Unit 2 -q&a Flashcards
Simple diffusion and facilitated diffusion share which
of the following characteristics?
Do not require adenosine triphosphate (ATP)
What is the osmolarity of a solution containing 10
millimolar NaCl, 5 millimolar KCl, and 10 millimolar
CaCl2 (in mOsm/L)?
100
Which of the following best describes the equilibrium
potential for Cl− (in millivolts)?
−85
Which of the following best describes the equilibrium
potential for K+ (in millivolts)?
−88
The net driving force is greatest for which ion when the membrane potential of this cell is −85 millivolts?
Ca++
If this cell were permeable only to K+, what would be
the effect of reducing the extracellular K+ concentration from 5 to 2.5 millimolar?
19 millivolts hyperpolarization
Which of the following best describes the changes in
cell volume that will occur when red blood cells (previously equilibrated in a 280-milliosmolar solution of NaCl) are placed in a solution of 140-millimolar NaCl
containing 20-millimolar urea, a relatively large but
permeant molecule?
Shrink, then return to original volume
A clinical study is conducted to determine the actions
of an unknown test solution on red blood cell volume.
One milliliter of heparinized human blood is pipetted
into 100 milliliters of test solution and mixed. Samples are taken and analyzed immediately before and at 1-second intervals after mixing.
The results show that red blood cells placed into the test solution immediately swell and burst. Which of the following best describes the tonicity and osmolarity of the test solution?
Hypotonic; could be hyperosmotic, hypo-osmotic,
or iso-osmotic
A single contraction of skeletal muscle is most likely to be terminated by which of the following actions?
Removal of sarcoplasmic Ca++
A model cell with three different transporters (X, Y, and Z) and a resting membrane potential of −75 millivolts is shown in the above figure. Consider the intracellular and extracellular concentrations of all three ions to be typical of a normal cell.
Which of the following best
describes transporter Y?
Secondary active transport
Which of the following best describes an attribute of
visceral smooth muscle not shared by skeletal muscle?
Contracts in response to stretch
The resting potential of a myelinated nerve fiber is
primarily dependent on the concentration gradient of which of the following ions?
K+
Calmodulin is most closely related, both structurally
and functionally, to which of the following proteins?
Troponin C
In the figure below, two compartments (X and Y) are
separated by a typical biological membrane (lipid bilayer).
The concentrations of glucose in compartments X
and Y at time zero are shown. There are no transporters for glucose in the membrane, and the membrane is impermeable to glucose. Which of the figures best represent the volumes of compartments X and Y when the system reaches equilibrium?
B
During a demonstration for medical students, a neurologist uses magnetic cortical stimulation to trigger firing of the ulnar nerve in a volunteer. At relatively low-amplitude stimulation, action potentials are recorded only from muscle fibers in the index finger.
As the amplitude of the stimulation is increased, action potentials are recorded from muscle fibers in both the index finger and the biceps muscle.
What is the fundamental principle
underlying this amplitude-dependent response?
Large motor neurons that innervate large motor
units require a larger depolarizing stimulus
A neurotransmitter activates its receptor on an ion
channel of a neuron, which causes the water-filled
channel to open. Once the channel is open, ions move through the channel down their respective electrochemical gradients. A change in membrane potential follows. Which of the following best describes the type of channel and mechanism of ion transport?
Ligand gated
Simple diffusion
A 55-year-old woman has a serum potassium of 6.1
mEq/L (normal: 3.5-5.0 mEq/L) and a serum sodium
of 150 mEq/L (normal: 135-147 mEq/L). Which of the
following sets of changes best describe the K+ Nernst
potential and resting membrane potential in a typical
neuron in this woman compared to normal? (Assume
normal intracellular ion concentrations.)
K+ Nernst Potential is Less negative
Resting Membrane Potential is
Less negative
Which of the following decreases in length during the
contraction of a skeletal muscle fiber?
I band of the sarcomere
Equilibrium potentials for three unknown ions are
shown in the above figure. Note that ions S and R
are positively charged and that ion Q is negatively
charged. Assume that the cell membrane is permeable to all three ions and that the cell has a resting membrane potential of −90 millivolts. Which of the following best describes the net movement of the various ions across the cell membrane by passive diffusion?
Outward
Inward
Inward
Tetanic contraction of a skeletal muscle fiber results
from a cumulative increase in the intracellular concentration of which of the following?
Ca++
Weight lifting can result in a dramatic increase in skeletal muscle mass. This increase in muscle mass is primarily attributable to which of the following?
Hypertrophy of individual muscle fibers
Which of the following transport mechanisms is not
rate limited by an intrinsic Vmax?
E (big)
Five hypothetical nerve axons are shown in the above figure. Axons A and B are myelinated, whereas axons C, D, and E are non-myelinated.
Which axon is most likely to have the fastest conduction velocity for an action potential?
B
Which of the following is primarily responsible for the change in membrane potential between points B and D?
Movement of Na+ into the cell
Which of the following is primarily responsible for the change in membrane potential between points D and E?
Movement of K+ out of the cell
The axon of a neuron is stimulated experimentally with a 25-millivolt pulse, which initiates an action potential with a velocity of 50 meters per second. The axon is then stimulated with a 100-millivolt pulse.
What is the action potential velocity after the 100-millivolt stimulation pulse (in meters per second)?
100
The delayed onset and prolonged duration of smooth muscle contraction, as well as the greater force generated by smooth muscle compared with skeletal muscle, are all consequences of which of the following?
Slower cycling rate of the smooth muscle myosin cross-bridges
An experimental drug is being tested as a potential therapeutic treatment for asthma. Preclinical studies have shown that this drug induces the relaxation of cultured porcine tracheal smooth muscle cells precontracted with acetylcholine. Which of the following mechanisms
of action is most likely to induce this effect?
Stimulation of adenylate cyclase
Which of the following best describes muscle B compared with muscle A?
Innervated by smaller nerve fibers
The delay between the termination of the transient depolarization of the muscle membrane and the onset of muscle contraction observed in both muscles A and B reflects the time necessary for which of the following
events to occur?
Ca++ to accumulate in the sarcoplasm
The increased muscle strength observed during the
Tensilon test is due to an increase in which of the following?
Levels of ACh at the muscle end plates
What is the most likely basis for the symptoms described in this patient?
Autoimmune response
Which of the following drugs would likely alleviate this patient’s symptoms?
Neostigmine
The figure above shows a relationship between contraction velocity and force for five different skeletal muscles. Which of the following muscles (A-E) is most likely to correspond to muscle number 1 on the figure shown? (Assume that all muscles shown are at their normal resting lengths.)
E
the isometric length-tension relationship in a representative intact skeletal muscle:
So-called “active” or contraction-dependent tension
B
the isometric length-tension relationship in a representative intact skeletal muscle:
The muscle length at which active tension is maximal
E
the isometric length-tension relationship in a representative intact skeletal muscle:
The contribution of noncontractile muscle elements to total tension
C
Smooth muscle contraction is terminated by which of
the following?
Dephosphorylation of myosin light chain
Based on these findings, which of the following is the
most likely cause of this patient’s leg weakness?
Impaired presynaptic voltage-sensitive Ca++ influx
A preliminary diagnosis is confirmed by the presence
of which of the following?
Antibodies against the voltage-sensitive Ca++ channel
The molecular mechanism underlying these symptoms is most similar to which of the following?
Botulinum toxin
Point at which the membrane potential (Vm) is closest to the Na+ equilibrium potential
D
Point at which the driving force for Na+ is the greatest
F
Point at which the ratio of K+ permeability to Na+ permeability (PK/PNa) is the greatest
F
A physiology experiment is conducted in which a motoneuron that normally innervates a predominantly fast type II muscle is anastomosed to a predominantly
slow type I muscle. Which of the following is most
likely to decrease in the type I muscle after the transinnervation surgery?
Mitochondrial content
In the experiment illustrated in part A of the above
figure, equal volumes of solutions X, Y, and Z are placed into the compartments of the two U-shaped vessels shown.
The two compartments of each vessel are separated by semipermeable membranes (i.e., impermeable
to ions and large polar molecules). Part B illustrates the fluid distribution across the membranes at equilibration. Assuming complete dissociation, identify each of the solutions shown
1 M glucose 1 M NaCl 1 M CaCl2
Trace A best describes the kinetics of which event?
Transport of K+ into a muscle cell
Trace B best describes the kinetics of which of the following events?
Transport of O2 across an artificial lipid bilayer
Trace A in the above figure represents a typical action potential recorded under control conditions from a normal nerve cell in response to a depolarizing stimulus. Which of the following perturbations would explain the conversion of the response shown in trace A
to the action potential shown in trace B?
Replacement of the voltage-sensitive Na+ channels with “slow” Ca++ channels
Which of the following perturbations would account
for the failure of the same stimulus to elicit an action
potential in trace C?
Blockade of voltage-sensitive Na+ channels
A 17-year-old soccer player sustained a fracture to the left tibia. After her lower leg has been in a cast for 8 weeks, she is surprised to find that the left gastrocnemius muscle is significantly smaller in circumference than it was before the fracture. What is the most likely explanation?
Temporary reduction in actin and myosin protein synthesis
Smooth muscle that exhibits rhythmical contraction in the absence of external stimuli also necessarily exhibits which of the following?
Intrinsic pacemaker wave activity
Ouabain-sensitive transport of Na+ ions from the cytosol to the extracellular fluid
Primary active transport
Glucose uptake into skeletal muscle
Facilitated diffusion
Na+-dependent transport of Ca++ from the cytosol to
the extracellular fluid
Counter-transport
Transport of glucose from the intestinal lumen into an intestinal epithelial cell
Co-transport
Movement of Na+ ions into a nerve cell during the upstroke of an action potential
Simple diffusion
Traces A, B, and C in the above figure summarize the
changes in membrane potential (Vm) and the underlying membrane permeabilities (P) that occur in a nerve cell over the course of an action potential. Choose the
combination below that identifies each of the traces
Vm PNa PK
If the intracellular concentration of a membrane permeant substance doubles from 10 to 20 millimolar and the extracellular concentration remains at 5 millimolar, the rate of diffusion of that substance across
the plasma membrane will increase by a factor of how much?
3
An apparently healthy 15-year-old boy dies during a
minor surgical procedure while under general anesthesia. The boy’s grandfather had also died during a surgical procedure. A clinical assessment team determines that the child had malignant hyperthermia (MH).
MH is an inherited disease in which triggering agents, such as certain anesthetics, stimulate calcium release from storage sites in muscle, leading to elevated concentrations of myoplasmic calcium. The MH crisis is most likely to be associated with which of the following?
Defective ryanodine receptors
A 24-year-old woman is admitted as an emergency to
University Hospital after an automobile accident in which severe lacerations to the left wrist severed a major muscle tendon. The severed ends of the tendon were overlapped by 6 cm to facilitate suturing and reattachment. Which of
the following would be expected after 6 weeks compared with the preinjured muscle? Assume that series growth of sarcomeres cannot be completed within 6 weeks.
Increase Decrease
The length-tension diagram above was obtained from a skeletal muscle with equal numbers of red and white fibers. Supramaximal tetanic stimuli were used to initiate an isometric contraction at each muscle length studied. The resting length was 20 cm. What is the maximum amount of active tension that the muscle is capable of generating at a preload of 100 grams?
55 to 65 grams
The sensitivity of the smooth muscle contractile apparatus to calcium is known to increase in the steady state under normal conditions. This increase in calcium sensitivity can be attributed to a decrease in the levels of which of the following substances?
Myosin light chain phosphatase (MLCP)
Which of the following best describes the correct temporal order of events for skeletal muscle?
Nerve action
potential
Muscle action
potential
Muscle
contraction
Which of the following best describes a physiological
difference between the contraction of smooth muscle compared with the contraction of cardiac muscle and skeletal muscle?
Does not require an action potential
The above figure shows the force-velocity relationship for isotonic contractions of skeletal muscle. The differences in the three curves result from differences in which of the following?
Myosin ATPase activity
A 12-year-old boy presents with a 4-month history of
diminished vision and diplopia. He also experiences
tiredness toward the end of the day. He has no other
symptoms. On examination, the patient has ptosis of
the left eye that improves after a period of sleep.
Clinical examination is otherwise normal. No evidence of weakness of any other muscles is found. Additional testing indicates the presence of anti-acetylcholine antibodies in the plasma, a normal thyroid function test, and a normal computed tomography scan of the brain and orbit. What is the initial diagnosis?
Juvenile myasthenia gravis
