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Central Nervous System Definition: The Brain- Parts & Functions

Jul 7, 2022

An Overview 

According to the central nervous system definition, the CNS is made up of two components:

  • The brain 
  • The spinal cord

It is called “central” because it integrates information from across the body and coordinates action throughout the whole organism.


The skull, also known as the cranial cavity, shelters the brain. The spinal cord goes from the hindbrain down the middle of the spinal cord and terminates in the lumbar region of the lower back.

The meninges are a protective three-layered membrane surrounding the spinal cord and the brain.


Physiologists and anatomists have extensively researched the central nervous system, yet it still retains many secrets. It regulates the following central nervous system functions in our body:

  • Thoughts 
  • Actions
  • Emotions
  • Desires

Also, the functions of the central nervous system include regulating our core temperature, heart rate, respiration, hormone secretion, and more.


Along with the brain and spinal cord, the optic nerve, the retina, olfactory epithelium, and olfactory nerves are sometimes considered part of the CNS. This is because they make direct connections with brain tissue without using intermediary nerve fibres.

Central Nervous System (CNS) Definition

The CNS is the body’s serving centre and is made up of the brain and spinal cord. Both are shielded by three coatings of membranes known as meninges.


Now let’s take a closer look at the components and the functions of the central nervous system, beginning with the brain.

The Brain 

The brain is the most intricate organ in the human body; the cerebral cortex (the brain’s outermost layer and biggest by volume) has approximately 15–33 billion neurons, each of which is linked to thousands of other neurons.


The human brain comprises about 1,000 billion glial (supporting) cells and 100 billion neurons. Our brain consumes around 20% of our whole bodily energy. The brain is the body’s primary control module that coordinates activities from physical movement to hormone production, memory formation, and emotional feeling.

Some parts of the brain are specialised in performing these duties. However, many higher activities, like problem-solving, reasoning, and creativity, require diverse regions to collaborate in networks.


The brain is further segregated into four lobes:

  • Temporal lobe
  • Occipital lobe
  • Parietal lobe
  • Frontal lobe
Nervous System 1

Consider the central nervous system diagram given above to understand the lobes of the brain.


Temporal lobe

  • It is responsible for processing sensory information and attaching emotional meaning to it.
  • It is also important in the formation of long-term memories. Language perception is also covered in this section.

Occipital lobe

  • It is the brain’s visual processing area, which houses the visual cortex.

Parietal lobe

  • It combines sensory information such as spatial awareness, touch, and navigation.
  • It receives touch sensations from the skin. 
  • It also helps with language processing.

Frontal lobe

  • It occupies the front region of the brain 
  • It includes the bulk of dopamine-sensitive neurons. 
  • It is involved in reward, motivation, attention, short-term memory, and planning.

Regions of Brain 

Next, we’ll glance at some specific areas of the brain:

Basal Ganglia

  • It controls voluntary motor movements, makes judgments, and learns procedures. 
  • Huntington’s disease and Parkinson’s disease are two diseases that impact this region.


  • It is mostly responsible for muscle control but also for attention and language.
  • The major sign of cerebellar injury is impaired muscle control, known as ataxia.

Broca’s Area

  • This tiny part of the brain on the left side (often on the right in left-handed people) is vital for language comprehension. 
  • When a person’s speech is impaired, they can still understand what is being said. 
  • Stammering is occasionally related to a hypoactive Broca’s area.

Corpus Callosum 

  • It is a large girdle of nerve fibres connecting the brain’s right and left hemispheres. 
  • It is an extensive white matter arrangement in the brain.
  • It permits communication between the right and left hemispheres. 
  • Left-handed folks, musicians, and ambidextrous people often have bigger corpus callosum than dyslexic kids.

Medulla oblongata

  • It extends below the skull.
  • It is responsible for involuntary processes such as breathing, vomiting, sneezing, and maintaining proper blood pressure.


  • It is approximately the size of an almond.
  • It sits immediately above the glands that secrete several neurohormones and the brain stem.
  • It controls thirst, body temperature regulation, and appetite.


  • It is settled in the middle part of your brain.
  • It absorbs motor and sensory information and distributes it to the remainder of the cerebral cortex. 
  • It helps to regulate sleep, alertness, consciousness, and attentiveness.

Amygdala: a pair of almond-shaped nuclei located deep within the temporal lobe. They play a role in decision-making, memory, and emotional reactions, especially unpleasant emotions.

Spinal Cord 

The spinal cord runs the whole length of the back virtually. It not only transmits signals between the brain and the body, but it also performs additional central nervous system functions. Thirty-one spinal nerves enter the spinal cord from the brainstem, where the spinal cord joins the brain.

It links with nerves of the peripheral nervous system (PNS) that flow from the muscles, skin, and joints along its length. Motor orders from the brain flow from the spine to the muscles, while sensory information passes from sensory tissues like the skin to the spinal cord and then to the brain.

The spinal cord comprises circuits that govern reflexive reflexes, such as the automatic movement of your arm if your finger accidentally touches a flame. More sophisticated motions, like running, can also be generated by the circuits inside the spine. Even without brain input, the spinal nerves can regulate all the muscles required for walking. 

For example, if a cat’s brain is severed from its spine such that it has no touch with its body, it will begin walking autonomously when positioned on a treadmill. The brain is only needed to halt and restart the process or to make alterations if, for example, an item arrives in your route.

Gray and white matter

Nervous System 2

The CNS is split into two parts: 

  • The white matter
  • The grey matter

In general, the brain is made up of an exterior grey matter cortex and an interior region with white matter tracts.

Glial cells, which support and protect the neurons, are found in both tissue types. White matter is largely made up of: 

  • Axons (nerve projections)
  • Oligodendrocytes (kind of glial cell)

The grey matter is mostly made up of neurons. The above central nervous system diagram explains the grey matter and white matter. 

Glial cells 

Glial cells 

Glial cells are also known as neuroglia. They are frequently referred to as support cells for neurons. They outnumber nerve cells in the brain by a factor of ten. Without glial cells, growing nerves frequently disorient and fail to create central nervous system function of synapses.

Glial cells are present in both the PNS and the CNS. However, the kinds differ. The following are brief explanations of the many kinds of CNS glial cells:

Refer to the above central nervous system diagram to understand the different types of glial cells. 

  • Astrocytes 

    • These are cells with many projections that connect neurons to their blood supply. 
    • They help keep the local environment in check by recycling neurotransmitters and eliminating excess ions.
  • Oligodendrocytes 

    • These are important for forming the myelin sheath, which wraps nerve cells and allows them to relay impulses efficiently and swiftly.
  • Ependymal cells

    • These cells line the spinal cord and the brain’s ventricles (fluid-filled compartments)
    • The cells produce and discharge cerebrospinal fluid (CSF).
    • They use whip-like cilia to keep it flowing.
  • Radial glia

    • They function as scaffolding for new nerve cells during embryonic nervous system development.

Cranial Nerves

The nerves of the cranium are 12 pairs of nerves that emerge from the brain and travel through perforations in the skull rather than the spinal cord. These nerves gather and transmit data between the brain and other regions of the body, primarily the head and the neck.

  • The olfactory and optic nerves are two of the 12 pairs. These nerves come from the forebrain and are part of the central nervous system.
  • Olfactory nerves (cranial nerve I) convey odour information from the upper nasal cavity to the olfactory bulbs at the base of the brain.
  • Optic nerves (cranial nerve II) transport vision impulses from the retina to the brain’s major visual centres. Each optic neuron has around 1.7 million nerve fibres.


According to the central nervous system definition, unlike most other organ systems, the central nervous process is a powerful and multi-tasking organ system. The function of the central nervous system is to govern both deliberate and involuntary behaviours. It also aids in processing your dreams, ideas, perceptions, and feelings.

Frequently Asked Questions

What are the symptoms of a faulty CNS?

Symptoms of damaged CNS are as follows:
1. Persistent or abrupt development of a headache 
2. A headache that shifts or differs
3. Tingling or loss of sensation
4. Muscle weakness or lack of strength
5. Blindness or double vision
6. Memory lapses
7. Impairment in mental abilities
8. Coordination is lacking

Is nerve injury irreversible?

Your prognosis may be great if a medical problem can be identified and addressed. However, even when the underlying cause is cured, nerve damage might be irreversible. Chronic pain can be a significant issue for certain people. Numb feet might cause unhealed ulcers of the skin.

How many bones are there in the spinal cord?

The average person is born with 33 individual bones (the vertebrae) that interact and connect through pliable joints called facets. By the time an individual reaches adulthood, most have only 24 vertebrae because of some vertebrae at the bottom end of the spine fuse during normal growth and development.

Central Nervous System


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