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At least 307 records · Page 17Linked to original sources
PubMed2006

Mechanical load of the lumbar spine during forward bending motion of the trunk-a biomechanical study.

STUDY DESIGN: We investigated the mechanical load of the lumbar spine caused by changes of posture and carried load. OBJECTIVE: To clarify the relationship between the actual and theoretical load of the lumbar spine with and without application of external weights. SUMMARY OF BACKGROUND DATA: There is sparse knowledge regarding the relationship between the intradiscal pressure and trunk muscle activities during forward bending motion. METHODS: The measurements of intradiscal pressure, electromyogram activities of the trunk muscles, and motion analysis of the trunk in 3 young healthy men were performed simultaneously with and without lifting a weight of 10 kg. The recorded values were compared with theoretical values based on the principle of levers. RESULTS: The load of the lumbar spine and electromyogram activities of the back muscles increased in proportion to the tilting angle with and without external weights. However, the external weights induced no significant activity in the abdominal muscles. The actual measurement values were larger than the theoretical values at all tilting angles of the trunk. CONCLUSIONS: We found that the increase of the actual spinal load during trunk flexion in healthy individuals consisted of the theoretical spinal load and load generated by the back muscle activities.

Adult↗
PubMed1983

Assessment of abdominal and back extensor function. A quantitative approach and results for chronic low-back patients.

A method was developed to obtain static and dynamic measures of trunk flexor and extensor strength and endurance. The method was evaluated using 32 normal subjects. Variables of trunk strength and endurance were used to compare 24 normals (12 men and 12 women) and 24 patients (16 men and eight women) with chronic low-back dysfunction. The Iowa Trunk Dynamometer is acceptably reliable and provides for assessment of isolated function of the abdominal and back muscles. For peak abdominal and back extensor strength, the range of superiority of men over women was 39-57%, and the range of superiority of normals over patients with chronic low-back dysfunction was 48-82%. Using time to percent decrement of peak strength as a criterion, the abdominals were more susceptible to fatigue than the back extensors, women demonstrated more endurance than men, and the endurance for normals was less than those patients who were able to perform dynamic reciprocal trunk movements.

Abdominal Muscles↗
PubMed2004

The effect of short-term Swiss ball training on core stability and running economy.

The purpose of this study was to investigate the effect of a short-term Swiss ball training on core stability and running economy. Eighteen young male athletes (15.5 +/- 1.4 years; 62.5 +/- 4.7 kg; sigma9 skinfolds 78.9 +/- 28.2 mm; VO2max 55.3 +/- 5.7 ml.kg(-1).min(-1)) were divided into a control (n = 10) and experimental (n = 8) groups. Athletes were assessed before and after the training program for stature, body mass, core stability, electromyographic activity of the abdominal and back muscles, treadmill VO2max, running economy, and running posture. The experimental group performed 2 Swiss ball training sessions per week for 6 weeks. Data analysis revealed a significant effect of Swiss ball training on core stability in the experimental group (p < 0.05). No significant differences were observed for myoelectric activity of the abdominal and back muscles, treadmill VO2max, running economy, or running posture in either group. It appears Swiss ball training may positively affect core stability without concomitant improvements in physical performance in young athletes. Specificity of exercise selection should be considered.

Abdominal Muscles↗
PubMed2006

[Experimental study of the dental follicle's function in tooth root development].

OBJECTIVE: To study role of dental follicle in tooth root development. METHODS: Sixteen mandibular first molar dental germs from eight five-day postnatal Balb/c mice were divided into two groups randomly. Dental follicle of germs in one group was undetached and that of another group was removed. Subsequently, each of the germs was separately transplanted to back-muscles of adult nude mice. At seventh and fourteenth day after transplanting, the germs were collected, fixed, demineralized, dehydrated, and embedded in wax in sequence. Serial sections of 5 microm thick were made following the routine methods, stained with haematoxylin-eosin dying solution, and observed under a light microscope. RESULTS: All implantations were located in the back-muscles with abundant capillary vasculature. Under microscope, although all tooth germs could further develop after grafting, tooth germs without dental follicle developed slowly with small size and low calcification compared to those with dental follicle. Although position of Hertwig's epithelial root sheath of all germs seemed no changing, roots of the group with dental follicle could further develop and the roots develop toward the apical direction; this tendency couldn't be seen in the germs of another group. Inflammatory cells could be seen in and out of the pulp cavity of the two groups at 7th day after grafting, while no obvious inflammatory cell was observed at 14th day after grafting. CONCLUSION: Dental follicle play an important role in tooth root development. It probably can lead tooth root to develop in normal direction.

Animals↗
PubMed2003

Temporal and spatial expression profiles of BMP receptors and noggin during BMP-2-induced ectopic bone formation.

UNLABELLED: The mechanism of ectopic bone formation has not been clear. After BMP-2 implantation into the back muscles of 198 mice, expression of BMPR-1A, -2, and Noggin was increased during the early phase of the reaction. The results suggest that positive and negative feedback mechanisms modulate ectopic osteogenesis induced by this growth factor. INTRODUCTION: The expression of bone morphogenetic protein receptors (BMPRs) and Noggin during ectopic bone formation after implantation of BMP-2 into the back muscles of adult mice was investigated in this study. METHODS: One hundred ninety-eight male ddy mice were divided into groups and received either collagen disks containing BMP-2, collagen disks alone, or sham surgery with no disk implantation. Changes in the temporal and spatial expression profiles of BMPRs and Noggin were examined by Northern blotting, in situ hybridization, Western blotting, and immunohistochemistry. RESULTS AND CONCLUSIONS: In the BMP group, expression of BMPR-1A, -2, and Noggin mRNA and protein was enhanced 2-4 days after implantation in undifferentiated mesenchymal cells and regenerating muscle fibers located close to the BMP-retaining implants. On day 7, the expression was also observed in cartilage cells, and after day 14, in the osteoblastic cells around bone tissue. The level of expression peaked at day 4 after implantation and persisted at a much lower level during the bone forming process. No significant expression of BMPR-1B was detected at the mRNA and protein levels during the bone-forming reaction. In the BMP free control groups, a mild enhancement of BMPR-2 expression was also noted around the implant, but this was not observed for BMPR-1A, -1B, or Noggin. Upregulated expression of BMPR-1A, -2, and Noggin in undifferentiated mesenchymal cells and regenerating muscle fibers occurs during the early phase of BMP-2-induced bone formation. The coordinate expression of these positive and negative regulators of BMP signaling points to a potential regulatory mechanism for bone induction.

Animals↗
PubMed2004

The role of genetics and environment in lifting force and isometric trunk extensor endurance.

BACKGROUND AND PURPOSE: Our understanding of what different back performance tests are measuring is limited. The purpose of this study was to investigate the relative contributions of genetics and unique and common environmental factors for 3 tests of back muscle performance in a classic twin analysis. SUBJECTS: The subjects were a population-based sample of 122 monozygotic and 131 dizygotic male twin pairs aged 35 to 69 years (mean=49.9, SD=7.7). METHODS: Variance component analysis was applied to estimate genetic and environmental influences on isokinetic and psychophysical lifting and isometric trunk extensor endurance test performance. The Cholesky decomposition genetic factor model was used to estimate genetic and environmental correlations of these variables. Path analysis was applied to study determinants of isokinetic and psychophysical lifting and isometric trunk extensor endurance test performance. RESULTS: Genetic effects accounted for 60%, 33%, and 5% of the total variance of isokinetic and psychophysical lifting forces and isometric trunk extensor endurance, respectively, and unique environmental factors accounted for 35%, 49%, and 61% of the variance. DISCUSSION AND CONCLUSION: Genetics had a dominant role in isokinetic lifting and unique environmental factors in isometric trunk extensor endurance. The relatively high role of genetics in lifting force suggests the potential to increase and sustain changes in back muscle force in the general population may be particularly challenging.

Adult↗
PubMed2003

Free shoulder space requirements in the design of high backrests.

The objective of this study was to determine the influence of scapular support on the effects of lumbar support and to prove that a high and straight backrest is inappropriate. In literature the importance of a lumbar support is noted, although data about optimal dimensions is an under-researched topic and in earlier studies on force distribution and muscle activity the backrest had a fixed form. The lumbar support is needed to maintain the lumbar lordosis but no studies deal with the question of the precise dimensions of the backrest at shoulder level. With a specially designed apparatus, forces on shoulder and seat were measured separately, and the force on the pelvis calculated, while varying seat and backrest inclination within the range from 0 degrees to 17 degrees. Seat-to-backrest angle (at the level of lumbar support) was kept constant at 90 degrees. The distance between the tangent to the lumbar support and the parallel tangent to the scapular support was varied from 0, 2, 4, 6 and 8 cm. This distance is called the free shoulder space. Electromyography was measured at the erector spinae at the levels of the L1, T8 and T5 vertebrae. For all seat angles, a free shoulder space of d=0 cm resulted in the highest back muscle activity. In agreement with the biomechanical model, EMG activity reduced with an increase of seat tilt and increase of free shoulder space. With increasing free shoulder space, a larger part of the total backrest force was carried by the lumbar support. This study shows that a high and straight backrest overrules lumbar support. Offering free shoulder space of at least 6 cm reduces back muscle activity and allows for lumbar support.

Adult↗
PubMed2001

Variability in the control of head movements in seated humans: a link with whiplash injuries?

The aim of this study was to determine how context and on-line sensory information are combined to control posture in seated subjects submitted to high-jerk, passive linear accelerations. Subjects were seated with eyes closed on a servo-controlled linear sled. They were asked to relax and received brief accelerations either sideways or in the fore-aft direction. The stimuli had an abrupt onset, comparable to the jerk experienced during a minor car collision. Rotation and translation of the head and body were measured using an Optotrak system. In some of the subjects, surface electromyographic (EMG) responses of selected neck and/or back muscles were recorded simultaneously. For each subject, responses were highly stereotyped from the first trial, and showed little sign of habituation or sensitisation. Comparable results were obtained with sideways and fore-aft accelerations. During each impulse, the head lagged behind the trunk for several tens of milliseconds. The subjects' head movement responses were distributed as a continuum in between two extreme categories. The 'stiff' subjects showed little rotation or translation of the head relative to the trunk for the whole duration of the impulse. In contrast, the 'floppy' subjects showed a large roll or pitch of the head relative to the trunk in the direction opposite to the sled movement. This response appeared as an exaggerated 'inertial' response to the impulse. Surface EMG recordings showed that most of the stiff subjects were not contracting their superficial neck or back muscles. We think they relied on bilateral contractions of their deep, axial musculature to keep the head-neck ensemble in line with the trunk during the movement. About half of the floppy subjects displayed reflex activation of the neck muscles on the side opposite to the direction of acceleration, which occurred before or during the head movement and tended to exaggerate it. The other floppy subjects seemed to rely on only the passive biomechanical properties of their head-neck ensemble to compensate for the perturbation. In our study, proprioception was the sole source of sensory information as long as the head did not move. We therefore presume that the EMG responses and head movements we observed were mainly triggered by the activation of stretch receptors in the hips, trunk and/or neck. The visualisation of an imaginary reference in space during sideways impulses significantly reduced the head roll exhibited by floppy subjects. This suggests that the adoption by the central nervous system of an extrinsic, 'allocentric' frame of reference instead of an intrinsic, 'egocentric' one may be instrumental for the selection of the stiff strategy. The response of floppy subjects appeared to be maladaptive and likely to increase the risk of whiplash injury during motor vehicle accidents. Evolution of postural control may not have taken into account the implications of passive, high-acceleration perturbations affecting seated subjects.

Acceleration↗
PubMed1997

In vivo study of a calcium phosphate cement consisting of alpha-tricalcium phosphate/dicalcium phosphate dibasic/tetracalcium phosphate monoxide.

Prehardened calcium phosphate cement consisting of alpha-tricalcium phosphate (alpha-TCP), dicalcium phosphate dibasic (DCPD) and tetracalcium phosphate monoxide (TeCP) was implanted in rabbit mandibles and back muscles, and studied histologically and microradiographically. In the mandibles, new bone formation occurred around the implants and increased in quantity the longer the implant period lasted. Histology, microradiography and scanning electron microscopy (SEM) demonstrated direct contact of bone and cement. Bone response to this cement was essentially the same as to hydroxyapatite (HA) ceramics, known as a biocompatible bone substitute. Material resorption was recognized, which increased with the implant period and was greater in the surface bound by soft tissue than the surface bound by bone tissue. In the back muscles, however, no calcified tissue formation occurred. Resorption proved to be faster than in the case of the mandible implants. It was concluded that the cement, in prehardened form, has good biocompatibility and is a promising material as a bone substitute.

Animals↗
PubMed1991

Effect of isolation rearing on 5-HT agonist-induced responses in the rat.

Rats were reared from weaning (21 days of age) either in isolation or in social groups of five for 30 days and were then tested for spontaneous locomotor activity and 7 days later for 5-hydroxytryptamine (5-HT) agonist-induced behaviour. Isolation-reared animals displayed locomotor hyperactivity when placed in a novel environment. 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) (2 mg/kg IP) and 8-hydroxy-2-(di-n-propyl-amino) tetralin (8-OH-DPAT) (0.32 mg/kg SC) elicited various components of the "5-HT behavioural syndrome" in both groups of animals, with forepaw treading and flat body posture being significantly more pronounced in isolation-reared animals. 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (2.5 mg/kg IP), a 5-HT2 selective agonist, produced a significantly greater number of back muscle contractions in isolation-reared animals but there was no difference between the two groups in the number of wet-dog shakes produced. Forepaw treading and flat body posture are thought to be mediated by 5-HT1A receptor activation, and stimulation of this receptor by either 5-MeODMT or 8-OH-DPAT produced greater responding in isolation-reared rats, suggesting supersensitivity of the post-synaptic 5-HT1A receptor. Wet-dog shakes are thought to be mediated by 5-HT2 and other (none-5-HT) receptors while back muscle contractions have been shown to be mediated by 5-HT2 receptors, indicating that there is also an increase in 5-HT2 receptor responsiveness in the socially-isolated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1991

Acute and chronic effects of intrathecal galanin on behavioural and biochemical markers of spinal motor function in adult rats.

The spinal motor effects of galanin, which co-exists with 5-hydroxytryptamine (5-HT) and thyrotrophin-releasing hormone (TRH) in bulbospinal raphe neurones innervating spinal motoneurones, were examined by administering this neuropeptide through indwelling intrathecal cannulae to conscious adult Wistar rats. The acute effect of intrathecal galanin on spontaneous motor behaviour and the motor behaviours (back muscle contractions and wet-dog shakes) elicited by intrathecal injection of the non-selective 5-HT receptor agonist, 5-methoxy-N, N'-dimethyltryptamine (5-MeODMT) or the TRH analogue, RX 77368 analogue, RX 77368 (pGlu-His-3,3'-dimethyl-ProNH2), respectively, and the chronic effect of galanin on neurochemical markers for bulbospinal raphe neurones and spinal motoneurones were determined. Intrathecal galanin (0.1 to 10 micrograms) did not produce any notable motor behaviours when given alone, but pretreatment with the neuropeptide (0.1 micrograms) significantly attenuated both the number of wet-dog shakes and the amount of forepaw-licking induced by RX 77368, without affecting 5-MeODMT-induced back muscle contractions. Repeated intrathecal galanin administration (1 microgram, twice daily for 5 d) significantly elevated 5-HT (but not 5-hydroxyindoleacetic acid) and substance P-like immunoreactive (LI) levels and choline acetyltransferase (ChAT) activity in the dorsal, but not in the ventral, portion of the thoraco-lumbar spinal cord. In contrast, chronic intrathecal galanin did not alter the TRH- or calcitonin gene-related peptide (CGRP)-LI levels in either spinal cord region.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1984

Phasic modulation of trunk muscle efferents during fictive spinal locomotion in cats.

In high spinal paralysed cats electromyograms were recorded from nerves supplying lumbar back muscles (longissimus dorsi) and abdominal muscles (obliquus abdominis externus) during fictive locomotion induced by I.V. injection of nialamide and L-DOPA. Activity in nerves to hind-limb muscles was also recorded. During periods of stable 'locomotor' activity in the hind-limb nerves the efferents to the back and abdominal trunk muscles were generally also rhythmically active. Three different patterns of activity were observed. The predominant rhythmic pattern showed a synchronous activation of the efferents to the back and abdominal muscles of one side together with an activation of the hind-limb flexors of that side, alternating with activation of the efferents to the corresponding contralateral muscles. This pattern was very stable and could last for about 3 h. Such a pattern of activity would be expected during the alternate stepping characteristic of walking and trotting. The second type of rhythmic locomotor activity was characterized by a synchronous bilateral activation of the efferents to the back muscles, alternating with activation of the abdominal muscles on both sides. This pattern occurred only for short periods and appears to correspond to the activity during in-phase stepping such as occurs during a gallop. Beside these well co-ordinated patterns less well co-ordinated rhythmic activities were also observed. These included regular rhythmic activity which occurred independently in different muscle groups as well as irregular rhythmic activity with unstable phase relations between different muscle groups. The rhythmic locomotor activity in efferents to trunk and limb muscles could be modulated by afferent nerve stimulation and by hypoxia. The results reveal that the spinal cord deprived of its supraspinal and peripheral control may generate a variety of different locomotor patterns, which incorporate the trunk muscles in an apparently meaningful way.

Abdominal Muscles↗
PubMed1975

Physiological studies of the dying-back phenomenon. Muscle stretch afferents in acrylamide neuropathy.

(1) The responses of 1,001 medial gastrocnemius afferents with conduction velocities of 24-126 m/sec have been studied in cats with experimental acrylamide neuropathy. (2) Many units which conducted at velocities indicating that they innervated muscle stretch receptors failed to discharge during muscle stretch or contraction. In animals with mild neuropathy 10 per cent of 366 units were non-responsive. In animals with moderate or severe neuropathy the proportion of non-responsive units was 68 per cent of 315 fibres and 89 per cent of 320 fibres respectively. Group I fibres were involved to a greater extent than Group II fibres. (3) The distributions of identified functioning units with respect to conduction velocity were normal, indicating that acrylamide did not produce conduction slowing before failure of function. (4) Electrophysiological and histological findings indicate that acrylamide initially produces failure of impluse conduction and subsequent fibre breakdown in the terminal axon while normal impulse conduction is preserved more proximally.

Acrylamides↗
PubMed2005

Lumbar position sense acuity during an electrical shock stressor.

BACKGROUND: Optimal motor control of the spine depends on proprioceptive input as a prerequisite for co-ordination and the stability of the spine. Muscle spindles are known to play an important role in proprioception. Animal experiments suggest that an increase in sympathetic outflow can depress muscle spindle sensitivity. As the muscle spindle may be influenced by sympathetic modulation, we hypothesized that a state of high sympathetic activity as during mental stress would affect the proprioceptive output from the muscle spindles in the back muscles leading to alterations in proprioception and position sense acuity. The aim was to investigate the effect of mental stress, in this study the response to an electrical shock stressor, on position sense acuity in the rotational axis of the lumbar spine. METHODS: Passive and active position sense acuity in the rotational plane of the lumbar spine was investigated in the presence and absence of an electrical shock stressor in 14 healthy participants. An electrical shock-threat stressor lasting for approximately 12 minutes was used as imposed stressor to build up a strong anticipatory arousal: The participants were told that they were going to receive 8 painful electrical shocks however the participants never received the shocks. To quantify the level of physiological arousal and the level of sympathetic outflow continuous beat-to-beat changes in heart rate (beats x min(-1)) and systolic, diastolic and mean arterial blood pressure (mmHg) were measured. To quantify position sense acuity absolute error (AE) expressed in degrees was measured. Two-way analysis of variance with repeated measurements (subjects as random factor and treatments as fixed factors) was used to compare the different treatments. RESULTS: Significant increases were observed in systolic blood pressure, diastolic blood pressure, and heart rate during the stress sessions indicating elevated sympathetic activity (15, 14 and 10%, respectively). Despite pronounced changes in the sympathetic activity and subjective experiences of stress no changes were found in position sense acuity in the rotational plane of the lumbar spine in the presence of the electrical shock stressor compared to the control period. CONCLUSION: The present findings indicate that position sense acuity in the rotational plane of the spine was unaffected by the electrical shock stressor.

Adult↗
PubMed2003

[Histochemical study of the sensory endings of muscle spindles in rat longissimus muscles].

Most studies concerning the structure and function of muscle spindles have utilized the hind limbs of experimental animals. However, little is known about muscle spindles of the back muscles. The purpose of this study was to investigate the sensory innervation of muscle spindles of the paravertebral muscle in the rat. The subjects were 10 normal male rats. The longissimus muscles were isolated and frozen in cooled isopentane (-160 degrees C), and serial transverse sections were made with a cryostat. Histochemical preparations were then made using nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) stain and modified Gomori-trichrome stain. The muscle spindles in each segment were identified microscopically by observing the equatorial and polar regions. NADH-TR staining was employed to distinguish nuclear bag1, nuclear bag2, and nuclear chain intrafusal muscle fibers. A total of 20 spindle poles were surveyed. The mean polar length of intrafusal fibers as well as that of each region (A, B, and C) were measured. NADH-TR staining also demonstrated the terminal sites of sensory fibers along intrafusal fibers. All spindle poles surveyed were innervated by secondary sensory fibers in addition to primary sensory fibers. Eight spindle poles were intermediate type muscle spindles that were innervated by one primary sensory fiber and one secondary sensory fiber. Twelve spindle poles were complex type muscle spindles that were innervated by one primary sensory fiber and multiple secondary sensory fibers. The mean length of the A region was 223.1+/-37.9 microm (n=8) for intermediate type spindles and 493.8+/-157.0 microm (n=12) for complex type spindles. The length of the A region was significantly longer in the complex type spindles than in the intermediate type spindles (p<0.001). The results suggest that the innervations of secondary sensory fibers were well developed in the longissimus muscle spindles in the rat. The morphological features of muscle spindles of the longissimus muscle may represent the structural basis for qualitatively different afferent discharges that relate to the characteristic types of locomotion served by paravertebral muscles.

Animals↗
PubMed2006

Effects of a new industrial lifting belt on back muscular activity, hand force, and body stability during symmetric lifting.

This work investigated how wearing a new design of back belt affects erector spinae activity, hand force, and body stability. The belt was first tested with static holding tasks and found to significantly decrease the back muscle activity. Actual lifting tasks were further carried out to test the effect of the belt. Ten male subjects performed a symmetric lifting task of low-lying loads (11 and 16 kg) at natural toting velocity, using either a squat or stoop lifting posture, both with and without a belt. The study measured various independent variables using electromyography (EMG), load cells, and motion capture device. The results demonstrated that the belt reduced the load on the erector spinae, as well as the triceps brachii and biceps brachii. The overall mean values of the peak (hand) force did not appear significantly affected while wearing the belt, but the force peaks appeared postponed. The belt did not alter body stability while lifting. From the present findings, the belt effectively changed the force distribution during lifting, at least reducing the muscle load on the back. The belt may be a potentially useful device for symmetric industrial lifting tasks.

Adult↗
PubMedDate not supplied

Motor unit action potential (MUAP) parameters affected by editing duration cursors.

INTRODUCTION: Quantitative electromyography (QEMG) allows fast analysis of motor unit action potential (MUAP) parameters such as amplitude, duration, size index (SI), phases, turns and firing rate. When automated duration cursor placement is incorrect, the electrodiagnostician will manually edit this function potentially introducing bias to the final results. OBJECTIVE: To identify that (1) size index is the MUAP parameter least affected by manually editing duration cursors and (2) MUAP amplitude will influence the manual cursor correction rate. MATERIALS AND METHODS: Included were twenty-one consecutive patients who had QEMG with monopolar needle electrode for diagnostic evaluation of their myofascial pain symptoms. Evaluated for neck pain included 6 bilateral upper limb and cervical paraspinal muscles and for lower back pain were 5 bilateral lower limb and lower back muscles. Twenty MUAPs were recorded from each muscle and hardcopies of data obtained before and after manual edit. RESULTS: Of a total of 5360 MUAPs analyzed 1764 (33%) required manual editing of duration cursors. Cursor correction rate 120 MUAP s/individual muscle analyzed was also similar at 33+/-17%. Percentage change in duration more so than turns, before and after correction, was significantly larger than that of other parameters. No significant differences in percentage changes noted between SI and phases. CONCLUSIONS: SI and phases are least influenced by the manual correction of duration cursors since there is insubstantial amplitude and area at the tail-end of the MUAP.

Action Potentials↗