Chapter 11: Muscular Tissue Flashcards
3 types of muscular tissue
Skeletal, Cardiac, Smooth
Excitability (responsiveness)
chemical signals, stretch, and electrical changes across the plasma membrane
Conductivity
Local electrical excitation sets off a wave of excitation that travels along the muscle fiber
Contractility
Shortens when stimulated
Extensibility
Capable of being stretched between contractions
Elasticity
Returns to its original rest length after being stretched
Myofiber
Muscle cell/Muscle Fiber as long as 30 cm
Connective tissue wrappings
Endomysium: connective tissue around muscle cell
Perimysium: connective tissue around muscle fascicle
Epimysium: connective tissue surrounding entire muscle
Collagen
Stretches slightly under tension and recoils when released
Resists excessive stretching and protects muscle from injury
Returns muscle to its resting length
Contributes to power output and muscle efficiency
Sarcolemma
Plasma membrane of a muscle fiber
Sarcoplasm
Cytoplasm of a muscle fiber
Myofibrils
long protein cords occupying most of sarcoplasm
Glycogen
carbohydrate stored to provide energy for exercise
Myoglobin
red pigment; provides some oxygen needed for muscle activity
Myoblasts
stem cells that fused to form each muscle fiber early in development
Satellite Cells
unspecialized myoblasts remaining between the muscle fiber and endomysium
Sarcoplasmic Reticulum
Forms network around each myofibril. Acts as a calcium reservoir; it releases calcium through channels to activate contraction
Thick Filaments
Made of several hundred myosin molecules. Double myosin head shaped like golf clubs.
Thin Filaments
Two intertwined strands of fibrous actin.
String of globular (G) actin subunits each with an active site that can bind to head of myosin molecule
Tropomyosin blocks active sites on G (actin)
Troponin molecule: small, calcium-binding protein on each tropomyosin molecule
Elastic Filaments
Titin: huge, springy protein
Run through core of thin filament and anchor it to Z disc and M line
Help stabilize and position the thick filament
Prevent overstretching and provide recoil
Contractile Proteins
myosin and actin do the work of contraction
Regulatory Proteins
tropomyosin and troponin
Act like a switch that determines when fiber can (and cannot) contract
Contraction activated by release of calcium into sarcoplasm and its binding to troponin
Troponin changes shape and moves tropomyosin off the active sites on actin
Dystrophin
clinically important protein
Links actin in outermost myofilaments to membrane proteins that link to endomysium
Transfers forces of muscle contraction to connective tissue ultimately leading to tendon
Genetic defects in dystrophin produce disabling disease muscular dystrophy
A-Band (Dark)
“A” stands for anisotropic
Darkest part is where thick filaments overlap a hexagonal array of thin filaments
H band: not as dark; middle of A band; thick filaments only
M line: middle of H band
I-Band (Light)
“I” stands for isotropic
The way the bands reflect polarized light
Z disc: provides anchorage for thin filaments and elastic filaments
Bisects I band
Sarcomere
segment from Z disc to Z disc
Functional contractile unit of muscle fiber
Somatic Motor Neurons
Nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles
Somatic Motor Fibers
their axons that lead to the skeletal muscle
Motor Unit
one nerve fiber and all the muscle fibers innervated by it. Average motor unit contains 200 myofibrils
Resting Membrane Potential
about −90 mV in skeletal muscle cells
Maintained by sodium–potassium pump
ECF
Excess Na+
ICF
Excess K+
Excitation
Process in which nerve action potentials lead to muscle action potentials
Excitation- Contraction Coupling
Events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract
Contraction
Step in which the muscle fiber develops tension and may shorten
Relaxation
When stimulation ends, a muscle fiber relaxes and returns to its resting length
