Cerebrum

The cerebrum is the largest and most prominent part of the human brain, occupying the uppermost region of the cranial cavity. It is responsible for a wide range of complex functions including voluntary motor activity, sensory perception, speech, reasoning, learning, memory, and emotional regulation. It is divided into left and right hemispheres and is highly convoluted to maximize cortical surface area.

Structure

The cerebrum is composed of two hemispheres — left and right — connected by a thick band of white matter called the corpus callosum. Each hemisphere is further divided into four lobes: frontal, parietal, temporal, and occipital. The surface of the cerebrum is characterized by ridges called gyri and grooves called sulci. Deep grooves, such as the longitudinal fissure and lateral sulcus, demarcate major divisions between lobes and hemispheres.

• Cerebral cortex: The outermost layer of gray matter, responsible for conscious thought, perception, and voluntary motor activity.
• White matter: Subcortical tissue that contains myelinated axons facilitating communication between brain regions.
• Basal nuclei: Deep gray matter structures involved in motor control, including the caudate nucleus, putamen, and globus pallidus.
• Limbic structures: Includes the hippocampus and amygdala, involved in memory and emotion.

Location

The cerebrum is located in the supratentorial compartment of the cranial cavity, above the tentorium cerebelli. It overlays the diencephalon and brainstem and fills most of the cranial vault. The central sulcus separates the frontal lobe from the parietal lobe, while the lateral sulcus separates the frontal and parietal lobes from the temporal lobe.

Hemispheres and Lateralization

The left and right cerebral hemispheres are structurally similar but functionally specialized. In most right-handed individuals, the left hemisphere is dominant for language, logic, and analytical tasks, while the right hemisphere is more involved in spatial awareness, creativity, and holistic processing. The hemispheres communicate via commissural fibers, primarily through the corpus callosum.

Lobes of the Cerebrum

Frontal Lobe

• Located anterior to the central sulcus.
• Contains the precentral gyrus (primary motor cortex), premotor cortex, Broca’s area (speech production), and prefrontal cortex (executive functions).

Parietal Lobe

• Located posterior to the central sulcus.
• Contains the postcentral gyrus (primary somatosensory cortex), responsible for processing tactile sensory information.

Temporal Lobe

• Located inferior to the lateral sulcus.
• Contains the primary auditory cortex, Wernicke’s area (language comprehension), and hippocampus (memory formation).

Occipital Lobe

• Located at the posterior pole of the brain.
• Contains the primary visual cortex and visual association areas.

Function

The cerebrum governs higher cognitive functions and integrates input from various sensory modalities to generate appropriate responses. Major functional domains include:

• Motor control: Voluntary movements initiated by the primary motor cortex in the frontal lobe.
• Sensory processing: Interpretation of touch, temperature, pain, and proprioception by the somatosensory cortex.
• Visual processing: Managed by the occipital lobe.
• Auditory processing: Handled by the temporal lobe.
• Language: Broca’s area for speech production and Wernicke’s area for comprehension.
• Memory: Hippocampus and adjacent temporal structures are key for memory encoding and retrieval.
• Emotional regulation: Limbic structures, especially the amygdala, influence emotional behavior.
• Executive functions: Prefrontal cortex handles planning, decision-making, and social behavior.

Blood Supply

The cerebrum receives its blood supply from three main pairs of cerebral arteries:

• Anterior cerebral artery (ACA): Supplies the medial portions of the frontal and parietal lobes.
• Middle cerebral artery (MCA): Supplies most of the lateral surfaces of the cerebral hemispheres.
• Posterior cerebral artery (PCA): Supplies the occipital lobe and inferior temporal lobe.

These arteries are branches of the internal carotid and vertebral-basilar systems and are connected via the Circle of Willis.

Venous Drainage

Venous blood from the cerebrum drains into the dural venous sinuses via superficial and deep cerebral veins. Major sinuses include the superior sagittal sinus, straight sinus, and transverse sinuses, which ultimately drain into the internal jugular veins.

Development

The cerebrum develops from the telencephalon, the anterior-most part of the embryonic forebrain. By the fifth gestational week, the telencephalic vesicles expand and differentiate. Neuronal migration and cortical folding begin by mid-gestation and continue postnatally. The cerebral cortex becomes increasingly convoluted, forming gyri and sulci that allow for greater surface area and functional complexity.

Histology

The cerebral cortex is made up of six distinct layers of neurons (in most areas), known as the neocortex. These layers include pyramidal cells, interneurons, and glial cells. The white matter beneath contains bundles of myelinated axons organized as projection fibers (to/from subcortical regions), commissural fibers (between hemispheres), and association fibers (within a hemisphere).

Clinical Significance

• Stroke: Interruption of cerebral blood flow can lead to infarction, commonly affecting the MCA territory.
• Epilepsy: Abnormal cortical discharges originate in the cerebrum and can cause seizures.
• Neurodegenerative diseases: Conditions like Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease involve progressive cerebral atrophy or dysfunction.
• Brain tumors: Gliomas, meningiomas, and metastases can affect different parts of the cerebrum, leading to focal neurological deficits.
• Trauma: Traumatic brain injury often involves contusions or diffuse axonal injury in cerebral regions.
• Aphasia: Language disorders due to damage to Broca’s or Wernicke’s areas.