mechanoreceptorsMerkel

Merkel cell–neuron complexes are a type of mechanoreceptor in the skin. They consist of a Merkel cell, a specialized epidermal cell, in close contact with a small-diameter afferent nerve ending of a myelinated Aβ fiber. In humans they are most concentrated in areas of high tactile acuity, such as the fingertips and lips, and are present in both glabrous and hairy skin, though regional density varies.

Function and response properties: Merkel complexes detect fine details of shape, texture, and edges through sustained or slowly varying indentation. They have small receptive fields and respond with a slowly adapting (SA1) discharge when indentation is maintained, supporting high spatial resolution and texture discrimination.

Transduction and signaling: Mechanical stimulation opens mechanosensitive channels, notably Piezo2, in Merkel cells. Merkel cells are thought to release neurotransmitter to the adjacent nerve ending, thereby activating the afferent fiber; the exact transmitter is still debated, but glutamatergic signaling is implicated. The afferent signal travels to the dorsal root ganglion and relays to the brain via the dorsal column–medial lemniscus pathway.

Structure and development: The receptor is a coordinated two-part complex (Merkel cell and associated nerve ending) embedded at the epidermal-dermal junction. Merkel cell density can change with age and injury, affecting tactile acuity.

Clinical relevance: Merkel cell dysfunction can reduce tactile discrimination. Merkel cell carcinoma is a rare, aggressive skin cancer arising from Merkel cells; it tends to occur in sun-exposed areas and requires prompt diagnosis and management.