Muscles Flashcards
(24 cards)
skeletal muscle
attached to bones or (some facial muscles) to skin
cell shape and appearance: singe, very long, cylindrical, multinucleate cells with obvious striations
elaborate sarcoplasmic reticulum: yes, large terminal cisterns
presence of gap junctions: no
cells exhibit individual neuromuscular junctions: yes
regulation of contraction: voluntary via axon terminals of the somatic nervous system
source of Ca2+ for contraction: SR
site of calcium regulation: troponin on actin-containing thin filaments
presence of pacemaker(s): no
effect of nervous system stimulation: excitation
speed of contraction: slow to fast
rhythmic contraction: no
response to stretch: contractile strength increases with degree of stretch(to a point)
metabolism: aerobic and anaerobic
cardiac muscle
walls of the heart
cell shape and appearance: branching chains of cells; uni- or binucleate cells; has striations
elaborate sarcoplasmic reticulum: less than skeletal muscle(1-8% of cell volume): small terminal cisterns
presence of gap junctions: yes, at intercalated discs
cells exhibit individual neuromuscular junctions: no
regulation of contraction: involuntary; contraction initiated by intrinsic pacemaker cells; regulated by the autonomic nervous system, hormones, and stretch
source of Ca2+ for contraction: SR and extracellular fluid
site of calcium regulation: troponin on actin-containing thin filaments
presence of pacemaker(s): yes
effect of nervous system stimulation: excitation or inhibition
speed of contraction: slow(don’t want a quick change in blood flow)
rhythmic contraction: yes
response to stretch: contractile strength increases with degree of stretch
metabolism: aerobic
smooth muscle
unitary muscle in walls of hollow visceral organs(other than the heart), multi-unit muscle in intrinsic eye muscles, airways, large arteries
cell shape and appearance: singe, spindle-shaped, uninucleate, no striations
elaborate sarcoplasmic reticulum: equivalent to cardiac muscle(1-8% of cell volume); some SR contacts the sarcolemma
presence of gap junctions: yes, in unitary muscle
cells exhibit individual neuromuscular junctions: not in unitary muscle, yes in multi-unit muscle
regulation of contraction: involuntary, initiated by intrinsic pacemaker cells(in unitary muscle) or autonomic nerves(in multi-unit muscle); regulated by local chemicals, hormones, and stretch
source of Ca2+ for contraction: SR + extracellular fluid
site of calcium regulation: calmodulin in the cytosol
presence of pacemaker(s): yes (in unitary muscle only)
effect of nervous system stimulation: excitation or inhibition
speed of contraction: very slow
rhythmic contraction: yes in unitary muscle
response to stretch: stress-relaxation response
metabolism: mainly aerobic
general structure of skeletal muscle
bone - tendon - epimysium(surrounds the fascicles) - fascicles(chunks of muscle fibers) - perimysium( wraps around fascicles) - endomysium(within a fascicle between individual muscle fibers) - muscle fibers(many within a fascicle, muscle cells) - myofibrils(in the muscle fibers) - sarcomeres(units of myofibrils)
skeletal muscle (structure and organizational levels)
a muscle consists of hundred to thousands of muscle cells(fibers), plus connective tissue wrappings, blood vessels, and nerve fibers
covered externally by the epimysium
fascicle
discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath - perimysium
muscle fiber (cell)
elongated multinucleate cell, has a striated/banded appearance
surrounded by endomysium - aerolear connective tissue, more flexible
contains many myofibrils
myofibril
each sarcomere within a myofibril extends from Z disc to Z disc
M line - middle of sarcomere where myosin (thick filaments) are linked by accessory proteins
H zone - middle area of the sarcomere, only has myosin located there
A band - middle part of the sarcomere, doesn’t change length when there is a contraction, the center only has myosin
I band - on each side where only actin is located, shortens when the muscle contracts
titin
elastic filaments
connects actin to the other actin on the other sarcomere
t tubules
allows the action potential to travel down into the muscle cell
skeletal muscle contraction (steps)
- motor neuron fires an AP down its axon
- the motor neuron’s axon terminal releases acetylcholine into the synaptic cleft
- ACh binds receptors on the junctional folds of the sarcolemma
- ACh binding causes a local depolarization because of an influx of Na+ - called an end plate potential (EPP)
- the local depolarization (EPP) triggers an AP in the adjacent sarcolemma
- AP in sarcolemma travels down T tubules
- sarcoplasmic reticulum releases Ca2+
- Ca2+ binds to troponin, which shifts tropomyosin to uncover the myosin-binding sites on actin –> myosin heads bind actin
- contraction occurs via cross-bridge cycling
neuromuscular junction
where the motor neuron contacts the skeletal muscle
sarcolemma
plasma membrane of the muscle fiber/cell
events at the neuromuscular junction
- AP arrives at the axon terminal
- voltage-gated calcium channels open, calcium enters the motor neuron
- calcium entry causes the release of ACh neurotransmitter into the synaptic cleft
- ACh diffuses across to ACh receptors(Na+ chemical gates) on the sarcolemma
- ACh binding to receptors, open gates, allowing Na+ to enter resulting in end plate potential (local depolarization)
- acetylcholinesterase degrades ACh
myasthenia gravis
disease characterized by drooping upper eyelids, difficulty swallowing and talking, and generalized muscle weakness
involves shortage of ACh receptors because person’s ACh receptors are attacked by own antibodies
suggests this is an autoimmune disease
cross bridge cycling (lead up w/ Ca2+)
- at higher intracellular Ca2+ concentrations, Ca2+ binds to troponin
- troponin changes shape and moves tropomyosin away from myosin-binding sites
- myosin heads then allowed to bind to actin, forming cross bridge
- cycling is initiated, causing sarcomere shortening and muscle contraction
- when nervous stimulation ceases, Ca2+ is pumped back into SR, and contraction ends
cross bridge cycling (myosin steps)
1) cross bridge formation: high-energy myosin head attaches to actin thin filament active site
2) working(power) stroke: myosin head pivots and pulls thin filament toward M line
3) cross bridge detachment: ATP attaches to myosin head, causing cross bridge to detach
4) cocking of myosin head: energy from hydrolysis of ATP “cocks” myosin head into high-energy state –> this energy will be used for power stroke in next cross bridge cycle
isotonic (concentric) contraction
bicep curl
muscle shortens and then extends
isometric contraction
holding a squat hold
muscle does not shorten but still under tension
short-duration exercise vs. prolonged-duration exercise (energy sources)
short-duration, high-intensity:
6 sec - use ATP stored in muscles
10 sec - form ATP from creatine phosphate and ADP
30-40 sec to end - break down glycogen to glucose to oxidize to get ATP(anaerobic pathway)
prolonged-duration exercise:
hours - ATP generated by the breakdown of several nutrient energy fuels by aerobic pathway
factors that increase the force of skeletal muscle contraction
- high frequency of stimulation(AP - temporal summation and tetanus)
- large number of muscle fibers recruited
- large muscle fibers
- muscle and sarcomere stretched to slightly over 100% of resting length
(optical sarcomere operating length 80-120% of resting length)
all of this increases contractile force (more cross bridges attached)
slow oxidative fibers
speed of contraction: slow
myosin ATPase activity: slow
primary pathway for ATP synthesis: aerobic
myoglobin content(binds O2): high
glycogen stores: low
recruitment order: first
rate of fatigue: slow (fatigue-resistant)
best suited for: endurance-type activities (running a marathon, maintaining posture - antigravity muscles)
fiber diameter: small
mitochondria: many
capillaries: many
color: red
fast oxidative fibers
speed of contraction: fast
myosin ATPase activity: fast
primary pathway for ATP synthesis: aerobic (some anaerobic glycolysis)
myoglobin content(binds O2): high
glycogen stores: intermediate
recruitment order: second
rate of fatigue: intermediate (moderately fatigue-resistant)
best suited for: sprinting, walking
fiber diameter: large
mitochondria: many
capillaries: many
color: red to pink
fast glycolytic fibers
speed of contraction: fast
myosin ATPase activity: fast
primary pathway for ATP synthesis: anaerobic glycolysis
myoglobin content(binds O2): low
glycogen stores: high
recruitment order: third
rate of fatigue: fast (fatigable)
best suited for: short-term intense or powerful movements (ex - hitting a baseball)
fiber diameter: intermediate
mitochondria: few
capillaries: few
color: white (pale)
