cells of the SC

Cells of the Spinal Cord

The spinal cord is composed of many neurons, axons, and supporting cells (21). In addition, it must have many trophic factors in order to grow and function properly (21, 27).

1. Neurons- nerve cells that provide the communication pathway through the body (31). There are as many as 10,000 subtypes of neurons which are specialized to receive and send information (2), detect changes in the environment, and organize immediate and long-term responses to change. Each neuron is made up of a cell body, axons, and dendrites (2, 31) The nucleus is located in the cell body which, along with the dendrites and neuroglial cells makes up the butterfly shaped "gray matter" in the center of the spinal cord (21).

Picture adapted from Starr and Taggart

a. Dendrites- the input centers of the neuron. They are tree-like extensions from the cell body, that receive signals from other cells at the synaptic junction (26, 25, 27)

b. Axons- the output centers of the neuron that extend from the cell body. They connect with either the dendrite of another neuron, a muscle, or a gland, where they release neurotransmitters of the activities of other cells to propagate the nerve impulse (26, 25). Most axons are covered by a myelin sheath, which insulates the axon and gives them their white color. Thus, the outer region of the spinal cord where the axons are located is called "white matter" (26)

2. Glial cells- supporting cells of the nervous system that serve many functions:

a. physical support

b. response to injury

c. the maintenance of chemical balance of surrounding cells

d. aid in the blood-brain and blood-spinal-cord barriers (21).

e. The formation of the myelin sheath of neural pathways

f. The regulation of neurons during development. They may also produce substances that inhibit the regeneration of neurons after injury to the spinal cord. The most common types of glial cells in the central nervous system are astrocytes, oligodendrocytes, and microglia. (21)

3. Astrocytes- the largest, most abundant (21), and principle glial cells of the central nervous system (27). Astrocytes aid neurons by providing extra energy and by producing neurotrophic factors necessary for neuron sustenance (2). They contribute to the blood-brain barrier (21) and maintain the chemical environment by destroying harmful proteins and chemicals that could damage the neurons (2). After a spinal cord injury, astrocytes multiply and contribute to the formation of the glial scar (2, 27)

4. Oligodendrocytes- a type of glial cell located in the brain and spinal cord that produces myelin that surrounds the axons making impulse conduction faster and more reliable (2, 21, 27). Oligodendrocytes also manufacture substances that prevent axon regeneration in the adult central nervous system (21).


Picture provided by The National Institutes of Health
A. Oligodendrocyte; B. Axons; C. Node of Ranvier; D. Myelin; E. Myelin Sheaths

5. Microglia- immune cells located in the brain that become functional only after injury. When activated by injury microglial cells aid in ridding the injury of dying cells, dead cells, and other wastes that accumulate at the injury site. Microglia also manufacture cytokins, molecules that activate other immune cells to aid at the injury site (2).