Page 141 - Anatomy and Physiology of Farm Animals, 8th Edition

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of the triceps can flex the shoulder joint as (4) superficial bursae, between the skin
and olecranon process of the ulna at the
well as extend the elbow, any muscle that
VetBooks.ir opposes flexion of the shoulder joint is a point of the elbow and between the skin and
superficial digital flexor tendon at the point
synergist of elbow flexion. The m. supraspi-
natus and m. brachiocephalicus are syner­ of the hock; and (5) the navicular bursa,
gists for this particular action. between the deep digital flexor tendon
Whether a given muscle is classified as and the navicular (distal sesamoid) bone.
an agonist, an antagonist, or a synergist Normally, a bursa contains only enough fluid
depends entirely on the specific action. If to reduce friction between adjacent parts.
flexion (instead of extension) of the elbow Inflammation of a bursa, usually
is the desired action, the m. biceps brachii associated with increased fluid within it,
and m. brachialis become agonists, and the is called bursitis. Enlargement of bursae
m. triceps brachii and m. anconeus become may be due to trauma, as is usually the
antagonists. case with capped hock, capped elbow
(shoe boil), and carpal hygroma. Inflam-
mation may be followed by formation of
Synovial Structures a draining tract; this is the phenomenon
underlying the equine conditions poll
Synovial structures of the body include joint evil (at the atlantal bursa) and fistulous
capsules, bursae, and synovial (tendon) withers (at the supraspinous bursa).
sheaths. The inner layer of each consists of a A bursa gives adequate protection to
connective tissue membrane that produces structures that move only a short distance in
synovial fluid to reduce friction. Synovial relation to each other. However, tendons that
joints were described in detail in Chapter 6. must travel a long distance (sometimes as
A bursa is a synovial sac between two much as several inches) over moving joints
structures that tend to rub against each require protection and friction‐free move­
other, typically a tendon where it lies in ment for their entire length. This is afforded
contact with a bony prominence (Fig. 7‐4). by a synovial sheath (Figs. 6‐3, 7‐4).
Clinically important bursae include: (1) A synovial sheath resembles an elon­
the bicipital bursa, between the biceps gated bursa placed between the tendon and
brachii tendon and the proximal end of the underlying tissue, with the edges of the
humerus; (2) the cranial nuchal bursa, synovial membrane reflected around the
between the ligamentum nuchae and tendon until they meet. This results in an
atlas; (3) the supraspinous bursa, between inner layer of synovium on the surface of
the ligamentum nuchae and the spinous the tendon and a superficial layer of the syn­
process of the second thoracic vertebra; ovium outside the tendon, forming a closed

Synovial (tendon) sheath
Mesotendon

Tendon Tendon
Synovial bursa

Bone Bone
Figure 7-4. Synovial structures. Left, a synovial sheath surrounds a tendon over a greater distance and
facilitates its frictionless movement. Reflection of the synovial membrane creates the supporting meso­
tendon, through which vessels and nerves gain access to the tendon. Right, a bursa lies interposed between
a tendon or ligament and a bony prominence.