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

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.

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.

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 

ASCENDING FIBRES (SENSORY FIBRES)

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.

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

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

ARTERIAL SUPPLY

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.

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