Internal capsule

ANATOMY OF INTERNAL CAPSULE

1. INTERNAL CAPSULE

2. The internal capsule is a compact bundle of projection fibres between the thalamus and caudate nucleus medially. and the lentiform nucleus laterally .)

3. Relations Medially: Head of caudate nucleus Thalamus Laterally: Lentiform nucleus ( globus pallidus & putamen )

4. When traced upwards, the fibres of capsule continue with the corona radiata , and when traced downward then fibres continue with the crus cerebi of mid brain,

5. Parts Of The Internal Capsule Anterior limb Posterior limb Genu Retrolentiform part Sublentiform part

6. Anterior limb : lies between the head of caudate nucleus medially and the anterior part of the lentiform nucleus laterally. Posterior limb : lies between the thalamus medially and the posterior part of the lentiform nucleus laterally. Genu : is the bend between the anterior and posterior limbs with concavity of the bend facing laterally. Retrolentiform part: lies behind the lentiform nucleus. Sublentiform part: lies below the lentiform nucleus .

7. Fibres Of The Internal Capsule REPRESENTED BY SYMBOLS

8. Sensory Motor CEREBRAL CORTEX THALAMUS BRAINSTEM: MidBrain Pons Medulla Oblogata SPINAL CORD Named according to the lobe from which they arise FROM FRONTAL, PARIETAL, OCCIPITAL AND TEMPORAL Thalamocortical Frontopontine - AL, G, PL Parietopontine - RetroLF Occipitopontine - RetroLF Temporopontine – Sub LF Corticonuclear - G Corticospinal - PL Corticorubral - PL Corticostriate - PL Corticonigral - PL Anterior thalamic radiation Posterior thalamic radiation   Superior thalamic radiation Inferior thalamic radiation

9. SENSORY FIBRES - Thalamocortical Fibres According to the direction of these fibres the thalamic radiation is divided into following subgroups:   Anterior Thalamic Radiation:  the fibres of anterior thalamic radiation are directed anteriorly and connects thalamus to frontal lobe cortex. Superior Thalamic Radiation :  is directed superiorly. Connect frontal and parietal lobes. Posterior Thalamic Radiation  : is directed posteriorly . Connect occipital lobe forming  optic radiation, Inferior Thalamic Radiation : connects medial geniculate body with primary auditory cortex. (auditory radiation)

10. Arterial Supply of Internal Capsule Medial and lateral striate branches of the middle cerebral artery: One of the lateral striate branches is larger and more frequently ruptured. It is often termed  Charcot's artery of cerebral haemorrhage . It supplies the posterior limb of the internal capsule. Striate branches of anterior cerebral artery : One of these branches is larger and takes a recurrent course. It is termed  recurrent artery of Huebner . It arises just proximal to the anterior communicating artery & supply the genu and anterior limb of the internal capsule. Central branches of the anterior choroidal artery:  supply the sublentiform part. Some direct branches from the internal carotid artery:  supply the genu . Central branches of the posterior cerebral artery: supply the retrolentiform and sublentiform parts of the internal capsule. Central branches of the posterior communicating artery .

11. Applied Damage to the internal capsule, due to haemorrhage or infarction leads to loss of sensations and spastic paralysis of the opposite half of the body ( contralateral hemiplegia ).  

12. The haemorrhage commonly occurs due to rupture of artery of cerebral haemorrhage  (also called Charcot's artery of cerebral haemorrhage ), which supplies the posterior limb of the internal capsule. The spastic paralysis of the opposite half of the body occurs due to the involvement of the pyramidal and extrapyramidal fibres for the upper limb, trunk and lower limb. Rupture of Charcot's artery of cerebral haemorrhage is the most common cause of the hemiplegia .

13. Involvement of recurrent artery of Huebner (due to thrombosis/rupture) results in paralysis of the face and upper limb on the opposite side (because of the involvement of corticonuclear fibres in genu and adjacent pyramidal fibres in the posterior limb for the upper limb). Lesions of the posterior one-third of the posterior limb, and sublentiform and retrolentiform parts of the internal capsule lead to visual ( hemianopia ) and auditory (loss of hearing) defects. These lesions usually occur due to thrombosis of the anterior choroidal artery, a branch of internal carotid artery .