Glial cells are also important components of nervous systems

Neurons are not the only type of cell in the nervous system. In fact, there are more glial cells than neurons in the human brain. Like neurons, glial cells come in several forms and have a diversity of functions. Some glial cells physically support and orient the neurons and help them make the right contacts during embryonic development. Other glial cells insulate axons.

In the peripheral nervous system, Schwann cells wrap around the axons of neurons, covering them with concentric layers of insulating plasma membrane (Figure 44.3). Other glial cells called oligodendrocytes perform a similar function in the central nervous system. Myelin is the covering produced by Schwann cells and oligodendrocytes, and it gives many parts of the nervous system a glistening white appearance. Later in this chapter we will see how the electrical

(a) Myelin-producing Schwann cell

Site and direction of myelin growth

(a) Myelin-producing Schwann cell

Site and direction of myelin growth

Schwann Cell
44.3 Wrapping Up an Axon (a) Schwann cells wrap axons in the peripheral nervous system with layers of myelin, a type of plasma membrane that provides electrical insulation. (b) A myelinated axon, seen in cross section through an electron microscope.

insulation provided by myelin increases the speed with which axons can conduct nerve impulses.

Glial cells are well known for the many supportive roles they play. Some supply neurons with nutrients; others consume foreign particles and cell debris. Glial cells also help maintain the proper ionic environment around neurons. Although they have no axons and do not generate or conduct nerve impulses, some glial cells communicate with one another electrically through gap junctions, a special type of connection that enables ions to flow between cells.

Glial cells called astrocytes (because they look like stars) contribute to the blood-brain barrier, which protects the brain from toxic chemicals in the blood. Blood vessels throughout the body are very permeable to many chemicals, including toxic ones, which would reach the brain if this special barrier did not exist. Astrocytes help form the blood-brain barrier by surrounding the smallest, most permeable blood vessels in the brain. The barrier is not perfect, however. Since it consists of plasma membranes, it is permeable to fat-soluble substances such as anesthetics and alcohol.

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  • amalda zaragamba
    What is the deepest part of a schwann cell?
    8 years ago

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