Q2 LONG ANSWER 10M ★ High-yield

Describe the functional areas of the cerebral cortex and the blood supply of the cerebrum. Add a note on aphasia.

Anatomy · 1st Professional — Pre-Clinical

General Features

The cerebrum consists of two hemispheres joined by the corpus callosum, each with a cortex of grey matter, underlying white matter, and deep nuclei.

The surface is folded into gyri separated by sulci, increasing the cortical area threefold
Each hemisphere has four main lobes — frontal, parietal, temporal and occipital — with the insula buried in the lateral sulcus

Sulcus	Separates
Central sulcus (of Rolando)	Frontal from parietal lobe
Lateral sulcus (of Sylvius)	Temporal from frontal and parietal
Parieto-occipital sulcus	Parietal from occipital
Calcarine sulcus	Divides the visual cortex

Functional Areas

Area	Brodmann	Position	Function
Primary motor	4	Precentral gyrus	Voluntary movement of the opposite half of the body
Premotor and supplementary motor	6	In front of area 4	Planning and sequencing of movement
Frontal eye field	8	Middle frontal gyrus	Conjugate gaze to the opposite side
BROCA (motor speech)	44, 45	Inferior frontal gyrus of the dominant hemisphere	Production of speech
Primary sensory	3, 1, 2	Postcentral gyrus	General sensation from the opposite side
Wernicke (sensory speech)	22	Superior temporal gyrus of the dominant hemisphere	Comprehension of speech
Primary visual	17	Around the calcarine sulcus	Vision
Primary auditory	41, 42	Superior temporal gyrus (Heschl)	Hearing — bilateral representation

Both the motor and sensory areas are mapped as an inverted homunculus — the leg on the medial surface, the face laterally
The area devoted to a part reflects its functional importance, not its size — hence the huge hand, face and tongue
The leg area lies on the medial surface, in the territory of the anterior cerebral artery; the face and hand laterally, in the middle cerebral territory. This single fact predicts the pattern of a stroke

Blood Supply

Artery	Supplies	Effect of occlusion
Anterior cerebral	Medial surface; the leg area	Contralateral leg weakness, greater than the arm; incontinence
Middle cerebral	Lateral surface; face and arm areas; Broca and Wernicke; internal capsule (via lenticulostriate branches)	Contralateral face and arm weakness, hemianaesthesia, aphasia if the dominant side
Posterior cerebral	Occipital lobe and inferior temporal	Contralateral homonymous hemianopia with macular sparing

White Matter Fibres

Association fibres — connect areas within the same hemisphere; the arcuate (superior longitudinal) fasciculus links Wernicke to Broca
Commissural fibres — connect the two hemispheres; the corpus callosum, anterior and posterior commissures, fornix
Projection fibres — to and from the brainstem and cord; converge as the internal capsule, then fan out as the corona radiata

Cerebral Dominance

The left hemisphere is dominant in about 95% of people, including most left-handers
Dominant hemisphere — language, calculation, analytical reasoning
Non-dominant — spatial awareness, music, recognition of faces
Lesions of the non-dominant parietal lobe cause neglect of the opposite side and dressing apraxia, which patients may deny entirely

Upper and Lower Motor Neurone Lesions

Feature	Upper motor neurone	Lower motor neurone
Tone	Increased — spasticity, clasp-knife	Decreased — flaccid
Power	Weakness in a pyramidal distribution	Weakness of the muscles supplied
Reflexes	Exaggerated; clonus	Diminished or absent
Plantar response	Extensor (Babinski)	Flexor or absent
Wasting	Slight, from disuse only	Marked and early
Fasciculation	Absent	Present
Distribution	A whole limb or half the body	Segmental or a single nerve

Spinal shock — immediately after a cord transection the reflexes are absent, so the picture mimics a lower motor neurone lesion for days to weeks before spasticity develops

Applied Aspects

Broca aphasia — speech is non-fluent, effortful, telegraphic, with comprehension intact; the patient is aware and frustrated
Wernicke aphasia — speech is fluent but meaningless, with comprehension lost; the patient is unaware of the deficit
Conduction aphasia — from a lesion of the arcuate fasciculus; comprehension and fluency preserved but repetition impaired
Jacksonian epilepsy — a focal seizure marching along the homunculus, indicating an irritative lesion of the motor cortex
Middle meningeal artery is torn in a fracture of the pterion, the thinnest part of the skull, causing extradural haematoma with a lucid interval
Watershed infarcts occur between arterial territories after profound hypotension, giving a "man in a barrel" pattern of proximal weakness
The insula is buried in the lateral sulcus and is concerned with taste, visceral sensation and autonomic control

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