Essentials of Human Anatomy & Physiology PDF

Essentials of Human Anatomy & Physiology Thirteenth Edition Global Edition Chapter 6 The Muscular System Lecture Presentation by...

Essentials of Human Anatomy & Physiology Thirteenth Edition Global Edition Chapter 6 The Muscular System Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Muscular System Muscles are responsible for all types of body movement Three basic muscle types are found in the body 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Types (1 of 6) Skeletal and smooth muscle cells are elongated (muscle cell = muscle fiber) Contraction and shortening of muscles are due to the movement of microfilaments All muscles share some terminology – Prefixes myo- and mys- refer to “muscle” – Prefix sarco- refers to “flesh” Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (1 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (2 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Table 6.1 Comparison of Skeletal, Cardiac, and Smooth Muscles (3 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Types (2 of 6) Skeletal muscle – Most skeletal muscle fibers are attached by tendons to bones – Skeletal muscle cells are large, cigar-shaped, and multinucleate – Also known as striated muscle because of its obvious stripes – Also known as voluntary muscle because it is the only muscle tissue subject to conscious control Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Types (3 of 6) Skeletal muscle cells are surrounded and bundled by connective tissue – Endomysium—encloses a single muscle fiber – Perimysium—wraps around a fascicle (bundle) of muscle fibers – Epimysium—covers the entire skeletal muscle ▪ Fascia—on the outside of the epimysium Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.1 Connective Tissue Wrappings of Skeletal Muscle Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Types (4 of 6) The epimysium of skeletal muscle blends into a connective tissue attachment – Tendons—cordlike structures ▪ Mostly collagen fibers ▪ Often cross a joint because of their toughness and small size – Aponeuroses—sheetlike structures ▪ Attach muscles indirectly to bones, cartilages, or connective tissue coverings Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Types (5 of 6) Smooth muscle – No striations – Involuntary—no conscious control – Found mainly in the walls of hollow visceral organs (such as stomach, urinary bladder, respiratory passages) – Spindle-shaped fibers that are uninucleate – Contractions are slow and sustained Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.2a Arrangement of Smooth and Cardiac Muscle Cells Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Types (6 of 6) Cardiac muscle – Striations – Involuntary – Found only in the walls of the heart – Uninucleate – Branching cells joined by gap junctions called intercalated discs – Contracts at a steady rate set by pacemaker Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.2b Arrangement of Smooth and Cardiac Muscle Cells Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Functions Whereas all muscle types produce movement, skeletal muscle has three other important roles: – Maintain posture and body position – Stabilize joints – Generate heat Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Microscopic Anatomy of Skeletal Muscle (1 of 6) Sarcolemma—specialized plasma membrane Myofibrils—long organelles inside muscle cell – Light (I) bands and dark (A) bands give the muscle its striated (banded) appearance Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.3a Anatomy of a Skeletal Muscle Fiber (Cell) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Microscopic Anatomy of Skeletal Muscle (2 of 6) Banding pattern of myofibrils – I band = light band ▪ Contains only thin filaments ▪ Z disc is a midline interruption – A band = dark band ▪ Contains the entire length of the thick filaments ▪ H zone is a lighter central area ▪ M line is in center of H zone Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.3b Anatomy of a Skeletal Muscle Fiber (Cell) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Microscopic Anatomy of Skeletal Muscle (3 of 6) Sarcomere—contractile unit of a muscle fiber – Structural and functional unit of skeletal muscle Organization of the sarcomere – Myofilaments produce banding (striped) pattern ▪ Thick filaments = myosin filaments ▪ Thin filaments = actin filaments Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Microscopic Anatomy of Skeletal Muscle (4 of 6) Thick filaments = myosin filaments – Composed mostly of the protein myosin – Contain ATPase enzymes to split ATP to release energy for muscle contractions – Possess projections known as myosin heads – Myosin heads are known as cross bridges when they link thick and thin filaments during contraction Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Microscopic Anatomy of Skeletal Muscle (5 of 6) Thin filaments = actin filaments – Composed mostly of the contractile protein actin – Actin is anchored to the Z disc At rest, within the A band there is a zone that lacks actin filaments called the H zone During contraction, H zones disappear as actin and myosin filaments overlap Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.3c Anatomy of a Skeletal Muscle Fiber (Cell) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Microscopic Anatomy of Skeletal Muscle (6 of 6) Sarcoplasmic reticulum (SR) – Specialized smooth endoplasmic reticulum – Surrounds the myofibril – Stores and releases calcium ▪ Calcium provides the final “go” for contraction Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Stimulation and Contraction of Single Skeletal Muscle Cells Special functional properties of skeletal muscles – Irritability (also called responsiveness)—ability to receive and respond to a stimulus – Contractility—ability to forcibly shorten when an adequate stimulus is received – Extensibility—ability of muscle cells to be stretched – Elasticity—ability to recoil and resume resting length after stretching Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Nerve Stimulus and Action Potential (1 of 7) Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract Motor unit—one motor neuron and all the skeletal muscle cells stimulated by that neuron Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.4a Motor Units Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.4b Motor Units Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Nerve Stimulus and Action Potential (2 of 7) Neuromuscular junction – Association site of axon terminal of the motor neuron and sarcolemma of a muscle Neurotransmitter – Chemical released by nerve upon arrival of nerve impulse in the axon terminal – Acetylcholine (ACh) is the neurotransmitter that stimulates skeletal muscle Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Nerve Stimulus and Action Potential (3 of 7) Synaptic cleft – Gap between nerve and muscle filled with interstitial fluid – Although very close, the nerve and muscle do not make contact Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Nerve Stimulus and Action Potential (4 of 7) Events at the neuromuscular junction: – Step 1: Nerve impulse reaches the axon terminal of the motor neuron – Step 2: Calcium channels open, and calcium ions enter the axon terminal – Step 3: Calcium ion entry causes some synaptic vesicles to release acetylcholine (ACh) – Step 4: ACh diffuses across the synaptic cleft and attaches to receptors on the sarcolemma of the muscle cell Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Nerve Stimulus and Action Potential (5 of 7) – Step 5: If enough ACh is released, the sarcolemma becomes temporarily more permeable to sodium ions (Na+ ) ▪ More sodium ions enter than potassium ions leave ▪ Entry of sodium ions produces an imbalance in which interior has more positive ions (depolarization), thereby opening more Na+ channels Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Nerve Stimulus and Action Potential (6 of 7) – Step 6: Depolarization opens more sodium channels that allow sodium ions to enter the cell ▪ An action potential is created ▪ Once begun, the action potential is unstoppable ▪ Conducts the electrical impulse from one end of the cell to the other – Step 7: Acetylcholinesterase (AChE) breaks down acetylcholine into acetic acid and choline ▪ AChE ends muscle contraction ▪ A single nerve impulse produces only one contraction Copyright © 2022 Pearson Education, Ltd. All Rights Reserved The Nerve Stimulus and Action Potential (7 of 7) Cell returns to its resting state when: 1. Potassium ions (K + ) diffuse out of the cell 2. Sodium-potassium pump moves sodium and potassium ions back to their original positions Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (1 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (2 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (3 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (4 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (5 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (6 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (7 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.5 Events at the Neuromuscular Junction (8 of 8) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.6 Comparing the Action Potential to a Flame Consuming a Dry Twig Copyright © 2022 Pearson Education, Ltd. All Rights Reserved A&P Flix : Events at the Neuromuscular Junction https://mediaplayer.pearsoncmg.com/assets/apf-events-at-the-neuromuscular-junction Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Mechanism of Muscle Contraction: The Sliding Filament Theory What causes filaments to slide? – Calcium ions (Ca2+ ) bind regulatory proteins on thin filaments and expose myosin-binding sites, allowing the myosin heads on the thick filaments to attach – Each cross bridge pivots, causing the thin filaments to slide toward the center of the sarcomere – Contraction occurs, and the cell shortens – During a contraction, a cross bridge attaches and detaches several times – ATP provides the energy for the sliding process, which continues as long as calcium ions are present Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.7a Schematic Representation of Contraction Mechanism: The Sliding Filament Theory Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.7b Schematic Representation of Contraction Mechanism: The Sliding Filament Theory Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.7c Schematic Representation of Contraction Mechanism: The Sliding Filament Theory Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.8 Diagrammatic Views of a Sarcomere Copyright © 2022 Pearson Education, Ltd. All Rights Reserved A&P Flix : The Cross Bridge Cycle https://mediaplayer.pearsoncmg.com/assets/apf-cross-bridge-cycle Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Contraction of a Skeletal Muscle as a Whole (1 of 7) Graded responses – Graded responses are different degrees of skeletal muscle shortening – Muscle fiber contraction is “all-or-none,” meaning the muscle fiber (not the whole muscle) will contract to its fullest extent when stimulated adequately – Within a whole skeletal muscle, not all fibers may be stimulated during the same interval – Different combinations of muscle fiber contractions may give differing responses Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Contraction of a Skeletal Muscle as a Whole (2 of 7) Graded responses can be produced in two ways – By changing the frequency of muscle stimulation – By changing the number of muscle cells being stimulated at one time Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Contraction of a Skeletal Muscle as a Whole (3 of 7) Muscle response to increasingly rapid stimulation – Muscle twitch ▪ Single, brief, jerky contraction ▪ Not a normal muscle function Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.9a A Whole Muscle’s Response to Different Stimulation Rates Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Contraction of a Skeletal Muscle as a Whole (4 of 7) Muscle response to increasingly rapid stimulation – In most types of muscle activity, nerve impulses are delivered at a rapid rate – As a result, contractions are “summed” (added) together, and one contraction is immediately followed by another Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.9b A Whole Muscle’s Response to Different Stimulation Rates Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Contraction of a Skeletal Muscle as a Whole (5 of 7) Muscle response to increasingly rapid stimulation – When stimulations become more frequent, muscle contractions get stronger and smoother – The muscle now exhibits unfused (incomplete) tetanus Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.9c A Whole Muscle’s Response to Different Stimulation Rates Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Contraction of a Skeletal Muscle as a Whole (6 of 7) Muscle response to increasingly rapid stimulation – Fused (complete) tetanus is achieved when the muscle is stimulated so rapidly that no evidence of relaxation is seen – Contractions are smooth and sustained Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.9d A Whole Muscle’s Response to Different Stimulation Rates Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Contraction of a Skeletal Muscle as a Whole (7 of 7) Muscle response to stronger stimuli – Muscle force depends upon the number of fibers stimulated – Contraction of more fibers results in greater muscle tension – When all motor units are active and stimulated, the muscle contraction is as strong as it can get Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Providing Energy for Muscle Contraction (1 of 5) ATP – Only energy source that can be used to directly power muscle contraction – Stored in muscle fibers in small amounts that are quickly used up – After this initial time, other pathways must be utilized to produce ATP Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Concept Link Recall that ATP can be compared to a tightly coiled spring that is ready to uncoil with tremendous energy when the “catch” is released (Chapter 2, p. 76). Remember that all bonds store energy and that the “catch” in this example is one of the characteristic high- energy phosphate bonds in ATP. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Providing Energy for Muscle Contraction (2 of 5) Three pathways to regenerate ATP 1. Direct phosphorylation of ADP by creatine phosphate 2. Aerobic pathway 3. Anaerobic glycolysis and lactic acid formation Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Providing Energy for Muscle Contraction (3 of 5) Direct phosphorylation of ADP by creatine phosphate (CP)—fastest – Muscle cells store CP, a high-energy molecule – After ATP is depleted, ADP remains – CP transfers a phosphate group to ADP to regenerate ATP – CP supplies are exhausted in less than 15 seconds – 1 ATP is produced per CP molecule Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.10a Methods of Regenerating ATP During Muscle Activity Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Providing Energy for Muscle Contraction (4 of 5) Aerobic respiration – Supplies ATP at rest and during light/moderate exercise – A series of metabolic pathways, called oxidative phosphorylation, use oxygen and occur in the mitochondria – Glucose is broken down to carbon dioxide and water, releasing energy (about 32 ATP) – Slower reaction; requires continuous delivery of oxygen and nutrients Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.10b Methods of Regenerating ATP During Muscle Activity Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Providing Energy for Muscle Contraction (5 of 5) Anaerobic glycolysis and lactic acid formation – Reaction that breaks down glucose without oxygen – Glucose is broken down to pyruvic acid to produce about 2 ATP – Pyruvic acid is converted to lactic acid Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.10c Methods of Regenerating ATP During Muscle Activity Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Fatigue and Oxygen Deficit If muscle activity is strenuous and prolonged, muscle fatigue occurs Suspected factors that contribute to muscle fatigue include: – Ion imbalances (Ca2+ , K + ) – Oxygen deficit and lactic acid accumulation – Decrease in energy (ATP) supply After exercise, the oxygen deficit is repaid by rapid, deep breathing Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Types of Muscle Contractions Isotonic contractions – Myofilaments are able to slide past each other during contractions – The muscle shortens, and movement occurs – Example: bending the knee; lifting weights, smiling Isometric contractions – Muscle filaments are trying to slide, but the muscle is pitted against an immovable object – Tension increases, but muscles do not shorten – Example: pushing your palms together in front of you Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Muscle Tone Muscle tone – State of continuous partial contractions – Result of different motor units being stimulated in a systematic way – Muscle remains firm, healthy, and constantly ready for action Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Effect of Exercise on Muscles Exercise increases muscle size, strength, and endurance – Aerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue ▪ Makes body metabolism more efficient ▪ Improves digestion, coordination – Resistance (isometric) exercise (weight lifting) increases muscle size and strength ▪ Individual muscle fibers enlarge Copyright © 2022 Pearson Education, Ltd. All Rights Reserved Figure 6.11 The Effects of Aerobic Training Versus Strength Training Copyright © 2022 Pearson Education, Ltd. All Rights Reserved