The second glial cell is referred to as a Schwann cell. This cell makes the myelin sheath around axons in a similar way as oligodendrocytes but with one key difference. Schwann cells wrap around and make myelin for just one axon segment, while the oligodendrocyte reaches out to multiple axon segments at once.
GANGLIA A ganglion is a group of nerve cells, similar to a nucleus, but in the periphery. There can be sensory or autonomic ganglia. The most common type of sensory ganglion is called a dorsal root ganglion. These contain the cell bodies that have axons that become the sensory endings in the periphery, such as the skin. They also have projections that extend upward to the CNS via the dorsal nerve root. The dorsal root ganglion also contains nerve bundle fibers belonging to the dorsal nerve root. Another common sensory ganglion is one of the cranial nerve ganglia. These are like the dorsal root ganglion but are associated with a cranial nerve rather than a spinal nerve. The ganglia reside outside of the skull and send branches out to the cranial nerves. Still another type of ganglion are those associated with the autonomic nervous system. There are sympathetic chain ganglia—a row of identical ganglia that receive input from the lateral horn of the thoracic and upper lumbar spinal cord. Above this chain are the paravertebral ganglia in the cervical region. There are three other autonomic/sympathetic ganglia called the prevertebral ganglia—located anterior to the vertebral column. These are multipolar neurons that make synapses with the spinal cord neurons. Each of these three types of ganglia (chain, paravertebral, and prevertebral) send out axons to the head, neck, thoracic, abdominal, and pelvic cavities to regulate organ homeostasis located in these cavities. Another type of autonomic ganglia is the terminal ganglia. These receive input from the cranial nerves or the sacral spinal nerves, being responsible for the regulation of the parasympathetic nervous system in the head, neck, chest, abdominal, and pelvic cavities. The terminal ganglia oppose the sympathetic ganglia. There are two sets of terminal ganglia—those located in the
157
