Targeting the Nervous System
Nathan Keighley in 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
Nassir H. Sabah in 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.
Clinical and electrodiagnostic evaluations of the peripheral nervous system
James W. Albers, Stanley Berent in Neurobehavioral Toxicology: Neurological and Neuropsychological Perspectives, 2005
Blink reflex studies are evoked responses and are performed as part of the nerve conduction examination. Blink reflex studies are used to evaluate function of cranial nerves V (trigeminal) and VII (facial). Unlike most of the other components of the EMG evaluation, blink reflex studies also reflect a central nervous system component that includes a polysynaptic pathway that crosses the midline (Small & Borus, 1983). The blink reflex has teleological protective eye function, and the reflex produces eyelid closure in response to stimulation of the face or eye. The reflex arc consists of a trigeminal sensory afferent limb, neuronal brainstem relays in the pons and medulla, and a facial nerve efferent motor pathway terminating in facial muscles. The electrically elicited blink reflex has two principal components, R1 and R2 (Esteban, 1999). The blink reflex is evoked in response to percutaneous electrical stimulation of the supraorbital nerve and recorded from surface electrodes placed over the orbicularis oculi muscle (Kimura, 1989). The afferent limb of the reflex is mediated by the trigeminal nerve, and the efferent component is mediated by the facial nerve. Measures include ipsilateral and contralateral response latencies. The R1 component has the shortest latency and is recorded from the orbicularis oculi muscle ipsilateral to the supraorbital stimulation. The R2 component has a longer latency than the R1 component and is recorded bilaterally following unilateral stimulation. The R2 latencies show substantial variability among individuals.
Oral neuromuscular training relieves hernia-related dysphagia and GERD symptoms as effectively in obese as in non-obese patients
Published in Acta Oto-Laryngologica, 2018
Thomas Franzen, Lita Ingrid Tibbling, Mary Karin Hägg
IQoro® (Figure 1), placed behind the lips, immediately triggers sensory input by stimulating the intra-oral membranes (n V), [12]. The sensory-motor reflex arc is engaged by the stimuli conducted by the afferent nerve pathways to the brain stem and the cortex and, in turn, the efferent signals transmitted from the brain stem to the muscles—the natural neurological process [16]. The relevant muscles are also activated by the mechanical flexing initiated by the IQoro® traction effect and the ensuing low-pressure thus created [12]. The entire chain of striated muscles from the lips to the upper third of the esophagus, and then to the diaphragm, are activated by both the neurological and the mechanical processes, whilst the smooth muscle is activated solely by the neurological commands from the sensory-motor reflex arc [17]. The positive results of this complex sensory-motor activity support earlier findings that IQNT improves lip force (LF) and swallowing capacity (SC) [12,18] and strengthens the striated muscles around the hiatal canal (Figure 2B) and improves hiatal competence similarly to HH surgery [19].
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).
Acoustic reflexes are common but not pervasive: evidence using a diagnostic middle ear analyser
Published in International Journal of Audiology, 2018
Kara D. McGregor, Gregory A. Flamme, Stephen M. Tasko, Kristy K. Deiters, William A. Ahroon, Christa L. Themann, William J. Murphy
The current study and Flamme et al. (2017) examined only the AR at 1 and 2 kHz in relation to the pervasiveness of the AR. This was a limitation of the NHANES data set, as those were the only two frequencies obtained. However, as our results showed, AR at 0.5 and 1 kHz were more common than AR at 2 and 4 kHz. Therefore, a more comprehensive study including all four test frequencies could lead to a different decision about inclusion in DRC and may be worthwhile to explore if the investigators in that study manage the capitalisation on chance across multiple observations. One complication to such a study, however, is that the inclusion of AR in a DRC would involve the generalisation of results obtained with non-impulsive sounds to impulsive sounds. In the current study, we judged a person as having an AR if reflexes were observed in at least one of the two elicitor frequencies under consideration, which represents as little as 50% of the elicitors presented. In such a case, the response observed to one elicitor stimulus was not shown to generalise to a similar stimulus of equal duration. The finding of AR for only one elicitor stimulus confirms the integrity of some portions of the reflex arc, but it is not sufficient evidence to ensure that this arc will be activated by a substantially different stimulus such as an impulse.
Related Knowledge Centers
- Autonomic Nervous System
- Motor Neuron
- Neural Pathway
- Reflex
- Sensory Neuron
- Somatic Nervous System
- Synapse
- Spinal Cord
- Brain
- Posterior Grey Column