Nerve endings, free

The pain appears to arise from the formation of melittin pores in the membranes of nociceptors, free nerve endings that detect harmful ( noxious —thus the name) stimuli of violent mechanical stress, high temperatures, and irritant chemicals. The creation of pores by melittin depends on the nociceptor membrane potential. Melittin in water solution is tetrameric. However, melittin interacting with membranes in the absence of a membrane potential is monomeric and shows no evidence of oligomer... 

Nociceptors are bare or free nerve endings therefore, they do not adapt, or stop responding, to sustained or repeated stimulation. This is beneficial in that it keeps the individual aware of the damaging stimulus for as long as it persists. Nociceptors are widely distributed in the skin, dental pulp, periosteum, joints, meninges, and some internal organs. The three major classes of nociceptors are ... 

Stimulation of free nerve endings known as nociceptors is the first step leading to the sensation of pain. These receptors are found in both somatic and visceral structures and are activated by mechanical, thermal, and chemical factors. Release of bradykinins, K1, prostaglandins, histamine, leukotrienes, serotonin, and substance P may sensitize and/or activate nociceptors. Receptor activation leads to action potentials that are transmitted along afferent nerve fibers to the spinal cord. 

Pain receptors in the skin (cutaneous) and other tissues (non-cutaneous) are all free nerve endings. They are widespread in the superficial layers of the skin and in certain internal tissues such as the arterial walls and joints. Most other deep tissues contain few free nerve endings and so tissue damage there is more likely to cause a slow, chronic, dull ache rather than acute pain in these areas. 

Non-ciliated receptors show much variation. Some resemble ciliated receptors in that they have a terminal dendritic bulb with a basal body but no distal cilium (85, 942). Others, as in H. nana (Fig. 2.9), show little structural specialisation and appear to be little more than free nerve endings which may have a single, double or triple structure. Endings which do not penetrate the tegument to the external environment may have a mechanoreceptive or proprioceptive (i.e. receptive to internal stimuli) -rather than chemoreceptive - function (12, 206, 942). 

Figure 3. Location of some oral chemosensory receptor systems. Taste buds (schematic upper right) are found on specialized papillae on the tongue and scattered on the palate and posterior oral structures. Free nerve endings are found...

Figure 4. Peripheral sensory ganglia that supply nerve endings to taste buds in the mammalian oral cavity. Trigeminal ganglion, which supplies free nerve endings to all oral surfaces, not shown.

Four cranial nerves subserve the sense of taste, three of these (facial, glossopharyngeal and vagus) innervate taste bud systems (Fig. 1) and one (trigeminal) supplies free nerve ending receptors. Both of these types of receptors respond to chemical stimuli. Only the taste bud systems of the facial and glossopharyngeal nerves have been studied in sufficient detail with many food compounds. 

Free nerve endings Opening of sweat duot... 

Intertwined with the dermal vasculature is a complex network of nerve plexuses consisting of both encapsulated and free nerve endings. These sensory and sensorimotor nerves ramify throughout the skin... 

Subjectively the abrasion feels unpleasant, but still painless to the patient, as the sandpaper is still a long way from the free nerve endings that are in the lower part of the epidermis. 

The term nociceptor refers to sensory receptors that respond to noxious stimuli (see Kruger et al. 2003 for review). A variety of cutaneous primary afferent nociceptors have been described, primary among them are the unmyelinated C fibers that are characterized by free nerve endings. The C-polymodal nociceptor responds to... 

The mechanism for this action may involve interaction with protein receptors in free nerve endings or induction of changes in membrane permeability through a disruption of the lipid bilayer. 

Beidler, L. M. Comparison of gustatory receptors, olfactory receptors, and free nerve endings. Cold Spring Harbor Symposium on Quantitative Biology, 1965, 30, 191-200. 

A receptor may consist of free nerve endings or specialized organelles. Some of fliem couple to axons, not dendrites. Nociceptors are coupled to slow, fliin, nonmyelinated axons (C-fibers). Muscle spindle receptors monitor the muscle tension and the electrotonus. 

---