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Analytical and Quantitative Cytology... Feb 2005To study the morphometric characteristics of the human muscle spindle in normal muscle and to investigate the influence of aging.
OBJECTIVE
To study the morphometric characteristics of the human muscle spindle in normal muscle and to investigate the influence of aging.
STUDY DESIGN
The following variables were studied in 72 spindles: area and diameter of the spindle; thickness of the capsule; number, area and diameter of fibers; and number and area of nuclei.
RESULTS
In deltoid and extensor digitorum brevis muscles, a reduction in the diameter of the spindle as a function of age was found, while no statistically significant change in the variables as a function of age was observed in the quadriceps femoris and biceps muscles. In the deltoid, a reduction in the number of fibers and an increase in their diameter were also observed.
CONCLUSION
These findings could prove useful in the study of the spindle in relation to disease.
Topics: Adult; Aged; Aged, 80 and over; Aging; Female; Humans; Image Processing, Computer-Assisted; Male; Middle Aged; Muscle Spindles; Muscle, Skeletal
PubMed: 15794446
DOI: No ID Found -
The Journal of Physiology Feb 2010
Topics: Amiloride; Animals; Calcium Channels; Epithelial Sodium Channel Blockers; Epithelial Sodium Channels; Humans; Muscle Spindles; Muscle, Skeletal; Neurobiology; Rats
PubMed: 20173076
DOI: 10.1113/jphysiol.2010.186924 -
Journal of Morphology Mar 1990The concept of parallel muscle combinations, in which spindle density is significantly higher in small muscles compared to their larger counterparts in large-small...
The concept of parallel muscle combinations, in which spindle density is significantly higher in small muscles compared to their larger counterparts in large-small muscle combinations acting across a joint, is supported by the results of this study regardless of the joint. Analysis of the canine data as well as previously published guinea pig forelimb and human pelvic limb data revealed no significant difference in spindle density between antigravity and non-antigravity muscles. Furthermore, a gradual increase in spindle density from proximal to distal on the limb was not found, although spindle density was significantly higher in the intrinsic manus or pes muscles compared to more proximal limb muscles in all three species. The significant differences in spindle densities in parallel muscle combinations and in manus/pes versus proximal muscles are discussed relative to their possible role in the control of locomotion.
Topics: Animals; Dogs; Female; Forelimb; Gravitation; Locomotion; Male; Muscle Spindles; Muscles
PubMed: 2140137
DOI: 10.1002/jmor.1052030309 -
Journal of Neurophysiology Apr 2019Studies on anesthetized animals have revealed that nociceptors can excite fusimotor neurons and thereby change the sensitivity of muscle spindles to stretch; such...
Studies on anesthetized animals have revealed that nociceptors can excite fusimotor neurons and thereby change the sensitivity of muscle spindles to stretch; such nociceptive reflexes have been suggested to underlie the mechanisms that lead to chronic musculoskeletal pain syndromes. However, the validity of the "vicious cycle" hypothesis in humans has yielded results contrasting with those found in animals. Given that spindle firing rates are much lower in humans than in animals, it is possible that some of the discrepancies between human experimental data and those obtained in animals could be explained by differences in background fusimotor drive when the leg muscles are relaxed. We examined the effects of tonic muscle pain during voluntary contractions of the ankle dorsiflexors. Unitary recordings were obtained from 10 fusimotor-driven muscle spindle afferents (6 primary, 4 secondary) supplying the ankle dorsiflexors via a microelectrode inserted percutaneously into the common peroneal nerve. A series of 1-min weak contractions was performed at rest and during 1 h of muscle pain induced by intramuscular infusion of 5% hypertonic saline into the tibialis anterior muscle. We did not observe any statistically significant increases in muscle spindle firing rates of six afferents followed during tonic muscle pain, although discharge variability increased slightly. Furthermore, a participant's capacity to maintain a constant level of force, while relying on proprioceptive feedback in the absence of visual feedback, was not compromised during pain. We conclude that nociceptive inputs from contracting muscle do not excite fusimotor neurons during voluntary isometric contractions in humans. NEW & NOTEWORTHY Data obtained in the cat have shown that muscle pain causes a marked increase in the firing of muscle spindles, attributed to a nociceptor-driven fusimotor reflex. However, our studies of muscle spindles in relaxed leg muscles failed to find any effect on spindle discharge. Here we showed that experimental muscle pain failed to increase the firing of muscle spindle afferents during weak voluntary contractions, when fusimotor drive sufficient to increase their firing is present.
Topics: Adolescent; Adult; Ankle; Feedback, Sensory; Female; Humans; Isometric Contraction; Male; Muscle Spindles; Myalgia; Nociception; Peroneal Nerve; Reflex
PubMed: 30699044
DOI: 10.1152/jn.00862.2018 -
Experimental Brain Research 1991The activities of human muscle spindle primary endings were recorded in the lateral peroneal nerve using the microneurographic method. The aim of the study was to test...
The activities of human muscle spindle primary endings were recorded in the lateral peroneal nerve using the microneurographic method. The aim of the study was to test whether voluntary isometric contraction causes any after-effects, first in the resting discharge of muscle spindle primary endings and secondly in their responses to a slow ramp stretch. To investigate the latter point, the initial angular position of the ankle was passively adjusted until the unit fell silent, in order to introduce a delay in the responses to muscle stretch. The results were as follows: (1) most of the units did not exhibit the "post-contraction sensory discharge" reported to occur in numerous animal experiments; this means that the muscle spindle resting discharge was essentially the same before and after isometric voluntary contraction. (2) Isometric voluntary contraction led to changes in muscle spindle stretch sensitivity which resulted in a reduction in the stretch threshold and a decrease in the muscle spindle dynamic sensitivity. These data suggest that the after-effects observed may have been triggered by static fusimotor neurones. The results are discussed with reference to the theory according to which the processing by the CNS of muscular proprioceptive messages deals mainly with signals arising from muscles stretched during movement, and it is concluded that the coactivation of alpha and gamma motoneurones during the contraction facilitates the coding of the parameters of forthcoming stretching movements, by the muscle spindles.
Topics: Adult; Electromyography; Humans; Isometric Contraction; Mechanoreceptors; Muscle Contraction; Muscle Spindles; Proprioception
PubMed: 1836997
DOI: 10.1007/BF00230541 -
The Journal of Physiology Jul 19801. These experiments were based on the recent observation of Gladden (1976), that acetylcholine (ACh) when applied to the isolated cat muscle spindle caused contraction...
1. These experiments were based on the recent observation of Gladden (1976), that acetylcholine (ACh) when applied to the isolated cat muscle spindle caused contraction of the dynamic and the static nuclear bag fibres, and not of the nuclear chain fibres, and that the dynamic nuclear bag fibre had the lower threshold to ACh than the static nuclear bag fibre. Subsequently, suxamethonium (SCh) has been shown to have similar effects on the intrafusal muscle fibres (Gladden & McWilliam, 1977). 2. In these experiments, the response of cat soleus muscle spindle primary, secondary and 'intermediate' sensory endings to repetitive ramp stretches during continuous slow infusions of SCh were studied. The changes observed are interpreted on the basis of the known action of SCh on the intrafusal muscle fibres of the isolated spindle. 3. Primary sensory endings, with afferent axon conduction velocities above 80 m/sec, were activated during SCh infusion in three stages. In Phase I of excitation, a gradual facilitation of the discharge of the Ia endings was seen, without potentiation of the dynamic or length sensitivity to stretch. In Phase II of excitation, the dynamic sensitivity of the Ia endings increased very markedly. In Phase III of excitation, an increase in length sensitivity was superimposed on the already enhanced dynamic sensitivity. 4. Secondary sensory endings, with afferent axon conduction velocities below 60 m/sec, only experienced a gradual facilitation of their discharge during SCh infusion, similar to the Phase I effects of SCh on primary endings. 5. The majority of 'intermediate' sensory endings, with afferent axon conduction velocities between 60 and 80 m/sec, were activated by SCh either in the same way as primary endings, or in the same way as secondary endings. However, a significant number of these sensory endings behaved in a truly intermediate manner during SCh infusion (cf. Rack & Westbury, 1966), and may represent an intermediate form of spindle sensory ending. 6. The afferent axon conduction velocities of these truly intermediate sensory endings were restricted to the range 69-77 m/sec. All the 'intermediate' endings which were activated in a primary-like manner had afferent axons conducting at velocities greater than 74 m/sec. 'Intermediate' endings which were activated in a secondary-like manner had afferent axon conduction velocities below 72 m/sec. 7. The probable contribution of the static and dynamic nuclear bag fibres to the discharge of each type of spindle sensory ending is discussed.
Topics: Action Potentials; Animals; Cats; Muscle Contraction; Muscle Spindles; Muscles; Neurons, Afferent; Succinylcholine
PubMed: 6449590
DOI: 10.1113/jphysiol.1980.sp013326 -
Pain May 2001Transient noxious chemical stimulation of small diameter muscle afferents modulates jaw movement-related responses of caudal brainstem neurons. While it is likely that...
Transient noxious chemical stimulation of small diameter muscle afferents modulates jaw movement-related responses of caudal brainstem neurons. While it is likely that the effect is mediated from the spindle afferents in the mesencephalic nucleus (Vmes) via the caudally projecting Probst's tract, the mechanisms of pain induced modulations of jaw muscle spindle afferents is not known. In the present study, we tested the hypothesis that jaw muscle nociceptors gain access to muscle spindle afferents in the same muscle via central mechanisms and alter their sensitivity. Thirty-five neurons recorded from the Vmes were characterized as muscle spindle afferents based on their responses to passive jaw movements, muscle palpation, and electrical stimulation of the masseter nerve. Each cell was tested by injecting a small volume (250 microl) of either 5% hypertonic and/or isotonic saline into the receptor-bearing muscle. Twenty-nine units were tested with 5% hypertonic saline, of which 79% (23/29) showed significant modulation of mean firing rates (MFRs) during one or more phases of ramp-and-hold movements. Among the muscle spindle primary-like units (n = 12), MFRs of 4 units were facilitated, five reduced, two showed mixed responses and one unchanged. In secondary-like units (n = 17), MFRs of 9 were facilitated, three reduced and five unchanged. Thirteen units were tested with isotonic saline, of which 77% showed no significant changes of MFRs. Further analysis revealed that the hypertonic saline not only affected the overall output of muscle spindle afferents, but also increased the variability of firing and altered the relationship between afferent signal and muscle length. These results demonstrated that activation of muscle nociceptors significantly affects proprioceptive properties of jaw muscle spindles via central neural mechanisms. The changes can have deleterious effects on oral motor function as well as kinesthetic sensibility.
Topics: Animals; Cats; Electric Stimulation; Electrophysiology; Jaw; Masseter Muscle; Movement; Muscle Spindles; Neurons, Afferent; Nociceptors; Proprioception; Saline Solution, Hypertonic
PubMed: 11323133
DOI: 10.1016/s0304-3959(00)00477-2 -
The Journal of Physiology Mar 19781. Single unit and multi-unit recordings of muscle spindle activity were made from the peroneal nerves of human subjects. While the subjects attempted to maintain a...
1. Single unit and multi-unit recordings of muscle spindle activity were made from the peroneal nerves of human subjects. While the subjects attempted to maintain a constant ankle joint position, an external load on the receptor-bearing muscle was altered unexpectedly. 2. The spindle discharge produced by a sudden increase in load was of similar strength when the receptor-bearing muscle was relaxed as when it was contracting at the moment of the impact. A motor response at a latency consistent with a spinal reflex mechanism occurred only when the muscle was contracting. It is concluded that the potentiation of the reflex mechanism during contraction was not due primarily to a fusimotor action. 3. Sudden decrease in load produced a pause in spindle discharge followed by a pause in on-going e.m.g. activity at a latency consistent with spinal reflex mechanisms. 4. Slow changes in load produced parallel changes in e.m.g. and spindle discharge. It is suggested that the voluntary effort involved in maintaining joint position in the face of gradually changing loads results in corticospinal activity adjusted in strength to the opposing torque and operating on alpha and gamma motoneurones in parallel.
Topics: Action Potentials; Ankle Joint; Biomechanical Phenomena; Humans; Muscle Contraction; Muscle Spindles; Muscles; Posture; Reflex
PubMed: 148508
DOI: 10.1113/jphysiol.1978.sp012225 -
Australian Paediatric Journal 1988Muscle is a complex sensory organ as well as a contractile apparatus, and disease processes that produce muscle weakness and wasting will affect the sensory information... (Review)
Review
Muscle is a complex sensory organ as well as a contractile apparatus, and disease processes that produce muscle weakness and wasting will affect the sensory information transmitted by receptors in muscle. In addition, one of the sensory structures in muscle, the muscle spindle, receives a motor innervation, the gamma-efferent or fusimotor system, with which the brain can alter the feedback that it receives from muscle. Muscle spindle activity forms the afferent limb of spinal reflexes, such as the tendon jerk, and long-loop reflexes that traverse supraspinal reflex pathways. Muscle spindle activity constitutes the major afferent cue for kinaesthetic sensations and contributes to updating the centrally generated programme for movement. This paper reviews briefly some aspects of muscle spindle activity and its fusimotor control as studied in human subjects using microneurography.
Topics: Afferent Pathways; Brain; Humans; Muscle Contraction; Muscle Spindles; Muscles; Neuromuscular Diseases; Reflex; Spinal Cord
PubMed: 2974277
DOI: No ID Found -
Journal of Neurophysiology Mar 19791. Chronically implanted microelectrode wires in the L7 and S1 dorsal root ganglia were used to record unit activity from cat hindlimb primary and secondary muscle... (Comparative Study)
Comparative Study
1. Chronically implanted microelectrode wires in the L7 and S1 dorsal root ganglia were used to record unit activity from cat hindlimb primary and secondary muscle spindle afferents. Units could be reliably recorded for several days, permitting comparison of their activity with homonymous muscle EMG and length during a variety of normal, unrestrained movements. 2. The general observation was that among both primary and secondary endings there was a broad range of different patterns of activity depending on the type of muscle involved and the type of movement performed. 3. During walking, the activity of a given spindle primary was usually consistent among similar step cycles. However, the activity was usually poorly correlated with absolute muscle length, apparently unrealted to velocity of muscle stretch, and could change markedly for similar movements performed under different conditions. 4. Spindle activity modulation not apparently related to muscle length changes was assumed to be influenced by fusimotor activity. In certain muscles, this presumption leads to the conclusion that gamma-motoneurons may be activated out of phase with homonymous alpha-motoneurons as well as by more conventional alpha-gamma-motoneuron coactivation. 5. Simultaneous recordings of two spindle primary afferents from extensor digitorum longus indicated that spindles within the same muscle may differ considerably with respect to this presumed gamma-motoneuron drive. 6. Spindle secondary endings appeared to be predominantly passive indicators of muscle length during walking, but could demonstrate apparently strong fusimotor modulation during other motor activities such as postural changes and paw shaking. 7. Both primary and secondary endings were observed to undergo very rapid modulation of firing rates in response to presumed reflexly induced intrafusal contractions. 8. It is suggested that the pattern of fusimotor control of spindles may be tailored to the specific muscle and task being performed, rather than necessarily dominated by rigid alpha-gamma coactivation.
Topics: Animals; Cats; Electromyography; Hindlimb; Male; Motor Neurons; Motor Neurons, Gamma; Movement; Muscle Spindles; Muscles
PubMed: 154557
DOI: 10.1152/jn.1979.42.2.420