Brain Structure & Organisation

All 10 Terms & Definitions

Cerebral hemispheres

The two symmetrical halves of the cerebrum (left and right), separated by the longitudinal fissure and connected by the corpus callosum. Each hemisphere controls the contralateral (opposite) side of the body. While largely mirror images anatomically, the hemispheres show functional lateralisation — particularly for language (predominantly left) and visuospatial processing (predominantly right).

Cerebral cortex

The thin (2–4 mm) outer layer of neural tissue that forms the surface of the cerebrum. The cortex is highly folded (gyrification) to pack a large surface area (~2,500 cm²) into the skull. It consists of six layers of neurons and is divided into four lobes. The cortex is responsible for conscious perception, voluntary movement, language, reasoning, and memory.

Frontal lobe

The largest cortical lobe, occupying the anterior third of the brain. Contains the primary motor cortex (voluntary movement), premotor and supplementary motor areas (movement planning), and the prefrontal cortex (executive functions, decision-making, working memory, personality). Broca's area — critical for speech production — is located in the left inferior frontal gyrus.

Parietal lobe

Located behind the frontal lobe, posterior to the central sulcus. Contains the primary somatosensory cortex (body sensation) and the parietal association cortex, which integrates sensory information to support spatial awareness, attention, and the sense of body position (proprioception). Damage to the right parietal lobe can produce hemispatial neglect — ignoring the left side of space.

Temporal lobe

Located on the lateral surface below the lateral fissure (Sylvian fissure). Processes auditory information (primary auditory cortex), and contains Wernicke's area (left temporal lobe, language comprehension), the fusiform face area (face recognition), and the parahippocampal cortex. The hippocampus and amygdala are located within the medial temporal lobe.

Occipital lobe

The most posterior lobe, dedicated primarily to visual processing. Contains the primary visual cortex (V1, striate cortex) and multiple visual association areas that process colour, motion, form, and object recognition. Lesions cause specific visual deficits such as cortical blindness (V1 damage) or prosopagnosia (inability to recognise faces, fusiform area damage).

Corpus callosum

The largest white matter commissure, a band of approximately 200 million axons connecting corresponding areas of the left and right hemispheres. Enables rapid interhemispheric communication. When severed (split-brain surgery, or callosotomy, once used for epilepsy), the two hemispheres operate independently, producing striking dissociations famously studied by Roger Sperry and Michael Gazzaniga.

Cerebellum

A large, cauliflower-shaped structure at the posterior base of the brain. Although it contains only ~10% of brain volume, it houses over 50% of all neurons. Critical for the coordination, timing, and fine-tuning of movement, as well as procedural learning and balance. Damage produces ataxia — uncoordinated, unsteady movements. Modern research also implicates the cerebellum in cognitive functions including language and timing.

Brainstem

The stalk-like structure connecting the cerebral hemispheres and cerebellum to the spinal cord. Consists of the midbrain, pons, and medulla oblongata. Controls life-critical autonomic functions (breathing, heart rate, blood pressure), sleep-wake cycles, and relays sensory and motor signals between brain and body. Most cranial nerves originate here. Damage to the brainstem is often fatal.

Sulci and gyri

The grooves (sulci, singular sulcus) and ridges (gyri, singular gyrus) of the cerebral cortex. Gyrification expands the cortical surface area by approximately threefold, allowing more neurons to be packed into the limited space of the skull. Some sulci are consistent across individuals (e.g., central sulcus, lateral sulcus) and serve as anatomical landmarks dividing the cortical lobes.