Human Brain Structure and Nervous System Functions

The brain comprises two hemispheres separated by a main path. It presents numerous folds called gyri, separated from each other by grooves or fissures.

Its activity causes the phenomenon of consciousness, which controls voluntary actions, receives information captured by the senses, interprets, and prepares a response. It is responsible for memory, creativity, ability to learn, and emotions. It is the basis of our intelligence.

It is located below the brain in the back. It is gray and is organized like the brain, divided into two hemispheres, with the area having deep grooves that delimit the cerebellar structures called lamellae. It presents external gray matter and internal white matter.

The cerebellum regulates and coordinates body movements. It receives information on the position of our body from the ear and is responsible for maintaining balance.

The brain stem connects the brain to the spinal cord, situated in front of the cerebellum. We distinguish three regions:

The medulla is located right at the base of the brain, continuing into the spinal cord. It is white because the gray matter is located on the outside and the white matter on the interior. At the bottom, motor and sensory nerve fibers cross from right to left and vice versa. Therefore, each cerebral hemisphere primarily controls the opposite side of the body. It regulates breathing, heart rate, and swallowing frequency.

The spinal cord is a cord-shaped organ, about 45 cm long, housed inside the cavity formed by the hole in the vertebrae along the spine.

In the spinal cord, the white matter (axons of neurons) is placed on the outside, and the gray matter is on the inside, unlike in the brain. In cross-section, it is shaped like butterfly wings or an H, with four outgoing horns from which nerve fibers leave or enter.

The spinal cord receives information from peripheral receptors and leads it to the brain, transmitting orders from the brain to the effector organs. It is also the center of reflex actions.

The reflex actions are movements that are performed automatically and involuntarily in response to certain stimuli, without the involvement of the brain.

The peripheral nervous system consists of ganglia and nerves.

Nerves are groups of neurons that connect the central nervous system and the different effector organs. Their function is to transmit information to the central nervous system and carry its replies to the effector organs.

The nerves are encased in sheaths formed by Schwann cells. In many nerve fibers, the sheath also produces the myelin sheath, a white fatty substance wrapping around the axon. Myelin is interrupted repeatedly; the area where myelin is absent is called the nodes of Ranvier.