Structure of the Nervous System – How Central and Peripheral Components Work Together

The human nervous system consists of two closely connected parts: the central nervous system (CNS) and the peripheral nervous system (PNS). Together, they ensure that signals from inside the body or the environment are processed and appropriate reactions are initiated.

Two-part cartoon illustration of a nerve cell shown in the central and peripheral nervous system – acting in a control center and body network — Central and peripheral nervous system – working together. The CNS processes signals, the PNS carries them to and from the body.

The Central Nervous System – The Body’s Control Center

The central nervous system includes the brain and spinal cord. It processes all sensory input, coordinates movement, and forms thoughts. The brain is protected by the skull; the spinal cord runs within the bony canal of the spine.

The brain itself is divided into several functional areas – including the cerebrum, cerebellum, and brainstem. The cerebrum is responsible for conscious thought, speech, memory, planning, and voluntary movement. The cerebellum coordinates movement and helps maintain balance. The brainstem regulates vital functions such as breathing, heart rate, and reflexes.

Simplified illustration of the central nervous system (CNS), including the brain and spinal cord. — The central nervous system (CNS) consists of the brain and spinal cord. Both are highly sensitive and are protected within the skull and spinal column.

The spinal cord serves as a key communication pathway between the brain and the body. It transmits incoming signals from the body to the brain and carries outgoing signals from the brain to the muscles. In certain situations – such as reflex actions – it can process information independently.

The central nervous system not only enables conscious actions but also regulates many automatic processes. It is closely connected to the peripheral nervous system, which acts as a link between the CNS and the rest of the body.

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This clip shows a rotating brain model. The preview displays a side view, but the video starts from the front. The cerebral hemispheres rest on the brainstem. The cerebellum is located at the back.
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The Peripheral Nervous System – The Body’s Communication Network

The PNS consists of all nerves that exit the brain or spinal cord. These nerves extend into the arms, legs, and internal organs. They carry sensory information such as touch, temperature, and pain to the brain and transmit motor commands to the muscles.

The peripheral nervous system can be divided into two main parts:

the somatic nervous system, which is involved in voluntary movement and sensory perception, and
the autonomic nervous system, which controls unconscious body functions such as breathing, digestion, and blood pressure regulation.

The autonomic system is further divided into the sympathetic, parasympathetic, and enteric systems.

Peripheral nerves follow defined anatomical pathways. They run alongside muscles, bones, and blood vessels and branch into the outer regions of the body. Most nerves carry both sensory and motor fibers, allowing information to flow in both directions – from the body to the CNS and back.

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This clip shows the human body, reduced to the skeleton and the peripheral nervous system. The peripheral nerves are shown in bright yellow. They emerge from within the skull and spine and extend to all areas of the body.
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Although individual nerve paths may vary, their general organization is well understood. Narrow anatomical passages, injury, or disease can interfere with signal transmission.

Overview of Arm and Leg Nerves

In the neck region, the brachial plexus gives rise to the major nerves of the arm, including:

Axillary nerve
Musculocutaneous nerve
Median nerve
Radial nerve
Ulnar nerve

These nerves allow precise movements and transmit sensory input from the upper limbs.

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This clip shows the peripheral nerves emerging from the cervical and upper thoracic spine. At the level of the collarbone, they form the brachial plexus, from which the five main nerves of the arm arise. These are shown with their branches all the way to the hand.
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In the lower back and pelvis, the lumbosacral plexus forms. It gives rise to important leg nerves such as:

Sciatic nerve (nervus ischiadicus)
Tibial nerve
Common peroneal (fibular) nerve
Femoral nerve
Obturator nerve

These nerves coordinate leg movement and carry sensory information from the lower extremities.

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This clip shows the nerves of the lumbosacral plexus that supply the leg. The video begins with a posterior view of the gluteal region, where the large sciatic nerve is visible. It divides into the tibial nerve and the peroneal nerve, which further branch out into the foot.
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What Nerves Look Like and How They Work

Nerves are composed of many fine fibers (axons), each protected by a surrounding layer. They travel through the body like bundled cables. The farther they extend from the center, the finer they become. This structural organization allows efficient signal transmission over long distances.

Signals are transmitted both electrically and chemically. At contact points (synapses), information is passed between nerve cells. This mechanism enables movement, sensation, and automatic functions such as sweating. These processes form the basis of normal nerve function in everyday life.

Cartoon-style nerve cell with glowing axon illustrating signal transmission in the nervous system — How nerves transmit signals. Signals are transmitted electrically and chemically through fine fibers and contact points – enabling movement, sensation, or reflexes.

Visualizing Nerves – Diagnostic Tools When Needed

In some cases, it may be helpful to take a closer look at nerve structures – for example, when symptoms such as tingling, numbness, pain, or muscle weakness persist.

High-resolution nerve ultrasound can visualize even small peripheral nerves in detail – in real time and without radiation. It provides information about the course, thickness, and potential structural changes of nerves.

Illustration of a high-resolution ultrasound scanner for nerves to perform nerve ultrasound. — Peripheral nerves can be visualized in detail using nerve ultrasound.

In certain situations, MRI-based imaging (MR neurography) can offer additional insights, particularly when deeper or more complex nerve pathways are involved. These imaging methods complement each other in assessing nerve structure.

MRI scanner for visualizing nerve structures and soft tissues – modern imaging for diagnosing nerve damage. — MRI (magnetic resonance imaging) delivers high-resolution soft tissue images, while MR neurography is specialized for nerve imaging and diagnostics.

For more information about diagnostic techniques for peripheral nerves, please see our separate overview page.

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Disclaimer: The information provided on this page is for general informational purposes only and does not constitute medical advice. It is not a substitute for personal consultation, examination, or treatment by a physician or other qualified healthcare professional. No guarantees of healing or cure are made. While we strive for accuracy and completeness, we cannot guarantee that all content is up to date or free from errors, and we accept no liability for any inaccuracies.