In this note, we are going to discuss the basic anatomy of the nervous system (systema nervosum).

This system provides communication among all other organ systems, monitors internal and external changes, and develops proper responses.

For ease of understanding, the nervous system is structurally subdivided into the central nervous system (or CNS) (systema nervosum centrale), which includes the brain (encephalon) and spinal cord (medulla spinalis), and the peripheral nervous system (or PNS) (systema nervosum periphericum), which includes nerves (nervi) and ganglia (ganglion) outside the CNS.

The peripheral nervous system is made up of two functional units: the somatic (that controls voluntary actions), and the autonomic (that controls the involuntary activities).

Nervous tissue

Both the central and peripheral parts of the nervous system consist of nervous tissue, which in turn is formed by neurons (or nerve cells) and neuroglia.

Neurons can receive, generate, and transmit electrical impulses, providing communication with other neurons as well as with effector cells, such as muscle cells.

Neurons consist of the cell body and two types of extensions, or processes, that arise from it.

Dendrites are short processes. Each neuron may have many such projections. They receive incoming signals from other neurons.

The second type, axons, are long. Each neuron has only one axon. It is used to transmit impulses to other neurons.

Some axons are covered with a layer of lipids and proteins that speed up the conduction of nerve impulses. This structure is called the myelin sheath.

The electrical impulse eventually reaches the distal parts of the axon, called the axon terminals.

They meet with the dendrite, the body, or with the axon of another neuron, and this contact site is called a synapse.

Depending on the location of a neuron within the nervous system, the number of its processes may vary:

• Multipolar neurons have several dendrites and a single axon;

• Bipolar neurons have one large dendrite and one axon;

• Unipolar neurons contain only one process; according to many researchers, this type of neuron is only present during embryogenesis;

• Pseudounipolar neurons have one process that arises from the body and immediately divides in a T-shaped manner. One part of this projection acts as an axon, and the other acts as a dendrite;

• Axonless neurons contain many processes, but the axon is so short that it cannot be distinguished from dendrites.

Neuroglia, or glial cells, are the other cell type found in the nervous system. There are several types of neuroglia, they function as a maintenance staff who support and nourish neurons.

Neurons and neuroglia are discussed in more detail in the relevant topics.

Central nervous system

Alright, now let’s discuss the central nervous system, which consists of the brain and spinal cord.

The main role of the central nervous system is to coordinate and integrate nerve impulses that arrive from the periphery. This provides the functioning of our muscles and internal organs and allows us to think, learn, and experience emotions.

The brain (encephalon) consists of several large parts.

• These include the cerebral hemispheres

• The diencephalon

• The cerebellum

• And the brainstem

The brainstem, in turn, includes:

• midbrain

• pons

• and the medulla oblongata

The spinal cord (medulla spinalis) divides into 31 segments.

• 8 cervical

• 12 thoracic

• 5 lumbar

• 5 sacral

• and 1 coccygeal

Next, let’s discuss two different colored areas of the nervous tissue: gray matter and white matter. You are most likely already familiar with these terms.

Gray matter histologically is made up of the neuron cell bodies. In the brain, gray matter forms the cortex and subcortical nuclei. In the spinal cord it is shaped like a butterfly and has two major divisions: the anterior horn, and the posterior horn.

White matter histologically consists of the processes of neurons, and the already-mentioned myelin sheath gives it its white color. In the central nervous system, axon bundles united by a specific function are called tracts or pathways.

Peripheral nervous system

The components of the PNS are similar to the CNS, but the terminology used is slightly different. In the PNS, a cluster of neuron bodies is called a ganglion (ganglion), and axon bundles are called nerves (nervi).

There are 31 pairs of spinal nerves (nervi spinales) and 12 pairs of cranial nerves (nervi craniales).

Cranial nerves exit the brain and innervate various structures of the head and neck.

These nerves can be divided into sensory, motor, and mixed.

Spinal nerves arise directly from the spinal cord via two roots: the anterior root

and the posterior root.

The posterior roots contain sensory (or afferent) fibers that transmit sensory information from the periphery to the posterior horn of the spinal cord.

The anterior roots contain motor (or efferent) fibers that transmit motor information from the anterior horn of the spinal cord to the organs (for example, skeletal muscles)

Remember that afferent fibers arrive and efferent fibers exit the spinal cord!

Both roots of the spinal cord merge to form a mixed spinal nerve, which has both motor and sensory fibers.

Each mixed spinal nerve almost immediately divides into two branches: the anterior ramus (ramus anterior) and the posterior ramus (ramus posterior).

Since both the anterior and posterior rami emerge from the mixed spinal nerves, they carry both sensory and motor fibers.

Anterior rami, heading to different areas of our body, give rise to multiple nerves and nerve plexuses (plexus).

Each segment of the spinal cord innervates a particular area of the body.

If we are talking about a specific area of the skin, it is called a dermatome, and if we are talking about a skeletal muscle or some part of it, it is called a myotome.

There are dermatome maps which are used in the diagnosis of sensory processing disorders.

Golosary

Introduction to the centraland peripheral nervous systems

nervous system

systema nervosum

central nervous system

systema nervosum centrale

brain

encephalon

spinal cord

medulla spinalis

peripheral nervous system

systema nervosum periphericum

nerves

nervi

ganglia

ganglia

nucleus

nucleus

ganglion

ganglion