c. Information Transmission. Information is carried as electrical impulses
along the length of the neuron.
d. Coverings. Some neuron processes have a covering that is a series of
Schwann cells, interrupted by nodes (thin spots). This gives the neuron branch the
appearance of links of sausages. The Schwann cells produce a lipid (fatty) material
called myelin. This myelin acts as an electrical insulator during the transmission of
5-5. TYPES OF NEURONS
Neurons may be identified according to shape, diameter of their branches, or
a. According to Shape. A pole is the point where a neuron branch meets the
cell body. To determine the type according to shape, count the number of poles.
(1) Multipolar neurons. Multipolar neurons have more than two poles (one
axon and two or more dendrites).
Bipolar neurons. Bipolar neurons have two poles (one axon and one
(3) Unipolar neurons. Unipolar neurons have a single process that
branches into a T-shape. One arm is an axon; the other is a dendrite.
b. According to Diameter (Thickness) of Branches. Neurons may be rated
according to the thickness of myelin surrounding the axon. In order of decreasing
thickness, they are rated A (thickest), B, and C (thinnest). The thickness affects the rate
at which impulses are transmitted. The thickest carry the impulses the fastest. The
thinnest carry the impulses the slowest.
According to Function.
(1) Sensorv neurons. In sensory neurons, impulses are transmitted from
receptor organs (for pain, vision, hearing, and so forth) to the central nervous system
(CNS). Sensory neurons are also known as afferent neurons.
(2) Motor neurons. In motor neurons, impulses are transmitted from the
central nervous system to muscles and glands (effector organs). Motor neurons may be
called efferent neurons.
(3) Interneurons. Interneurons transmit information from one neuron to
another. Interneurons connect sensory neurons with motor neurons.