Perikaryon

The perikaryon, also called the soma or cell body, is the central portion of a neuron that contains the nucleus and the cytoplasm. It is the metabolic and synthetic hub of the cell, where most transcription and protein synthesis occur and from which the axon and dendrites extend. The perikaryon is bounded by the plasma membrane and, in many neurons, lies adjacent to the dendritic tree and the axon hillock.

Structurally, the perikaryon houses a prominent nucleus with a nucleolus and a rich array of organelles. The cytoplasm contains rough endoplasmic reticulum and free ribosomes that form the Nissl substance, the Golgi apparatus, mitochondria, lysosomes, and cytoskeletal elements such as neurofilaments, microtubules, and microfilaments. Lipofuscin granules may accumulate with age. The perikaryon’s organelles support high levels of protein synthesis, membrane turnover, and energy production required for neuronal signaling and maintenance.

In the central nervous system, perikarya reside in gray matter or in specialized nuclei; in the peripheral nervous system, they are found in ganglia. The perikaryon integrates synaptic inputs received by dendrites, maintains ion homeostasis, and supplies proteins and membranes to the axon and synaptic terminals. Pathologically, changes in the perikaryon, such as chromatolysis after axonal injury, reflect neuronal stress or damage.