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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.
Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Neural reflexes could be somatic, affecting skeletal muscles, or autonomic, involving internal organs. The pathway from the receptor that normally initiates the reflex to the effector that executes the reflex action is the reflex arc. Depending on the type of neural reflex, the effector could be muscle – skeletal, smooth, or cardiac – or a gland. An example of an autonomic reflex is the control of blood pressure. When this falls, the pressure receptors in the aorta and carotid arteries cause the sympathetic system to increase the heart rate and the cardiac output so as to restore the blood pressure to its normal level. Neural reflexes are “wired” in the neuronal circuitry, but can be influenced by the action of inputs from other parts of the nervous system on various neurons in the reflex arc. Reflexes are thus modifiable, and almost all somatic reflexes can be overridden by voluntary control. The eyeblink reflex and the flexion reflex discussed below are examples of protective reflexes, whereas other reflexes, such as the aforementioned blood pressure and blood glucose level serve a regulatory function through negative feedback control.
The Autonomic Nervous System
Published in Bernard J. Dalens, Jean-Pierre Monnet, Yves Harmand, Pediatric Regional Anesthesia, 2019
Bernard J. Dalens, Jean-Pierre Monnet, Yves Harmand
The autonomic nervous system, also termed the visceral or vegetative nervous system, is concerned with the regulation of visceral functions and contributes nerves to internal organs and their coverings. This nervous system is not under voluntary control. It is regulated by neural reflex arcs involving afferent (sensory) and efferent (motor and secretory) fibers. It is organized as two antagonist systems, the sympathetic (or thoracolumbar) and parasympathetic (or craniosacral) systems, consisting of central and peripheral autonomic pathways with precise motor and secretory fibers (however, sympathetic and parasympathetic sensory fibers cannot be distinguished from one another).
Differentiation among bio- and augmented- feedback in technologically assisted rehabilitation
Published in Expert Review of Medical Devices, 2021
Giovanni Morone, Sheida Ghanbari Ghooshchy, Angela Palomba, Alessio Baricich, Andrea Santamato, Chiara Ciritella, Irene Ciancarelli, Franco Molteni, Francesca Gimigliano, Giovanni Iolascon, Pierluigi Zoccolotti, Stefano Paolucci, Marco Iosa
Feedbacks can be categorized also by the entity of their delay. All feedbacks have a delay, even those of sensorimotor control, often of few hundreds of milliseconds. For this reason, motor control exploits predictions of feedforward models [32]. Exteroceptive and proprioceptive signals contribute to the perception that can, in turn, be used as a predictive coding in which action can be seen as a discharge of motor neurons to cancel prediction errors through reflex arcs. In this scenario, perception could reduce perception errors by changing predictions, while action may reduce prediction errors by changing sensation, using top-down corticospinal projections not only as motor command per se, but as predictions about proprioceptive or kinesthetic sensations, according to active inference theory [57].
Thermoregulatory reflex control of cutaneous vasodilation in healthy aging
Published in Temperature, 2021
Jody L. Greaney, Anna E. Stanhewicz, S. Tony Wolf, W. Larry Kenney
In the present study, older adults also exhibited marked reductions in the sensitivity of both SSNA and vasodilatory responsiveness to passive heating. That is, the rate of the increase in sympathetic outflow and skin blood flow throughout progressive increases in b was lower in older adults, and this likely contributes, at least in part, to the age-related reduction in the overall magnitude of the increase in SSNA and CVC in response to heat exposure [8,12,13,16,32]. However, a limitation of the present analytical approach is that it only provides information on efferent outflow and thermoeffector output, and the functional link between these two components of the reflex arc – that is, the transduction of the neural signal into a sudomotor and vasomotor response – was not addressed. We previously demonstrated a reduction in both the range and slope of the linear relation between SSNA and CVC during heating in older adults [8], which is arguably a more relevant approach for examining the entire efferent thermoregulatory reflex axis. Nevertheless, the current data, coupled with our earlier findings [8,12,13], provide compelling support for the conclusion that blunted increases in efferent SSNA directly contribute to marked impairments in reflex cutaneous vasodilation in healthy older adults.
Female genito-pelvic reflexes: an overview
Published in Sexual and Relationship Therapy, 2019
Symen K. Spoelstra, Esther R. Nijhuis, Willibrord C. M. Weijmar Schultz, Janniko R. Georgiadis
Female genital responses rely on an active and responsive genital tract that shows involuntary activity triggered by – or associated with – sexual arousal, genital stimulation and/or orgasm (Levin, 2003; Ringrose, 1966). This pelvic and perineal reflexive muscle activity (“genito-pelvic reflexes”) may be an important constituent of female sexual (dys)functioning. A reflex is defined as an automatic stereotyped response to a specific stimulus, mediated by the central nervous system. It requires an intact reflex arc, i.e. a receptor, an afferent and efferent limb, an integrative centre and an effector (Guyton & Hall, 2011). However, this definition neither restricts reflexes to the spinal cord nor to skeletal (striated) muscles, which is highly relevant for sexual reflexes. In mammals other than humans, sexual genital responsiveness is under heavy brainstem and diencephalic control (Pfaus, 2009; Veening, Coolen, & Gerrits, 2014). In humans it is likely that, even when more expanded cortical and voluntary control is present (Beauregard, Levesque, & Bourgouin, 2001; Georgiadis & Kringelbach, 2012), automated or primordial neural control systems give rise to reflexive-like pelvic muscle activity (Huynh, Willemsen, Lovick, & Holstege, 2013).