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Progress in Brain Research 2022Direct and indirect pathways mediating the vestibulo-ocular reflexes, considering contributions made by the vestibular commissure, cerebellum, and vestibular efferent... (Review)
Review
Direct and indirect pathways mediating the vestibulo-ocular reflexes, considering contributions made by the vestibular commissure, cerebellum, and vestibular efferent neurons are reviewed. This background leads to a detailed treatment of three-dimensional aspects of the vestibulo-ocular reflex, comparing the planes of the labyrinthine semicircular canals with the pulling directions of the extraocular muscles. By applying matrix algebra and rotational vectors, Robinson provides insights into the comparative anatomy of the vestibular system in different species, how central circuits process raw vestibular signals in three dimensions, and how the directions of eye movement caused by brainstem and cerebellar lesions can be explained.
Topics: Eye Movements; Humans; Oculomotor Muscles; Reflex; Reflex, Vestibulo-Ocular; Semicircular Canals; Vestibule, Labyrinth
PubMed: 35074050
DOI: 10.1016/bs.pbr.2021.10.006 -
Handbook of Clinical Neurology 2019Late responses include F waves, A waves, H reflex, and the blink reflex. These responses help enhance routine nerve conduction studies. Despite the use of F waves in... (Review)
Review
Late responses include F waves, A waves, H reflex, and the blink reflex. These responses help enhance routine nerve conduction studies. Despite the use of F waves in multiple clinical applications, their studies can technically challenge even the most experienced electromyographers. They vary in latency, amplitude, and configuration, whereas A waves show no change in latency or morphology. Electrical stimulation of the supraorbital branch of the trigeminal nerve on one side results in a reflexive activation of the facial nucleus causing contraction of the orbicularis oculi muscle, short latency R1 ipsilaterally, and long latency R2 bilaterally. F waves can help determine the presence of a polyneuropathy. A waves can reflect axonal damage. H reflexes provide nerve conduction measurements along the entire length of the nerve, demonstrating abnormalities in neuropathies and radiculopathies. Abnormalities in the blink reflex can suggest the presence of an acoustic neuroma or a demyelinating polyneuropathy, which can affect the cranial nerves. This reflex, which also needs appropriate technical expertise, helps to assess cranial nerves V and VII along with their connections in the pons and medulla. The blink reflex, the electrical version of the corneal reflex, represents a polysynaptic reflex.
Topics: Blinking; Facial Muscles; Facial Nerve; H-Reflex; Humans; Nervous System Diseases; Trigeminal Nerve
PubMed: 31277850
DOI: 10.1016/B978-0-444-64032-1.00015-1 -
Reviews in Cardiovascular Medicine Feb 2022Heart failure with reduced ejection fraction is associated with increased exercise intolerance, morbidity, and mortality. Importantly, exercise intolerance in heart... (Review)
Review
Heart failure with reduced ejection fraction is associated with increased exercise intolerance, morbidity, and mortality. Importantly, exercise intolerance in heart failure with reduced ejection fraction is a key factor limiting patient quality of life and survival. Exercise intolerance in heart failure with reduced ejection fraction stems from a multi-organ failure to maintain homeostasis at rest and during exercise, including the heart, skeletal muscle, and autonomic nervous system, lending itself to a system constantly trying to "catch-up". Hemodynamic control during exercise is regulated primarily by the autonomic nervous system, whose operation, in turn, is partly regulated via reflexive information from exercise-stimulated receptors throughout the body (e.g., arterial baroreflex, central and peripheral chemoreceptors, and the muscle metabo- and mechanoreflexes). Persons with heart failure with reduced ejection fraction exhibit malfunctioning autonomic reflexes, which lead to exaggerated sympathoexcitation and attenuated parasympathetic tone. Chronic elevation of sympathetic activity is associated with increased morbidity and mortality. In this review, we provide an overview of how each main exercise-related autonomic reflex is changed in heart failure with reduced ejection fraction, and the role of exercise training in attenuating or reversing the counterproductive changes.
Topics: Exercise; Heart Failure; Hemodynamics; Humans; Quality of Life; Reflex; Stroke Volume
PubMed: 35229563
DOI: 10.31083/j.rcm2302072 -
Journal of Applied Physiology... Sep 2006Autonomic nerves in most mammalian species mediate both contractions and relaxations of airway smooth muscle. Cholinergic-parasympathetic nerves mediate contractions,... (Review)
Review
Autonomic nerves in most mammalian species mediate both contractions and relaxations of airway smooth muscle. Cholinergic-parasympathetic nerves mediate contractions, whereas adrenergic-sympathetic and/or noncholinergic parasympathetic nerves mediate relaxations. Sympathetic-adrenergic innervation of human airway smooth muscle is sparse or nonexistent based on histological analyses and plays little or no role in regulating airway caliber. Rather, in humans and in many other species, postganglionic noncholinergic parasympathetic nerves provide the only relaxant innervation of airway smooth muscle. These noncholinergic nerves are anatomically and physiologically distinct from the postganglionic cholinergic parasympathetic nerves and differentially regulated by reflexes. Although bronchopulmonary vagal afferent nerves provide the primary afferent input regulating airway autonomic nerve activity, extrapulmonary afferent nerves, both vagal and nonvagal, can also reflexively regulate autonomic tone in airway smooth muscle. Reflexes result in either an enhanced activity in one or more of the autonomic efferent pathways, or a withdrawal of baseline cholinergic tone. These parallel excitatory and inhibitory afferent and efferent pathways add complexity to autonomic control of airway caliber. Dysfunction or dysregulation of these afferent and efferent nerves likely contributes to the pathogenesis of obstructive airways diseases and may account for the pulmonary symptoms associated with extrapulmonary disorders, including gastroesophageal reflux disease, cardiovascular disease, and rhinosinusitis.
Topics: Animals; Autonomic Nervous System; Feedback; Humans; Lung; Muscle Contraction; Muscle, Smooth; Reflex
PubMed: 16728519
DOI: 10.1152/japplphysiol.00313.2006 -
Journal of the Neurological Sciences Mar 2006A method has been developed for measuring the Ia fibre input/motoneurone output relationship for the soleus H-reflex in healthy human volunteers. The shift in the... (Review)
Review
A method has been developed for measuring the Ia fibre input/motoneurone output relationship for the soleus H-reflex in healthy human volunteers. The shift in the relationship during weak toe extension, and in some subjects during weak plantar flexion, indicates the imposition of an inhibitory mechanism, presumably presynaptic. From these observations, and others previously made on long-loop reflexes, it is argued that the inhibitory mechanism may have evolved to suppress unwanted information from the periphery, not only during movement but in the resting state, and that this development was a necessary accompaniment of encephalisation.
Topics: Animals; Biological Evolution; Electric Stimulation; Electromyography; Humans; Models, Biological; Muscle, Skeletal; Reflex; Spinal Cord
PubMed: 16438987
DOI: 10.1016/j.jns.2005.11.018 -
Psychological Review Jul 1990This theoretical model of emotion is based on research using the startle-probe methodology. It explains inconsistencies in probe studies of attention and fear... (Review)
Review
This theoretical model of emotion is based on research using the startle-probe methodology. It explains inconsistencies in probe studies of attention and fear conditioning and provides a new approach to emotional perception, imagery, and memory. Emotions are organized biphasically, as appetitive or aversive (defensive). Reflexes with the same valence as an ongoing emotional state are augmented; mismatched reflexes are inhibited. Thus, the startle response (an aversive reflex) is enhanced during a fear state and is diminished in a pleasant emotional context. This affect-startle effect is not determined by general arousal, simple attention, or probe modality. The effect is found when affects are prompted by pictures or memory images, changes appropriately with aversive conditioning, and may be dependent on right-hemisphere processing. Implications for clinical, neurophysiological, and basic research in emotion are outlined.
Topics: Arousal; Attention; Blinking; Emotions; Humans; Reflex, Startle
PubMed: 2200076
DOI: No ID Found -
Annals of the New York Academy of... Jun 2001The Bezold-Jarisch reflex is an eponym for a triad of responses (apnea, bradycardia, and hypotension) following intravenous injection of veratrum alkaloids in... (Review)
Review
The Bezold-Jarisch reflex is an eponym for a triad of responses (apnea, bradycardia, and hypotension) following intravenous injection of veratrum alkaloids in experimental animals. The observation was first reported in 1867 by von Bezold and Hirt, and confirmed in 1938-1940 by Jarisch. The triad depends on intact vagi and is mediated through cranial nervous medullary centers controlling respiration, heart rate, and vasomotor tone. The respiratory effects are mediated through pulmonary vagal afferents and the bradycardia and vasodepression through cardiac vagal afferents. The veratrum alkaloids activate all known receptors in the carotid-aortic and cardiopulmonary areas. The cardiopulmonary receptors (baroreceptors, cough receptors, and parenchymal stretch receptors) also respond to other chemical substances: nicotine, capsaicin, venom, antihistaminics, halogenated anesthetics, diguanides, and serotonin (5-hydroxytryptamine). Derivatives of last-mentioned amine activate Type 1, 2, or 3 receptors and have potential therapeutic use. Since several types of cardiopulmonary receptors participate in the Bezold-Jarisch reflex, it has been difficult to develop a blockade to one type of receptor for therapeutic use (cough, bronchospasm, pulmonary hypertension, or coronary vasospasm). Axon reflexes influence pulmonary blood vessels, bronchial blood vessels, and bronchial smooth muscles. These intrapulmonary reflexes need further study as to how they relate to the Bezold-Jarisch reflex in health and disease. The cardiopulmonary and carotid-aortic reflexes can serve as defense mechanisms against chemical hazards that are likely to be inhaled in the workplace and in the environment.
Topics: Animals; Baroreflex; Heart; History, 19th Century; History, 20th Century; Humans; Lung; Neurology; Reflex
PubMed: 11458703
DOI: No ID Found -
The European Journal of Neuroscience Nov 2023Most individuals experience their dominant arm as being more dexterous than the non-dominant arm, but the neural mechanisms underlying this asymmetry in motor behaviour...
Most individuals experience their dominant arm as being more dexterous than the non-dominant arm, but the neural mechanisms underlying this asymmetry in motor behaviour are unclear. Using a delayed-reach task, we have recently demonstrated strong goal-directed tuning of stretch reflex gains in the dominant upper limb of human participants. Here, we used an equivalent experimental paradigm to address the neural mechanisms that underlie the preparation for reaching movements with the non-dominant upper limb. There were consistent effects of load, preparatory delay duration and target direction on the long latency stretch reflex. However, by comparing stretch reflex responses in the non-dominant arm with those previously documented in the dominant arm, we demonstrate that goal-directed tuning of short and long latency stretch reflexes is markedly weaker in the non-dominant limb. The results indicate that the motor performance asymmetries across the two upper limbs are partly due to the more sophisticated control of reflexive stiffness in the dominant limb, likely facilitated by the superior goal-directed control of muscle spindle receptors. Our findings therefore suggest that fusimotor control may play a role in determining performance of complex motor behaviours and support existing proposals that the dominant arm is better supplied than the non-dominant arm for executing more complex tasks, such as trajectory control.
Topics: Humans; Reflex, Stretch; Goals; Movement; Upper Extremity; Muscle, Skeletal; Electromyography; Reflex
PubMed: 37727025
DOI: 10.1111/ejn.16148 -
The Medical Journal of Australia Mar 1962
Topics: Humans; Reflex
PubMed: 13876281
DOI: No ID Found -
Neurology Aug 2015Uncertainty in diagnosing disorders of consciousness, and specifically in determining whether consciousness has been lost or retained, poses challenging scientific and...
Uncertainty in diagnosing disorders of consciousness, and specifically in determining whether consciousness has been lost or retained, poses challenging scientific and ethical questions. Recent neuroimaging-based tests for consciousness have cast doubt on the reliability of behavioral criteria in assessing states of consciousness and generate new questions about the assumptions used in formulating coherent diagnostic criteria. The reflex, a foundational diagnostic tool, offers unique insight into these disorders; behaviors produced by unconscious patients are thought to be purely reflexive, whereas those produced by conscious patients can be volitional. Further investigation, however, reveals that reflexes cannot be reliably distinguished from conscious behaviors on the basis of any generalizable empirical characteristics. Ambiguity between reflexive and conscious behaviors undermines the capacity of the reflex to distinguish between disorders of consciousness and has implications for how these disorders should be conceptualized in future diagnostic criteria.
Topics: Consciousness; Consciousness Disorders; Humans; Reflex; Reproducibility of Results
PubMed: 26085602
DOI: 10.1212/WNL.0000000000001748