Eur J Anat, 16 (1): 33-42 (2012)

Site-dependent difference in the density of sympathetic nerve fibers in muscle-innervating nerves: a histologic study using human cadavers

Tadashi Nakao¹, Kwang Ho Cho², Masahito Yamamoto¹, Shigeki Yamane¹, Gen Murakami³, Yoshinobu Ide¹, Shin-ichi Abe^1,4

¹Department of Anatomy, Tokyo Dental College, Chiba City, Japan ²Department of Neurology, Wonkwang University School of Medicine, Jeonbuk Regional Cardiocerebrovascular Disease Center, Institute of Wonkwang Medical Science, Iksan, Korea ³Division of Internal Medicine, Iwamizawa Kojin-kai Hospital, Iwamizawa, Japan ⁴Oral Health Science Center hrc-8, Tokyo Dental College, Chiba City, Japan

ABSTRACT The autonomic nerve supply of skeletal muscle has become a focus of interest because it is closely related to the adaptation of energy metabolism with aging. However, there is no comprehensive information concerning the sympathetic nerves present in muscle-innervating nerves (muscle-nerve). At the point of entry of muscle-nerves into 8 striated muscles (the soleus, extensor carpi radialis, infraspinatus, genioglossus, extra- ocular medial rectus, temporalis, lateral pterygoid, and digastricus anterior belly) in 15 cadavers of elderly people, we counted both tyrosine hydroxylasepositive nerve fibers (TH- fibers) and motor nerve fibers to estimate the ratio of THfiber/ motor fibers. The 3 limb muscles were found to have a high ratio (soleus, 58%; infraspinatus; 45%; extensor, 36%), whereas the 4 head muscles (digastricus, 23%; genioglossus, 15%; temporalis, 10%; lateral pterygoid, 6%; medial rectus, 1%) had relatively low ratios. The site- dependent characteristics of the THfibers seemed to reflect their commitment to muscle activity. However, some discrepant characteristics were noted: 1) In spite of the tonic and continuous activity required for both the genioglossus and infraspinatus, the proportions of TH-fibers were quite different between the tongue and the shoulder muscles; 2) Likewise, the soleus and extra-ocular rectus showed a considerable difference, even though rapid and phasic contraction is essential for both muscles. Rather than reflecting the influence of postnatal functional demand, these site- dependent characteristics might develop as a result of differences in sympathetic innervation of the striated muscles during fetal development, i.e., a short course along the arteries feeding the head muscles, or a long course along the muscle-nerves to the limb muscles.

Keywords: Tyrosine hydroxylase-positive nerve fibers, Sympathetic innervation, Striated muscles, Feeding artery, Muscle hilus