Muscle Tissue PDF

Muscle Tissue Outline Overview & properties of Muscle Tissue Characteristics of Skeletal Muscle Tissue Contraction of Skeletal Muscle Fibers Types of Skeletal Muscle Fibers Skeletal Muscle Fiber Organization Exercise Cardiac & Smooth Muscle  Tissues Four types of tissues: Epithel...

Muscle Tissue Outline Overview & properties of Muscle Tissue Characteristics of Skeletal Muscle Tissue Contraction of Skeletal Muscle Fibers Types of Skeletal Muscle Fibers Skeletal Muscle Fiber Organization Exercise Cardiac & Smooth Muscle  Tissues Four types of tissues: Epithelial tissue – covering Connective tissue – support Muscle tissue – movement Nervous tissue – control Overview-Muscle Tissue Fibrous Muscle is made up of many cells shaped like fibers Not elastic or collagen fiber, but fiber shaped living cells Nearly half of body’s mass Can transform chemical energy (ATP) into directed mechanical energy, which is capable of exerting force  Types of Muscle Tissue Terminologies: Myo, mys, sarco are prefixes for muscle Example: sarcoplasm: muscle cell cytoplasm Three type of muscle tissue Skeletal Cardiac Smooth Only skeletal and smooth muscle cells are elongated and referred to as muscle fibers There are over 700 skeletal muscles and together they form the muscular system Properties of Muscle Tissue 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 Three types of muscle Skeletal Attached to bone striated, voluntary, myofibers Cardiac Found in the heart striated, involuntary, branched, cardiocytes Smooth Lines hollow organs nonstriated, involuntary, fusiform in shape (spindle) Muscular System Skeletal Muscle—Characteristics? Skeletal Muscle Tissue 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 Each skeletal muscle is considered an organcontains all 4 tissue types Skeletal Muscle Tissue Also called voluntary muscle: can be consciously controlled Contract rapidly; tire easily; powerful Key words for skeletal muscle: skeletal, striated, and voluntary Functions of Skeletal Muscle Tissue 1. Produce movement: responsible for all locomotion and manipulation Example: walking, digesting, pumping blood 2. Maintain posture and body position 3. Stabilize joints 4. Generate heat as they contract—temperature regulation 5. Storage and movements of materials Gross 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 (actin & myosin) Cells of a skeletal muscle are called muscle fibers Levels of Muscle Structure Fascicles – bundle of muscle fibers Fibers (muscle fiber) – muscle cell Fibrils (Myofibrils) – bundles of myofilaments Filaments (myofilaments) Actin – thin filament Myosin – thick filament Gross Anatomy of Skeletal Muscle Organization of Connective Tissue Each muscle has three layers of concentric connective tissue composed of collagen and elastic fibers Epimysium surrounds muscle organ; dense irregular connective tissue Deep fascia: surrounds each muscle and separates muscles from each other Superficial fascia separates muscle from skin Perimysium sheathes bundles of muscle fibers (fascicles); dense irregular connective tissue Epimysium and perimysium contain blood vessels and nerves Endomysium covers individual muscle fiber; areolar connective tissue Electrically insulates each muscle fiber Tendons or aponeuroses attach muscle to bone or muscle Organization of Connective Tissue Each muscle has three layers of concentric connective tissue composed of collagen and elastic fibers Epimysium surrounds muscle organ; dense irregular connective tissue Deep fascia: surrounds each muscle and separates muscles from each other Superficial fascia separates muscle from skin Perimysium sheathes bundles of muscle fibers (fascicles); dense irregular connective tissue Epimysium and perimysium contain blood vessels and nerves Endomysium covers individual muscle fiber; areolar connective tissue Electrically insulates each muscle fiber 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 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 Skeletal Muscle Fibers Long, cylindrical cells that contain multiple nuclei Contain many components: Sarcolemma (cell membrane) Sarcoplasm (muscle cell cytoplasm) Sarcoplasmic reticulum (modified ER) Many glycosomes for glycogen storage, as well as myoglobin Sarcomeres—regular arrangement of myofibrils Transverse tubules (T-tubules) and myofibrils aid in contraction T tubules: deep invaginations of the sarcolemma that extend into the sarcoplasm; form a network of tubules that enables muscles impulses to spread quickly internally Terminal cisternae: Blind sacs of the sarcoplasmic reticulum Two terminal cisternae + T-tubule=triad Skeletal Muscle Fibers Long, cylindrical cells that contain multiple nuclei Contain many components: Sarcolemma (cell membrane) Sarcoplasm (muscle cell cytoplasm) Sarcoplasmic reticulum (modified ER) Many glycosomes for glycogen storage, as well as myoglobin Sarcomeres—regular arrangement of myofibrils Transverse tubules (T-tubules) and myofibrils aid in contraction T tubules: deep invaginations of the sarcolemma that extend into the sarcoplasm; form a network of tubules that enables muscles impulses to spread quickly internally Terminal cisternae: Blind sacs of the sarcoplasmic reticulum Two terminal cisternae + T-tubule=triad Myofibrils & Myofilaments Myofibrils: Cylindrical structures that extend the entire length of the cell Have the ability to shorten, resulting in contraction of the muscle fiber Myofilaments: Short bundles of proteins that comprise a myofibril; do not run into length of muscle fiber but are organized into repetitive groupings On myofibrils there are thick and thin filaments, which are important—responsible for muscle contraction Thick filaments contain myosin Thin filaments contain actin  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 Thin filaments: 5-6 nm in diameter Comprised of two strands (F actin) of spherical (G actin) molecules twisted around each other Two regulatory proteins are also part of the thin filament: Tropomyosin Troponin 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 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 https://www.youtube.com/ watch?v=P1zD_MpTo0M https://www.youtube.com/ watch?v=XoP1diaXVCI 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 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 Motor Unit Somatic motor neuron will innervate 3-1000 muscle fibers Motor Unit: Complex consisting of nerve fiber and muscle fiber Neuromuscular Junction 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 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 Cross bridge formation: high energy myosin heads attaches to thin filament Power stroke: myosin head pivots and pulls thin filament towards m line Cross bridge detachment—ATP attaches to myosin head and cross bridge detaches “Cocking” of myosin head—energy from hydolysis of ATP cocks the myosin head into high-energy state Video Summary  https://www.youtube.com/watch?v=8Hhttps://www.youtube.com/watch?v=sI Video Summary u5W_tFXLs H8uOg8ddw Animation W/ Text 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 fibers contracts completely or not at all When a motor unit is stimulated, all muscle fibers under its control will contract Motor Units Axon terminals at Spinal cord neuromuscular junctions Motor Motor Branching axon unit 1 unit 2 to motor unit Nerve Motor neuron cell body Motor neuron axon Muscle Muscle fibers (b) Branching axon terminals form neuromuscular (a) Axons of motor neurons extend from the spinal cord to junctions, one the muscle. There each axon divides into a number of per muscle fiber axon terminals that form neuromuscular junctions with (photomicrograph muscle fibers scattered throughout the muscle. 110). Figure 10.10 Muscle Tone Muscle tone refers to the constant tension in a resting muscle Motor units are stimulated randomly to avoid fatigue Two 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 Review Walk me through muscle contraction, step by step, beginning with the release of acetylcholine at the neuromuscular junction Types of Skeletal Muscle Fibers Skeletal muscles are comprised of a mixture of three different types 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 Types of Skeletal Muscle Fibers Skeletal muscles are comprised of a mixture of three different types 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 Distribution of Slow Oxidative, Fast Oxidative, and Fast Glycolytic Fibers Skeletal muscles usually contain all 3 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 Outline Overview & properties of Muscle Tissue Characteristics of Skeletal Muscle Tissue Contraction of Skeletal Muscle Fibers Types of Skeletal Muscle Fibers Skeletal Muscle Fiber Organization Exercise Cardiac & Smooth Muscle 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  Types of Muscle Tissue Terminologies: Myo, mys, sarco are prefixes for muscle Example: sarcoplasm: muscle cell cytoplasm Three type of muscle tissue Skeletal Cardiac Smooth Only skeletal and smooth muscle cells are elongated and referred to as muscle fibers There are over 700 skeletal muscles and together they form the muscular system  Cardiac Muscle Cardiac muscle tissue is found only in heart Makes up bulk of heart walls Striated One or two nuclei Involuntary: cannot be controlled consciously Contracts at steady rate due to heart’s own pacemaker, but nervous system can increase rate Join other adjacent cells to form junctions termed intercalated discs compared of gap junctions Autorhythmic: able to generate a muscle impulse without nervous stimulation Key words for cardiac muscle: cardiac, striated, involuntary Smooth Muscle Found in walls of hollow organs & blood vessels Examples: stomach, urinary bladder, airways Not striated: Lacks sarcomeres; thin filaments anchored to dense bodies Short, fusiform cells (widest in middle & tapered at end end) One centrally located nucleus No striations Thin filaments attached to dense bodies Involuntary: Cannot be controlled consciously Can contract on its own without nervous system stimulation Nervous system exerts influence Table 10.2 (1 of 3) Supplemental Step by step review—w/ text and animati ons Video Review—Neuromuscular Junction Video Review—Depolarization & E-C Coupling Video Review—Cross Bridge Cycle