The Anatomy of the Cerebrum

When most people envision the brain, they're thinking of the cerebrum. This largest portion of the brain fills the inside of the skull and is divided into two halves or hemispheres made up of the large folds and creases of tissue that give the brain its characteristic appearance. The cerebrum is responsible for processing sensory functions like vision, hearing, and touch, as well as engaging in reasoning and processing emotions—among many other tasks

Brain injuries and diseases can affect how the cerebrum functions and, by extension, can impact the way a person thinks, makes decisions, processes emotions, moves the body, or feels physical sensations.

The brain is the major part of every person's central nervous system (CNS), and the cerebrum is the largest portion of the brain. The two hemispheres of the cerebrum reside in the skull, above the brainstem (also called the "mid-brain") and the cerebellum at the very back (or bottom) of the brain.

The cerebrum is divided lengthwise into two halves, separated by a deep crease called the longitudinal fissure. From side-to-side, a crease called the central sulcus divides each hemisphere in half again.

Each hemisphere of the cerebrum contains four regions called lobes:

• Frontal lobe: resides at the very front of the brain and is responsible for personality traits and some smell processing
• Parietal lobe: located near the middle of the cerebrum, this area interprets pain and sensation, along with processing spatial relationships (such as the distance between your car and the one in front of you)
• Temporal lobe: sits at the sides of each hemisphere and is responsible for short-term memory, speech, and musical rhythm
• Occipital lobe: located at the very back of the cerebrum and is primarily responsible for vision processing

The cerebrum also contains many sub-structures that enable the brain to perform all the vital nervous functions required by the body:

• Corpus callosum: a band of tissue that joins the two halves of the cerebrum at the deep center of the brain. The corpus callosum coordinates nerve signals between the two hemispheres.
• Circle of Willis: a loop of arteries that receive blood from the two carotid arteries in the neck and the basilar artery near the base of the skull and then distribute the blood (oxygen) to the entire brain.
• Meninges: a trio of membranes that cover the cerebrum to protect it from traumatic injury and infection. The meninges also enclose the rest of the brain and the entire spinal cord. Three layers of tissues make up the meninges: the dura mater, a relatively fibrous tissue that sits between the bones of the skull and the cerebrum; the arachnoid, a delicate, fluid-filled structure that provides shock absorption in the event of brain movement; and the pia mater, a thin, paper-like structure that lays directly atop the cerebral tissue.

The cerebrum does not contain any muscles or ligaments, but it houses several different types of neurons (nerve cells). The three main types of nerve cells inside the cerebrum include:

• Sensory neurons (responsible for sensation)
• Motor neurons (responsible for voluntary and involuntary movement)
• Interneurons (nerves that connect with other nerves)

The role of the cerebrum is to coordinate and process sensory and motor functions required by the body, as well as to provide reasoning functions, process emotions and contribute the unique personality traits that make each human being an individual. The cerebrum performs these functions using communication between nerve cells. Some of these processes (such as reasoning) reside completely within the cerebrum itself, while other communications get transmitted down the spinal cord and out into the wider body via a network of neurons.

The cerebrum also processes signals returned to the brain from elsewhere in the body. Pain signals and other nervous communications travel up the spinal cord to the brain.

Traumatic injury and an array of medical conditions can affect the cerebrum.

• Brain trauma occurs if a high-force accident shakes the brain inside the skull or if a projectile penetrates the skull. This type of injury can cause many different types of problems with brain function depending on which areas of the cerebrum experienced the most tissue damage. Brain injury can cause trouble with reasoning, emotional regulation, and motor functions, among many other consequences.
• Infections like meningitis—inflammation of the meninges—can put pressure on delicate cerebral tissue and damage it. Similarly, hydrocephalus is a condition in which too much cerebrospinal fluid builds up under the arachnoid or within the cerebrum itself and raises pressure inside the skull cavity. Sometimes these conditions have no long-term effects on cerebral function, but other times they can result in significant brain damage.
• Cancerous and benign (non-cancerous) tumors can arise within the cerebral tissue. These lesions may require treatment, or doctors may take a "watchful waiting" approach to see if they cause symptoms like vision disturbance or personality changes.
• Stroke is a common condition that destroys cerebral tissue and often results in partial paralysis, difficulty speaking and other disabilities. Stroke occurs when a blood clot blocks oxygen from reaching a particular region of the brain or when a blood vessel inside the cerebrum bleeds onto the surrounding tissue, destroying it.
• Alzheimer's and other dementias have various causes. Alzheimer's appears to be caused by the buildup of certain types of plaques that interfere with neural communications. Vascular dementia may be caused by disease processes that cause narrowing of the cerebral arteries and disruption of blood flow within the cerebrum. Certain types of dementias, like Lewy body dementia, are associated with other conditions, such as Parkinson's disease. All dementias usually cause progressive memory loss, trouble with reasoning and sometimes personality changes.

Some cerebral conditions are not diagnosed primarily through medical testing. Diagnosing Alzheimer's disease, for example, may rely on a person's individual and family medical histories, as well as through cognitive function testing.

Other cerebral conditions may be diagnosed through different types of medical testing—alone, or in combination.

• Lumbar puncture may be used to obtain a sample of the cerebrospinal fluid for microscopic examination to determine if infection or inflammation is present.
• Imaging studies, including computed tomography (CT) and magnetic resonance imaging (MRI), can provide pictures of tumors or other structural abnormalities of the cerebrum.
• Neurological examinations that evaluate a person's strength and ability to perform common tasks like touching the nose with the fingers can be used to evaluate neural function.