Muscular System PDF

THE MUSCULAR SYSTEM Presented by: Lovely Joy L. Calantoc, BS BIO, CSE Muscular System Myology: study of muscles Myo=muscle logy=study of sarco=flesh Three types of muscular tissue in the human body—skeletal, cardiac, and smooth. Types of Muscle Tissue Properties of Muscle...

THE MUSCULAR SYSTEM Presented by: Lovely Joy L. Calantoc, BS BIO, CSE Muscular System Myology: study of muscles Myo=muscle logy=study of sarco=flesh Three types of muscular tissue in the human body—skeletal, cardiac, and smooth. Types of Muscle Tissue Properties of Muscle Tissue Excitability Allows muscles to respond to stimuli with electrical signals Contractility Enables muscles to generate force and move objects Extensibility Permits safe stretching without being damaged Elasticity Allows muscles to return to their original size/shape after use  Functions of Muscular Tissue 1 Producing Body Movements 3 Storing and Moving Substances within the Body 2 Stabilizing Body Positions. 4 Thermogenesis  Organization of Muscle Tissue Muscles are comprised of: *Muscle Fibers *Nerves *Blood vessels *Connective Tissue Muscles are made up of many wrapped bundles: Epimysium Outer layer that surrounds the entire muscle. Perimysium surrounding fascicles Fascicles Bundle of muscle fibers Endomysium Penetrates inside each fascicle to wrap around individual muscle fibers. It’s mostly made of fine reticular fibers.  Organization of Muscle Tissue Muscle Fiber: muscle cell Nuclei Capillary Sarcolemma: plasma membrane of a muscle cell wrapping myofibrils Sarcoplasm: the cytoplasm of a muscle fiber; contains myoglobin that is found only in muscle Transverse tubule: membrane canals that reach deep myofibrils Mitochondria Sarcoplasmic reticulum Endoplasmic reticulum of muscle cells. Store/Release Ca+2 into the cell cytoplasm, which is required for muscle contraction. Myofibril contractile organelles of skeletal muscle Contains filaments or myofilaments ( actin & myosin) Microscopic Anatomy of Skeletal Muscle  Myofilaments (Actin & Myosin) The two contractile proteins in muscle are myosin and actin. Myosin is the main component of thick filaments Myosin tail: points towards the M line in the center of sarcomere Myosin head: has two binding sites 1. an actin-binding site and; 2. An ATP-binding site. -functions as an ATPASE—an enzyme that hydrolyzes ATP to generate energy for muscle contraction Actin: main component of the thin filament; on each actin molecule is a myosin-binding site, where a myosin head can attach. Two regulatory proteins—tropomyosin and troponin--are also part of the thin filament.  Myofilaments (Actin & Myosin) The filaments inside a myofibril are arranged in compartments called sarcomere. Actin and Myosin Structure Microscopic Anatomy of Skeletal Muscle  Skeletal Muscle Contraction Physiology Somatic Motor Neurons Neurons responsible for stimulating skeletal muscle fibers, triggering contraction. They have long thread-like axons that extend from the brain or spinal cord to target groups of muscle fibers. Muscle Fiber Contraction: A muscle fiber contracts when action potentials (electrical signals) travel along its membrane (sarcolemma) and through its T-tubules (tiny channels). These action potentials start at the Neuromuscular Junction (NMJ), where the neuron meets the muscle fiber.  Neuromuscular Junction (NMJ) Components of the NMJ: Axon Terminal and Synaptic End Bulbs: The end of the motor neuron (axon terminal) splits into clusters of synaptic end bulbs. Each synaptic end bulb contains synaptic vesicles—tiny sacs that hold thousands of neurotransmitters called acetylcholine (ACh). Synaptic cleft a small gap between the neuron and muscle cell where signals are transmitted chemically. Motor End Plate The section of the muscle fiber’s sarcolemma that faces the synaptic end bulbs The motor end plate contains 30 to 40 million ACh receptors, which are proteins that specifically bind with acetylcholine. The ACh receptors on the motor end plate are ligand-gated ion channels, meaning they open in response to the binding of acetylcholine, allowing sodium ions to flow and initiate a muscle contraction. These receptors are embedded in junctional folds—grooves that increase the surface area for ACh binding.  Neuromuscular Junction (NMJ) Physiology 1. Nerve Impulse and Calcium Influx A nerve impulse arrives at the motor neuron’s synaptic end bulbs, opening voltage-gated calcium channels Calcium ions (Ca²⁺), more concentrated outside the neuron, flow into the neuron. 2. Release of Acetylcholine (ACh) The Ca²⁺ influx prompts synaptic vesicles to fuse with the neuron’s membrane, releasing Ach into the synaptic cleft. 3. Diffusion and Binding of Ach ACh diffuses across the synaptic cleft to the muscle fiber’s motor end plate. ACh binds to receptors on the motor end plate; each receptor needs two ACh molecules to activate. 4. Opening of Ion Channels Activated ACh receptors open ion channels , allowing sodium ions (Na⁺) to enter the muscle fiber. 5. Production of Muscle Action Potential The Na⁺ influx changes the muscle fiber’s membrane charge, making it more positive. This change triggers a muscle action potential that spreads along the sarcolemma and T tubules. The action potential causes the sarcoplasmic reticulum to release stored Ca²⁺ into the muscle cell, leading to contraction. 6. Termination of ACh Activity Acetylcholinesterase (AChE) on the motor end plate quickly breaks down ACh into acetyl and choline. This stops ACh receptor activation, ending the contraction signal. Neuromuscular Junction Neuromuscular Junction  Sliding Filament Theory According to this theory, muscle contraction occurs as a result of the sliding movement between two types of protein filaments within muscle fibers: actin (thin filaments) and myosin (thick filaments). Sliding Filament Theory Summary of Skeletal Muscle Contraction  Muscle Relaxation 1. Muscle relaxation begins when acetylcholine is no longer released at the neuromuscular junction. 2. The cessation of action potentials along the sarcolemma stops the release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum. 3. Ca²⁺ is actively transported back into the sarcoplasmic reticulum. 4. As Ca²⁺ concentration decreases in the sarcoplasm, calcium ions diffuse away from troponin molecules. 5. The troponin-tropomyosin complex reestablishes its position, blocking the active sites on actin molecules. 6. Consequently, cross-bridges cannot re-form once they are released, leading to muscle relaxation.  Production of ATP for Muscle contraction THREE PATHWAYS: CREATINE PHOSPHATE Creatine phosphate, formed from ATP while the muscle is relaxed, transfers a high-energy phosphate group to ADP, forming ATP during muscle contraction. ANAEROBIC GLYCOLYSIS Breakdown of muscle glycogen into glucose and production of pyruvic acid from glucose via glycolysis produce both ATP and lactic acid. AEROBIC RESPIRATION Within mitochondria, pyruvic acid, fatty acids, and amino acids are used to produce ATP via aerobic respiration, an oxygen-requiring set of reactions. Production of ATP for Muscle contraction  Muscle Fatigue The inability of a muscle to maintain force of contraction after prolonged activity Several factors: One is inadequate release of calcium ions from the SR, resulting in a decline of Ca2+ concentration in the sarcoplasm. Depletion of creatine phosphate. Insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP, and failure of action potentials in the motor neuron to release enough acetylcholine  Types of Muscle Contraction Isotonic contraction Isometric contraction The muscle changes length as it The muscle generates force without contracts, causing movement. changing its length. No movement occurs, but tension is maintained. Concentric: The muscle shortens while contracting, generating force. For Ex: Holding a plank position or example, lifting a weight during a bicep curl. holding a weight steady without moving. Eccentric: The muscle lengthens while contracting under tension, often to control the movement. For example, lowering a weight slowly during a bicep curl.  Effects of Exercise On Muscles Aerobic or endurance Resistance or Isometric Jogging, biking Push-up, Pull-up Stronger, more flexible muscles The muscles are pitted against with greater resistance to fatigue some immovable objects Enhance neuromuscular Forcing the muscle to contract coordination with as much force as possible The heart enlarge Fat depositions are cleared Lungs become more efficient in gas exchange Improves digestion