A&p.cardiac.and.smooth.exam.4.

Front 1

what are four important physical characteristics of cardiac muscle tissue

Back 1

1. striated appearance
2. contain intercalated disks
3. endomysium and perimysium
4. limited repair

Front 2

why do cardiac muscles have a striated appearance?

Back 2

-same actin-myosin arrangement as in skeletal muscle
-cells are smaller and branches

Front 3

how are cardiac fibers connected?

Back 3

by intercalated discs that contain desmosomes and gap junctions

Front 4

what membranes does cardiac muscles contain?

Back 4

endomysium and perimysium but no epimysium; therefore, there is no thick CT holding this together on the outside

Front 5

why is there limited repair for cardiac muscle?

Back 5

because there are no myosatellite cells; the muscles are incomplete with loss of function

Front 6

in a cardiac muscle cell why is the AP prolonged and what else is extended because of it?

Back 6

its prolonged because Ca2+ ions continue to enter the cell for an extended period which also extends the period of contraction

Front 7

why cant summation occur?

Back 7

because the refractory period continues until relaxation is well under way

Front 8

why is it vital that tetanic contractions do not occur in cardiac muscle?

Back 8

because a heart in tetany couldn't pump blood

Front 9

what are the three stages involved in an action potential and contraction in a cardiac fiber?

Back 9

1. depolarization
2. plateau
3. repolarization

Front 10

what happens during depolarization of cardiac fiber?

Back 10

-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

Front 11

what are fast sodium channels?

Back 11

they're used in cardiac muscle fibers during depolarization; they open quickly and remain open for only a few milliseconds

Front 12

what is a plateau and why does it occur?

Back 12

-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)

Front 13

what happens during the plateau of a cardiac muscle cell?

Back 13

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

Front 14

what two things happen once the Ca2+ ions are released during the plateau period?

Back 14

1. the calcium triggers the calcium release from the SR due to the influx of calcium from interstitial fluid
2. contraction is triggered

Front 15

what are slow calcium channels?

Back 15

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

Front 16

explain the contraction state of a cardiac muscle fiber compared to a skeletal.

Back 16

-its 0.25 seconds compared to .001 seconds in skeletal; its a much longer contraction state

Front 17

what is a benefit of the 0.25 seconds contraction state compared to .001?

Back 17

it prevents early repolarization and the refractory period lasts longer

Front 18

is the depolarization faster or slower in a cardiac muscle fiber than a skeletal?

Back 18

faster

Front 19

what happens during repolarization of a cardiac fiber?

Back 19

potassium channels open, K+ ions rush out of the cell and repolarization occurs

Front 20

why is the repolarization of cardiac fiber rapid?

Back 20

because the Ca2++ close and increase the permeability

Front 21

what is the diameter of a smooth muscle fuber?

Back 21

5-10um

Front 22

what is the length of a smooth muscle fiber?

Back 22

30-200um

Front 23

how many nuclei are in a smooth muscle?

Back 23

1

Front 24

what is the ratio of thick:thin filaments?

Back 24

1:10-1:15

Front 25

why are there no striations in smooth muscle?

Back 25

because there are no sarcomeres so there are no myofibrils

Front 26

what are the three characteristics of thin and thick filaments in a smooth muscle fiber?

Back 26

1. no sarcomeres; no myofibrils; no striations
2. myosin heads along entire thick filament length
3. arranged diagonally so contract is in a twist

Front 27

what are three characteristics of the intermediate filaments of a smooth muscle?

Back 27

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

Front 28

what two things does the smooth muscle lack?

Back 28

striations and t-tubules

Front 29

what are the caveolae of the smooth muscle and what two things do they contain?

Back 29

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

Front 30

what does the sarcoplasmic reticulum do in smooth muscles?

Back 30

release Ca2+ when triggered by influx via caveolae

Front 31

how is an AP of a smooth muscle fiber initiated?

Back 31

by Ca2+, not Na+; Ca2+ is the depolarizating factor

Front 32

what does Ca2+ cause in the smooth muscle fiber?

Back 32

the release of Ca2+ ions from SR

Front 33

what are the two possible names of cardiac muscle (CM) cells?

Back 33

cardiocytes and cardiomyosites

Front 34

what are the two types of CM cells?

Back 34

1. contracting cells- atrin and ventricles
2. conducting cells- areas surrounding and connecting ventricles and atrin

Front 35

what are the two different types of smooth muscle fibers?

Back 35

1. multiunit smooth muscle cells
2. visceral smooth muscle cells

Front 36

what are multiunit smooth muscle cells?

Back 36

-involuntary motor unit innervation
-1 or more motor neurons per cell
-AP propagated over sarcolemma

Front 37

how many motor neurons per cell are there in multiunit smooth muscle cells and why?

Back 37

1 or more because every cell acts independently: one can contract without the other

Front 38

Where is the AP propagated in a multiunit smooth muscle cell?

Back 38

over the sarcolemma

Front 39

why are the contractions slower in multiunit smooth muscle fibers than skeletal and cardiac?

Back 39

because the myosin enzyme is slower

Front 40

where are multiunit smooth muscle fibers found?

Back 40

iris, male reproductive tract, large artery walls, arrector pili muscles

Front 41

what are visceral smooth muscle cells?

Back 41

-no direct neuronal contact
-connected by gap junctions

Front 42

what 5 things do visceral smooth muscle cells respond to?

Back 42

1. chemicals
2. hormones
3. O2 or CO2
4. stretching or irritation
5. pacesetter cells

Front 43

where are visceral smooth muscle fibers found?

Back 43

the walls of viscera- digestive system, etc

Front 44

what are the three main functions of smooth muscle tissue?

Back 44

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

Front 45

what is the cell arrangement in smooth muscle tissue?

Back 45

regular

Front 46

based on innervation and control, what two subtypes can a smooth muscle be divided into?

Back 46

1. multi-unit smooth muscle
2. visceral smooth muscle

Front 47

what do pacesetter cells do to the visceral smooth muscle?

Back 47

trigger rhythmic cycles of activity that contract spontaneously at regular intervals

Front 48

why is tension development and resting length not directly related?

Back 48

because the thin and thick filaments of smooth muscle are scattered and are not organized into sarcomeres

Front 49

what does a stretched smooth muscle do?

Back 49

adapts to its new length and retains the ability to contract on demand- plasticity

Front 50

what is plasticity?

Back 50

ability to function over a wide range of lengths