Exam 3 (chapter 12 part 2)

Question 1

sequence of events whereby an action potential in the sarcolemma causes contraction

• dependent of neural input from the motor neuron
• requires Ca++ release from the sarcoplasmic reticulum

Answer 1

excitation contraction coupling (skeletal muscle)

Question 2

what is excitation contraction coupling in skeletal muscle dependent on and what does it require?

Answer 2

neural input (from motor neuron) Ca++ release (from SR)

Question 3

SR =

Answer 3

sarcoplasmic reticulum

Question 4

point of contact between a motor neuron and a skeletal muscle cell

Answer 4

neuromuscular junction

Question 5

• each motor neuron innervates ___________ muscle cells

- each muscle fiber receives input from ___________ motor neuron

Answer 5

several, one

Question 6

what neurotransmitter is released at the neuromuscular junction?

Answer 6

acetylcholine

Question 7

The region of a sarcolemma adjacent to the axon terminals at a neuromuscular junction is called the _________ ________ __________.

• high density of acetylcholine receptors
• highly folded

Answer 7

motor end plate

Question 8

does the motor end plate have high or low surface area? why?

Answer 8

high (folded), more acetylcholine receptors

Question 9

Synaptic potential at Neuromuscular junction

Answer 9

end plate potential

Question 10

T/F: motor neuron action potentials always create muscle cell action potentials

Answer 10

True

Question 11

what happens if there is no Ca++?

Answer 11

troponin holds tropomyosin over myosin binding sites on actin (no cross bridges form, muscle relaxed)

Question 12

what are the 6 steps of excitation-contraction coupling in skeletal muscle?

Answer 12

action potential in sarcolemma, action potential down T tubules, Ca++ channels open on SR, Ca++ increases in cytosol, Ca++ binds to troponin shifting tropomyosin, crossbridge cycling occurs

Question 13

action potential in sarcolemma, action potential down T tubules, Ca++ channels open on SR, Ca++ increases in cytosol, Ca++ binds to troponin shifting tropomyosin, crossbridge cycling occurs

Answer 13

the 6 steps of excitation-contraction coupling in skeletal muscle

Question 14

SR Ca++ channels are _________ gated and coupled to _____ ____________

Answer 14

voltage, T tubules

Question 15

how is a contraction terminated in skeletal muscle (3 steps)?

Answer 15

Ca++ leaves troponin, tropomyosin covers myosin binding sites on actin, Ca++ removed from cytoplasm

Question 16

how is Ca++ removed from the cytoplasm?

Answer 16

Ca++ ATPase actively transports to the SR

Question 17

contraction produced in a muscle fiber in response to a single action potential

• all or nothing event for a muscle fiber at rest
• can be defined for a muscle fiber, motor unit, or whole muscle

Answer 17

Twitch

Question 18

what are the 3 phases of the twitch?

Answer 18

latent period, contraction phase, relaxation phase

Question 19

time from action potential in muscle cell to onset of contraction

• only a few milliseconds
• excitation-contraction coupling

Answer 19

latent period

Question 20

time that tension is increasing

• 10-100 msec
• crossbridge cycling

Answer 20

contraction phase

Question 21

what occurs during the latent period of a twitch?

Answer 21

excitation contraction coupling

Question 22

what occurs during the contraction phase of a twitch?

Answer 22

crossbridge cycle

Question 23

time that tension is decreasing back to zero

• longer than contraction phase
• Ca++ reuptake

Answer 23

relaxation phase

Question 24

what occurs during the relaxation phase of a twitch?

Answer 24

Ca++ reuptake

Question 25

contractile elements | - repeating units of myosin and actin (myofibrils)

Answer 25

sarcomeres

Question 26

series of elastic elements

Answer 26

connective tissue, tendons

Question 27

force exerted by contracting muscle

Answer 27

tension

Question 28

force opposing contraction | Ex: weight to be moved

Answer 28

load

Question 29

length of muscle is constant - contractile elements contract, generating tension - LOAD > TENSION - stretches series of elastic elements - does NOT shorten (load not lifted)

Answer 29

isometric twitch contraction

Question 30

LOAD > TENSION

Answer 30

isometric twitch contraction

Question 31

tension of muscle is constant - TENSION > LOAD - load is lifted as muscle shortens

Answer 31

isotonic twitch contraction

Question 32

TENSION > LOAD

Answer 32

isotonic twitch contraction

Question 33

what is an example of isometric twitch contraction?

Answer 33

Trying to lift a building, pushing a wall

Question 34

what is an example of isotonic twitch contraction?

Answer 34

lifting a 10 pound weight

Question 35

purely isotonic contractions are __________

Answer 35

rare

Question 36

why are purely isotonic contractions rare?

Answer 36

load changes as limb position changes (isometric continues until tension exceeds load)

Question 37

what 2 factors do graded muscle contractions depend on?

Answer 37

tension produced by each fiber (number of cross bridges that bind to actin), number of fibers contracting

Question 38

more cross bridges that bind = _____________ force

Answer 38

more

Question 39

T/F: tension remains constant as muscle shortened (isotonic)

Answer 39

True

Question 40

increases in _____ of action potentials increase tension in two ways - treppe - summation

Answer 40

frequency

Question 41

stepwise increase in force when the frequency of stimulation is increased - one motor unit - tension goes back to 0 before increasing again

Answer 41

treppe

Question 42

contractions overlapping and summing due to repeated action potentials - one muscle fiber - not all Ca++ removed, so tension does not go back to 0

Answer 42

contraction summation (recruitment)

Question 43

A smooth sustained muscle contraction, such as occurs in skeletal muscle when stimulation frequency is high enough

Answer 43

tetanus

Question 44

Latent period is _____ the twitch and has __ slope

Answer 44

before, no slope

Question 45

The contraction phase is at the _____ of the twitch, and has a ____ slope

Answer 45

beginning | positive

Question 46

The relaxation phase is ____ of the twitch and has a _____ slope

Answer 46

the second half | negative

Question 47

one nerve stimulus arrives at a muscle fiber so soon that the fiber has only partially relaxed from the previous twitch

Answer 47

incomplete tetanus

Question 48

When a muscle is stimulated repeatedly at a high rate, the amount of tension gradually increases to a sustained maximum tension.

Answer 48

complete tetanus

Question 49

____ _____ ______: inherent ability of a muscle to generate force - depends on the number of cross bridges in each sarcomere and the geometric arrangement of sarcomere

Answer 49

force generating capacity

Question 50

more crossbridges/sarcomere = __________ force

Answer 50

more

Question 51

more sarcomeres in parallel (not in series) = ___________ force

Answer 51

more

Question 52

number of thick and thin filaments per area is ___________ even though fiber diameter varies

Answer 52

constant

Question 53

larger diameter leads to more filaments which leads to ___________ force

Answer 53

more

Question 54

lower diameter leads to less filaments which leads to _____ force

Answer 54

less

Question 55

length of a fiber at the onset of a contraction affects ___________ generated

Answer 55

force

Question 56

resting length of muscle at which the fiber can develop the greatest amount of tension - due to maximum overlap of thick filament cross bridges and thin filaments

Answer 56

optimal length (for force generation)

Question 57

when are most muscles at optimal length?

Answer 57

normal body positions

Question 58

what is optimal fiber length due to?

Answer 58

maximum overlap of thick filament cross bridges and thin filaments

Question 59

does muscle growth increase the number of cells? if not, what happens?

Answer 59

no, they grow larger (increase diameter (hypertrophy)

Question 60

______: Increase in muscle size

Answer 60

Hypertrophy

Question 61

what is the work of a muscle cell?

Answer 61

generate force

Question 62

length that decreases cross bridge overlap

Answer 62

longer than normal body position (longer than optimal length)

Question 63

thin filaments overlap each other

Answer 63

less than optimal length

Question 64

amount of tension developed depends on the amount of _______ bound to troponin

Answer 64

Ca2+

Question 65

at high frequencies, release exceeds _____________ | - Ca++ increase in cytosol

Answer 65

reuptake

Question 66

- all troponin has Ca++ bound to it - Crossbridge cycling maxed out - Maximum tetanic contraction

Answer 66

saturation