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72 Cards in this Set

  • Front
  • Back
Muscle cells are derived from?
Mesenchyme, formed by mesenchymal cells, derived from mesoderm, middle layer of embryo
Muscle Fiber
Myofiber = Muscle Cell
Sarcoplasm
Cytoplasm of muscle fiber
Sarcolemma
Plasma membrane of muscle fiber
Sarcoplasmic Reticulum
Smooth ER of muscle fiber
Basal Lamina
Sheetlike extracellular material produced by and located between cells (muscle, adipose, epithelial, schwann) and the subajacent CT
Basal Lamina - Function
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
Skeletal Muscle Tissue - surface coverings
Epimysium
Perimysium
Endomysium
Epimysium
Dense irregular CT, surrounds entire skeletal muscle
Perimysium
Loose CT, surrounds bundles of skeletal muscle fibers called fascicles
Endomysium
Loose CT composed of basal lamina and reticular fibers, collectively forming a basement membrane, which surrounds individual skeletal muscle fibers
Skeletal Muscle Tissue Contains
Blood vessels, lymph vessels, nerves
Skeletal Muscle Architecture
Myofilaments -> Myofibrils -> Muscle Fibers -> Muscle Fasciculi (Parallel Bundles) -> Muscle
Microscopic Structure of (Extrafusal) Skeletal Muscle Fibers
Cylindrical (tapered ends), unbranched, 1-30cm long, 10-100um in diameter
Capable of Hypertrophy but not Hyperplasia
Myofibrils
Each muscle fiber contains dozens to hundreds of myofibrils, oriented parallel to long axis of muscle fiber
Composed of sarcomeres arranged in series
Sarcomere
Contractile unit of striated muscle fibers.
From Z line to Z line
Shorten with contraction
2.5um long
Z-Line
Dark line bisecting I band
Contains cytoskeletal proteins that anchor thin filaments and "tie" adjacent sarcomeres together
Alpha Actin
I Band
Light region bisected by Z line
Thin filaments that do not overlap thick filaments
Shorten with contraction
A Band
Dark central region
Primarily thick filaments + overlapping thin filaments
H Band
Center of A band
Only thick filaments
Shorten wiht contraction
M Line
Bisects H band
Region where adjacent thick filaments are connected
Thick Filaments
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
Thin Filaments
2 Twisted chains of actin w/tropomyosin and its attached troponin positioned in groove between actin chains.
Troponin
Contains calcium binding site when bound to Ca++ causes change in configuration of thin filament to allow interaction with thick filament
Sarcolemma - Transverse T-Tubules - Structure
Invaginations of the sarcolemma that lie perpendicular to long axis of muscle fibers encircling myofibrils at regular intervals
Sarcolemma - Transverse T-Tubules - Function
Conduct electrical impulses from surface to interior of muscle fiber
Organelles - Sarcoplasmic Reticulum - Structure
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
Organelles - Sarcoplasmic Reticulum - Function
Calcium storage and mobilization
Triad - T-Tubule + 2 terminal cisternae (either side)
Nucleus - Muscle Cell
Numerous, Peripherally Located
Motor Unit
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.
Mutability
Muscle fibers are capable of altering "type" in response to hormones, neural input, and/or load or activity pattern placed upon the muscle
Mechanism of Contraction - Excitation Contraction Coupling
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
Sliding Filament Theory
Thin filaments slide relative to thick filaments causing shortening of the sarcomere.
Neuromuscular Junction
One NMJ per muscle fiber. Consist of: Alpha Motor Neuron, Synaptic Cleft, Skeletal Muscle Fiber
Alpha Motor Neuron
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.
Synaptic Cleft
Space btw neuron and muscle, in which lies the basal lamina which contains the enzyme 'cholinesterase' which breaks down ACh.
Skeletal Muscle Fiber
Region of sarcolemma has clefts and ridges called junctional folds which contain ACh receptors
Proprioceptors: Muscle Spindle - Structure
Specialized skeletal muscle fibers (intrafusal) encapsulated by a fibrous connective tissue.
Middle is surrounded by sensory nerve fibers
Proprioceptors: Muscle Spindle - Function
Detect changes in muscle length and relay info to spinal cord
Spindles -> Stretch
Proprioceptors: Muscle Spindle - Distribution
Throughout skeletal muscle
Connected in parallel w/extrafusal muscle fibers
Proprioceptors: Golgi Tendon Organs - Struture
Composed of a network of sensory nerve fibers intertwined w/bundles of collagen fibers of a tendon and encapsulated by fibrous connective tissue
Proprioceptors: Golgi Tendon Organs - Function
Detect changes in muscle tension and relay info to spinal cord
Tendon -> Tension
Proprioceptors: Golgi Tendon Organs - Distribution
At musculotendinous junction
Connected in series w/extrafusal muscle fibers
Satellite Cells
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)
Satellite Cells - Structure
Mono-nucleated spindle shaped
Lie within basal lamina surrounding each mature muscle fiber
Skeletal Muscle: Aging - Structural Changes
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
Skeletal Muscle: Aging - Functional Changes
Loss of muscle mass (sarcopenia) and consequent decrease in strength
Cardiac: Surface Coverings - Endomysium
Loose CT composed of basal lamina and reticular fibers (Basal Membrane), surrounds individual muscle fibers
Mechanically transmit forces generated by contracting muscle cells
Cardiac: Surface Coverings - Contain
Blood vessels
Lymph vessels
Nerves
Muscle Architecture
Myofilaments -> Myofibrils -> Muscle Fibers -> Muscle Fasciculi (Interwoven Bundles) -> Heart
Microscopic Structure of Cardiac Muscle Fibers
Cylindrical, branced, 85 to 100um long, 15um diameter
Cross striations not as prominent as skeletal muscle
Capable of hypertrophy, not hyperplasia
Cardiac: Cytoplasm (Sarcoplasm) contents
Myofibrils
T-Tubules
SR
Mitochondria
Intercalated Discs
Nucleus
Cardiac: Myofibrils
Structure and function same as skeletal muscle
Cardiac: T-Tubules and SR
Not as organized as skeletal muscle fibers
Cardiac: Mitochondria
Numerous (many more than skeletal muscle)
Cardiac: Intercalated Discs - Structure
Contain three types of junctions, including gap
Cardiac: Intercalated Discs - Function
Anchor myofilaments
Bind ends of cardiac muscle fibers together
Provide ionic continuity btw cardiac muscle fibers
Cardiac: Nucleus
One or two centrally located
3 Hallmarks to differentiate Cardiac from Skeletal
Branched fibers
Intercalated Discs
Centrally located nucleus (1 or 2)
Innervation of Cardiac Muscle (2 types)
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
Cardiac: Regulation of Contraction
Calcium and ionic coupling by gap junctions
Smooth Muscle: Surface Coverings
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
Smooth Muscle: Architecture
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
Microscopic Structure of Smooth Muscle
Fusiform, unbranced, 20 to 500um in size
No cross striations (no myofibrils)
Capable of hypertrophy and hyperplasia
Smooth Muscle: Cytoplasm (Sarcoplasm) - Contents
No myofibrils or T-Tubules
Rudimentary SR
Thick and Thin myofilaments in criss/cross pattern throughout
Contain Dense Bodies
Smooth Muscle: Dense Bodies - Structure
Composed of protein a-actinin (alpha)
Smooth Muscle: Dense Bodies - Function
Transmit contractile force to adjacent smooth muscle cells and surrounding connective tissue
Smooth Muscle: Nucleus
Single centrally located
Smooth Muscle: Innervation
Enteric Nervous System
ANS
Smooth Muscle: Enteric Nervous System
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.
Smooth Muscle: ANS (visceral and multiunit)
Visceral Smooth Muscle (Hollow Organs): Poor innervation, specialized for slow prolonged contraction.
Multiunit Smooth Muscle (Iris): Rich innervation, specialized for precise graded contractions
Smooth Muscle: Regulation
Calcium and ionic coupling via gap junctions