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Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
9Anatomy of Muscles and Muscle Tissue
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Muscle Overview
The three types of muscle tissue are skeletal, cardiac, and smooth
These types differ in structure, location, function, and means of activation
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Muscle Similarities
Skeletal and smooth muscle cells are elongated and are called muscle fibers
Muscle contraction depends on two kinds of myofilaments – actin and myosin
Muscle terminology is similar:
Sarcolemma – muscle plasma membrane
Sarcoplasm – cytoplasm of a muscle cell
Prefixes – myo, mys, and sarco all refer to muscle
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Skeletal Muscle Tissue
Packaged in skeletal muscles that attach to and cover the bony skeleton
Has obvious stripes called striations
Is controlled voluntarily (i.e., by conscious control)
Contracts very rapidly, but tires easily
Is responsible for overall body motility
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Cardiac Muscle Tissue
Occurs only in the heart
Is striated like skeletal muscle but is involuntary (controlled by the autonomic nervous system)
Contracts at a fairly steady rate set by the heart’s pacemaker cells
Neural controls allow the heart to respond to changes in bodily needs
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Cardiac Muscle Cells
A. General Features
1. involuntary muscle
2. one, centrally located nucleus
3. mitochondria larger and more numerous
B. Structure of Tissue
1. muscle fibers branch and interconnect
2. intercalated disc - thickening of sarcolemma
3. cells connected by gap junctions
a. allow passage of ions like Calcium
b. makes adjacent cells electrically linked
c. allows for rhythmic, domino-like contraction
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Smooth Muscle Tissue
Found in the walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages
Forces food and other substances through internal body channels
It is not striated and is involuntary (controlled by the autonomic nervous system)
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Smooth Muscle
Composed of spindle-shaped fibers with a diameter of 2-10 m and lengths of several hundred m
Lack the coarse connective tissue sheaths of skeletal muscle, but have fine endomysium
Organized into two layers (longitudinal and circular) of closely apposed fibers
Found in walls of hollow organs (except the heart)
Peristalsis – alternating contractions and relaxations of smooth muscles that mix and squeeze substances through the lumen of hollow organs
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Smooth Muscle
Figure 9.24
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Smooth Muscle Cells
A. General Features
1. non-striated
2. 5-10 um in diameter; 30-200 um long
3. thick in middle; thinner, tapering off to the end
4. single oval centrally located nucleus
5. actin and myosin fibers not arranged as sarcomere
6. lack of organization (no bands) --> smooth muscle
7. also contain intermediate filaments
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Smooth Muscle Cells
B. Difference in Contraction
1. intermediate filaments attach to dense bodies
2. as muscle cell contracts, twists like corkscrew
3. caveolae - like T tubules of skeletal muscle
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Smooth Muscle Cells
C. Two Kinds of Smooth Muscle
1. visceral (single unit) musclea. small arteries and veinsb. viscera - stomach, intestines, uterus, bladderc. continuous network with gap junctionsd. action spreads from one cell to another
2. multiunit muscle
a. each fiber (cell) has it own nerve endingb. no gap junctionsc. large arteries, large airways, arrector pili
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Skeletal Muscle: Nerve and Blood Supply
Each muscle is served by one nerve, an artery, and one or more veins
Each skeletal muscle fiber is supplied with a nerve ending that controls contraction
Contracting fibers require continuous delivery of oxygen and nutrients via arteries
Wastes must be removed via veins
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Skeletal Muscle
Each muscle is a discrete organ composed of muscle tissue, blood vessels, nerve fibers, and connective tissue
The three connective tissue sheaths are:
Endomysium – fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber
Perimysium – fibrous connective tissue that surrounds groups of muscle fibers called fascicles
Epimysium – an overcoat of dense regular connective tissue that surrounds the entire muscle
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Figure 9.2 (a)
One Skeletal Muscle in Cross Section
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One Skeletal Muscle Cell (Fiber)
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One Skeletal Muscle Cell Myofibril
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Each Myofibril composed of many Sarcomeres
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Myofibrils
Myofibrils are densely packed, rodlike contractile elements
They make up most of the muscle volume
The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident
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Many Myofibrils in One Muscle Cell
Figure 9.3 (b)
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Sarcomeres
The smallest contractile unit of a muscle
The region of a myofibril between two successive Z discs
Myofilaments are of two types – thick and thin
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Many Sarcomeres make up a single Myofibril
Figure 9.3 (c)
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Myofilaments: Banding Pattern
Thick filaments (myosin filaments) – extend the entire length of an A band
Thin filaments (actin filaments) – extend across the I band and partway into the A band
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Myofilaments: Banding Pattern
Figure 9.3 (c, d)
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Ultrastructure of Myofilaments: Thick Filaments
Thick filaments are composed of the protein myosin
Each myosin molecule has a rodlike tail and two globular heads
Tails – two interwoven, heavy polypeptide chains
Heads – two smaller, light polypeptide chains called cross bridges
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Ultrastructure of Myofilaments: Thick Filaments
Figure 9.4 (a)(b)
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Ultrastructure of Myofilaments: Thin Filaments
Thin filaments are composed of the protein actin
Each actin molecule is a helical polymer of globular subunits called G actin
The subunits contain the active sites to which myosin heads attach during contraction
Tropomyosin and troponin are regulatory subunits bound to actin
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Ultrastructure of Myofilaments: Thin Filaments
Figure 9.4 (c)
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Arrangement of the Filaments in a Sarcomere
Longitudinal section within one sarcomere
Figure 9.4 (d)
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Sarcoplasmic Reticulum (SR)
SR is an elaborate, smooth endoplasmic reticulum that mostly runs longitudinally and surrounds each myofibril
Functions in the regulation of intracellular calcium levels
T tubules associate with the paired terminal cisternae to form triads
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Sarcoplasmic Reticulum (SR)
Figure 9.5
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Neuromuscular Junction (NMJ)
1. motor neuron - nerve cell that innervates muscle
2. motor end plate - where axon meets muscle cell
3. neuromuscular junction - entire muscle/nerve site
4. synapse – name for where nerve terminal meets target cell
5. synaptic vesicles - inclusions in the axon terminal
a. neurotransmitter - chemical messenger
i. acetylcholine ACh (for muscular synapse)
6. synaptic cleft - space between axon and cell
7. motor unit - a neuron and all muscle cells it stimulates
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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle Hypertrophy and Atrophy
1. muscular hypertrophy
a. increase in size of myofibers (muscle cells)
b. allows for increased strength
c. adult muscle cells are amitotic (do not divide)
2. muscular atrophy
a. progressive loss of myofibrils
i. disuse atrophy
ii. denervation atrophy (neuron lost)
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Interactions of Skeletal Muscles
Skeletal muscles work together or in opposition
Muscles only pull (never push)
As muscles shorten, the insertion generally moves toward the origin
Whatever a muscle (or group of muscles) does, another muscle (or group) “undoes”
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Muscle Classification: Functional Groups
Prime movers – provide the major force for producing a specific movement
Antagonists – oppose or reverse a particular movement
Synergists – work cooperatively to achieve a certain action
Add force to a movement
Reduce undesirable or unnecessary movement
Fixators – synergists that immobilize a bone or muscle’s origin
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Naming Skeletal Muscles
1. Location of muscle – bone or body region associated with the muscle
2. Shape of muscle – e.g., the deltoid muscle (deltoid = triangle)
3. Relative size – e.g., maximus (largest), minimus (smallest), longus (long)
4. Direction of fibers – e.g., rectus (fibers run straight), transversus, and oblique (fibers run at angles to an imaginary defined axis)
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Naming Skeletal Muscles
5. Number of origins – e.g., biceps (two origins) and triceps (three origins)
6. Location of attachments – named according to point of origin or insertion
7. Action – e.g., flexor or extensor, as in the names of muscles that flex or extend, respectively
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