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Chapter 9 Muscle Physiology
Terms in this set (74)
a muscle cell, long and cylindrical with multiple nuclei
plasma membrane of a muscle cell/fiber
cytoplasm of a muscle cell
actin and myosin proteins responsible for muscle contraction
non striated and responsible for involuntary contractions, regulated by the ANS, and hormones
striated and responsible for involuntary movement, responds to ANS, and hormonal stimulation
striated and voluntary, and controlled by somatic nerves from the PNS
a network of delicate connective tissue that surrounds individual muscle fibers
surrounds a bundle of muscle fibers and is made of connective tissue
also known as the fascia, a dense fibrous connective tissue that is continuous with perimysium and also with tendons
each muscle has
1 nerve, 1 artery, and 1 or more veins
the repeating series of dark A-bands and I-bands in a myofibril
thin myofilament. a double helix strand of protein filaments that attaches to the z disc at the end of the sarcomere. troponin and tropomyosin on it.
the smallest contractile unit of a muscle. Z disk to Z disk.
small area between the actin filaments that decreases as a sarcomere contracts. thick filaments only
middle area in the sarcomere where thick and thin filaments are found.
contain the Z-disc and extend between sarcomeres. thin filaments only
a sheet of proteins that separates sarcomeres, and acts as an anchor for each myofibril
thin proteins in the H-zone that the myosin attaches to. thick filaments linked with accessory proteins
where does the myosin head bind?
the G-actin globular molecule
troponin and tropomyosin
regulate interactions between G-actin and myosin
bundle up to form muscle fibers and contain the sarcomere
when we bring those z lines closer together, sarcomere contracts. mechanical event that can take up to 1 sec.
shaped like golf clubs, have heads and tails
enzyme necessary for breaking down ATP into adp and phosphate, contained in the head of the myosin protein
sliding filament theory
actin myofilaments slide over myosin myofilaments. the actin is anchored to the end of the muscle fibers and the ends are drawn closer together during contraction. the fibers do not change length
passive process caused by the action of gravity or antagonistic muscles
smooth endoplasmic reticulum in muscle cells filled with calcium pumps, which use ATP to save up a bunch of calcium ions.
sarcoplasmic relticulum is studded with these. these guys are linked to voltage sensitive proteins in the membrane of the muscle cell
what happens when we want to move our arm
My brain sends an action potential along the motor neuron until it synapses with a muscle cell in my arm.
binds to receptors on the sarcolemma, receptors called ligand gated NA+ channels open up, creating a local potential on the muscle cell membrane
what happpens when Ach is released from the motor neuron into the synaptic cleft?
an action potential is produced and contraction will follow
what happens if the local potential exceeds threshold?
where nerve meets with muscle
contains the neurotransmitter AcH
separates the axon(presynaptic neuron) from the motor end plate (sarcolemma) of the muscle fiber
ca++ ions enter via voltage gated channels in the axon membrane.
what happens when the action potential reaches the terminal axon?
ca++ ions fuse with secretory vesicles that contain AcH and cause Ach to be released into the synaptic cleft
what happens after Ca++ enters the axon terminal/presynaptic neuron?
tube-like invaginations found along the sarcolemma that are continuous with the external environment and extend transversely through the muscle fiber. The action potential zips along these tubes and eventually triggers the voltage sensitive proteins on the membrane that are linked to those calcium channels on the cell's sarcoplasmic reticulum.
the calcium stored inside rushes into the rest of the cell and myosin is like YES!
what happens when the calcium channels are thrown open?
loves to bind with calcium
the inside of a muscle cell is negative compared to the outside
what does it mean when we say that the sarcolemma is polarized?
less negative on the inside (depolarization)
When Ach binds to the receptors on the sarcolemma, it opens ligand gated Na+ channels, and allows Na+ to move into the interior the cell causing it to become..
a wave of depolarization that passes along the length of a cell membrane and begins as a local potential on one section of the membrane. if the stimulus is strong enough it will spread.
Na+ channels open up and the membrane becomes more positive and less negative
what happens when the membrane depolzarizes?
the action potential is propagated
what happens as the local potential spreads to adjacent parts of the cell membrane and causes voltage gated Na+ channels to open?
Na+ channels close and K+ channels open and the cell goes back to its original state
What occurs during repolarization?
There is no stopping the generation of an AP and it will continue until the entire cell is depolarized. However, no AP will be generated if the local potentials are not strong enough to cause the spontaneous depolarization along the cell membrane.
What happens in the All or None Law?
excitation contraction coupling
an action potential in the skeletal muscle cell triggers the muscle contraction, and what group of steps happens?
AP's along the sarcolemma depolarize the T-tubules, which brings the depolarization into the interior of the muscle fiber
First thing that happens in excitation coupling
the depolarization causes voltage gated Ca++ channels to open in the sarcoplasmic reticulum and Ca++ diffuses out and binds to troponin molecules on actin.
what happens in excitation coupling after the depolarization of the interior of the muscle fiber?
the troponin/tropomyosin complex to move deeper into the grooves and expose G-actin sites for binding
what happens when calcium binds to troponin?
myosin head attaches to the open binding G-actin sites on the actin molecules
what occurs during the cross bridge attachment?
within 30ms of action potential generation, and when Ca++ levels drop the tropomyosin blockade resumes
when does the Ca++ signal end?
myosin binds to the open binding sites on actin molecules and the heads move at a hinged portion to move the actin molecules closer together. ADP and phosphate are released from the myosin head as it returns to its low energy state
what happens in the power stroke?
once all the energy is used up, the myosin head releases the actin, and uses another ATP molecule to begin the process of recocking so they can attach once again.
what happens in cross bridge detachment?
the breakdown (hydrolysis) of ATP into ADP and phosphate by ATPase and causes the myosin head to recock and thus returning to its high energy state
what happens during the cocking of the myosin head?
the sarcoplasmic reticulum will release Ca++ ions causing the muscle to contract
what happens when the sarcolemma is depolarized?
a group of muscle fibers that all get their signals from the same, single motor neuron
precise movement of a muscle
motor neurons can innervate less than 10 motor fibers apiece during...
1 neuron to 300 muscle fibers
when gross or postural movement is needed, the ratio of neurons to motor fibers can be...
this is a contraction of a muscle in response to a stimulus that causes an action potential
phases of a muscle twitch
latent phase, contraction phase, and relaxation phase
immediately after muscle fiber is stimulated by the nerve - when the calcium ions begin flooding flooding into the sarcomeres to pull away those two bodyguards of troponin and tropomyosin from the actin - The stimulus has arrived but no force is being produced. what phase of a muscle twitch is this?
when the myosin heads are binding, and pulling, and releasing over and over again and the muscle fibers contract - it lasts 10-100ms - what phase of a muscle twitch is this?
actin and myosin stop the binding cycle and the muscle relaxes - last 10-100ms - what phase of a muscle twitch is this?
the AP is an electro-chemical event that requires about ___ to occur
the increasing of AP frequency that causes muscle twitches to occur so rapidly that their is not lag between them. each individual muscle twitch sums up to resemble one continuous contraction. (tetanic contractions). allows muscle to have smooth contraction over its entire length.
running out of ATP
what will cause a muscle to fatigue?
increases stimulus strength, motor unit summation, as the stimulus increases and more AP's generated, more motor fibers can be recruited in the muscle to provide a graded (gradual) increase in the contraction of a muscle. this is how muscles can contract with a great amount of force of a small amount of force.
isometric muscle contraction
length of muscle does not change but the tension increases. for example, lifting a grand piano.
isotonic muscle contraction
length of muscle changes and tension remains constant
muscles contract as they shorten
muscles contract as they are being stretched, or muscle braking
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