An Overview of the Brain

The brain is an organ located inside your head. The brain and the spinal cord form the central nervous system. This complex system controls everything we do. Each part of the brain has a different job. Here are some examples of functions that the brain controls:

  • movement such as walking or stretching
  • seeing, smelling, touching, tasting, and hearing (the 5 senses)
  • emotions, thoughts, and memory
  • breathing and heartbeat
  • digesting food
  • talking and understanding

The brain is like a busy city. Each part has different functions and is made up of different types of cells. To work, different parts of the brain need to send messages to each other, and to other parts of the body.

Read further to find out the different parts of the brain and what they do, how the brain is organized, and what the brain is made of.

Brain Anatomy
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Parts of the brain

There are three major parts of the brain: the cerebrum, the cerebellum, and the brainstem.

What does the cerebrum do?

The cerebrum is often used as another word for the brain. It is the largest part of the brain and fills most of the upper skull. The cerebrum uses information from our 5 senses to help us understand what is happening around us. Then it tells our body how to respond. It also controls our emotions, and our ability to talk, think, read, and learn. The surface of the cerebrum is called the cerebral cortex or “grey matter.” Underneath the surface is the “white matter.”

Cerebral Hemispheres
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The left cerebral hemisphere controls the right side of the body. The right cerebral hemisphere controls the left side of the body.
The cerebrum has two parts: the right and left cerebral hemispheres. In most people, they perform the following functions.

The left hemisphere plays an important role in language, verbal memory, reading, writing, and arithmetic. It controls the muscles on the right side of the body.

The right hemisphere plays a large part in interpreting what we see and touch, and in non-verbal memory, music, and emotions. It controls the muscles on the left side of the body.

Each hemisphere is divided into lobes: frontal, temporal, parietal, and occipital lobes.

  • The frontal lobes are large, complex structures. They control movement of the eyes, and are important for speech, planning, problem solving, social behaviour, self-awareness, and self-control.
  • The occipital lobes contain areas that help us visually recognize objects, and understand what written words mean.
  • The temporal lobes are the main area responsible for memory and emotion. They are also very important for hearing, and help us understand language and sounds such as music.
  • The parietal lobes interpret sensations and messages from other parts of the brain. They make connections between the information from all the different senses and store memories. These lobes interpret touch, temperature, pain, sounds, and visual information about objects and the environment. They help us understand shape, size, and direction.

What does the cerebellum do?

The cerebellum is located under the cerebrum at the back of the brain. It coordinates our balance and movement. For example, actions such as walking or playing the piano are coordinated by the cerebellum. It contributes to the control of speech, and also participates in many of the functions controlled by the cerebrum in ways that are not understood fully.

What does the brainstem do?

The brainstem connects the brain and the spinal cord. It passes messages back and forth between parts of the body and the brain. The brainstem controls functions such as breathing, blood pressure, body temperature, heart rhythms, hunger and thirst, and sleep patterns. It is made of three parts: the midbrain, pons, and medulla oblongata.

  • The midbrain is located between the pons and cerebral hemispheres. It allows messages to be relayed for sight and hearing.
  • The pons sends messages between the cerebrum and cerebellum and the spinal cord.
  • The medulla oblongata connects the brain with the spinal cord. It controls breathing, our heartbeat, and vomiting.

Other important parts of the brain

Some other important parts of the brain are the thalamus, the hypothalamus, the pituitary gland, the basal ganglia, and the limbic system. The brain also contains four fluid-filled structures called ventricles, which make cerebrospinal fluid (CSF). Twelve cranial nerves start in the brainstem and direct many functions, such as smelling and moving our eyes.

What does the thalamus do?

The thalamus is a structure located on top of the midbrain. All the messages for the cerebrum pass through the thalamus. It has a role in feeling pain.

What does the hypothalamus do?

The hypothalamus is below the thalamus. It helps control appetite, sleeping, body temperature, emotions, and blood pressure. It releases important hormones, which are chemical signals, to the pituitary gland.

What does the pituitary gland do?

The pituitary gland is attached to the hypothalamus. It receives messages from the hypothalamus. It also releases important hormones, which are chemical signals to other parts of the body.

What do the basal ganglia do?

The basal ganglia are a group of structures around the thalamus, including the putamen, globus pallidus, and caudate nucleus. The basal ganglia are important for voluntary movement.

What does the limbic system do?

The limbic system consists of several parts including the amygdala and hippocampus. The amygdala and hippocampus are located next to the lateral ventricles in the temporal lobes. The limbic system is important for two reasons. First, it is important for the control of emotional behaviour, and second, it is important for storing long-term memories. The hippocampus is necessary to perform this second function.

What is the ventricular system?

The ventricular system consists of 4 fluid-filled spaces in the brain called ventricles. The ventricles are connected by tubes and holes (foramen). The choroids plexus is a structure in the ventricles that produces cerebrospinal fluid (CSF).

The ventricles are located in the following areas:

  • The first two ventricles are located in the cerebral hemispheres. They are called the lateral ventricles
  • The third ventricle is in the centre of the brain. The thalamus and hypothalamus make up part of its walls.
  • The fourth ventricle is behind the brainstem (behind the pons and medulla oblongata), between the brainstem and the cerebellum.

Cerebrospinal Fluid
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What is cerebrospinal fluid (CSF)?

CSF is a clear fluid that is produced by cells in the ventricles. CSF flows through the ventricles and in the space between the layers of tissue that cover the brain and spinal cord ( meninges). CSF carries nutrients from the blood to the brain and spinal cord, removes waste products from the brain, and cushions and supports the brain and spinal cord.

What are cranial nerves?

There are 12 pairs of nerves that leave from underneath the brain. These are called the cranial nerves. Except for the vagus nerve, these nerves send and receive information from the sense organs and muscles of the head, neck, and shoulders. All but the olfactory and optic nerves connect to the brainstem. Each nerve has a special role. Here are the nerves and the functions they control.

Brain Organization

Different areas of the brain are also described by their location with respect to the tentorium.

Cranial Nerves
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What is the tentorium?

This is a flap made of the meninges folded back on itself. It separates the cerebrum from the cerebellum.

What is the supratentorium?

This is an area at the top of the brain above the tentorium. It contains the cerebrum and other parts of the brain.

What is the infratentorium?

This is an area at the back of the brain below the tentorium. It contains the cerebellum and the brainstem. It is also called the posterior fossa.

What is posterior fossa?

This is an area at the back of the brain that contains the cerebellum and the brainstem. It is also called the infratentorium.

What is the brain made of?

The brain is made up of two types of cells. One type is nerve cells, which are called neurons. The other type is supporting cells, which are called neuroglial cells.

The brain is covered by bones called the cranium. The cranium, together with other bones that protect the face, form the skull.

Three layers of tissue called the meninges cover the brain and spinal cord.

The brain is also cushioned by a clear liquid called cerebrospinal fluid (CSF). It flows through the ventricles and in the spaces around the meninges.

The surface of the cerebrum, called the cortex, is made up of the cell bodies of neurons and supporting neuroglial cells. Because of its colour, it is called “grey matter." Underneath the cortex, the axons of the neurons and supporting neuroglial cells form “white matter.” Axons are like wires that carry messages between neurons.

Grey Matter and White Matter
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The outer layer (or cortex) of the brain is called grey matter, and is made mostly of neuron cell bodies and synapses. White matter is underneath the grey matter, and is made up of long neuronal axons covered by a fatty sheath called myelin. Myelin insulates the axons and facilitates the conduction of electrical impulses.
What is the spinal cord made of?

The spinal cord is made up of neurons that connect the brain to most parts of the body. The spinal cord is covered by 3 layers of tissue called the meninges. Like the brain, the spinal cord is cushioned by a clear liquid called cerebrospinal fluid (CSF). It is protected by a bony covering called the vertebral or spinal column.

What is the meninges made of?

The meninges has three thin layers of tissue. They are called the dura mater, the arachnoid, and the pia mater. Cerebrospinal fluid flows in between the arachnoid and pia mater membranes. This area is called the subarachnoid space.

What is a neuron?

A neuron is a nerve cell that sends and receives messages.

What are neuroglial cells?

Neuroglial cells, or neuroglia, protect and support nerve cells. These cells are also called glia or glial cells. They are the most common type of cells involved in brain tumours. Some different types of neuroglial cells are oligodendroglia, astrocytes, and ependymal cells.

Eric Bouffet, MD, FRCPC