Chapter 10 (1)

• Muscles constitute nearly half of the body’s weight and are of central interest in several fields of health care and fitness.
• Muscle functions include; movement, stability, control of openings, heat production, and glycemic control.
• Movement is the ability to move from place to place, move body parts, and move body contents in breathing, circulation, and digestion. It is also used in communication such as speech, writing, facial expressions, and other nonverbal communications.
• Stability means maintaining posture by preventing unwanted movements. Antigravity muscles prevent us from falling over. They stabilize joints by maintaining tension.
• Control of openings and passageways basically means sphincters which are the internal muscular rings that control the movement of food, blood, and other materials within body.
• Heat is produced by skeletal muscles. As much as 85% of our body heat.
• With glycemic control muscles absorb and store glucose which helps regulate blood sugar concentration within the normal range.
• Structural and Functional Organization of Muscles; There are about 600 human skeletal muscles and they constitute about half of our body weight. There are three kinds of muscle tissue; skeletal, cardiac, and smooth. They are all specialized for one major purpose which is converting the chemical energy in ATP into the mechanical energy of motion. Myology is the study of the muscular system.
• Muscle Connective Tissues, Fascicles, and Compartments: Endomysium, Perimysium, Epimysium, and Fascia.
• Endomysium is the thin sleeve of loose connective tissue around each fiber. It allows room for capillaries and nerve fibers and provides a chemical environment for muscle fibers.
• Perimysium is the thicker layer of connective tissue that wraps fascicles. Fascicles are bundles of muscle fibers wrapped together and they carry nerves, blood vessels, and stretch receptors.
• Epimysium is the fibrous sheath surrounding the entire muscle. The outer surface grades into fascia which are the inner surface projections that form perimysium.
• Fascia is the sheet of connective tissue that separates neighboring muscles or muscle groups from each other and the subcutaneous tissue.
• The strength of a muscle and the direction of its pull are determined partly by the orientation of its fascicles.
• Classification of muscles according to fascicle orientation; Fusiform muscles, Parallel muscles, Triangular (convergent) muscles, and Pennate muscles.
• Fusiform muscles are thick in the middle and tapered at each end. Parallel muscles have uniform widths and parallel fascicles. Triangular (convergent) muscles are broad at one end and narrow at the other, e.g. circular muscles (sphincters) that form rings around body openings. Pennate muscles are feather-shaped. There are three types of pennate muscles: Unipennate fascicles approach the tendon from one side, Bipennate the fascicles approach tendon from both sides, and multipennate which are bunches of feathers that converge to a single point.
• Muscle compartments are a group of functionally related muscles enclosed by fascia. They also contain nerves and blood vessels that supply the muscle group. Intermuscular septa are very thick fascia that separates one compartment from another.
• Muscle attachments; Indirect attachment to bone, and Direct (fleshy) attachment to bone.
• Indirect attachment to bone; Tendons connect muscle to bone as the collagen fibers of the endo-, peri-, and epimysium continue into thetendon and from there into the periosteum and matrix of bone. The aponeurosis is where the tendon is a broad, flat sheet (palmar aponeurosis) and the retinaculum is the connective tissue band that tendons from separate muscles pass under.
• Direct (fleshy) attachment to bone has little separation between muscle and bone. The muscle seems to emerge directly from the bone. It used to be called origin (stationary) and insertion (moving). But this is often not accurate. Some anatomists prefer nontraditional descriptions ofattachments by proximal versus distal or superior versus inferior. Some muscles attach not to bone but to the fascia or tendon of another muscle or on collagen fibers of the dermis. For example, many facial muscles attach to the skin.