1.41. Nerve Cells and Nerve Impulses http://www.ck12.org
FIGURE 1.73
The axons of many neurons, like the one
shown here, are covered with a fatty layer
called myelin sheath. The sheath covers
the axon, like the plastic covering on an
electrical wire, and allows nerve impulses
to travel faster along the axon. The node
of Ranvier, shown in this diagram, is any
gap in the myelin sheath; it allows faster
transmission of a signal.- Many dendrites.
- One axon.
Thecell bodycontains the nucleus and other organelles. Dendrites and axons connect to the cell body, similar to
rays coming off of the sun.Dendritesreceive nerve impulses from other cells.Axonspass the nerve impulses on to
other cells. A single neuron may have thousands of dendrites, so it can communicate with thousands of other cells
but only one axon. The axon is covered with amyelin sheath, a fatty layer that insulates the axon and allows the
electrical signal to travel much more quickly. Thenode of Ranvieris any gap within the myelin sheath exposing
the axon, and it allows even faster transmission of a signal.
Types of Neurons
Neurons are usually classified based on the role they play in the body. Two main types of neurons are sensory
neurons and motor neurons.
- Sensory neuronscarry nerve impulses from sense organs and internal organs to the central nervous system.
- Motor neuronscarry nerve impulses from the central nervous system to organs, glands, and muscles—the
opposite direction.