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The Human Brain, Explained

Learn about the most complex organ in the human body, from its structure to its most common disorders.
The brain is the most complex organ in the human body. As part of the nervous system, the brain coordinates all of the body’s functions. In adult humans, the brain is a three pound gelatinous mass of fat and protein. It’s comprised of four main regions– the cerebrum, the cerebellum, the brainstem, and the diencephalon. And each one controls specific tasks. The largest section is the cerebrum. And it makes up over 3/4 of the brain’s volume. It consists of neurons and nerve fibres that transmit information from the neurons throughout the brain and body. The cerebrum controls higher functions such as learning, reasoning, and speech, plus senses like sight and hearing.
Under the cerebrum is the second largest part of the brain, the cerebellum. Much like the cerebrum, the cerebellum has nerve cells and nerve fibres. It carries signals to other parts of the brain and the spinal cord. The cerebellum is responsible for coordinating muscle movements, particularly those that help maintain the body’s balance and posture. The third region, the brain stem, lies in front of the cerebellum and anchors the brain to the spinal cord.
The brain stem is a collection of structures that include the pons– a mass of nerve fibres that carry sensory information, the midbrain– a region of fibres and structures that help control movement along with auditory and visual processing, and the medulla oblongata, which creates motor and sensory pathways between the midbrain, the pons, and the spinal cord. Altogether, the parts of the brain stem controlled vital bodily functions such as cardiac activity, respiration, digestion, and sleep.
The fourth region is located above the brain stem and makes up the core of the brain, the diencephalon. About the size of an apricot, the diencephalon is a grouping of several structures. The thalamus, which processes and transmits information from all senses except smell, and the hypothalamus and pituitary gland, which work together to produce and regulate neurochemicals. These structures help govern sensations, weight regulation, energy, and instinctual behaviours such as eating, drinking, and having sex.
The brain’s four main components, the diencephalon, brain stem, cerebellum, and cerebrum work in sync to ensure bodily functions are fully operational. The brain has even evolved mechanisms to protect itself. One such mechanism is the blood brain barrier, a semi permeable cellular wall that only allows specific chemicals to enter from the body’s bloodstream into the brain. Despite this protection, tumours and other complications can lead to life threatening problems and diseases in the brain, such as dementia. Thankfully, scientists have found ways to improve brain health. Staying physically active and eating a balanced diet may preserve cognitive function and even reduce the risk of developing Alzheimer’s.
So while the brain only makes up a small percentage of the body, it plays a crucial role in the body’s functions and overall well-being.

Learn about the most complex organ in the human body, from its structure to its most common disorders.

As part of the body’s nervous system, the brain coordinates all of the body’s functions. Weighing in at around 1.4 kg (3 pounds), the human brain is more complex than any other known structure in the universe and is responsible for all of the body’s functions and learning.

It is comprised of 4 regions:

  • Cerebrum – ¾ of the brain’s volume – controls higher functions such as learning, reasoning, speech and senses (sight and hearing).

  • Cerebellum – coordinates muscle movements (balance and posture).

  • Brain Stem – sensory information, movement, auditory and visual processing – the motor and sensory pathways responsible for cardiac activity, respiration, digestion and sleep.

  • Diencephalon – made up of the thalamus, hypothalamus and pituitary gland – these regulate sensations, control weight, energy and instinctual behaviours.

After watching the video above, consider the following question:

What activities improve brain health?


Zuckerman, C (2009, Oct 15). The human brain, explained Learn about the most complex organ in the human body, from its structure to its most common disorders. National Geographic . Retrieved from:​
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