Ganglia are aggregations of nerve cells

Ganglia

Ganglia are aggregations of nerve cells (ganglion cells) outside the CNS. Cranial nerve and dorsal root ganglia are surrounded by a connective tissue capsule, which is continuous with the dorsal root epi- and perineurium. Individual ganglion cells are surrounded by a layer of flattened satellite cells. Neurones in cranial nerve and dorsal root ganglia are pseudounipolar. They have a T-shaped process. The arms of the T represent branches of the neurite connecting the ganglion cell with the CNS (central branch) and the periphery (peripheral branch). Both branches function as one actively conducting axon, which transmits information from the periphery to the CNS. The stem is connected to the perikaryon of the ganglion cell and is the only process originating from it. Ganglion cells in dorsal root ganglia do not receive synapses. Their function is the trophic support of their neurites.

Early in development two processes emerge from the perikaryon of dorsal root ganglion cells, which merge in the course of development. These ganglion cells are therefore also called pseudounipolar neurones. Two processes emerge from the perikaryon of bipolar neurones. The majority of CNS neurones are multipolar, i.e. more than two processes (but only one axon) emerge from their perikaryon.

Autonomic ganglia docontain synapses, and the ganglion cells within them dohave dendrites. They receive synapses from the first neurone of the two-neurone chain, which characterises most of the efferent connections of the autonomic nervous system. The second neurone is the ganglion cell itself. Some autonomic ganglia are embedded within the walls of the organs which they innervate (intramural ganglia - e.g. GIT and bladder).

Suitable Slides

sections of dorsal root ganglia and autonomic ganglia - H&E, toluidine blue, Giemsa, luxol fast blue/cresyl/violet (LFB/CV)

Dorsal Root Ganglion, cat - H&E and Autonomic Ganglion - H&E
Ganglion cells will typically be several times larger than other cells in the ganglia. The perikaryon is very large and surrounds a large and light nucleus. Only the cells immediately surrounding the ganglion cells as one flattened layer are satellite cells. With a lot of luck you may see the process of a ganglion cell as it passes out of the capsule of satellite cells. Ganglion cells are of course in contact with other parts of the nervous system and with the peripheral tissues which they innervate. Consequently, nerve fibers will be visible close to or within the ganglion. Lipofuscin, a brownish pigment, accumulates with age not only in ganglion cells, but also in several other cell types of the body, e.g., cardiac muscle cells or endocrine cells.
Sketch the appearance of the spinal ganglion section at low magnification. Draw a small section of the spinal ganglion and peripheral ganglion at high magnification. Label ganglion cells, satellite cells and, if visible, nerve fibres and connective tissue elements.