Chapter 9: Muscles and Muscle Tissues Flashcards
Muscle Fiber
skeletal muscle or smooth muscle CELL; but NOT a cardiac muscle cell
What prefixes mean “muscle”?
myo, mys, sarco
What are the types of muscle tissue?
skeletal, cardiac, smooth
Skeletal Muscle Tissue
attached via tendon to bone (most); striated and voluntary
Cardiac Muscle Tissue
striated (but not as distinct as skeletal), involuntary and ahs intercalated discs; branched
Smooth Muscle Tissue
walls of hollow organs; nonstriated and involuntary
Characteristics of Muscles in General
excitability, contractility, extensibility, and elasticity
Excitability
aka responsiveness; ability to respond to a stimulus by changing its membrane potential
Contractility
ability to shorten forcibly when adequately stimulated
Extensibility
ability to stretch when relaxed
Elasticity
ability to recoil after stretching
Functions of Muscles
produce movement; maintain posture and body position; stabilize joints (muscle tone); generate heat
Structural Hierarchy of Skeletal Muscle
biggest to smallest; muscle (a bunch of fascicles) to fascicle (bunch of muscle fibers) to muscle fiber (cell)
What tissues are involved with skeletal muscles?
muscle fibers, blood vessels (muscle is well vascularized), connective tissue sheaths, attachments
Nerve and Blood Supply of Skeletal Muscle
has 1 nerve, 1 artery and 1 or more veins that supply each muscle; all enter or exit near muscle center
Connective Tissue Sheaths
epimysium, perimysium, endomysium
Epimysium
dense irregular CT that surrounds the entire muscle
Perimysium
dense irregular CT that surrounds a fascicle (bundle of muscle fibers)
Endomysium
areolar CT that surrounds each muscle fiber
Attachments of Skeletal Muscles
all skeletal muscles have at least 2 points of attachment; an insertion and origin
Insertion
end of muscle attached to bone that moves
Origin
end of muscle attached to bone that move less
Origins and Insertions may be…
direct or indirect
Direct
epimysium of muscle fused to periosteum or perchondrium
Indirect
tendon or aponeurosis anchors muscle to periosteum, perichondrium or epimysium of another muscle
Deep Fascia
what connective tissue sheaths and attachments are collectively referred to as
What does each skeletal muscle fiber have?
sarcolemma, sarcoplasm, special structures such as myofibrils, sarcoplasmic reticulum, and T Tubules
Sarcolemma
plasma membrane of muscle fibers
Sarcoplasm
cytoplasm of muscle fibers; contains large number of mitochondria, glycosomes (glycogen granules), and myoglobin (stores O2)
Myofibrils
make up 80% of cell volume; extend entire length or muscle cell; each consists of sarcomeres (repeating units) laid end to end with an internal arrangement of myofilaments
Sarcomeres
Smallest contractile units (functional units) or skeletal muscle; contain a dark A band and 1/2 of a light I band
Myofilaments
thick filaments: consist of many myosin molecules; head protrude at opposite ends of filaments; thin filaments: consist of 2 strands of actin subunits and 2 types of regulatory proteins (troponin, tropomyosin)
Tropomyosin
blocks myosin binding sites on think filaments
Arrangement of thick and thin filaments…
responsible for banding pattern of myofibrils (the A and I bands or dark and light bands)
A Band
dark region of overlapping thick and thin filaments
H Zone
region within A band lacking thin filaments
M Line
region within H zone containing proteins that anchor thick filaments
I Band
light region of thin filaments only
Z Disc
region within I band where thick and thin filaments anchor to sarcolemma
Elastic Filaments
composed of the protein titin; functions to 1) hold thick filaments in place; 2) helps muscle cells spring back into shape; 3) prevent sarcomeres from separating
Sarcoplasmic Reticulum
SR; interconnecting tubules that encase myofibrils; most tubules run parallel to myofibrils; other tubules form terminal cisterns (large perpendicular cross channels) at A band-I band junctions; functions to store calcium ions
T Tubules
invaginations of the sacrolemma that run between adjacent terminal cisterns and extend deep into the cells interior; function to conduct electrical impulses which trigger calcium ions to release from the terminal cisterns
Contraction of Skeletal Muscle
occurs when thick and thin filaments slide past each other as the sarcomeres contract (sliding filament model of contraction); sarcomeres shorten but thick and thin filaments do not; I bands shorten; H zones dissappear; A bands move closer together, but do not shorten
All cell membranes are…
charged; a difference in electrical charge on either side of membrane; positive on outside and negative on inside; all cells have a negative resting potential
Only muscle cells and neuron cells are…
excitable; respond to stimuli by altering their membrane potential
Chemically Gated Ion Channels
closed unless a chemical messenger opens it; ex) acetylcholine (ACh); generate local depolarization (which reverse polarity) called end plate potentials
Voltage Gated Ion Channels
open/close in reponse to changes in membrane potential; generate large changes in membrane potential called action potential
Motor Neurons
innervate skeletal muscle cells; exist spinal cord through nerves; branch within muscle forming multiple neuromuscular junction (only one per muscle fiber); motor unit = a motor neurons and all muscle cells it stimulates
Contraction of One Muscle Fiber: Phase 1- events at the neuromuscular junction
1) action potential arrives at neuromuscular junction; 2) voltage gated calcium ion channels open and calcium ions enter axon terminal; 3) calcium ion entry causes ACh to be realeased from synaptic vesicles in synaptic cleft; 4) ACh binds to ACh receptors on sarcolemma motor end plate; 5) ACh binding opens chemically gated ion channels that allow sodium ions to enter cell and potassium ions to exit cell which generates a local depolarization; 6) ion channels closes when ACh in synaptic cleft is broken down by acetylcholinestrase (AChE)
Contraction of One Muscle Fiber Phase 2: Muscle Fiber Excitation
1) end plate potential spreads to sarcolemma (if strong enough, it will open voltage gated sodium ion channels); 2) influx of sodium ions reverses membrane polarity (action potential depolarization); 3) efflux of potassium ions restores membrane polarity (action potential repolarization)
Contraction of One Muscle Fiber Phase 3: Excitation- Contraction Coupling
sequence of events that link the action potential (electrical stimulus) to contraction of the muscle (mechanical action); 1) action potential moves along sarcolemma and down t-tubules; 2) calcium ions released from sarcoplasmic reticulum into sarcoplasm (in relaxed muscle cells, troponin position tropomysin such taht it blocks myosin binding site on actin subunits); 3) released calcium ions binds to troponin causing tropomysin strands to shift, unblocking the myosin binding sites; 4) myosin heads bind to actin forming cross bridges
Contraction of One Muscle Fiber Phase 4: Cross Bridge Cycle
sequence of events during which myosin heads pull thin filaments toward center of sarcomere; 1) cross bridge formation; 2) power stroke occurs (myosin head bends pulling thin filaments toward m line); 3) corss bridge detachment occurs when ATP binds to myosin head; 4) cocking of the myosin head; cycle continues as long as ATP and calcium ions are available
ATP is needed for…
muscles to relax NOT to contract
Rigor Mortis
basically when all the muscles in a dead body start to contract because there is no ATP to cause the muscles to relax; begins 3-4 hours after death and peaks at 12 hours; after 12 hours muscles start to relax because they start to decompose
Contraction of a Whole Muscle
each muscles is served by at least one nerve; each nerve contains axons; each muscle cell has only one neuromuscular joints
Motor Unit
consits of one neuron and all muscle fibers it innervates; number of muscle fibers per motor unit varies (4- hundreds); fibers of large motor units spread throughout muscle
A Muscle Twitch
response of a whole muscle to a single stimulus; recorded on a myogram (graph showing the amount of tension a muscle develops when its length is heald constant as it contracts); muscle develops tension when stimulated but does not shorten
Each Muscle Twitch has Three Phases which are…
latent period: no reponse by cross bridges begin to cycle; period of contraction: cross bridges are cycling and tension increases; period of relaxation: tension decreases and then to zero (longer than contractile period)
Graded Muscle Contractions
variations in the degree of muscle contraction by altering either the frequency or the strength of a stimulus
FOR ALTERaTING STIMULUS FREQUENCY KNOW THE PICS AND DESCRIPTIONS OR MAKE A QUIZIZZ OF IT
Altering Stimulus Strength
an increase in stimulus strength result in recruitment (which is the activation of more motor units)
Subthreshold Stimuli
produce no observable contraction
Threshold Stimulus
smallest stimulus to initiate a contraction
Maximal Stimulus
smallest stimulus needed for a maximal contraction; or all motor units have been recruited
Smallest Fiber Units Recruited
controlled by highly excitable neurons (lowest threshold)
Large Fiber Motor Units Recruited
controlled by least excitable neurons (highest threshold); activated only when maximal contraction is necessary
Isotonic Contractions
muscle tension overcomes load and muscle length changes
Concentric Contractions
muscle generates tensions as it shortens
Eccentric Contractions
muscle generates tension as it lengthens
Isometric Contraction
muscle tensions does NOT overcome load; muscle length remains the same
ATP Roles in Muscle Contraction
provides energy for movement of cross bridges; required for muscle cell relaxation; provides energy for sarcoplasmic reticulum to reclaim dumped calcium ions; provides energy for Na/K pump to maintain membrane potential
What are the three mechanisms of ATP regeneration?
direct phosphorylation; anaerobic pathway; aerobic pathway
Direct Phosphorylation
phosphate tranferred from stored creative phosphate (CP) to ADP to form ATP; very rapid; first source muscles use; provides ~15 secs of ATP
Anaerobic Pathway
glycolysis and lactic acid formation; inefficient but fast; ~40 seconds of ATP; accumulation of lactic acid in muscles is partly responsible for muscle soreness
Aerobic Pathway
glucose broken down completely to CO2 and H2O; slow but efficient; hours of energy; 30 ATP’s generated per glucose; prefers to use glucose/carbs; will use lipids second; and will use proteins but at that point your kinda dying of starvation
ATP and Creatine Phosphate fuel activities….
requiring a surge of power for only a few seconds; weight lifting, diving, sprinting
Glycolysis and Lactic Acid Formation fuel activities…
requiring slightly longer bursts of activity; tennis, soccer, 100m dash, or swim
Aerobic Respiration fuels activities….
all light to moderate activities and prolonged activites that focus on endurance; running a marathon, competing in a triatholon
