Home About us Contact
|
Home About us Contact | ||
|
|
||
Reflex Arc (reflex + arc)
Selected AbstractsNeuroanatomical correlates of the near response: voluntary modulation of accommodation/vergence in the human visual systemEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2000Hans O. Richter Abstract This study identifies brain regions participating in the execution of eye movements for voluntary positive accommodation (VPA) during open-loop vergence conditions. Neuronal activity was estimated by measurement of changes in regional cerebral blood flow (rCBF) with positron emission tomography and 15O-water. Thirteen naive volunteers viewed a checkerboard pattern with their dominant right eye, while a lens interrupted the line of gaze during alternate 1.5 s intervals. Three counterbalanced tasks required central fixation and viewing of a stationary checkerboard pattern: (i) through a 0.0 diopter (D) lens; (ii) through a ,5.0-D lens while avoiding volitional accommodation and permitting blur; and (iii) through a ,5.0-D lens while maintaining maximal focus. The latter required large-amplitude, high-frequency VPA. As an additional control, seven of the subjects viewed passively a digitally blurred checkerboard through a 0.0-D lens as above. Optometric measurements confirmed normal visual acuity and ability to perform the focusing task (VPA). Large-amplitude saccadic eye movements, verified absent by electro-oculography, were inhibited by central fixation. Image averaging across subjects demonstrated multifocal changes in rCBF during VPA: striate and extrastriate visual cortices; superior temporal cortices; and cerebellar cortex and vermis. Decreases in rCBF occurred in the lateral intraparietal area, prefrontal and frontal and/or supplementary eye fields. Analysis of regions of interest in the visual cortex showed systematic and appropriate task dependence of rCBF. Activations may reflect sensorimotor processing along the reflex arc of the accommodation system, while deactivations may indicate inhibition of systems participating in visual search. [source] Surgical treatment of migraine headaches.HEADACHE, Issue 3 2003B Guyuron Plast Reconstr Surg. 2002 Jun;109(7):2183-2189 This prospective study was conducted to investigate the role of removal of corrugator supercilii muscles, transection of the zygomaticotemporal branch of the trigeminal nerve, and temple soft-tissue repositioning in the treatment of migraine headaches. Using the criteria set forth by the International Headache Society, the research team's neurologist evaluated patients with moderate to severe migraine headaches, to confirm the diagnosis. Subsequently, the patients completed a comprehensive migraine headaches questionnaire and the team's plastic surgeon injected 25 units of botulinum toxin type A (Botox) into each corrugator supercilii muscle. The patients were asked to maintain an accurate diary of their migraine headaches and to complete a monthly questionnaire documenting pertinent information related to their headaches. Patients in whom the injection of Botox resulted in complete elimination of the migraine headaches then underwent resection of the corrugator supercilii muscles. Those who experienced only significant improvement underwent transection of the zygomaticotemporal branch of the trigeminal nerve with repositioning of the temple soft tissues, in addition to removal of the corrugator supercilii muscles. Once again, patients kept a detailed postoperative record of their headaches. Of the 29 patients included in the study, 24 were women and five were men, with an average age of 44.9 years (range, 24 to 63 years). Twenty-four of 29 patients (82.8 percent, p < 0.001) reported a positive response to the injection of Botox, 16 (55.2 percent, p < 0.001) observed complete elimination, eight (27.6 percent, p < 0.04) experienced significant improvement (at least 50 percent reduction in intensity or severity), and five (17.2 percent, not significant) did not notice a change in their migraine headaches. Twenty-two of the 24 patients who had a favorable response to the injection of Botox underwent surgery, and 21 (95.5 percent, p < 0.001) observed a postoperative improvement. Ten patients (45.5 percent, p < 0.01) reported elimination of migraine headaches and 11 patients (50.0 percent, p < 0.004) noted a considerable improvement. For the entire surgical group, the average intensity of the migraine headaches reduced from 8.9 to 4.1 on an analogue scale of 1 to 10, and the frequency of migraine headaches changed from an average of 5.2 per month to an average of 0.8 per month. For the group who only experienced an improvement, the intensity fell from 9.0 to 7.5 and the frequency was reduced from 5.6 to 1.0 per month. Only one patient (4.5 percent, not significant) did not notice any change. The follow-up ranged from 222 to 494 days, the average being 347 days. In conclusion, this study confirms the value of surgical treatment of migraine headaches, inasmuch as 21 of 22 patients benefited significantly from the surgery. It is also evident that injection of Botox is an extremely reliable predictor of surgical outcome. Comment: Many small placebo-controlled studies and much anecdotal literature suggests that botulinum toxin may be effective in prevention of migraine, perhaps to the same extent as conventional prophylactic treatment. Larger, randomized clinical trials are underway to resolve this issue. In the meantime, those who believe in the effectiveness of botulinum toxin prophylaxis argue about how it works, that is whether its antinociceptive properties are due to peripheral effects, central or presynaptic effects, or both. Dr. Guyuron's group favors the idea that botulinum toxin interrupts a reflex arc between the central nervous system (CNS) and peripheral musculature, and that after establishing efficacy by low dose botulinum injection in the corrugator supercilii muscles, surgical resection of these muscles results in prolonged and effective prophylaxis. The idea is radical but intriguing and should not be dismissed out of hand. However, a trial is necessary in which both the botulinum toxin injections are blinded with vehicle, and the study of the surgery involves a sham surgery control group with extended long-term follow-up, before these forms of prophylaxis can be recommended to patients. SJT [source] Penile vibratory stimulation and electroejaculation in the treatment of ejaculatory dysfunction,INTERNATIONAL JOURNAL OF ANDROLOGY, Issue 6 2002JENS SØNKSEN Summary The purpose of this review is to present the current understanding of penile vibratory stimulation (PVS) and electroejaculation (EEJ) procedures and its clinical use in men with ejaculatory dysfunction. Unfortunately, the record of treating such individuals has been quite poor, but within recent years development and refinement of PVS and EEJ in men with spinal cord injury (SCI) has significantly enhanced the prospects for treatment of ejaculatory dysfunction. The majority of spinal cord injured men are not able to produce antegrade ejaculation by masturbation or sexual stimulation. However, approximately 80% of all spinal cord injured men with an intact ejaculatory reflex arc (above T10) can obtain antegrade ejaculation with PVS. Electroejaculation may be successful in obtaining ejaculate from men with all types of SCI, including men who do not have major components of the ejaculatory reflex arc. Because vibratory stimulation is very simple in use, non-invasive, it does not require anaesthesia and is preferred by the patients when compared with EEJ, PVS is recommended to be the first choice of treatment in spinal cord injured men. Furthermore, EEJ has been successfully used to induce ejaculation in men with multiple sclerosis and diabetic neuropathy. Any other conditions which affect the ejaculatory mechanism of the central and/or peripheral nervous system including surgical nerve injury may be treated successfully with EEJ. Finally, for sperm retrieval and sperm cryopreservation before intensive anticancer therapy in pubertal boys, PVS and EEJ have been successfully performed in patients who failed to obtain ejaculation by masturbation. Nearly all data concerning semen characteristics in men with ejaculatory dysfuntion originate from spinal cord injured men. Semen analyses demonstrate low sperm motility rates in the majority of spinal cord injured men. The data give evidence of a decline in spermatogenesis and motility of ejaculated spermatozoa shortly after (few weeks) an acute SCI. Furthermore, it is suggested that some factors in the seminal plasma and/or disordered storage of spermatozoa in the seminal vesicles are mainly responsible for the impaired semen profiles in men with chronic SCI. Home insemination with semen obtained by penile vibratory and introduced intravaginally in order to achieve successful pregnancies may be an option for some spinal cord injured men and their partners. The majority of men will further enhance their fertility potential when using either penile vibratory or EEJ combined with assisted reproduction techniques such as intrauterine insemination or in-vitro fertilization with or without intracytoplasmic sperm injection. [source] Neural control of eustachian tube function,,THE LARYNGOSCOPE, Issue 6 2009Murat Songu MD Abstract Objectives/Hypothesis: It has been hypothesized that middle ear pressure can be controlled by the Eustachian tube through a neuronal reflex arc in animal models. We aimed to define the role of the neuronal control mechanisms in regulating middle ear pressure in humans. Study Design: Prospective study. Methods: The study population consisted of 95 ears of 95 volunteers. The mechanoreceptors on the tympanic membrane and the baroreceptors in the middle ear, which are assumed to form the afferent plexus of the neuronal reflex arc, were blocked by topical administration of lidocaine hydrochloride, in various patient groups. The Eustachian tube functions forming the efferent plexus of the neuronal reflex arc were evaluated by manometric tests both before and after blocking the possible afferent plexus in each study group. Results: The baroreceptors established in the tympanic plexus might possibly have an effective role in this mechanism where the mechanoreceptors on the tympanic membrane seem to have a minor effect. Conclusions: Neuronal control mechanism could play an important role in regulating Eustachian tube function in humans. Laryngoscope, 2009 [source] MULTIPLE LEVELS OF SENSORY INTEGRATION IN THE INTRINSIC SENSORY NEURONS OF THE ENTERIC NERVOUS SYSTEMCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 11 2004Paul P Bertrand SUMMARY 1.,The enteric nervous system (ENS) is present in the wall of the gastrointestinal tract and contains all the functional classes of neuron required for complete reflex arcs. One of the most important and intriguing classes of neuron is that responsive to sensory stimuli: sensory neurons with cell bodies intrinsic to the ENS. 2.,These neurons have three outstanding and interrelated features: (i) reciprocal connections with each other; (ii) a slow excitatory post-synaptic potential (EPSP) resulting from high-speed firing in other sensory neurons; and (iii) a large after-hyperpolarizing potential (AHP) at the soma. Slow EPSP depolarize the cell body, generate action potentials (APs) and reduce the AHP. Conversely, the AHP limits the firing rate and, hence, reduces transmission of slow EPSP. 3.,Processing of sensory information starts at the input terminals as different patterns of APs depending on the sensory modality and recent sensory history. At the soma, the ability to fire APs and, hence, drive outputs is also strongly determined by the recent firing history of the neuron (through the AHP) and network activity (through the slow EPSP). Positive feedback within the population of intrinsic sensory neurons means that the network is able to drive outputs well beyond the duration of the stimuli that triggered them. 4.,Thus, sensory input and subsequent reflex generation are integrated over several hierarchical levels within the network on intrinsic sensory neurons. [source] | ||||||||||