Spinal Cord and Neuronal Cell Body with Motor, Sensory, and Autonomic Components of the Peripheral Nerve

Each neuronal cell body contains many dendrites, which are peripheral extensions from the cell body that, along with the smaller dendritic spines (gemmules), receive the input from other neurons. Each dendrite receives excitatory or inhibitory potentials from the nerve terminals of neighboring neurons at the axodendritic synapses. The dendrites and the cell body of a single neuron may have hundreds of synapses from many different neurons. Each of the postsynaptic excitatory or inhibitory potentials are summated to determine whether an action potential will or will not be initiated within the neuron. When initiated, an action potential originates at the axon hillock, the region of the cell body at which the axon originates. Distal to the axon hillock is the axon, which is the structure that conducts the electrical activity and trophic factors away from the cell body toward other neurons or organs. The course of the axons and route of conduction of the electrical signals varies according to the type of neuron and its function.

The somas of the somatic sensory neurons are located in the dorsal root ganglion, just lateral to the spinal cord and typically within the intervertebral foramen. The somatic sensory neurons are bipolar neurons with two axonal extensions, one conducting impulses from the sensory receptors, including free nerve endings and pacinian corpuscles, toward the dorsal root ganglion through the peripheral nerves and dorsal rami, and the other extending from the dorsal root ganglion through the dorsal root into the dorsal column of the spinal cord.

The cell bodies (anterior horn cells) of the somatic motor neurons are located in the anterior gray matter of the spinal cord. The motor neurons are unipolar neurons, and each neuron has an axon that extends through the ventral root and then through either the dorsal ramus (innervating paraspinal skeletal muscles) or the ventral ramus (innervating limb and peripheral skeletal muscles) and into individual nerves.

The cell bodies of the sympathetic autonomic peripheral neurons are located in spinal cord. The preganglionic sympathetic neurons extend through the ventral root and through the white ramus communicans, and they synapse in peripherally located ganglia—either the sympathetic chain adjacent to the spinal cord or the collateral sympathetic ganglia near the organs that the neurons supply. After synapsing at either site, the postganglionic sympathetic neurons course to the end organs, including vascular smooth muscle, sweat glands, and arrector pili muscles in the skin or the smooth muscles and glands of other organs.

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