The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. The central nervous system is made up of the brain and spinal cord, and the peripheral nervous system is made up of the somatic and autonomic nervous systems.

The Central Nervous System (CNS) – Characteristics

The central nervous system is divided into two main parts: the brain and the spinal cord.

Central Nervous System – Components


The brain is inside the skull and is shaped like a mushroom. The brain is made up of four main parts:

The brain stem
The brain
The cerebellum
The diencephalon

The brain weighs approximately 1.3 to 1.4 kg. It has nerve cells called neurons and supporting cells called glia. There are two subjects, gray and white. The first receives and stores impulses. The second in the brain is responsible for sending impulses to the gray. It consists of nerve fibers (axons).

The brain rests on the brain stem. The brain is divided into two hemispheres. Each hemisphere controls the activities of the side of the body opposite that hemisphere.

The hemispheres are divided into four lobes:

Frontal lobe
Temporal lobes
lobe Occipital lobe


This is behind and below the brain.

The brain stem

The brainstem is also known as the medulla oblongata. It is located between the pons and the spinal cord and is one inch long.

The Diencephalon

The diencephalon is also known as the front brainstem. It includes the thalamus and the hypothalamus. The thalamus is where sensory and other impulses go and merge.

The hypothalamus is a smaller part of the diencephalon

Other parts of the brain

Other parts of the brain include the midbrain and pons:

The midbrain provides conduction pathways to and from the higher and lower centers,
the pons acting as a pathway to higher structures; it contains conduction pathways between the medulla and higher brain centers.

Spinal cord

The spinal cord is along a tube-like structure that extends from the brain. The spinal cord is made up of a series of 31 segments. A pair of spinal nerves exits each segment. The region of the spinal cord from which a pair of spinal nerves originate is called the spinal segment.

The spinal cord measures approximately 17 inches in older women and 18 inches in older men (in length) and weighs about 35-40 grams. It is found within the spinal column, the collection of bones (back bone).

Other parts of the central nervous system

The meninges are three layers or membranes that cover the brain and spinal cord. The outermost layer is the dura. The middle layer is the arachnoid, and the innermost layer is the pia mater. The meninges offer protection for the brain and spinal cord by acting as a barrier against bacteria and other microorganisms.

Cerebrospinal fluid (CSF) circulates around the brain and spinal cord. Protects and nourishes the brain and spinal cord.


The neuron is the basic unit in the nervous system. It is a specialized conductive cell that receives and transmits electrochemical nerve impulses. A typical neuron has a cell body and long arms that conduct impulses from one part of the body to another part of the body.

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There are three different parts of the neuron:

Cell Body

Cell body of a neuron

The cell body is like any other cell with a nucleus or control center.


The cell body has several thick, highly branched extensions that look like wires and are called dendrites. The exception is a sensory neuron presenting a dendrite. Motor neurons have multiple thick dendrites. The function of the dendrite is to carry a nerve impulse to the cell body.


An axon is a long, thin process that transmits impulses from the cell body to another neuron or tissue. Usually there is only one axon per neuron.

Myelin sheath

Schwann cells surround the neuron. These are white segments that wrap around axons and dendrites of many peripheral neurons. The coverage is continuous along the axons or dendrites, except at the termination point and at the nodes of Ranvier.

The neurilemma is the Schwann cell layer with a nucleus. Its function is to allow damaged nerves to regenerate. They do not have a neurilemma and therefore cannot recover when damaged.

Somatic nervous system

The somatic nervous system consists of peripheral nerve fibers that pick up sensory information or sensations from peripheral or distant organs (those that are far from the brain, such as the extremities) and carry them to the central nervous system.

These also consist of motor nerve fibers that exit the brain and take the necessary movement and action messages for skeletal muscles. For example, when touching a hot object, the sensory nerves transmit information about heat to the brain, which in turn, via the motor nerves, signals the muscles in the hand to withdraw it immediately.

The whole process takes less than a second to happen. The cell body of the neuron that carries information is often located within the brain or spinal cord and projects directly into skeletal muscle.

Autonomic nervous system

Another part of the nervous system is the Autonomic Nervous System. It has three parts:

the sympathetic nervous system
the parasympathetic
nervous system the enteric nervous system

This nervous system controls the nerves of the internal organs of the body over which humans have no conscious control. This includes the heartbeat, digestion, breathing (except conscious breathing), etc.

The nerves of the autonomic nervous system enervate the involuntary smooth muscles of the (internal organs) and the glands and cause them to function and secrete their enzymes, etc.

The enteric nervous system is one third of the autonomic nervous system. A complex network of nerve fibers make up the SN. These innervate the organs within the abdomen, such as the gastrointestinal tract, pancreas, gallbladder, etc. It contains about 100 million nerves.

Peripheral nervous system – Characteristics of neurons

The smallest worker in the nervous system is the neuron. For each of the impulse chains there is a preganglionic neuron, or one before the cell body or ganglion, which is like a central control body for numerous peripherally exiting neurons.

The preganglionic neuron is found in the brain or spinal cord. In the autonomic nervous system, this preganglionic neuron projects into an autonomic ganglion. The postganglionic neuron projects to the target organ.

In the somatic nervous system, there is only one neuron between the central nervous system and the target organ, while the autonomic nervous system uses two neurons.

Samantha Robson
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Dr. Samantha Robson ( CRN: 0510146-5) is a nutritionist and website content reviewer related to her area of ​​expertise. With a postgraduate degree in Nutrition from The University of Arizona, she is a specialist in Sports Nutrition from Oxford University and is also a member of the International Society of Sports Nutrition.

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