Brain 101

The Brain

The brain is the body’s control centre. It’s made up of billions of nerve cells called neurons. The neurons are arranged in patterns that work together to control how we think, feel, act, see, taste, touch, and move. They also control our breathing, heart rate, and blood pressure.

Each neuron gives off chemicals that trigger an action in other neurons. These chemicals are called neurotransmitters (like epinephrine, norepinephrine, or dopamine). They act like messages that are sent down through the axon, or tail, to other cells. Where it meets is called the synapse. How fast the message is sent depends on the path to the cell (the axon) and how they “talk” to each other through the chemicals released at the synapse (Figure 1).​​


Figure 1: A nerve cell

Information goes through many nerves that connect to certain parts of the brain: One main route from the brain to the rest of your body is the spinal cord.

Messages sent to your brain tells it about things like hot and cold, pressure, pain, and where your arms and legs are positioned.

Other nerves carry information from the eyes, ears, tongue, and muscles on the face to the brain. These are called cranial nerves.

The brain then sends messages to the muscles through a different set of nerves so you can do things like move, walk, talk, and swallow.

The brain is covered by three layers (membranes). These are called the dura, arachnoid, and pia mater (Figure 2).


Figure 2: Three membranes covering the brain

The brain and spinal cord sits in a clear fluid that bathes the brain and circulates into the ventricles of the brain. This is called the cerebrospinal fluid or CSF (Figure 3).


Figure 3: CSF bathing brain

Four major arteries supply the brain with oxygen and other nutrients:

  • two vertebral arteries that follow the spinal column up into the brain
  • two carotid arteries that come up on either side of the throat

These four major arteries branch and join to form a network that carries oxygen, nutrients, and blood to the brain (Figure 4).


Figure 4: Arteries to the brain

Areas of the Brain

The brain is divided into two halves (called cerebral hemispheres). While the two halves look nearly the same, they do different things.

For most people, the left half of the brain controls verbal functions like language, thought, and memory-involving words.

The right half controls non-verbal function like recognizing the differences in visual patterns and designs, reading maps, and enjoying music. The right half is also involved in expressing and understanding emotions.

Although each half of the brain does different things, the two parts actually work closely together to control the activity of the body. The left side of the brain controls movement and sensation in the right side of the body and the right side of the brain controls movement and sensation in the left side. This means that damage to the right side of the brain may cause movement problems or weakness left side of the body.

Left side of the brain
Right side of the brain
​Controls the right side of the body. Controls the left side of the body.
​Listening, reading, speaking, and writing. Judging the position of things in space and knowing body position in space.
​Memory for spoken and written messages. Understanding and remembering things we do and see.
​Analyzes information in detail. Putting bits of information together to make up an entire picture.
​Receives sensation signals from the right side of the body and space. Receives sensation signals from the left side of the body and space.

The two halves of the brain are divided into four areas called lobes, the cerebellum, and the brain stem (Figure 5). Each area of the brain has a different function.


Figure 5: Four lobes of the brain and the brain stem

Occipital lobe

  • Damage to the left occipital lobe may cause problems seeing things on the right side of space.
  • Damage to the right occipital lobe may cause problems seeing things on the left side of space.

Parietal lobes

  • Damage to the left parietal lobe may lead to problems in reading and math. It can also cause a loss of sensation on the right side of the body. This means that the person would have changes in how he feels touch or pain, his vision, or temperature changes on his right side.
  • Damage to the right parietal lobe may lead to problems with spatial tasks, like making sense out of pictures, diagrams, and reading maps. Damage to the right lobe may cause changes in sensation on the left side.

Frontal lobes

Damage to either frontal lobe may lead to problems with emotional control, social skills, judgment, planning, and organization.

  • Damage to the left frontal lobe may cause problems with speech and moving the right arm or leg.
  • Damage to the right frontal lobe may cause problems moving the left arm or leg.

Temporal lobes

  • Damage to the left temporal lobe may cause problems in understanding and remembering language.
  • Damage to the right temporal lobe may cause problems in understanding and remembering non-verbal information such as pictures, diagrams, body language cues, and other visual messages.

Brain stem

The brain stem is the control centre for breathing and for the heartbeat. Damage to the brain stem can cause many physical and sensory problems. The brain stem gives commands to the muscles of the face, eyes, mouth, and throat.


Damage to the cerebellum may cause problems with co-ordination, balance, or muscle tone in different parts of the body.

Print this Brain Injury Worksheet and ask your healthcare provider to review the area(s) of the brain that have been injured.​

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