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MCBM Part 2 > Talbot - Excitable Cells and Muscle Contraction > Flashcards

Talbot - Excitable Cells and Muscle Contraction Flashcards

1
Q

what are 5 types of excitable cells

A

neurons, cardiac, smooth, skeletal muscle and beta pancreatic cells

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2
Q

what does it mean to be an excitable cell

A

capable of developing an action potential across a plasma membrane with voltage-gated channels

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3
Q

what is the plasma membrane called in muscles

A

sarcolemma

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4
Q

what are muscle cells called and how many nuclei do they have

A

myofiber with many nuclei (*syncytium - mass of cytoplasm containing many nuclei)

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5
Q

what makes up a myofiber

A

myofibrils

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6
Q

what are myofibrils made of

A

end-to-end sarcomeres (created striations)

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7
Q

what are the two domains in skeletal muscle

A

sarcolemma and sarcoplasmic reticulum (SR)

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8
Q

what 3 types of channels are located in the sarcolemma

A

invaginations called T-tubules with Cl- channels (ClC-1) and Na+ and K+ channels

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9
Q

where is Ca2+ stored in the muscle

A

in the sarcoplasmic reticulum

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10
Q

what are the 2 domains within the sarcoplasmic reticulum

A

longitudinal elements and terminal cisternae (end sacs)

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11
Q

what makes up a triad in the sarcoplasmic reticulum

A

1 T-tubule + 2 terminal cisternae of SR regions

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12
Q

how is the resting membrane potential different in skeletal muscle from neuronal

A

it is more negative or more hyperpolarized (-90mV vs -70mV)

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13
Q

why is the resting membrane potential more negative in skeletal muscle than neurons

A

increased K+ gradient (higher [K+]) and increased Cl- gradient (lower [Cl-]) = higher permeability to Cl- than most cells

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14
Q

what is the difference in action potentials for skeletal muscles and neurons

A

the skeletal muscle does not hyperpolarize - the Vm is much closer to Ek than neuronal (the K+ channels allow for repolarization)

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15
Q

are skeletal muscles neurogenic action potentials or myogenic action potentials

A

neurogenic - they need a neurotransmitter (acetylcholine) to induce action potential

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16
Q

are cardiac muscles neurogenic action potentials or myogenic action potentials

A

myogenic - they can spontaneously produce an action potential

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17
Q

how are cardiac muscles connected

A

they are branched and the myocytes connect through intercalated discs

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18
Q

what are the 2 types of connections in the cardiac intercalated discs

A

gap junctions and desmosomes

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19
Q

why are the gap junctions important in cardiac muscle

A

they allow direct electrical coupling (AP jumps to neighboring cells) of myocytes and rapid conduction of AP’s

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20
Q

why are desmosomes important in cardiac muscles

A

allow force transfers between cells and keep them from pulling apart when heart contracts

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21
Q

what are 3 types of cardiac muscle cells

A

autorhythmic, conduction, and contractile

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22
Q

what are autorhythmic cells

A

pacemaker or nodal cells found in SA and AV nodes - spontaneously depolarize to generate AP

23
Q

what are contractile cells

A

the main cell type in cardiac muscle - striated and get depolarized through gap junctions

24
Q

what is unique about the action potentials in autorhythmic cells

A

don’t maintain a stable resting potential - has pacemaker potential instead and AP is longer than neuron or skeletal muscle

25
Q

what channel does the autorhythmic cell have that is permeable to Na and K

A

If channels -> creates a slow net depolarization

26
Q

what type of Ca channels are in the autorhythmic cells

A

Fast Ca2+ channels *only type of cell where depolarization is carried by Ca and not Na

27
Q

what is different about contractile action potentials

A

they have slow L-type Ca2+ channels that open in response to depolarization and keeps membrane depolarized creating a plateau phase (fast K channels have closed prolonging the phase)

28
Q

what is different about EC coupling in cardiac cells vs skeletal muscle cells

A

DHP receptors and ryanodine receptors in SR are not physically coupled

29
Q

what is tetanus in skeletal muscles

A

state of prolonged muscle contraction that occurs when high frequency of incoming AP’s keeps membrane depolarized - allowing continued efflux of Ca2+ from SR

30
Q

what is excitation-contraction (EC) coupling

A

mechanism that allows the excitation of muscle membrane (production of AP) to induce release of Ca2+ from SR = muscle contraction

31
Q

how is Ca2+ released during the EC coupling in skeletal muscle

A

the depolarization is sensed by DHP receptors in T-tubule - conformational change in DHP - physically pushes on ryanodine (RyR) receptor inducing it to open and Ca2+ enters cytoplasm

32
Q

where are acetylcholine receptors located on the muscle cell and what are they called

A

at the motor end plate - ACh receptor or nicotinic AChR

33
Q

what is a sarcomere

A

contractile unit of muscle (skeletal and cardiac) actin, myosin, and other accessory proteins

34
Q

what 2 binding proteins are located on actin filaments

A

tropomyosin and troponin complex (Tn T, Tn I, and Tn C)

35
Q

what does tropomyosin do

A

runs along side of 2 strands of actin and physically blocks myosin binding sites “steric hindrance” in the absence of Ca2+

36
Q

what does troponin do

A

the Tn C subunit binds to Ca2+ to pull tropomyosin off myosin binding sites

37
Q

what are the + end and - end binding proteins on actin

A

+ end = tropomodulin

- end = CapZ and alpha actinin

38
Q

what is neculin accessory protein

A

an actin stabilizing protein - helps set the length of actin

39
Q

what is titin accessory protein

A

runs Z-disc to middle of thick myosin filament - helps set length of myosin and helps pull sarcomere back to resting length at end of contraction

40
Q

what is myomesin accessory protein

A

stabilizes the sarcomere - visible as M line

41
Q

what is the A band

A

length of myosin filament - dark region in middle of sarcomere, may overlap actin

42
Q

what is the I band

A

region of actin that does not overlap myosin - light region - spans 2 sarcomeres A-band to A-band

43
Q

what is the H band/zone

A

lighter region in middle of A band - myosin does not overlap actin (only myosin)

44
Q

what is the Z disc/line

A

end of sarcomeres - point of actin attachment

45
Q

what happens during the sliding filament muscle contraction

A

myosin heads walk along actin pulling Z-discs closer to each other - shortens H zone and I band increasing amount of overlap

46
Q

are actin and myosin touching/interacting when muscle is at rest

A

no

47
Q

what is happening to the myosin head when muscle is at rest

A

has bound and hydrolyzed ATP and still has the ADP and Pi non-covalently bound to it = high energy phase - “cocked” myosin head

48
Q

what induces myosin head to release Pi and ADP and attach to actin

A

Ca2+ (released from SR) exposing the myosin binding sites on actin

49
Q

what is the myosin low energy conformation

A

rigor - myosin head is “stuck” on actin and cannot release without ATP present

50
Q

how is contraction different in smooth muscles

A

+ ends of actin attach to dense bodies and terminate at protein plaques - actin only has tropomyosin (no troponin) - and maintains contraction longer

51
Q

where is single unit (unitary) smooth muscle located

A

walls of visceral organs and blood vessels - use gap junctions

52
Q

where is multi-unit smooth muscle located

A

trachea, iris, ciliary body, piloerector of skin and some blood vessels

53
Q

which type of smooth muscle is myogenic and which is neurogenic

A

single unit = myogenic

multi-unit = neurogenic

54
Q

what is the depolarization phase carried out by in smooth muscle

A

Ca2+

MCBM Part 2 (15 decks)

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