Nervous tissue is composed of neurons and neuroglia. Neurons transmit electrical signals while neuroglia support neuron function. The nervous system is divided into the central nervous system (brain and spinal cord) and peripheral nervous system (nerves throughout the body). The autonomic nervous system regulates involuntary functions like digestion. Neurons transmit signals through electrical impulses. Neuroglia support neurons through roles like insulation and nutrient supply. There are different types of neurons defined by their functions and structures.

1. Nervous Tissue
Nervous tissue is the term for groups of organized cells in the nervous system, which is the organ
system that controls the body’s movements, sends and carries signals to and from the different
parts of the body, and has a role in controlling bodily functions such as digestion. Nervous tissue
is grouped into two main categories: neurons and neuroglia. Neurons, or nerves, transmit
electrical impulses, while neuroglia do not; neuroglia have many other functions including
supporting and protecting neurons.
Function of Nervous Tissue
Nervous tissue makes up the nervous system. The nervous system is subdivided in several
overlapping ways. The central nervous system (CNS) is composed of the brain and spinal cord,
which coordinates information from all areas of the body and sends nerve impulses that control
all bodily movements. The peripheral nervous system (PNS) consists of peripheral nerves that
branch all throughout the body. It connects the CNS to the rest of the body and is directly
responsible for controlling movements of specific parts of the body; for example, just before arm
movement the CNS sends nerve impulses to the PNS nerves in the arm, which causes the arm to
move.
Another subdivision of the nervous system is into the sympathetic nervous system (SNS) and
the parasympathetic nervous system (PSNS). The SNS activates in order to stimulate a fight-or-
flight response in an organism when that organism encounters a threat and must decide whether
to fight or flee from it. The nerves of the SNS have diverse effects on different parts of the body.
Activation of the SNS causes the pupils of the eyes to dilate, inhibits digestion, increases
sweat secretion, and increases the heart rate. Conversely, the PSNS is activated during moments
of “rest and digest”, when an organism is not facing an immediate threat. Nerves of the PSNS
work to stimulate activities that can occur at rest such as digestion, waste excretion, and sexual
arousal, and they also decrease the heart rate.
The enteric nervous system (ENS) controls the gastrointestinal tract (digestive tract). This
division of the nervous system, along with the SNS and PSNS, are collectively referred to as

2. the autonomic nervous system (ANS). The ANS regulates activities that are performed
unconsciously; we don’t have to think about digesting food for it to occur, for example. By
contrast, the somatic nervous system (SoNS) controls voluntary body movements. It is made up
of afferent and efferent nerves that send signals to and from the CNS, causing
voluntary muscle contraction to occur.
Types of Nervous Tissue
Neurons
Neurons are cells that can transmit signals called nerve impulses, or action potentials. An action
potential is a quick rise and fall in the electrical membrane potential of the neuron, which
transmits signals from one neuron to the next. These are the different types of neurons:
• Sensory, or afferent neurons, relay information from the PNS to the CNS; different types
of sensory neurons can detect temperature, pressure, and light.
• Motor, or efferent neurons, send signals from the CNS to the PNS; these signals provide
information to sensory neurons to “tell” them what to do (e.g., initiate muscle
movement).
• Interneurons connect sensory and motor neurons to the brain and spinal cord; they act as
connectors to form neural circuits and are involved with reflex actions and higher brain
functions like decision-making.
While neurons can be specialized and look very different from one another, they each have
components in common. Each neuron has a soma, or cell body, that contains the nucleus.
Dendrites, finger-like projections that receive nerve impulses, branch off from the soma. The
axon is a larger projection that branches off from the soma. Nerve impulses travel along the axon
in the form of an action potential. The axon splits into axon terminals, which branch off to other
neurons. Neurotransmitters are released from the ends of the axon terminals, and these travel
across the synaptic cleft to reach receptors on the dendrites of other neurons. In this way, neurons
communicate with each other and can send signals that reach many other neurons.
Neuroglia

3. Neuroglia, or glial cells, are cells that support neurons, supply them with nutrients, and get rid of
dead cells and pathogens such as bacteria. They also form insulation between neurons so that
electrical signals do not get crossed, and can also aid the formation of synaptic connections
between neurons. There are several types of neuroglia:
• Astroglial cells, also called astrocytes, are star-shaped cells found in the brain and spinal
cord. They provide nutrients to neurons, maintain ion balance, and remove unneeded
excess neurotransmitters from the synaptic cleft.
• Ependymal cells are also found in the CNS. There are two types of ependymal cells.
Non-ciliated ependymal cells form cerebrospinal fluid, while ciliated ependymal cells
help the cerebrospinal fluid circulate. Cerebrospinal fluid cushions the brain and spinal
cord.
• Oligodendrocytes are found in the CNS and provide physical support to neurons. They
form a myelin sheath around some neurons in the CNS. The myelin sheath is a fatty
substance wrapped around the axons of some neurons; it provides electrical insulation.
• Schwann cells also form myelin sheaths around some neurons, but they are only found in
the PNS. Neurons that are myelinated can conduct electrical impulses faster than non-
myelinated neurons.
• Microglial cells, or microglia, are small macrophage cells in the CNS that protect against
disease by engulfing pathogens through phagocytosis (“cell eating”). They can also
destroy infected neurons and promote the regrowth of neurons. All of the other types of
neuroglia above are larger and collectively called macroglia.

4. This diagram shows the two types of cells, neurons and neuroglia, that make up nervous tissue.
Related Biology Terms
• Tissue – An organized group of cells that carries out a certain function.
• Nervous system – The organ system responsible for controlling and coordinating body
movements and functions.
• Action potential – A sudden rise and fall in the electrical membrane potential of a
neuron that leads to a signal being transmitted to other neurons or the target body
organ.
• Synapse – A small gap between two nerve cells that neurotransmitters travel across.
Neuron Structure
A neuron consists of three parts: a cell body that contains the nucleus, dendrites attached to the
cell body that receives signals, and the axon that plays a role in the propagation of these signals.
A neuron is a cell in the nervous tissue that transmits electrical and chemical signals throughout
the body. A neuron has three main parts: a cell body, dendrites, and a single axon. The neuron's
cell body contains the nucleus and other major organelles. The dendrite is an extension from the
neuronal cell body that receives input from other cells. Another extension, the axon, transmits

5. the signal to receiving cells. Information moves in one direction starting from the dendrite to the
cell body and ending at the axon. To help with the transmission of an electrical signal, the nerve
impulse travels quickly through neurons as well as a myelin sheath, which is a lipid-rich
material that wraps around the axon and helps impulses travel through neurons. The myelin
sheath insulates the axon to prevent the electric current of the nerve impulse signal from leaving
the axon and increases the speed of the signal. A gap between myelin sheaths where the axon is
uncovered is called a node of Ranvier. The propagation of nerve impulses from one node of
Ranvier to another, across myelinated axons, is called saltatory conduction. This process allows
impulses to move quickly without degrading over the long distance of the axon. The end of an
axon is the axon terminal where nerve impulses are released to the next neuron via chemical
transmission to the next neuron.
A neuron consists of a cell body that contains the nucleus, dendrites, and an axon. When
information is received from an external or internal stimulus, it is propagated down the neuron's
axon as a nerve impulse. Eventually this information terminates at the axon terminal, where it is
chemically transmitted to another neuron.
Types of Neurons
Neurons differ based on function (afferent, efferent, interneurons) and structure (multipolar,
bipolar, unipolar, anaxonic), which is defined by the number and type of projections extending
from the cell body.
The nervous system consists of different types of neurons. These neurons are classified
according to where they transmit information. An afferent neuron carries sensory information
from sensory organs (e.g., eyes, ears, and skin) to the central nervous system (CNS). An efferent
neuron carries motor information, such as when the body should move, from the CNS to
effector organs including muscles and glands. The effector organ responds to a stimulus from a
nerve. An interneuron relays information between an afferent (sensory) neuron and an efferent
(motor) neuron. Interneurons are located in the brain and spinal cord to help process sensory
information and coordinate motor activities. For example, if a person’s hand touches a hot stove,
a signal is first sent through an afferent neuron to an interneuron, which interprets the

6. information. The interneuron transmits this signal to an efferent neuron, which stimulates the
muscles in the hand to move.
Individual neurons also vary in structure and are named based on how dendrites and axons are
arranged around the cell body. A unipolar neuron is a sensory neuron that has a single, long
axon extending from the cell body. It is found in the spine and cranial nerve ganglia. A bipolar
neuron consists of a cell body with one dendrite and one axon extending off of it in opposite
directions from each end. Bipolar neurons are found in the retina, the inner ear, and the nasal
cavity. Neurons are most commonly multipolar. A multipolar neuron has a single axon and
many dendrites that extend from the cell body. These neurons are typically motor neurons found
in the CNS. An anaxonic neuron has multiple dendrites and often no axons. These cells are
found in the brain and retina.
Neuroglia
Oligodendrocytes, ependymal cells, microglia, and astrocytes are neuroglia found in the central
nervous system (CNS), while Schwann cells and satellite cells are neuroglia found in the
peripheral nervous system (PNS).
Neuroglia, also known as glial cells, are cells that support and protect neurons. Unlike neurons,
they do not carry neural impulses. Different types of neuroglia are found in the central nervous
system (CNS) and peripheral nervous system (PNS). The following glial cells are found in the
CNS:
• An oligodendrocyte is a glial cell that generates myelin, which wraps around axons in
the CNS.
• An ependymal cell lines the spinal cord and ventricles of the brain. It produces and
secretes cerebrospinal fluid (CSF).
• A microglia cell mediates immune responses in the CNS. It can transform into a special
type of macrophage that can clear up neuronal debris via phagocytosis.
• An astrocyte is a star-shaped glial cell that supports neurons by connecting them to
nutrient supplies and repairing nervous tissue after injury.

7. Schwann cells and satellite cells are neuroglia found in the PNS. Like an oligodendrocyte in the
CNS, the Schwann cell provides myelination to axons in the PNS. Each individual Schwann cell
sheaths only one axon. It has phagocytic activity, which means it can engulf and clear cellular
debris in order to facilitate the regrowth for PNS neurons. A satellite cell is a glial cell in the
PNS that surrounds the cell bodies of neurons in sensory, sympathetic, and parasympathetic
ganglia. A ganglion is a mass of tissues that contains several cell bodies. By functioning in this
capacity, satellite cells provide support in a way that is similar to astrocytes in the CNS. Satellite
cells also modulate the PNS following injury and inflammation.
There are different types of neuroglia in the central and peripheral nervous systems. Astrocytes
and satellite cells provide support. Oligodendrocytes and Schwann cells provide insulation,
microglia provide immune surveillance, and ependymal cells help create cerebrospinal fluid.
These neuroglia have unique morphologies and distributions in the nervous system.