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The nervous system
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
A reflex occurs when a stimulus elicits an automatic, involuntary response—a response that occurs without conscious effort. Reflexes are specific and predicable, and purposeful. For example, the withdrawal reflex causes a body part to be pulled away from a painful stimulus. In this way, tissue injury is avoided.
Physiology of the nervous system
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2015
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The withdrawal reflex is an important cutaneous reflex, which quickly removes the body from a painful or noxious stimulus. The receptors are pain receptors on the free nerve endings of Aδ and C fibres, and the effector organs are skeletal muscles that withdraw the body from the stimulus. The withdrawal reflex is via a polysynaptic pathway with several interneurons linking the pain receptor with the α motor neuron of the limb, producing contraction of the flexor muscles. A continuation of the withdrawal reflex occurs even after the receptor stops firing because reverberating circuits produced by branches of interneurons re-excite and prolong the motor neuron discharge, known as ‘afterdischarge’. Interneurons from pathways that cross the spinal cord can stimulate the extensor motor neurons on the opposite side of the body to produce the cross-extensor reflex. Inhibition of antagonist muscles to the flexor muscles may occur when a reflex activates one group of motor neurons with a simultaneous inhibition of its antagonistic motor neurons – ‘reciprocal innervation’.
Developmental neurobiology of nociception
Published in Pamela E Macintyre, Suellen M Walker, David J Rowbotham, Clinical Pain Management, 2008
Flexor-withdrawal responses to mechanical and thermal stimuli can be measured from birth, but thresholds are lower, and the reflex response has greater amplitude, longer latency, and a higher degree of variability.2, 37, 71, 72 The increase in withdrawal reflex thresholds with age reflects a gradual decrease in the excitability of spinal cord neurons, increased inhibitory input, and reorganization of sensory connections that reduce the size of the receptive field.26 Reflex responses are initially less organized, can be evoked by both noxious and innocuous stimuli, and may result in inappropriate generalized movements. Maturation of sensory and motor inputs, and an activity-dependent process that involves strengthening of appropriate connections and suppression of erroneous movements, leads to tuning of the receptive fields of each withdrawal reflex module. As a result, more specific motor responses develop that selectively move the stimulated area away from the stimulus.73, 74, 75
How Does Our Brain Generate Sexual Pleasure?
Published in International Journal of Sexual Health, 2021
Barry R. Komisaruk, Maria Cruz Rodriguez del Cerro
Perhaps the difference between pleasurable stimulation and painful stimulation is the relative intensity and the contribution of neuronal inhibition. Neuronal inhibition is as crucial to normal neural processes as neuronal excitation. It is estimated that 40% of the synapses in the human brain are inhibitory, utilizing GABA as the neurotransmitter (Bowery & Smart, 2006). Without neuronal inhibition our movements would be spastic. Neuronal inhibition enables us to move gracefully and with precision. At a biologically fundamental level, we have hard-wired inhibitory systems that enable coordinated behavior. Our spinal cord neuronal circuitry enables a noxious stimulus (heat) applied to the finger to elicit a withdrawal reflex (pulling the hand away from the heat). While the spinal cord neuronal hard-wiring activates the flexor motor neurons, e.g. the biceps, which withdraw the hand, the noxious stimulus simultaneously activates hard-wired inhibitory neurons that relax the antagonistic triceps muscles. This is a protective reflex in which the hard-wiring controls these “antagonistic” muscles, so that we don’t tear the triceps muscle when we contract the biceps. This system functions even if the spinal cord is severed from the brain, further evidence of the fundamental, role of neuronal active inhibition. Another type of biologically fundamental spinal cord-level protective reflex is the Golgi tendon organ reflex, in which sudden, intense stretch of a muscle immediately inhibits it, as if you try to catch a 100-pound bag of concrete and suddenly drop it. That protective inhibitory reflex prevents a muscle from being ripped from its tendon.
Techniques for lung transplantation in the rat
Published in Experimental Lung Research, 2019
The donor animal is induced with isoflurane five parts per million (ppm) and either maintained with isoflurane 3 ppm via a nose cone or intubated. The advantage of intubation is that the lungs are inflated with positive pressure during the entire procurement, similar to the situation in human donors. Inflation of the lungs during flushing with the preservative allows for a lower pulmonary vascular resistance and presumably more uniform flushing. The chest and abdomen are shaved and the skin is disinfected with alcohol. Before skin incision it is very important to confirm adequate depth of anesthesia by firmly pinching the animal’s toes with a forceps. If no withdrawal reflex is elicited, the operation can proceed.
Clinical outcomes following conservative management of chronic traumatic cervical myelopathy: A case report
Published in Physiotherapy Theory and Practice, 2018
Justin Bridges, Roberto Sandoval
The screening measures for cervical myelopathy included Hoffmann’s sign, muscle stretch reflexes (biceps, triceps, and brachioradialis), inverted supinator sign, suprapatellar tendon reflex, hand withdrawal reflex, Babinski sign, and clonus. The patient exhibited diminished, but present muscle stretch reflex response (grade 1+) for the biceps and triceps stretch and a brisk response (grade 3+) for the brachioradialis. The patient exhibited a positive Hoffman’s sign, hand withdrawal reflex, and finger escape sign. Hoffman’s sign was elicited by repetitively flicking the distal third phalanx and was interpreted to be positive with resulting ipsilateral finger flexion and thumb adduction, Figure 1 (Cook et al. 2009, 2011). The hand withdrawal reflex was invoked by tapping the dorsum of the patients hand and was considered to be positive with corresponding atypical hand flexor response, Figure 2 (Cook et al. 2009, 2011). The finger escape sign was confirmed to be positive due to the patient’s inability to achieve and maintain adduction of his right fifth digit, Figure 3 (Cook et al. 2009, 2011). Hoffman’s sign and the hand withdrawal reflex have an established sensitivity of 44% and 41% and a positive likelihood ratio of 1.8 and 1.1 at the 95% confidence interval, respectively, when used as clinical screening tools for cervical myelopathy (Cook et al. 2011). The patient also reported pain reproduction with axial compression to the top of his head (Spurling’s test) on the right side of his neck with the spine in a neutral position, and upper-limb tension testing for the radial and ulnar nerves more readily reproduced symptoms on the right arm when compared to the left. Cervical distraction testing improved pain localized at the base of the patient’s neck but had no effect on the peripheralization of neurological symptoms into his right upper extremity.