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MABS Physiology > Lecture 5 > Flashcards

Lecture 5 Flashcards

General Principles of Skeletal, Cardiac & Smooth Muscle

1
Q

name the three types of muscles?

A

skeletal muscle, smooth muscle, and cardiac muscle

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2
Q

which muscle of the three named acts on the skeleton, is it voluntary or involuntary?

A

skeletal muscle; voluntary

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3
Q

what is skeletal muscle responsible for?

A

it plays a key role in posture, locomotion, speech, and respiration

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4
Q

what kind of striations are found in skeletal muscle?

A

it exhibits transverse striations (2-3 micrometers) that result from the highly organized arrangement of actin and myosin molecules

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5
Q

skeletal muscle is striated or non striated?

A

striated

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6
Q

what kind of muscle is the heart? voluntary or involuntary?

A

its composed of cardiac muscle; involuntary

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7
Q

what controls the heart?

A

controlled by an intrinsic pacemaker and modulated by the autonomic nervous system

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8
Q

striations are found in the smooth muscle, T/F?

A

False

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9
Q

smooth muscle is voluntary or involuntary? where is it found?

A

involuntary; found lining the hollow organs such as the intestine and blood vessels

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10
Q

what is it called when each skeletal muscle fiber contains bundles of filaments? where are these found

A

myofibrils; running along the axis of the cell and so this pattern results from repeating pattern in the myofibrils

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11
Q

what comprises the tropomyosin molecule?

A

consists of two identical alpha helices that coil around each other and sit near the two grooves formed by two helical actin strands

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12
Q

what comprises the troponin molecule?

A

a heterotrimer consisting of troponin T, C, and I

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13
Q

what is troponin T?

A

this binds to a single molecule of tropomyosin

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14
Q

what is troponin C?

A

this binds Ca2+

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15
Q

what is troponin I?

A

this binds to actin and inhibits contraction

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16
Q

how does the muscle work in the contracted state?

A

a ratchet action of myosin which pulls actin toward the center of the sarcomere

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17
Q

what is the function of the heart?

A

pumps blood through the circulatory system accomplished by the highly organized contraction of cardiac muscle cells

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18
Q

what do muscle cells form when they are connected together?

A

electrical syncytium through electrical and mechanical connections between adjacent cardiac muscle cells

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19
Q

how does the action potential pass through the heart?

A

because the heart is arranged in way that forms an electrical syncytium via gap junctions, an action potential is therefore able to pass quickly throughout the heart to facilitate synchronized contraction of the cardiac muscle cells important for the pumping of the heart; ultimately refilling of the heart requires synchronized relaxation of the heart

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20
Q

cardiac muscle are larger or smaller than skeletal cells?

A

cardiac muscle cells are smaller and measure 10 micrometers in diameter by 100 micrometers in length

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21
Q

what are the connections between cardiac cells called?

A

intercalated disks

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22
Q

what are intercalated disks?

A

a combination of mechanical junctions and electrical connections

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23
Q

why are the mechanical connections in the heart important?

A

these are the fascia adherent and desmosomes and these keep the cells from pulling apart when contracting

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24
Q

gap junctions are electrical connections or mechanical connections in the heart?

A

these are between the heart cells and provide electrical connections between cells to allow propagation of the action potential throughout the heart

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25
Q

how do the connections in the heart facilitate the movement of a single action potential within the heart?

A

the action potential is generated within the SA node to pass thoughout the heart so that the heart can contract in a synchronous wave like fashion

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26
Q

what ion is responsible for the initiation of the action potential?

A

calcium

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27
Q

there is more connective tissue in the skeletal muscle than cardiac tissue?

A

more in the heart

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28
Q

what is the reason for having more connective tissue in the heart?

A

it helps prevent muscle rupture like in skeletal muscle but also prevents the overstretching of the heart

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29
Q

what does the heart require to contract?

A

extracellular calcium, different from skeletal muscle which can contract in the total absence of extracellular calcium; this is important because this allows for the excitation contraction coupling in the heart, which means the the SR can then release the calcium; this is called a calcium dependent calcium release and in the skeletal muscle its called voltage dependent calcium release

30
Q

how fast does the action potential pass through the entire heart?

A

within 220 ms after initiation in the sinoatrial node.

31
Q

how long does the contraction of the cardiac muscle typically last?

A

300 ms, this rapid conduction promotes nearly synchronous contraction of the heart muscle cells which is different from that of skeletal muscle where cells are grouped into motor units recruited independently as the force of contraction is increased

32
Q

the heart cell is voltage dependent and the skeletal cell is calcium dependent, T/F?

A

F, the heart cell is calcium dependent and voltage gated and the skeletal cell is voltage dependent

33
Q

T/F. skeletal, cardiac and smooth muscles have T tubules?

A

false, cardiac and skeletal muscles have T tubules, smooth muscles have alveoli similar to the way T tubules work

34
Q

how does the tension length chart work? define RT, TT, AT variables also

A 
RT= resting tension
TT= total tension
AT= active tension

even if we are not using all of our muscles they will have a resting tension; all muscles also have an optimum length of the bone which means actin and myosin sit on top of each other perfectly so that when ATP binds to myosin head to reach maximum contraction or maximal tension meaning that no matter how much ATP is provided it cannot get any shorter;

example if we have a muscle tension of of 0.8 nm - 1.6 nm, anything below or above these limits tension is not any greater because they are either overlapping too much or overstretched

35
Q

describe tension length of heart muscle?

A

heart muscles are not stretched as much as they are in the skeletal muscles, but remember that active tension is in the bell shaped curve

36
Q

how can you tell a difference between cardiac and skeletal muscle tension on the tension curve?

A

note the resting tension and keep in mind that heart muscle has more connective tissue increasing its resistance to stretch

37
Q

how does excitation contraction coupling work?

A

you have the flow of extracellular calcium into the cells via voltage gated L-tyoe Ca++ channels that bind to the ryanodine receptor and this communicates with the SR and so the sarcomere releases more calcium and this allows for the contraction to occur; no extracellular entry point in skeletal muscle and hyper/hypocalcemia affects heart much more early on than skeletal muscle

38
Q

what is PLB?

A

phospholamban protein affects the heart rate, keep in mind that calcium is the driving force in the heart cell because its pumped in and out, and so this protein works in tandem with B1 receptor and sympathetic arch, affecting calcium levels affecting contraction

39
Q

T/F, every heart muscle we have we use for contraction? T/F muscle cells recruit more or less depending on the work being done

A

T; T

40
Q

T/F, you can change the rate of the cardiac heart cells?

A

T

41
Q

how does calcium relate to the force of contraction in the heart?

A

Relaxation of the heart occurs by reducing cytosolic free [Ca++], with Ca++ sequestration by the SR accounting for the majority of the decrease in cytosolic [Ca++] (≈70%; panel B). Some Ca++ extrusion occurs through the 3Na+-1Ca++ antiporter (≈28%), with very little Ca++ extrusion by the sarcolemmal Ca++ pump (<2%). NCX, sodium-calcium exchanger.

42
Q

why would tetany of the heart be lethal? how do we counteract it?

A

it would defeat the critical pumping action of the heart (relax and contract); the long action potential found in the cardiac muscle which is due to activation of the voltage gated L type Ca2+ channel results in a long refractory period which in turn prevents tetany

43
Q

why would the electrical syncytium be important to the heart?

A

all of the cardiac muscle cells contract during a single beat, and is not possible to increase the force of contraction by recruiting more muscle cells

44
Q

how does action potential for cardiomyocytes work?

A

go up, plateau, then come down for calcium and longer if more calcium to allow for the heart to empty the blood from the ventricles into systemic circulation

45
Q

how does relaxation of the skeletal muscle occur?

A

re-accumulation of Ca2+ by the SR thought the action of the SR Ca2+ pump (SERCA)

46
Q

how is some Ca2++ extruded from the cardiac muscle cell?

A

cell though the sarcolemmal 3Na+-1Ca++ antiporter and a sarcolemmal Ca++ pump.

47
Q

how does the anti porter use the Na+ gradient across the cell to power the uphill movement of Ca2+ out of the cell?

A

3 Na+ ions enter the cell in exchange for 1 Ca++ ion

The sarcolemmal Ca++ pump uses ATP to extrude Ca++ from the cell.

48
Q

what contributes to the relaxation of cardiac muscle

A

both extrusion mechanisms and SERCA decrease cytosolic Ca2+

49
Q

describe the chart for the relaxation of cardiac muscle?

A

action potential happens and comes down, then calcium release happens, then you see the contraction of the muscle

50
Q

how is calcium related to force generation?

A

higher levels of calcium allow for a stronger force and this done through active tension generation so that you have a higher total tension

51
Q

what happens when we stimulate B-adrenergic receptors?

A

heart increases the force of contraction

52
Q

how do the B-adrenergic receptors of the heart work?

A

binding occurs between receptor and epinephrine, these receptors are g-protein coupled receptors (alpha, beta, gamma portions), and this is GS type which means its stimulatory and cAMP levels increase and this affects the phospholamban through phosphorylation, more calcium can come in from cytosol into SR to prevent them from being sent out via exchangers to increase SR concentration of calcium so that next heart beat releases more calcium into cell for better contractility and this is done via Beta-1 receptors

53
Q

T/F, smooth muscle is striated?

A

false, they are non striated muscle cells that are a major component of hollow organs such as the alimentary canal, airways, vasculature and urogenital tract

54
Q

how does the contraction of the smooth muscle work?

A

serves to alter the dimensions of the organ, which may result in either propelling the contents of the organ like in peristalsis or increasing the resistance to flow like in vasoconstriction

55
Q

how is the contraction of smooth muscle regulated? how does it compare with skeletal muscle?

A

a thick filament regulated nad requires an alteration in myosin before it can interact with actin; contraction of striated muscle is thin filament regulated and requires movement of the troponin-tropomyosin complex on the actin filament before myosin can bind to actin

56
Q

so smooth muscles can be put into multiunit and unitary form, what is the difference?

A

unitary form brings the autonomic neuron, autonomic nervous system because smooth muscles are involuntary and these fall under the autonomic nervous system, and communicates with multiple cells at the same time and they contract in unitary action; they can be individually contracted smooth muscle like from top to bottom in bladder to push urine out

57
Q

why do we have to have tension on arteries and veins?

A

to return blood back to heart, always some type of tension on blood vessel

58
Q

where are the caveolus?

A

Caveolae are small vesicular invaginations of the cell membrane, in this case, the small intestine

59
Q

how does excitation-contraction coupling in smooth muscle occur?

A

1) Ca2+ enters the cytoplasm through channels located in the caveoli
2) Ca2+ release from the sarcoplasmic reticulum can occur either via Ca2+ induced Ca2+ release or more importantly, via IP3 activation of SR Ca2+ channels; lots smooth muscle receptors under ANS control and you can activate through g protein coupled receptors affecting concentration of calcium

60
Q

main difference in smooth muscle cells versus the other 2 muscles is because?

A

cross bridge cycling and how its activated

61
Q

how does cross bridge cycling occur in smooth muscle?

A

The first step is the binding of four Ca2+ ions to calmodulin, which is closely related to troponin C.

Next, the Ca2+-CaM complex activates an enzyme known as myosin light chain kinase (MLCK), which in turn phosphorylates the regulatory light chain that is associated with the myosin-II molecule.

Phosphorylation of the light chain alters the conformation of the myosin head, which greatly increases its ATPase activity and allows it to interact with actin and act as a molecular motor.

Thus, in smooth muscle, CaM rather than troponin C is the Ca2+-binding protein responsible for transducing the contraction-triggering increases in [Ca2+]i.

62
Q

why is smooth muscle unique?

A

in its ability to generate various degrees of tension at a constant concentration of intracellular calcium.

63
Q

how can we attribute changes in calcium sensitivity of smooth muscle?

A

attributed to differences in the activity of myosin light chain

64
Q

how does the smooth muscle contract?

A

when the myosin light chain is phosphorylated by the actions of myosin light chain kinase (MLCK).

65
Q

how do we dephosphorylate smooth muscle contractions?

A

MCLP is a phosphatase that can dephosphorylate the myosin light chain, rendering it inactive and therefore attenuating the muscle contraction.

66
Q

explain the phasic contraction of smooth muscle contraction

A

A brief period of stimulation is associated with Ca++ mobilization, followed by cross-bridge phosphorylation and cycling to produce a brief phasic, twitch-like contraction.

67
Q

explain the tonic contraction of smooth muscle contraction

A

In a sustained tonic contraction produced by prolonged stimulation, the Ca++ and phosphorylation levels fall from an initial peak.

68
Q

what can we say is significant about maintaining force during tonic contractions?

A

Force is maintained during tonic contractions at a reduced [Ca++] (and hence a low level of myosin light-chain phosphorylation), with lower cross-bridge cycling rates manifested by lower shortening velocities and ATP consumption.

69
Q

how many cross bridge states does covalent regulation of the smooth muscle allow?

A

8 cross bridge states

70
Q

how is phosphorylation by MLCK significant?

A

its obligatory for cross bridge attachment. Phosphorylated cross bridges cycle comparatively rapidly

71
Q

what is the effect of dephosphorylation of a cross bridge during a cycle by a constitutively active MP?

A

it slows cycling rates and produces the latch state, calcium regulates cross bridge cycling by determining phosphorylation rates

72
Q

what allows eight cross bridge states in smooth muscle

A

covalent regulation

MABS Physiology (57 decks)

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