Muscles and Muscle Tissue Part 1 PDF

Muscles and Muscle Tissue Part 1 Copyright © 2025 Pearson Education, Inc. All Rights Reserved Learning Objectives for today Compare and contrast the three types of muscle tissue in terms of the structure, location, and their functional characteristics List the major functions of...

Muscles and Muscle Tissue Part 1 Copyright © 2025 Pearson Education, Inc. All Rights Reserved Learning Objectives for today Compare and contrast the three types of muscle tissue in terms of the structure, location, and their functional characteristics List the major functions of the muscular system Describe the different tissues involved in the anatomy of a skeletal muscle Describe the cellular and molecular components of an individual muscle fiber Explain the sliding filament mechanism of muscle contraction Describe the structure of the neuromuscular junction Describe the events at a neuromuscular junction that lead to the release of acetylcholine (ACh) Copyright © 2025 Pearson Education, Inc. All Rights Reserved 9.1 Muscle Tissue Muscles makes up nearly half of body’s mass Can transform chemical energy (ATP) into directed mechanical energy, which is capable of exerting force Copyright © 2025 Pearson Education, Inc. All Rights Reserved Types of Muscle Tissue (Objective 1) (1 of 4) Terminologies: myo-, mys-, and sarco- are prefixes for muscle – Example: sarcoplasm: muscle cell cytoplasm Three types of muscle tissue – Skeletal – Cardiac – Smooth Copyright © 2025 Pearson Education, Inc. All Rights Reserved Types of Muscle Tissue (Objective 1) (2 of 4) Skeletal muscle – Skeletal muscle tissue is packaged into skeletal muscles: organs that are attached to bones and skin – Skeletal muscle fibers are longest of all muscle and have striations (stripes) – Also called voluntary muscle: can be consciously controlled – Contract rapidly; tire easily; powerful – Key words for skeletal muscle: skeletal, striated, and voluntary Copyright © 2025 Pearson Education, Inc. All Rights Reserved Types of Muscle Tissue (Objective 1) (3 of 4) Cardiac muscle – Cardiac muscle tissue is found only in heart ▪ Makes up bulk of heart walls – Striated – Involuntary: cannot be controlled consciously ▪ Contracts at steady rate due to heart’s own pacemaker, but nervous system can increase rate – Key words for cardiac muscle: cardiac, striated, and involuntary Copyright © 2025 Pearson Education, Inc. All Rights Reserved Types of Muscle Tissue (Objective 1) (4 of 4) Smooth muscle – Smooth muscle tissue: found in walls of hollow organs ▪ Examples: stomach, urinary bladder, and airways – Not striated – Involuntary: cannot be controlled consciously – Key words for smooth muscle: visceral, nonstriated and involuntary Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 9.3-1 Comparison of Skeletal, Cardiac, and Smooth Muscle (1 of 2) Characteristic Skeletal Cardiac Smooth Body location Attached to bones or (for some Walls of the heart Unitary muscle in walls of facial muscles) to skin hollow visceral organs (other than the heart); multi unit An illustration shows the walls of heart composed of cardiac muscles. muscle in intrinsic eye muscles, An illustration shows a hand holding a dumbbell and skeletal muscle is highlighted in the upper arm. airways, large arteries An illustration shows a stomach as a visceral organ composed of smooth muscles. Cell shape and Single, very long, cylindrical, Branching chains of cells; uni- Single, spindle shaped, appearance multinucleate cells with obvious or binucleate; striations uninucleate; no striations striations A micrograph shows a section of cardiac muscle that has branching chain of cells with striations studded with peripheral nucleus. A micrograph shows a section of smooth muscle that has spindle-shaped uninucleate cells with no striations. A micrograph shows a section of skeletal muscle that has striations studded with peripheral nuclei. A long cylindrical skeletal muscle with multi-nuclei is shown. A branched-chain of cardiac muscle with a few nuclei is shown. A spindle-shaped smooth muscle cell is shown with a central nucleus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Muscle Functions (Objective 2) Four important functions – Produce movement: responsible for all locomotion and manipulation ▪ Example: walking, digesting, pumping blood – Maintain posture and body position – Stabilize joints – Generate heat as they contract Copyright © 2025 Pearson Education, Inc. All Rights Reserved 9.2 Skeletal Muscle (Objective 3) Skeletal muscle is an organ made up of different tissues: – Nerves and blood supply – Connective tissue sheaths – Attachments Copyright © 2025 Pearson Education, Inc. All Rights Reserved Skeletal Muscle: Nerve and Blood Supply (Objective 3) Each muscle receives a nerve, artery, and veins – Consciously controlled skeletal muscle has nerves supplying every fiber to control activity Contracting muscle fibers require huge amounts of oxygen and nutrients – Also need waste products removed quickly Copyright © 2025 Pearson Education, Inc. All Rights Reserved Skeletal Muscle: Connective Tissue Sheaths (Objective 3) Each skeletal muscle, as well as each muscle fiber, is covered in connective tissue Support cells and reinforce whole muscle Sheaths from external to internal: – Epimysium: dense irregular connective tissue surrounding entire muscle; may blend with fascia – Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers) – Endomysium: fine areolar connective tissue surrounding each muscle fiber Copyright © 2025 Pearson Education, Inc. All Rights Reserved Connective Tissue Sheaths of Skeletal Muscle: Epimysium, Perimysium, and Endomysium (1 of 2) Figure 9.1 Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Skeletal Muscle: Attachments (Objective 3) Muscles span joints and attach to bones or other structures Attachments can be direct or indirect – Direct (fleshy) attachments: epimysium fused to periosteum of bone or perichondrium of cartilage – Indirect attachments: connective tissue wrappings extend beyond muscle ▪ Ropelike tendon ▪ Sheetlike aponeurosis Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 9.1-1 Structure and Organizational Levels of Skeletal Muscle Connective Tissue Structure and Organizational Level Description Wrappings Muscle (organ) A muscle consists of hundreds Covered externally by to thousands of muscle cells, the epimysium An illustration of the muscle (organ) presents the following structures: Epimysium, fascicle, muscle, and tendon. plus connective tissue wrappings, blood vessels, and axons (nerve fibers). Fascicle (a portion of the muscle) A fascicle is a discrete bundle of Surrounded by muscle cells, segregated from perimysium An illustration of a fascicle (a portion of the muscle) presents the following structures: Part of fascicle, perimysium, and muscle fiber. the rest of the muscle by a connective tissue sheath. Muscle fiber (cell) A muscle fiber is an elongated Surrounded by multinucleate cell; it has a endomysium An illustration of a muscle fiber (cell) presents the following structures: Part of muscle fiber, nucleus, endomysium, sarcolemma, and myofibril. banded (striated) appearance. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 9.3 Skeletal Muscle Fibers (Objective 4) Skeletal muscle fibers are long, cylindrical cells that contain multiple nuclei Sarcolemma: muscle fiber plasma membrane Sarcoplasm: muscle fiber cytoplasm Contains many glycosomes for glycogen storage, as well as myoglobin for O2 storage Specialized structures within skeletal muscle cells: – Myofibrils – Sarcoplasmic reticulum – T tubules Copyright © 2025 Pearson Education, Inc. All Rights Reserved Myofibrils (Objective 4) (1 of 7) Myofibrils are densely packed, rodlike elements – Single muscle fiber can contain 1000s – Accounts for 80% of muscle cell volume Myofibril features – Striations – Sarcomeres – Myofilaments – Molecular composition of myofilaments Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of a Skeletal Muscle Fiber (1 of 4) Figure 9.2b Microscopic anatomy of a skeletal muscle fiber. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Myofibrils (Objective 4) (2 of 7) Striations: stripes formed from repeating series of dark and light bands along length of each myofibril – A bands: dark regions – I bands: lighter regions ▪ Z disc (line): coin-shaped sheet of proteins on midline of light I band Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of a Skeletal Muscle Fiber (2 of 4) Figure 9.2a Microscopic anatomy of a skeletal muscle fiber. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Myofibrils (Objective 4) (3 of 7) Sarcomere – Smallest contractile unit (functional unit) of muscle fiber – Contains A band with half of an I band at each end ▪ Consists of area between Z discs – Individual sarcomeres align end to end along myofibril, like boxcars of train Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of a Skeletal Muscle Fiber (3 of 4) Figure 9.2c Microscopic anatomy of a skeletal muscle fiber. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Myofibrils (Objective 4) (4 of 7) Myofilaments – Orderly arrangement of actin and myosin myofilaments within sarcomere – Actin myofilaments: thin filaments ▪ Extend across I band and partway in A band ▪ Anchored to Z discs – Myosin myofilaments: thick filaments ▪ Extend length of A band ▪ Connected at M line Copyright © 2025 Pearson Education, Inc. All Rights Reserved Microscopic Anatomy of a Skeletal Muscle Fiber (4 of 4) Figures 9.2 d,e Microscopic anatomy of a skeletal muscle fiber. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Composition of Thick and Thin Filaments (1 of 2) Figure 9.3 Composition of thick and thin filaments. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Composition of Thick and Thin Filaments (2 of 2) Figure 9.3 Composition of thick and thin filaments. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Sarcoplasmic Reticulum and T Tubules (Objective 4) (1 of 3) Sarcoplasmic reticulum: network of smooth endoplasmic reticulum tubules surrounding each myofibril – Most run longitudinally – SR functions in regulation of intracellular Ca 2+ levels – Stores and releases Ca2+ Copyright © 2025 Pearson Education, Inc. All Rights Reserved Sarcoplasmic Reticulum and T Tubules (Objective 4) (2 of 3) T tubules – Tube formed by protrusion of sarcolemma deep into cell interior ▪ Allow electrical nerve transmissions to reach deep into interior of each muscle fiber – Tubules penetrate cell’s interior at each A–I band junction between terminal cisterns ▪ Triad: area formed from terminal cistern of one sarcomere, T tubule, and terminal cistern of neighboring sarcomere Copyright © 2025 Pearson Education, Inc. All Rights Reserved Sarcoplasmic Reticulum and T Tubules (Objective 4) (3 of 3) Triad relationships – T tubule contains integral membrane proteins that protrude into intermembrane space (space between tubule and muscle fiber sarcolemma) – SR cistern membranes also have integral membrane proteins that protrude into intermembrane space – When an electrical impulse passes by, T tubule proteins change shape, causing SR proteins to change shape, causing release of calcium into cytoplasm Copyright © 2025 Pearson Education, Inc. All Rights Reserved Relationship of the Sarcoplasmic Reticulum and T Tubules to Myofibrils of Skeletal Muscle Figure 9.5 Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Sliding Filament Model of Contraction (Objective 5) (1 of 5) Contraction: the activation of cross bridges to generate force Contraction ends when cross bridges become inactive Copyright © 2025 Pearson Education, Inc. All Rights Reserved Sliding Filament Model of Contraction (Objective 5) (2 of 5) In the relaxed state, thin and thick filaments overlap only slightly at ends of A band Sliding filament model of contraction states that during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more When nervous system stimulates muscle fiber, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) process to begin Copyright © 2025 Pearson Education, Inc. All Rights Reserved Sliding Filament Model of Contraction (4 of 5) Figure 9.6-1 Sliding filament model of contraction. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Sliding Filament Model of Contraction (5 of 5) Figure 9.6-2 Sliding filament model of contraction. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 9.4 Motor Neurons Stimulate Skeletal Muscle Fibers to Contract Background and Overview Decision to move is activated by brain, signal is transmitted down spinal cord to motor neurons which then activate muscle fibers Neurons and muscle cells are excitable cells capable of action potentials (APs) – Excitable cells are capable of changing resting membrane potential voltages AP crosses from neuron to muscle cell via the neurotransmitter acetylcholine (ACh) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Skeletal Muscle Contraction (1 of 3) Figure 9.7 Overview of skeletal muscle contraction. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Skeletal Muscle Contraction: Background and Overview (Objective 6) (3 of 4) Anatomy of Motor Neurons and the Neuromuscular Junction (cont ) inued – Axon terminal (end of axon) and muscle fiber are separated by gel-filled space called synaptic cleft – Stored within axon terminals are membrane-bound synaptic vesicles ▪ Synaptic vesicles contain neurotransmitter acetylcholine (ACh) – Infoldings of sarcolemma, called junctional folds, contain millions of ACh receptors – NMJ consists of axon terminals, synaptic cleft, and junctional folds Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Skeletal Muscle Contraction (2 of 3) Figure 9.7 Overview of skeletal muscle contraction. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Events at the Neuromuscular Junction (Objective 7) Events at the neuromuscular junction: 1. Action potential (AP) arrives at axon terminal 2. Voltage-gated calcium channels open, calcium enters motor neuron 3. Calcium entry causes release of acetylcholine (Ach) neurotransmitter into synpatic cleft 4. ACh diffuses across to ACh receptors on sarcolemma 5. ACh binding to receptors, opens gates, allowing Na+ to enter resulting in graded potential 6. Acetylcholinesterase degrades ACh Copyright © 2025 Pearson Education, Inc. All Rights Reserved When a Nerve Impulse Reaches a Neuromuscular Junction, Acetylcholine (ACh) is Released (6 of 6) Focus Figure 9.1 Events at the Neuromuscular Junction Copyright © 2025 Pearson Education, Inc. All Rights Reserved Concept Check! Copyright © 2025 Pearson Education, Inc. All Rights Reserved