Acta anat. 93: 543 -553 (1975)
Significance of the pattern of motor innervation of the intrinsic laryngeal muscles of cat M .A . A b o E
l - E n en f.
A/.har Medical School, Cairo. Egypt
Key words. Pattern • Motor innervation • Intrinsic laryngeal muscles Abstract. Simple and compound forms of motor endings, showing a particular distribution, were found in the intrinsic laryngeal muscles of the cat. The muscles carrying compound and multiple endings were stained densely black with Sudan black B : while Lhc muscles with simple and single endings showed black and pale fdtres. A probable relationship is suggested between the contraction properties and the pattern of motor innervation of intrinsic laryngeal muscles of the cat.
Introduction
Received: February 3, 1972.
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There is little information in the literature about the histological forms of the motor endings in intrinsic laryngeal muscles. Electromyographic investigations by W e d d e l l , F elnstein and B attle [1944] showed that, similar to the facial and lingual muscles of man, the motor units of laryngeal muscles were small and of the diffuse or scattered type. This is in agreement with the anatomical observation by Cla rk [1931], F e in d e l , H inshaw and W ed d e l l [1952], and by T o rr e [1953|. that motor units in muscles which are responsible for delicate movements, in contrast to those of limb muscles, were composed of few muscle fibres. The question of polyncuronal innervation of individual fibres of laryngeal muscles has been raised by Hunt and K u ffler [1954]. Using intracellular record ings, they obtained action potentials from the same muscle fibre on stimulation of separate efferent axons in the cricothyroid of the cat. Applying the same technique on the rabbit. Van H arr ev eld ami T achiban.a 119611concluded that polyncuronal innervation of laryngeal muscles was the exception rather than the rule.
544
A bo E l-E nknk
M aterial anil methods Tlie forms of motor endings were studied in longitudinal sections of laryngeal muscles stained with silver impregnation (Bielchowsky. Romanes and Glees), and in gold chloride and silver leased IB a rk er . 19631 preparations. The distribution of motor bands and the form of the subneural apparatus were studied in sections treated by K o ei .i .e and F rtedenwai.d ’ s [1949] technique for acetylcholine-esterase. Transverse sections stained with Sudan black B were examined for the distribu tion of pale and dark fibres in laryngeal muscles.
Observations
F ig .l. Intramuscular nerve plexus in cricothyroid muscle. A pair of nerve cells is also visible. Barker. X 40. F ig .2. Broad motor band in lateral cricoarytenoid muscle. It is localised in the middle third of the muscle, koelle and Friedenwakl. 31.
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1. In gold and silver stained preparations, plexiform arrangement of the intramuscular nerve trunks was frequently observed (lig. 1).
Significance of the pattern of motor innervation
545
/
2. A single broad band of motor endings was found in tlie middle third of the lateral cricoarytenoid muscle (fig. 2). The thyroarytenoid muscle showed two distinct zones: the lateral (or thyroid) part had a broad motor band exactly similar to that of the lateral cricoarytenoid: the medial (or voealis) part had a very thin motor band (fig.3). In the cricothyroid and posterior cricoarythenoid muscles the motor end ings were scattered and did not form a definite band (fig.4). 3. Two forms of motor endings were recognized :
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Fig. 3. Motor band in the middle third of the thyroarytenoid muscle. The band is thin in the voealis part (A), and broad in the thyroid part (B). Koelle and Friedenwald. X 20. Fig. /. Motor endings in cricothyroid muscle. They do not form a definite band but are scattered in the muscle. The end-plates are of the simple and single type. Koelle and Friedenwald. X 31.
546
A bo E l-E nene
a) the sim ple end-plate measured 20-50 /) the compound end-plates occupied a much larger portion (50-150 /tin) of the muscle fibre and the terminal branches of its motor fibre were more elaborate (fig.6).
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F ig .5. Simple end-plates in the voealis part of thyroarytenoid muscle. Glees. X 400. F ig .6. Compound end-plates in thyroarytenoid muscle, lateral part. Glees. X 400.
Significance of the pattern of motor innervation
547
The distribution of these two forms of motor endings was also characteristic. The simple plates were the only type of ending present in the medial (vocalis) part of the thyroartenoid, in the cricothyroid and in the posterior cricoarythenoid muscles; in these muscles each fibre carried only one motor ending (fig.4, 5, 7a). The compound
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Fig. 7.
Significance of the pattern of motor innervation of the intrinsic laryngeal muscles of cat M .A . A b o E
l - E n en f.
A/.har Medical School, Cairo. Egypt
Key words. Pattern • Motor innervation • Intrinsic laryngeal muscles Abstract. Simple and compound forms of motor endings, showing a particular distribution, were found in the intrinsic laryngeal muscles of the cat. The muscles carrying compound and multiple endings were stained densely black with Sudan black B : while Lhc muscles with simple and single endings showed black and pale fdtres. A probable relationship is suggested between the contraction properties and the pattern of motor innervation of intrinsic laryngeal muscles of the cat.
Introduction
Received: February 3, 1972.
Downloaded by: King's College London 137.73.144.138 - 1/14/2019 9:53:45 AM
There is little information in the literature about the histological forms of the motor endings in intrinsic laryngeal muscles. Electromyographic investigations by W e d d e l l , F elnstein and B attle [1944] showed that, similar to the facial and lingual muscles of man, the motor units of laryngeal muscles were small and of the diffuse or scattered type. This is in agreement with the anatomical observation by Cla rk [1931], F e in d e l , H inshaw and W ed d e l l [1952], and by T o rr e [1953|. that motor units in muscles which are responsible for delicate movements, in contrast to those of limb muscles, were composed of few muscle fibres. The question of polyncuronal innervation of individual fibres of laryngeal muscles has been raised by Hunt and K u ffler [1954]. Using intracellular record ings, they obtained action potentials from the same muscle fibre on stimulation of separate efferent axons in the cricothyroid of the cat. Applying the same technique on the rabbit. Van H arr ev eld ami T achiban.a 119611concluded that polyncuronal innervation of laryngeal muscles was the exception rather than the rule.
544
A bo E l-E nknk
M aterial anil methods Tlie forms of motor endings were studied in longitudinal sections of laryngeal muscles stained with silver impregnation (Bielchowsky. Romanes and Glees), and in gold chloride and silver leased IB a rk er . 19631 preparations. The distribution of motor bands and the form of the subneural apparatus were studied in sections treated by K o ei .i .e and F rtedenwai.d ’ s [1949] technique for acetylcholine-esterase. Transverse sections stained with Sudan black B were examined for the distribu tion of pale and dark fibres in laryngeal muscles.
Observations
F ig .l. Intramuscular nerve plexus in cricothyroid muscle. A pair of nerve cells is also visible. Barker. X 40. F ig .2. Broad motor band in lateral cricoarytenoid muscle. It is localised in the middle third of the muscle, koelle and Friedenwakl. 31.
Downloaded by: King's College London 137.73.144.138 - 1/14/2019 9:53:45 AM
1. In gold and silver stained preparations, plexiform arrangement of the intramuscular nerve trunks was frequently observed (lig. 1).
Significance of the pattern of motor innervation
545
/
2. A single broad band of motor endings was found in tlie middle third of the lateral cricoarytenoid muscle (fig. 2). The thyroarytenoid muscle showed two distinct zones: the lateral (or thyroid) part had a broad motor band exactly similar to that of the lateral cricoarytenoid: the medial (or voealis) part had a very thin motor band (fig.3). In the cricothyroid and posterior cricoarythenoid muscles the motor end ings were scattered and did not form a definite band (fig.4). 3. Two forms of motor endings were recognized :
Downloaded by: King's College London 137.73.144.138 - 1/14/2019 9:53:45 AM
Fig. 3. Motor band in the middle third of the thyroarytenoid muscle. The band is thin in the voealis part (A), and broad in the thyroid part (B). Koelle and Friedenwald. X 20. Fig. /. Motor endings in cricothyroid muscle. They do not form a definite band but are scattered in the muscle. The end-plates are of the simple and single type. Koelle and Friedenwald. X 31.
546
A bo E l-E nene
a) the sim ple end-plate measured 20-50 /) the compound end-plates occupied a much larger portion (50-150 /tin) of the muscle fibre and the terminal branches of its motor fibre were more elaborate (fig.6).
Downloaded by: King's College London 137.73.144.138 - 1/14/2019 9:53:45 AM
F ig .5. Simple end-plates in the voealis part of thyroarytenoid muscle. Glees. X 400. F ig .6. Compound end-plates in thyroarytenoid muscle, lateral part. Glees. X 400.
Significance of the pattern of motor innervation
547
The distribution of these two forms of motor endings was also characteristic. The simple plates were the only type of ending present in the medial (vocalis) part of the thyroartenoid, in the cricothyroid and in the posterior cricoarythenoid muscles; in these muscles each fibre carried only one motor ending (fig.4, 5, 7a). The compound
Downloaded by: King's College London 137.73.144.138 - 1/14/2019 9:53:45 AM
Fig. 7.
