motor unit population of the rat hind limb muscles

ABSTRACT

I. To localize and estimate the size, number and segmental distribution of motoneurons whose axons form the tibial nerve [TN] and common peroneal nerve [CPN] in albino rat. II. To localize the motor end-plates on skeletal myofibres supplied by TN and CPN. Ill. The average size of motor unit was assessed as the ratio between the number of alpha motoneurons of the nerve and the motor end-plates innervated by that nerve. SETTING: Department of Anatomy, Basic Medical Sciences Institute, Jinnah Postgraduate Medical Centre, Karachi. SUBJECTS: Male adult albino rats of Charles River Strain. PERIOD One year. MATERIAL AND METHODS: Horseadish peroxidase [HRP] method of tracing neuronal technique for TN and CPN motoneurons. For localization of motor end-plates, Bromo-indigo and urea-silver method was used in adult albino rat. The motoneurons forming the TN and CPN extended between caudal part of L3 to rostral part of S1 segment of the spinal cord. The somal diameter of motoneurons for TN ranged between 18 and 54 [micro]m and for CPN between 12 and 56 [micro]m. The motoneurons measuring more than 25 [micro]m [presumably alpha neurons] were 75.3% for TN and 78.1% for CPN. A total of 690 motor units with the size of 39 skeletal myofibres innervated by TN and 396 units with the size of 28 skeletal myofibres innervated by CPN have been observed in the present study