The nerves of the skin
Human skin is permeated by a complex network of neural pathways, stretching from the subcutaneous fatty tissue through the dermis up to the topmost living layers of the epidermis.
More than a million sensory receptors are distributed throughout human skin. Some important sensory receptors are the Pacinian corpuscles in the subcutis which react to vibration and the Meissner’s corpuscles which detect touch, acting as pressure keys at the epidermal/dermal border, and being responsible for perceiving touch and pressure.
In the dermis there are also the Ruffini corpuscles (stretch receptors) and Krause’s corpuscles or end bulbs (mechanoreceptors). Intra-epithelial nerve endings are sensory nerve fibres in the skin, which produce sensations of heat, cold, pain, touch and pressure.
The nerves in the skin are in constant communication with the brain and the environment. This is how the skin is able to fulfil its function as an organ of perception and communication. The immune system is regulated via the nerves in the skin, thus, for example, initiating skin inflammations and irritations.
The sensory nerves perceive external and internal stimuli to the skin, such as touch, tension, pain, heat and cold. The autonomic nerves control the vessels, the appendages of the skin and the smooth muscles which make the hairs stand upright.
The keratinocytes form 90% of the epidermis. From the germinal layer to the granular cell layer they are called keratinocytes, in the stratum corneum the corneocytes.
Their main tasks are to form an effective protective wall against environmental influences, and to participate in immune system reactions.
Keratinocytes are renewed every 28 days and die off in the form of scaly cells containing keratin.
Melanocytes form the skin pigment melanin. Melanin can be red, yellow, brown or black in colour. Melanocytes are found in the germinal layer of the epidermis and in the hair follicle.
They have long cell processes which extend into the upper layers of the epidermis, and through these they give pigment to the keratinocytes. Thus, a melanocyte supplies 36 keratinocytes on average.
(Named after the German doctor and discoverer, Paul Langerhans)
The Langerhans cells are termed the “outposts” of the immune system and are found in the basal cell layer. They have a double function in the skin’s immune system.
One is to capture harmful substances which have penetrated and to report the incident to the immune system.
The other, in their capacity as what are termed phagocytes, is to take part in the destruction of the pathogens.
The fibroblasts are found in the dermis. They play an important part in the production of the extracellular matrix. The main product of the fibroblasts is the structural protein collagen. This ensures the firmness of the tissue and its resistance to mechanical stress (such as blows, pulling and pushing).
Another structural protein is elastin. It is, as its name suggests, very elastic and very stretchable. The elastic fibres surround the collagen fibres and thus ensure that the skin is proof against stretching and tearing.