Närviteed

Närviteed are bundles of axons located in the central nervous system, forming part of the brain’s and spinal cord’s white matter. They connect different regions of the nervous system and enable the rapid transmission of information between cortical, subcortical and brainstem structures, as well as between the brain and the spinal cord. The term is commonly used in Nordic neuroanatomy to describe what English speakers call nerve tracts or white-matter tracts.

Structurally, närviteed consist primarily of myelinated axons, which increase conduction speed. They are organized into named tracts or fasciculi that share similar origins and destinations. In the brain, tracts connect the cerebral hemispheres with the brainstem and cerebellum, while spinal tracts link the spinal cord with various levels of the brain. Examples of well-known tracts include corticospinal tracts, which convey motor commands from the cortex to the spinal cord, and dorsal column–medial lemniscus pathways, which carry fine touch and proprioceptive information to the brain.

Functionally, tracts are commonly categorized as ascending (sensory) or descending (motor). Ascending tracts transmit sensory information from the periphery to the brain, whereas descending tracts carry motor signals from the brain to the muscles and other effectors. The precise arrangement of tracts underpins coordinated movement, perception, and autonomic regulation.

Clinical relevance arises when tracts are damaged by traumatic injury, stroke, demyelinating disease, or other neuropathologies. Because specific tracts support particular functions, localized tract lesions produce characteristic neurological deficits that help localize injury within the CNS.