Discussions (D)
Terence R. Anthoney in Neuroanatomy and the Neurologic Exam, 2017
Though it is difficult to find statements as to where a nerve ends peripherally, the term “nerve ending” is usually applied to the most distal portions of peripheral axons, such as free sensory nerve endings (e.g., C&S, p. 160) and motor end plates (e. g., C&S, p. 174). Some authors, however, do not necessarily consider every nerve to include its entire peripheral ramification. For example, Williams and Warwick state that “The sensory root (nervus intermedins) consists of the central processes of the unipolar cells of the genicular ganglion” (1980 p. 1071); and Brodal (1981) notes that “the central processes of these cells [in the vestibular ganglion] form the vestibular nerve” (p. 472) and that “The cochlear nerve is composed of the central processes, or axons, of the bipolar spiral ganglion cells” (p. 606). At one extreme, then, the term “nerve” can refer to the entire course of the fibers found in its trunk, from their deep origin in the CNS (a lá W&W, p. 1053) to their most distal peripheral endings (e. g., DeJ, p. 82). At the other extreme, a nerve could be limited to its trunk, by considering its roots and branches to be separate structures (e. g., Snel, p. 25).
Homeostasis
David Sturgeon in Introduction to Anatomy and Physiology for Healthcare Students, 2018
The next type of nerve ending found in the dermis (and epidermis) are pain receptors or nociceptors. The term nociception is derived from the Latin word nocere meaning ‘harm’ or ‘injurious’. As the name suggests, they are activated in response to potentially harmful or tissue-damaging stimulation although it is the sensory cortex of the brain that actually interprets the information as ‘painful’ (see Chapter 12). The reason sunburn (a first-degree burn) is more painful than a full thickness burn is, paradoxically, because it is so superficial. Overexposure to UV light and radiation damages the epidermis of the skin and stimulates excessive production of a protein that irritates the nociceptors below. Full thickness burns, on the other hand, destroy the epidermis, dermis and possibly the subcutaneous fat and underlying structures. Consequently, since the nerves themselves have been destroyed, the wound is often painless. One of the major complications of partial and full thickness burns (second and third degree burns) is fluid loss. If the waterproof barrier of the skin is breached, plasma and plasma proteins are lost. This can result in such severe fluid loss that the heart is unable to pump enough blood to the tissue resulting in circulatory collapse (hypovolemic shock). Fluid replacement therapy for burns victims is calculated, therefore, according to the percentage of body surface area affected.
The Somatosensory System
Golara Honari, Rosa M. Andersen, Howard Maibach in Sensitive Skin Syndrome, 2017
Nociceptors do not show the kinds of adaptation response found with rapidly adapting LTMs (i.e., they fire continuously to tissue damage), but pain sensation may come and go, and pain may be felt in the absence of any nociceptor discharge. They rely on chemical mediators around the nerve ending, which are released from nerve terminals and skin cells in response to tissue damage. Koltenzenburg et al. (30) showed that nerve growth factor (NGF) is an important mediator in painful inflammatory skin states, with levels increasing in inflamed tissue. Following carrageenan inflammation of rodent skin, a marked increase in the proportion of nociceptors which displayed an ongoing activity was observed, and this was reflected in a significant increase in the average ongoing discharge activity. Spontaneously active C fibers were sensitized to heat and displayed a more than twofold increase in their discharge to a standard noxious heat stimulus. Furthermore, the number of nociceptors responding to the algesic mediator bradykinin increased significantly from 28% to 58%.
The early history of the knee-jerk reflex in neurology
Published in Journal of the History of the Neurosciences, 2022
Some neurophysiological unknowns were described by Westphal at the very outset. There was no clear reflex-mediating (sensible) muscle nerves. The tendon was not necessary to elicit the knee jerk. Were there nerves in the tendon affected by its stretching? Could the quadriceps be stimulated directly? Of particular interest would be their crucial ignorance of the function of muscle spindles, the organs that detect muscle stretch and stimulate associated sensory neurons transmit afferent impulses. Batten (1897) summarized what was known of the muscle spindle at that time. What came to be called the muscle spindle was first described by Miescher in 1843. Its function was not known by the end of the century. It was described as muscle and nerve in development, as degenerating muscle, as sensory nerve endings, as a protection to the nerve ending during contraction, and as having a special connection with the lymphatic system. Kühne first called it Die Muskelspindeln in 1863. In 1889, Kölliker studied the muscle spindle in frogs, rabbits, and humans and held to the developmental explanation. In 1896, Dutil concluded the spindles were sensory in function, similar to Golgi’s tendon organs.
Resolution of persistent traumatic supraorbital pain after neuroma excision
Published in Orbit, 2022
Matthew Tukel, Robert Beaulieu, Alon Kahana
Stump neuromas are almost always fully excised as they lack distal function and pose a low risk of additional functional impairment. Conversely, neuromas in continuity first require intraneural neurolysis with selective neuroma excision to spare remaining nerve function.12 Once neuroma excision is complete, the surgeon must determine the optimal reconstructive strategy that considers the regenerative capacity of the nerve stump and promotes maximal neuronal regeneration.13 Reconstructive strategies following neuroma excision are divided into two broad categories based on the presence or absence of the distal nerve ending.11 In cases where the terminal nerve ending is intact, techniques that include auto or allograft placement and hollow tube reconstruction are commonly employed. In the absence of an identifiable nerve ending, reconstructive techniques include muscular or interosseous implantation, relocation nerve grafting, nerve cap placement, “end-to-side” neurorrhaphy, and targeted muscle reinnervation.11
Intramuscular Distribution of the Abducens Nerve in the Lateral Rectus Muscle for the Management of Strabismus
Published in Current Eye Research, 2018
Hyun Jin Shin, Shin-Hyo Lee, Kang-Jae Shin, Ki-Seok Koh, Wu-Chul Song
Our results for the anatomical structure are consistent with those of the previous study employing Sihler’s staining by Nam et al.10 Those authors suggested that the abducens nerve branch generally penetrated the LR by 30–32 mm from the muscle insertion. Our data (#7) fall within this range, with a mean distance of 31.2 mm. They also reported that the most anteriorly located intramuscular nerve ending was observed at 24.2 mm from the muscle insertion. In the present study, the mean distance from the muscle insertion point to the anterior end of the nerve plexus (#8) was 24.8 mm. However, the mean intramuscular nerve length (#4) was 6.3 mm, which is slightly longer than that of 4.38 mm reported by Nam et al.10 This discrepancy might be related to the difficulty of clearly defining where a weakly stained nerve plexus ends.
Related Knowledge Centers
- Axon
- Cutaneous Receptor
- Nociception
- Nociceptor
- Sensory Neuron
- Stratum Granulosum
- Skin
- Afferent Nerve Fiber
- Nerve
- Stimulus Modality