On the function of muscle and reflex partitioning

Windhorst, U.; Hamm, Thomas M.; Stuart, Douglas G.

doi:10.1017/s0140525x00024985

Cited by 166 publications

(112 citation statements)

References 276 publications

(245 reference statements)

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“…We have loosely referred to components of FDP which flex individual digits as 'muscles', although it is unlikely that there are absolute criteria which define a muscle, particularly when multitendoned structures are considered (Windhorst, Hamm & Stuart, 1989). FPL and FDP can be considered distinct muscles, with different characteristics: FDP is multitendoned, with the index portion enclosed in fascia, and anatomically distinct from the middle, ring and little finger components.…”

Section: Mechanical Linkages Between 'Muscles'mentioning

confidence: 99%

Limited independent flexion of the thumb and fingers in human subjects.

Kilbreath

Gandevia

1994

The Journal of Physiology

243

220

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1. We investigated whether human subjects can activate selectively flexor pollicis longus (FPL) and digital portions of flexor digitorum profundus (FDP). These muscles were selected because they are the only flexors of the distal phalanges. 2. Electromyographic activity (EMG) was recorded with intramuscular electrodes from one digital component of the deep flexors (‘test’) while subjects lifted weights by flexing the distal interphalangeal joint of the other digits in turn (‘lifting’ digits). Only recording sites at which single motor units were recruited selectively at low forces were used. The weights lifted represented 2.5‐50% of the maximal voluntary contraction (MVC). We measured the lowest weight lifted which produced phasic and tonic coactivation in the ‘test’ muscle. 3. The extent of coactivation varied with the ‘distance’ between the test and lifting digits although no significant difference occurred in the pattern of coactivation thresholds among the digital flexors. The extent of coactivation increased when angular displacement or velocity at the distal interphalangeal joint of the lifting digit increased but was not critically dependent on restraint of the hand. 4. Because mechanical ‘connections’ could interfere with the ability to move a distal phalanx independently, the arms of nine cadavers were studied. The separation of tendons between the thumb (FPL) and the index portion of FDP, and between the index and middle portions of FDP, usually extended more proximally in the forearm than separation between the tendons to the middle and ring fingers and between the ring and little fingers. Direct intertendinous links were also noted. 5. It is not possible to direct a sufficiently focal motor command to flex selectively the distal joint of the fingers and thumb when forces exceeding 2.5% MVC are generated. For the middle, ring and little fingers in particular, movement of adjacent digits may also involve ‘in‐series’ mechanical links between adjacent components of FDP.

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Section: Mechanical Linkages Between 'Muscles'mentioning

confidence: 99%

Limited independent flexion of the thumb and fingers in human subjects.

Kilbreath

Gandevia

1994

The Journal of Physiology

243

220

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“…Recently, however, muscles in various mammalian species have been shown to consist of multiple functional subdivisions (Burke, 1995;English et al, 1993;Windhorst et al, 1989). Within such a muscle, each subdivision consists of a region of muscle fibers innervated by a separate branch of the muscle nerve (English and Letbetter, 1982;English and Weeks, 1984;Balice-Gordon and Thompson, 1988;English, 1990;Segal et al, 1991;Drake et al, 1993;Serlin and Schieber, 1993;Sanders, et al, 1994;Vanden Noven et al, 1994).…”

Section: Introductionmentioning

confidence: 99%

“…Within such a muscle, each subdivision consists of a region of muscle fibers innervated by a separate branch of the muscle nerve (English and Letbetter, 1982;English and Weeks, 1984;Balice-Gordon and Thompson, 1988;English, 1990;Segal et al, 1991;Drake et al, 1993;Serlin and Schieber, 1993;Sanders, et al, 1994;Vanden Noven et al, 1994). In many of these muscles, the MUs of different subdivisions comprise functional sub-pools that the nervous system can activate differentially, exerting biomechanically different forces on the tendon of the muscle(s) (Herring et al, 1979;Pare et al, 1981;English, 1984;English and Weeks, 1987;Windhorst et al, 1989;Chanaud et al, 1991;Schieber, 1993).…”

Section: Introductionmentioning

confidence: 99%

Tension Distribution of Single Motor Units in Multitendoned Muscles: Comparison of a Homologous Digit Muscle in Cats and Monkeys

et al. 1997

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To determine whether single motor units (MUs) in multitendoned muscles distribute tension to multiple tendons or instead focus tension selectively on a single tendon, we examined the distribution of tension generated by single MUs in the cat extensor digitorum lateralis (EDLat), and in its macaque homolog, the extensor digiti quarti et quinti (ED45). General properties of MUs (maximal tetanic tension, axonal conduction velocity, and twitch rise time) were similar in these muscles to those reported for other limb muscles in cats and monkeys. Most cat EDLat MUs were found to exert tension rather selectively on one of the three tendons of the muscle. Fast fatigable MUs were slightly but significantly more selective than fast fatigue-resistant and slow MUs. In contrast, and contrary to expectation, the macaque ED45 contained a lower proportion of MUs that exerted tension selectively on one of the two tendons of the muscle, and a higher proportion of relatively nonselective MUs. These findings suggest that the cat EDLat may consist of three functional subdivisions, each acting preferentially on a different tendon, whereas the macaque ED45 is more likely to function as a single multitendoned muscle.

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“…Current muscle research has demonstrated that many mammalian skeletal muscles are composed of NMCs which are active independently according to task requirements and can be defined by anatomical, histochemical, and electrophysiological criteria. Anatomically, separate intramuscular nerve branches can be seen to innervate distinct regions in a compartmentalized muscle (English and Ledbetter, 1982a;English and Weeks, 1987;Windhorst et al, 1989;Chanaud et al, 1991a;Sanders et al, 1994;Sanders, 1998b, 2000). Histochemically, the compartmentalized muscle is often characterized by uneven muscle fiber-type distribution (English and Ledbetter, 1982b;Richmond and Armstrong, 1988;Chanaud et al, 1991b;Sanders, 1998b, 2000, in press), which is termed muscle fiber-type regionalization (Chanaud et al, 1991a, b).…”

Section: Nmcs Within the Human Ipc Musclementioning

confidence: 99%

Neuromuscular compartments and fiber‐type regionalization in the human inferior pharyngeal constrictor muscle

Sanders

2001

Anat. Rec.

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The inferior pharyngeal constrictor (IPC) muscle functions during swallowing, respiration, and vocalization. The most-caudal portion of the IPC is believed to be part of the functional upper esophageal sphincter (UES). We hypothesized that the caudal fibers of the human IPC may have enzyme-histochemical characteristics similar to those of the cricopharyngeus muscle, a major component of the UES. In this study, human IPC muscles obtained from autopsy were studied using Sihler's stain to examine innervation patterns, and using myofibrillar ATPase, NADH tetrazolium reductase (NADH-TR), and succinic dehydrogenase (SDH) techniques to investigate the distribution and oxidative capacity of the slow-(type I) and fast-(type II) twitch fibers in the muscle. The results showed that the human IPC consists of at least two neuromuscular compartments (NMCs): rostral and caudal. Each of the NMCs was innervated by a separate nerve branch derived from the pharyngeal branch of the vagus nerve. The rostral NMC is faster (39% type I, 61% type II) than the caudal NMC (70% type I, 30% type II). In addition, two histochemically-delineated fiber layers were identified in the human IPC: a slow inner layer (SIL) with predominantly type I fibers (66%), and a fast outer layer (FOL) with predominantly type II fibers (62%) (P Ͻ 0.01). However, the dimensions of both fiber layers and proportions of the muscle fiber types varied with the NMCs. Specifically, the ratio of the thickness of the SIL to FOL was ϳ2:1 for the caudal NMC and ϳ1:2 for the rostral NMC, respectively. In the SIL the type I fibers accounted for 84% for the caudal NMC and 69% and 44% for the lower and upper portions of the rostral NMC. In contrast, the type II fibers in the FOL accounted for 46% for the caudal NMC and 67% and 74% for the lower and upper portions of the rostral NMC, respectively (P Ͻ 0.01). The caudal NMC of the IPC shared histochemical characteristics with the cricopharyngeus muscle, in that it contained predominantly slow oxidative fibers. Overall, the caudal NMC and the SIL in the IPC had high NADH-TR and SDH activities. However, different patterns of oxidative enzyme activity were identified in both type I and type II fibers. This study provided histochemical evidence for the concept that the caudal NMC within the IPC contributes to the functional UES. In addition, the two histochemically-defined fiber layers in the IPC may be a specialized adaptation in humans to enable different upper-airway functions during respiration, swallowing, and speech. Anat

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On the function of muscle and reflex partitioning

Cited by 166 publications

References 276 publications

Limited independent flexion of the thumb and fingers in human subjects.

Limited independent flexion of the thumb and fingers in human subjects.

Tension Distribution of Single Motor Units in Multitendoned Muscles: Comparison of a Homologous Digit Muscle in Cats and Monkeys

Neuromuscular compartments and fiber‐type regionalization in the human inferior pharyngeal constrictor muscle

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