A fine-structural study of the termination of intrafusal muscle fibres in the Chinese hamster

1983 ◽  
Vol 234 (3) ◽  
Author(s):  
Junzo Desaki ◽  
Yasuo Uehara
Keyword(s):  
Structural Study ◽  
Chinese Hamster ◽  
Muscle Fibres ◽  
Intrafusal Muscle

scholarly journals The Influence of Bag 2 and Chain Intrafusal Muscle Fibres on Secondary Spindle Afferents in the Cat

2003 ◽  
Vol 550 (1) ◽  
pp. 263-278 ◽  
Author(s):  
R. Durbaba ◽  
A. Taylor ◽  
P. H. Ellaway ◽  
S. Rawlinson
Keyword(s):  
Muscle Fibres ◽  
Intrafusal Muscle

The spindle and extrafusal innervation of a frog muscle

1957 ◽  
Vol 146 (924) ◽  
pp. 416-430 ◽  
Keyword(s):  
Muscle Fibre ◽  
Short Distance ◽  
Frog Muscle ◽  
Muscle Fibres ◽  
Intrafusal Muscle ◽  
Intrafusal Fibre ◽  
Unmyelinated Axons ◽  
Intrafusal Fibres ◽  
Break Up ◽  
Tonic System

In the frog muscle, ext. long. dig. IV, there are two or three spindle systems. Each consists of a bundle of intrafusal muscle fibres with two, three or four discrete encapsulated sensory regions distributed in mechanical series along it. A sensory region is usually comprised of the coiled branches of one afferent axon. These embrace the intrafusal fibres and ultimately form long fine varicose endings on or near them. The intrafusal striations appear to be lost for a short distance within the sensory region, and in this region the intrafusal fibre nuclei crowd together. The ‘small’ extrafusal efferents break up into trusses of fine unmyelinated axons and terminate as ‘grape’ end-plates, several of which can occur on the same muscle fibre. This is the ‘tonic’ system. The ‘large’ extrafusal efferents terminate as ‘Endbiischel’ end-plates on muscle fibres not supplied by grape endings. This is the ‘twitch’ system. Both ‘grape' and ‘twitch’ end-plates occur on the intrafusal bundle (probably on separate fibres) between the sensory regions. They are supplied by branches of ‘small’ or ‘large’ axons respectively, which also innervate extrafusal fibres. Thus like the extrafusals the intrafusal bundle is composed of ‘tonic’ and ‘twitch’ muscle fibres. This situation contrasts with that of the mammal, where extrafusals are exclusively ‘twitch’ fibres and intrafusals ‘tonic’.

The Innervation of the Muscle-Spindle

1948 ◽  
Vol s3-89 (6) ◽  
pp. 143-185
Author(s):  
D. BARKER
Keyword(s):  
Muscle Spindles ◽  
Muscle Fibres ◽  
Gold Chloride ◽  
Nerve Fibres ◽  
Intrafusal Muscle ◽  
Intrafusal Fibre ◽  
Afferent Discharge ◽  
Tendon Organ ◽  
Nuclear Bag ◽  
Secondary Fibre

A study of the morphology and innervation of muscle-spindles from the quadriceps of the rabbit and cat has shown that: 1. The intrafusal muscle-fibres do not subdivide in their course through the spindle, as is maintained in some descriptions, but retain their individuality from pole to pole. 2. There is no constant feature which is characteristic of one pole of a spindle and not the other. A distinction can be made between the proximal and distal ends only when it is possible to orientate the spindle according to the proximal and distal ends of the muscle. The extreme ends of the spindle are attached indifferently to extrafusal endomysium, tendon, or perimysial connective tissue. 3. In the equatorial region each muscle-fibre of the spindle contains a dense aggregation of spherical central nuclei (‘nuclear bag’). On either side of this aggregation oval nuclei are disposed in the form of a chain within a central core of protoplasm (‘myotube region’). The nuclear bag is devoid of cross-striations and presumably non-contractile. The two polar portions of the muscle-fibre on either side of the bag are striated and each receives a motor innervation; hence they are presumed to function as independent contractile units. 4. The number of end-plates possessed by a spindle is approximately double its number of intrafusal muscle-fibres, with half the total number of end-plates situated at each pole. The ratio is rarely exact, since one polar half of an intrafusal fibre frequently bears two end-plates; these are innervated by nerve-fibres which retain their individuality as far as they can be traced back from the spindle. Both small nerve-fibres (3-4 µ in gold chloride preparations) and relatively large nerve-fibres (6-7 µ in gold chloride preparations) take part in the motor innervation of muscle-spindles, as was deduced on physiological grounds by Leksell (1945). 5. An analysis of the sensory innervation has confirmed many of Ruffini's (1898) observations. Primary or ‘annulo-spiral’ and secondary or ‘flowerspray’ endings occur and they are innervated by independent nerve-fibres; it is suggested that Ruffini's terms ‘primary’ and ‘secondary’ be adopted since the descriptive terms cannot always be applied. In the rabbit the secondary ending is ‘annulo-spiral’ in form and differs little from the primary ending; in the cat it is more irregular and could be termed ‘flower-spray’. The primary ending is always present and is associated with the nuclear bags of the intrafusal muscle-fibres; in some instances its ramifications are more extensive and also entwine the myotube regions. The primary ending may be the only sensory termination present, or it may be accompanied by one or by two secondary endings. These are borne by the myotube regions of the musclefibres. In the rabbit's quadriceps and interossei, spindles with one primary and one secondary ending were the most frequent in the samples taken; in the cat's quadriceps spindles with one primary and two secondary endings were the most numerous. Both the primary and secondary nerve-fibres invariably ramify so as to innervate each intrafusal fibre in the muscle-bundle. The two sensory terminations are often closely intercalated but do not overlap with one another to any great extent. As estimated from measurements made on fresh, silver, and gold chloride preparations the total diameter of the primary fibre lies between 8 and 12 µ, that of the secondary fibre between 6 and 9 µ. 6. Apart from small sympathetic fibres innervating the vascular supply of the spindle, other finer fibres may occasionally be seen ramifying within the walls of the capsule and over the polar regions. It is possible that they are somatic sensory fibres subserving the sensation of pain. 7. The nature of the reflex effects of the afferent impulses discharged by the muscle-spindle and tendon-organ is considered, and it is concluded that the balance of evidence indicates that the afferent discharge from the spindle is excitatory and that from the tendon-organ inhibitory to the motor neurones of the same muscle. However, the identification of the spindle as the receptor which excites the stretch reflex is found to rest largely upon equivocal evidence, its acceptance depending ultimately upon Matthews's finding (1933) of a considerable difference-in threshold between the spindle and tendon-organ in response to stretch. It is suggested that the large primary fibre innervating the spindle should be identified as the ‘stretch afferent’ rather than the smaller secondary fibre specified by Matthews, for the rapid con duction rate of the afferent discharge exciting the stretch reflex (Lloyd, 1943) indicates that sensory fibres of the largest diameter are employed. The functional significance of the secondary fibres is obscure and the specific reflex functions of the sensory fibres innervating both the spindle and the tendon organ clearly require further elucidation.

The Early Development of Muscle Spindles in the Rat

1973 ◽  
Vol 12 (1) ◽  
pp. 175-195
Author(s):  
ALICE MILBURN
Keyword(s):  
Close Association ◽  
Large Diameter ◽  
Muscle Spindles ◽  
Muscle Fibres ◽  
Intrafusal Muscle ◽  
Intrafusal Fibres ◽  
Fusimotor Innervation ◽  
Nuclear Chain ◽  
Intramuscular Nerve

The morphogenesis of muscle spindles in rat lower hind-limb muscles has been investigated using the electron microscope. The earliest detectable spindles are seen in the 19.5-day foetus and consist of a single myotube bearing simple nerve terminals of the large primary afferent axon from nearby unmyelinated intramuscular nerve trunks. The capsule forms by an extension of the perineural epithelium of the supplying nerve fasciculus, and is confined initially to the innervated zone. Myonuclei accumulate in this region, so that the first intrafusal muscle fibre to develop is a nuclear-bag fibre. Myoblasts, present within the capsule of the spindle throughout its development, fuse to form a smaller less-differentiated myotube by the 20-day foetal stage. This new myotube matures by close association with the initial fibre, and by birth (21-22 days gestation) has formed the smaller, intermediate bag fibre, that has been identified histochemically and ultrastructurally in the adult. The nuclear-chain fibres develop in the same way; myoblasts fuse to form satellite myotubes that mature in pseudopodial apposition to one of the other fibres within its basement membrane. This apposition consists of extensions of sarcoplasm from the developing myotube into the supporting fibre. By the 4-day postnatal stage the full adult complement of 4 intrafusal muscle fibres is present, although ultrastructural variations, seen in the adult, are not differentiated. The fusimotor innervation begins to arrive at birth, but is not mature until the 12th postnatal day, when the myofibrillar ultrastructural differentiation, including the loss of the M-line in the large-diameter bag fibre, is complete. The periaxial space appears at the same time. It is suggested that the sequential development of the intrafusal fibres is a reflexion of the decreasing morphogenetic effect of the afferent innervation, whereas the role of the fusimotor innervation is in ultrastructural, myofibrillar differentiation.

Form and classification of motor endings in mammalian muscle spindles

1985 ◽  
Vol 225 (1239) ◽  
pp. 195-212 ◽  
Keyword(s):  
Muscle Fibre ◽  
Fibre Type ◽  
Muscle Spindles ◽  
Muscle Fibre Type ◽  
Motor Axon ◽  
Muscle Fibres ◽  
Intrafusal Muscle ◽  
Axon Terminals ◽  
Hindlimb Muscle

The presynaptic features of 234 motor endings supplied to cat hindlimb muscle spindles have been studied in teased, silver preparations, and the postsynaptic features of a further 27 endings have been studied in serial, 1 μm thick, transverse sections. In the presynaptic study motor endings received by the three types of intrafusal muscle fibre were compared with the endings supplied to spindles by the various functional categories of motor axon. Three forms of motor ending were found that had significantly different presynaptic features. These forms correspond closely to those previously identified in the literature as p 1 (β), p 2 (dynamic γ) and trail (static γ). The results of the postsynaptic study showed that the degree of indentation of the intrafusal muscle fibres by motor axon terminals increases with greater distance from the primary ending, irrespective of muscle-fibre type. We conclude that the postsynaptic form of intrafusal motor endings is determined by distance from primary ending and muscle-fibre type. It is not determined by type of motor axon, and cannot be correlated with presynaptic form so as to produce a unified classification of intrafusal motor endings.

scholarly journals Acetylcholine receptors in the equatorial region of intrafusal muscle fibres modulate mouse muscle spindle sensitivity

2019 ◽  
Vol 597 (7) ◽  
pp. 1993-2006 ◽  
Author(s):  
Laura Gerwin ◽  
Corinna Haupt ◽  
Katherine A. Wilkinson ◽  
Stephan Kröger
Keyword(s):  
Muscle Spindle ◽  
Acetylcholine Receptors ◽  
Equatorial Region ◽  
Muscle Fibres ◽  
Mouse Muscle ◽  
Intrafusal Muscle

scholarly journals Glycogen depletion elicited in tenuissimus intrafusal muscle fibres by stimulation of static gamma-axons in the cat.

1984 ◽  
Vol 346 (1) ◽  
pp. 341-352 ◽  
Author(s):  
L Decorte ◽  
F Emonet-Dénand ◽  
D W Harker ◽  
L Jami ◽  
Y Laporte
Keyword(s):  
Muscle Fibres ◽  
Glycogen Depletion ◽  
Intrafusal Muscle ◽  
Stimulation Of
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