The external capsule is a structure in the brain that is involved in motor control and sensory processing. Its spelling can be tricky, but it follows the rules of English phonetics. "External" is pronounced as /ɪkˈstɜːrnəl/, with stress on the second syllable and a silent 'e'. "Capsule" is pronounced as /ˈkæpsjuːl/, with stress on the first syllable and a short 'a' sound. Taken together, the word is spelled as /ɪkˈstɜːrnəl ˈkæpsjuːl/, with stress on the second syllable of "external" and the first syllable of "capsule".
The external capsule is a structure in the brain that serves as a pathway for transmitting nerve signals between different regions of the cerebral cortex and other parts of the central nervous system. It is located within the deep white matter of the brain, lying lateral to the anterior part of the lentiform nucleus.
The external capsule consists of a compact bundle of myelinated nerve fibers that carry both sensory and motor information. It acts as a major connecting link between the thalamus and the cerebral cortex, facilitating communication between these regions. Specifically, it connects the thalamus, which is responsible for relaying sensory information to the cortex, with the prefrontal cortex and motor areas, which control voluntary movement.
The external capsule also serves as a boundary between the insula, a region of the brain involved in various functions including emotion and self-awareness, and the lentiform nucleus, which is part of the basal ganglia involved in motor control. It helps to maintain the organization and integrity of these different brain structures.
Damage to the external capsule can lead to various neurological symptoms depending on the affected fibers and regions of the brain. For example, disruption of the motor fibers within the external capsule can result in motor deficits, whereas damage to the sensory fibers can lead to sensory impairments. Additionally, its involvement in cognitive and emotional processes makes it relevant to conditions such as schizophrenia and depression.
Capsula externa.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.
The word "external capsule" has its origins in Latin and Greek.
The term "external" comes from the Latin word "externus", which means "outer" or "outside". It signifies something that is present on the outer side or outer layer.
The word "capsule" comes from the Latin word "capsula", which means "small box" or "case". It refers to a small container or a shell-like structure.
In the context of the brain, the "external capsule" refers to a bundle of nerve fibers located superficially in the brain, which is enclosed within a dense white matter. It is called the "external capsule" because it is positioned on the outer side of other structures in the brain and resembles a capsule-like formation.
Therefore, the term "external capsule" refers to a collection of nerve fibers situated on the outer side of the brain, encapsulated within a white matter structure.