An intricate network of over a hundred billion wires running across the control unit sending messages at about 100 metres per second. That’s the human brain! Come to think of it, the lines that Emily Dickinson wrote make perfect sense:

“The Brain — is wider than the sky —For put them side by side      The one the other will containWith ease — and You — beside”

An organ that weighs just about a kilo and a half and controls the actions and behaviour of a person, the human brain is truly a wonderful organ.

Parts of the Brain

Parts of a Human Brain.

The brain is divided into three parts — cerebrum, cerebellum, and brainstem. The cerebrum is the largest part of the brain, where functions like touch, vision, hearing, speech, learning, emotions, and reasoning are interpreted. It is divided into two hemispheres — Left and Right hemispheres, each of these hemispheres are divided into four regions called lobes. The four lobes — frontal lobe, parietal lobe, occipital lobe, and temporal lobe — are further divided into smaller areas that perform specific functions. The frontal lobe is the seat of functions like emotions, speech, body movement, intelligence, and problem-solving ability. The parietal lobe, on the other hand, interprets languages, the sense of touch, signals from hearing, seeing and orientation. The occipital lobe interprets vision including light, colour, and movement. And the temporal lobe has areas that govern memory, hearing, organization, and understanding a language.

Under the cerebrum is the cerebellum, a part that constitutes about 11 per cent of the brain. This part of the brain coordinates muscle movements and helps in maintaining posture and balance. It fine-tunes thoughts, emotions and senses. It also helps with learning.

The brainstem, which is situated below the cerebellum and runs to the spinal cord, controls the automatic functions of the body. These functions include breathing, body temperature, wake and sleep cycles, heart rate, blood pressure, digestion, vomiting, coughing, and swallowing.

Cells of the brain

Each of these parts is made up of cells — the wires of the system — that can be classified into two main types: (i) the neurons, (ii) the glia. While neurons send messages across, the glia support and protect the neurons.

Let’s zoom into a neuron. A neuron has these basic parts — a cell body, an axon, and dendrites. The cell body is the heart of the neuron. The short offshoots that project outward from the cell body are called dendrites. Then there is the long extension from the cell body, called the axon. Covering most of the axon is a layer made up of fat called the myelin sheath.

The brain is made up of about 86 million neurons.

Zoom out a bit. Neurons form such complex networks and lie so close to each other. But they have gaps in between them. They are placed such that the dendrites of one neuron lie close to the axon of another. The gap between these is called a synapse. 

How these cells work

The neurons relay information by sending and receiving electrical impulses, and by using chemicals called neurotransmitters. When a neuron is activated, it sends an electrical impulse from the cell body to the end of the axon. But there should be a way to send this information from one neuron to another across the synapse. Here, the neurotransmitters come to help. The information is carried from one neuron to the next through neurotransmitters that are stored in small pouches called vesicles. These neurotransmitters, therefore, activate the next neuron and the process continues.

Electrical or chemical signals are passed from one neuron to another.

Some examples of these neurotransmitters are glutamate, dopamine, acetylcholine, etc. Neurons are classified into different types based on the neurotransmitter they release. For instance, neurons that release dopamine are called dopaminergic neurons. Likewise, there are different types of neurons in the brain, which release different kinds of neurotransmitters and thus help in performing different kinds of functions. 

Summary

In summary, the brain is a “Wonder Organ” that regulates all the activities of mammals. It is divided into three major parts — cerebrum, cerebellum, and brainstem. Each of these parts is made up of cells called neurons or glia. Neurons send and receive messages to and from different parts of the body using a combination of electrical signals and chemical neurotransmitters. A snap in this network — a broken wire or lack of neurotransmitters — would crash the system. It could affect your memory, hamper your movement, paralyze you, or even kill you.

This article is a part of the series on Neurodegeneration. Find the rest of the articles from this series here.

Illustrator: Leeba Ann Chacko

Edited by: দেবদত্ত পাল। Debdutta Paul