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Wednesday, October 08, 2008

All are composite muscles except..Rectus Femoris

Question 4
All are composite muscles except..
A) Pectineus
B) Rectus femoris
C) Adductor Magnus
D) Biceps Femoris
Answer
B) Rectus Femoris
Reference
Gray’s Anatomy 38th Edition Pages 873, 874, 875, 879,
Quality
Thinker
Status
New
Discussion
A muscle is called as a composite muscle when it is innervated by two nerves. Some books also call a muscle as a composite muscle when it is derived from two embryological compartments (Eg Flexor and Extensor)
Explanation
A) Pectineus is innervated by the Femoral nerve, L2 and 3; and accessory obturator, L3, when present.
B) Rectus Femoris is supplied by the femoral nerve, L2, 3 and 4.
C) Adductor magnus is composite and is doubly innervated by the obturator nerve and the tibial division of the sciatic nerve (L2, 3 and 4); the latter nerve supplies the ischiocondylar part. Both nerves are derived from anterior divisions in the lumbrosacral plexus, indicating a primitive flexor origin for both parts of the muscle.
D) Biceps Femoris is innervated by the Sciatic nerve, L5, S1 and 2, (the long head through the tibial division and the short head through the common peroneal division, reflecting the composite derivation from flexor and extensor musculature.)
Comments
The composite character of the tongue is indicated by its innervation.
Diaphragm has a composite origin from many different mesenchyme sources.
Tips : Another Classification that is often asked
It is possible to attempt a classification of muscles based on their general shape and the predominant orientation of their fibres relative to the direction of pull
Ä     Muscles with fibres that are largely parallel to the line of pull vary in form from flat, short and quadrilateral (e.g. thyrohyoid) to long and straplike (e.g. sternohyoid, sartorius).
o       In such muscles, individual fibres may run for the entire length of the muscle, or over shorter segments when there are transverse, tendinous intersections at intervals (e.g. rectus abdominis).
o       In a fusiform muscle, the fibres may be close to parallel in the 'belly', but converge to a tendon at one or both ends.
Ä     Where fibres are oblique to the line of pull, muscles may be
o       Triangular (e.g. temporalis, adductor longus)
o       Pennate ( = 'feather-like') in construction.
§         Unipennate (e.g. flexor pollicis longus),
§         Bipennate (e.g. rectus femoris, dorsal interossei)
§         Multipennate (e.g. deltoid).
§         In some muscles the fibres pass obliquely between deep and superficial aponeuroses, in a kind of 'unipennate' form (e.g. soleus).
§         In other sites muscle fibres start from the walls of osteofascial compartments, and converge obliquely on a central tendon in circumpennate fashion (e.g. tibialis anterior).
Ä     Some muscles have a spiral or twisted arrangement (e.g. sternocostal fibres of pectoralis major and latissimus dorsi, which undergo a 180° twist between their median and lateral attachments).
Ä     Some muscles spiral around a bone (e.g. supinator, which winds obliquely around the proximal radial shaft).
Ä     Another type of spiral arrangement is shown by muscles, sometimes referred to as cruciate, that have two or more planes of fibres arranged in differing directions; sternocleidomastoid, masseter and adductor magnus are all partially spiral and cruciate.
Many muscles have more than one of these major types of arrangement, and show regional variations that correspond to contrasting, and in some cases independent, actions.

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