Free nerve ending


A free nerve ending or bare nerve ending, is an unspecialized, afferent nerve fiber sending its signal to a sensory neuron. Afferent in this case means bringing information from the body's periphery toward the brain. They function as cutaneous nociceptors and are essentially used by vertebrates to detect noxious stimuli that often result in pain.

Structure

Free nerve endings are unencapsulated and have no complex sensory structures. They are the most common type of nerve ending, and are most frequently found in the skin. They mostly resemble the fine roots of a plant. They penetrate the dermis and end in the stratum granulosum. FNEs infiltrate the middle layers of the dermis and surround hair follicles.

Types

Free nerve endings have different rates of adaptation, stimulus modalities, and fiber types.

Rate of adaptation

Different types of FNE can be rapidly adapting, intermediate adapting, or slowly adapting. A delta type II fibers are fast-adapting while A delta type I and C fibers are slowly adapting.

Modality

Free nerve endings can detect temperature, mechanical stimuli or danger. Thus, different free nerve endings work as thermoreceptors, cutaneous mechanoreceptors and nociceptors. In other words, they express polymodality.

Fiber types

The majority of Aδ fibers and C fibers end as free nerve endings.