Physiology of the Human Muscular System PDF

Physiology of the Human Muscular System By Lou Sandino L. Castro Topic Outline 1. Overview/Basic Anatomy of Muscle Tissue a. Skeletal Muscle: Structure, Function, and Voluntary Control b. Cardiac Muscle: Structure, Function, and Voluntary Control c. Smooth Muscle: Structure, Fun...

Physiology of the Human Muscular System By Lou Sandino L. Castro Topic Outline 1. Overview/Basic Anatomy of Muscle Tissue a. Skeletal Muscle: Structure, Function, and Voluntary Control b. Cardiac Muscle: Structure, Function, and Voluntary Control c. Smooth Muscle: Structure, Function, and Voluntary Control 1. Molecular Mechanism of Muscle Contraction a. Sliding Filament Theory b. The Cross-Bridge Cycle c. Actin and Myosin Interaction d. Role of Troponin, Tropomyosin, and Calcium Ions e. ATP’s Role in Muscle Contraction 1. Electrophysiology in Muscle Contraction 2. Muscle Fiber Types and Architecture 3. Neuromuscular Coordination and Control 4. Muscle-related Disorders and Injuries 1. Overview/Basic Anatomy of Muscle Tissue Objective: 1. To understand the basic structure of the muscular system. 2. To differentiate between the types of muscle tissues in the body. Key Points: 1. The muscular system is responsible for voluntary and involuntary movements. 2. Muscles work by contracting and relaxing, a process controlled by the nervous system. 3. The body contains 3 primary types of muscle tissue: skeletal, cardiac, and smooth muscles. 1. Overview/Basic Anatomy of Muscle Tissue a. Skeletal Muscle - Composed of long, cylindrical fibers that are multinucleated and striated. - They attach to bones via tendons and are responsible for voluntary movements. - Controlled by the somatic nervous system. - Generate force by contracting, pulling on bones to produce movement. - Help maintain body posture and balance. 1. Overview/Basic Anatomy of Muscle Tissue b. Cardiac Muscle - Fibers are striated, branched, and have a single central nucleus. - They are connected by intercalated discs, which allow for coordinated contractions. - Controlled involuntarily by the autonomic nervous system. - Functions to contract rhythmically to pump blood. - Has the inherent ability to contract without external nervous stimulation. 1. Overview/Basic Anatomy of Muscle Tissue c. Smooth Muscle - Fibers are spindle-shaped, non-striated, and have a single central nucleus. - Found in the walls of hollow organs and blood vessels. - Controlled involuntarily by the autonomic nervous system. - Facilitate the movement of food in the G.I. tract (peristalsis) - Regulates blood flow in blood vessels by contracting and relaxing. 1. Overview/Basic Anatomy of Muscle Tissue Key Terms: Sarcomere - the basic unit of a skeletal muscle fiber. Myofibril - Rod-like structures within muscle fibers containing sarcomeres Intercalated discs - specialized junctions between cardiac muscle cells that facilitate synchronized contraction. 1. Overview/Basic Anatomy of Muscle Tissue Basic Anatomy of Muscle Tissue - Muscle Fiber (myocyte): a single muscle cell that can be quite long and contains multiple nuclei. - Myofibrils: bundles of protein filaments within each muscle fiber that contain actin and myosin, the proteins responsible for contraction. - Sarcomere: the repeating unit within a myofibril, composed of overlapping actin and myosin filaments, responsible for the striated appearance of skeletal and cardiac muscles. - Muscle fibers contract when myofibrils slide past one another, - shortening the sarcomere. 1. Overview/Basic Anatomy of Muscle Tissue Connective Tissue Components Epimysium: the outermost layer of connective tissue surrounding the entire muscle. Perimysium: the connective tissue surrounding groups of muscle fibers, forming bundles called fascicles. Endomysium: the connective tissue surrounding each individual muscle fiber - Connective tissues provide structural support and protection. 1. Overview/Basic Anatomy of Muscle Tissue Key Terms: Tendon - a tough band of fibrous connective tissue that connects muscle to bone. Fascia - a connective tissue layer that surrounds muscles, groups of muscles. Blood vessels, and nerves, binding some structures together while allowing others to slide smoothly over each other. Sarcoplasm - the cytoplasm of a muscle fiber/cell Sarcoplasmic Reticulum - a specialized ER that stores and releases Ca ions, triggering muscle contraction. 2. Molecular Mechanisms of Muscle Contraction Objective: 1. To understand the fundamental process of muscle contraction and how it enables movement. Key Points: 1. Muscle contraction is essential for all voluntary and many involuntary movements. 2. The process is driven by the interaction between actin and myosin filaments within muscle fibers. 3. Energy (ATP) is crucial for muscle contraction and relaxation. 2. Molecular Mechanisms of Muscle Contraction Introduction Muscle contraction is a complex process that enables muscles to shorten and generate force, allowing movement and various bodily functions. This lesson will delve into the molecular mechanisms behind muscle contraction, focusing on the interactions between key proteins within muscle fibers. Key Points: - Muscle contraction is essential for all voluntary and many involuntary movements. - The process is driven by the interaction between actin and myosin filaments within muscle fibers. - Energy in the form of ATP is crucial for muscle contraction and relaxation. 2. Molecular Mechanisms of Muscle Contraction The Sliding Filament Theory - the foundational model for muscle contraction. Structure - Sarcomere: the basic functional unit of a muscle fiber, defined by the area between two Z-discs. - Actin (thin filament): a protein filament that attaches to the Z-discs and extends towards the center of the sarcomere. - Myosin (thick filament): a protein filament that lies in the center of the sarcomere, overlapping with actin filaments. 2. Molecular Mechanisms of Muscle Contraction The Sliding Filament Theory Function - Contractile Units: sarcomeres are the contractile units of muscle fibers, where the actual process of muscle shortening occurs. - Striations: the alternating light and dark bands seen in skeletal and cardiac muscle fibers are due to the organized arrangement of actin and myosin. 2. Molecular Mechanisms of Muscle Contraction The Sliding Filament Theory - Z-Disc: the boundary structure of a sarcomere. Where actin filaments are anchored. - H-Zone: the central region of the sarcomere where only myosin filaments are present, which shortens during contraction. - A-Band: the region of the sarcomere that includes the length of the myosin filament, which remains constant during contraction. Relaxed state Contracted state In the image in the previous slide, notice the difference between the relaxed state and the contracted state of the sarcomere. My question is, did any of the filaments shorten? Answer: NO Only the I bands shortened. No molecules/filaments changed in length during contraction. This is because they only slide past each other. Walang umiksi, lumapit lang sila sa isa’t isa. Gets? 2. Molecular Mechanisms of Muscle Contraction The Sliding Filament Theory Role of Actin and Myosin - Actin: this filament is composed of globular actin (G-actin) subunits that polymerize to form filamentous actin (F-actin). - Binding Sites: each G-actin has a binding site for myosin, which is regulated by troponin and tropomyosin - Myosin: has a long tail and globular head. The head contains ATpase activity and is responsible for binding to actin. - Cross-Bridges: The myosin heads form cross-bridges with actin filaments, generating the force needed for muscle contraction. 2. Molecular Mechanisms of Muscle Contraction The Cross-Bridge Cycle Steps 1. Cross-Bridge Formation - Myosin heads attach to exposed binding sites on actin to form a cross-bridge. - The binding occurs after calcium ions bind to troponin, causing tropomyosin to shift and expose the active sites on actin. 2. Molecular Mechanisms of Muscle Contraction The Cross-Bridge Cycle Steps 2. Power Stroke - The myosin head pivots, pulling the actin filament towards the center of the sarcomere. - During this phase, ADP and inorganic phosphate (Pi) are released from the myosin head. 2. Molecular Mechanisms of Muscle Contraction The Cross-Bridge Cycle Steps 3. Cross-Bridge Detachment - A new molecule of ATP binds to the myosin head, causing it to detach from the actin filament. - This step is essential for the myosin head to release from actin and prepare for the next cycle. 2. Molecular Mechanisms of Muscle Contraction The Cross-Bridge Cycle Steps 4. Reactivation of Myosin Head - The ATP molecule is hydrolyzed to ADP and Pi by the ATPase activity of the myosin head. - The energy released from ATP hydrolysis “re-cocks” (“kasa” in tagalog) the myosin head, returning it to its high-energy state, ready to form a new cross-bridge. 2. Molecular Mechanisms of Muscle Contraction The Cross-Bridge Cycle ATP’s Role - Without ATP, muscles would remain in a state of contraction, a condition known as rigor mortis. - ATP is continuously supplied by cell respiration, highlighting the importance of energy metabolism in muscle function. 2. Molecular Mechanisms of Muscle Contraction The Cross-Bridge Cycle Role of Calcium Ions - The sarcoplasmic reticulum stores calcium ions and releases them in response to an action potential. - Transverse tubules (T-tubules) transmit the action potential from the cell membrane into the muscle fiber, triggering calcium release from the SR. - Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from actin’s binding sites. - With the binding sites exposed, myosin heads can attach to actin, initiating the cross-bridge cycle. 3. Electrophysiology of Muscle Contraction Electrophysiology refers to the study of electrical properties of cells and tissues. In muscle contraction, electrophysiology is crucial because it explains how electrical signals within the body trigger muscle fibers to contract. This process is vital for voluntary movements, reflexes, and many involuntary functions such as heartbeat and digestion. Muscle contraction is initiated by electrical signals called action potentials. These electrical signals are generated and propagated by the movement of ions across cell membranes. 3. Electrophysiology of Muscle Contraction The Steps of Muscle Contraction and the Role of Electrical Signals 1. The process begins at the neuromuscular junction, where a motor neuron communicates with a muscle fiber. 2. The motor neuron releases acetylcholine which binds to receptors on the muscle fiber’s membrane, generating an action potential. 3. The action potential travels along the muscle fiber’s membrane and into its interior via the T-tubules, triggering the release of calcium ions from the sarcoplasmic reticulum. 4. Calcium ions enable the interaction between actin and myosin filaments, leading to muscle contraction. 3. Muscle Fiber Types and Architecture Type I (Slow-Twitch) Muscle Fibers Characteristics - Contraction Speed: Slow - Force Production: Low - Fatigue Resistance: High - Metabolism: Primarily oxidative, relying on aerobic respiration Function - Specialized for endurance activities. Can sustain long periods of contraction without fatigue due to their high oxidative capacity and efficient use of oxygen. Contain a high density of mitochondria, myoglobin, and blood capillaries, which facilitate sustained energy production. Ex. cycling, swimming, marathon. 3. Muscle Fiber Types and Architecture Type II (Fast-Twitch) Muscle Fibers Type IIa (Fast Oxidative-Glycolytic or FOG) Fibers Characteristics - Contraction Speed: Fast - Force Production: Intermediate - Fatigue Resistance: Moderate - Metabolism: Both oxidative (aerobic) and glycolytic (anaerobic) 3. Muscle Fiber Types and Architecture Type II (Fast-Twitch) Muscle Fibers Type IIa (Fast Oxidative-Glycolytic or FOG) Fibers Function - Versatile, capable of generating moderate force and maintaining activity for a moderate duration. - These fibers can switch between aerobic and anaerobic metabolism, making them suitable for activities that require both endurance and strength. Examples: Soccer, Swimming sprints, middle-distance running. 3. Muscle Fiber Types and Architecture Type II (Fast-Twitch) Muscle Fibers Type IIx (Fast Glycolytic) Fibers Characteristics - Contraction Speed: Very Fast - Force Production: High - Fatigue Resistance: Low - Metabolism: Primarily glycolytic, relying on anaerobic respiration. 3. Muscle Fiber Types and Architecture Type II (Fast-Twitch) Muscle Fibers Type IIx (Fast Glycolytic) Fibers Function - Designed for short, explosive bursts of power and speed. - They generate the most force but fatigue quickly due to their reliance on anaerobic metab, which produces energy rapidly but unsustainably. - Examples: Sprinting, weightlifting, jumping 3. Muscle Fiber Types and Architecture Parallel (Longitudinal) Muscle Architecture Characteristics - Run parallel to the long axis of the muscle. - Typically longer fibers with fewer per cross-sectional area. Function - Designed for speed and a greater range of motion. - Capable of shortening more than other muscle types, allowing for fast and extensive movements. - Examples: Biceps brachii, sartorius (consult your books for the location and function of these!!!) 3. Muscle Fiber Types and Architecture Pennate Muscle Architecture Characteristics - Arranged obliquely to the central tendon, resembling a feather. - Can be further classified into unipennate, bipennate, and multipennate based on the fiber arrangement. Function - Designed for force generation rather than speed or range of motion. - The arrangement allows for more fibers to be packed into a given muscle volume, increasing the muscle’s cross-sectional area and its ability to generate force. 3. Muscle Fiber Types and Architecture Pennate Muscle Architecture Examples: - Unipennate: Extensor digitorum longus in the leg - Bipennate: Rectus femoris - Multipennate: Deltoid 3. Muscle Fiber Types and Architecture Convergent Muscle Architecture Characteristics - Muscle fibers converge from a broad origin to a single narrow insertion point. - Typically has a fan-like appearance. Function - Allow for versatile movements as they can pull on the insertion point from multiple directions. - Example: Pectoralis major (nasa chest ito. Look for it in the atlas) 3. Muscle Fiber Types and Architecture Circular Muscle Architecture Characteristics - Arranged in concentric circles around an opening or orifice. Function - Control the opening and closing of bodily orifices. - They act as sphincters, regulating the passage of substances thru an opening. - Examples: Orbicularis oculi, orbicularis oris 4. Neuromuscular Coordination and Control Neuromuscular coordination and control involve the intricate interaction between the nervous system and muscles to produce smooth, purposeful movements. The CNS plans and initiates movements, while the PNS executes them through motor units. Sensory feedback from proprioceptors allows for real-time adjustments, ensuring movements are precise and controlled. Reflexes provide rapid, automatic responses to protect the body and maintain stability. Complex movements require careful coordination of multiple muscle groups, and motor learning enhances neuromuscular control over time. 5. Muscle-Related Disorders and Injuries 1. Muscle Strains - This occurs when muscle fibers are overstretched or torn. This is one of the most common muscle injuries, particularly among athletes. Causes: Sudden, forceful movements, overuse of a muscle without rest, improper warm-up before physical activity. Symptoms: Pain and tenderness, swelling and bruising, limited range of motion, weakness Treatment: Rest, ice, compression, elevation to reduce pain/swelling (RICE) Prevention: Proper warm-up, gradual progression in activities, rest. 5. Muscle-Related Disorders and Injuries 2. Muscle Contusions (Bruises) - Caused by a direct blow or impact to the muscle, leading to bleeding under the skin. Causes: Blunt force trauma from falls, collisions in accidents/sports. Symptoms: Discoloration, swelling, pain, stiffness, limited movement. Treatment: RICE, NSAIDS Prevention: Wear protective gear, strengthen muscles to absorb impact better. 5. Muscle-Related Disorders and Injuries 3. Muscular Dystrophy - A group of genetic disorders characterized by progressive muscle weakness and degeneration. Causes: Genetic mutation that interfere with the production of proteins necessary for muscle health, such as dystrophin. Symptoms: Progressive muscle weakness and wasting. Treatment: Physical therapy, corticosteroids, braces and wheelchairs. Prevention: Genetic counselling for families with history, regular monitoring and supportive care to manage symptoms. 5. Muscle-Related Disorders and Injuries 4. Myasthenia Gravis - An autoimmune disorder that causes weakness and rapid fatigue of voluntary muscles due to the immune system attacking acetylcholine receptors at the neuromuscular junction. Causes: Unknown, but believed to involve genetic and envi factors. Symptoms: Weakness that worsens with activity, drooping eyelids, difficulty swallowing/speaking. Treatment: Acetylcholinesterase inhibitors, plasmapheresis, thymectomy. Management: Regular monitoring, lifestyle modification. 5. Muscle-Related Disorders and Injuries 5. Muscle Cramps and Spasms (Pulikat) - Sudden, involuntary contractions of a muscle or group of muscles, often causing significant pain. Causes: Dehydration and electrolyte imbalance, overuse of a muscle, poor circulation, nerve compression, diabetes, hypothyroidism. Symptoms: Sudden, sharp pain, tightness, soreness after the cramp. Treatment: Stretching the affected muscle, hydration, massage, heat. Prevention: Staying hydrated especially during exercise, balanced diet, regular stretching.