Talbot - Excitable Cells and Muscle Contraction

Question 1

what are 5 types of excitable cells

Answer 1

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

Question 2

what does it mean to be an excitable cell

Answer 2

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

Question 3

what is the plasma membrane called in muscles

Answer 3

sarcolemma

Question 4

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

Answer 4

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

Question 5

what makes up a myofiber

Answer 5

myofibrils

Question 6

what are myofibrils made of

Answer 6

end-to-end sarcomeres (created striations)

Question 7

what are the two domains in skeletal muscle

Answer 7

sarcolemma and sarcoplasmic reticulum (SR)

Question 8

what 3 types of channels are located in the sarcolemma

Answer 8

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

Question 9

where is Ca2+ stored in the muscle

Answer 9

in the sarcoplasmic reticulum

Question 10

what are the 2 domains within the sarcoplasmic reticulum

Answer 10

longitudinal elements and terminal cisternae (end sacs)

Question 11

what makes up a triad in the sarcoplasmic reticulum

Answer 11

1 T-tubule + 2 terminal cisternae of SR regions

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

are skeletal muscles neurogenic action potentials or myogenic action potentials

Answer 15

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

Question 16

are cardiac muscles neurogenic action potentials or myogenic action potentials

Answer 16

myogenic - they can spontaneously produce an action potential

Question 17

how are cardiac muscles connected

Answer 17

they are branched and the myocytes connect through intercalated discs

Question 18

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

Answer 18

gap junctions and desmosomes

Question 19

why are the gap junctions important in cardiac muscle

Answer 19

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

Question 20

why are desmosomes important in cardiac muscles

Answer 20

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

Question 21

what are 3 types of cardiac muscle cells

Answer 21

autorhythmic, conduction, and contractile

Question 22

what are autorhythmic cells

Answer 22

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

Question 23

what are contractile cells

Answer 23

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

Question 24

what is unique about the action potentials in autorhythmic cells

Answer 24

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

Question 25

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

Answer 25

If channels -> creates a slow net depolarization

Question 26

what type of Ca channels are in the autorhythmic cells

Answer 26

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

Question 27

what is different about contractile action potentials

Answer 27

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)

Question 28

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

Answer 28

DHP receptors and ryanodine receptors in SR are not physically coupled

Question 29

what is tetanus in skeletal muscles

Answer 29

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

Question 30

what is excitation-contraction (EC) coupling

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

at the motor end plate - ACh receptor or nicotinic AChR

Question 33

what is a sarcomere

Answer 33

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

Question 34

what 2 binding proteins are located on actin filaments

Answer 34

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

Question 35

what does tropomyosin do

Answer 35

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

Question 36

what does troponin do

Answer 36

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

Question 37

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

Answer 37

+ end = tropomodulin | - end = CapZ and alpha actinin

Question 38

what is neculin accessory protein

Answer 38

an actin stabilizing protein - helps set the length of actin

Question 39

what is titin accessory protein

Answer 39

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

Question 40

what is myomesin accessory protein

Answer 40

stabilizes the sarcomere - visible as M line

Question 41

what is the A band

Answer 41

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

Question 42

what is the I band

Answer 42

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

Question 43

what is the H band/zone

Answer 43

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

Question 44

what is the Z disc/line

Answer 44

end of sarcomeres - point of actin attachment

Question 45

what happens during the sliding filament muscle contraction

Answer 45

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

Question 46

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

Answer 46

no

Question 47

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

Answer 47

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

Question 48

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

Answer 48

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

Question 49

what is the myosin low energy conformation

Answer 49

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

Question 50

how is contraction different in smooth muscles

Answer 50

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

Question 51

where is single unit (unitary) smooth muscle located

Answer 51

walls of visceral organs and blood vessels - use gap junctions

Question 52

where is multi-unit smooth muscle located

Answer 52

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

Question 53

which type of smooth muscle is myogenic and which is neurogenic

Answer 53

single unit = myogenic | multi-unit = neurogenic

Question 54

what is the depolarization phase carried out by in smooth muscle

Answer 54

Ca2+