Muscles Flashcards
What are the three types of muscles in vertebrates?
- cardiac
- smooth
- skeletal
Smooth muscle
-simplest
-mononucleated
-spindle-shaped
-smooth sheets
-NO striated > actin and myosin NOT arranged regularly
-moves food through digestive tract, controls blood flow, empties urinary bladder
Cardiac muscle
-branched into a meshwork
-striated
-in electrical contact w/ each other by gap junctions
-heart will beat bc of special pacemaker muscle cells that have self-generated heartbeat
Skeletal muscle
-voluntary movements (under conscious control)
-striated muscle
-aka muscle fibers, many nuclei
-moves body by contraction by antagonistic muscle pairs (one contracting, one relaxing)
What composes connective tissue?
Ligaments and tendons
Ligaments
Hold bones together at a joint
Tendons
Attach the muscles to the bones
Structure of skeletal muscle
Each muscle fiber is packed w/ bundles of myofibrils made up of thin actin units surrounding thick myosin units
Sarcomeres
-make up myofibrils
-surrounded by Z lines that anchor the thin actin filaments
-Center: A band (houses all myosin filaments)
-M band: contains proteins that support the myosin filaments
-H zone and I band are areas where actin and myosin do not overlap in relaxed muscle and appear less dense
How are the bundles of myosin filaments held in?
By titin
Titin
Runs the full length of the sarcomere from Z line to Z line, each titin molecule runs through the myosin bundle
Contraction of Sarcomeres
- muscle contracts
- sarcomere shortens
- H zone and I band become much narrower
- Z lines move toward the A band
- actin filaments slide into region previously occupied only by myosin filaments (sliding filament theory)
What is a thin filament?
two chains of actin molecules twisted together w/ troponin and tropomyosin
Troponin has 3 binding sites for what?
actin, tropomyosin, and Ca2+
What is a thick filament?
many myosin molecules arranged in parallel
Structure of myosin
two long polypeptide chains coiled together ending in a large globular head, the heads have sites that bind to actin forming bridges between actin and myosin, myosin heads have ATPase activity
Contractile Cycle (actin/myosin)
- myosin head is bound to ATP and is in its low energy conformation
- myosin hydrolyses ATP to ADP + Pi (high energy)
- myosin head binds actin forming cross-bridges
- myosin releases ADP + Pi and returns to low energy and slides the actin filament
- Binding a new ATP releases the myosin from actin
- Cycle restarts
Contractile Cycle (troponin, tropomyosin, Ca2+)
- Muscle at rest: tropomyosin and troponin block myosin binding sites on the actin filament
- If troponin binds Ca2+, troponin and tropomyosin go through a conformational change and unmask the myosin binding sites
- W/ binding sites exposed, actin-myosin bonds are made and filaments are pulled past each other
How are contractions in skeletal muscle initated?
by action potentials from motor neurons
What are T tubules?
a system of tubules that branch through the cytoplasm of a muscle cell that is continuous w/ the plasma membrane
What is the sarcoplasmic reticulum?
a network of intracellular membranes (modified ER) only in muscle cells that stores Ca2+
What are the levels of Ca2+ in the SR at rest?
high concentration of Ca2+ in SR, low in cytoplasm
Muscle Contraction Full Cycle
- ACh from synaptic terminal diffuses across synaptic cleft and binds to receptor proteins on muscle fiber’s PM which triggers an action potential
- Action potential is propagated along PM and down T tubules
- Action potential triggers Ca2+ release from SR
- Ca2+ bind to troponin and troponin changes shape, removing blocking action of tropomyosin. Myosin-binding sites exposed
- Myosin cross-bridges attach to actin and detach, pulling actin filaments toward center of sarcomere (powered by ATP)
- Cytosolic Ca2+ is removed by active transport into SR after action potential ends
- Tropomyosin blockage of myosin-binding sites is restored, contraction ends, and muscle fiber relaxes
What causes temporal summation?
faster twitching of INDIVIDUAL fibers
What causes spatial summation?
an increase in the NUMBER OF UNITS in the contraction
What is tetanus?
At high stimulation levels (like in spatial summation), the Ca2+ pumps in SR can no longer remove Ca2+ btwn action potentials and maximum tension is generated
Oxidative muscle fibers
-many mitochondria
-a lot of myoglobin
-provide steady, prolonged ATP production
-long-term aerobic work
Glycolytic fibers
-fewer mitochondria
-very little myoglobin
-high ATPase activity but cannot replenish ATP fast enough to sustain long-time contraction
-sudden, maximum strength
Strength exercises increase _____________
the number of new actin and myosin filaments (bigger muscles)
Aerobic exercises enhances ______________
the oxidative capacity of muscles by increasing the density of capillaries in the muscles, myoglobin content, and number of mitochondria in fast twitch fibers
Slow oxidative fibers
-large amts of myoglobin
-many mitochondria
-many blood capillaries
-high capacity for generating ATP but split at slow rate
-resistant to fatigue
-long distance running
Fast oxidative fibers
-large amts of myoglobin
-many mitochondria
-many blood capillaries
-high capacity for generating ATP but split at very rapid rate
-not as resistant to fatigue as slow ox
-middle distance running and swimming
Fast glycolytic fibers
-low myoglobin content
-few mitochondria
-few blood capillaries
-large amt of glycogen
-splits ATP very quickly
-fatigues easily
-sprinting
What effect does CURARE have on muscles?
paralyzes muscles by blocking ACh from reaching receptors
-death occurs bc the muscles that move the diaphragm become paralyzed and breathing stops (asphyxiation)
Botulism
-food poisoning from ingesting neurotoxin produced by bacterium Clostridium botulinum
Effect of botulism
causes paralysis; toxins attach themselves to proteins necessary for ACh release at neuromuscular junctions (blocks ACh release)
Botox
-low doses
-after a few hours to a couple of days after injection, contractions are reduced or eliminated altogether
-effects are not permanent
-injected directly into a certain muscle or muscle group to limit the spread
