q&a smooth muscles Flashcards
The action potential of skeletal muscle
spreads inward to all parts of the muscle via the T tubules.
The functions of tropomyosin in skeletal muscle include
acting as a “relaxing protein” at rest by covering up the sites where myosin
binds to actin.
The cross-bridges of the sarcomere in skeletal muscle are made up of
myosin
The contractile response in skeletal muscle
produces more tension when the muscle contracts isometrically than when
the muscle contracts isotonically
Gap junctions
are present and provide the pathway for rapid spread of excitation from one cardiac muscle fiber to another
Which of the following characteristics is
shared by simple and facilitated diffusion of
glucose?
Occurs down an electrochemical gradient
During the upstroke of the nerve action
potential
there is net inward current and the cell
interior becomes less negative
Solutions A and B are separated by a
semipermeable membrane that is perme
able to K+, but not to Cl–. Solution A is
100 mM KCl, and solution B is 1 mM KCl.
Which of the following statements about
solution A and solution B is true?
K+ will diffuse from solution A to solu
tion B until a membrane potential
develops with solution A negative with
respect to solution B
The correct temporal sequence for events
at the neuromuscular junction is
uptake of Ca2+ into the presynaptic terminal; release of acetylcholine (ACh);
depolarization of the muscle end plate
Which characteristic or component is
shared by skeletal muscle and smooth muscle?
Elevation of intracellular [Ca2+] for
excitation–contraction coupling
Repeated stimulation of a skeletal muscle
fiber causes a sustained contraction (tetanus).
Accumulation of which solute in intracellular
fluid is responsible for the tetanus?
Ca2+
Solutions A and B are separated by a mem
brane that is permeable to Ca2+ and imper
meable to Cl–. Solution A contains 10 mM
CaCl2, and solution B contains 1 mM CaCl2.
Assuming that 2.3 RT/F = 60 mV, Ca2+ will be
at electrochemical equilibrium when
solution A is –30 mV
A 42-year-old man with myasthenia gravis
notes increased muscle strength when he is
treated with an acetylcholinesterase (AChE)
inhibitor. The basis for his improvement is
increased
levels of ACh at the muscle end plates
In a hospital error, a 60-year-old woman
is infused with large volumes of a solution
that causes lysis of her red blood cells
(RBCs). The solution was most likely
300 mM urea
During a nerve action potential, a stimulus is delivered as indicated by the arrow
shown in the following figure. In response
to the stimulus, a second action potential
will not occur
Solutions A and B are separated by a
membrane that is permeable to urea.
Solution A is 10 mM urea, and solution B is
5mM urea. If the concentration of urea in
solution A is doubled, the flux of urea across
the membrane will
triple
A muscle cell has an intracellular [Na+] of
14 mM and an extracellular [Na+ ] of 140 mM.
Assuming that 2.3 RT/F = 60 mV, what would
the membrane potential be if the muscle cell
membrane were permeable only to Na+?
+60 mV
At which labeled point on the action
potential is the K+ closest to electrochemical
equilibrium?
5
What process is responsible for the
change in membrane potential that occurs
between point 1 and point 3?
Movement of Na+ into the cell
What process is responsible for the
change in membrane potential that occurs
between point 3 and point 4?
Movement of K+ out of the cell
The velocity of conduction of action
potentials along a nerve will be increased by
myelinating the nerve
Solutions A and B are separated by a semi
permeable membrane. Solution A contains
1mMsucrose and 1 mM urea. Solution B con
tains 1 mM sucrose. The reflection coefficient
for sucrose is one and the reflection coefficient
for urea is zero. Which of the following statements about these solutions is correct?
Solution A is hyperosmotic with
respect to solution B, and the solutions
are isotonic
Transport of D- and L-glucose proceeds at
the same rate down an electrochemical gradient by which of the following processes?
Simple diffusion
Which of the following will double
the permeability of a solute in a lipid bilayer?
Doubling the oil/water partition coefficient of the solute
A newly developed local anesthetic
blocks Na+ channels in nerves. Which of the
following effects on the action potential
would it be expected to produce?
Decrease the rate of rise of the upstroke
of the action potential
At the muscle end plate, acetylcholine
(ACh) causes the opening of
Na+ and K+ channels and depolarization
to a value halfway between the Na+ and
K+ equilibrium potentials
An inhibitory postsynaptic potential
hyperpolarizes the postsynaptic membrane by opening Ca2+ channels
Which of the following would occur as a
result of the inhibition of Na+,K+-ATPase?
Increased intracellular K+ concentration
Which of the following temporal
sequences is correct for excitation
contraction coupling in skeletal muscle?
Action potential in the muscle mem
brane; depolarization of the T tubules;
release of Ca2+ from the sarcoplasmic
reticulum (SR)
Which of the following transport process
es is involved if transport of glucose from the
intestinal lumen into a small intestinal cell is
inhibited by abolishing the usual Na+ gradient
across the cell membrane?
Cotransport
In skeletal muscle, which of the following
events occurs before depolarization of the
T tubules in the mechanism of excitation
contraction coupling?
Depolarization of the sarcolemmal
membrane
Which of the following is an inhibitory
neurotransmitter in the central nervous system (CNS)?
γ-Aminobutyric acid (GABA)
Adenosine triphosphate (ATP) is used indirectly for which of the following processes?
Absorption of glucose by intestinal
epithelial cells
Which of the following causes rigor in
skeletal muscle?
An increase in adenosine triphosphate
(ATP) level
Degeneration of dopaminergic neurons
has been implicated in
Parkinson’s disease
Assuming complete dissociation of all
solutes, which of the following solutions
would be hyperosmotic to 1 mM NaCl?
1 mM CaCl2
A new drug is developed that blocks the
transporter for H+ secretion in gastric parie
tal cells. Which of the following transport
processes is being inhibited?
Primary active transport
A 56-year-old woman with severe mus
cle weakness is hospitalized. The only
abnormality in her laboratory values is an
elevated serum K+ concentration. The elevated serum K+ causes muscle weakness
because
Na+ channels are closed by depolarization
Which of the following hormones causes
contraction of vascular smooth muscle?
Antidiuretic hormone (ADH)
Which of the following hormones causes
constriction of vascular smooth muscle
through an inositol 1,4,5-triphosphate (IP3)
second messenger system?
Antidiuretic hormone (ADH)
Which of the following substances
acts on its target cells via an inositol 1,4,5
triphosphate (IP3)–Ca2+ mechanism?
Oxytocin acting on myoepithelial cells
of the breast
A key difference in the mechanism of
excitation–contraction coupling between
the muscle of the pharynx and the muscle of
the wall of the small intestine is that
Ca2+ binds to troponin C in the pharynx,
but not in the small intestine, to initiate
contraction
norepinephrine inhibits contraction of smooth muscle in the __________
intestine
norepinephrine stimulates contraction of smooth muscle in ___________
blood vessels
