Chapter 4B

Question 1

Na+ initiates muscle action potential in the skeletal muscle fiber

true/false

Answer 1

true, p. 34

Question 2

A nerve impulse (action potential) elicits a muscle action potential. Steps:

1.Binding of two molecules of ACh to the receptor on
the motor end plate opens a fast ion-channel in the Ach receptor

2. Arrival of the nerve impulse at the synaptic end bulbs
   stimulates voltage-gated channels to open
3. The inflow of Na+ makes the inside of the
   muscle fiber more positively charged. This change in the membrane potential
   triggers a muscle action potential
4. small cations,
   most importantly Na+, enters the muscle cell downhill
5. Each nerve impulse normally elicits one muscle
   action potential. The muscle action potential then propagates along the
   sarcolemma into the system of T tubules
6. The
   entering Ca2+ stimulates the synaptic vesicles to undergo exocytosis liberating ACh
   into the synaptic cleft. The ACh then diffuses across the synaptic cleft
7. This causes the sarcoplasmic reticulum
   to release its stored Ca2+ into the sarcoplasm, and the muscle fiber subsequently
   contracts
8. Ca2+ enters the nerve cell downhil

Answer 2

2. Arrival of the nerve impulse at the synaptic end bulbs
   stimulates voltage-gated channels to open
3. Ca2+ enters the nerve cell downhil
4. The
   entering Ca2+ stimulates the synaptic vesicles to undergo exocytosis liberating ACh
   into the synaptic cleft. The ACh then diffuses across the synaptic cleft
   1.Binding of two molecules of ACh to the receptor on
   the motor end plate opens a fast ion-channel in the Ach receptor
5. Small cations,
   most importantly Na+, enters the muscle cell downhill
6. The inflow of Na+ makes the inside of the
   muscle fiber more positively charged. This change in the membrane potential
   triggers a muscle action potential
7. Each nerve impulse normally elicits one muscle
   action potential. The muscle action potential then propagates along the
   sarcolemma into the system of T tubules
8. This causes the sarcoplasmic reticulum
   to release its stored Ca2+ into the sarcoplasm, and the muscle fiber subsequently
   contracts

Question 3

Almost everything discussed in Chapter 3 regarding initiation and conduction of action
potentials in nerve fibers applies equally to skeletal muscle fibers

Answer 3

see p.36

Question 4

Almost everything discussed in Chapter 3 regarding initiation and conduction of action
potentials in nerve fibers applies equally to skeletal muscle fibers, except for small
quantitative differences:

1. Lower resting membrane potential: −80 to −90 mV in skeletal fibers and …
   mv in neurons.
2. Longer duration of action potential
3. Faster velocity of conduction: 3 to 5 m/sec (about 1/13 the velocity of
   conduction in the large myelinated nerve fibers that excite skeletal muscle).

Answer 4

−70

Question 5

Excitation–contraction coupling: the sequence of events that links excitation (a muscle
action potential) to contraction (sliding of the filaments).

Triad: 1 transverse T tubule and 2 opposing terminal cisterns of the sarcoplasmic reticulum.

Answer 5

ok

Question 6

• The T tubule and terminal cisterns are mechanically linked together by two groups of
  integral membrane proteins: voltage-gated Ca2+ channels and Ca2+ release channels

Answer 6

ok

Question 7

When a skeletal muscle fiber is excited and an action potential travels along the
T tubule, the voltage-gated Ca2+ channels/Ca2+ release
channels detect the change in voltage and
undergo a conformational change that ultimately causes the Ca2+ channels/Ca2+ release
channels to open.
* Large amounts of Ca2+ flow out of the sarcoplasmic reticulum around the thick
and thin filaments.

Answer 7

Ca2+ channels
Ca2+ release channels

Question 8

END OF MUSCLE ACTION POTENTIAL:

Termination of ACh activity. Effect of ACh binding lasts only briefly because it is
rapidly broken down by acetylcholinesterase (geef afkorting): enzyme located on the
extracellular side of the motor end plate membrane.

Answer 8

(AChE)

Question 9

END OF MUSCLE ACTION POTENTIAL: true or false?

• If another nerve impulse releases more acetylcholine, the acetylcholine is broken down
• If action potentials cease, ACh is no longer released and acetylcholinesterase
  rapidly breaks down the Ach already present in the synaptic cleft .

Dit gebeurt al direct na ACh is releaseden bindt aan receptors

Answer 9

false: If another nerve impulse releases more acetylcholine, steps 2 and 3 repeat.

De rest klopt

Question 10

the removal of ACh ends the production of muscle
action potentials, the Ca2+ moves
from the sarcoplasm of the muscle
fiber back into the X, and the Ca2+ release
channels in the sarcoplasmic
reticulum membrane close.

Answer 10

sarcoplasmic
reticulum

Question 11

Strength of skeletal muscle contraction is hardly affected by moderate changes in
extracellular fluid calcium concentration because it is caused almost entirely by
calcium ions released from the X inside the skeletal muscle fiber.

Answer 11

sarcoplasmic reticulum

Question 12

Voor een volledige samenvatting van muscle contraction, zie p.43

Answer 12

ok

Question 13

True/false?

• Like cardiac muscle tissue, smooth muscle tissue is usually activated involuntarily.
• It is composed of far larger fibers than skeletal muscle
• The attractive forces between myosin and actin filaments that cause contraction
  are the same that skeletal muscle, but the internal physical arrangement of smooth
  muscle fibers is different.
• Contraction in a smooth muscle fiber starts quicker and lasts much longer
  than skeletal muscle fiber contraction.
• Another difference is that smooth muscle can both shorten and stretch to a
  lesser extent than the other muscle types.

Answer 13

*True
*False
*True
*False: starts slower
*False: to a greater extent

Question 14

SMOOTH MUSCLE FIBER
* Two types:
1. X-unit smooth muscle tissue
2. X-unit smooth muscle tissue (syncytial or visceral)

Answer 14

Multi
Single

Question 15

SMOOTH MUSCLE FIBER: MULTI-UNIT

Discrete, separate smooth muscle fibers.

• Each fiber operates independently/dependently of the others and often is
  innervated by a single nerve ending: stimulation of one multiunit fiber causes contraction of that fiber only.
• Outer surfaces of fibers covered by a thin layer of basement
  membrane–like substance: insulate/joins the separate fibers

Answer 15

independently
insulate

Question 16

SMOOTH MUSCLE FIBER: SINGLE-UNIT

Mass of hundreds to thousands of smooth muscle fibers that contract together as a
single unit.

• Fibers arranged in sheets or bundles with cell membranes adhered to each other
  (force generated in one muscle fiber can be transmitted to the next).

Cell membranes are joined by many X through which ions can flow freely
from one muscle cell to the next.

When a neurotransmitter, hormone, or autorhythmic signal stimulates one fiber, the
muscle action potential is transmitted to neighboring fibers, which then contract individually/in
unison

Answer 16

X gap junctions
in unison

Question 17

The sarcoplasm contains thick filaments (myosin), thin filaments (actine) and also
intermediate filaments.

True/false

Answer 17

True

Question 18

Filaments have no regular pattern of overlap: no striations (smooth appearance)
true/false

Answer 18

true

Question 19

Smooth muscle fibers also have transverse tubules and have only a small amount of
sarcoplasmic reticulum for storage of Ca2+

true/false

Answer 19

false: they lack transverse tubules

Question 20

Smoth muscle fiber:

There are small pouchlike invaginations of
the plasma membrane called caveolae that
contain extracellular X that can be used
for muscular contraction

Answer 20

Ca2+

Question 21

smooth muscle fiber:

The thin filaments attach to structures called X bodies that are dispersed
throughout the sarcoplasm or attached to the sarcolemma.

• Bundles of intermediate filaments also attach to X bodies and stretch from one
  X body to another.

Answer 21

dense

Question 22

Smooth muscle fiber

During contraction, the sliding filament mechanism involving thick and thin filaments
generates tension that is transmitted to X filaments.
* These in turn pull on the dense bodies attached to the sarcolemma, causing a
lengthwise shortening of the muscle fiber.

Answer 22

intermediate

Question 23

As a smooth muscle fiber
contracts, it rotates as a
corkscrew turns: fiber twists
in a helix as it contracts, and
rotates in the opposite
direction as it relaxes.

true/false

Answer 23

true

Question 24

Different stimuli modify the
membrane potential of smooth
muscle cells:
* action potentials from the
autonomic nervous system
* local factors: changes in pH,
oxygen and carbon dioxide
levels, temperature, and ion
concentrations
* stretching
* X

Answer 24

hormones

Question 25

When the membrane potential reaches threshold, the muscle action potential occurs, propagates and opens voltage-gated Ca2+ channels in the sarcolemma. So, important: X initiates muscle action potential in the smooth muscle fiber!!

Answer 25

Ca2+

Question 26

PHYSIOLOGY OF SMOOTH MUSCLE Ca2+ enters into sarcoplasm from interstitial fluid. Intracellular calcium increases and binds to X leading to activation of calmodulin

Answer 26

calmodulin

Question 27

Force of contraction of smooth muscle is usually highly dependent on extracelular fluid calcium ion concentration. true/false

Answer 27

true

Question 28

Smooth muscle: Because there are no transverse tubules, it takes longer for Ca2+ to reach the filaments in the center of the fiber and trigger the contractile process (slower that skeletal). true/false

Answer 28

true

Question 29

DIFFERENCES BETWEEN CARDIAC AND SKELETAL MUSCLE * Cardiac muscle fibers are shorter/longer in length and less/more circular in transverse section than skeletal muscle fibers. * The ends of cardiac muscle fibers connect to neighboring fibers by irregular/regular transverse thickenings of the sarcolemma called intercalated discs. * The discs contain desmosomes (hold fibers together) and gap junctions (allow muscle action potentials to conduct from one muscle fiber to its neighbors: entire myocardium contracts as a single, coordinated unit (syncytium).

Answer 29

shorter less circular irregular

Question 30

Cardiac muscle fibers have the same arrangement of actin and myosin, and the same bands, zones, and Z discs, as skeletal muscle fibers true/fals

Answer 30

true

Question 31

Transverse tubules of cardiac muscle are wider but less abundant than those of skeletal muscle: two transverse tubules per sarcomere located at the Z disc. true/false

Answer 31

false: one transverse tubule per sarcomere

Question 32

There are two types of cardiac fibers or cardiomyocytes: 1. autorhytmic cells (excitatory system, at the nodes and special bundles) 2. cardiac or ventricular working cells

Answer 32

ok

Question 33

PHYSIOLOGY OF CARDIAC MUSCLE When an action potential passes over the X cardiac muscle membrane, the action potential spreads to the interior of the cardiac muscle fiber along the membranes of the transverse (T) tubules (same that skeletal)

Answer 33

ventricular

Question 34

The mechanism of contraction is similar in cardiac and skeletal muscle: the electrical activity (action potential) leads to the mechanical response (contraction) after a short delay. As Ca2+ concentration rises inside a contractile fiber, Ca2+ binds to the regulatory protein troponin, which allows the actin and myosin filaments to begin sliding past one another, and tension starts to develop. There is however a difference: The action potential in cardiac muscle is longer/shorter and exhibits a plateau before the abrupt repolarization

Answer 34

shorter

Question 35

Action muscle potential of skeletal muscle is caused by fast sodium channels: tremendous numbers of Na+ ions enter the skeletal muscle fiber from the extracellular fluid for few thousandths of a second and then abruptly close and repolarization occurs. Ventricular cardiac muscle has three types of membrane ion channels that play important roles in causing the voltage changes of the action potential: 1. fast sodium channels 2. slow sodium-X channels 3. fast and slow potassium channels

Answer 35

calcium

Question 36

Cardiac muscle: Which of these enters the cell upon voltage changes (despolarize) of the action potential and which of these exit the cell (repolarize)? Na+, Ca+, K+

Answer 36

Na+ and Ca2+ enter the cell K+ exits the cell

Question 37

Cardiac action potential: put the following events in the right order Phase X (plateau): the calcium channels (which were slowly opening since phase 0) are finally open and Ca2+ begins to enter the cell. At the same time, fast K+ channels close. Phase X (resting membrane potential): membrane potential at -90mV Phase X (initial repolarization): Na+ channels close rapidly. The cell begins to repolarize: fast K+ channels open and K+ begins to flow out of the cell Phase X (depolarization): opening of the fast Na+ is responsible for the rapid upstroke spike of the action potential observed in ventricular muscle: the rapid entry of Na into the fiber rapidly depolarizes it * Phase X (rapid repolarization): Ca2+ channels close and slow K+ channels open: potassium ions rapidly exit the cell, ending the plateau and returning the cell's membrane potential to its resting level.

Answer 37

Phase 2 Phase 4 Phase 1 Phase 0 Phase 3

Question 38

Differences in muscle type: what belongs to which type (skeletal, cardiac, smooth) 1. stimuli A Pacemaker cells (Chapter 5) initiate cardiac action potential (rhythm can be modified by neurotransmitters from autonomic motor neurons and hormones). Initiated cardiac action potential (depolarization current) spread to ventricular cardiac cells through Gap junctions: positive charges enter the cell B Neurotransmitters from autonomic motor neuron, hormones, stretching etc. C Ach. from autonomic motor neuron

Answer 38

A Cardiac B Smooth C Skeletal

Question 39

Differences in muscle type: what belongs to which type (skeletal, cardiac, smooth) 2. Cation triggering muscle action potential A Na+ B Ca2+ C Na2+ starts it, Ca2+ keeps it (plateau)

Answer 39

A Skeletal B Smooth C Cardiac

Question 40

Differences in muscle type: what belongs to which type (skeletal, cardiac, smooth) 3. Sarcoplasmic reticulum A Big B Medium C Small

Answer 40

A Skeletal B Cardiac C smooth

Question 41

Differences in muscle type: what belongs to which type (skeletal, cardiac, smooth) 4. Cation for contraction A Ca2+ from inside the SR and outside the cell B Ca2+ mostly from outside the cell C Ca2+ from inside the SR

Answer 41

A cardiac B smooth C skeletal

Question 42

Differences in muscle type: what belongs to which type (skeletal, cardiac, smooth) 5. Regulatory protein that binds Ca2+ for contraction A Troponin B Troponin C Calmodulin

Answer 42

A Skeletal B Cardiac C smooth

Question 43

Differences in muscle type: what belongs to which type (skeletal, cardiac, smooth) 6. speed of conraction A Moderate B Slow C Fast

Answer 43

A Cardiac B Smooth C Skeletal

Question 44

Which of the muscle types has its contractile proteins not organized in sarcomeres?

Answer 44

smooth

Question 45

The SR is abundant/some/very little in which muscle types?

Answer 45

abundant: skeletal some: cardiac Very little: smooth

Question 46

Transverse tubules not present: which muscle type?

Answer 46

smooth

Question 47

which muscle type has no junctions between fibers?

Answer 47

skeletal

Question 48

does skeletal muscle type have autorhythmicity?

Answer 48

no

Question 49

Which of the muscle types only has the SR as source of Ca2+ for contraction, opposing to the SR + interstitial fluid?

Answer 49

Skeletal

Question 50

Which muscle type has other regulator proteins for contraction than troponin and tropomyosin?

Answer 50

calmodulin & light chain kinase: smooth muscle

Question 51

Contraction regulation: which belongs to which muscle type? A ACh B ACh + norepinephrine + several hormones+ local chemic changes + stretching C ACh + norepinephrine + several hormones

Answer 51

A skeletal B smooth C cardiac