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PubMed2001

The interaction of somatosensory evoked potentials between mixed-sensory nerves and sensory-sensory nerves.

The interactions between two different nerves occur by occlusion or inhibition when two nerves share the synaptic connections. In our previous study, we have demonstrated that posterior tibial nerve and peroneal nerve sensory inputs interact with each other, i.e., preceding stimulus to one nerve suppresses the somatosensory evoked potential (SEP) of the other nerve when two stimuli are delivered in close sequence. The course of suppression follows two phases; the first one occurring at short interstimulus intervals (ISIs) of the two nerves less than 10 msec, and the second one being at around 30 msec ISI after partial recovery following the first suppression phase. In that study, we have postulated that the second phase suppression was equivalent for the movement induced "gating" mechanism. In this study, the interactions of mixed nerve (posterior tibial) and sensory nerve (sural), and also sensory (sural) and sensory (saphenous) nerves were examined. We found that the mixed nerve (posterior tibial) exerted similar dual phases of suppression (as was seen in posterior tibial--peroneal nerve study) on to the sural nerve SEP, but the reverse was not true. Also the sensory and sensory nerve interactions were not mutually equal; the sural nerve stimulation caused two phases suppression but the reverse condition did not show significant suppression. The above findings suggest (1) interference input from the sensory nerve to the mixed nerve is much weaker than the reverse condition, and (2) sensory and sensory nerves interactions occur but two nerves' interference inputs are not necessarily equal and one could dominant the other.

Adult↗
PubMed1987

Distribution of myelinated nerves in ascending nerves and myenteric plexus of cat colon.

The parts of the colon differ in motor function and in responses to extrinsic and intrinsic nerve stimulation. The distribution of myelinated nerve fibers in the colonic myenteric plexus is not known. Because these fibers might be largely extrinsic in origin, their distribution might indicate the domain of influence of extrinsic nerves and help to explain the different behaviors of the different parts of the colon. Myelinated fibers were examined by electron microscopy in cross sections of the ascending nerves and in myelin-stained whole-mount preparations in the colon. The ascending nerves are much like one another. They have the structure of peripheral nerves, not that of myenteric plexus. The proportion of myelinated fibers in the ascending nerves declines rostrad with no uniform change in total nerve fiber number. Cross-sectional areas of ascending nerves, 3,304 to 7,448 microns 2; total number of nerve fibers per profile, 703-2,651; and mean myelin coat thickness, 0.45 +/- 0.01 micron, do not change uniformly along the ascending nerves. Myelinated fibers are about 2% of total fibers in the extramural colonic nerves, 7-9% in the ascending nerves in the sigmoid colon, and 2-3% at the rostrad ends of the ascending nerves in the transverse colon. Blood vessels lie at the core of each ascending nerve and on the nerve sheath. Myelinated fibers in the ascending nerves degenerate after section of colonic branches of the pelvic plexus and after section of the pudendal nerves, indicating that myelinated nerves reach the colon through both pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed2002

Assessment of nerve graft donor sites used for reconstruction of traumatic digital nerve defects.

Several donor nerve graft sites commonly are used when repairing segmental defects in sensory nerves distal to the wrist. The cross-sectional area and number of fascicles of donor nerves and specific digital nerve segments were investigated to provide guidelines for selection of nerve graft harvest sites according to defects encountered. Nerve segments were harvested from 10 fresh cadavers (20 upper extremities). Five sites of nerve graft were harvested: lateral and medial antebrachial cutaneous nerves (LABCN, MABCN), posterior and anterior interosseous nerves (PIN, AIN), and sural nerves. Four sites of typical segmental nerve defects were harvested in a zone protocol: common digital nerve (zone 4), proper digital nerve (zone 3), digital nerve distal to main dorsal branch at the metacarpophalangeal joint (zone 2), and digital nerve distal to trifurcation at fingertip (zone 1). Sural nerve is the most anatomically similar nerve graft for defects in zone 4 by cross-sectional area and number of fascicles. Lateral antebrachial cutaneous nerve is most appropriate for zone 2 and 3 injuries by both criteria. Fingertip grafts for zone 1 injuries displayed cross-sectional area similarity to PIN, AIN, and MABCN. With regard to number of fascicles, zone 1 digital nerves are most similar to LABCN donors.

Brachial Plexus↗
PubMed1990

Ipsilateral and cross-over elongation of the motor nerve by nerve grafting: an experimental study in sheep.

In difficult reconstructions, ipsilateral or cross-over nerve grafting is sometimes necessary to achieve reinnervation and motor function. This experimental study in sheep was to answer the question of limitation of elongation of a motor nerve by grafting, the question of the optimal time for suturing the nerve graft to the muscle nerve, and the question of the successful application of this surgical technique in extremities. In 18 sheep, the vastus nerve was elongated by a saphenous nerve graft as long as possible up to 30 cm (step 1). In 10 animals the nerve graft was applied ipsilaterally, and in 8 animals it was used as a cross-over nerve graft to the contralateral limb. The time between nerve grafting and connection of the distal end of the nerve graft to the freshly cut rectus nerve supplying the rectus femoris muscle (step 2) was variable: 0, 3, 6, 9, and 12 months. In all animals, the final experiments (step 3) were performed 6 months after the last operation (step 2). Muscle force measurements in the rectus femoris muscle and quantitative analysis of the number and diameter of myelinated nerve fibers in cross sections of the nerve biopsies at different levels showed that elongation of a motor nerve by nerve grafting is principally not limited. The functional results were rather inhomogeneous and therefore unpredictable (ipsilateral group: maximum tetanic tension = 27 to 172 N; cross-over group: 0 to 227.5 N). Nevertheless, crossover nerve grafting is recommended for selected cases even in extremities. There was no correlation between the time interval between the two operations and the functional or morphologic results, although better functional results were obtained when the distal nerve suture (step 2) was performed some months after nerve grafting (step 1). A clear correlation was found only between the number of regenerated axons in the rectus nerve behind the second suture line and the muscle function.

Animals↗
PubMed2005

Variability in nerve patterns of the adductor muscle group supplied by the recurrent laryngeal nerve.

INTRODUCTION: Accurate knowledge of the nerve supply of each individual muscle is needed to achieve a successful selective reinnervation of the larynx. The aim of the present work was to study the nerve supply of the adductor laryngeal muscles supplied by the recurrent laryngeal nerve. STUDY DESIGN: Morphologic study of human larynges. METHODS: The muscular nerve supply was studied in a total sample of 75 human larynges obtained from necropsies (47 males and 28 females, age range from 41-95 years) and examined by careful dissection using a surgical microscope. RESULTS: The arytenoid muscle received one branch from each recurrent nerve. In 88% of cases, this branch arose in a common trunk with the upper branch of the posterior cricoarytenoid muscle. In 8% of cases, the nerve for the arytenoid muscle also had a branch going to the lateral cricoarytenoid muscle. The arytenoid muscle also received from one to three pairs of branches from the posterior division of the internal laryngeal nerve; these were interconnected ipsi- and contralaterally and were also connected to the two branches coming from the recurrent laryngeal nerve. The lateral cricoarytenoid muscle received from one to six branches from the recurrent nerve, but in 5.8% of cases, it also received a twig from a connecting branch between the recurrent nerve and the external (5.6%) or the internal laryngeal nerves (0.2%). The thyroarytenoid muscle received from one to four branches from the recurrent nerve, but in 5.6% of cases, it also received a twig from a connecting branch between the recurrent nerve with the external (4.6%) or the internal (1%) laryngeal nerves. CONCLUSION: No abductor or adductor division of the recurrent laryngeal nerve was found in the present study. In 88% of cases, the nerve supply to the arytenoid muscle (adductor) and the posterior cricoarytenoid muscle (abductor) arose from a common trunk, which in 8% of cases, also had a branch to the lateral cricoarytenoid muscle. Furthermore, the high incidence of branches innervating the adductor muscles from connections between the recurrent laryngeal nerve and the internal and external laryngeal nerves led us to reconsider the contribution of these nerves in the supply to this muscle group.

Adult↗
PubMed2000

Selective demonstration of mural nerves in ganglionic and aganglionic colon by immunohistochemistry for glucose transporter-1: prominent extrinsic nerve pattern staining in Hirschsprung disease.

OBJECTIVE: Hypertrophic nerves have long been considered a histopathologic feature of the aganglionic segment in Hirschsprung disease, but they remain incompletely explained. The purpose of this study was to define the nature and diagnostic importance of hypertrophic nerves in Hirschsprung disease and to clarify their relation to nearby smaller nerve fibers. METHODS: We used an immunoperoxidase staining technique to compare the distribution of 2 nerve markers-erythrocyte-type glucose transporter (GLUT-1), a marker of perineurium, and nerve growth factor receptor, a marker of both nerve fibers and perineurium-in aganglionic tissue (12 resected specimens and 4 rectal biopsies) and control tissue (6 autopsy specimens and 17 rectal biopsies) of children. RESULTS: In control ganglionic tissue, the myenteric and submucosal areas contained only occasional GLUT-1-positive nerves (usually less than 50 microm in diameter), but extramural extrinsic (serosal) nerves were invariably positive for GLUT-1. In aganglionic tissue, GLUT-1-positive nerves in the myenteric and submucosal areas were frequent and included both large (50-150 microm) and small (<50 microm) diameter nerves. Nerve growth factor receptor-positive fibers were frequent in all layers of all tissue studied. In aganglionic bowel, a distinct perineurium could be identified in the largest nerves, but nerve growth factor receptor had poor discrimination for small perineurium-sheathed nerves. CONCLUSION: Most nerves, of both large and small diameter, in the myenteric and submucosal plexus of aganglionic bowel are GLUT-1 positive. Serosal extrinsic nerves stain identically, supporting the interpretation that the mural nerves are of extrinsic origin. Mural GLUT-1-positive nerves, when they are multiple and especially when they are greater than 50 microm in diameter (a figure which may be used as a threshold for hypertrophic nerves), are suggestive of Hirschsprung disease.

Biopsy↗
PubMed1976

[Quantitative studies on the regeneration of myelinated nerve fibers. II. Variations of the number and size of regenerating nerve fibers after localized crushing or total section].

1. The number and size of myelinated nerve fibers have been determined at standard levels, in the nerve to medial head of right and left gastrocnemius muscles of 112 rats in which the left sciatic nerve had suffered an experimental lesion according one of the following four modalities: localized crushing, total section followed or not by suture and resection of a nervous segment of about 1 cm. 2. In the nerve to medial head of right gastrocnemius muscle (contralateral nerve used as control), the number of myelinated fibers decreased in average to 10% after crushing, 5% or 4% after section followed or not by suture. However, an increase of 6% was observed after resection. The mean values of the mean diameters showed a decrease of 8% after crushing and 5% after section without suture. This value did not seem to be affected by section followed by immediate suture and after resection, it increased of 11%. On the whole, male rats appeared to be more sensitive than female to the effects of the operation. 3. The nerves of 12 rats have been observed from 15 to 334 days after resection of about 1 cm of sciatic nerve. The 20% of the regenerating myelinated nerve fibers which have succeeded to cross over such a distance had a distribution which remained unimodal; the diameter of the large fibres did not exceed 8 micronm. 4. 34 rats have been sacrificed from 15 to 715 days after sciatic nerve section which was not followed by suture. The number of myelinated nerve fibers became normal again during the 4th month and reached afterwards a mean value of 130%, with very marked variations. The nerve fibre distribution was most frequently unimodal, but may came bimodal one year after the operation in certain nerves. Their mean diameter never exceeded 60% of the normal. 5. The nerves of 34 rats have been examined from 15 to 720 days after section and immediate suture. The number of myelinated nerve fibers returned to normal during the second month and increased afterwards to an average of 150% with very important variations. The nerve fiber distribution was generally unimodal, but may become bimodal 7 months after the operation. Their mean diameter reached only 50 to 55% of the normal. 6. 32 rats have been sacrificed from 10 to 720 rats after a localized crushing. The number of myelinated nerve fibers come back to normal during the 4th week and later increased up to a mean of 115%. Their distribution became early bimodal from the 97th day onwards. Although, their mean diameter nerver exceeded 80% of the normal, the histograms of the regenerating nerve and of the control nerve could be almost superposed during the second year.

Animals↗
PubMed1997

Distribution of primary motor nerve branches and terminal nerve entry points to the forearm muscles.

BACKGROUND: The information available on innervation pattern of the human forearm muscles in standard anatomy texts, although adequate for routine procedures, is not detailed enough for surgical reconstruction in complex injuries of the limb and for paralytic conditions of the forearm from peripheral nerve and spinal cord injuries. METHODS: The innervation pattern in 10 cadaveric forearms was studied. The contributions of the main nerve trunks to each forearm muscle was examined. The location and number of the primary motor nerve branching points and of the terminal nerve entry points to each muscle were investigated. The location of both the primary nerve branching points and terminal nerve entry points was presented as a percentage of forearm length measured from the lateral humeral epicondyle to the radial styloid. RESULTS: Seven of 19 forearm muscles were innervated from a single branch from the main nerve trunk. The remaining 12 received more than one primary branch. Two of 19 forearm muscles had only one terminal nerve entry point. The others had two or more each. In 13 of 19 forearm muscles, the statistical median location of the primary motor nerve branching points was within the proximal one-third of the forearm length and either more proximally or distally for the remainder. The statistical median location of the terminal nerve entry points was within the proximal one-third in 9 forearm muscles and within the middle one-third of the forearm in 8 forearm muscles. In two, it was located proximal to the elbow and in the distal one-third of the forearm, respectively. CONCLUSIONS: In lacerations across the forearm, where main nerve trunks are divided, mere repair of the nerve trunks would not address the denervation of muscle or segments of muscle by the division of the primary (or secondary) nerve branches traversing the wound and which took origin proximal to the laceration either from the divided nerve trunks or from other undamaged nerve trunks. Although the main nerve trunks may be intact, segmental crush injuries will defunction muscles by direct muscle damage or by damage to the terminal nerve entry points to the muscle. Knowledge of the location of the nerve branches and the terminal nerve entry points facilitates the insertion of electrodes at the motor points of forearm muscles for functional electrical stimulation in upper motor neuron lesions. The information in this study may also be usefully applied in selective denervation procedures to balance muscles in spastic upper limbs.

Adult↗
PubMed1990

Nerves and nerve plexuses of the human vertebral column.

The origin, distribution, and termination pattern of nerves supplying the vertebral column and its associated structures have been studied in the human fetus by means of an acetylcholinesterase whole-mount method. The vertebral column is surrounded by ventral and dorsal nerve plexuses which are interconnected. The ventral nerve plexus consists of the nerve plexus associated with the anterior longitudinal ligament. This longitudinally oriented nerve plexus has a bilateral supply from many small branches of the sympathetic trunk, rami communicantes, and perivascular nerve plexuses of segmental arteries. In the thoracic region, the ventral nerve plexus also is connected to the nerve plexuses of costovertebral joints. The dorsal nerve plexus is made up of the nerve plexus associated with the posterior longitudinal ligament. This nerve plexus is more irregular and receives contributions only from the sinu-vertebral nerves. The sinu-vertebral nerves originate from the rami communicantes and, in the cervical region, also from the nerve plexus of the vertebral artery. Thick and thin sinu-vertebral nerves are found. Most frequently three types of thick sinu-vertebral nerves are observed, i.e., ascending, descending, or dichotomizing ones. Finally, the distribution of the branches of the ventral and dorsal nerve plexuses and of the sinu-vertebral nerves is described.

Cervical Plexus↗
PubMed2006

Repair of peripheral nerve defect with direct gradual lengthening of the proximal nerve stump in rats.

We investigated the effect of direct gradual lengthening on the proximal nerve stump and subsequent nerve regeneration in rats. A 10-mm-long nerve segment was resected from the sciatic nerve of each rat. The proximal nerve stump was directly lengthened at a rate of 1 mm/day using an original external nerve distraction device. Experiment I: After distraction periods of 10, 15, and 20 days, the length of each nerve was evaluated, and the lengthened nerve stump was also examined by immunohistochemical analysis. Experiment II: After a distraction period of 20 days, both nerve stumps were refreshed and direct end-to-end neurorrhaphy was performed. For control, 10-mm nerve grafting was immediately performed after nerve resection. Nerve regeneration was evaluated electrophysiologically and histologically 7, 9, and 15 weeks after nerve resection in both groups. The whole proximal nerve stump, including the endoneurium and the axon, could be lengthened in proportion to the distraction period. There were no significant differences in motor nerve conduction velocity and tetanic muscle contraction force between both groups. Histologically, the total number of myelinated fibers was significantly greater in the nerve lengthening group than in the autografting group. This study demonstrated that the whole proximal nerve stump including the endoneurium and the axon could be lengthened by direct gradual distraction, and that this method might have potential application in the repair of peripheral nerve defects.

Animals↗
PubMed2004

Functional, electrophysiologic, and morphometric evaluation of nerve regeneration from coaptation on regenerated nerve fibers: experimental study in rabbits.

The importance of a sufficient number of nerve fibers at a proximal coaptation site is indisputable for the successful repair of nerves; however, the quality of nerve fibers required at this site has yet to be defined. The present study deals with the question of whether it is necessary to trim nerves back to unaffected neuronal tissue or whether the coaptation on recently regenerated nerve fibers, commonly believed to produce a poor quality of repair can, in fact, produce adequate nerve regeneration. Twenty New Zealand White rabbits received a standardized crush lesion on the peroneal nerves of both hind legs. Four weeks later, the nerves of the left hind legs (n = 20) were transected 10 mm distal to the previous crush lesion and coapted to the freshly regenerated nerve fibers. For comparison, on 10 right hind legs, the nerves were transected at the site of previous crushing (Group A, superimposition) or 10 mm proximal to the site of crushing on unscathed nerve fibers (Group B). Eleven weeks later, the quality of nerve regeneration was assessed by the toe-spreading reflex, electrophysiologic data, muscle weight, and histomorphologic evaluation. In the animals of Group A, the quality of nerve regeneration following coaptation on the regrown axons did not differ in any of the examined parameters from the quality of nerve fibers outgrown from the site of the superimposed lesion. Both lesions led to a completely functional reinnervation. Also in Group B, nerve action potential recording and histologic data on both sides did not reveal a significant difference between the number and maturation of nerve fibers equidistant from the suture site, shortly before muscle entrance. With this coaptation model, it could be demonstrated in the peroneal nerve of rabbits, that coaptation to recently regenerated nerve fibers leads to a significant functional regeneration.

Anastomosis, Surgical↗
PubMed2001

Selective restoration of motor function in the ulnar nerve by transfer of the anterior interosseous nerve. An anatomical feasibility study.

BACKGROUND: Proximal ulnar-nerve lesions have an unfavorable prognosis. The goal of the present study was to evaluate the feasibility of selective restoration of motor function of the ulnar nerve by the transfer of the anterior interosseous nerve or one of its branches to the motor branch of the ulnar nerve. METHODS: Ten cadaveric arms were used in the present study. The ulnar nerve and its motor and sensory branches as well as the anterior interosseous nerve and its branches were dissected. The widths of the motor branch of the ulnar nerve and the anterior interosseous nerve and its motor branches as well as the relevant distances from the points of divergence were measured. The axons were counted, and the distances from the end of the main anterior interosseous nerve, its motor branches, and the motor branch of the ulnar nerve to the level of the dorsal sensory branch of the ulnar nerve were measured. RESULTS: Our results indicate that the length, width, and number of axons of the branch of the anterior interosseous nerve to the pronator quadratus make it suitable for transfer to the motor branch of the ulnar nerve. The use of the main anterior interosseous nerve or its motor branches to the flexor pollicis longus and the flexor digitorum profundus is less feasible because of the need to graft a long segment and the longer distance from the level of transfer to the motor end points. CONCLUSIONS: The findings of the present study confirm the feasibility of motor-nerve transfer for reconstruction after an injury of the ulnar nerve. Nerve-grafting would be needed for injuries distal to the level of the dorsal sensory branch of the ulnar nerve.

Arm↗
PubMed2001

Axonal elongation through long acellular nerve segments depends on recruitment of phagocytic cells from the near-nerve environment. Electrophysiological and morphological studies in the cat.

The distal nerve stump plays a central role in the regeneration of peripheral nerve but the relative importance of cellular and humoral factors is not clear. We have studied this question by freezing the tibial nerve distal to a crush lesion in cat. The importance of constituents from the near-nerve environment was assessed by modification of the contact between the tibial nerve and the environment. Silicone cuffs, containing electrodes for electrophysiological assessment of nerve regeneration, were placed around the tibial nerve distal to the crush site. The interaction between long acellular frozen nerve segments (ANS) and the near-nerve environment was ascertained by breaching the silicone cuff to allow access of cellular or humoral components. Tibial nerves were crushed and frozen for 40 mm and enclosed in nerve cuffs with 0.45-microm holes or 2.0-mm holes to allow access of humoral factors or tissue ingrowth, respectively. In a second set of experiments, tibial nerves were crushed and either frozen for 20+20 mm, leaving a 10 mm segment with viable cells in the center (stepping-stone segment) or frozen for 50 mm. These nerves were enclosed in cuffs with 2.0 mm holes corresponding to the viable nerve segment. The regeneration was monitored electrophysiologically by implanted electrodes and after 2 months the nerves were investigated by light and electron microscopy. The results indicate that soluble substances in the near-nerve environment, such as nutrients, oxygen or tropic substances did not exert any independent beneficial effect on the outgrowing axons. However, phagocytic cells entering the acellular segment from the near-nerve environment were crucial for axonal outgrowth in long ANS.

Animals↗
PubMed1992

[An aberrant muscular nerve to the latissimus dorsi muscle from the posterior cutaneous nerve of the arm].

In the 1987 student course on gross anatomy dissection of cadavers at Iwate Medical University School of Medicine, an aberrant muscular nerve to the latissimus dorsi muscle arising from the posterior cutaneous nerve of the arm was found bilaterally in a 65-year-old female who had died of acute pneumonia. The case was investigated anatomically. The posterior cutaneous nerve of the arm arose from the radial nerve approximately at the lateral axial border as the first branch independently on the right, and by forming a trunk with the nerve to the long head of the triceps brachii muscle on the left. The aberrant muscular nerve originated from the posterior cutaneous nerve of the arm about 3 cm distally to the point of the branching of the cutaneous nerve from the radial nerve. This aberrant nerve entered the latissimus dorsi muscle near the transitional area from the muscular part to the tendinous part while dividing into three on the right, and without dividing on the left. The side into which the aberrant nerve entered was just the reverse of the side into which the thoracodorsal nerve and artery supplied. The muscular part innervated by the aberrant nerve was bounded by a tendinous intersection for the most part of the latissimus dorsi muscle innervated by the thoracodorsal nerve. The intramuscular nerve distribution of the aberrant nerve was investigated under a binocular dissecting microscope. It was revealed that there was no communication between the ramification of the aberrant nerve and that of the thoracodorsal nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1998

The function of sensory nerve fibers in lumbar radiculopathy. Use of quantitative sensory testing in the exploration of different populations of nerve fibers and dermatomes.

STUDY DESIGN: The function of sensory nerve fibers in patients with lumbar radiculopathy and in control individuals was evaluated using quantitative sensory testing. OBJECTIVES: To investigate the effect of lumbar nerve root compression on different populations of nerve fibers and to explore the function of sensory nerve fibers in neighboring nerve roots not involved in the mechanical compression. BACKGROUND DATA: Results from experimental and clinical studies indicate that chronic compression of lumbar nerve roots affects the large myelinated nerve fibers. The majority of nerve fibers involved in the sensation of pain, however, are small afferent nerve fibers. It is therefore of interest to study the effect of compression on large and small sensory afferent channels. Several authors have elucidated the biochemical interaction between disc tissue and nerve roots. Chemical substances in the epidural space can reach the nerve fibers in nerve roots at the same or neighboring lumbar segments. In this way, fibers not involved in the mechanical compression may be affected. METHODS: The small nerve fibers were studied using tests for thermal thresholds (thermotest), and the large myelinated fibers were studied by vibrametry. Forty-two patients were investigated in the symptomatic and the asymptomatic leg, and the results were compared with those of 21 healthy individuals. RESULTS: The thresholds of cold, warmth, and vibration were significantly increased in the dermatome of the compressed nerve root, indicating that large and small sensory nerve fibers were affected. Further, the thresholds were significantly increased in the neighboring dermatomes in the symptomatic and the asymptomatic leg. CONCLUSION: Large and small sensory afferent nerve fibers are affected in lumbar radiculopathy. The increase in sensation thresholds in the ipsilateral neighboring dermatome and in the dermatomes in the asymptomatic leg indicates that adjacent nerve roots are involved in the pathophysiology of sciatica in patients with lumbar disc herniation.

Adult↗
PubMed2000

Permanent nerve involvement resulting from inferior alveolar nerve blocks.

BACKGROUND: This is a prospective study of patients referred to a tertiary care center with permanent alteration in sensation of the inferior alveolar nerves, lingual nerves or both that could have resulted only from an inferior alveolar nerve block. METHODS: Working with a subject pool of 83 patients, the researchers outlined and photographed the area of altered sensation on each patient, tested it with von Frey's hairs and two-point discrimination and tested temperature sensation and direction sense. RESULTS: Among a study population of 55 women and 28 men with a mean age of 41.2 years, the lingual nerve was affected in 79 percent of patients and the inferior alveolar nerve in 21 percent of patients. In 47 patients, the causative inferior alveolar nerve block was painful when administered, but to the other 36 patients [corrected], it felt like a normal injection. Of the local anesthetic agents used, prilocaine was found to be more frequently linked to cases of nerve involvement in this study. DISCUSSION: Occasionally, an inferior alveolar nerve block can result in permanent involvement of the inferior alveolar nerve, lingual nerve or both. The incidence and exact mechanism of involvement still are unknown. By extrapolation from this study, an incidence of anywhere between 1:26,762 and 1:160,571 inferior alveolar nerve blocks can be surmised to result in this complication. A difference in referral rates for male and female patients is difficult to explain. The 34 percent [corrected] incidence of dysesthesia in the patients in this study is of concern. CONCLUSION: Permanent nerve involvement after receiving an inferior alveolar nerve block is a documented but very rare complication of the inferior alveolar nerve block, and the exact mechanism involved is still unknown. CLINICAL IMPLICATIONS: Permanent nerve damage can very occasionally occur as a result of an inferior alveolar nerve block. The exact mechanism is unknown, and there is no means of prevention. Knowledge of the risks and complications of local anesthesia is essential.

Adult↗
PubMed1996

Retinotopy of the human retinal nerve fibre layer and optic nerve head.

The organisation of the primate nerve fibre layer and optic nerve head with respect to eccentricity or the positioning of central and peripheral axons remains controversial. Crystals of the carbocyanine dyes DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), or DiA (4-[4-didecylaminostryryl]-N-methylpridiniumiodide) were used to trace retinal ganglion cell axons within the nerve fibre layer, optic nerve head, and optic nerve. The present study demonstrated that peripheral retinal axons were scattered throughout the vitreal-scleral depth of the nerve fibre layer. This scattered distribution was maintained as the fibres passed through the optic nerve head and into the optic nerve. Axons of the arcuate bundles showed a bias towards the scleral portions of the nerve fibre layer and a variable degree of fibre scatter across the nerve fibre layer which was not as evident in labelling from other retinal regions. There was a rough topographic representation within the optic nerve head according to retinal circumference such that both peripheral and central fibres were mixed within a wedge extending from the periphery to the centre of the nerve. Foveal fibres occupied a large proportion of the temporal aspect of the optic nerve head and nerve, whereas fibres from areas temporal to the fovea appeared to be displaced to more superior and inferior regions. Consistent with the scleral bias seen in the retina, arcuate fibres maintained a peripheral position as they passed through the optic nerve head and occupied a more peripheral position in the nerve. The present results suggest that any degree of order present within the optic nerve is not an active process; optic axons are not instructed to establish a retinotopic order within the initial portions of the visual pathway.

Adult↗
PubMed1986

Undulating course of nerve fibres and bands of Fontana in peripheral nerves of the rat.

The undulating course of nerve fibres and the optical effect of that course, i.e. the bands of Fontana, were studied in the peripheral nerves of the adult rat using light microscopy. The arrangement of collagen fibres in the endoneurium of these nerves was evaluated using transmission and scanning electron microscopy. No nerve fibres undulation was noted on the intracranial sections of the cranial nerves or on the spinal roots. In their endoneurium a few, irregularly arranged collagen fibrils were found. In contrast, the nerve fibres undulation and Fontana's bands were a constant feature in the peripheral course of the nerve trunks. They were discernible in vivo and on excised unfixed as well as fixed nerves. The nerve fibres follow a sine-curve course of variable frequency and amplitude. Exposed in vivo, the nerve fibres retained their wave-like course even after removal of the epineurium and perineurium. The endoneurium of these nerves contained numerous undulating longitudinally oriented bundles of collagen fibrils. These findings suggest that the undulating course of the nerve fibres in peripheral nerves is conditional upon the quantity and arrangement of their endoneurial collagen fibrils. When the nerve was stretched in the course of movement, the undulation became straightened out until it disappeared. Conversely, nerve shortening enhanced the undulation. Thus the wave-like alignment of the nerve fibres represents a physiological reserve length for nerve stretching.

Animals↗