Cortical Anatomy

Figure 2.1 demonstrates the following relevant key areas on the cortical surface:

Figure 2.1 Lateral surface of cerebral hemisphere demonstrating cortical surface anatomy.

• Primary motor cortex: Situated anterior to central sulcus (frontal lobe) in the precentral gyrus; involved in contralateral motor function—Brodmann’s (Br.) Area 4.
  
• Primary somatosensory cortex: Situated posterior to central sulcus (parietal lobe) in the postcentral gyrus; involved in contralateral sensory function—Br. Areas 1, 2 and 3.
  
• Motor speech area: In the dominant hemisphere only (left hemisphere for right-handed subjects and usually left hemisphere for left-handed people); anatomically situated in the inferior frontal gyrus (pars triangularis and opercularis); also known as ‘Broca’s area’ and involved in speech output—Br. Area 44.
  
• Wernicke’s area: In the dominant hemisphere; anatomically situated in the supramarginal gyrus—Br. Area 40 (part of inferior parietal lobule) and posterior part of superior temporal gyrus; involved in comprehension of speech.
  
• Primary visual cortex: In the occipital lobe adjacent to the calcarine sulcus—Br. Area 17; part of the visual pathway.

Brainstem and Cranial Nerves (CN)

The midbrain is the most rostral part of the brainstem; CN III (oculomotor) and IV (trochlear) arise from the midbrain. The pons is situated between the midbrain and the medulla with CN V (trigeminal), VI (abducens), VII (facial) and VIII (vestibulocochlear) nerve entering into or exiting from ventral pons. The medulla is caudal to pons being continuous with spinal cord. Fibres of the CN IX (glossopharyngeal), X (vagus) and XII (hypoglossal) nerves enter into or exit from the ventral aspect of the medulla. The basic clinical features of lesions associated with cranial nerves are presented in Table 3.3.