Anatomy of the brain

What is the brain?

Your brain is the most complex organ in your body. It consists of over 100 billion specialized nerve cells called neurons and it acts as a command centre for everything you do, think, sense and say. These neurons depend on the blood vessels in your brain for oxygen and nutrients. Neurons cannot duplicate or repair themselves.

Different parts of the brain control different functions. When someone has a stroke, the functions that are affected depend upon which area of the brain was damaged and how much damage occurred. Learning what the different parts of the brain do can help you understand why the effects of stroke can be so different among different people.

What are the parts of the brain?

The brain is divided into three areas, the brain stem, cerebellum and cerebrum:

Brain Stem

The brain stem sits at the base of the brain and connects to the top of your spine. It maintains important body functions such as breathing, swallowing, digestion, eye movement and your heartbeat. Strokes in the brain stem are often fatal, but when they are not, they affect many of these functions.


The cerebellum is located at the bottom of the brain, at the back of your head. It is attached to the back of the brain stem, and looks like a miniature brain. It helps control some automatic responses and behaviours, simple movements such as picking up a small object, and more complicated tasks such as balancing. A stroke in this part of the brain could cause a lack of coordination, clumsiness, shaking or other movement disorders.


Also known as the "thinking brain," the cerebrum is the main, bulky part of your brain. This is where thinking and muscle control occurs. The cerebrum is made of two halves or hemispheres. Each hemisphere is divided into portions called lobes.

Usually, one of these hemispheres is slightly more developed and is called the dominant side. The dominant side is where written and spoken language is organized. In almost all of us, the left hemisphere is dominant even if you are right handed. Because the nervous system is set up in a cross-over design, the right side of your brain controls the left side of your body, and vice versa.

Right hemisphere
The right side of the brain controls artistic functions such as music, awareness of art and insight. It also controls the ability to understand spatial relations, recognize faces and focus your attention on something. People with a stroke on the right side may have trouble with these functions.

Left hemisphere
The left side of the brain is responsible for scientific function, such as the ability to work with numbers (mathematical skills) and reasoning. It also is largely responsible for the ability to understand spoken language and the written word.

The lobes

The entire cerebrum is made up of two layers. The outermost layer is called the cerebral cortex (gray matter). The cortex is deeply wrinkled and three of the deepest folds are used to artificially divide the hemispheres into four distinct areas or lobes.

Frontal lobe: In each hemisphere, the frontal lobe is responsible for movement (motor functions). A stroke in the right side of the frontal lobe will affect your ability to move the left side of your body, and vice versa.

Parietal lobe: Behind the frontal lobe lies the parietal lobe. It is concerned mainly with sensory activities, such as receiving and interpreting information from all parts of the body. A stroke to the parietal lobes in the right hemisphere can cause agnosia, which means you can feel, see and hear, but may not be able to understand what you are perceiving. In other cases, a condition called neglect may develop. People with neglect have many sensory problems on the stroke-involved side of the body. As a result, they may ignore everything on that side.

Temporal lobe: The temporal lobe controls hearing and memory and is also involved with auditory perception. Strokes in the temporal lobe of the dominant hemisphere (usually the left hemisphere) can cause a speech disorder known as Wernickes aphasia. Memories are stored in the inner part of the temporal lobe. Unless both the left and right lobes are damaged, memory loss after stroke is usually only temporary.

Occipital lobe: The occipital lobe lies at the back of the head and is responsible for vision. A stroke in the left occipital lobe may result in losing the right side of your vision. Damage to the right occipital lobe can cause vision loss on your left side. In both cases, the eyes are functioning normally and the problem lies with the brain's ability to process information from the eyes.

Last reviewed: April 2011.