Lecture 9.2 main points

Question 1

what must happen in order for electrical signals in motor neurons to be communicated to muscle

Answer 1

electrical signals (action potentials) from motor neurons must be transformed into chemical signals ( neurotransmitters)

Question 2

where does the electrical signal in motor neurons communication to muscle

Answer 2

at the neuromuscular junction

Question 3

as a result of the electrical signals, what do the chemicals cause in a muscle cell

Answer 3

chemical signals then stimulate electrical signals in sarcolemma of the muscle fiber ( if strong enough)
the electrical signal in the muscle fiber (action potential) then activate a series of events that leads to the shortening of the skeletal muscle fiber

Question 4

what is the predominant theory of skeletal muscle contraction

Answer 4

sliding filament model of contraction

Question 5

brief description of sliding filament model of contraction

Answer 5

interactions between thick and thin filaments of the sarcomere produce the contraction (shortening) of a skeletal muscle cell
-in a relaxed state, thin and thick filaments overlap slight
-during contraction thin filaments slide toward the M-line past the thick filaments (acting and myosin overlap more)

Question 6

chemical gradients of certain ions are necessary for what

Answer 6

proper electrical, and contractile activity of skeletal muscle

Question 7

three main ions in muscle cells. concentration at rest intracellular vs extracellular

Answer 7

intracellular [Ca] very low
intracellular [Na] very low
intracellular [K] high

Question 8

what is the numeric value of intracellular charge at rest

Answer 8

-95 mV

Question 9

what is the extracellular charge at rest

Answer 9

0 mV

Question 10

what two events must occur for skeletal muscle to contract

Answer 10

activation and excitation-contraction coupling

Question 11

how does activation occur and what must it generate

Answer 11

must be nervous system stimulation, must generate action potential in sarcolemma
happens at the neuromuscular junction

Question 12

what does action potential (excitation) produce that is necessary for contraction

Answer 12

action potential propagated along sarcolemma
intracellular Ca levels must briefly rise leading to the onset of contraction

Question 13

list the steps in sequence for phase 1 in which the motor neuron stimulates the muscle fiber (activation)

Answer 13

AP arrives at axon terminal at neuromuscular junction
Ach is released, binds to receptors on sarcolemma
Ion permeability of sarcolemma changes
Local change in membrane (depolarization) occurs
Local depolarization (end plate potential) ignites the AP in sarcolemma

Question 14

list the steps in sequence for phase 2 in which excitation (action potential) - contraction coupling occurs

Answer 14

AP travels across the entire sarcolemma
AP travels along T tubules
SR releases Ca, Ca binds to troponin,
myosin binding sites on actin exposed
myosin heads bind to actin, contraction begins

Question 15

what type of neuron connects to, and stimulates, a skeletal muscle cell, is it voluntary or involuntary

Answer 15

somatic motor neurons, voluntary

Question 16

how do somatic motor neuron axons travel to skeletal muscle

Answer 16

travel via nerves (bundles of mostly neuron axons)

Question 17

are somatic motor neuron axons branched or unbranched

Answer 17

may form several branches as it enters the whole muscle

Question 18

each axon ending forms a neuromuscular junction with what

Answer 18

a single muscle fiber

Question 19

events of the motor neuron at the NMJ (neuromuscular junction)

Answer 19

1. action potential arrives at the axon terminal of motor neuron
2. voltage gated Ca channels open. Ca enters the axon terminal moving it down its electrochemical gradient
3. Ca entry causes Ach to be released by exocytosis
4. Ach diffuses across the synaptic cleft and binds to its receptors on the sarcolemma
5. Ach binding opens ion channels in the receptors that allow SIMULTANEOUS passage of Na INTO the muscle fiber and K OUT OF the muscle fiber
   more Na enters than K exits which produces a local charge in the membrane potential called the end plate potential
6. Ach effects are terminated by its breakdown in the synaptic cleft by acetylcholinerase and diffusion away from the junction

Question 20

at the NMJ do calcium channels open or close briefly

Answer 20

open briefly allowing calcium to enter the axon terminal

Question 21

at the NMJ what ion moves through the channel and where does it go

Answer 21

calcium moves through the channel and goes into the cell

Question 22

what is the purpose of calcium inside the axon terminal? What does it cause?

Answer 22

causes acetylcholine to be release by exocytosis

Question 23

what is the neurotransmitter used for chemical communication between the motor neuron and skeletal muscle fiber

Answer 23

Ach (acetylcholine)

Question 24

into what space is acetylcholine released

Answer 24

the synaptic cleft

Question 25

what Ach destroying enzyme waits in the synaptic cleft

Answer 25

acetylcholinesterase

Question 26

why is acetylcholinesterase important

Answer 26

breaks down Ach to acetate and choline prevents continued muscle fiber contraction in the absence of addition stimulation

Question 27

as Ach makes it to the surface of the muscle cell at the NMJ what receptor does it bind to?

Answer 27

nicotinic acetylcholine receptor (nAchr)

Question 28

as Ach binds to nAchr does the ion channel open or close

Answer 28

open

Question 29

what two ions are allowed to pass through the post synaptic ion channel

Answer 29

sodium and potassium sodium in, potassium out

Question 30

does Na or K flow through the channel in greater amounts in the post synaptic membrane

Answer 30

Na

Question 31

what effect does the ion flow have on the membrane charge of -95mV

Answer 31

makes it more positive, depolarization

Question 32

the change in sarcolemma membrane charge at the NMJ is called what

Answer 32

end plate potential

Question 33

is the end plate potential a local event or entire cell event

Answer 33

local, only happens at the NMJ not on the whole cell

Question 34

what is depolarization

Answer 34

when the membrane voltage gets closer to zero from its initial -95. Becomes less polar (different)

Question 35

what chemical directly affects the release of acetycholine

Answer 35

calcium

Question 36

term for critical value voltage that must be reached in order to illicit an action potential

Answer 36

threshold

Question 37

once threshold is reached, what ion channels open in large amounts

Answer 37

voltage gated sodium channels

Question 38

what do voltage gated sodium channels allow to pass

Answer 38

sodium into the cell

Question 39

what is the effect on the intracellular membrane voltage with the increasing flow of sodium into the cell

Answer 39

intracellular membrane voltage becomes more positive

Question 40

what phase of AP generation involves the opening of sodium channels called

Answer 40

depolarization phase

Question 41

what phase follows depolarization and what does it do for the electrical condition of the membrane voltage (intracellular)

Answer 41

repolarization, becomes less negative due to more potassium exiting than sodium entering

Question 42

during repolarization many voltage gated sodium channels begin to close, what channels begin to open

Answer 42

voltage gated K channels

Question 43

during repolarization, as sodium channels close, what happens to the amount of sodium flowing into the cell

Answer 43

decreases the influx of sodium

Question 44

during repolarization as potassium channels begin to open what happens to potassium flow outside of the cell

Answer 44

potassium flow more rapidly outside of the cell

Question 45

what is the effect of lessening sodium influx into the cell and increasing potassium efflux out of the cell, does the intracellular membrane voltage change?

Answer 45

intracellular membrane voltage becomes more negative

Question 46

what happens when potassium channels close

Answer 46

membrane potential is restored back to resting

Question 47

what cannot happen during the refractory period

Answer 47

another action potential cannot be stimulated

Question 48

what is the latent period

Answer 48

when E-C (excitation- contraction) coupling events occur, time between AP initiation and beginning of contraction

Question 49

certain voltage-sensitive proteins are found in the membrane of the T-Tubule, what is their name

Answer 49

DHP receptors

Question 50

what ion passes through DHP receptors

Answer 50

small amounts of calcium to flow into the sarcoplasm

Question 51

DHP receptors are connected to special protein channels called what

Answer 51

Ryanodine receptors

Question 52

where are ryanodine receptors found

Answer 52

in the terminal cisterns of the sarcoplasmic reticulum

Question 53

what is the function of ryanodine receptors

Answer 53

to release calcium from the sarcoplasmic reticulum into the sarcoplasm

Question 54

when stimulated by DHP receptors, ryanodine receptors allow what ion to pass through their channel

Answer 54

calcium

Question 55

where does the calcium flow when passed through ryanodine receptors

Answer 55

from the sarcoplasmic reticulum into the sarcoplasm

Question 56

how does the influx of calcium ions into the sarcoplasm affect sarcoplasmic Ca concentration

Answer 56

it increases

Question 57

excitation coupling events

Answer 57

single muscle AP causes brief activation of DHP receptors followed by activation of the ryanodine receptords allowing a brief release of calcium into the sarcoplasm. the DHP receptors deactivate therefore closing the Ryanodine receptors, ending the release of Ca into the sarcoplasm

Question 58

what happens if after the first AP there isn't a subsequent

Answer 58

sarcoplasmic Ca will fall due to removal by SERCA pumps - pumping calcium back into the SR and sarcolemma ATPases that pump calcium out of the cell