Internal capsule : lecture notes summary

 

Internal capsule

The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain.

1. It is a V shaped white matter (projection fibres) with its concavity directed laterally
2. It situated  between the thalamus and caudate nucleus medially and the lentiform nucleus laterally
3. Corona radiata : rostral part of projection fibres is known as corona radiata
4. Caudally it continue as crus cerebri of midbrain
5. Internal capsule contain nerve fibres which responsible for the sensory and motor inntervation of opposite half of the body

 

Parts of internal capsule

•        Anterior limb

•        Genu

•        Posterior limb

•        Retrolentiform part

•        Sublentiform part

Types of fibres present within the internal capsule

•        Motor fibres

1. Corticopontine fibres
2. Pyramidal fibres :  arises from cerebrum and relay lower motor neuron within the brain stem  and spinal cord --corticonuclear fibres and corticospinal fibres
3. Extrapyramidal fibres : arises from cerebrum and relay into  subcortical grey matter like red nucleus, corpus striatum, substantia nigra

Sensory fibres

1. Thalamocortical fibres
2. Subgroups of thalamocortical fibres
3. Anterior , superior, posterior and inferior thalamic radiation

Blood supply of internal capsule

•        The arterial supply of the internal capsule is of great clinical significance

1. Medial and lateral striate branches of middle cerebral artery :

•        SN:  lateral striate branch of middle cerebral artery is larger and frequently ruptured so  it is known as Charcot’s artery of cerebral haemorrhage :

•        it is mainly supply posterior limb of internal capsule . Posterior limb contain pyramidal and extrapyramidal fibers of upper limb, trunk and lower limb so rupture of this artery causes hemiplegia

•        Striate branches of anterior cerebral artery : it supply genu and anterior limb of internal capsule

•        Central branches of anterior choroidal artery : it supply sublentiform part of internal capsule

•        Posteriorlateral central branches of the posterior cerebral artery supply the retrolentiform and sublentiform parts of the internal capsule

 

Function: From the cerebral cortex to the brainstem, the internal capsule provides an essential conduit for the transmission of motor and sensory data. To reach the brainstem and spinal cord and regulate voluntary movements, motor fibers originating from the motor cortex pass through the internal capsule. It is also through which sensory fibers that transmit data from the thalamus to the cerebral cortex pass.

Clinical significance: Damage to the internal capsule may cause severe motor and sensory deficiencies, including hemiplegia, which is the paralysis of one side of the body, and hemianaesthesia, which is the lack of feeling on one side of the body.

Motor and sensory deficits on the opposite side of the body may result from a stroke that affects the blood supply to the internal capsule.

Development: Axons from the growing cerebral cortex reach into subcortical tissues, including the thalamus, brainstem, and spinal cord, during embryonic development, forming the internal capsule. In the central nervous system, this process is essential for creating functional connections.

Systems of Neurotransmitters: Axons within the internal capsule use a variety of neurotransmitters, including as glutamate for excitatory transmission and gamma-aminobutyric acid (GABA) for inhibitory signaling. The internal capsule and its surrounding areas are home to numerous neurotransmitter systems that are crucial for controlling neuronal activity.

Functional Organization: There is a somatotopic organization in the internal capsule, which means that distinct bodily parts are represented by different areas of the structure. For instance, compared to fibers regulating the lower limb, those delivering motor information for the upper limb are situated in different regions.

Pathology: A variety of disorders affecting the internal capsule can result in motor and sensory impairments, including multiple sclerosis, brain tumors, and traumatic brain injury, in addition to stroke.
The motor symptoms typical of neurodegenerative disorders such as Parkinson's disease and Huntington's disease can also be caused by the degradation of fibers that pass through the internal capsule.