Cerebrum

The cerebrum is the largest part of the human brain and is responsible for higher brain functions, including voluntary movement, sensory perception, cognition, and language. It is divided into two hemispheres and is highly convoluted to increase surface area, allowing for complex neural processing. Understanding its anatomy and function is essential in both clinical and research settings.

Introduction

The cerebrum, also known as the telencephalon, constitutes the bulk of the brain’s mass and forms the superior portion of the cranial cavity. It integrates sensory inputs, executes voluntary motor actions, and mediates complex behaviors such as reasoning, learning, and memory. Its structural organization includes cortical and subcortical regions that interact to support a wide range of neurological functions.

Anatomy

Gross Anatomy

The cerebrum consists of two cerebral hemispheres separated by the longitudinal fissure. Each hemisphere is divided into four major lobes:

• Frontal lobe: involved in motor control, executive functions, and personality.
• Parietal lobe: responsible for somatosensory processing and spatial orientation.
• Temporal lobe: involved in auditory perception, memory, and language comprehension.
• Occipital lobe: dedicated to visual processing.

The surface of the cerebrum contains gyri and sulci, which increase the cortical surface area. Key landmarks include the precentral gyrus (primary motor cortex), postcentral gyrus (primary somatosensory cortex), and central sulcus, which separates the frontal and parietal lobes.

Cortical Layers

• The neocortex consists of six layers (I–VI), each containing distinct neuron types and connections.
• Layer I: molecular layer, contains mostly dendrites and axons.
• Layer II–III: involved in corticocortical communication.
• Layer IV: primary recipient of thalamic sensory input.
• Layer V: contains large pyramidal neurons projecting to subcortical structures.
• Layer VI: provides feedback to the thalamus.

Subcortical Structures

• Basal ganglia: involved in motor control and coordination.
• Internal capsule: major white matter tract connecting cortex with subcortical structures.
• White matter tracts: include corpus callosum for interhemispheric communication and association fibers connecting different cortical regions.

Ventricular System

• Lateral ventricles located within each hemisphere contain cerebrospinal fluid and the choroid plexus.
• Ventricular system facilitates cushioning, nutrient transport, and waste removal.

Blood Supply

• Anterior cerebral artery: supplies medial and superior aspects of frontal and parietal lobes.
• Middle cerebral artery: supplies lateral cortical surfaces, including primary motor and sensory areas.
• Posterior cerebral artery: supplies occipital lobe and inferior temporal lobe.

Nerve Supply and Connections

• Corticospinal and corticobulbar tracts mediate voluntary motor control.
• Commissural fibers, such as the corpus callosum, allow interhemispheric communication.
• Association fibers connect different regions within the same hemisphere, enabling integrated processing.

Physiology

Motor Functions

The cerebrum controls voluntary movements through the primary motor cortex located in the precentral gyrus. Signals from pyramidal neurons are transmitted via the corticospinal and corticobulbar tracts to skeletal muscles, allowing precise motor control. Premotor and supplementary motor areas contribute to planning and coordinating complex movements.

Sensory Functions

• Somatosensory information from the body is processed in the postcentral gyrus, enabling perception of touch, pressure, pain, and temperature.
• Visual information is primarily processed in the occipital lobe, while auditory information is processed in the temporal lobe.
• Integration of multisensory input allows spatial awareness and coordinated responses.

Cognitive Functions

• Memory and learning are mediated by interactions between the temporal lobe, hippocampus, and associated cortical regions.
• Language processing involves Broca’s area in the frontal lobe for speech production and Wernicke’s area in the temporal lobe for comprehension.
• Executive functions, decision-making, and problem-solving are largely localized to the prefrontal cortex.

Integration and Coordination

Interhemispheric communication via the corpus callosum allows coordination between the two hemispheres. Cortical-subcortical interactions, including feedback from the basal ganglia and thalamus, facilitate smooth execution of motor and cognitive tasks.

Development

Embryology

• The cerebrum develops from the telencephalon during embryogenesis.
• Lobes and cortical layers differentiate from the ventricular zone through processes of neuronal proliferation, migration, and differentiation.
• Subcortical structures, including the basal ganglia, arise concurrently to support motor and cognitive functions.

Postnatal Development

• Synaptogenesis occurs extensively during the first few years of life, establishing cortical networks.
• Myelination of white matter tracts continues into adolescence, enhancing signal conduction and neural efficiency.
• Refinement of sensory and motor pathways allows improved coordination and cognitive abilities over time.

Neuroplasticity

• The cerebrum exhibits plasticity, allowing reorganization of cortical circuits in response to learning, experience, or injury.
• Neuroplastic changes can aid recovery following stroke, trauma, or surgical intervention.
• Environmental enrichment and rehabilitation therapies enhance adaptive cortical remodeling.

Clinical Correlations

Neurological Disorders

• Stroke: Ischemic or hemorrhagic events affecting specific cerebral regions, leading to motor, sensory, or cognitive deficits.
• Traumatic Brain Injury: Focal or diffuse injury causing structural and functional impairment of the cerebrum.
• Tumors: Primary or metastatic lesions can compress cortical or subcortical structures, resulting in neurological symptoms.

Neurodegenerative Diseases

• Alzheimer’s Disease: Progressive cortical atrophy primarily affecting memory and cognitive function.
• Parkinson’s Disease: Cortical involvement may occur alongside basal ganglia pathology, contributing to cognitive and executive dysfunction.
• Huntington’s Disease: Degeneration of cortical and subcortical regions leading to motor, cognitive, and behavioral impairments.

Seizure Disorders

• Focal seizures arise from localized cortical areas, whereas generalized seizures involve widespread cerebral networks.
• Epileptogenic zones within the cerebrum may be identified through imaging and electrophysiological studies.

Behavioral and Cognitive Impairments

• Aphasia: language deficits depending on involvement of Broca’s or Wernicke’s areas.
• Apraxia: inability to perform purposeful movements despite intact motor function.
• Hemispatial neglect: often resulting from parietal lobe lesions, leading to impaired spatial awareness.

Imaging and Diagnostic Evaluation

CT and MRI

• Computed tomography (CT) allows rapid assessment of structural abnormalities, hemorrhage, and mass effect.
• Magnetic resonance imaging (MRI) provides detailed visualization of cortical and subcortical structures, enabling detection of infarcts, tumors, and demyelinating lesions.

Functional Imaging

• Functional MRI (fMRI) identifies areas of cortical activation during specific tasks, useful in pre-surgical planning.
• Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) evaluate cerebral metabolism and perfusion.

Electrophysiological Studies

• Electroencephalography (EEG) records cortical electrical activity, aiding in diagnosis of seizures and encephalopathies.
• Evoked potentials assess sensory and motor pathway integrity and cortical responsiveness.

Surgical and Therapeutic Considerations

Neurosurgical Approaches

• Craniotomy for tumor resection, hemorrhage evacuation, or decompression of mass effect.
• Deep brain stimulation targeting subcortical structures to manage movement disorders or epilepsy.
• Minimally invasive techniques, including endoscopic approaches for select lesions.

Rehabilitation

• Cognitive therapy to restore memory, attention, and executive functions after cerebral injury.
• Motor rehabilitation focusing on strength, coordination, and balance to recover voluntary movement.
• Occupational and speech therapy to improve daily functioning and communication skills.

Pharmacologic Management

• Medications affecting cortical neurotransmission, such as cholinesterase inhibitors for cognitive impairment.
• Antiepileptic drugs for seizure control originating from cerebral foci.
• Neuroprotective agents under investigation to limit secondary injury after stroke or trauma.

References

1. Purves D, Augustine GJ, Fitzpatrick D, et al. Neuroscience. 6th edition. Sunderland: Sinauer Associates; 2018.
2. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd edition. London: Elsevier; 2020.
3. Kandel ER, Schwartz JH, Jessell TM, et al. Principles of Neural Science. 6th edition. New York: McGraw-Hill; 2021.
4. Bear MF, Connors BW, Paradiso MA. Neuroscience: Exploring the Brain. 4th edition. Philadelphia: Wolters Kluwer; 2020.
5. Hall JE, Guyton AC. Guyton and Hall Textbook of Medical Physiology. 14th edition. Philadelphia: Elsevier; 2021.
6. Rowland LP, Pedley TA. Merritt’s Neurology. 14th edition. Philadelphia: Wolters Kluwer; 2021.
7. Heinrichs RW. Cognitive functions of the cerebral cortex. Curr Opin Neurol. 2013;26(2):127-132.
8. Gazzaniga MS, Ivry RB, Mangun GR. Cognitive Neuroscience: The Biology of the Mind. 5th edition. New York: W.W. Norton; 2019.
9. Saraf-Lavi E, Bagic AI. Clinical Neurophysiology. Philadelphia: Elsevier; 2018.
10. Haines DE. Fundamental Neuroscience for Basic and Clinical Applications. 5th edition. Philadelphia: Elsevier; 2019.