Topic 3 - The Muscle Tissue - Revision.pdf

Human Anatomy and Physiology Elaine N. Marieb and Suzanne M. Keller The Muscular System: Muscle Tissue This slide deck contains animations. Please disable animations...

Human Anatomy and Physiology Elaine N. Marieb and Suzanne M. Keller The Muscular System: Muscle Tissue This slide deck contains animations. Please disable animations if they cause issues with your device. Copyright ©2021 John Wiley & Sons, Inc. Types of Muscular Tissue 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle Somatic nervous system Autonomic nervous system Functions of Muscular Tissue 1. Producing body movements: whole body such as walking and running, and localized movements such as grasping a pencil, or typing. 2. Stabilizing body positions: Skeletal muscle contractions stabilize joints and help maintain body positions, such as standing or sitting. 3. Storing and moving substances within the body: ringlike smooth muscle sphincters control the movement of contents of hollow organs e.g. food in the stomach or urine in the urinary bladder. 4. Generating heat: As muscular tissue contracts, it produces heat e.g. during shivering. Properties of Muscular Tissue 1. Electrical excitability: the ability to respond to certain stimuli by producing electrical signals called action potentials (impulses) 2. Contractility: the ability of muscular tissue to contract forcefully when stimulated by a nerve impulse 3. Extensibility: the ability of muscular tissue to stretch, within limits, without being damaged 4. Elasticity: the ability of muscular tissue to return to its original length and shape after contraction or extension Copyright ©2021 John Wiley & Sons, Inc. 4 Gross Anatomy of Skeletal Muscles Three layers of connective tissue protect and strengthen skeletal muscle – i) Epimysium, ii) Perimysium and iii) Endomysium. Epimysium - outer layer, encircling the entire muscle. Consists of dense irregular connective tissue.  Gross Anatomy of Skeletal Muscles Perimysium: a layer of dense irregular connective tissue that Surrounds groups of 10 to 100 or more muscle fibers/ bundles called muscle fascicles Endomysium: penetrates the interior of each muscle fascicle and separates individual muscle fibers from one another. The endomysium is mostly reticular fibers. Levels of Organization within a Skeletal Muscle  Cellular Components of a Muscle Fiber Sarcolemma Plasma membrane of a muscle fibre that forms T tubules Sarcoplasm Cytoplasm of the muscle fiber that contains myofibrils Myofibril Consists of bundles of myofilament and plays a key role in muscle contraction Myofilament Consists of thick and thin filaments that give muscle tissue its striated appearance and play a role in muscle contraction Myoglobin A reddish brown pigment (gives muscle tissue its dark-red colour) that stores oxygen for muscle contraction T tubule Permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration. Sarcoplasmic reticulum A storage site for calcium ions Copyright ©2021 John Wiley & Sons, Inc. 8 Microanatomy of Skeletal Muscle Fibre Copyright ©2021 John Wiley & Sons, Inc. 9  The Arrangement of a Sarcomere Sarcomere: basic functional unit of a myofibril. Contains thin and thick filaments and other structural components/proteins. A sarcomere extends from one Z disc to the next Z disc. The components of a sarcomere are organized into a variety of bands and zones  Components of a Sarcomere Myosin & Actin Only Actin Only Myosin Hold the myosin in place Copyright ©2021 John Wiley & Sons, Inc. 11 Muscle Proteins Contractile: Regulatory: Structural Proteins: Myosin Troponin Titin Actin Tropomyosin Nebulin Alpha-actin Myomesin Dystrophin Copyright ©2021 John Wiley & Sons, Inc. 12 Muscle Proteins Regulatory Proteins: help switch muscle contraction process on and off Tropomyosin -when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, preventing myosin from binding to actin. Troponin - when calcium ions (Ca2+) bind to troponin, it changes shape; moves tropomyosin away from myosin binding sites on actin and myosin binds to actin. Copyright ©2021 John Wiley & Sons, Inc. 13 The Contraction Cycle The Contraction Cycle Interactions Animation Contraction of Skeletal Muscle Cells The neuromuscular junction or neuromuscular synapse, parts of a muscle fiber, and the contraction cycle Copyright ©2021 John Wiley & Sons, Inc. 15  The Neuromuscular Junction (NMJ) or Neuromuscular Synapse (NMS) Events at the NMJ (or NMS) produce a muscle action potential: 1. Release of Acetylcholine (ACh): Voltage-gated calcium channels in a neuron’s synaptic end bulb open, resulting in calcium influx. This causes exocytosis of a neurotransmitter (ACh) into synaptic cleft 2. Activation of ACh Receptors: ACh binds to ligand-gated Na+ channels on the motor endplate, which causes an influx of N a+ into muscle 3. Production of muscle action potential- depolarizes the muscle and results in Ca2+ release from the sarcoplasmic reticulum 4. Termination of ACh Activity: ACh gets broken down by acetlycholinesterase The Neuromuscular Junction (NMJ)  Excitation-Contraction (EC) Coupling This concept connects the events of: a muscle action potential with the sliding filament mechanism Rigor Mortis (Rigidity of death) Is the stiffening of skeletal muscle several hours after death; This occurs because ATP levels fall as nutrients and oxygen needed to form ATP are no longer supplied to cells from circulation. THEREFORE BREAKAGE OF LINK (cross bridging) BETWEEN ACTIN AND MYOSIN DOES NOT OCCUR Stiffness of rigor mortis disappears after 2-3 days when muscle tissue disintegrates Copyright ©2021 John Wiley & Sons, Inc. 19 Muscle Metabolism Muscles have 3 ways to produce ATP: 1. Creatine phosphate (Direct phosphorylation of ADP) 2. Anaerobic glycolysis (Anaerobic glycolysis and lactic acid formation) 3. Aerobic respiration Copyright ©2021 John Wiley & Sons, Inc. 20 1. Creatine Phosphate (CP) Creatine kinase catalyzes the transfer of a phosphate group from Creatine Phosphate to ADP to rapidly yield ATP Produces 1 ATP (Direct Phosphorylation) 2. Anaerobic Glycolysis When CP stores are depleted, glucose is converted into pyruvic acid to generate ATP Produces 2 ATP Molecules  3. Aerobic Respiration Under aerobic conditions (requires oxygen) - pyruvic acid can enter the mitochondria and undergo reactions to generate large amounts of ATP Produces 30/32 ATP Molecules Muscle Fatigue Muscle fatigue is the inability to maintain force of contraction after prolonged activity The onset of fatigue is due to:** 1. Inadequate release of Ca2+ from SR 2. Depletion of CP, oxygen, and nutrients 3. Build up of lactic acid and ADP 4. Insufficient release of Acetyl Choline (ACh) at the Neuromuscular Junction (NMJ) 5. Dehydration Isotonic vs. Isometric Contractions (1 of 2) 1. Isotonic – tension is constant while muscle length changes. Isotonic contractions are used for body movements and for moving object Two types: Concentric - the muscle shortens during contraction Eccentric- the muscle lengthens during contraction 2. Isometric – muscle contracts but does not change length. Important for maintaining posture and for supporting objects in a fixed position Copyright ©2021 John Wiley & Sons, Inc. 25  Cardiac Muscle Cardiac muscle has the same arrangement as skeletal muscle, but also has intercalated discs Intercalated discs contain desmosomes and gap junctions that allow muscle action potentials to spread from one muscle fiber to another Copyright ©2021 John Wiley & Sons, Inc. 26  Smooth Muscle Smooth muscle looks quite different than cardiac and skeletal muscle. It is thick in the middle, tapered on the ends, and is not striated It can be arranged as either single-unit or multi-unit fibers Gap Junction No Gap Junction Copyright ©2021 John Wiley & Sons, Inc. 27  Smooth Muscle Smooth muscle contractions start more slowly and last longer than skeletal and cardiac muscle contractions. Smooth muscle can shorten and stretch to a greater extent than skeletal and cardiac muscle. Smooth muscle fibers shorten in response to stretch. Smooth muscle can regenerate compared to the other types of tissues Copyright ©2021 John Wiley & Sons, Inc. 28 Summary of Major Features of Three Types of Muscular Tissue Copyright ©2021 John Wiley & Sons, Inc. 29