Gross anatomy lecture, Peter Nassar (exercise physiologist). MUSCLE: muscle function - studied in exercise physiology, fiber mechanics, etc. some functions include: -providing stability to joints, limbs, skeleton -heat production via shivering and exercising, maintaining constant body temp in endoderms. *contraction* Prime directive of muscle is to contract. All muscles generate tension longitudinally--usually causing the muscle to shorten or contract. While contracting, muscles may transfer their force to a bone/limb or they may oppose the pull of other muscles. MUSCLE CELL TYPES: All muscle is derived from the mesoderm. Three types can be distinguished. Smooth- gut, uterus, blood vessels small, thin, long, flat, spindle shaped, contractile cells with single central nuclei. connected by gap junction. slow contractibility rate. non-striated Innervated by autonomic nervous system (involuntary). Cardiac - muscle of the contractile portion of the heart. striated muscle with branching cells. Single branching cells are conneted end to end by gap junction and desmosomes, which make up the intercalated disks (electrical cell gap junctions), giving the striated appearance. Involuntary muscle, innervated by the autonomic nervous system (ANS) Skeletal muscle - striated cylindrical fibers. cells multinuclear with peripherally located nuclei. voluntary muscle, innervated by somatic NS. Accounts for about 40-45% of body weight. Contraction: "Active state" - muscle is "on". Isometric - muscle maintains constant length while contracting - does NOT shorten. Force of contraction = mass * acceleration. Isotonic - constant tension. muscle DOES shorten - does WORK. Work = force * displacement. muscle doing prime action = AGONIST opposing muscle = ANTAGONIST other muscles act as stabilizers et al. PHYSIOLOGY: FIBER TYPES: Tonic: slow contracting fibers, multiply innervated. Used for maintaining posture. Found in lower vertebrates - all animals except mammals. slow, prolonged contractions, used to maintain tone or force (eg, postural). Found in appendicular muscles of all animals except mammals. Twitch: capable of rapid force developement, each fiber is functionally independed and organized as motor units. Three types: Type I = slow fibers, oxidative, red. high mitochondria content, high myoglobin content. Generates ATP via oxidative phosphorylation (aerobic respiration), large capillary supply, very fatigue resistant. aka Red fibers, slow twitch fibers, "dark meat". Type IIA = Red in color, oxidative (aerobic), good for long term activity. Type IIB = White in color. Non oxidative (glycolytic/anaerobic) good for sprinting. Contracts quickly, fast twitch. Low capillary density, little to no myoglobin, few mitochondria. Ectotherms, flight muscles. Can be fatigue resistant or easily fatigued (several types). Type IIA and B are mixed in the same muscle. Most mammalian muscles contain a mixed proportion of red, white, and intermediate fiber types. The muscle is innervated by a motor neuron - combination is called a motor unit. MOTOR UNIT = alpha motor neuron, its cell body, and the dendrites all located in the ventral horn of the spinal cord, the axon, the collateral axons, the motor end plates plus the fibers it innervates. A motor neuron can innervate up to 1500 fibers. In the ocular muscle, the motor neuron only innervates 3 or 4 fibers. When the motor neuron fires, it produces an all or none response. To have a graded response you need to vary the number of motor units being used. Muscle structure - skeletal muscle consists of parallel, multinucleated fibers which run through the majoriy of the muscle belly. skeletal muscle hierarchy: EPIMYSIUM envelops entire muscle belly PERIMYSIUM surrounds the fasciculi ENDOMYSIUM surrounds the single muscle fibers the MUSCLE FIBERS are made of myofibrils MYOFIBRILS are composed of repeated units of sarcomeres, which are bounded by Z-lines SARCOMERE is the functional unit of striated muscle the main mass of muscle fibers is the muscle belly. The muscle has two attachments - a stationary origin and a mobile insertion. The belly is made of a bunch of fibers - fasciculi. one FASCICULUS is made of individual muscle fibers, wrapped in fascia. FIBERS are made of MYOFIBRILS MYOFIBRILS are made of SARCOMERES SARCOMERES are made of actin and myosin. The binding of actin and myosin causes muscle contraction or extension (theory of crossbridging.) Muscle does NOT attach directly to bone - always to tendon which then connects to periosteum. When the tendon is too short to be viewed, muscle is said to have "fleshy attachment". Tendon consists of mostly longitudinally oriented collagen fibers nd a small number of elastic fibers useful in absorbing and storing elastic energy during locomotion. Tensile strength of tendon is about 225 X that of muscle (18000 #/sq.in. compared to about 80psi for muscle), so muscle or periosteum will generally fail before the tendon. Poor compressive strength, though, and poor vascular supply so poor healing. APONEUROSIS: broad, flat, thin, sheet of dense connetive tissue (CT) for muscle attachment. Utilized especially by abdominal muscles. FASCIA: sheets of CT wrapped around the body. Superficial, deep (dense; between muscles; muscle groups), retinacula (thickened band crossing over tendons at a joint), raphe (line of union between two bilaterally symmetrical structures. BURSA: CT sac filled with synovial fluid. Associated w/muscles or tendons as they move against other muscles or bone. Provides cushioning and prevents fraying of tendons due to compression. TENDON SHEATH: elongated bursa that wraps around one or more tendons as they course over bony surfaces. prevents fraying. ORIGIN: more proximal or central attachement - static, stationary. INSERTION: more distal or peripheral site - dynamic, mobile. (actually, which end remains fixed depends on various circumstances.) AGONIST: prime mover. the muscle initiating the particular movement ANTAGONIST: opposes the action of the agonist. generally situated on the opposite side of the joint. SYNERGIST: muscle that indirectly aids in a movement by steadying a joint, thus preventing unwanted movements and allowing the agonists to move more efficiently. CO-CONTRACTION: co-contraction of synergistic and antagonistic muscles are often necessary to produce the smooth coordinated motions as well as the finer and more precise motions that are typical of vertebrates. FIXATION: muscls which stabilize a joint; involves the co-contraction of muscles which oppose each other when the joint is moved. prime movers, antagonists, synergists. Muscles may have one or several bellies. Since muscle fibers contract longitudinally, muscles function most effectively when their fibers are running parallel to each other. Parallel fibered muscles are capable of contracting up to 30% of their resting length (60% of their stretched length). Some examples include: strap muscles fusiform/spindle-shaped ------ -------- ||| |||| |||| ||| |||| ---- ||| |||| |||| /|\ |||| ---- / | \ |||| |||| | | | |||| ---- \ | / |||| |||| \|/ |||| ---- ||| |||| |||| -------- ------ some muscles have their fibers running at an angle to a central tendon. These are known as pennate (feather like) muscles. Pennation increases the number of muscle fibers within a given per-unit volume, allowing the muscle to increase its strength of contraction. All of the muscle fibers are shorter, however, so the speed of contraction is reduced as is the range of motion. pennate muscles: /|\ //|\\ ///|\\\ ///|\\\ (just a lame example, sorry.) Muscle physiologists tend to look at the tension length curve. To increase force, increase # of cross bridges by increasing cross sectional area of the muscle. Anatomical cross section - transverse cut through the belly of the muscle, and physiological cross section - cut perpendicular through the fibers of the muscle. In a parallel fiber muscle, the cross sections are both the same. In a bi-pinnate fiber muscle /|\ //|\\ ///|\\\ ---------- anatomical cross section ///|\\\ /|\ \//|\\/ physiological cross section - more surface area than anatomical /\/|\/\ ///\|/\\\ (see diag.), the physiologic cross section is bigger, and can generate more force - but it is slower. the parallel fiber muscle is faster. So, you can maximize EITHER speed or force, not both. ISOTONIC - W=Fd (see diagram) See handout for biomechanics notes. This is too hard to type in :) Peter jumped off the ground - found max height about one foot. But, he can jump down several feet just fine. note the F vs d curve - can create about 4x amt force when extending compared to contracting. note, muscles act like springs, with elastic mechanism to them. When you walk or run, the elasticity helps you run more efficiently w/each step. Final way to look at this...think of muscles as levers. A lever is any beam rotating around a point. Think of a door. (top view) ^fi ^l--Lo-l l | fo =============o <-----hinge /\ Lpush l----Li------l pushing at the spot marked generates fi, the in force. Fo = out force Lever arms _|_ distance bet. forces and fulcrum. the hing is the fulcrum. Li = in lever Lo = out lever Fi*Li=Fo*Lo with muscle systems, you generally want to maximize Fo and Fi, so you want to make the distance between the force and fulcrum as long as possible. The triceps/humerus/ulna system is a type two lever. (see diagram) Type III - see diagram. (biceps humerus ulna) velocity can be substituted for force. Vo=ViLo/Li To maximize speed, maximize the length of the out lever, minimize the in lever.