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Central Nervous System (CNS): structure, functions and diseases

Central Nervous System (CNS): structure, functions and diseases

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The Central Nervous System (CNS) is formed by the brain and spinal cord. It is known as "central", since it integrates the information of the whole body and coordinates the activity throughout the body.


  • 1 What makes up the Central Nervous System
  • 2 Differences between the Central Nervous System and the Peripheral Nervous System
  • 3 White Matter and Gray Matter, differences and functions
  • 4 The Glial Cells
  • 5 The Spinal Cord
  • 6 The Cranial Nerves
  • 7 The Brain, anatomy and physiology
  • 8 Diseases of the Central Nervous System

What makes up the Central Nervous System

The CNS consists of the brain and spinal cord. The brain is housed and protected by the skull (the cranial cavity) and the spinal cord flows from the back of the brain, in the center of the spine through the spinal canal, stopping in the lumbar region.

The brain and spinal cord are both housed within a three-layer protective membrane like the meninges.

The Central Nervous System has been studied for decades by doctors, anatomists and physiologists, but it still holds many secrets. Our thoughts, our movements, our emotions and our desires are generated within, but we still have a long way to go to know all its mysteries.

Differences between the Central Nervous System and the Peripheral Nervous System

The CNS is considered a separate entity from the Peripheral Nervous System (SNP), although the two systems are closely intertwined. The term SNP refers to any part of the nervous system that is outside the brain and spinal cord.

There are a number of differences between the CNS and the SNP, one of them is the difference in cell size. The axons of the nerves of the Central Nervous System (the thin projections of the nerve cells or neurons that carry the impulses) are significantly shorter. In contrast, the axons of the nerves of the SNP can be up to 1 m in length (for example, the nerve that innervates the big toe), while in the CNS it is rarely more than a few millimeters.

Other important difference between the SNC and the SNP is its regeneration capacity. Much of the SNP has the ability to regenerate; If a nerve in a finger is cut, it can grow back. On the other hand, the SNC does not have this capacity.

White Matter and Gray Matter, differences and functions

The CNS is made up of two types of substances, white matter and gray matter. The brain has an outer cortex called gray matter and an inner zone that consists of extensions of white matter.

Both types of tissue contain glial cells and neurons. The white substance is mainly composed of myelinated nerve fibers (coated with myelin), nerve fibers contain mostly axons, while gray matter is mainly composed of soma and neuronal bodies, which do not have myelin.

The white matter The brain has always been considered as a passive support of neuronal activity. Its main function is the transmission of brain information. This substance transfers the electrochemical pulses emitted by the brain to the rest of the body. Its main function is to coordinate communication between the different systems of the human body, both inside and outside the brain. Recent research shows that also intervenes in learning, cognitive and emotional processing, and in the generation of mental illnesses.

The Gray matter lacking myelin, it is not able to quickly transmit nerve impulses. Instead its function is related to the processing of information and therefore also of reasoning. It is responsible for developing the appropriate responses to the different stimuli.

Glial Cells

Also called neuroglias, glial cells function as support cells for neurons. They carry out a wide range of tasks and outnumber nerve cells in the brain in a ratio of 1: 10-50, which gives a good indication of their importance.

Its main functions include controlling the cellular ionic microenvironment, neurotransmitter levels and the supply of cytokines and other growth factors.

Without glial cells, the developing nerves would be unable to reach their destinations and, if they do not find their way, they are not able to form functional synapses.

Glial cells are found in both the CNS and the SNP, but each system has its own specific subtypes. The following are brief descriptions of the CNS glial cell types:

  • Astrocytes: These cells have numerous projections and supply blood to anchor neurons. They also regulate the local environment by removing excess ions and recycling neurotransmitters. Astrocytes are further divided into two distinct groups: protoplasmic and fibrous.
  • Oligodendrocytes: They are responsible for the creation of the myelin sheath, a thin layer that lines the nerve cell, which allows them to send signals quickly and efficiently.
  • Ependymal cells: They cover the spinal cord and the ventricles of the brain, they create and secrete cerebrospinal fluid and keep it in circulation through its cilia.
  • Radial glia: These cells act as scaffolds for new neuronal cells during the creation of the embryonic nervous system.

Spinal cord

Through the spinal cord you can coordinate the movement of muscles throughout the body.

The spinal cord runs through the back of the body and carries the information between the brain and the body, but also performs other tasks. From the brainstem, where the spinal cord meets the brain, there are up to 31 spinal nerves connected to the nerves of the SNP, which are responsible for giving sensitivity and function to the skin, muscles and joints.

The motor orders travel from the brain, pass through the spine and reach the muscles. Sensory information travels from sensory tissues (such as the skin) to the spinal cord and, finally, to the brain.

The spinal cord contains special circuits for reflex responses, such as the involuntary movement that a hand could make if the finger comes into contact with a flame.

Circuits within the spine can also generate more complex movements such as walking. Even without the involvement of the brain, spinal nerves can coordinate all the muscles needed to walk. What they will not be able to do will be to start, stop or make changes in said movement, since this is an exclusive function of the brain.

The Cranial Nerves

We have 12 pairs of cranial nerves that arise directly from the brain and pass through holes in the skull to travel along the spinal cord. These nerves collect and send information between the brain and the different parts of the body, especially the neck and head.

Of these 12 pairs, the olfactory, optic and terminal nerves arise from the anterior brain and are considered to be part of the Central Nervous System:

  • Olfactory nerves: transmit information on the smell of the upper section of the nasal cavity to the olfactory bulbs at the base of the brain.
  • Optic nerves: carry visual information from the retina to the primary visual nuclei of the brain. Each optic nerve is made up of about 1.7 million nerve fibers.
  • Terminal cranial nerves: they are the smallest of the cranial nerves, their role is not yet clear. Some believe that they may be vestigial (an evolutionary byproduct that has no remaining function) or that they participate in the function of pheromones (secreted hormone hormones that elicit responses in social animals).

The Brain, anatomy and physiology

The brain is the most complex organ in the human body. The cerebral cortex (the outermost part of the brain and the largest part in volume) contains between 15-33 million neurons, each of which are connected to thousands of other neurons.

In total there are about 100 billion neurons and 1,000 glial cells that make up the human brain.

The brain is the central control module of the body and coordinates a multitude of tasks. From the physical movement to the secretion of hormones, through the creation of memories and the feeling of emotion, among many others.

To carry out all these functions, some sections of the brain have specific functions. However, many of the higher functions such as reasoning, problem solving or creativity, involve different areas that work together in a network.

The brain is broadly divided into four lobes:

  • Temporal lobe: The temporal lobe is important for the processing of sensory and emotional information. He also participates in the fixation of long-term memories in relation to the hippocampus. Some aspects of language perception are also found here.
  • Occipital lobe: The occipital lobe is the region of visual processing of the mammalian brain. Damage to the primary visual cortex can cause blindness.
  • Parietal lobe: The parietal lobe integrates sensory information that includes touch, spatial perception and orientation. Touch stimulation of the skin is ultimately sent to the parietal lobe. It also plays a role in language processing.
  • Frontal lobe: located in the frontal part of the brain, the frontal lobe contains the majority of dopamine neurons and is involved in attention, reward, short-term memory, motivation and planning.

The following are some specific regions of the brain with a summary of their functions:

  • Basal ganglia: the basal ganglia are involved in the control of voluntary motor movements and the learning process. The diseases that affect this area are Parkinson's disease and Huntington's disease
  • Cerebellum: is mainly responsible for the control of fine and precise movements, also participates in the process of language and attention. If the cerebellum is damaged, the main symptom is the interruption of motor control, known as the ataxia.
  • Broca's area: This small area located on the left side of the brain (sometimes right in left-handed people), has an important function in language processing. When it is damaged, the person has difficulty speaking, but is still able to understand speech. Stuttering is sometimes associated with low activity in the Broca area.
  • Hard body: It is a wide band of nerve fibers that join the left and right hemispheres. It is the largest structure of white matter in the brain and allows the two hemispheres to communicate. It has been seen that dyslexic children have the smallest corpus callosum, while left-handed people, ambidextrous people and musicians usually have it larger.
  • Spinal bulb: It is located under the skull, it is an essential structure for numerous involuntary functions, such as breathing, sneezing, vomiting and maintaining the correct blood pressure.
  • Hypothalamus: It is located just above the brain stem and is about the size of an almond. It secretes a whole series of neurohormones and influences a variety of responses including control of body temperature, hunger and thirst.
  • Thalamus: placed in the center in the brain, the thalamus receives the sensory and motor inputs and transmits them to the rest of the cerebral cortex. It is involved in the regulation of consciousness, sleep and alertness.
  • Amygdala: they are two almond-shaped nuclei in the inner zone of the temporal lobe. They are involved in decision making, memory and emotional responses, especially negative emotions.

Central Nervous System Diseases

A system as complex and extensive as the SNC can malfunction for many reasons. Below are the main causes of the disorders that affect the Central Nervous System:

The CNS is susceptible to many diseases and injuries, ranging from infection to cancer.

  • Trauma: Any significant injury to the brain or spinal cord can cause negative health consequences. Depending on the site of the injury, symptoms can vary widely, from motor paralysis to cognitive or mood disorders.
  • Infections: various microorganisms and viruses can invade the central nervous system. These include fungi (cryptococcal meningitis), protozoa (malaria) bacteria (leprosy) and viruses of different types.
  • Degeneration: The spinal cord or brain can degenerate, causing different problems depending on which areas degenerate. An example is Parkinson's disease, which involves the gradual degeneration of dopamine-producing cells in the black substance of the basal ganglia.
  • Structural defects: the most common examples within this category are birth defects; An example is anencephaly, where the main parts of the skull, brain and scalp are missing at birth.
  • Tumors: Both cancerous and non-cancerous tumors can affect parts of the central nervous system. Both types can cause damage and produce a series of symptoms, depending on where they develop.
  • Autoimmune disorders: In some cases, an individual's immune system can attack healthy cells. For example, acute disseminated encephalomyelitis is characterized by an immune response against the brain and spinal cord, attacking myelin (isolation of the nerves) and, therefore, destroying white matter.
  • Cerebral vascular accident (AVC): a stroke is an interruption of the blood supply to the brain; The consequent lack of oxygen causes the tissue in the affected area to die.


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