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50 Cards in this Set

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  • Back
what are four important physical characteristics of cardiac muscle tissue
1. striated appearance
2. contain intercalated disks
3. endomysium and perimysium
4. limited repair
why do cardiac muscles have a striated appearance?
-same actin-myosin arrangement as in skeletal muscle
-cells are smaller and branches
how are cardiac fibers connected?
by intercalated discs that contain desmosomes and gap junctions
what membranes does cardiac muscles contain?
endomysium and perimysium but no epimysium; therefore, there is no thick CT holding this together on the outside
why is there limited repair for cardiac muscle?
because there are no myosatellite cells; the muscles are incomplete with loss of function
in a cardiac muscle cell why is the AP prolonged and what else is extended because of it?
its prolonged because Ca2+ ions continue to enter the cell for an extended period which also extends the period of contraction
why cant summation occur?
because the refractory period continues until relaxation is well under way
why is it vital that tetanic contractions do not occur in cardiac muscle?
because a heart in tetany couldn't pump blood
what are the three stages involved in an action potential and contraction in a cardiac fiber?
1. depolarization
2. plateau
3. repolarization
what happens during depolarization of cardiac fiber?
-stable at RMP -90mv
-at threshold, voltage-gated sodium channels open and the membrane becomes permeable to Na+; influx of Na+ causes a rapid depolarization
what are fast sodium channels?
they're used in cardiac muscle fibers during depolarization; they open quickly and remain open for only a few milliseconds
what is a plateau and why does it occur?
-it is a time of maintained depolarization
-occurs when influx=efflux:
Opening of K+ channels begins (efflux) and opening of Ca+ channels in sarcolemma (influx)
what happens during the plateau of a cardiac muscle cell?
transmembrane remains near 0; once approaches +3-mV, the sodium channels close and the cell begins to pump Na+ out of the cell. as they close, calcium gated channels are opening and the entry of Ca2+ balances the loss of Na+ and the membrane hovers near 0mV
what two things happen once the Ca2+ ions are released during the plateau period?
1. the calcium triggers the calcium release from the SR due to the influx of calcium from interstitial fluid
2. contraction is triggered
what are slow calcium channels?
theyre involved in the plateau period of cardiac fiber; they open slowly and remain open for a long period of time and are present when K+ channels open and close
explain the contraction state of a cardiac muscle fiber compared to a skeletal.
-its 0.25 seconds compared to .001 seconds in skeletal; its a much longer contraction state
what is a benefit of the 0.25 seconds contraction state compared to .001?
it prevents early repolarization and the refractory period lasts longer
is the depolarization faster or slower in a cardiac muscle fiber than a skeletal?
faster
what happens during repolarization of a cardiac fiber?
potassium channels open, K+ ions rush out of the cell and repolarization occurs
why is the repolarization of cardiac fiber rapid?
because the Ca2++ close and increase the permeability
what is the diameter of a smooth muscle fuber?
5-10um
what is the length of a smooth muscle fiber?
30-200um
how many nuclei are in a smooth muscle?
1
what is the ratio of thick:thin filaments?
1:10-1:15
why are there no striations in smooth muscle?
because there are no sarcomeres so there are no myofibrils
what are the three characteristics of thin and thick filaments in a smooth muscle fiber?
1. no sarcomeres; no myofibrils; no striations
2. myosin heads along entire thick filament length
3. arranged diagonally so contract is in a twist
what are three characteristics of the intermediate filaments of a smooth muscle?
1. lattice arrangement of non-contractile filaments
2. attach to dense bodies tethered to sarcolemma
3. anchor thin filaments (compare to Z discs) that are also attached to dense bodies
what two things does the smooth muscle lack?
striations and t-tubules
what are the caveolae of the smooth muscle and what two things do they contain?
they are envaginations on plasma membrane;
contain:
1. many Ca2+ channels and some Na+ channels along the sarcolemma
2. contain extracellular Ca2+ used for muscle contraction
what does the sarcoplasmic reticulum do in smooth muscles?
release Ca2+ when triggered by influx via caveolae
how is an AP of a smooth muscle fiber initiated?
by Ca2+, not Na+; Ca2+ is the depolarizating factor
what does Ca2+ cause in the smooth muscle fiber?
the release of Ca2+ ions from SR
what are the two possible names of cardiac muscle (CM) cells?
cardiocytes and cardiomyosites
what are the two types of CM cells?
1. contracting cells- atrin and ventricles
2. conducting cells- areas surrounding and connecting ventricles and atrin
what are the two different types of smooth muscle fibers?
1. multiunit smooth muscle cells
2. visceral smooth muscle cells
what are multiunit smooth muscle cells?
-involuntary motor unit innervation
-1 or more motor neurons per cell
-AP propagated over sarcolemma
how many motor neurons per cell are there in multiunit smooth muscle cells and why?
1 or more because every cell acts independently: one can contract without the other
Where is the AP propagated in a multiunit smooth muscle cell?
over the sarcolemma
why are the contractions slower in multiunit smooth muscle fibers than skeletal and cardiac?
because the myosin enzyme is slower
where are multiunit smooth muscle fibers found?
iris, male reproductive tract, large artery walls, arrector pili muscles
what are visceral smooth muscle cells?
-no direct neuronal contact
-connected by gap junctions
what 5 things do visceral smooth muscle cells respond to?
1. chemicals
2. hormones
3. O2 or CO2
4. stretching or irritation
5. pacesetter cells
where are visceral smooth muscle fibers found?
the walls of viscera- digestive system, etc
what are the three main functions of smooth muscle tissue?
1. forms sheets, bundles, or sheaths around other tissues in almost every organ
2. regulate blood flow through vital organs
3. regulate the movement of materials along internal passageways
what is the cell arrangement in smooth muscle tissue?
regular
based on innervation and control, what two subtypes can a smooth muscle be divided into?
1. multi-unit smooth muscle
2. visceral smooth muscle
what do pacesetter cells do to the visceral smooth muscle?
trigger rhythmic cycles of activity that contract spontaneously at regular intervals
why is tension development and resting length not directly related?
because the thin and thick filaments of smooth muscle are scattered and are not organized into sarcomeres
what does a stretched smooth muscle do?
adapts to its new length and retains the ability to contract on demand- plasticity
what is plasticity?
ability to function over a wide range of lengths