The cerebrum (plural: cerebra), also known as the telencephalon or endbrain, is the largest and uppermost portion of the brain. It accounts for approximately two-thirds of the total weight of the brain and about 80% of its volume. In humans, the cerebrum is the most developed of the five major divisions of the brain and is considered the seat of conscious mental processes.
Anatomy and Structure
The cerebrum is divided by the longitudinal fissure into two cerebral hemispheres (left and right), which are connected by a thick band of white matter called the corpus callosum. Each hemisphere contains an outer layer of gray matter known as the cerebral cortex, an inner core of white matter composed of myelinated nerve fibers, and several subcortical structures including the basal ganglia, hippocampus, and olfactory bulb.
The cerebral cortex has a highly convoluted appearance, consisting of ridges (gyri) and grooves (sulci) that increase its surface area to approximately 2,000 square cm (310 square inches). The cortex is generally classified into four lobes, named after the overlying cranial bones: the frontal lobe, parietal lobe, temporal lobe, and occipital lobe. A fifth lobe, the insular lobe (insula), is located deep within the lateral sulcus.
White Matter Tracts
The white matter of the cerebrum is organized into three types of tracts:
- Commissural tracts — connect the two hemispheres (e.g., corpus callosum, anterior commissure)
- Association tracts — connect different regions within the same hemisphere
- Projection tracts — connect the cerebral cortex to lower brain regions and the spinal cord (e.g., internal capsule)
Functions
The cerebrum controls all voluntary actions in the human body and is responsible for higher neurological functions. Different lobes have specialized roles:
- Frontal lobe — motor function (primary motor cortex in the precentral gyrus), speech production (Broca's area), higher intellect, personality, behavior, judgment, working memory, and decision-making (prefrontal cortex)
- Parietal lobe — somatosensory processing (primary somatosensory cortex in the postcentral gyrus), touch, pain, temperature, proprioception, language, and spatial awareness
- Temporal lobe — auditory processing (primary auditory cortex), language comprehension (Wernicke's area), memory formation (hippocampus), and emotional processing (amygdala)
- Occipital lobe — visual processing (primary visual cortex)
- Insular lobe — taste (gustatory cortex), homeostasis, empathy, and self-awareness
The cerebrum is contralaterally organized: the right hemisphere processes signals predominantly from the left side of the body, and the left hemisphere processes signals predominantly from the right side. In approximately 95% of the population, language functions are localized to the left hemisphere.
Vasculature
The cerebrum receives its blood supply from three paired arterial branches:
- Anterior cerebral arteries — supply the anteromedial aspect
- Middle cerebral arteries — supply most of the lateral portions
- Posterior cerebral arteries — supply the posterior aspects
Venous drainage occurs via cerebral veins that empty into the dural venous sinuses.
Development
Embryologically, the cerebrum develops from the prosencephalon (forebrain), which further differentiates into the telencephalon and diencephalon. The dorsal telencephalon (pallium) gives rise to the cerebral cortex, while the ventral telencephalon (subpallium) becomes the basal ganglia.
Comparative Anatomy
In lower vertebrates (hagfishes, lampreys), the cerebrum is a simple structure primarily devoted to olfactory sensation. In reptiles, a three-layered cerebral cortex appears. Birds have enlarged cerebra with a pallium homologous to the mammalian neocortex. In mammals, the cerebral cortex expands to cover almost the entire cerebral hemispheres, with the most complex convolutions found in higher mammals. Among non-human species, dolphins have cerebra accounting for as much as 2% of their body weight, second only to humans.
Related Medical Conditions
Conditions affecting the cerebrum include stroke (cerebrovascular accident), Alzheimer's disease, traumatic brain injury, epilepsy, Parkinson's disease, brain tumors, infections, and various congenital disorders. The specific functional deficits depend on the location and extent of the damage.
