Anatomy Of The Human Brain

Overview

Although every living organism on Earth has one, the human brain is different from any other brain.

It is responsible for controlling and performing all the functions in our body such as breathing, blood pressure, heart rate, metabolism, etc.

First, it gathers information from the environment through the five senses. Then, it interprets it and finally responds to the interpreted stimuli. The brain is also responsible for our dreams, thinking, emotions, movement, sitting, speaking, etc.

Even though it weighs only about 1300-1400 grams on average, it consists of about 86 billion neurons – nerve cells. Brain processes are comparable to the world telephone network because they are both composed of a large number of wires and signals that are activated on a daily basis.

However, the functioning of the brain is even more complex. If there is a wire break or a signal transmission problem, the damage is quickly repaired and the telephone network resumes normal operation.

On the other hand, even the smallest injury or difficulty results in breaking of all the connections in the area – as if all telephone wires in one city were cut off. Recovery may take a year or even longer.

Neurons

Neurons consist of the cell body and the extensions by which they receive and send signals – nerve impulses (2).

The signal is sent to another cell through an axon, a long branch, while the neuron receives nerve impulses from other cells through dendrites, shorter branches.

The axon contains end nodules filled with chemical substances that reach the neighboring neuron, thus transmitting a nerve impulse. The signal can be sent to another neuron or any part of the body. Therefore, a nerve cell is called a neuron and it consists of the 3 main parts:

1.    Cell body

The main part of a neuron that consists of the fundamental parts of each cell: the nucleus, ribosome, etc. If the damage occurs to the body of a neuron, it can no longer function, that is, it is destroyed.

2.    Axon

The longest extension of a neuron that transmits a nerve impulse to other cells by chemical substances located at the ends of the neuron.

3.    Dendrites

These are the tiny extensions of neurons that merge with the axon of another nerve cell.  Thus it helps to convey the message.

Neurons differ in the functions they perform:

a) Sensory neurons – They transmit a signal from different parts of the body to the central nervous system.

b) Motor neurons – They transmit a signal from the central nervous system to different parts of the body.

c) Receptors – They take information from the environment and translate it into an electrochemical impulse.

d) Interneurons – They connect neurons from the brain to those in the spinal cord.

Receiving and transmitting information

Almost all information from the body passes through the spinal cord, which is connected to the brain at the very bottom. Without the spinal cord, we would not be able to move or feel any stimuli.

Only visual and auditory information go directly to the brain. As a result, during paralysis, people cannot move or feel parts of the body lower than the neck, but normally they see and hear. The spinal cord receives stimuli from the body which then travels to the midbrain and finally reaches the surface of the brain.

The human brain is divided into two parts: the right and the left. The right half is in charge of the visual stimuli so it collects all the information coming from the visual receptors. The left half of the brain analyzes that information and names it.

As a result, by using the right half of the brain, we recognize objects, while using the left half of the brain helps us name those things that we had already identified with the right half.

Parts of the brain and brain anatomy

1.    The cerebellum

It is located in the back of the cranial cave (1). The gray mass is located on the surface, while the white mass is located in the interior.

Its key function is coordinating the movements of the hands and feet, which are controlled from the center of the brain and influenced by our will. It is important for walking and standing.

It is the center of our balance. It coordinates reflexive and voluntary movements. It is where some cognitive functions take place.

For example, attention and language processes happen in the cerebellum. The cerebellum is a center for coordinating movements, planning, and balance.

2.    The telencephalon

It occupies the largest part of the cranial cavity (2). With its furrows and twists, it is divided into both the left and right hemispheres.

It is divided into 4 lobes:

Frontal lobe – the center of personality and planning

Parietal lobe – the center for touch

Temporal lobe – the center for sound and sound coordination with the image

Occipital lobe – an area for seeing and storing visual memory

The key functions of the telencephalon include intelligence, memory center, opinion, learning, behavioral control, etc.

3. The Amygdala – the center of our emotions

The amygdala is made up of two interconnected glands, almond-shaped and sized, located on either side of our brain near the temples (2). It houses the memories that cause our fears.

Therefore, when one is in a state of fear, these glands immediately send an alarm to the rest of the brain. Consequently, your heart starts beating rapidly, your palms are sweating and you are in a prestressed state. The amygdala decides when and how we feel, it is a sensor of positive or negative energy.

It is also responsible for the perception of music. The information first arrives in the amygdala, which evokes repressed memories of the specific melody and stimulates the response of emotions in accordance with it (sadness, relaxation, anxiety, happiness, …).

The amygdala helps us recognize danger. Without this part of our brain, we would not recognize the fears, feelings, people – our relatives, even those who are the closest to us.

4.    The Diencephalon – The posterior part of the Forebrain

The main sections of the diencephalon include the thalamus, hypothalamus, and epithalamus (1).

Thalamus is a steam structure consisting of a series of nuclei (about 35), which have the function of receiving impulses, processing them and transferring them to certain sensory areas of the cerebral cortex; receive impulses from other parts of the thalamus that are associated with areas of the forebrain.

Hypothalamus is very important for regulating the automatic functions related to the internal organs. It supervises body temperature, heart rate, blood pressure, eating, drinking, and is involved in managing emotions and motivation. It is associated with the pituitary gland.

Epithalamus is a part of the central nervous system that includes the epiphysis and some smaller parts of the brain.

There are also two endocrine glands in this part of the brain. Those are the Pituitary and the Pineal gland.

The pituitary gland is a gland with internal secretion. It has a form of a pea associated with the hypothalamus.

It secretes hormones that enhance or weaken the function of some other glands. In other words, this gland represents the brain for other glands. It affects kidney function, blood pressure, and the flow of substances through the body.

It itself produces important hormones, such as growth hormone, luteinizing hormone, prolactin, ACT hormone, oxytocin, antidiuretic hormone, and melanocyte.

The Pineal gland is an organ that has a comb-like shape. It is located exactly where the two cerebral hemispheres are separated. It is the first gland to develop in our body (5-8 mm).

Around 75 % of the light introduced through the eyes reaches into the hypothalamus and then goes into the epiphysis, stimulating it to secrete the hormones into the brain and blood (all other glands receive energy from the body).

The epiphysis or the pineal gland is considered to be the connection between the mind and the body. It is in charge of the man’s universal understanding of life, the world. Simply put, we see through our eyes, but we understand through the pineal gland.

Thanks to the sunlight (the basic food for the pineal gland), every cell of our body, every organ (liver, kidneys, skin, …) gets energy. It boosts the immune system, the circulatory system, the motoric system, our sleeping rhythm, and generally our mood.

The pineal gland secretes the hormone of happiness –serotonin. When the night falls, the pineal gland turns this particular hormone into melatonin, which is further transmitted to the brain and blood.

Melatonin is responsible for the regeneration of the internal organs, skin, hair, sexual organs (regulation of the menstrual cycle). Moreover, it is responsible for a youthful appearance and quality of sleep.

5. Brain Stem

The brain stem or the Truncus encephali in Latin consists of the midbrain, the medulla oblongata or the long medulla, the Varoli’s bridge, the spinal cord, and the spinal cord.

The midbrain has a complex structure, with a mixed gray and white mass, connecting the fourth to the third brain chamber(2). Many centers of the autonomic nervous system are located in the lower parts of the brain stem.

On the back, there are two pairs of nodules: the lower –auditory nodules, which are parts of the auditory tract and the upper –visual nodules, responsible for receiving information from the retina and the cerebral cortex and serve to adjust the position of the eye.

The function of the brainstem is related to vision, hearing, sleep, arousal, attention, and temperature control. It controls muscle tension and maintains body position.

Medulla oblongata connects the brain and the spinal cord and forms part of the central nervous system. Its function is important because it houses the centers that control reflex functions such as breathing, digestion, blood flow, blood pressure, coughing, swallowing, …It is often referred to as the Node of Life because it contains centers that manage life-important functions.

Varoli’s bridge connects the cerebellum and the midbrain to build a brain stem. Its function is maintaining balance and position of the head and body in space.

It receives impulses from the receptors important for maintaining the balance of the middle ear, adjusts facial mimicry, receives stimuli from the skin on our face, ears, and teeth.

It is important for chewing and sucking, as well as defense reflex centers for tears and blinking. It also houses a center that interrupts spontaneous inhalation and thus regulates breathing frequency.

The spinal cord allows the passage of nerve impulses from different parts of the body to the brain and vice versa – reflexes of movement, posture, muscle spasms. It also conducts the functions of the spinal cord.

6. Hippocampus

It is a horseshoe-shaped brain region that helps fuse information from short-term memory into long-term memory (2). It is a part of the limbic system associated with emotions and long-term memory.

It participates in the formation, organization, and storage of memories. Due to the amount of the receptors for Glucocorticoid hormones, it is extremely susceptible to degenerative processes, mainly related to chronic stress, psychiatric diagnoses, but also endocrine disorders (related to the thyroid gland).

7.  Brain envelopes

These structures protect the brain, create a supporting frame for arteries and veins, and form venous sinuses, close the fluid-filled cavity, a subarachnoid space necessary for a normal brain function.

8. Gray and white matter

These matters ensure a good connection between the center and the periphery of the brain. The brain, cerebral cortex, and the spinal cord are made up of gray and white matter (1).

Gray matter is built up from nerve cells and dendrites and processes impulses.

White matter is built up from axons of the nerve cells enveloped in a myelin sheath. The impulses are transmitted in a certain direction through the white matter. White matter connects different brain regions. Memory loss is associated with the white matter and impairment of cognitive functions.

References

  1. Marshall JC, Morriss-Kay GM. Functional anatomy of the human brain. J Anat. 2004 Dec;205(6):415. doi: 10.1111/j.0021-8782.2004.00360.x. PMCID: PMC1571395.  Found online at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1571395/
  2. Batista-García-Ramó K, Fernández-Verdecia CI. What We Know About the Brain Structure-Function Relationship. Behav Sci (Basel). 2018 Apr 18;8(4):39. doi: 10.3390/bs8040039. PMID: 29670045; PMCID: PMC5946098.Found online at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5946098/