based on their anatomical and functional context:

• In the somatic nervous system, notable ganglia include:
  • Dorsal root ganglia (also known as spinal ganglia), which contain the cell bodies of sensory (afferent) neurons
  • Trigeminal ganglion, which contains the cell bodies of sensory neurons associated with the trigeminal nerve (cranial nerve V)

• In the autonomic nervous system (ANS), ganglia are divided into:
  • Sympathetic ganglia, containing the cell bodies of postganglionic sympathetic fibers
  • Parasympathetic ganglia, containing the cell bodies of postganglionic parasympathetic fibers

These ganglia are responsible for transmitting autonomic signals from the CNS to various organs, muscles, and glands.

Structure

Ganglia are composed primarily of:

• Neuron somata (cell bodies)
• Dendritic structures
• Supporting glial cells
• Connective tissue encapsulation

These components are often bundled together, and ganglia may interconnect with each other to form complex networks known as plexuses. These structures act as important relay centers between the CNS and peripheral target tissues.

Types of Ganglia in Vertebrates

Among vertebrates, ganglia are broadly categorized into three major types:

• Dorsal root ganglia: Located along the spinal cord, these contain the cell bodies of sensory (afferent) neurons that transmit information from the periphery to the CNS.
• Cranial nerve ganglia: Associated with cranial nerves, such as the trigeminal ganglion, geniculate ganglion, and others, these contain sensory neuron cell bodies.
• Autonomic ganglia: Part of the autonomic nervous system and involved in involuntary bodily functions. These include:
  • Sympathetic chain ganglia (paravertebral ganglia)
  • Prevertebral ganglia (e.g., celiac, superior mesenteric)
  • Terminal ganglia (near or within target organs, mainly in the parasympathetic division)

Neural Pathways

In the autonomic nervous system, signal transmission follows a two-neuron chain:

• Preganglionic fiber: Originates in the CNS and projects to a ganglion
• Postganglionic fiber: Originates in the ganglion and projects to the effector organ (e.g., smooth muscle, cardiac muscle, glands)

Pseudoganglion

A pseudoganglion resembles a true ganglion in appearance but lacks neuron cell bodies. It consists only of nerve fibers and supportive connective tissue, and thus does not perform the same integrative functions as true ganglia.

Related Concepts

• Neuron
• Peripheral nervous system
• Central nervous system
• Autonomic nervous system
• Sensory neuron
• Motor neuron
• Nerve plexus
• Glial cell

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