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72 Cards in this Set
- Front
- Back
Muscle cells are derived from?
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Mesenchyme, formed by mesenchymal cells, derived from mesoderm, middle layer of embryo
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Muscle Fiber
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Myofiber = Muscle Cell
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Sarcoplasm
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Cytoplasm of muscle fiber
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Sarcolemma
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Plasma membrane of muscle fiber
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Sarcoplasmic Reticulum
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Smooth ER of muscle fiber
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Basal Lamina
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Sheetlike extracellular material produced by and located between cells (muscle, adipose, epithelial, schwann) and the subajacent CT
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Basal Lamina - Function
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Barrier that limits or regulates exchanges between connective tissue and other tissues
In muscle tissue - binds muscle cells into a single functional mass, allows "transmission" of contractile forces |
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Skeletal Muscle Tissue - surface coverings
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Epimysium
Perimysium Endomysium |
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Epimysium
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Dense irregular CT, surrounds entire skeletal muscle
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Perimysium
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Loose CT, surrounds bundles of skeletal muscle fibers called fascicles
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Endomysium
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Loose CT composed of basal lamina and reticular fibers, collectively forming a basement membrane, which surrounds individual skeletal muscle fibers
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Skeletal Muscle Tissue Contains
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Blood vessels, lymph vessels, nerves
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Skeletal Muscle Architecture
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Myofilaments -> Myofibrils -> Muscle Fibers -> Muscle Fasciculi (Parallel Bundles) -> Muscle
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Microscopic Structure of (Extrafusal) Skeletal Muscle Fibers
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Cylindrical (tapered ends), unbranched, 1-30cm long, 10-100um in diameter
Capable of Hypertrophy but not Hyperplasia |
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Myofibrils
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Each muscle fiber contains dozens to hundreds of myofibrils, oriented parallel to long axis of muscle fiber
Composed of sarcomeres arranged in series |
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Sarcomere
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Contractile unit of striated muscle fibers.
From Z line to Z line Shorten with contraction 2.5um long |
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Z-Line
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Dark line bisecting I band
Contains cytoskeletal proteins that anchor thin filaments and "tie" adjacent sarcomeres together Alpha Actin |
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I Band
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Light region bisected by Z line
Thin filaments that do not overlap thick filaments Shorten with contraction |
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A Band
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Dark central region
Primarily thick filaments + overlapping thin filaments |
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H Band
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Center of A band
Only thick filaments Shorten wiht contraction |
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M Line
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Bisects H band
Region where adjacent thick filaments are connected |
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Thick Filaments
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Myosin
Rodlick tail region and globular (double) head region Each "Head" region contains ATP binding site, w/ATPase activity, and an actin binding site Rodlike portions overlap and globular head regions direct towards either end of sarcomere |
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Thin Filaments
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2 Twisted chains of actin w/tropomyosin and its attached troponin positioned in groove between actin chains.
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Troponin
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Contains calcium binding site when bound to Ca++ causes change in configuration of thin filament to allow interaction with thick filament
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Sarcolemma - Transverse T-Tubules - Structure
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Invaginations of the sarcolemma that lie perpendicular to long axis of muscle fibers encircling myofibrils at regular intervals
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Sarcolemma - Transverse T-Tubules - Function
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Conduct electrical impulses from surface to interior of muscle fiber
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Organelles - Sarcoplasmic Reticulum - Structure
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System of tubules that runs in long axis of muscle fibers and surrounds individual myofibrils.
Dilated terminal segments adjacent to sides of T-Tubules called Terminal Cisterns |
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Organelles - Sarcoplasmic Reticulum - Function
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Calcium storage and mobilization
Triad - T-Tubule + 2 terminal cisternae (either side) |
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Nucleus - Muscle Cell
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Numerous, Peripherally Located
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Motor Unit
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Single motor neuron and all of hte muscle fibers that it innervates. All muscle fibers in a motor unit are of the same type.
Most muscles are composed of both fiber types. |
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Mutability
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Muscle fibers are capable of altering "type" in response to hormones, neural input, and/or load or activity pattern placed upon the muscle
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Mechanism of Contraction - Excitation Contraction Coupling
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AP in Alpha Motor Neuron
ACh release @ NMJ ACh binds to muscle receptor Sarcolemma depolarizes AP conducted via T-Tubules Signal SR to release Ca++ Ca++ binds to troponin Actin-Myosin interaction (ATP) Ca++ re-uptake |
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Sliding Filament Theory
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Thin filaments slide relative to thick filaments causing shortening of the sarcomere.
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Neuromuscular Junction
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One NMJ per muscle fiber. Consist of: Alpha Motor Neuron, Synaptic Cleft, Skeletal Muscle Fiber
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Alpha Motor Neuron
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Travels through perimysium towards the muscle fiber, giving rise to several terminal twigs. At site of innervation it loses its myelin sheath and forms a dilated terminal bud.
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Synaptic Cleft
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Space btw neuron and muscle, in which lies the basal lamina which contains the enzyme 'cholinesterase' which breaks down ACh.
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Skeletal Muscle Fiber
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Region of sarcolemma has clefts and ridges called junctional folds which contain ACh receptors
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Proprioceptors: Muscle Spindle - Structure
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Specialized skeletal muscle fibers (intrafusal) encapsulated by a fibrous connective tissue.
Middle is surrounded by sensory nerve fibers |
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Proprioceptors: Muscle Spindle - Function
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Detect changes in muscle length and relay info to spinal cord
Spindles -> Stretch |
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Proprioceptors: Muscle Spindle - Distribution
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Throughout skeletal muscle
Connected in parallel w/extrafusal muscle fibers |
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Proprioceptors: Golgi Tendon Organs - Struture
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Composed of a network of sensory nerve fibers intertwined w/bundles of collagen fibers of a tendon and encapsulated by fibrous connective tissue
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Proprioceptors: Golgi Tendon Organs - Function
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Detect changes in muscle tension and relay info to spinal cord
Tendon -> Tension |
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Proprioceptors: Golgi Tendon Organs - Distribution
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At musculotendinous junction
Connected in series w/extrafusal muscle fibers |
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Satellite Cells
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Muscle stem cells that persist after skeletal muscle differentiation
When activiated, can proliferate and fuse to form muscle fibers (regenerate muscle cell if satellite cell and blood supply are both present) |
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Satellite Cells - Structure
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Mono-nucleated spindle shaped
Lie within basal lamina surrounding each mature muscle fiber |
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Skeletal Muscle: Aging - Structural Changes
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Decrease in # of muscle fibers and muscle fiber size
Motor unit: remodeling, decrease in total number, increase in size of remaining, increase in proportion of type I motor units |
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Skeletal Muscle: Aging - Functional Changes
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Loss of muscle mass (sarcopenia) and consequent decrease in strength
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Cardiac: Surface Coverings - Endomysium
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Loose CT composed of basal lamina and reticular fibers (Basal Membrane), surrounds individual muscle fibers
Mechanically transmit forces generated by contracting muscle cells |
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Cardiac: Surface Coverings - Contain
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Blood vessels
Lymph vessels Nerves |
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Muscle Architecture
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Myofilaments -> Myofibrils -> Muscle Fibers -> Muscle Fasciculi (Interwoven Bundles) -> Heart
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Microscopic Structure of Cardiac Muscle Fibers
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Cylindrical, branced, 85 to 100um long, 15um diameter
Cross striations not as prominent as skeletal muscle Capable of hypertrophy, not hyperplasia |
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Cardiac: Cytoplasm (Sarcoplasm) contents
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Myofibrils
T-Tubules SR Mitochondria Intercalated Discs Nucleus |
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Cardiac: Myofibrils
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Structure and function same as skeletal muscle
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Cardiac: T-Tubules and SR
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Not as organized as skeletal muscle fibers
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Cardiac: Mitochondria
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Numerous (many more than skeletal muscle)
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Cardiac: Intercalated Discs - Structure
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Contain three types of junctions, including gap
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Cardiac: Intercalated Discs - Function
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Anchor myofilaments
Bind ends of cardiac muscle fibers together Provide ionic continuity btw cardiac muscle fibers |
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Cardiac: Nucleus
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One or two centrally located
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3 Hallmarks to differentiate Cardiac from Skeletal
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Branched fibers
Intercalated Discs Centrally located nucleus (1 or 2) |
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Innervation of Cardiac Muscle (2 types)
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Myogenic - spontaneous, intrinsic rhythmic activity of cardiac muscle fibers
ANS - via rhythmic impulse-generating and conducting structures (SA, AV, AV Bundle, Purkinje) - modifies contractile activity |
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Cardiac: Regulation of Contraction
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Calcium and ionic coupling by gap junctions
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Smooth Muscle: Surface Coverings
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Individual fibers surrounded by basal lamina and reticular fibers (basement membrane)
Fibers bound together by a network of loose CT Contain: blood & lymph vessels, nerves |
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Smooth Muscle: Architecture
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The tapered end of one smooth muscle fiber lies adjacent to large midpoint of neighboring smooth muscle fibers
(large region of one next to thin of other) Muscle fiber -> Muscle fasciculi (irregular branching) -> Smooth muscle -> Sheet or multiunit |
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Microscopic Structure of Smooth Muscle
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Fusiform, unbranced, 20 to 500um in size
No cross striations (no myofibrils) Capable of hypertrophy and hyperplasia |
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Smooth Muscle: Cytoplasm (Sarcoplasm) - Contents
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No myofibrils or T-Tubules
Rudimentary SR Thick and Thin myofilaments in criss/cross pattern throughout Contain Dense Bodies |
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Smooth Muscle: Dense Bodies - Structure
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Composed of protein a-actinin (alpha)
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Smooth Muscle: Dense Bodies - Function
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Transmit contractile force to adjacent smooth muscle cells and surrounding connective tissue
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Smooth Muscle: Nucleus
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Single centrally located
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Smooth Muscle: Innervation
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Enteric Nervous System
ANS |
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Smooth Muscle: Enteric Nervous System
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Motor and sensory neurons in two interconnected plexuses in walls of GI tract.
Control coordinated contraction and relaxation of intestinal smooth muscle and regulate gastric secretion and blood flow. |
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Smooth Muscle: ANS (visceral and multiunit)
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Visceral Smooth Muscle (Hollow Organs): Poor innervation, specialized for slow prolonged contraction.
Multiunit Smooth Muscle (Iris): Rich innervation, specialized for precise graded contractions |
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Smooth Muscle: Regulation
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Calcium and ionic coupling via gap junctions
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