Human Anatomy: Chapter 10 Muscle Tissue and the Sliding Filament Mechanism PDF

Chapter 10 Muscle Tissue and the Sliding Filament Mechanism By: Dr. R. Knudsen Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1  Outline Properties of Muscle Tissue Characteristics of Skeletal...

Chapter 10 Muscle Tissue and the Sliding Filament Mechanism By: Dr. R. Knudsen Copyright © McGraw-Hill Education. Permission required for reproduction or display. 1  Outline Properties of Muscle Tissue Characteristics of Skeletal Muscle Tissue Contraction of Skeletal Muscle Fibers Types of Skeletal Muscle Fibers Skeletal Muscle Fiber Organization Exercise and Skeletal Muscle Levers and Joint Biomechanics (continued) 2  Outline—continued The Naming of Skeletal Muscles Characteristics of Cardiac and Smooth Muscle Aging and the Muscular System Development of the Muscular System 3  Introduction There are 3 types of muscle tissue in the body: 1. Skeletal 2. Cardiac 3. Smooth There are over 700 skeletal muscles and together they form the muscular system 4  Properties of Muscle Tissue There are 4 unique characteristics of muscle tissue: 1. Excitability: Muscle cells are responsive to input from stimuli 2. Contractility: Stimulation of muscle fiber can lead to contraction and shortening of the muscle fiber 3. Elasticity: A contracted muscle cell can return to resting length when applied tension is removed 4. Extensibility: The ability of a muscle fiber to be stretched beyond its resting length 5  Characteristics of Skeletal Muscle Tissue Each skeletal muscle is considered an organ – Contains all four tissue types Striated Usually attached to bones Voluntary 6  Functions of Skeletal Muscle Tissue 1. Body movement 2. Maintenance of posture 3. Temperature regulation 4. Storage and movement of materials 5. Support 7  Anatomy of Skeletal Muscle Each muscle is comprised of muscle fibers organized into bundles called fascicles Muscle fibers contain myofibrils Myofibrils are composed of myofilaments 8  Organization of Skeletal Muscle Figure 10.1 9 10 Connective Tissue Components Each muscle has 3 layers of concentric connective tissue called “mysium” composed of collagen and elastic fibers This connective tissue provides protection, sites for blood vessel and nerve distribution, and a means of attaching the muscle to the skeleton 11 Connective Tissue Components Endomysium: Innermost layer that surrounds and electrically insulates each muscle fiber – Areolar connective tissue Perimysium: Surrounds the fascicles – Dense irregular connective tissue Epimysium: Surrounds the entire muscle – Dense irregular connective tissue – Deep fascia surrounds each muscle and separates muscles from each other – Superficial fascia separates muscle from skin 12  Muscle Attachments At the ends of each muscle, all of the connective tissue merge to form a tendon, which attaches the muscle to bone, skin, or another muscle A tendon is usually cordlike in appearance, but some appear as a flat sheet, termed an aponeurosis 13  Muscle Attachments Most muscles extend over a joint and have attachments to both articulating bones of that joint Upon contraction of the muscle, one of the articulating bones moves and the other one does not The less moveable point of attachment is called the origin The more moveable point of attachment is called the insertion 14  Muscle Origin and Insertion Figure 10.2 15  Microscopic Anatomy of Skeletal Muscle Skeletal muscle fibers have many of the same components of a typical cell, but some are named differently Examples: Sarcolemma: Plasma membrane Sarcoplasm: Cytoplasm Sarcoplasmic reticulum: Smooth ER 16  Microscopic Anatomy of Skeletal Muscle There are 2 main structures that are unique to muscle fibers: 1. Transverse tubules (T-tubules): Deep invaginations of the sarcolemma that extend into the sarcoplasm Form a network of tubules that enables muscle impulses to spread quickly internally 2. Terminal cisternae: Blind sacs of the sarcoplasmic reticulum Two terminal cisternae + T-tubule = triad 17  Formation, Structure, and Organization of a Skeletal Muscle Fiber Figure 10.3 18  Myofibrils and Myofilaments Myofibrils: – Cylindrical structures that extend the entire length of the cell – Have the ability to shorten, resulting in contraction of the muscle fiber 19  Myofibrils and Myofilaments Myofilaments: – Short bundles of proteins that comprise a myofibril – Myofilaments do not run the entire length of the muscle fiber, but are organized into repetitive groupings – Myofilaments are of 2 types: 1. Thick filaments 2. Thin filaments 20  Myofilaments Thick filaments: – 11 nm in diameter (twice as thick as thin filaments) – Composed of bundled molecules of myosin – Myosin molecule has a head and elongated tail – The heads form crossbridges with the thin filaments during contraction 21  Myofilaments Thin filaments: – 5–6 nm in diameter – Comprised of two strands (F-actin) of spherical (G-actin) molecules twisted around each other – 2 regulatory proteins are also part of the thin filament: Tropomyosin Troponin 22  Molecular Structure of Thin and Thick Filaments 23 Figure 10.5 24  Molecular Structure of Thick and Thin Filaments Organization of thin and thick filaments causes the striated appearance of skeletal muscle The dark bands (A bands) contain the entire myosin molecule and an overlapping portion of actin The light bands (I bands) contain thin filaments but no thick filaments The I bands also contain the protein titin 25  Molecular Structure of Thick and Thin Filaments Using an electron microscope, other components can be seen within both A bands and I bands: 1. H zone (H band): Light, central region of the A band where there are no thin filaments 2. M line: A protein meshwork in the H zone that keeps the thick filaments aligned 3. Z disc (Z band): A protein structure in the middle of the I band that serves as the attachment site for one end of the thin filaments 26  Organization of a Sarcomere The sarcomere is the functional contractile unit in a muscle fiber Defined by the area between 2 adjacent Z discs Myofibrils contain multiple and repeating sarcomeres Each sarcomere shortens as the muscle fiber contracts 27  Structure of a Sarcomere Figure 10.6 28 29  Contraction of Skeletal Muscle Fibers Muscle fibers shorten by the interaction between thin and thick filaments within each sarcomere – Generate tension The mechanism for contraction is explained by the sliding filament theory 30  The Sliding Filament Theory During contraction, the thick and thin filaments interact and slide past each other. This causes the following changes within each sarcomere: – Width of A band remains constant, but H zone disappears – Z discs in each sarcomere move closer together – Sarcomere narrows in length – I bands narrow Length of the thick and thin filaments never changes whether the muscle is contracted or relaxed; only their position changes 31  Sliding Filament Theory of Contraction Figure 10.7a 32  Sliding Filament Theory of Contraction Figure 10.7b 33  Sliding Filament Theory of Contraction Figure 10.7c 34  Neuromuscular Junctions Muscle contraction begins when a motor neuron impulse stimulates an impulse in a muscle fiber The neuromuscular junction is the region where the motor neuron comes into close proximity to the muscle fiber 35  Components of the Neuromuscular Junction 1. Synaptic knob: Expanded tip of an axon 2. Synaptic vesicles: Membrane sacs filled with acetylcholine (ACh) 3. Motor end plate: Region of sarcolemma that has folds and indentations to increase the surface area covered by the synaptic knob 4. Synaptic cleft: Narrow space separating the synaptic knob and the motor end plate 5. ACh receptors: On the motor end plate; bind ACh 6. Acetylcholinesterase (AChE): Enzyme in the synaptic cleft that rapidly breaks down ACh 36  Neuromuscular Junction Figure 10.8 37  Physiology of Muscle Contraction 1. A nerve impulse causes ACh to be released into the synaptic cleft 2. ACh binds to receptors in the motor end plate initiating a muscle impulse along the sarcolemma and T-tubule membranes 3. Spread of the impulse down T-tubules causes calcium to leak out of terminal cisternae and into the sarcoplasm 38  Physiology of Muscle Contraction 4. Calcium ions bind to troponin, causing tropomyosin to uncover active sites on G- actin 5. Myosin heads bind to actin and form crossbridges 6. In the presence of ATP, myosin cycles through attachment, pivot, detach, and return events – ATP is also necessary for relaxation of the muscle fiber 39 Events in Muscle Contraction Figure 10.9 40  Motor Units A motor unit consists of a single motor neuron and the muscle fibers it controls A motor unit typically controls only some of the muscle fibers in an entire muscle Size of motor unit and degree of control provided are inversely related – Small motor units provide precise control, and vice versa Each muscle fiber obeys the all-or-none principle, which means a muscle fiber contracts completely or not at all When a motor unit is stimulated, all muscle fibers under its control will contract 41  A Motor Unit Figure 10.10 42  Muscle Tone Muscle tone refers to the constant tension in a resting muscle – Motor units are stimulated randomly to avoid fatigue 2 types of muscle contraction: 1.Isometric contraction: Length is constant; tension is changing 2.Isotonic contraction: Tension is constant; length is changing Concentric contraction: Muscle is shortening Eccentric contraction: Muscle is lengthening 43  Isometric VS Isotonic Contraction Figure 10.11 44  Types of Skeletal Muscle Fibers Skeletal muscles are comprised of a mixture of three different type of muscle fibers: 1. Slow oxidative (SO) fibers 2. Fast oxidative (FO) fibers 3. Fast glycolytic (FG) fibers The ratio of fiber types within a muscle determines the speed and sustainability of the contraction 45  Structural and Functional Characteristics of Different Types of Skeletal Muscle Fibers 46  Comparison of Fiber Types in Skeletal Muscle Figure 10.12 47 Distribution of Slow Oxidative, Fast Oxidative, and Fast Glycolytic Fibers Skeletal muscles usually contain all three muscle fiber types A single motor unit controls only muscle fibers of the same type Slow fibers dominate postural muscles, such as those in the back and calf, which contract almost continually There are no slow muscle fibers in muscles that require swift but brief contractions, such as those in the eye and hand 48  Skeletal Muscle Fiber Organization Muscle fibers are organized into fascicles within a muscle There are four different patterns of fascicle arrangements: 1. Circular 2. Parallel 3. Convergent 4. Pennate Unipennate Bipennate Multipennate 49 Skeletal Muscle Architecture 50 Exercise and Skeletal Muscle Muscle atrophy: A wasting of tissue that results in reduction of muscle size, tone, and power; can be caused by a lack of stimulation Muscle hypertrophy: An increase in muscle fiber size (not an increase in number of muscle fibers); results from repetitive stimulation of muscle fibers – Mitochondria increase in number, therefore the amount of ATP increases – Both myofibrils and myofilaments increase in number, all resulting in the muscle increasing in size 51 Levers and Joint Biomechanics A lever is an elongated, rigid object that rotates around a fixed point called a fulcrum Rotation occurs when an effort applied to one point of the lever exceeds a resistance located at some other point Three classes of levers in human body: – First-class levers – Second-class levers – Third-class levers 52  Classes of Levers Figure 10.13 53  Actions of Skeletal Muscles Agonist: Produces a specific movement when it contracts; also called a prime mover – Example: The triceps brachii is an agonist that causes forearm extension Antagonist: A muscle whose action opposes that of an agonist – Example: The biceps brachii is an antagonist to the triceps brachii Synergist: A muscle that assists the agonist in performing its action 54 The Naming of Skeletal Muscles Muscle names provide clues to their identification, and are named according to several criteria: 1. Muscle action 2. Specific body regions 3. Muscle attachments 4. Orientation of muscle fibers 5. Muscle shape and size 6. Muscle heads/tendons of origin 55  Muscle Naming Figure 10.14 56  Characteristics of Cardiac and Smooth Muscle 3 types of muscle in the human body: – Skeletal muscle – Cardiac muscle – Smooth muscle There are similarities and differences among the three types of muscle tissue 57  Cardiac Muscle Cardiac muscle cells are found within the heart wall and have the following qualities: – Striated – One or two nuclei – Form Y-shaped branches – Join other adjacent cells to form junctions termed intercalated discs comprised of gap junctions – Autorhythmic: Able to generate a muscle impulse without nervous stimulation – Under involuntary control 58  Cardiac Muscle Figure 10.15 59  Smooth Muscle Smooth muscle is found in the walls of viscera and blood vessels, and has several features of interest: – Short fusiform cells (widest in the middle and tapered at each end) – One centrally located nucleus – No striations – Thin filaments attached to dense bodies – Under involuntary control 60  Smooth Muscle Figure 10.16 61  Development of Skeletal Muscle 62 Figure 10.17 Muscle Tissue Types: General Comparison 63 Muscle Tissue Types: General Comparison 64