Glial Cells of the PNS

appropriate motor response. This happens in the central nervous system because it

requires memory and higher cognitive functioning to generate the correct responses.

The nervous system has three major parts. The first is the somatic nervous system or SNS. This

is responsible for the reception of conscious stimuli, perception, and voluntary motor

responses. While these are voluntary, it doesn’t mean that they have to be entirely conscious.

A startle response involves the somatic nervous system but rarely does one actually think

before startling, which involves movement of skeletal muscles. Other things that are part of the

SNS that aren’t truly conscious are things that are done automatically. These happen because

of “procedural memory” or the learning of habits.

The second part is the autonomic nervous system or ANS. The autonomic nervous system is

involuntary in nature and responsible for achieving and maintaining homeostasis. Homeostasis

involves the regulation of the internal environment so that it achieves and maintains a steady

state. Sensory input can be external or internal but the output is to cardiac and smooth muscles

rather than skeletal muscles. Things like the heart, sweat glands, and certain smooth muscle

functions of the GI tract are under autonomic control.

The third part of the nervous system is the enteric nervous system or ENS. This controls the

function of the glandular tissue in the digestive system and most of the smooth muscle function

of the digestive tract. This is largely independent and does not rely on the central nervous

system. There is some overlap between the functions of the autonomic nervous system and

the enteric nervous system.

GLIAL CELLS OF THE PNS

There are two types of glial cells found in the PNS. The first is the “satellite cell.” This type of

cell is found in the autonomic and sensory ganglia, where they surround the cell bodies of

neurons. They are largely supportive cells and are similar to the astrocytes in the central

nervous system. In fact, the only difference is that these satellite cells do not establish the

blood-brain barrier as is seen in the CNS.