China
Africa
Explore chapters and articles related to this topic
The painful nail
Published in Robert Baran, Dimitris Rigopoulos, Chander Grover, Eckart Haneke, Nail Therapies, 2021
The distal digit has sensory and autonomic nerves. Autonomic nerves are nonmyelinated and end in fine arborizations. Sensory nerves end in either free nerve endings or special end-organ receptors. Pain and temperature are perceived by a dermal network of unmyelinated free nerve endings. Special receptors include abundant Merkel-Ranvier endings, Meissner’s corpuscles, and Vater-Pacini corpuscles. Merkel’s endings are touch receptors that associate with basal cells in the deep aspect of intermediate rete ridges, and they also are generally found elsewhere in the skin. In contrast, Meissner’s and Vater-Pacini corpuscles are associated especially in the distal digit, although they are not unique to this site (Morgan et al., 2001).
An introduction to skin and skin disease
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
Recently, very fine nerve fibres have been identified in the epidermis, but most of the fibres run alongside the blood vessels in the dermal papillae and deeper in the dermis. There are several types of specialized sensory receptor in the upper dermis that detect particular sensations. Free nerve endings perceive touch, temperature, pain, and itch. Pacinian corpuscles respond to deep pressure and vibrations. Other sensory receptors include Golgi-Mazzoni corpuscles, Krause end bulbs, Meissner’s corpuscle (responding to dynamic pressure), Ruffini corpuscles (responding to stretching of the skin), and mucocutaneous end organs.
Physiology of the Pain System
Published in Sahar Swidan, Matthew Bennett, Advanced Therapeutics in Pain Medicine, 2020
Nociception is carried on primary afferent fibers by Aδ fibers or C fibers. Aδ-fibers are smaller in diameter and thinly myelinated, making them slower conducting (4–30 m/sec) than Aβ-fibers but much quicker than C-fibers.2 Aδ fibers are mechanoreceptors or thermoreceptors that respond to either low- or high-threshold stimuli. Aδ fibers are small, myelinated, and fast conducting. Myelinated axons usually contain specialized terminals that are sensitive to mechanical distortion.1 C-fibers are the smallest fibers and non-myelinated, making them the slowest conducting fiber type (2.5 m/sec).3 These free nerve endings are activated by high-intensity stimuli. C-fibers are polymodal—meaning they respond to mechanical stimuli, thermal stimuli, chemical stimuli, or a combination. Some C-fibers respond only to thermal stimuli. Almost all C-fibers respond to chemical stimuli—specifically capsaicin.4
Spinal cord involvement in COVID-19: A review
Published in The Journal of Spinal Cord Medicine, 2023
Ravindra Kumar Garg, Vimal Kumar Paliwal, Ankit Gupta
The SARS-CoV-2 virus can enter the spinal cord via the hematogenous route infecting the endothelial cells and invading the spinal cord. The SARS-CoV-2 virus can bypass the blood-brain-barrier since it uses the inflammatory cells as a Trojan horse.7 The inflammatory changes produced by the virus thus result in spinal cord inflammation. It has been observed that the virus enters inside the sensory neurons after peripheral inoculation, resulting in ganglionitis.42 Shiers et al. have also demonstrated that the human dorsal root ganglia contain the angiotensin-converting enzyme 2 receptors that help the SARS-CoV-2 virus to spread to the spinal cord. The entry point can be free-nerve endings present in the skin as well as the intestinal mucosa.43
Vanadium inhalation effects on the corneal ciliary neurotrophic factor (CNTF): study in a murine model
Published in Cutaneous and Ocular Toxicology, 2023
Isis Mendoza-Aldaba, Nelly López-Valdez, María Eugenia Cervantes-Valencia, Teresa Imelda Fortoul
The cornea occupies the sixth anterior part of the ocular globe and is its principal refraction element. It is structured by five layers: (1) The epithelium, (2) Bowman’s layer, (3) stroma, (4) Descemet’s membrane and (5) the endothelium. A new layer has been described recently in the human cornea as pre-Descemet’s layer or Dua’s layer which is rich in Type VI collagen and located in the posterior area of the stroma below the final layer of keratinocytes [2,3]. The anterior corneal epithelium consists of layers of squamous cells interspersed with dendritic cells and sensitive axons [4]. It has a notorious regenerative capacity, which is sustained from the stem cells in the sclerocorneal limbus and has numerous trigeminal free nerve endings. Additionally, it produces and releases neurotrophic factors to support nerve tropism and healing [5]. Bowman’s layer consists of interwoven collagen fibres which function as a barrier against infection dissemination. This layer has no regenerative properties. The stroma comprises 90% of the whole corneal thickness and builds parallel collagen fibres. Descemet’s layer is made up of Type IV collagen which is produced continuously by the endothelial cells. This layer has regenerative properties. The endothelium is a single squamous cell layer attached by desmosomes and occludens junctions that works as a semipermeable membrane, rich in Na+, K+-ATPase pump sites in the lateral membranes [6], and allows metabolic exchange between the cornea and the aqueous humour [7].
A review of dry eye disease therapies: exploring the qualities of varenicline solution nasal spray
Published in Expert Review of Ophthalmology, 2023
Siddharth Bhargava, Ranjani Panda, Asma M Azam, John D Sheppard
Discomfort associated with DED is not limited to tear film parameters [24–26]. It is thought that pain and discomfort associated with dry eyes could potentially stem from dysfunction of the somatosensory nerves that are part of the LFU [5,26–28]. As free nerve endings are incorporated into the superficial epithelial layers, they are also susceptible to damage from the aforementioned inflammatory factors found in the tear film [29–33]. In addition to the sustained direct damage, studies focusing on inflammation in animal models have demonstrated the decreased function of peripheral nerves. This results in an increased expression of serotonin receptors, which have been found to mediate pain in the trigeminal system [34–38]. Expectedly, this multifactorial disease requires nuanced and patient-centric treatment modalities to restore ocular surface homeostasis caused by decreased tear production, inflammation, and impaired cell growth.