1. Sahana Hebsur MBBS Student Kasturba Medical College, Mangalore
INTERNAL CAPSULE
Sahana Hebsur
MBBS Student
Kasturba Medical College, Mangalore

2. White matter of cerebral hemispheres
Association fibres – connect one gyrus to another in the same hemisphere. Examples are cingulum, uncinate fasciculus
Commisural fibres – connect the corresponding gyri of the two hemispheres. Examples are corpus callosum, anterior and posterior commisures
Projection fibres – connect the cerebral cortex to other regions of CNS below it. Examples are corona radiata and internal capsule.

3. RELATIONS TO THE INTERNAL CAPSULE
Medial – thalamus and the caudate nucleus
Lateral – lentiform nucleus
The fibres of the internal capsule fan out cranially to form the corona radiata and condense caudally to form the crus cerebri of the midbrain.

4. PARTS OF THE INTERNAL CAPSULE
The internal capsule is made up of five parts.
Anterior limb
lies between the head of the caudate nucleus medially and the lentiform nucleus laterally
Genu
lies medial to the apex of the lentiform nucleus 
Posterior limb
lies between the thalamus medially and the lentiform nucleus laterally 
Retrolentiform part
lies behind the lentiform nucleus 
Sublentiform part
lies below the lentiform nucleus 

5. ASCENDING FIBRES (SENSORY FIBRES)

6. Anterior thalamic radiation – fibres to the frontal lobe
Anterior thalamic radiation – fibres to the frontal lobe. They pass through the anterior limb of the internal capsule. The fibres arise mainly from the medial and anterior nuclei of the thalamus. They also carry fibres from hypothalamus and limbic structures to the frontal cortex.
Superior thalamic radiation – consist of fibres traveling from the ventral posterior nuclei of thalamus to the somatosensory area (in post central gyrus). These fibres occupy the genu and posterior limb of the capsule. These are the 3rd order sensory neurons responsible for conveying sensations to the cerebral cortex.
Posterior thalamic radiation – consist of fibres from thalamus to the occipital lobe. This includes the optic radiation from LGB to the visual cortex. They lie in the retrolentiform part of the capsule.
Inferior thalamic radiation – consist of fibres from thalamus to the temporal lobe. It includes the auditory radiation from MGB to the acoustic area of cerebral cortex. The fibres pass through the sublentiform part of the capsule.

8. Descending fibres (sensory fibres)
CORTICOPONTINE FIBRES : named according to the lobe they arise from.
Frontopontine fibres : pass through anterior limb, genu, posterior limb
Parietopontine fibres : mainly pass through retrolentiform part and some through the sublentiform part
Temporopontine fibres : pass through sublentiform part
Occipitofrontine fibres : pass through retrolentiform part
PYRAMIDAL FIBRES :
Corticonuclear fibres : pass through genu
Corticospinal fibres : pass though posterior limb

9. OTHERS : (From the cerebral cortex to the sub-cortical area named)
Corticothalamic fibres
Corticostriate fibres
Corticorubral fibres
Corticoreticular fibres

10. ARTERIAL SUPPLY

11. 1. Striate branches of Middle Cerebral Artery (MCA) : supply upper parts of anterior limb, genu and posterior limb. (posterior limb supplied by one of the larger branches called Charcot’s artery of cerebral hemorrhage)
2. Striate branches of (ACA) Anterior Cerebral Artery (Recurrent artery of Heubner) : lower part of anterior limb
3. Striate branches of Internal Carotid Artery (ICA) : lower part of genu
4. Anterior Choroidal Artery : lower part of posterior limb, retrolentiform and sublentiform part.

12. CLINICAL SIGNIFICANCE thrombosis stroke hemiplegia
Micro aneurysm/Thrombosis in lenticulostriate arteries (most common in Charcot’s artery of cerebral hemorrhage) -
• contralateral side of the body :
– Hemiplegia
– Impaired sensation
– Paralysis of lower half of face
Thrombosis in recurrent branch of ACA
– Upper limb paralysis
Thrombosis in Anterior choroidal artery
• may be symptomless – collateral circulation