Anatomy And Physiology

Anatomy Physiology



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The brain is a pretty unprepossessing pinkish-grey organ that fills the head, and, merely looking at it, one would be hard pressed to believe that it is by far the most important organ in our bodies, for this less than attractive looking mass is a phenomenal piece of equipment which coordinates all the multifarious activities that are required so that we can continue to live and function; activities ranging from such unconscious ones as breathing to the most conscious ones such as driving a car. The brain, which is the core of the central nervous system, may be viewed as one super duper computer, faster, more energy efficient and carrying out more tasks every minute than the combination of all the Cray and Fujitsu super computers on earth could. Indeed, in the entire known universe, the human brain is the most complex piece of equipment in existence, albeit the least understood. So, what's with this magnificent piece of equipment?

The human brain is divided into three main parts. (i) The cerebrum, or front part, is the larger part of the brain and is divided into two sections or hemispheres which are mirror images of each other, and which are connected one to the other by a thick bundle of nerves called the corpus callosum. The right hemisphere receives and processes information from and controls the actions of the left side of the body and vice versa. Amongst right handed people, who constitute the vast majority of the human population, the left hemisphere controls such skills as talking, reading and writing, while the right hemisphere takes charge of such things as artistic and imaginative activity, but the functions may be reversed amongst left handed people. (ii) The cerebellum, the lower posterior part of the brain, which is responsible for the co-ordination of voluntary movements and the maintenance of balance. (iii) The brain stem which connects the cerebrum and the cerebellum to each other and also to the spinal cord, together with which the brain forms the central nervous system. The human brain has the same general structure as do all mammalian brains, but compared to other animals, man is definitely brain heavy; factoring in body size, the human brain is 500% larger than the average mammalian brain!

It is estimated that the average brain contains something in the region of a hundred billion, yes, that's billion, microscopic nerve cells known as neurons; that's something like one cell for every star that forms part of the Milky Way, and more than all the humans who have ever lived and are likely to live for quite a considerable period of time to come! But, impressive as the numbers are, even more impressive is the connective activity that takes place in the brain.

Each and every neuron is equipped with a slender projection known as an axon which links the particular neuron to some other part of the central nervous system and some of these axons extend the entire length of the spinal cord, up to a metre or more, making them the longest cells in the human body (just imagine how long an axon would be in a blue whale!). But these 100 billion or so connections are only a small part of the story, for, in addition to the axons, each neuron comes complete with additional connectors known as dendrites, which may be as many as fifty thousand on a single neuron, with which it connects to its neighbouring neurons! We're talking tens and tens of trillions of connections, more than all the telephone and IT connections in the whole wide world right there in our little heads!

When sensory information reaches the brain, it is stored, analysed and acted upon by means of electrochemical impulses moving from neuron to neuron through the dendrite connection system. An incredible amount of information processing is going on in our brains 24 hours a day, seven days a week, for the brain never lets up; even when we are asleep, the brain is at work. Indeed, the average human brain processes more information every hour than all the information processing systems on earth could do in a week.

This wonderful little organ is, on average, about 3% of our total body mass and it will treble in size between birth and adulthood to an average of 1.4 kilograms for men and 1.3 kilograms for women, after which it starts to lose mass. By age fifty, the brain would have shed about 0.3 kilogram of its mass. The difference in size between the male and female brains is a mere statistic; it is a function of the difference in the average mass of men and women. Brain size has no correlation with intelligence. Interestingly,. From a Helium point of view, both the largest brain on record as well as the smallest belonged to writers. The Russian writer, Ivan Turgenev (1818-1883) has the record for the largest brain, weighing in at 2.012 kilograms. On the other hand, the French writer, Anatole France (1844-1924) has the record for the smallest brain, weighing in at 1.017 kilograms.

Given the sterling work that the brain performs, it will not come as a surprise that the brain is the most energy consuming organ in the human body. 20% of the oxygen that we breathe, 20% of all the calories that we consume and 15% of the entire blood supply in our bodies are reserved entirely for the brain. A sudden blockage or haemorrhage of an artery which supplies blood to the brain (a stroke), can produce catastrophic results such as an almost immediate loss of consciousness, function or even death.

The brain is the most protected organ in the human body, which is not surprising given its role in the continued survival of the human organism. Housed in the head, the brain is protected by the thick bones of the skull and it is protected by three membranes, meninges (singular: meninx), which provide further physical protection, as well as being suspended in a bath of cerebrospinal fluid which provides both physical and chemical protection and it is isolated from the blood stream by the blood-brain barrier. Yet in spite of this formidable array of protection, the brain faces considerable risk of injury or disease.. One major risk is that of physical damage resulting from strokes, blows to the head or poisoning from neurotoxins i.e. chemicals that injure the brain. Apart from physical injury, there is also the risk of infection, which can be serious when it occurs. The most common are genetically based diseases such as multiple sclerosis, Parkinson's disease, etc. Also, it is thought that some psychiatric disorders such schizophrenia may, at least to some extent, be caused by some form of brain dysfunction.

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