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Bell Ringer 9.01 What are the 3 types of muscle tissue? 9.02 Which type primarily makes up the “Muscular System”? 9.03 How many of these muscles does the human body have? © 2016 Pearson Education, Inc.
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© 2016 Pearson Education, Inc.
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I. Overview of Muscle Tissue
A. Terminology 1. Terminologies: Myo, mys, and sarco are prefixes for muscle a. Ex. sarcoplasm: muscle cell cytoplasm 2. Three types of muscle tissue a. Skeletal b. Cardiac c. Smooth i. Only skeletal and smooth muscle cells are elongated and referred to as muscle fibers © 2016 Pearson Education, Inc.
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B. Types of Muscle Tissue 1. Skeletal muscle
a. Skeletal muscle fibers are longest of all muscle and have striations (stripes) b. Also called voluntary muscle i. can be consciously controlled c. Contract rapidly; tire easily; powerful © 2016 Pearson Education, Inc.
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a. Cardiac muscle tissue is found only in heart
i. Makes up bulk of heart walls b. Striated c. Involuntary i. cannot be controlled consciously © 2016 Pearson Education, Inc.
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3. Smooth muscle a. Smooth muscle tissue: found in walls of hollow organs i. Ex: stomach, bladder, & airways b. Not striated c. Involuntary i. cannot be controlled consciously © 2016 Pearson Education, Inc.
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Table 9.3-1 Comparison of Skeletal, Cardiac, and Smooth Muscle
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C. Characteristics of Muscle Tissue
1. All muscles share four main characteristics: a. Excitability (responsiveness) i. ability to receive & respond to stimuli b. Contractility i. ability to shorten forcibly when stimulated c. Extensibility i. ability to be stretched d. Elasticity i. ability to recoil to resting length © 2016 Pearson Education, Inc.
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1. Four important functions
D. Muscle Functions 1. Four important functions a. Produce movement i. Ex. walking, digesting food, pumping blood b. Maintain posture and body position c. Stabilize joints d. Generate heat as they contract © 2016 Pearson Education, Inc.
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Bell Ringer 9.04 What is another name for a muscle cell? 9.05 What are the 3 main prefixes for muscle? © 2016 Pearson Education, Inc.
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II. Skeletal Muscle Anatomy
A. Nerve and Blood Supply 1. Each muscle has a nerve, artery, & veins a. Consciously controlled skeletal muscle has nerves supplying every fiber to control activity 2. Contracting muscle fibers require huge amounts of oxygen and nutrients a. Also need waste products removed quickly © 2016 Pearson Education, Inc.
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B. Connective Tissue Sheaths 1
B. Connective Tissue Sheaths 1. Each skeletal muscle, as well as each muscle fiber, is covered in connective tissue a. Support cells and reinforce whole muscle © 2016 Pearson Education, Inc.
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2. Sheaths from external to internal:
a. Epimysium i. surrounds entire muscle b. Perimysium: i. surrounds fascicles (groups of muscle fibers) c. Endomysium i. surrounds each muscle fiber © 2016 Pearson Education, Inc.
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Perimysium wrapping a fascicle
Figure 9.1 Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium. Epimysium Epimysium Bone Perimysium Tendon Endomysium Muscle fiber in middle of a fascicle Blood vessel Perimysium wrapping a fascicle Endomysium (between individual muscle fibers) Muscle fiber Fascicle Perimysium © 2016 Pearson Education, Inc.
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1. Muscles attach to bone in at least two places
C. Attachments 1. Muscles attach to bone in at least two places a. Insertion i. attachment to movable bone b. Origin i. attachment to immovable or less movable bone © 2016 Pearson Education, Inc.
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Epimysium Bone Tendon Blood vessel Perimysium wrapping a fascicle
Figure 9.1a Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium. Epimysium Bone Tendon Blood vessel Perimysium wrapping a fascicle Endomysium (between individual muscle fibers) Muscle fiber Fascicle Perimysium © 2016 Pearson Education, Inc.
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Table 9.1-1 Structure and Organizational Levels of Skeletal Muscle
© 2016 Pearson Education, Inc.
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Bell Ringer 9.06 What structures are found inside a muscle fiber? 9.07 What is a group of muscle fibers called? © 2016 Pearson Education, Inc.
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III. Muscle Fiber Microanatomy and Sliding Filament Model
A. Skeletal muscle fibers are long, cylindrical cells that contain multiple nuclei 1. Sarcolemma a. muscle fiber plasma membrane 2. Sarcoplasm a. muscle fiber cytoplasm 3. Modified organelles a. Myofibrils b. Sarcoplasmic reticulum c. T tubules © 2016 Pearson Education, Inc.
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1. Densely packed, rodlike elements
B. Myofibrils 1. Densely packed, rodlike elements a. Single muscle fiber can contain 1000s b. Accounts for ~80% of muscle cell volume © 2016 Pearson Education, Inc.
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Figure 9.2b Microscopic anatomy of a skeletal muscle fiber.
Diagram of part of a muscle fiber showing the myofibrils. One myofibril extends from the cut end of the fiber. Sarcolemma Mitochondrion Myofibril Dark A band Light I band Nucleus © 2016 Pearson Education, Inc.
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2. Striations a. stripes formed from repeating series of dark and light bands along length of each myofibril b. A bands: dark regions i. H zone: lighter region in middle of dark A band ii. M line: line of protein (myomesin) that bisects H zone vertically c. I bands: lighter regions i. Z disc (line): sheet of proteins on midline of I band © 2016 Pearson Education, Inc.
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Figure 9.2c Microscopic anatomy of a skeletal muscle fiber.
Thin (actin) filament Z disc H zone Z disc Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere extends from one Z disc to the next. Thick (myosin) filament I band A band I band M line Sarcomere © 2016 Pearson Education, Inc.
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Figure 9.2a Microscopic anatomy of a skeletal muscle fiber.
Photomicrograph of portions of two isolated muscle fibers (700×). Notice the obvious striations (alternating dark and light bands). Nuclei Dark A band Light I band Fiber © 2016 Pearson Education, Inc.
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a. Smallest contractile unit (functional unit) of muscle fiber
3. Sarcomere a. Smallest contractile unit (functional unit) of muscle fiber b. Contains A band with half of an I band at each end i. area between Z discs c. Individual sarcomeres align end to end © 2016 Pearson Education, Inc.
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Figure 9.2c Microscopic anatomy of a skeletal muscle fiber.
Thin (actin) filament Z disc H zone Z disc Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere extends from one Z disc to the next. Thick (myosin) filament I band A band I band M line Sarcomere © 2016 Pearson Education, Inc.
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4. Myofilaments (Muscle Proteins)
a. Actin myofilaments: thin filaments i. Extend across I band and partway in A band ii. Anchored to Z discs iii. Tropomyosin and troponin: regulatory proteins bound to actin (act as “body guards”) b. Myosin myofilaments: thick filaments i. Extend length of A band ii. Connected at M line © 2016 Pearson Education, Inc.
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C. Sarcoplasmic Reticulum and T Tubules 1
C. Sarcoplasmic Reticulum and T Tubules 1. Sarcoplasmic reticulum (SR) a. network of smooth endoplasmic reticulum tubules surrounding each myofibril b. Stores and releases Ca2+ © 2016 Pearson Education, Inc.
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2. T tubules a. Tube formed by protrusion of sarcolemma deep into cell interior i. Increase muscle fiber’s surface area ii. Allow electrical nerve transmissions to reach deep into interior of each muscle fiber b. When an electrical impulse passes by, T tubule proteins change shape, causing SR proteins to change shape, causing release of calcium into cytoplasm © 2016 Pearson Education, Inc.
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Part of a skeletal muscle fiber (cell) I band A band I band Z disc
Figure 9.5 Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle. Part of a skeletal muscle fiber (cell) I band A band I band Z disc H zone Z disc M line Sarcolemma Myofibril Triad: • T tubule • Terminal cisterns of the SR (2) Sarcolemma Tubules of the SR Myofibrils Mitochondria © 2016 Pearson Education, Inc.
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D. Sliding Filament Model of Contraction
1. Contraction: the activation of cross bridges to generate force a. Contraction ends when cross bridges become inactive b. When nervous system stimulates muscle fiber, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) process to begin © 2016 Pearson Education, Inc.
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Figure 9.6-1 Sliding filament model of contraction.
Fully relaxed sarcomere of a muscle fiber Z H Z l A l © 2016 Pearson Education, Inc.
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b. Neither thick nor thin filaments change length, just overlap more
2. Sliding filament model of contraction states that during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more a. In the relaxed state, thin and thick filaments overlap only slightly at ends of A band b. Neither thick nor thin filaments change length, just overlap more © 2016 Pearson Education, Inc.
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b. Z discs are pulled toward M line c. I bands shorten
3. Cross bridge attachments form and break several times, each time pulling thin filaments a little closer toward center of sarcomere in a ratcheting action a. Causes shortening of muscle fiber b. Z discs are pulled toward M line c. I bands shorten d. Z discs become closer e. H zones disappear f. A bands move closer to each other © 2016 Pearson Education, Inc.
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Figure 9.6-1 Sliding filament model of contraction.
Fully relaxed sarcomere of a muscle fiber Z H Z l A l © 2016 Pearson Education, Inc.
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Figure 9.6-2 Sliding filament model of contraction.
Fully contracted sarcomere of a muscle fiber Z Z l A l © 2016 Pearson Education, Inc.
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Bell Ringer 9.08 What are the two myofilaments found within myofibrils? 9.09 What ion does the SR store and release? 9.10 What causes the SR to release this ion? © 2016 Pearson Education, Inc.
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IV. Whole Muscle Contraction
Motor unit 1. consists of the motor neuron and all muscle fibers (four to several hundred) it supplies a. Smaller the fiber number, the greater the fine control 2. Stimulation of a single motor unit causes only weak contraction of entire muscle © 2016 Pearson Education, Inc.
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Branching axon terminals form neuromuscular junctions, one per muscle
Figure 9.10 A motor unit consists of one motor neuron and all the muscle fibers it innervates. Spinal cord Axon terminals at neuromuscular junctions Branching axon to motor unit Motor unit 1 Motor unit 2 Nerve Motor neuron cell body Motor neuron axon Muscle Muscle fibers Branching axon terminals form neuromuscular junctions, one per muscle fiber (photomicrograph 330×). Axons of motor neurons extend from the spinal cord to the muscle. At the muscle, each axon divides into a number of axon terminals that form neuromuscular junctions with muscle fibers scattered throughout the muscle. © 2016 Pearson Education, Inc.
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B. Graded Muscle Responses
1. Normal muscle contraction is relatively smooth, and strength varies with needs 2. Graded muscle responses vary strength of contraction for different demands a. Responses are graded by: i. Changing frequency of stimulation ii. Changing strength of stimulation © 2016 Pearson Education, Inc.
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Figure 9.12a A muscle’s response to changes in stimulation frequency.
Tension Maximal tension of a single twitch Contraction Relaxation Stimulus 100 200 300 Time (ms) Single stimulus: single twitch. A single stimulus is delivered. The muscle contracts and relaxes. © 2016 Pearson Education, Inc.
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Figure 9.12b A muscle’s response to changes in stimulation frequency.
Partial relaxation Tension Stimuli 100 200 300 Time (ms) Low stimulation frequency: unfused (incomplete) tetanus. If another stimulus is applied before the muscle relaxes completely, then more tension results. This is wave (or temporal) summation and results in unfused (or incomplete) tetanus. © 2016 Pearson Education, Inc.
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Figure 9.12c A muscle’s response to changes in stimulation frequency.
Tension Stimuli 100 200 300 Time (ms) High stimulation frequency: fused (complete) tetanus. At higher stimulus frequencies, there is no relaxation at all between stimuli. This is fused (complete) tetanus. © 2016 Pearson Education, Inc.
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Proportion of motor units excited
Figure 9.13 Relationship between stimulus intensity (graph at top) and muscle tension (tracing below). Stimulus strength Maximal stimulus Stimulus voltage Threshold stimulus 1 2 3 4 5 6 7 8 9 10 Stimuli to nerve Proportion of motor units excited Strength of muscle contraction Maximal contraction Tension Time (ms) © 2016 Pearson Education, Inc.
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Figure 9.14 The size principle of recruitment.
Skeletal muscle fibers Tension Time Motor unit 1 recruited (small fibers) Motor unit 2 recruited (medium fibers) Motor unit 3 recruited (large fibers) © 2016 Pearson Education, Inc.
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C. Types of Muscle Contractions 1
C. Types of Muscle Contractions 1. Isotonic contractions: muscle changes in length and moves load a. Concentric contractions: muscle shortens and does work i. Example: biceps contract to pick up a book b. Eccentric contractions: muscle lengthens and generates force i. Example: laying a book down causes biceps to lengthen while generating a force © 2016 Pearson Education, Inc.
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Figure 9.15a-1 Isotonic (concentric) and isometric contractions.
Isotonic contraction (concentric) On stimulation, muscle develops enough tension (force) to lift the load (weight). Once the resistance is overcome, the muscle shortens, and the tension remains constant for the rest of the contraction. Tendon Muscle contracts (isotonic contraction) 3 kg Tendon 3 kg © 2016 Pearson Education, Inc.
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Figure 9.15a-2 Isotonic (concentric) and isometric contractions.
Isotonic contraction (concentric) 8 Amount of resistance Muscle relaxes 6 Tension developed (kg) 4 Peak tension developed 2 Muscle stimulus Resting length 100 90 Muscle length (percent of resting length) 80 70 Time (ms) © 2016 Pearson Education, Inc.
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2. Isometric contractions
a. Load is greater than the maximum tension muscle can generate, so muscle neither shortens nor lengthens © 2016 Pearson Education, Inc.
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Figure 9.15b-1 Isotonic (concentric) and isometric contractions.
Muscle is attached to a weight that exceeds the muscle’s peak tension-developing capabilities. When stimulated, the tension increases to the muscle’s peak tension-developing capability, but the muscle does not shorten. Muscle contracts (isometric contraction) 6 kg 6 kg © 2016 Pearson Education, Inc.
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Figure 9.15b-2 Isotonic (concentric) and isometric contractions.
8 Amount of resistance 6 Muscle relaxes Tension developed (kg) 4 Peak tension developed 2 Muscle stimulus Resting length 100 90 Muscle length (percent of resting length) 80 70 Time (ms) © 2016 Pearson Education, Inc.
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V. Adaptation to Exercise
Aerobic (endurance) exercise 1. jogging, swimming, biking leads to increased: a. Muscle capillaries b. Number of mitochondria 2. Results in greater endurance, strength, and resistance to fatigue © 2016 Pearson Education, Inc.
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Resistance Exercise B. Resistance exercise (typically anaerobic),
1. weight lifting or isometric exercises, leads to: a. Increased mitochondria, myofilaments, and connective tissue b. Increased muscle strength and size © 2016 Pearson Education, Inc.
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