The brain (from Latin cerebellum, diminutive of cerebrum) is the most complex organ in the human body. Seat of our thoughts, our emotions and master of our movements (except reflexes), it is the key element of the nervous system.

The brain belongs to the encephalon, which also includes the diencephalon, brainstem and cerebellum.

The brain is housed in the cranial box which protects it from shocks. It is also surrounded by three protective membranes, the meninges (dura mater, arachnoid, and pia mater). In adults, it weighs about 1,3 kg and contains several billion nerve cells: neurons. It is in suspension in the cerebrospinal fluid, a shock absorbing fluid which allows the transport of molecules and the recovery of waste.

External structure

The brain is divided into two parts: the right hemisphere and the left hemisphere. Each hemisphere controls an opposite part of the body: the left hemisphere controls the right side of the body and vice versa.

The left hemisphere is generally associated with logic and language, while the right is the seat of intuitions, emotions and artistic sense. They communicate through a structure of nerve fibers: the corpus callosum. The surface of the hemispheres is covered with cerebral cortex, it is the gray matter because it contains the cell bodies of the neurons. The cortex is traversed by convolutions, which are folds of the brain tissue.

Each hemisphere is divided into five lobes:

• the frontal lobe, in front, just behind the forehead
• the parietal lobe, behind the frontal
• the temporal lobe is on the side, near the temporal bone
• the occipital lobe, behind, at the level of the occipital bone
• a 5th lobe is not visible on the surface, it is the insula or island lobe: it is inside the brain.

The lobes are delimited between them by grooves, which are grooves on the surface of the cortex.

Cranial nerves originate in the brain and brainstem. There are twelve pairs of them that are involved in vision, taste, smell or hearing or even in the expressiveness of the face.

The brain is supplied by the left internal carotid artery and the vertebral artery, which provide nutrients and oxygen necessary for the proper functioning of cells.

Internal structure

The inside of the brain is made up of brain tissue called white matter. It is made up of nerve fibers that carry nerve impulses to or from the cortex. These fibers are surrounded by myelin, a whitish protective sheath (hence white substance) which accelerates the electrical transmission of nerve messages.

In the center of the brain are also chambers called ventricles which allow the circulation of cerebrospinal fluid.

The brain is:

• 2% of our weight
• 20% of the energy consumed

The brain communicates with the whole organism. This communication is provided largely by the nerves. The nerves allow the very rapid transmission of electrical messages such as nerve impulses.The brain, the body’s control tower

Associated with the spinal cord, the brain constitutes the central nervous system. This system is our command and control center: it interprets sensory information from the environment (inside and outside the body) and can send responses in the form of motor commands (activation of muscles or glands).

Functions such as speech, the interpretation of sensations or voluntary movements originate in the cerebral cortex. Neurons in the cortex interpret sensory messages and develop appropriate responses at regions specializing in information processing. These regions are found at the level:

• Of the parietal lobe, with the areas involved in sensory perceptions (taste, touch, temperature, pain)
• Of the temporal lobe, with the areas of hearing and smell, comprehension of language
• From the occipital lobe, with the centers of vision
• From the frontal lobe, with reasoning and task planning, emotions and personality, voluntary movements and language production.

Lesions in these areas can lead to malfunctions. For example, a lesion of the area dedicated to the production of language then suppresses the ability to pronounce the words. People know what they want to say but they cannot utter the words.

Stroke (stroke) : follows a blockage or rupture of a blood vessel, which causes the death of nerve cells. It includes cerebral embolism or thrombosis.

Alzheimer’s disease : neurodegenerative disease which causes a progressive decline of cognitive faculties and memory.

Epileptic crisis : is characterized by discharges of abnormal nerve impulses in the brain.

Depression : one of the most frequent psychiatric disorders. Depression is a disease that affects mood, thoughts and behavior, but also the body.

Brain-dead state (or encephalic death): state of irreversible destruction of the brain which results in a total cessation of cerebral functions and an absence of blood circulation. This condition may follow a head trauma or stroke, for example.

Hydrocéphalie : corresponds to an excess of cerebrospinal fluid in the brain when the evacuation of this fluid is not done correctly.

Headache (headache) : very common pain felt in the cranial box.

Charcot’s disease (amyotrophic lateral sclerosis or Lou Gehrig’s disease): neurodegenerative disease. It progressively affects the neurons and causes muscle weakness and then paralysis.

Parkinson disease : neurodegenerative disease that results from the slow and progressive death of neurons in an area of ​​the brain that plays an important role in controlling our movements. This is why people with the disease gradually make rigid, jerky and uncontrollable gestures.

Meningitis : inflammation of the meninges which may be caused by a virus or bacteria. That of bacterial origin is generally much more serious.

Migraine : particular form of headache which manifests itself in attacks that are longer and more intense than the headache.

Schizophrenia : psychiatric illness which causes so-called psychotic episodes: the affected person most often suffers from delusions and hallucinations.

Multiple sclerosis : autoimmune disease that affects the central nervous system (brain, optic nerves and spinal cord). It causes lesions which cause disturbances in the transmission of nerve messages which affects the control of movements, sensory perception, memory, speech, etc.

Head trauma : designates a shock received to the head at the level of the skull, regardless of its violence. They are very common and have different stages (weak, moderate, severe). Severe trauma causes brain damage and is the leading cause of death among 15-25 year olds. Road accidents are the main cause of injuries but also sports-related accidents or assaults.

Brain tumor (brain cancer): the multiplication of abnormal cells in the brain. The tumor maybe benign ou smart.

Prevention

In 2012, the World Health Organization (WHO) 6 estimated that 17,5 million deaths were due to cardiovascular disease such as stroke. Having a healthy lifestyle would prevent 80% of these strokes. Indeed, adopting a healthy diet, practicing regular physical activity and avoiding tobacco and excess alcohol would prevent these diseases.

According to the WHO (7), Alzheimer’s disease is the most common cause of dementia and causes 60-70% of cases. Unfortunately, there is no conclusive prevention technique. However, paying attention to your diet, maintaining physical activity and mental training are avenues for prevention. Other diseases, such as brain tumor or multiple sclerosis, cannot be prevented because the causes are unknown. Parkinson’s disease is not preventable either, but scientific research indicates certain behaviors that could provide so-called protective effects.

Preventing a headache is possible, however, when it is too persistent or the usual medications do not work. This prevention can involve reducing stress or reducing alcohol consumption, for example.

Treatments

Taking certain medications (including antidepressants, muscle relaxants, sleeping pills, anxiolytics, or even antihistamines for allergies) can cause memory loss. But in these cases, they can be reversible.

According to an American study (8), the exposure of pregnant women to very toxic atmospheric pollutants (resulting from the combustion of wood or charcoal for example) would cause disturbances in the development of the embryo. The children would present in particular behavioral problems and a decrease in intellectual capacities.

biopsy : examination which consists in taking a sample of the brain tumor in order to know the type of tumor and to choose the most suitable treatment.

Echo-doppler transcrânien : test which observes the circulation of blood in the large vessels of the brain. It allows, among other things, the evaluation of head trauma or the diagnosis of brain death.

Electroencéphalogramme : test that measures the electrical activity of the brain, it is mainly used to diagnose epilepsy.

Brain MRI : magnetic resonance imaging technique, MRI is an examination allowing the detection of brain abnormalities. It is used, among other things, to confirm the diagnosis of stroke or the detection of a tumor.

PET scan : also called positron emission tomoscintigraphy, this functional imaging examination makes it possible to visualize the functioning of organs by injection of a radioactive liquid visible in imaging.

Brain and spinal scanner : also called computed tomography or computed tomography, this imaging technique uses X-rays to visualize the structures of the skull or spine. It is the main examination for the detection of cancer.

Physical examination : it is the first step in any diagnosis of disorders of the brain or nervous system. It is performed by an attending physician or a brain specialist. First, he asks the patient about his family history, his symptoms, etc. then he performs a physical examination (checking reflexes, hearing, touch, vision, balance, etc.) (9).

Lumbar puncture : cerebrospinal fluid sampling using a needle from the lower back (lumbar vertebrae). In this case, its analysis can determine the presence of cancer cells.

First discoveries

The electrical nature of nerve messages was first demonstrated by an Italian physician, Luigi Galvani in 1792, through an experiment on a frog’s paw! Almost two centuries later, in 1939, Huxley and Hodgkin first recorded an action potential (nerve impulse) in a giant squid nerve fiber (10).

Brain size and intelligence

Scientists have long believed that brain size and intelligence could be linked. According to an international study11, intelligence is not determined by the size of the brain, but rather by its structure and the connections between white matter and gray matter. It is also mentioned that men, who generally have larger brains than women, did not exhibit higher intellectual functions. Likewise, participants with unusually large brains scored below average on intelligence tests.

For example, Einstein had a smaller than average brain.