Afferenzen

Afferenzen are the neural pathways that carry sensory information from peripheral receptors toward the central nervous system. They are the counterpart of efferenzen, which carry commands from the brain and spinal cord to muscles and glands. The term Afferenzen (afferent fibers) encompasses a range of sensory neurons in peripheral nerves and cranial nerves and their central projections.

Anatomy and pathway: In somatosensory systems, the first-order neurons have cell bodies in dorsal root ganglia (for body sensations) or in cranial nerve ganglia (for head and face). Peripheral processes innervate receptors, while central processes enter the spinal cord or brainstem and synapse on second-order neurons. These neurons relay information to the thalamus, particularly the ventral posterior nuclei, and from there to cortical sensory areas. Proprioceptive and some visual and vestibular afferents also reach the cerebellum or other subcortical structures.

Modalities: Afferenzen convey diverse modalities, including mechanosensation (touch, pressure, vibration), proprioception, temperature, nociception (pain), and special senses such as vision, audition, taste, and smell. Receptors include mechanoreceptors, thermoreceptors, nociceptors, proprioceptors, photoreceptors, and chemoreceptors.

Clinical relevance: Damage to afferent pathways produces sensory deficits in the corresponding regions or modalities, such as numbness, reduced touch or proprioception, pain disorders, or sensory ataxia. Assessment of afferent pathways helps diagnose peripheral neuropathies, radiculopathies, and central lesions.