Human Anatomy
Cranial Nerve Nuclei and Cerebral Hemispheres
Cranial nerve nuclei and cerebral hemisphere anatomy for MBBS: cortical areas, white matter, basal ganglia, thalamus and the circle of Willis, mapped to NMC codes AN62.1 to AN62.6.
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Cranial Nerve Nuclei and Cerebral Hemispheres
Cranial nerve nuclei and cerebral hemisphere anatomy for MBBS: cortical areas, white matter, basal ganglia, thalamus and the circle of Willis, mapped to NMC codes AN62.1 to AN62.6.
This chapter maps the columnar arrangement of the cranial nerve nuclei and the functional anatomy of the cerebral hemispheres, including their cortex, white matter, deep grey masses and arterial supply. It links these structures to speech, movement, sensation and the common patterns of stroke.
High-yield: Cranial Nerve Nuclei and Cerebral Hemispheres
- The cranial nerve nuclei are arranged in functional columns in the brainstem, motor nuclei medially and sensory nuclei laterally.
- The precentral gyrus is the primary motor area, Brodmann area 4, arranged as an inverted homunculus.
- The postcentral gyrus is the primary somatosensory area, Brodmann areas 3, 1 and 2.
- Broca's motor speech area lies in the inferior frontal gyrus of the dominant hemisphere, and its lesion gives non-fluent aphasia.
- Wernicke's area lies in the posterior superior temporal gyrus of the dominant hemisphere, and its lesion gives fluent but meaningless speech.
- The primary visual cortex lies around the calcarine sulcus in the occipital lobe, area 17.
- The corpus callosum is the largest commissure, connecting the two hemispheres, with genu, body, splenium and rostrum.
- The internal capsule carries corticospinal, corticobulbar and thalamocortical fibres; its posterior limb is a common site of stroke.
- The basal ganglia comprise the caudate nucleus, putamen and globus pallidus, with the substantia nigra and subthalamic nucleus functionally linked.
- The caudate and putamen together form the striatum; the putamen and globus pallidus form the lentiform nucleus.
- The thalamus is the great sensory relay, and the medial geniculate body relays hearing while the lateral geniculate body relays vision.
- The hypothalamus controls the autonomic nervous system, the endocrine system through the pituitary, temperature, hunger and thirst.
- The limbic lobe, including the hippocampus and amygdala, governs emotion and the formation of new memories.
- The circle of Willis is formed by the two internal carotid and the basilar arteries, linked by the communicating arteries.
- The middle cerebral artery, the largest branch of the internal carotid, is the commonest site of embolic stroke.
Functional cortical areas and deep grey masses
- **Motor and sensory strips:** Precentral gyrus (area 4) for movement; postcentral gyrus (areas 3, 1, 2) for sensation, both as an inverted homunculus.
- **Language areas:** Broca's in the inferior frontal gyrus (non-fluent aphasia); Wernicke's in the superior temporal gyrus (fluent aphasia), dominant hemisphere.
- **Basal ganglia:** Caudate, putamen, globus pallidus; striatum equals caudate plus putamen; lentiform equals putamen plus globus pallidus.
- **Circle of Willis:** Internal carotids and basilar artery joined by anterior and posterior communicating arteries; middle cerebral artery is the commonest stroke site.
NMC competencies in this chapter
- **AN62.1:** Cranial nerve nuclei and their functional components
- **AN62.2:** Surfaces, sulci, gyri, poles and functional areas of the cerebral hemisphere
- **AN62.3:** White matter of the cerebrum
- **AN62.4:** Parts and major connections of the basal ganglia and limbic lobe
- **AN62.5:** Boundaries, parts, relations, nuclei and connections of the thalamus, hypothalamus, epithalamus, metathalamus and subthalamus
- **AN62.6:** Formation, branches and areas of distribution of the circle of Willis
Frequently Asked Questions
How are the cranial nerve nuclei organised in the brainstem?
They lie in functional columns. Motor nuclei sit closer to the midline and sensory nuclei more laterally, a pattern that reflects the way the neural tube develops.
What is the difference between Broca's and Wernicke's aphasia?
A Broca's area lesion in the inferior frontal gyrus gives non-fluent, effortful speech with preserved comprehension. A Wernicke's area lesion in the superior temporal gyrus gives fluent but meaningless speech with poor comprehension.
Why is the internal capsule clinically important?
It is a compact band of ascending and descending fibres, so a small lesion, especially in the posterior limb, can cause a dense contralateral hemiplegia and sensory loss.
What forms the circle of Willis?
The two internal carotid arteries and the basilar artery, connected by the anterior communicating artery in front and the two posterior communicating arteries behind, forming an anastomotic ring at the base of the brain.
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