The human brain is a soft, greyish-pink, deeply-grooved organ weighing about 1.4 kg and occupying most of the space within the skull. It consists of an enormous number of nerve cells, nerve fibers and connecting and supporting tissue.
It is surrounded by the meninges (three membranes), between two of which lies a layer of fluid, the cerebrospinal fluid, that bathes the human brain and helps to cushion and protect it. The human brain has many connections with the rest of the body using nerves.
Those nerves that supply structures in the head run directly into the brain; those for the remainder of the body are connected to the brain by way of its extension, the spinal cord.
What are the functions of the human brain?
The human brain is the central controlling organ of the body, the initiator of all bodily movement, the information center of the body and the seat of consciousness and pleasure.
It holds the memory, which includes a record of all the significant individual experiences and learning undergone from birth, that also underlies the personality and capabilities of the individual. Moreover, the brain incorporates data relating to inherited instincts and normal human patterns of response.
How is the human brain constructed?
The largest part of the human brain is called the cerebrum, containing much of the brain’s gray matter. It consists of two almost identical mirror-image hemispheres connected by a large knot called the corpus callosum.
Beneath and towards the back of the cerebrum, is the cerebellum, a smaller structure concerned mainly with body balance and the coordination of controlled movements.
Just in front of the cerebellum, and running downwards from the middle of the underside of the cerebrum, is the brain stem. This is a thick stalk carrying significant nerve tracts from the brain down into the spinal cord and containing the origins of most of the 12 pairs of nerves which emerge directly from the brain.
From the human brain stem, the spinal cord runs down through a large hole in the base of the skull to occupy a canal in the spine from where it sends out nerves to all parts of the body.
The cerebral cortex (thin outer layer of the cerebrum) is divided into areas that operate or coordinate various functions such as voluntary movement, the first senses, speech, language comprehension, visual interpretation, and so on.
Memory is not located in any particular area but is distributed throughout the brain. However, the functions of registration and recall of memories are found in a known area. Compound nerve connections between the different parts of the cortex are the basis for all the higher functions such as imagination, creativity, intellectual ability, learning, social responsibility and artistic skills.
These connections form part of the white matter below the cortex. The more primitive functions such as bodily appetites, hunger, sexual interest, the emotions, automatic responses, and aggression, are served by nerve cell masses (ganglia) lying in the white matter near the base of the cerebrum.
How does the human brain control the body?
At all times, even during sleep, the human brain is receiving information. This comes from the eyes, the ears, the nerve endings for the smell in the nose, the taste buds on the tongue, and from specialized nerve endings in the surface of the skin, in the muscles, joints, and internal organs.
From all these sources the brain is continuously supplied with data about the environment, about the relative position of the limbs and the state of the internal organs. Some of this incoming information never reaches consciousness but results in automatic adjustment of the many functions of the body.
However, a great deal of it results in conscious awareness of external events, or of some change in bodily function or state, and the brain response by initiating voluntary action.
What is the human brain damage?
This can mean the kind of significant injury involved in a severely depressed skull fracture, with laceration of the brain, or damage to the nerve cells, which cannot repair or recover.
The commonest cause of brain damage is a deprivation of oxygen, glucose, and other nutrients, usually from an inadequate blood supply. Cerebral thrombosis (blockage of the human brain arteries by blood clots) or cerebral hemorrhage (bleeding into the brain substance) cause strokes. Other causes of brain damage include:
- Major head injuries, without necessarily fracturing the skull.
- Exposure to toxic substances, primarily excess alcohol.
- Asphyxia (suffocation) leading to inadequate oxygen in the blood.
- Cardiac arrest with the undue delay in restarting the heart.
- Partial drowning.
- Bacterial toxins which may be released in the course of brain infection.
- Meningitis (inflammation of the meninges).
- Encephalitis (brain inflammation) almost al-ways caused by a virus, including HIV.
- Repeated small hemorrhages caused by blows sustained in boxing.
- Multiple sclerosis (a progressive degeneration of the nervous system).
- Degenerative brain disease, for example, Alzheimer’s disease.
- Brain tumors, either arising in the brain substance or metastases from other parts of the body.
Any such damage may have the same range of effects, at widely varying severities. These include paralysis, loss of sensation, visual field loss, amnesia (loss of memory), mental defect, speech disturbances, aphasia (loss of word comprehension), apraxia (loss of motor skills) and disturbances of thought and judgment.
Severe brain damage may result in amentia (almost complete loss of all the higher mental functions).