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The cervical muscles have a dual postural and dynamic function, in order to ensure both the stability and the motility of the cervical spine. The functional duality together with the complexity of the cervico-cephalic system render the study of the cervical muscles difficult, and their physiology is not fully understood in humans. This study has been carried out on ten samples from the m. longus colli, taken during a surgical procedure in patients aged between 36 to 62 years. The histological study combined enzyme histochemical (ATPases) and immunohistochemical techniques (using antibodies specific for the slow and the fast isoforms of the myosin heavy chains). Our results indicate that, in all cases, the m. longus colli is composed of muscle fibers with peripheral nuclei and with a relative dispersion in size. Histochemically, the type 1 and type 2 fibers express exclusively either the slow or the fast myosin heavy chain. From a quantitative point of view, the proportion of the slow fibers varies between extreme values of 30 and 73%; in addition, the dispersion in fiber size predominates on the fast type 2 fibers which are smaller than the slow type 1 fibers. Thus, most of the muscles that we have studied have histologically a slow predominance. This predominant expression of a slow phenotype in the m. longus colli corresponds to its important postural function, in addition to its phasic role during the flexion of the cervical spine.

In adults, the predominant expression of a slow phenotype in the m. longus colli corresponds to its important postural function. Morphologically, there is a dispersion in fiber size predominating on the fast type 2 fibers which are significantly smaller than the slow type 1 fibers. We deemed it of interest, therefore, to analyze the metabolic differentiation of the muscle longus colli during its development. This study has been carried out on six anatomical samples, in foetuses aged between 16 and 40 weeks of pregnancy and in an 18 month-old child. The histological study combined H&E staining and immunohistochemical techniques (using antibodies specific for the slow and the fast isoforms of the myosin heavy chains). Our results indicate that the m. longus colli differentiates during the foetal period in a way which is quite comparable to that of other skeletal muscles, such as the quadriceps. In this series, a major slow predominance with a significant dispersion in fiber size was first observed in the 18 month-old child. Thus, it can be concluded that the establishment of the adult phenotype of this muscle starts during postnatal life, following the development of the mechanisms holding up the head and neck and leading to the appearance of the cervical lordosis.

Cricopharyngeal myotomy is not effective in all cases of dysphagia. However, it should be the specific treatment in cases of dysphagia caused by a primary cricopharyngeal muscle dysfunction. Of a group of 10 patients with swallowing disorders in the absence of any defined cause, 7 (mean age, 81.6 years) were improved by a myotomy and 3 were not. The cricopharyngeal muscle was studied histologically and biochemically and compared to muscle obtained from nondysphagic subjects. In the muscle of the 7 improved patients, homogeneous histologic abnormalities were demonstrated: connective tissue infiltration, inflammatory cell infiltration, and degenerative changes of the muscle fibers. Conversely, muscles of the nonimproved patients and of the controls did not present the same degree of histologic lesions.

To determine the postural role of longus colli (LC) and dorsal neck muscles, we have studied the relationship between their cross-sectional areas related to their force of contraction and the lordosis and the length of the cervical spine. This study was carried out in 36 healthy subjects. Muscle cross-sectional areas were measured by computerized tomography. The index of lordosis and the length of the cervical spine were measured on an X-ray profile. The cross-sectional area of LC was correlated to the lordosis index (R = -0.432, p < 0.02) whereas all the other parameters were not correlated. The authors conclude that LC counteracts the lordosis increment related to the weight of the head and to the contraction of the dorsal neck muscles. Postural functions of LC and postcervical muscles are complementary. They form a sleeve which encloses and stabilizes the cervical spine in all positions of the head.

Biomechanical models of the cervical spine require knowledge of the position, size and orientation of the individual muscles that act on the cervical spine. We have developed a technique to stereometrically measure anatomical specimens. The apparatus is composed of three graduated metallic rods, which slide along a fixed support. This method is accurate to map the anatomy of individual muscles and provides quantitative data on their lines of action. Results are obtained from one specimen. The computer processing of the collected data allows formulation of a three-dimensional model of the neck muscles in man.