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School of Medicine
How the Brain Works
The brain is a soft mass of supportive tissues and nerves connected to the spinal cord. Some of the nerves in the brain go right to the eyes, ears and other parts of the head. Other nerves connect the brain with other parts of the body through the spinal cord to control personality, senses and body functions from breathing to walking.
Together, the brain, spinal cord and nerves form the central nervous system.
Learning about how the brain and spinal cord work will help you better understand brain tumors:
- What a brain tumor is
- The symptoms of brain tumors
- How a brain tumor is diagnosed
- How a brain tumor is treated
Main parts of the brain
The brain has three main parts:
- Brain stem
The cerebrum, the large, outer part of the brain, controls reading, thinking, learning, speech, emotions and planned muscle movements like walking. It also controls vision, hearing and other senses.
The cerebrum is divided two cerebral hemispheres (halves): left and right. The right half controls the left side of the body. The left half controls the right side of the body.
Each hemisphere has four sections, called lobes: frontal, parietal, temporal and occipital. Each lobe controls specific functions. For example, the frontal lobe controls personality, decision-making and reasoning, while the temporal lobe controls, memory, speech, and sense of smell.
The cerebellum, in the back of the brain, controls balance, coordination and fine muscle control (e.g., walking). It also functions to maintain posture and equilibrium.
The brain stem
The brain stem, at the bottom of the brain, connects the cerebrum with the spinal cord. It includes the midbrain, the pons, and the medulla. It controls fundamental body functions such as breathing, eye movements, blood pressure, heartbeat, and swallowing.
Protecting the central nervous system
Because of the fragility of the brain and spinal cord, the human body has a built-in defense system against injury.
The skull and the meninges — the lining of the brain — protect the brain, while the bones of the spinal column protect the spinal cord, and cerebrospinal fluid surrounds and cushions both the brain and the spinal cord.
The skull is the bony framework of the head made up of 21 bones. The cranium, the part of the skull that covers the brain, is made up of four major bones: frontal, occipital, temporal and parietal. The skull base, the bony shelf, is made of a complex series of bones that also interact with the bones of the neck and face. There are four other bones in the cranium: two temporal bones, on the sides and base of the skull, and two parietal bones, at the top of the skull.
The meninges are three layers of tissue. The outermost layer, the dura mater, is thick and like leather. The second and third layers, the arachnoid and pia mater, are thin.
Cerebrospinal fluid is a watery fluid that flows in and around the four hollow spaces of the brain (called ventricles) and the spinal cord, and between two of the meninges. The ventricles are connected.
The spinal column (also called the backbone) starts at the base of the skull and goes down to the tailbone. It has 33 irregular, spool-shaped bones (vertebrae) that are stacked on each other and protect the spinal cord. The spinal column is divided into five sections: cervical, thoracic, lumbar, sacral* and coccygeal*.
(* By adulthood, the 5 sacral vertebrae fuse to form one bone, and the 4 coccygeal vertebrae fuse to form one bone.)
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