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Journal of Anatomy Aug 2015Information forwarded by individual muscle spindles is modulated by the dynamic and static gamma motoneurons in a differentiated way, depending on the coupling between... (Review)
Review
Information forwarded by individual muscle spindles is modulated by the dynamic and static gamma motoneurons in a differentiated way, depending on the coupling between the fusimotor neurons and the various intrafusal muscle fibres. Further modulation of this information at the level of spinal neurons is also differentiated because connections between individual muscle spindles and their spinal target cells are quite variable. This review illustrates this variability with respect to the spinal trajectory of muscle spindle primary afferents and the distribution of their synaptic contacts on motoneurons and other spinal neurons. It also discusses some of the consequences of this variability for the processing of information from proprioceptors.
Topics: Action Potentials; Animals; Axons; Electrical Synapses; Humans; Motor Neurons; Motor Neurons, Gamma; Muscle Spindles; Neurons, Afferent; Signal Transduction; Spinal Cord
PubMed: 26179024
DOI: 10.1111/joa.12331 -
Journal of Anatomy Oct 2023The spatial distribution of the medial gastrocnemius muscle spindles of 10 male and 10 female rats was analysed under a light microscope, and for the first time,...
The spatial distribution of the medial gastrocnemius muscle spindles of 10 male and 10 female rats was analysed under a light microscope, and for the first time, visualised using a 3D model of the muscle. Serial cross-sections of the medial gastrocnemius muscles were separated into 10 divisions along with the proximo-distal axis. The muscle spindles of the rat medial gastrocnemius were predominantly distributed on the proximo-medial divisions of the muscle. There were no sex-related differences in the distribution of the studied receptors. A single division contained an average of 2.71 receptors for animals of both sexes. Moreover, the calculated lengths of male and female rat muscle spindles were comparable, and average lengths did not significantly differ (3.30 ± 1.47 mm for male and 3.26 ± 1.32 mm for female rats). Therefore, the present results fill gaps in recent observations concerning similarities in muscle spindle numbers between male and female animals, despite significant differences in muscle mass and size.
Topics: Rats; Animals; Male; Female; Muscle Spindles; Muscle, Skeletal
PubMed: 37230935
DOI: 10.1111/joa.13895 -
Cell Dec 2014Spinal cord injuries alter motor function by disconnecting neural circuits above and below the lesion, rendering sensory inputs a primary source of direct external drive...
Spinal cord injuries alter motor function by disconnecting neural circuits above and below the lesion, rendering sensory inputs a primary source of direct external drive to neuronal networks caudal to the injury. Here, we studied mice lacking functional muscle spindle feedback to determine the role of this sensory channel in gait control and locomotor recovery after spinal cord injury. High-resolution kinematic analysis of intact mutant mice revealed proficient execution in basic locomotor tasks but poor performance in a precision task. After injury, wild-type mice spontaneously recovered basic locomotor function, whereas mice with deficient muscle spindle feedback failed to regain control over the hindlimb on the lesioned side. Virus-mediated tracing demonstrated that mutant mice exhibit defective rearrangements of descending circuits projecting to deprived spinal segments during recovery. Our findings reveal an essential role for muscle spindle feedback in directing basic locomotor recovery and facilitating circuit reorganization after spinal cord injury.
Topics: Animals; Early Growth Response Protein 3; Feedback, Physiological; Locomotion; Mice; Muscle Spindles; Neurons; Spinal Cord Injuries; Spinal Cord Regeneration
PubMed: 25525880
DOI: 10.1016/j.cell.2014.11.019 -
The Journal of Physiology Apr 19781. The responses of forty-one muscle spindle endings, mostly in tibialis anterior, were studied in human subjects during voluntary movements of the ankle joint performed...
1. The responses of forty-one muscle spindle endings, mostly in tibialis anterior, were studied in human subjects during voluntary movements of the ankle joint performed at various speeds against different external loads. 2. During slow shortening contractions, the discharge rates of spindle endings in the contracting muscle accelerated after the appearance of the first e.m.g. potentials but before sufficient force had been generated to move the limb. With some endings, the discharge rate decreased during the shortening movement while the e.m.g. activity was increasing, but it always remained higher than before the onset of contraction. If the speed of the movement was increased fewer spindle discharges were seen during muscle shortening. If the shortening contraction was opposed by an external load, so that greater effort was required to perform the same movement, more discharges were seen and the discharge pattern became less modulated by the change in muscle length. 3. These findings indicate that during shortening contractions the fusimotor system is activated together with the skeletomotor system. However, the fusimotor drive is generally insufficient to maintain a significant spindle discharge unless movement is slow or the muscle is shortening against an external load. 4. During lengthening contractions the spindle responses were greater than to passive stretch of similar amplitude and velocity, suggesting heightened fusimotor outflow. 5. During shortening and lengthening contractions small iregularities in the speed of movement occurred commonly. Unintended acceleration of a shortening movement caused a pause in spindle firing, and unintended acceleration of a lengthening movement caused an increased discharge from spindle endings. These spindle responses were associated with corresponding alterations in the discharge pattern of the voluntarily activated motor units at latencies consistent with the operation of spinal reflex mechanisms. 6. It is suggested that a functional role for the fusimotor activation during slow shortening contractions is to provide spindle endings with a background discharge so that they can detect irregularities in the movement and initiate the appropriate reflex correction.
Topics: Action Potentials; Adolescent; Adult; Ankle Joint; Humans; Middle Aged; Motor Neurons; Movement; Muscle Contraction; Muscle Spindles; Muscles; Neurons, Afferent
PubMed: 148511
DOI: 10.1113/jphysiol.1978.sp012265 -
Scientific Reports Apr 2023Pompe disease is a debilitating medical condition caused by a functional deficiency of lysosomal acid alpha-glucosidase (GAA). In addition to muscle weakness, people...
Pompe disease is a debilitating medical condition caused by a functional deficiency of lysosomal acid alpha-glucosidase (GAA). In addition to muscle weakness, people living with Pompe disease experience motor coordination deficits including an instable gait and posture. We reasoned that an impaired muscle spindle function might contribute to these deficiencies and therefore analyzed proprioception as well as muscle spindle structure and function in 4- and 8-month-old Gaa mice. Gait analyses showed a reduced inter-limb and inter-paw coordination in Gaa mice. Electrophysiological analyses of single-unit muscle spindle proprioceptive afferents revealed an impaired sensitivity of the dynamic and static component of the stretch response. Finally, a progressive degeneration of the sensory neuron and of the intrafusal fibers was detectable in Gaa mice. We observed an increased abundance and size of lysosomes, a fragmentation of the inner and outer connective tissue capsule and a buildup of autophagic vacuoles in muscle spindles from 8-month-old Gaa mice, indicating lysosomal defects and an impaired autophagocytosis. These results demonstrate a structural and functional degeneration of muscle spindles and an altered motor coordination in Gaa mice. Similar changes could contribute to the impaired motor coordination in patients living with Pompe disease.
Topics: Mice; Animals; Glycogen Storage Disease Type II; Muscle Spindles; Muscle, Skeletal; Disease Models, Animal; alpha-Glucosidases; Glucan 1,4-alpha-Glucosidase; Muscular Diseases
PubMed: 37085544
DOI: 10.1038/s41598-023-33543-y -
European Spine Journal : Official... Jul 2022Proprioceptive deficits are common in low back pain. The multifidus muscle undergoes substantial structural change after back injury, but whether muscle spindles are...
PURPOSE
Proprioceptive deficits are common in low back pain. The multifidus muscle undergoes substantial structural change after back injury, but whether muscle spindles are affected is unclear. This study investigated whether muscle spindles of the multifidus muscle are changed by intervertebral disc (IVD) degeneration in a large animal model.
METHODS
IVD degeneration was induced by partial thickness annulus fibrosus lesion to the L3-4 IVD in nine sheep. Multifidus muscle tissue at L4 was harvested at six months after lesion, and from six age-/sex-matched naïve control animals. Muscle spindles were identified in Van Gieson's-stained sections by morphology. The number, location and cross-sectional area (CSA) of spindles, the number, type and CSA of intrafusal fibers, and thickness of the spindle capsule were measured. Immunofluorescence assays examined Collagen I and III expression.
RESULTS
Multifidus muscle spindles were located centrally in the muscle and generally near connective tissue. There were no differences in the number or location of muscle spindles after IVD degeneration and only changes in the CSA of nuclear chain fibers. The thickness of connective tissue surrounding the muscle spindle was increased as was the expression of Collagen I and III.
CONCLUSION
Changes to the connective tissue and collagen expression of the muscle spindle capsule are likely to impact their mechanical properties. Changes in capsule stiffness may impact the transmission of length change to muscle spindles and thus transduction of sensory information. This change in muscle spindle structure may explain some of the proprioceptive deficits identified with low back pain.
Topics: Animals; Collagen; Collagen Type I; Intervertebral Disc; Intervertebral Disc Degeneration; Low Back Pain; Muscle Spindles; Paraspinal Muscles; Sheep
PubMed: 35618974
DOI: 10.1007/s00586-022-07235-6 -
ELife Feb 2023The proprioceptive system is essential for the control of coordinated movement, posture, and skeletal integrity. The sense of proprioception is produced in the brain...
The proprioceptive system is essential for the control of coordinated movement, posture, and skeletal integrity. The sense of proprioception is produced in the brain using peripheral sensory input from receptors such as the muscle spindle, which detects changes in the length of skeletal muscles. Despite its importance, the molecular composition of the muscle spindle is largely unknown. In this study, we generated comprehensive transcriptomic and proteomic datasets of the entire muscle spindle isolated from the murine deep masseter muscle. We then associated differentially expressed genes with the various tissues composing the spindle using bioinformatic analysis. Immunostaining verified these predictions, thus establishing new markers for the different spindle tissues. Utilizing these markers, we identified the differentiation stages the spindle capsule cells undergo during development. Together, these findings provide comprehensive molecular characterization of the intact spindle as well as new tools to study its development and function in health and disease.
Topics: Mice; Animals; Muscle Spindles; Multiomics; Proteomics; Muscle, Skeletal; Proprioception
PubMed: 36744866
DOI: 10.7554/eLife.81843 -
Experimental Physiology Jan 2024
Topics: Muscle Spindles; Mechanotransduction, Cellular; Proprioception; Muscle, Skeletal
PubMed: 38160398
DOI: 10.1113/EP091431 -
Anatomical Record (Hoboken, N.J. : 2007) Apr 2011Significant changes in extrafusal fiber type composition take place in the human masseter muscle from young age, 3-7 years, to adulthood, in parallel with jaw-face... (Comparative Study)
Comparative Study
Significant changes in extrafusal fiber type composition take place in the human masseter muscle from young age, 3-7 years, to adulthood, in parallel with jaw-face skeleton growth, changes of dentitions and improvement of jaw functions. As motor and sensory control systems of muscles are interlinked, also the intrafusal fiber population, that is, muscle spindles, should undergo age-related changes in fiber type appearance. To test this hypothesis, we examined muscle spindles in the young masseter muscle and compared the result with previous data on adult masseter spindles. Also muscle spindles in the young biceps brachii muscle were examined. The result showed that muscle spindle composition and distribution were alike in young and adult masseter. As for the adult masseter, young masseter contained exceptionally large muscle spindles, and with the highest spindle density and most complex spindles found in the deep masseter portion. Hence, contrary to our hypothesis, masseter spindles do not undergo major morphological changes between young age and adulthood. Also in the biceps, young spindles were alike adult spindles. Taken together, the results showed that human masseter and biceps muscle spindles are morphologically mature already at young age. We conclude that muscle spindles in the human young masseter and biceps precede the extrafusal fiber population in growth and maturation. This in turn suggests early reflex control and proprioceptive demands in learning and maturation of jaw motor skills. Similarly, well-developed muscle spindles in young biceps reflect early need of reflex control in learning and performing arm motor behavior.
Topics: Adult; Age Factors; Aging; Autopsy; Child; Child, Preschool; Female; Humans; Male; Masseter Muscle; Motor Activity; Muscle Development; Muscle Fibers, Skeletal; Muscle Spindles; Reflex
PubMed: 21370492
DOI: 10.1002/ar.21347 -
Journal of Neurophysiology Jun 1997Single jaw-muscle spindle afferent axons were characterized physiologically and intracellularly stained to determine whether particular physiological types of spindle...
Single jaw-muscle spindle afferent axons were characterized physiologically and intracellularly stained to determine whether particular physiological types of spindle afferent show distinctive morphologies. Microelectrodes filled with either horseradish peroxidase (HRP) or biotinamide (Neurobiotin) were advanced into the mesencephalic trigeminal nucleus (Vme) in anesthetized rats. Intracellular recordings then were characterized by their response: to palpation of the jaw muscles; when pressure was applied to the teeth and during passive ramp and hold and sinusoidal jaw movement. Seventy-one afferents were characterized physiologically and injected with HRP; an additional 61 afferents were typed and injected with biotinamide. The response of 43 stained neurons was recorded in the presence of suxamethonium. The major projection areas of these afferents were the: trigeminal motor nucleus (Vmo); region dorsal to Vmo; reticular formation, spinal trigeminal nucleus, superior cerebellar peduncle and Vme. One afferent type was modulated strongly during stretching of the jaw-elevator muscles. Based on their high sensitivity during stretching of the jaw muscles and/or their silencing during the release phase of muscle stretch, these afferents were classified as primary-like spindle afferents. These afferents projected most strongly to Vmo. A second type of afferent was modulated only modestly during stretching of the jaw-elevator muscles. These tonic afferents were classified as secondary-like spindle afferents because of their low dynamic sensitivity during ramp muscle stretch and their continued discharge during the release phase of muscle stretch. Secondary-like afferents projected most strongly to the region dorsal to Vmo. Boutons (n = 3,834) from 11 afferents were studied in detail. Secondary-like afferents had statistically larger boutons within Vmo. In both secondary- and primary-like spindle afferents, only a small number of boutons were associated closely with the somata and proximal dendrites of trigeminal motoneurons. In these cases, however, two to five boutons appeared to contact individual motoneurons, implying multiple monosynaptic inputs to a selective subset of jaw-elevator motoneurons. Some "giant" boutons were present dorsal to Vmo and in Vme. These results demonstrate that dynamically sensitive and nondynamically sensitive jaw-elevator muscle spindle afferents project preferentially to different regions. Primary-like spindle afferents are capable of providing feedback related to the dynamic phases of muscle stretch and project most heavily to Vmo. Secondary-like spindle afferents can transmit a feedback signal associated with muscle length and project most strongly to the supratrigeminal region. Both types of afferent have projections caudal to Vmo that may serve longer latency jaw-muscle stretch reflexes and/or the projection of proprioceptive information to the thalamus and cerebellum.
Topics: Afferent Pathways; Animals; Brain Mapping; Cerebellum; Evoked Potentials; Image Processing, Computer-Assisted; Jaw; Male; Masticatory Muscles; Muscle Spindles; Proprioception; Rats; Rats, Wistar; Reaction Time; Reflex, Stretch; Reticular Formation; Synapses; Trigeminal Nuclei; Trigeminal Nucleus, Spinal
PubMed: 9212247
DOI: 10.1152/jn.1997.77.6.2925