The Muscular System (PDF)

The Muscular System  Objectives Discuss types of muscle tissue. Identify the functions of muscular tissue. Discuss the properties of muscular tissue. Describe the structure and function of different skeletal muscles. Define the sarcomere. Understand muscle contraction an...

The Muscular System  Objectives Discuss types of muscle tissue. Identify the functions of muscular tissue. Discuss the properties of muscular tissue. Describe the structure and function of different skeletal muscles. Define the sarcomere. Understand muscle contraction and relaxation. Discuss effects of exercise on skeletal muscle tissue. Describe the effect inactivity on skeletal muscle tissue.  The Muscular System The muscular system consists of all the muscles of the body. Skeletal muscles Cardiac Smooth most of them muscles form muscles move bones of the most of the lack striations skeleton heart wall Which muscle type is striated? Which is voluntary?  What are skeletal muscles? Muscles usually play a vital role in body movements. The skeletal muscle tissue is closely anchored to the skeletal bones. The striated or striped skeletal muscle fibers are packed together in a typical muscle (e.g., biceps). Normally, they are arranged in a parallel fashion. Also, a sheath of connective tissue covers these bundles.  What are smooth muscles? Seen lining the walls of internal They also have organs, such as The smooth It is usually the the stomach, muscle fibers They do not connective intestine and show stripes cell junctions that are fusiform tissue sheaths blood vessels. hold them or tapered at or striations. together. similar to other Moreover, they are involuntary both ends. muscles. (functions are not directly controlled) in nature.  What is a myocardium?  Myocardium or cardiac muscle is a contractile tissue present only in the heart.  The plasma membranes of the cells in the cardiac muscle are fused together by cell junctions.  The communication junctions at the fusion point help them to contract as a unit. Thus, one cell receives a contraction signal, and it stimulates its neighbouring cell to contract.  How do muscles contract? Muscle contraction is initiated through signals. The tension-creating sites in muscle cells are activated for it to contract. The myosin and actin filaments work together to produce movement during this contraction. This process is usually followed by muscle relaxation, where the cells return to their low-tension state.  Functions of the Muscular System Produces movement. Stabilizes body positions. Stores and moves substances Produces within the heat body. (thermogenesi s). Muscle tone: low levels of muscle contraction that occur when a muscle is not producing movement. Properties of Muscular Tissue + The ability of muscle to contract forcefully when stimulated by a nerve impulse. + The ability of a muscle to receive and respond to a stimulus (e.g. nerve impulse) by changing its membrane potential. + The ability of muscle to stretch, within limits, without being damaged. + The ability of muscle to return to its  Structure of a Skeletal Muscle + Epimysium: a sheath of dense, irregular connective tissue that surrounds the whole skeletal muscle. It allows a muscle to contract and move powerfully while maintaining its structural integrity. It separates muscle from other tissues and organs in the area. + Perimysium: a layer of dense irregular connective tissue that surrounds a group of muscle fibers, separating them into bundles  Structure of a Skeletal Muscle + Endomysium: a layer of areolar connective tissue that surrounds each muscle fiber. It functions to electrically insulate the muscle fibers. + Tendon: all three connective tissue layers may extend beyond the muscle fibers to form a tendon that attaches a muscle to the periosteum of a bone. Muscle Shapes and Fascicle Arrangement Muscle Shapes and Fascicle Arrangement + All muscle fibers are parallel to one another within a fascicle. + Different fascicles forms one of five patterns with respect to the tendons: parallel, fusiform, circular, convergent, or pennate.  Muscle Shapes and Fascicle Arrangement + Fascicular arrangement affects a muscle’s power and range of motion. + The longer the fibers in a muscle, the greater the range of motion it can produce. + Muscle power depends on its total cross- sectional area. The more fibers per unit of cross-sectional area a muscle has, the more power it can Muscle Shapes and Fascicle Arrangement 1. Parallel muscles: most skeletal muscles in the body have parallel organization. Fascicles are arranged in the same direction as the long axis of the muscle. 2. Fusiform muscles: Similar to parallel muscle but with a central, large belly that is spindle-shaped. 3. Circular muscles: Fascicles have concentric circular arrangement. Muscle Shapes and Fascicle Arrangement 4. Convergent muscles: Fascicles spread over broad area converge at thick central tendon. 5. Pennate muscles: Short fascicles in relation to total muscle length. Tendon extends nearly entire length of muscle. Unipenn Bipenn Multipenn ate ate ate  Muscle Histology Myoblasts fuse to form a skeletal muscle fibers Myoblasts Muscle stem cell (during development) Satellite cell Muscle fiber Muscle stem cell present in (skeletal muscle cell) muscle tissue during The major cells in skeletal adulthood to assist in repair muscle of muscles. tissue.  Skeletal Muscle Cells (Muscle Fibers) Muscle fibers are long and cylindrical multinucleated cells. Why? Muscle fiber  Skeletal Muscle Cells (Muscle Fibers) Sarcolemma: plasma membrane of a muscle fiber. Muscle fiber Sarcoplasmic reticulum: specialized smooth endoplasmic reticulum, which Sarcoplasm: cytoplasm of a muscle stores, releases, and retrieves fiber.  Skeletal Muscle Cells (Muscle Fibers) Myofibrils: composed of Muscle bundles of myofilaments arranged as sarcomeres. fiber Myofilaments: are contractile proteins within myofibrils. It has thin and thick filaments. Myofibril Sarcomere: a highly organized arrangement of contractile myofilaments and considered as the functional unit of the muscle fiber.  The Sarcomere  A sarcomere is the smallest functional unit of striated muscle tissue.  It is the basic contractile unit of a muscle fiber.  The Sarcomere  Thick filament: consists of myosin protein.  Thin filament: consists of actin, tropomyosin, and troponin proteins. 25/10/202 2  The Sliding Filament Theory  Skeletal muscle contraction results from the sliding of actin filaments on myosin filaments toward the center, shortening the muscle fiber. Relaxed Contracted muscle muscle  The Sliding Filament Theory Muscle contraction results from the sliding of actin filaments on  Skeletal Muscle Contraction  A nerve impulse is delivered to the muscle fiber by a nerve cell.  The nerve impulse causes the release of calcium from the sarcoplasmic reticulum of the muscle fiber.  Once calcium is released, it exposes the myosin binding site present on actin filaments.  The myosin head is attracted to actin, and myosin binds actin at its actin-binding site, forming the cross-bridge.  the interaction of thick and thin filaments of the sarcomere leads to  Skeletal Muscle Cells (Muscle Fibers) Sarcolemma: plasma membrane of a muscle fiber. Muscle fiber Sarcoplasmic reticulum: Sarcoplasm: cytoplasm of a muscle specialized smooth fiber. endoplasmic reticulum, which stores, releases, and retrieves 3. Muscle contraction detail Concept Cell Biology - YouT ube Acti n Myosi n  Skeletal Muscle Relaxation  Calcium is pumped back into the sarcoplasmic reticulum.  This causes the tropomyosin to cover the myosin binding sites on the actin strands.  The sarcomere relaxes leading to relaxation of the muscle. Dr. Samah 30 Kalakh Bing Videos Exercise and Skeletal Muscle Tissue  The number of skeletal muscle fibers in a muscle is genetically determined and does not change.  Mature muscles cells cannot divide.  Physical training alters the appearance of skeletal muscles and can produce How? changes in muscle performance.  Effect of Resistance Exercise on Skeletal Muscle Tissue  Resistance exercise increases the formation of myofibrils, increasing the thickness of muscle fibers.  Because this muscular enlargement is achieved by the addition of structural proteins, athletes trying to build muscle mass often take large amounts of protein in  Muscle Atrophy  The loss of structural proteins and muscle mass due to lack of use leading to decreased performance and muscle appearance.  Tissue is replaced with connective and adipose tissue (fat). Use it or lose it!  Age-related Muscle Atrophy  Between the ages of 30 and 50, humans lose skeletal muscle mass (~10%).  Muscle tissue is replaced by connective tissue and adipose tissue (fat).  In part, this decline may be due to decreased levels of physical activity.