Lectures Muscular.htm - The MUSCULAR SYSTEM The muscular...

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The MUSCULAR SYSTEM The muscular system , as in the skeletal system, develops primarily from mesenchyme or the myotome of somites mesoderm with the exception of facial muscle that are derived from ectoderm . The muscular system has four critical functions in the body. 1. Movement . 2. Thermoregulation . 3. Posture, body and organ support . 4. Cardiovascular pump . There are three basic types of muscle tissue. These are: 1. Skeletal muscle tissue — this tissue is striated and under voluntary nervous control. 2. Cardiac muscle tissue — this tissue is striated and under involuntary nervous control. 3. Smooth muscle tissue — this tissue is non-striated and under involuntary nervous control. There are four basic characteristics of muscle tissue. These, in combination, are unique to muscle tissue. 1. Irritability (= excitability) — the ability to respond to a nervous stimulus. 2. Contractility — the ability to respond by shortening. 3. Extensibility (=tensility) — the ability to stretch. 4. Elasticity — the ability to return to the original shape. There are more than 600 skeletal muscle in the body. The muscles, like bones, can be classified into groups according to their shape or architecture . These are: 1. Parallel muscles 2. Convergent muscles 3. Pennate muscles
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4. Circular muscles The skeletal muscles can also be classified on the manner in which they function. 1. Agonists — these are the prime movers of a particular action. 2. Antagonists — these work in opposition to the agonists. 3. Synergists — these work with agonists to accomplish a motion more easily and strongly. 4. Fixators — these work to stabilize the joint so that a specific movement is accomplished. We will restrict our discussion of muscle tissue for now to skeletal muscle tissue . We will begin our discussion with the gross anatomy of a typical skeletal muscle. Skeletal muscles consist of at least three distinct structures. Two tendons and the muscle itself. Tendons are composed of dense regular connnective tissue. The origin tendon always attaches to a bone; it is also the most proximal and/or least mobile portion of the muscle. The insertion tendon usually attaches to a bone or may attach to the skin or an organ; it is usually the most distal and/or most mobile protion of a muscle. The belly is the region of contraction as it consists of muscle tissue; it is the only portion of the muscle that does contract.
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Skeletal muscles are constructed by using increasingly smaller portions of dense and loose connective tissue to ensheath the components.
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