Central Nervous System

Central Nervous System

The Central Nervous System (CNS) is responsible for receiving and transmitting information to the entire organism. We can define it with the command center that coordinates the activities of the body.

The Nervous System has several divisions. Anatomically, it is divided into:

  • Central Nervous System (CNS): brain and spinal cord;
  • Peripheral Nervous System (PNS): nerves and nerve ganglia that connect the CNS to the body’s organs.

Anatomy of the Central Nervous System

The Central Nervous System is formed by the brain and spinal cord . We can say that it is located inside the axial skeleton, even if some nerves penetrate the skull or spine.

The Central Nervous System is protected by bone parts. The brain is protected by the skull and the spinal cord by the spine.

Anatomy of the Central Nervous System
Anatomy of the Central Nervous System

Anatomy of the Central Nervous System


The brain is formed by the brain, cerebellum and brain stem. It has around 35 billion neurons and weighs approximately 1.4 kg.


The brain is the most massive portion and the main organ of the Nervous System. He is responsible for commanding motor actions, sensory stimuli and neurological activities such as memory, learning, thinking and speech.

It is formed by two halves, the right and left hemispheres, separated by a longitudinal fissure. The two hemispheres comprise the telencephalon.

They work together, however, there are some specific functions for each hemisphere. The right hemisphere controls the left side of the body and the left hemisphere controls the right side.

Blood flow in the brain is quite high, surpassed only by the kidneys and heart.


The cerebellum or metencephalon represents 10% of the volume of the brain. It is related to the maintenance of body balance, control of muscle tone and motor learning.

Thus, as in the brain, the cerebellum has two hemispheres separated by a narrow band, the vermis.

Brain Stem

The brain stem consists of the midbrain, bridge and bulb.

The midbrain is the smallest part of the brain stem, located between the bridge and the brain. The bridge is located between the midbrain and the bulb. In the bulb, the lower part connects to the spinal cord and the upper part to the bridge.

Spinal cord

The spinal cord is the longest part of the central nervous system. It is characterized by a cylindrical cord, composed of nerve cells, located in the internal channel of the vertebrae of the spine.

The function of the spinal cord is to establish communication between the body and the nervous system. It also coordinates reflexes, occasions when the body needs a quick response.

It is from the spinal cord that the 31 pairs of spinal nerves originate. They connect the spinal cord to sensory cells and various muscles throughout the body.

Learn more about the Nervous System.


The entire Central Nervous System is covered by three membranes that isolate and protect it, the meninges.

The meninges are:

  • Dura mater : It is the most external, being thick and resistant. Formed by connective tissue rich in collagen fibers. Its outermost portion is in contact with the bones.
  • Arachnoid : It is the intermediate membrane, between the dura and the pia mater. Its structure looks like a spider web, hence its name.
  • Pia mater : It is the most internal and delicate, in direct contact with the CNS.

The arachnoid and pia mater are separated by cerebrospinal fluid or cerebrospinal fluid . It provides mechanical protection and shock absorption to the organs of the Central Nervous System. It still provides nutrients to the brain.

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