Journal of Neurophysiology, Vol 60, Issue 1 46-59, Copyright © 1988 by APS
Fiber architecture and histochemistry in the cat neck muscle, biventer cervicis
F. J. Richmond and J. B. Armstrong
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
1. Biventer cervicis (BC) is an anatomically complex muscle that is divided
by tendinous inscriptions into five in-series compartments of motor units.
We have analyzed the fiber architecture and fiber-type composition of these
different compartments using microdissection and histochemical methods. 2.
BC narrows as it runs rostrally, but its in-series compartments have
similar cross-sectional areas. The tapered shape of BC comes about because
tendinous inscriptions and the tendon of insertion are oriented obliquely
and muscle fibers attach in a progressively offset fashion from the medial
to the lateral muscle edge. 3. Individual compartments of BC differ from
one another in their architecture. The rostral two compartments (1 and 2)
contain fibers of similar length that run between two plates of tendinous
tissue. Compartments 3 and 4 are divided into two or three in-parallel
subvolumes whose fiber bundles differ in their lengths and sites of
attachment. Compartment 5 is the most variable in its structure. In some
cats it is separated from compartment 4 by a tendinous inscription, but in
other cats, it blends with a dorsomedial part of compartment 4 to form a
single subvolume. 4. The relative lengths of fibers in different
compartments were analyzed when the head and neck were held in different
postures. Fibers in rostromedial regions were stretched more effectively
when the head was flexed at suboccipital joints, and appeared to be less
sensitive to movements at lower cervical joints. Movements across lower
cervical joints produced substantial length changes in caudolateral parts
of BC. 5. Muscle fibers of different histochemical types were not
distributed evenly within each muscle compartment. Slow, oxidative (SO)
fibers accounted for the majority of fibers near the nuchal midline but for
only 30%-45% of fibers in lateral muscle regions. Proportions of fast,
glycolytic (FG) fibers were greatest in lateral regions. Fast,
oxidative-glycolytic (FOG) fibers were distributed quite uniformly
throughout each compartment. 6. The specialized architecture of BC may
shape its physiological capabilities. The complex internal structures of
different compartments may alter the length-tension properties of
BC.(ABSTRACT TRUNCATED AT 400 WORDS)
