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Quadrupedal Mechanics - Anatomy & Physiology (view source)
Revision as of 22:21, 28 November 2013
, 22:21, 28 November 2013→A severe restriction on limb function: passive insufficiency
==='''A severe restriction on limb function: passive insufficiency'''===
==='''A severe restriction on limb function: passive insufficiency'''===
[[File:QMFig 8.10.png|thumb|'''Fig 8.10 Ligamentous adaptations of longhead muscles''']]
Even when a longheaded muscle is a strap muscle and has the longest range of contraction possible (44% of fully stretched length: see Fig. 4.3), it is not possible to allow for full independent movement of both the joints it acts over. Thus when the hip of any quadruped, and also any but the most limber human, is fully flexed, the stifle cannot be fully extended. In this case, the semitendinosus muscle is insufficient but for a different reason to that for the actively insufficient shortheaded muscle described above. Longheaded muscles are intrinsically passively insufficient, especially so when they are highly pennate.
Even when a longheaded muscle is a strap muscle and has the longest range of contraction possible (44% of fully stretched length: see Fig. 4.3), it is not possible to allow for full independent movement of both the joints it acts over. Thus when the hip of any quadruped, and also any but the most limber human, is fully flexed, the stifle cannot be fully extended. In this case, the semitendinosus muscle is insufficient but for a different reason to that for the actively insufficient shortheaded muscle described above. Longheaded muscles are intrinsically passively insufficient, especially so when they are highly pennate.
:::::'''Fig 8.10 Ligamentous adaptations of longhead muscles'''
:::::M. fibularis of the horse is entirely ligamentous. Stifle flexion (b) therefore produces hock flexion automatically, and M. gastrocnemius is kept at optimal length. The action of M. flexor digitorum superficialis also ensures that stifle extension (a) is also accompanied by hock extension. The position of the limb in (a) and (b) represent the retraction and protraction phases of a fast gallop as in Fig. 8.1.
:::::M. fibularis of the horse is entirely ligamentous. Stifle flexion (b) therefore produces hock flexion automatically, and M. gastrocnemius is kept at optimal length. The action of M. flexor digitorum superficialis also ensures that stifle extension (a) is also accompanied by hock extension. The position of the limb in (a) and (b) represent the retraction and protraction phases of a fast gallop as in Fig. 8.1.
==='''Limbs are controlled proximally by key joints and nerves'''===
==='''Limbs are controlled proximally by key joints and nerves'''===