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    From Nervous System

    Conus Medullaris
    Terminal end of the spinal cord.
    Cerebellar Hemispheres
    Lateral portions of the cerebellum.
    Midbrain
    Controls visual and auditory systems and body movement.
    Choroid Plexus
    Produces cerebrospinal fluid.
    Substantia Nigra
    Involved in movement and reward.
    Medulla Oblongata
    Controls autonomic functions like breathing and heart rate.
    Sacral Spinal Cord
    Bottom portion of the spinal cord.
    Epithalamus
    Contains the pineal gland, involved in circadian rhythms.
    Cerebrospinal Fluid (CSF)
    Protective fluid in brain and spinal cord.
    Tentorium Cerebelli
    Separates cerebellum from cerebrum.
    Cerebral Cortex
    Outer layer of cerebrum responsible for complex thought processes.
    Thoracic Spinal Cord
    Middle portion of the spinal cord.
    Hippocampus
    Essential for memory formation.
    Brachial Plexus
    Nerve network for the upper limb.
    Sacral Plexus
    Nerve network for pelvis and lower limb.
    Sympathetic Chain
    Series of ganglia for sympathetic nervous system.
    Thalamus
    Relay station for sensory and motor signals to the cerebral cortex.
    Amygdala
    Involved in emotion and memory.
    Cerebral Aqueduct
    Connects third and fourth ventricles.
    Filum Terminale
    Fibrous extension from conus to coccyx.
    Pons
    Connects upper and lower parts of the brain.
    Pineal Gland
    Secretes melatonin to regulate sleep-wake cycles.
    Cervical Plexus
    Network of nerves supplying neck and shoulder.
    Cervical Spinal Cord
    Upper part of the spinal cord.
    Insular Cortex
    Involved in consciousness, emotion, and homeostasis.

    Internal Capsule

    Reviewed by our medical team

    White matter structure that carries information to and from the cerebral cortex.

    1. Overview

    The internal capsule is a crucial white matter structure in the brain that consists of a dense bundle of myelinated axons. It acts as a major communication pathway between the cerebral cortex and various subcortical structures, including the brainstem and spinal cord. The internal capsule is involved in transmitting motor commands, sensory information, and higher-order cognitive signals. It is also a key pathway for the execution of voluntary motor movements and the processing of sensory input from the body to the brain. Due to its central role in communication between different brain regions, damage to the internal capsule can result in significant neurological deficits, including motor and sensory impairments.

    2. Location

    The internal capsule is located deep within the brain, situated between two important structures: the caudate nucleus and the lentiform nucleus. It is part of the basal ganglia's communication pathways and forms the boundary between the thalamus and the basal ganglia. The internal capsule extends from the cerebral cortex in the upper regions of the brain down towards the brainstem, where it continues as part of the corticospinal tract. It lies just beneath the corona radiata, a fan-like arrangement of nerve fibers, and its fibers are organized into distinct sections based on their function.

    3. Structure

    The internal capsule is a compact and organized structure that consists of several regions, each responsible for specific types of communication between the brain's different areas. The key features of its structure include:

    • Anterior limb: The anterior limb of the internal capsule is located between the caudate nucleus and the lentiform nucleus. It contains fibers that are primarily involved in transmitting information between the frontal lobe and the thalamus. It also carries fibers related to emotional and cognitive functions.

    • Genu: The genu is the bend of the internal capsule, located between the anterior and posterior limbs. It contains fibers that connect the motor cortex of the frontal lobe with the brainstem, particularly those related to facial and oral motor functions. The genu also serves as a critical pathway for connections between the brainstem and the cerebral cortex.

    • Posterior limb: The posterior limb is the largest part of the internal capsule and is located between the thalamus and the lentiform nucleus. It contains fibers involved in motor and sensory pathways, including the corticospinal tract, which is responsible for voluntary motor control. It also carries sensory information from the body to the sensory cortex in the parietal lobe.

    • Retrolenticular part: Located just behind the lentiform nucleus, this part of the internal capsule contains fibers that transmit visual information from the lateral geniculate nucleus of the thalamus to the visual cortex.

    • Sublenticular part: The sublenticular part contains fibers involved in auditory processing, particularly the auditory pathway from the medial geniculate body of the thalamus to the auditory cortex in the temporal lobe.

    4. Function

    The internal capsule is a highly functional structure that facilitates the transmission of information between various regions of the brain. Its main functions include:

    • Motor control: The internal capsule contains the corticospinal tract, which is responsible for transmitting motor commands from the motor cortex to the spinal cord. These signals are crucial for voluntary movement, particularly for fine motor control of the limbs and face.

    • Sensory processing: The internal capsule also carries sensory information from the body to the brain. It transmits signals from the thalamus to the somatosensory cortex, enabling the brain to process sensations such as touch, pain, temperature, and proprioception (sense of body position).

    • Emotional and cognitive processing: The anterior limb of the internal capsule contains fibers involved in regulating emotional and cognitive functions, particularly those connected to the frontal lobe. This allows the brain to integrate information related to motivation, emotional responses, and higher-order cognitive processes such as decision-making.

    • Auditory and visual pathways: The retrolenticular and sublenticular parts of the internal capsule carry sensory information related to vision and hearing. These pathways connect the thalamus to the visual and auditory cortices, respectively, enabling the brain to process and respond to sensory stimuli.

    • Facial and oral motor control: The genu of the internal capsule plays a crucial role in controlling the motor functions of the face and mouth. It contains fibers that facilitate speech, facial expressions, and other oral motor movements.

    5. Physiological Role(s)

    The physiological roles of the internal capsule are essential for the smooth operation of the brain and the integration of sensory, motor, and cognitive functions. These roles include:

    • Voluntary movement: The internal capsule plays a central role in voluntary motor control by transmitting motor commands from the primary motor cortex to the spinal cord. This pathway is essential for executing voluntary movements of the limbs, face, and trunk.

    • Somatosensory processing: The internal capsule's involvement in sensory pathways enables the brain to process and interpret sensory inputs from the body. By transmitting sensory information to the sensory cortex, it allows for the perception of touch, pain, temperature, and body position.

    • Coordination of cognitive and emotional responses: The internal capsule helps integrate emotional and cognitive responses with sensory and motor input, supporting behaviors that require both emotional regulation and decision-making. This function is crucial for social interaction, problem-solving, and adapting to changing environments.

    • Integration of auditory and visual information: The internal capsule's pathways also support the integration of auditory and visual information. This allows for the processing of environmental stimuli related to sight and sound, enabling appropriate behavioral responses.

    6. Clinical Significance

    The internal capsule is clinically significant because damage to this structure can lead to a variety of neurological impairments. Some key clinical conditions related to the internal capsule include:

    • Stroke: The internal capsule is a common site of damage in patients who experience a stroke, particularly in cases of lacunar infarctions (small vessel strokes). Damage to the internal capsule can lead to motor deficits, including hemiparesis (weakness on one side of the body), and sensory loss, often affecting the face, arms, and legs.

    • Motor dysfunction: Lesions in the internal capsule, particularly in the posterior limb, can result in motor deficits such as paralysis or weakness in specific muscle groups. These deficits may be contralateral (affecting the opposite side of the body) due to the decussation (crossing) of motor fibers in the internal capsule.

    • Sensory deficits: Damage to the internal capsule can also impair the sensory pathways that transmit information from the body to the brain. This can result in sensory loss, including the inability to feel touch, pain, or temperature sensations, or disturbances in proprioception (the sense of body position).

    • Hemianopia: Lesions in the retrolenticular or sublenticular parts of the internal capsule can affect the visual pathways, leading to a condition known as hemianopia, where a person loses vision in one half of their visual field in both eyes.

    • Thalamic pain syndrome: Damage to the internal capsule, particularly the sensory pathways, can lead to a phenomenon known as thalamic pain syndrome. This condition is characterized by intense, burning pain on the affected side of the body, often in response to minor stimuli.

    • Multiple sclerosis (MS): MS, a disease characterized by the degeneration of myelin in the central nervous system, can lead to damage in the internal capsule. This can result in motor, sensory, and cognitive impairments, depending on the location of the lesions within the internal capsule.

    The internal capsule is essential for the smooth coordination of motor and sensory functions, as well as for higher cognitive and emotional processing. Damage to this structure can lead to significant neurological deficits, and early diagnosis and treatment are important for managing these conditions and improving patient outcomes.

    Did you know? Pain signals travel to the brain at the speed of 170 miles per hour.