The brain in vertebrates basically comprises the three major parts: the hindbrain, midbrain, and forebrain. Cerebellum (Latin for little brain) is a region of the hind brain. Among mammals, the brain has two new structures: ‘neocerebellum’ that is added to the cerebellum and the ‘neocortex’ that grows out of the front of the forebrain, called the prefrontal and frontal lobes.
Human beings are blessed with large convoluted mass of this grey neural matter comprising neocerebellar and neocortical tissue in the form of extensive foldings, valleys and ridges, which increase the surface area of the cortex and allow a maximum amount of grey matter to be packed within the confines of the skull. This is the reason why human beings enjoy the largest ratio of brain weight to body weight as compared to that of any other life form. Other intelligent mammals like dolphins and chimpanzees also have convoluted brains as compared to the smooth brains of lesser intelligent animals.
The unique abilities of the human brain—the powers of speech and written language, the power of thinking, observing, planning, reasoning, imagining etc.., reside in the cerebral cortex and this makes us what we are, different from other animals. Although, the size of the brain does define the intelligence of that being, it is actually the brain weight in relation to body weight that is a good indication of intelligence. It is for this reason again that the tiny hummingbird having a brain weighing less than a gram is remarkably equipped with a marvelous variety of behaviours!
The human brain has evolved from 44g organ, about 3-4 million years ago, to the present size of 1500g (1.5kg) that comprises about 10 billion specialized neutrons, capable of receiving, processing and relaying the electrochemical signals which control all our sensations, actions, thoughts and emotions. Scientists believe that human evolution has exceptionally involved a large number mutations in a large number of genes, including several genes involved in brain development. Interestingly, human intelligence is not just attributed to the number of neurons that the brain possesses but more importantly, it is how these neurons are organized and interconnected that makes a difference. More connections mean more vibrant communication links between the interconnecting neurons that results in myriad complex functions of the human brain that make this organ unique to our species.
What are the building blocks of the Human Brain ?
Neurons are the building blocks of the brain. All neurons share common structural features. A neuron basically has a cell body or ‘soma’ that contains the nucleus which, in turns, houses the complete genetic blueprint of the organism. The nucleus is surrounded by cytoplasm, the chemical ‘soup’ of the cell that contains the organelles essential to the functioning of the neuron. Thus, neurons are similar to other body cells, except that unlike most other cells they rarely divide to reproduce new neurons. For carrying out specialized tasks, every neuron has complex communicative channels—the structures called ‘dendrites’ – which are like many tentacles of an antenna system that receive signals from other neurons.
As soon as a dendrite is stimulated on receiving a chemical signal from a neuron connected to it, this signal travels rapidly as an electrochemical impulse from the cell body moving along the neuron’s single axon where it gets picked up by the dendrites of other neurons. Although the size of the neuron’s body is usually small, the length of its axon could be considerable, which means that one neuron may influence the firing of another neuron connected to it but present far away.
The points where two interconnected neurons are joined with each other are special junctions called ‘synapses’. Known as ‘synaptic junctions’, they normally connect the axon of one neuron with the dendrites of another. Unbelievably, a typical neuron in the cortex of the human brain has about 10,000 synapses, which constitutes a complex wiring system that is unparalleled to the complexity of even the most advanced supercomputers! Basically, this intricate wiring of neurons in the human brain bestows it the most amazing abilities this organ possesses.
The brain comprises not only the excitable cells called the neurons but also the non-excitable, support cells called the ‘neuroglia’ that in Latin means ‘nerve glue’ which largely comprise the glial cells. Besides neurons and glial cells, the brain has many blood vessels – arteries, veins and capillaries that also serve the brain tissue.
New Study on evolution of Human Brain released