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The Cause of Pressure Sores
Published in J G Webster, Prevention of Pressure Sores, 2019
The first and most important change is the loss of pain sensation. When tissue, particularly the skin, is becoming ischemic, a strong sensation of pain is normally sent by C fibers along the spinothalamic tracts through the spinal cord to the thalamus of the brain. From there the impulse is sent by neurons to a somatic sensory area in the postcentral gyrus of the cerebral cortex creating the feeling of pain (Ganong 1989). This uncomfortable feeling causes an individual to move, thus relieving the pressure and restoring blood flow to the tissue. Since the SCI person does not feel pain in portions of his body that are connected to the detached portion of the spinal cord, he is unaware when tissue damage is occurring in these regions. This problem is further enhanced since SCI persons tend to move less than mobile individuals thus increasing the opportunities for ischemia due to pressure to occur.
Control of Postoperative Pain by Self-Administered Opioids
Published in Robert B. Northrop, Endogenous and Exogenous Regulation and Control of Physiological Systems, 2020
Pain receptors pass their signals to the spinal cord through two types of nerve fibers: The Aδ fast fibers with conduction velocities of 6 to 30 m/sec carry fast-sharp pain signals. The slow-chronic pain signals travel on C fibers at velocities from 0.5 to 2 m/sec. On entering the spinal cord from the dorsal spinal roots, the Aδ and C fibers ascend or descend one to three spinal segments in the tract of Lissauer. They then synapse on neurons in the dorsal horns. Pain signals from the fast fibers in some cases participate in a local, spinal-cord-level, motor withdrawal reflex. For example, sudden application of heat to a foot causes reflex flexion of the leg and withdrawal of the foot.
Mechanism of peripheral nerve modulation and recent applications
Published in International Journal of Optomechatronics, 2021
Heejae Shin, Minseok Kang, Sanghoon Lee
When a single neuron is zoomed, it can be seen that the cell membrane is formed of a lipid-bilayer like other cells inside the body. Various proteins are distributed in this membrane. Among them, proteins such as voltage-gated Na+ channels and voltage-gated K+ channels have an important role in the formation of action potentials, which will be discussed next section. (Figure 1(c)). Neurons in PNS have relatively long axons and have different morphological characteristics depending on the role of neurons. They are classified according to the presence or absence of a myelin sheath as discussed above, and also according to the diameter of the axon, which differs from the conduction velocity of axons. Depending on these characteristics, the type of information transmitted by each axon also varies. For example, the A fiber which has the highest speed of transmission due to its large diameter and myelin sheath, and it serves as a channel for signals related to proprioception. In the case of C fiber that has low conduction velocity and relatively small diameter in absence of myelin sheath, it serves as a path for sensory information.[11] Therefore, selective stimulation for targeting specific fibers should be required to realize natural sensory feedback in bionic limb applications.[12]