SN1
SHORT NOTE
5M
★ High-yield
Describe the internal capsule with its parts, contents and blood supply. Add a note on capsular stroke.
Definition
The internal capsule is a compact band of projection fibres between the caudate nucleus and thalamus medially and the lentiform nucleus laterally.
- V-shaped in horizontal section, with the concavity directed laterally
- Continuous above with the corona radiata and below with the crus cerebri of the midbrain
Parts and Contents
| Part | Between | Contents |
|---|---|---|
| Anterior limb | Caudate and lentiform nuclei | Frontopontine fibres; anterior thalamic radiation |
| Genu | The bend | Corticonuclear (corticobulbar) fibres to the cranial nerve nuclei |
| Posterior limb | Thalamus and lentiform nucleus | Corticospinal fibres (in the anterior two-thirds, arranged face–arm–leg from before backward); superior thalamic radiation carrying all sensation |
| Retrolenticular part | Behind the lentiform nucleus | Optic radiation; parieto-occipito-pontine fibres |
| Sublenticular part | Below the lentiform nucleus | Auditory radiation; temporopontine fibres |
Blood Supply
- Lenticulostriate branches of the middle cerebral artery — the chief supply of the genu and posterior limb
- Anterior choroidal artery (from the internal carotid) — the lower posterior limb and the retrolenticular part
- Recurrent artery of Heubner (from the anterior cerebral) — the anterior limb
- All are end arteries, arising at right angles from large vessels — a mechanically unfavourable arrangement
Capsular Stroke
- Upper motor neurone pattern — spastic paralysis, exaggerated reflexes, extensor plantar (Babinski), clasp-knife rigidity, no wasting
- The face is spared above the eye, because the upper facial nucleus has bilateral cortical supply
- Lacunar infarcts in the capsule give a pure motor hemiplegia without sensory or visual loss — the commonest lacunar syndrome
Applied Aspects
- The internal capsule is the commonest site of a hypertensive stroke in India, and control of blood pressure is the single most effective preventive measure
- Somatotopy matters surgically — the face lies anteriorly and the leg posteriorly in the posterior limb, so a small lesion can spare one limb
- Optic radiation in the retrolenticular part means a capsular lesion may add a homonymous hemianopia to the hemiplegia
- Recovery is limited, because the fibres are so concentrated that there is little intact tissue left to compensate — unlike a cortical lesion
All questions in Neuroanatomy
- Q1Describe the external features and internal structure of the spinal cord. Describe its ascending and descending tracts and add a note on its lesions. ★
- Q2Describe the functional areas of the cerebral cortex and the blood supply of the cerebrum. Add a note on aphasia. ★
- Q3Describe the cerebellum under divisions, peduncles, connections and functions. Add a note on the signs of cerebellar disease. ★
- Q4Describe the parts of the brainstem and the arrangement of the cranial nerve nuclei. Add a note on the brainstem syndromes. ★
- Q5Describe the meninges and the ventricular system. Explain the formation, circulation and absorption of cerebrospinal fluid and add a note on hydrocephalus. ★
- SN1Describe the internal capsule with its parts, contents and blood supply. Add a note on capsular stroke. ★
- SN2Describe the circle of Willis with its formation and significance. Add a note on berry aneurysm. ★
- SN3Describe the basal ganglia with their connections and functions. Add a note on their disorders. ★
- SN4Describe the thalamus with its nuclei and connections. Add a note on the thalamic syndrome. ★
- SN5Describe the visual pathway and the effects of lesions at different levels. Add a note on the light reflex. ★
- SN6Describe the hypothalamus with its nuclei, connections and functions. ★
- SN7Compare the sympathetic and parasympathetic nervous systems. Add a note on Horner syndrome.