The brain is an organ that, together with the spinal cord, forms the central nervous system (CNS). Each part of the brain has a different job. The different parts of the brain are connected to each other in complex networks that control and coordinate everything we do.
Here are some examples of functions that the brain controls:
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movement such as walking or stretching
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seeing, smelling, touching, tasting, and hearing (the five senses)
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emotions, thoughts, and memory
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breathing and heartbeat
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digesting food
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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 about the different parts of the brain and what they do, how the brain is organized, and what parts make up the brain.
There are three major parts of the brain: the cerebrum, the cerebellum, and the brainstem.
The cerebrum
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 five 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” and deeper structures: the basal ganglia and the limbic system.
The cerebral cortex is divided into the right and left cerebral hemispheres. In most people, the two hemispheres perform distinct functions:
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The left hemisphere plays an important role in language, verbal memory, reading, writing, and arithmetic. It is concerned with sensation and movement on the right side of the body.
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The right hemisphere plays a large part in interpreting what we see and touch, and in non-verbal memory, music, and emotions. It is concerned with sensation and movement on the left side of the body.
The left hemisphere dominates language in almost all right-handed people and in many left-handed people. In some people, though, the two hemispheres share the language function more equally, and in a few people the right hemisphere may be dominant for language function.
The left and right cerebral hemispheres are connected by a bundle of nerve fibres called the corpus callosum, which allows the two cerebral hemispheres to communicate.
Each hemisphere is divided into lobes: frontal, temporal, parietal, and occipital lobes.
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The frontal lobes are large, complex structures. They contain the motor cortex, which controls movement, and are important for speech, planning, problem solving, social and emotional behaviour, self-awareness, and self-control.
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The occipital lobes contain the primary vision centres as well as areas that help us visually recognize objects and understand what written words mean.
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The temporal lobes are the main area responsible for memory about facts and events. Together with the limbic system, they help us express emotions and understand the emotions of other people. They seem to have an effect on personality. They are also very important for hearing, and help us understand language and sounds such as music.
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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, texture, and direction.
These functions often overlap in areas where two lobes meet. For instance, the area where the parietal and temporal lobes meet is responsible for helping us recognize faces.
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 is a complex network of brain areas that includes the amygdala and the hippocampus, as well as the interior parts of the temporal, frontal, and parietal lobes. The limbic system is the “primitive” or “animal” part of our brain. It controls our immediate, automatic responses to stimuli -- our “gut reactions.”
The amygdala and hippocampus are located next to the temporal lobes and communicate closely with them. The amygdala coordinates how emotions affect the autonomic and endocrine systems (for instance, the “fight or flight” response, which causes us to breathe quickly and produce adrenaline in response to fear). The hippocampus is important for storing long-term memories.
The cerebellum
The cerebellum is located under the cerebrum at the back of the brain. It coordinates our balance and complex movements. 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.
The brainstem
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.
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The midbrain is located between the pons and the cerebral hemispheres. It allows messages to be relayed for sight and hearing, and is also involved in movement.
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The pons sends messages between the cerebrum and cerebellum and the spinal cord.
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The medulla oblongata connects the brain with the spinal cord. Together with the pons, it controls autonomic functions such as breathing and heartbeat.
Other structures and nerves are associated with the brainstem. The thalamus and the hypothalamus sit above the brainstem and below the cerebrum. The 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 to and from 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 are cranial nerves?
The 12 pairs of cranial nerves connect to the brainstem and the thalamus. Except for the vagus nerve, these nerves send and receive information from the sense organs and muscles of the head, neck, and shoulders. Each nerve has a special role. The nerves and the functions they control are shown in the illustration.
The ventricular system and cerebrospinal fluid
The brain also contains four fluid-filled structures called ventricles, which make cerebrospinal fluid (CSF).
What are ventricles?
The ventricular system consists of four fluid-filled spaces in the brain called ventricles. The ventricles are connected by tubes and holes. The choroid plexus is a structure in the ventricles that produces cerebrospinal fluid (CSF).
The ventricles are located in the following areas:
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The first two ventricles are located in the cerebral hemispheres. They are called the lateral ventricles.
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The third ventricle is in the centre of the brain. The thalamus and hypothalamus make up part of its walls.
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The fourth ventricle is behind the brainstem (behind the pons and medulla oblongata), between the brainstem and the cerebellum.
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 meninges (the layers of tissue that cover the brain and spinal cord). 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 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 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.
Three layers of tissue called the meninges cover the brain and spinal cord.
The brain is also cushioned by CSF. It flows through the ventricles and in the spaces around the meninges.
The brain is covered by bones called the cranium. The bones of the cranium, together with other bones that protect the face, form the skull.
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. Like the brain, the spinal cord is covered by three layers of tissue called the meninges and cushioned by CSF. It is protected by a bony covering called the vertebral or spinal column.
What are the meninges made of?
The meninges are made up of three thin layers of tissue. They are called the dura mater, the arachnoid, and the pia mater. CSF 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. It consists of a body, where chemicals called neurotransmitters are produced, and a long axon that connects to other neurons. There are about 100 billion neurons in the human brain.
What are neuroglial cells?
Neuroglial cells, or neuroglia, protect and support nerve cells. These cells are also called glia or glial cells. Some different types of neuroglial cells are oligodendroglia, astrocytes, and ependymal cells.
What is a synapse?
A synapse is the gap between neurons. Nerve impulses (messages) travel through the synapse from one neuron to the next by means of chemicals called neurotransmitters.
What is a neurotransmitter?
A neurotransmitter is a chemical that carries a message from one neuron to the next across a synapse. If enough neurotransmitter molecules pass from one neuron to the next, they have an effect on that neuron. Some neurotransmitters excite neurons, causing them to fire; others suppress or inhibit them. Examples of neurotransmitters are gamma-aminobutyric acid (GABA), glutamate, neuropeptide Y, and dynorphin.
What is an ion channel?
Ion channels are proteins in the cell membrane that act as tiny gates or switches to control the flow of specific ions, and therefore electrical current, through the cell. There are different ion channels for sodium, potassium, calcium, and chloride ions, and different neurotransmitters switch on different ion channels. Differences in the mix of channels on a cell, the number of channels that are open or closed, and the balance of ions inside and outside the cell all have an effect on cell function and communication from one neuron to the next.
How does the brain work?
Millions of messages constantly move between different parts of the brain and along the nerves to and from the rest of the body.
These messages are tiny electrical impulses that propagate or travel along bundles of nerve fibres and between individual neurons. The impulses move from one neuron to the next by means of neurotransmitters. A neurotransmitter molecule is released by the first neuron and travels across the synapse. When it connects with a receptor on the second neuron, that neuron receives a message. What the second neuron does next depends on:
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the type of neurotransmitter: some are excitatory, causing neurons to fire, others are inhibitory, preventing them from firing
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the type of receptor
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what the neuron has just been doing
If enough neurons are excited or inhibited at the same time, there is an effect. If the neurons are in the part of the brain that controls movement, a body part moves. If they are in a part of the brain that controls emotion, you feel fear or happiness or another emotion.
Something as simple as noticing a pencil and picking it up involves many steps:
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Light bounces off the pencil, into your eye and off your retina.
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Receptors in the retina fire and send messages along the optic nerve to the occipital lobe of the brain.
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When the neurons in the occipital lobe get the message, they send further messages to other parts of the brain. These confirm that you are looking at a pencil and not a pen or a mug, decide whether you want it, and figure out how to get it.
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The planning areas of the brain send a message to the motor cortex, telling it to reach your hand over to where the pencil is.
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Neurons in the “hand and arm” section of the motor cortex fire. This sends electrical impulses to the muscles in your arm and hand, which move.
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When your fingers are touching the pencil, special touch receptors in the skin detect it. They fire, sending yet another message along the nerves to the sensory cortex in the brain.
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Various areas of the brain figure out whether your fingers are holding the pencil firmly enough and tell the motor cortex to lift your hand, with the pencil in it.
Obviously, the brain performs most of these steps without you having to think about it. You are only conscious of seeing the pencil and picking it up -- the whole process may take only a fraction of a second.