title: The motor-unit population of the cat tenuissimus muscle.
abstract: 1. We studied the organization of motor units in the tenuissimus (TEN) muscle of pentobarbital-anesthetized cats. The cat TEN is a long, delicate straplike muscle that spans hip and knee, which has a very flat length-tension curve through 22 mm of length change. 2. The TEN motor nucleus, labeled by retrograde transport of several forms of horseradish peroxidase, was composed of 8-31 cells in different cats, of which about half were, on average, in the size range of alpha-motoneurons. TEN motoneurons were scattered through the ventrolateral portion of lamina IX, over a rostrocaudal distance of up to 6.5 mm, making it relatively easy to isolate individual TEN motor axons for single motor-unit stimulation. 3. Individual TEN muscle units were classified into four groups [fast-twitch, fatigable (FF), intermediate, fatigue-resistant (Fint), fast-twitch, fatigue-resistant (FR), and slow-twitch, fatigue resistant (S)] on the basis of "sag" and fatigue index mechanical properties, as in other cat hindlimb muscles. There was a relatively large proportion of Fint units (28%) in the TEN sample, and the range of tetanic tension (approximately 19-fold) was much smaller than found in other cat hindlimb muscles. 4. A majority of TEN muscle fibers could be classified into the three major histochemical types (IIB, IIA, and I) found in other cat muscles, but a substantial minority remained "unclassified." A single type Fint muscle unit was successfully depleted of glycogen for histochemical study. It exhibited a typical type IIB histochemical profile. 5. Despite its unusual morphology, the cat TEN contains the same types of motor units found in larger, more "typical" limb muscles.
mesh_terms: D000110:Acetylcholinesterase / Q000032:analysis; D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D006003:Glycogen / Q000378:metabolism; D006651:Histocytochemistry; D006735:Horseradish Peroxidase; D008297:Male; D009045:Motor Endplate / Q000201:enzymology; D009046:Motor Neurons / Q000166:cytology / Q000502:physiology*; D009119:Muscle Contraction; D009132:Muscles / Q000166:cytology / Q000294:innervation* / Q000502:physiology; D011930:Reaction Time; D013116:Spinal Cord / Q000166:cytology* / Q000502:physiology; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014909:Wheat Germ Agglutinins
chemical_list: D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014909:Wheat Germ Agglutinins; D006003:Glycogen; D006735:Horseradish Peroxidase; D000110:Acetylcholinesterase