Human brain is the command center for the human nervous system. It receives signals from the body’s sensory organs and outputs information to the muscles. The human brain has the same basic structure as other mammal brains but is larger in relation to body size than any other brains.The brain is an amazing three-pound organ that controls all functions of the body, interprets information from the outside world, and embodies the essence of the mind and soul. Intelligence, creativity, emotion, and memory are a few of the many things governed by the brain. Protected within the skull, the brain is composed of the cerebrum, cerebellum, and brainstem.
The brain receives information through our five senses: sight, smell, touch, taste, and hearing – often many at one time. It assembles the messages in a way that has meaning for us, and can store that information in our memory. The brain controls our thoughts, memory and speech, movement of the arms and legs, and the function of many organs within our body.
The central nervous system (CNS) is composed of the brain and spinal cord. The peripheral nervous system (PNS) is composed of spinal nerves that branch from the spinal cord and cranial nerves that branch from the brain.
The brain works like a big computer. It processes information that it receives from the senses and body, and sends messages back to the body. But the brain can do much more than a machine can: humans think and experience emotions with their brain, and it is the root of human intelligence.
The human brain is roughly the size of two clenched fists and weighs about 1.5 kilograms. From the outside it looks a bit like a large walnut, with folds and crevices. Brain tissue is made up of about 100 billion nerve cells (neurons) and one trillion supporting cells which stabilize the tissue
The brain is composed of the cerebrum, cerebellum, and brainstem
Cerebrum: is the largest part of the brain and is composed of right and left hemispheres. It performs higher functions like interpreting touch, vision and hearing, as well as speech, reasoning, emotions, learning, and fine control of movement.
Cerebellum: is located under the cerebrum. Its function is to coordinate muscle movements, maintain posture, and balance.
Brainstem: acts as a relay center connecting the cerebrum and cerebellum to the spinal cord. It performs many automatic functions such as breathing, heart rate, body temperature, wake and sleep cycles, digestion, sneezing, coughing, vomiting, and swallowing
The cerebrum has a right half and a left half, known as the right and left hemispheres. The two hemispheres are connected via a thick bundle of nerve fibers called the corpus callosum. Each hemisphere is made up of six areas (lobes) that have different functions. The cerebrum controls movement and processes sensory information. Conscious and unconscious actions and feelings are produced here. It is also responsible for speech, hearing, intelligence and memory.
HOW IS THE BRAIN SUPPLIED WITH BRAIN?
The brain needs a steady flow of enough oxygen, glucose, and other nutrients. For that reason, it has a particularly good blood supply. Each side of the brain receives blood through three arteries:
- In the front, the anterior cerebral artery supplies the tissue behind the forehead and under the crown (the top of the head).
- The middle cerebral artery is important for the sides and areas that are further inside the brain. The anterior and middle cerebral artery split off from the internal carotid artery, a major blood vessel in the neck.
- The posterior cerebral artery supplies the back of the head, the lower part of the brain, and the cerebellum. It is supplied with blood from the vertebral arteries, which are also major arteries of the neck.
Before the three arteries reach “their” brain region, where they split into smaller branches, they are close together below the brain. In this area, they are connected to each other by smaller blood vessels – forming a structure similar to a traffic circle. The arteries are connected to each other in other areas as well. The advantage of these connections is that blood supply problems in the brain can be compensated for to some extent: For example, if a branch of an artery gradually becomes narrower, blood can still flow to the part of the brain it supplies through these alternative routes (collateral blood flow).
The smallest branches (capillaries) of the arteries in the brain supply the brain cells with oxygen and nutrients from the blood – but they do not let other substances pass as easily as similar capillaries in the rest of the body do. The medical term for this phenomenon is the “blood-brain barrier.” It can protect the delicate brain from toxic substances in the blood, for example.
After oxygen has passed into the cells, the oxygen-poor blood flows away through the veins of the brain (cerebral veins). The veins carry the blood to larger blood vessels known as sinuses. The sinus walls are strengthened by a tough membrane (Dura mater), which helps them keep their shape too. This keeps them permanently open and makes it easy for the blood to flow into the veins in the neck.