In cellular neuroscience, the soma (pl.: somata or somas; from Greek σῶμα (sôma) 'body'), or cell body, is the bulbous, non-process portion of a neuron or glial cell that contains the cell nucleus. The part of the soma without the nucleus is called the perikaryon (pl.: perikarya).
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👉 Cell body in the context of Motor neuron
A motor neuron (or motoneuron), also known as efferent neuron is a neuron that allows for both voluntary and involuntary movements of the body through muscles and glands. Its cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly muscles and glands. There are two types of motor neuron – upper motor neurons and lower motor neurons. Axons from upper motor neurons synapse onto interneurons in the spinal cord and occasionally directly onto lower motor neurons. The axons from the lower motor neurons are efferent nerve fibers that carry signals from the spinal cord to the effectors. Types of lower motor neurons are alpha motor neurons, beta motor neurons, and gamma motor neurons.
A single motor neuron may innervate many muscle fibres and a muscle fibre can undergo many action potentials in the time taken for a single muscle twitch. Innervation takes place at a neuromuscular junction and twitches can become superimposed as a result of summation or a tetanic contraction. Individual twitches can become indistinguishable, and tension rises smoothly eventually reaching a plateau.
In this Dossier
Cell body in the context of Neurofibrillary tangles
Neurofibrillary tangles (NFTs) are intracellular aggregates of hyperphosphorylated tau protein that are most commonly known as a primary biomarker of Alzheimer's disease. NFTs also are present in numerous other diseases known collectively as tauopathies. Little is known about their exact relationship to the different pathologies, but it is typically recognized that tauopathy is an important factor in the pathogenesis of several neurodegenerative diseases.
NFTs consist primarily of a misfolded, hyperphosphorylated microtubule-associated protein known as tau, which abnormally polymerizes into insoluble filaments within cells. Under the electron microscope, these polymers of tau are seen to take two basic forms: paired helical filaments (PHFs) and straight filaments. These basic types of tau filaments can vary structurally, especially in different tauopathies. The filaments bundle together to form the neurofibrillary tangles that are evident under the light microscope. Classical NFTs are located within the neuronal cell body, although it is now recognized that abnormal, filamentous tau occurs also in neuronal dendrites and axons (referred to as neuropil threads) and the dystrophic (abnormal) neurites that surround neuritic Abeta plaques. Mature NFTs in cell bodies can have a torch-like or globose appearance, depending on the type of neuron involved. When tangle-containing neurons die, the tangles can remain in the neuropil as extracellular "ghost tangles".
Cell body in the context of Autonomic ganglion
An autonomic ganglion is a cluster of nerve cell bodies (a ganglion) in the autonomic nervous system. The two types are the sympathetic ganglion and the parasympathetic ganglion.
Cell body in the context of Axon terminal
Axon terminals (also called terminal boutons, synaptic boutons, end-feet, or presynaptic terminals) are distal terminations of the branches of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell that conducts electrical impulses called action potentials away from the neuron's cell body to transmit those impulses to other neurons, muscle cells, or glands. Most presynaptic terminals in the central nervous system are formed along the axons (en passant boutons), not at their ends (terminal boutons).
Functionally, the axon terminal converts an electrical signal into a chemical signal. When an action potential arrives at an axon terminal (A), the neurotransmitter is released and diffuses across the synaptic cleft. If the postsynaptic cell (B) is also a neuron, neurotransmitter receptors generate a small electrical current that changes the postsynaptic potential. If the postsynaptic cell (B) is a muscle cell (neuromuscular junction), it contracts.
Cell body in the context of Alpha motor neuron
Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.
While their cell bodies are found in the central nervous system (CNS), α motor neurons are also considered part of the somatic nervous system—a branch of the peripheral nervous system (PNS)—because their axons extend into the periphery to innervate skeletal muscles.