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Neuromuscular Physiology
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
The smallest functional unit (transmission unit) of the nervous system is the neuron. In terms of information transmission, neurons are either motor (efferent) or sensory (afferent). Motor neurons transmit information from the CNS to effector cells. Sensory neurons transmit information from various sensory receptors to the CNS. Basic neuron anatomy is shown in Figure 1.19. Anatomically, the human nervous system consists of billions of neurons, having different shapes and sizes. Information transmission results from changes in the electrical potential of the cell.
Physiology of the Pain System
Published in Sahar Swidan, Matthew Bennett, Advanced Therapeutics in Pain Medicine, 2020
Sensory information is relayed via sensory neurons. Primary sensory neurons can be divided into two main categories: those which relay innocuous non-painful information (Aβ-fibers) and those that relay painful nociceptive information (Aδ and C-fibers). Innocuous information is communicated through the peripheral nerve on low-threshold Aβ-fibers which are large in diameter, highly myelinated, and allow for quick action potentials.
Targeting the Nervous System
Published in Nathan Keighley, Miraculous Medicines and the Chemistry of Drug Design, 2020
The nervous system is composed of two parts: the central nervous system (CNS; brain and spinal cord) and peripheral nervous system, which extends the entire body. Sensory neurons carry information from the body to the CNS, while motor nerves carry messages from the CNS to the rest of the body. Information from a stimulus is carried to the CNS by the sensory neurones; here, the messages are coordinated and the appropriate messages are then sent from the CNS to effectors, which can be organs or muscles, to generate a response to the stimulus. For example, if a person was to touch a hot object, for example they accidentally touch the ring on a hot cooker, the information from the stimulus, measured by temperature receptors in the skin, travels via a sensory neurone to a coordinator, such as a connector neurone within the CNS, which produces an automatic response to move the hand away from the heat by sending signals down motor neurones to the effector muscles. This pathway of neurones is known as a reflex arc. The response is immediate because only three neurones are involved and it is an automatic, involuntary response because it bypasses the brain to save time and avoid damage.
The use of passive cable theory to increase the threshold of nociceptors in people with chronic pain
Published in Physical Therapy Reviews, 2021
Ayman A. Mohamed, Motaz Alawna
Nociceptors respond nonlinearly to any painful stimulation [94–96]. Morisset and Nagy [95] have demonstrated that nociception signals are long-lasting inputs with prolonged after discharges. These nociceptors have slow activation kinetics and are voltage-dependent [94–96]. These two characteristics cause nociceptive sensory neurons to have non-linear input-output interactions in both the time and amplitude domains. Recently, Dik [94] conducted a bifurcation analysis of a nociceptive neuron model to investigate the alterations in the firing activity pattern due to the application of harmful pain stimulation on the dorsal ganglia of rats. He found that the firing patterns of nociceptive neurons were nonlinear in response to any damaging injury. This nonlinear behavior of nociceptive neurons occurs because they depend on ions diffusion between specific ion channels to initiate and propagate their signals (the action potential) [89]. Due to this nonlinear behavior of nociceptive neurons, they can be considered as nonlinear conductors [89].
A mini-review: Bridging the gap between autism spectrum disorder and pain comorbidities
Published in Canadian Journal of Pain, 2020
Chad O. Brown, Jarryll Uy, Karun K. Singh
Biophysical studies of Nav1.7 have implicated its function in action potential initiation and its regulation of subthreshold stimuli.44,52–54 Recent studies have highlighted efforts to sequence patients with pain phenotypes to determine a genetic etiology of pain syndromes such as erythromelalgia, paroxysmal extreme pain disorder, small fiber neuropathy, and channelopathy-associated congenital indifference to pain.54–60 A common observation was a convergence of unknown variants accumulating in SCN9A. This provided initial necessary observations, but further functional validation or phenotyping is needed to ensure that these variants are the cause of the pain syndromes observed in patients. Further evidence suggested that gain-of-function variants in SCN9A enhanced neuronal excitability, which was observed in erythromelalgia, paroxysmal extreme pain disorder, and small fiber neuropathy; loss-of-function variants recapitulated a hypoexcitable neuronal phenotype that exhibited as channelopathy-associated congenital indifference to pain. These experiments were primarily performed in HEK293 cells and, more recently, in human-derived sensory neurons with electrophysiology measuring both sodium currents and inactivation and activation properties of the currents. Many authors have highlighted the convergence of mutations in SCN9A, but a plethora of variants are still uncharacterized in patients with pain syndromes.
C. elegans: a sensible model for sensory biology
Published in Journal of Neurogenetics, 2020
Sensory neurobiology exists at the interface between biology, chemistry and physics. Our sensory processes mediate our interaction with the physical world. It is incredible that life has evolved to detect a vast array of forces and molecules present in our universe. Organisms as seemingly disparate as nematodes and humans have much in common in regard to their sensory processes. The relationship of an organism with its external and internal environments arguably begins with the sensory inputs and ends with behavioral output. Perception occurs via sensory neurons that activate in response to specific stimuli. These cues act upon sensory transduction machinery expressed by the sensory neuron itself or in specialized structures that communicate with the sensory neuron. Some of these sensory structures have evolved into large complex organs, such as the mammalian eye. However, such complexity incorporating large numbers of cells is not required for a sophisticated sensory system. Even a tiny one millimeter long organism with a compact nervous system of only 302 neurons can detect a surprisingly vast and varied array of physical stimuli, such as mechanical forces, chemicals, light, temperature, humidity and electromagnetic fields (Figure 1). The evolution of these sensory modalities confers numerous benefits to survival, including the ability to find food and mates and to avoid hazard.