Random Mix of Questions Flashcards
How does the micturition reflex prevent urination?
Higher control centers in the brain can inhibit the reflex by inhibiting the descending inputs that control the reflex from being expressed. (Parasympathetic neurons and somatic motor neurons)
Name the epithelial segments of the kidney:
Bowman’s capsule->Proximal Tubule->Loop of Henle->Distal tubule->Collecting ducts
Name the vascular segments of the kidney:
Afferent arteriole-> Efferent arteriole-> Peritubular capillaries
What vascular segments create the filtrant?
a. Afferent arteriole
b. Efferent arteriole
c. Peritubular capillaries
Afferent and Efferent arterioles
What vascular segment is responsible for reabsorption?
a. Afferent arteriole
b. Efferent arteriole
c. Peritubular capillaries
Peritubular capillaries
How much of the Cardiac Output is diverted to the kidneys?
a. 5L/min
b. 3L/min
c. 500 mL/min
d. 1 L/min
d. 1 L/min - which is 1/5 of the CO (5L)
What is in the filtrate?
a. red blood cells
b. plasma
c. electrolytes
d. plasma proteins
e. toxins
f. everything except red blood cells
f. everything except red blood cells
What are the 3 processes of the kidneys?
a. filtration
b. reabsorption
c. secretion
d. degradation
e. a, b, c
e. a, b, c
What are the steps the plasma must go through to enter Bowman’s capsule?
Plasma must:
1. Cross the endothelial cells (“fenistrated gaps” that are large enough for glucose, water and electrolytes to flow through. They have a negative charge).
2. Cross the epithelial cells (Podicytes) that have a negative charge
3. Fill the Bowman’s capsule
(negatively charged ions like Cl and large plasma proteins are repelled unless there is a state of inflammation which makes the “gaps” bigger and these can pass through)
The presence of proteins in the urine indicates what may be happening?
a. Protein intake is too high
b. Muscle wasting
c. Filtration barrier is breaking down
d. Filtration barrier is becoming more selective
c. Filtration barrier is breaking down
What lab value tells you how well the kidneys are doing at removing metabolic byproducts?
a. AST/ALT
b. Albumin
c. Hematocrit
d. BUN
d. BUN
A teenage boy is trying to control an asthma attack and inhales a beta-adrenergic agonist. The cardiovascular effect of this drug would be to:
a. decrease venous return
b. decrease heart rate
c. decrease peripheral resistance
d. decrease the height of the atrial wave
e. decrease the initial blood pressure reduction that occurs on standing
c. decrease peripheral resistance
Beta- adrenergic receptors relax the vascular smooth muscle, so peripheral resistance would decrease, and more blood would flow back to heart.
A man with prostate hypertrophy complains of difficulty in emptying the bladder, although pressing on him stomach during urination helps. Another aid to bladder emptying would be to:
a. increase the action of muscarinic receptors on the detrusor muscle
b. decrease adrenergic tone in the detrusor muscle
c. decrease the synthesis of nitric oxide in the corpus cavernous
d. block prostaglandin synthesis
e. block beta-adrenergic action on the internal sphincter of the bladder
a. increase the action of muscarinic receptors on the detrusor muscle
Stimulation of the parasympathetic nerves and subsequent activation of muscarinic receptors on the detrusor smooth muscle would cause bladder contraction.
A mother brings her 9 year old boy to the emergency department. He is having difficulty getting air into and out of his lungs. He wheezes, he strains his neck muscles, and he looks cyanotic. What statement is true about him?
a. He is contracting his neck muscles to force air out through his constricted bronchioles
b. part of his breathing difficulty is due to collapses of his small airways during expiration
c. His functional residual capacity has increased
d. His pulmonary blood pressure will decrease
e. His FEV1 has increased
c. His functional residual capacity has increased
The amount of air remaining in the lungs after quiet, unforced exhalation would increase during an asthma episode because the constricted bronchioles impede outflow.
An obese woman with hypertension complains of getting tired and out of breath after walking half a block. Lying down to rest does not alleviate her symptoms as well as resting in a sitting position. What statement about her breathing is true?
a. Slow, deep breathing would decrease the work of breathing for her
b. Her obesity is compressing her bronchioles
c. She has respiratory acidosis
d. The work of expanding her rib cage is increased because of her obesity
e. She needs a lower intrathoracic pressure than normal to move air into her lungs
d.The work of expanding her rib cage is increased because of her obesity
To lift her ribs up and out during inspiration, she has to lift the ribs and the heavy fat layers on top of them. A supine or prone position makes expanding the lungs even more difficult because the effect of gravity in pulling the diaphragm and abdominal contents downward is lost.
An escaped convict is shot by police while fleeing through the woods and being tracked down by bloodhounds. The bullet severes his left femoral artery, and he loses 2 L of blood before being transported to the hospital and stabilized. What statement would be true about his condition when he arrives at the hospital?
a. His Po2 would be decreased
b. Respiratory alkalosis would occur
c. Blood potassium levels would decrease
d. His glomerular filtration rate would be decreased
e. Albuminuria would occur
d. His glomerular filtration rate would be decreased
The loss of blood would decrease his blood pressure and cause sympathetically mediated constriction of his afferent glomerular arterioles. The reduced blood pressure and the constriction of his afferent arterioles would lessen blood flow through the glomeruli and decrease the glomerular filtration rate.
A woman has untreated diabetes mellitus and a high concentration of unreabsorbed glucose in her urine. This high urinary glucose would:
a. Increase urine volume
b. Increase sodium reabsorption
c. Increase urinary concentrating ability
d. Decrease inulin clearance
e. Alkalinize the urine
a. Increase urine volume
Unreabsorbed glucose would cause an osmotic diuresis.
A 60-year-old female alcoholic with cirrhosis has developed ascites. This abdominal fluid accumulation is due to:
a. Closure of lymphatic aquaporin channels resulting from the buildup of toxins no longer able to be metabolized by the diseased liver
b. Decreased plasma oncotic pressure in the capillaries
c. Increased hydrostatic pressure in the lymph ducts
d. A decreased supply of clotting factors
e. Increased extracellular fluid osmolality
b. Decreased plasma oncotic pressure in the capillaries
Because the cirrhotic liver does not synthesize sufficient albumin and other plasma proteins, the plasma oncotic pressure is low, allowing the plasma hydrostatic pressure (because it is less opposed by the plasma oncotic pressure) to drive fluid into the interstitium to produce the ascites.
An illegal immigrant crosses the Mexican border and is picked up by the border guards in the Arizona desert, where he has been walking lost, without food or water, for 2 days. The extreme heat and lack of water would:
a. Decrease aldosterone release from the adrenals
b. Cause constriction of the efferent glomerular arteries
c. Cause the release of atrial natriuretic factor
d. Decrease plasma sodium concentrations
e. Decrease the extracellular volume
e. Decrease the extracellular volume
Sodium is the predominant anion in the extracellular compartment, and loss of salt and water, from sweating and in the urine, would cause this compartment to shrink.
A 42-year-old woman ruptures her spleen during a skiing accident and has lost 2 L of blood into her abdominal cavity by the time she reaches the hospital. As a result of this blood loss, she would:
a. Have decreased viscosity in the blood remaining in her cardiovascular system
b. Have decreased plasma oncotic pressure
c. Become hyponatremic
d. Have an increased atrial Po2 − venous Po2 gradient
e. Have decreased plasma osmolarity
d. Have an increased atrial Po2 − venous Po2 gradient
Because her blood volume has decreased, she would extract more oxygen from the remaining blood as it passed through the capillary bed.
A 2-year-old girl is brought to the nephrology clinic because a urinalysis has found protein in her urine. She is diagnosed as having minimal change disease, a condition in which the glomerulus has become permeable to large molecules, such as plasma proteins. In addition to having albuminuria, this child might have:
a. Anemia because the kidney would stop producing erythropoietin
b. Metabolic acidosis from loss of bicarbonate in the urine
c. Edema because of reduced plasma oncotic pressure
d. A decrease in glucose resorption
e. A decreased glomerular filtration rate
c. Edema because of reduced plasma oncotic pressure
Urinary loss of albumin would decrease plasma oncotic pressure. This loss, by reducing the concentration of osmotically active particles in plasma relative to that in the interstitial fluid, would drive fluid into the interstitial space and produce edema.
A student in a Japanese restaurant ate sushi made using raw pufferfish containing tetrodotoxin, a poison that irreversibly blocks fast sodium channels. What would happen as a result of the sodium channel block?
a. Resting membrane potential would increase
b. The T wave of the electrocardiogram would become smaller
c. Conduction through the atrioventricular node would become slower
d. Neuromuscular transmission might fail
e. Aldosterone secretion would decrease
d.Neuromuscular transmission might fail
The action potential to the neuromuscular synapse is conducted by fast sodium channels. Blockage of these channels would block the conduction of this action potential and block the release of neurotransmitter at the neuromuscular junction.
A 28-year-old man, running in the Boston Marathon, weighs himself before and immediately after the marathon and finds that he has lost 3 lb during the race. One physiologic consequence of this weight loss would be:
a. An increase in plasma bicarbonate
b. A decrease in hematocrit
c. A decrease in cardiac output
d. An increase in plasma osmolality
e. A decrease in intraocular pressure
d. An increase in plasma osmolality
The weight loss is caused by the loss of hypotonic fluid through sweating and increased respiratory water loss. Loss of hypotonic fluid would increase plasma osmolality, an increase partly, but not completely, compensated for by a shift of water out of the cells and into the extracellular fluid.
A patient referred for pulmonary function testing purses his lips during exhalation and breathes slowly, but deeply. A blood sample, taken while he is breathing room air, gives the following values: pH 7.35, Paco2 55 mm Hg, Pao2 50 mm Hg, and HCO3− 28 mEq/L. What statement about this patient is true?
a. He has partly compensated metabolic acidosis
b. His central chemoreceptors have become desensitized to plasma carbon dioxide levels
c. Pulmonary artery pressure would be decreased
d. The low oxygen tension would cause increased destruction of red blood cells
e. His residual volume would be decreased
b.His central chemoreceptors have become desensitized to plasma carbon dioxide levels
The central chemoreceptors become desensitized to plasma CO2 levels over time if high CO2 concentrations are present, but the desensitization occurs in an indirect way. CO2 in the cerebrospinal fluid combines with oxygen to form carbonic acid, which dissociates into H+ and HCO3−. HCO3−, the portion of carbonic acid able to cross the blood-brain barrier into the central nervous system, makes the central chemoreceptors insensitive to the high H+ concentrations.
A Peace Corps volunteer contracts severe diarrhea from drinking untreated water. What would be expected to occur as a result of the patient’s massive diarrheal fluid loss?
a. Fluid loss would be from the extracellular compartment
b. Loss of electrolytes would cause cerebral edema
c. The patient would become alkalotic
d. The glomerular filtration rate would decrease
e. The patient would have increased plasma potassium concentrations
d. The glomerular filtration rate would decrease
The fluid loss would cause the plasma volume, blood pressure, and glomerular filtration rate to decrease.
A woman develops pulmonary fibrosis during her recovery from adult respiratory distress syndrome. This condition would cause:
a. An increased inspiratory reserve volume
b. Increased dead space
c. A decreased FEV1
d. Increased exhaled carbon dioxide
e. Rapid, shallow breathing
e. Rapid, shallow breathing
Fibrosis “stiffens” the lungs, and excessive force is required to increase their volume during inspiration. Rapid, shallow breathing is most energy-efficient and is used by patients with this disease.
An 88-year-old man’s prostate cancer has metastasized to the bone, and erosion of the bone by the cancer has released abnormal amounts of calcium into the blood. This release would:
a. Increase parathyroid hormone secretion
b. Increase osteoblast activity
c. Increase liver metabolism of vitamin D
d. Cause decreased absorption of dietary calcium
e. Decrease calcitonin release
d. Cause decreased absorption of dietary calcium
Hypercalcemia would decrease parathyroid secretion, which would decease calcium absorption.
A 15-year-old girl joins the cross-country team in the spring and runs 2 hours a day to improve her performance. She hopes to improve her endurance enough to compete in a regional half-marathon in the fall. How would this training schedule change her cardiovascular system?
a. Increase maximal heart rate
b. Increase hematocrit
c. Increase the number of mitochondria in skeletal smooth muscle
d. Increase resting arterial blood pressure
e. Decrease the lactate threshold
c. Increase the number of mitochondria in skeletal smooth muscle
The number and density of mitochondria in skeletal muscle increase as a result of endurance training, enhancing aerobic capacity.
An 80-year-old patient, during a physical examination needed before entering a retirement home, is found to have a blood pressure of 160/80 mm Hg and is told that he has systolic hypertension. His high systolic blood pressure is most probably due to:
a. Microvascular disease secondary to poorly controlled diabetes
b. Age-related desensitization of baroreceptors
c. Age-related loss of compliance of the arteries
d. Turbulent flow secondary to atherosclerosis
e. Renin release and angiotensin production secondary to renal arterial stenosis
c. Age-related loss of compliance of the arteries
As an individual ages, the arterial wall becomes more rigid and requires a larger force to distend it, and systolic pressure increases.
A 23-year-old woman, who had a blood clot in her calf vein the day after she gave birth, experiences sudden pain and dyspnea later from a pulmonary embolism originating from this clot. What would be expected to occur as an immediate result of this embolism?
a. Her ventilation/perfusion ratio would decrease
b. Pulmonary hypertension would occur
c. Symptoms of obstructive pulmonary disease would appear
d. Dead space would decrease
e. Her FEV1 would increase
b. Pulmonary hypertension would occur
Pulmonary vascular resistance would increase because with blockage of a portion of the blood vessels, blood must flow through a smaller cross-sectional area. This increase in resistance would increase pulmonary artery pressure.
A man with diabetic nephropathy has kidney function so compromised that it is recommended he start dialysis. In this process, blood is passed through a tube made with a semipermeable membrane that has isotonic fluid on the other side. What can be expected with this setup?
a. Water would not be excreted into the surrounding fluid unless a pressure gradient is applied across the semipermeable membrane
b. Excess thyroid hormone could be removed if thyrotoxicosis were present
c. Malignant hypertension can be avoided
d. Cholesterol levels can be reduced
e. Red blood cells may swell and burst while passing through the dialysis tube
a. Water would not be excreted into the surrounding fluid unless a pressure gradient is applied across the semipermeable membrane
Water would have a net transport across the membrane only in the presence of an osmotic gradient or a pressure gradient. Because the surrounding fluid is isotonic, and an osmotic gradient is absent, a pressure gradient would have to be supplied. This is usually done by increasing the hydrostatic pressure of the blood flowing through the tube.
A patient with metastatic cancer is given morphine for pain and lactulose, an osmotic laxative, to treat the constipation caused by the opiate. In addition to its laxative effect, lactulose administration could cause:
a. A decreased plasma potassium concentration
b. Metabolic alkalosis
c. Impaired fat absorption
d. Increased secretion of antidiuretic hormone
e. Irritate the bowel wall and increase its permeability to plasma proteins
d. Increased secretion of antidiuretic hormone
Osmotic diarrhea causes free water loss in the diarrhea fluid. Antidiuretic hormone would be secreted to counteract the free water loss in the diarrhea fluid by decreasing free water loss by the kidney.
Which of the following statements concerning skeletal muscle fibers is NOT correct?
A) Skeletal muscle fibers continue to divide throughout childhood as skeletal muscles grow B) Skeletal muscle fibers begin as undifferentiated cells called myoblasts during fetal development C) Skeletal muscle fibers are multinucleated cells D) Some skeletal muscle fibers may reach lengths of 20cm
A) Skeletal muscle fibers continue to divide throughout childhood as skeletal muscles grow
After development, growth of skeletal muscle occurs as a result of hypertrophy of existing muscle cells, not by increasing the number of cells. Satellite cells may produce some new skeletal muscle cells after muscle damage. During fetal development undifferentiated cells called myoblasts fuse to form a multinucleated cell that differentiates into a skeletal muscle fiber. Some fibers may extend for the entire length of a muscle, up to 20cm.
Reference: [See p. 252]].
Thick filaments are composed of ______, while thin filaments are composed of _______.
A) Actin; myosin, tropomyosin, and troponin B) Myosin, Troponin, and troponin; actin C) Tropomyosin and troponin; myosin D) Myosin; actin, tropomyosin, and troponin
D) Myosin; actin, tropomyosin, and troponin
Thick filaments are composed of the motor protein myosin. Thin filaments are primarily composed of actin, and they also contain smaller amounts of the regulatory proteins tropomyosin and troponin.
Reference: [See p. 253; see also Fig.
A cross-bridge is
A) The region of overlap between thick and thin filaments recognized as the A band
B) The proteins that connect two sarcomeres recognized as the Z line C) The portions of myosin molecules that extend from the surface of the thick filaments toward the thin filaments D) The portion of the actin covered by the tropomyosin
C) The portions of myosin molecules that extend from the surface of the thick filaments toward the thin filaments
Tension is generated in muscles when the heads of the myosin molecules (cross-bridges) extend to the thin filaments to develop tension. The A band represents the length of the thick filaments in a sarcomere. The Z lines define the two ends of a sarcomere. Tropomyosin covers the myosin binding sites on the actin.
Reference: [See p. 253; see also Figs. 9-6 and 9-7]
According to the sliding filament mechanism of skeletal muscle contraction, during contraction
A) The thick filaments stay the same size but the thin filaments shorten B) The sarcomeres shorten C) The thin filaments stay the same size but the thick filaments shorten D) Both thick and thin filaments shorten
B) The sarcomeres shorten
ATP is important for the dissociation of myosin from actin. It is the binding of a molecule of ATP to the myosin that breaks the link between actin and myosin. This allows the cross bridge cycle to be repeated. Hydrolysis of ATP by Ca++-ATPase in the sarcoplasmic reticulum provides the energy for active transport of Ca++ ions back into the sarcoplasmic reticulum from muscle cytosol. This restores cytosolic Ca++ to pre-release levels, ending the contraction and allowing the muscle fiber to relax. In skeletal muscle, actin does not get phosphorylated. The hydrolysis of ATP by myosin ATPase provides the energy for the myosin cross-bridge to bind actin and execute another cycle of power stroke. Calcium binds to troponin and causes the tropomyosin shift.
Reference: [See pp. 255-257; see also Fig. 9-8 and Table 9-1].
Which of the following is a “regulatory” muscle protein, not directly involved in the act of contraction?
A) Troponin B) Actin C) Tropomyosin D) Troponin and tropomyosin E) Myosin and actin
D) Troponin and tropomyosin
Troponin and tropomyosin are the regulatory proteins, regulating the initiation of contraction and relaxation. Troponin is activated by the high levels of intracellular calcium. When activated it causes displacement of tropomyosin from actin, thereby enabling the myosin cross-bridges to bind with actin sites. During relaxation, tropomyosin binds with actin preventing cross-bridge binding. Actin and myosin are the major contractile proteins of the muscle.
Reference: [See p. 257; see also Fig. 9-9].
Excitation-contraction coupling
A) Occurs after cross-bridge cycling
B) Is characterized by a graded potential in the plasma membrane of the muscle fiber
C) Involves a decrease in the cytosolic calcium concentration
D) Describes what happens in a muscle fiber between stimulation by acetylcholine and cross-bridge formation
D) Describes what happens in a muscle fiber between stimulation by acetylcholine and cross-bridge formation
Excitation-contraction coupling is the sequence of events that follow stimulation of the motor endplate by acetylcholine. These events include an action potential that spreads across the muscle fiber’s plasma membrane and the increase in cytosolic concentration of calcium. Excitation-contraction coupling must occur before cross-bridge cycling can occur.
Reference: [See pp. 257-258].
The ability of a muscle fiber action potential to cause an increase in cytosolic calcium concentration is dependent upon
A) The conduction of action potentials down T-tubules which are in intimate contact with the sarcoplasmic reticulum. B) The presence of the voltage sensitive protein called the ryanodine receptor in the T-tubule membrane C) The calcium channel protein called the dihydropyridine receptor which is located in the sarcoplasmic reticulum membrane D) Ca++-ATPase pumps in the sarcoplasmic reticulum
A) The conduction of action potentials down T-tubules which are in intimate contact with the sarcoplasmic reticulum.
As an action potential spreads down a T-tubule, it activates the voltage sensitive dihydropyridine receptor in the cell membrane. When the dihydropyridine receptor interacts with the ryanodine receptor in the sarcoplasmic reticulum, it causes the calcium channel in the ryanodine receptor to open and release calcium into the cytosol. The Ca++-ATPase pumps in the sarcoplasmic reticulum work to return calcium to the sarcoplasmic reticulum, and as such would reduce the cytosolic concentration of calcium.
Reference: [See pp. 258-259; see also Figs. 9-11 and 9-12].
Which of the following statements about motor neurons and muscle fibers is correct?
A) A single muscle fiber may be innervated by multiple motor neurons
B) Each motor neuron forms a single junction with a muscle fiber
C) A single motor neuron plus the muscle fibers it innervates is called a motor unit
D) Skeletal muscle fibers are innervated by neurons of the sympathetic system.
C) A single motor neuron plus the muscle fibers it innervates is called a motor unit
A single motor neuron plus all the muscle fibers it innervates is called a motor unit. Motor neurons branch multiple times, and each branch may form a junction with a muscle fiber called a neuromuscular junction. However, each muscle fiber is controlled by a branch from only one motor neuron. Skeletal muscles are innervated by the somatic motor system.
Reference: [See p. 260; see also Fig. 9-13].
At the neuromuscular junction,
A) The release of acetylcholinesterase from the motor neuron causes an EPP in the motor end plate
B) Acetylcholinesterase inhibits repolarization of the motor end - plate
C) An EPP is a graded potential
D) Summation of end-plate potentials is required to trigger an action potential in the muscle membrane
C) An EPP is a graded potential
At the neuromuscular junction acetylcholine (ACh) diffuses from the axon terminal to the motor end plate where it binds to nicotinic ACh receptors (AChR). This elicits an excitatory motor end-plate potential (EPP) by allowing sodium ions to enter the muscle from the extracellular fluid in the synaptic cleft. Also, some potassium leaves the muscle cell. The movement of these ions occurs through the channel of the AChR. Acetylcholinesterase (AChE) is located on the motor end-plate and is the enzyme that breaks down ACh by hydrolyzing it. When free ACh falls to low levels due to AChE enzyme action, lack of ACh binding to the receptor closes the ion channels and ion movement through the channel stops. The depolarized end-plate returns to resting potential and is ready to respond to the next round of ACh released in response to the next action potential. Although an EPP is a graded potential and not an action potential, summation of end-plate potentials is not required to trigger an action potential. One EPP is more than enough to depolarize the muscle plasma membrane adjacent to the end plate to its threshold leading to an action potential in the muscle fiber membrane.
Reference: [See pp. 260-261; see also Fig. 9-15].
Which of the following statements regarding the action of curare at a neuromuscular junction is true?
A) Curare is an acetylcholine agonist
B) Curare binds to acetylcholine receptors
C) Curare inhibits acetylcholinesterase
D) Curare inhibits acetylcholine release from motor neuron terminals
B) Curare binds to acetylcholine receptors
At the neuromuscular junction curare binds to acetylcholine receptors, preventing ACh from binding. Curare is an acetylcholine antagonist because it does not activate the ACh receptors. ACh has no effect on acetylcholinesterase or on acetylcholine release from presynaptic terminals.
A person exposed to a pesticide or nerve gas containing organophosphates might experience all of the following EXCEPT:
A) Failure to release acetylcholine at the neuromuscular junction B) Prolonged depolarization of the motor end plate C) Paralysis eventually leading to death D) Inability to break down acetylcholine
A) Failure to release acetylcholine at the neuromuscular junction
Organophosphates have no effect on the release of acetylcholine by motor neurons. Organophosphates inhibit acetylcholinesterase thus preventing the breakdown of acetylcholine. The sustained presence of acetylcholine would continue to stimulate receptors on the motor end plate leading to a prolonged depolarization. After a prolonged exposure the acetylcholine receptors eventually become insensitive leading to paralysis. If the paralysis affects the respiratory muscles, death may occur.
Which of the following statements concerning types of skeletal-muscle contraction is correct?
A) In a concentric contraction, the load equals the tension produced
B) In a concentric contraction, the load exceeds the tension produced
C) In an eccentric contraction, the tension produced exceeds the load
D) Concentric contractions begin as isometric contractions
D) Concentric contractions begin as isometric contractions
All contractions begin as isometric contractions. Initially, tension develops and increases in the muscle, but muscle fiber length stays the same (isometric contraction). In a concentric contraction (an isotonic contraction) the muscle shortens, which means that tension exceeds the load. In an eccentric contraction (an isotonic contraction) the muscle lengthens, which means the load exceeds the tension
Which of the following statements is NOT correct?
A) When a muscle contraction maintains a constant level of maximal tension it is said to be in fused tetanus
B) Summation occurs due to the repetitive stimulation of a muscle which maintains a steady increase in cytosolic calcium concentrations that leads to a steady increase in muscle tension
C) Unfused tetanus occurs at very low stimulation frequencies such that the muscle is allowed to completely relax between each stimulus
D) Tetanus occurs as a result of inhibiting the action of the Ca++-ATPase pump in the sarcoplasmic reticulum
C) Unfused tetanus occurs at very low stimulation frequencies such that the muscle is allowed to completely relax between each stimulus
Unfused tetanus occurs at low stimulation frequencies, but relaxation between each stimulus is only partial and is not complete. At higher stimulation frequencies a sustained contraction occurs, and a steady tension is achieved which is called fused tetanus or just tetanus. Summation occurs because with each additional stimulus, tension increases due to the sustained level of calcium in the cytosol. This is not due to the inhibition of the Ca++-ATPase pump in the sarcoplasmic reticulum, but rather due to the continued activation of the ryanodine receptor in the sarcoplasmic reticulum.
It is known that ATP is the direct source of energy for muscle contraction. If the level of ATP drops due to excessive contraction, which of the following compounds stores ATP and can rapidly produce ATP but in a very limited supply? A) ADP B) Creatine-phosphate C) Glucose D) Glycogen E) Fatty acids
B) Creatine-phosphate
Creatine-phosphate, which is abundant in the muscle cytoplasm, is an additional reserve of chemical energy for immediate use. Its phosphate group can be transferred to ADP to form the needed ATP. Creatine-phosphate is then replenished during muscle recovery. The amount of ATP available via the creatine-phosphate system is limited by the amount of creatine-phosphate present in the muscle cell. ADP is not a source of ATP energy, although it is needed to generate ATP. Glycogen is a storage form of glucose and although glucose and fatty acids can be oxidized and generate ATP, these events occur during the muscle recovery phase and cannot restore ATP levels rapidly while contraction is occurring.
Which of the following comparisons of type I (slow-oxidative) skeletal-muscle fibers and type IIb (fast-glycolytic) skeletal-muscle fibers is correct?
A) Type I fibers have fewer mitochondria
B) Type I fibers fatigue faster
C) Type I fibers store more glycogen
D) Type I fibers can generate more tension
E) Type I fibers have a smaller diameter.
E) Type I fibers have a smaller diameter.
Type I muscle fibers (slow-oxidative) have a smaller diameter when compared to Type IIb glycolytic fibers. Oxidative skeletal muscle fibers have more mitochondria than glycolytic fibers, and they are more resistant to fatigue. Glycolytic muscle fibers (Type IIb) contain more glycogen than do oxidative fibers. Type IIb fast glycolytic fibers can generate more tension because they have a greater total number of thick and thin filaments acting together to generate greater tension and velocity.
Muscles in the back have a higher proportion of fast-glycolytic fibers (type IIb) relative to slow oxidative (type I) than do muscles in the arms.
A) True
B) False
B) False
his statement is false. The arms have many fast-glycolytic fibers that are used for rapid, precise movements. Back muscles have few, if any, glycolytic muscle fibers. The back muscle fibers are mainly the slow oxidative type used for sustained contractions.
Reference: [See pp. 269-270].
Which of the following is involved in the hypertrophy of skeletal muscle fibers following exercise?
A) Only an increase in the number of muscle fibers
B) Only an increase in the diameter and size of muscle fibers
C) Only an increase in the number of muscle filaments per muscle fiber
D) An increase in the number of muscle filaments per muscle fiber and the resulting increase in the diameter and size of muscle fibers
E) An increase in the number of muscle fibers, an increase in the number of muscle filaments per muscle fiber, and the resulting increase in the diameter and size of muscle fibers
D) An increase in the number of muscle filaments per muscle fiber and the resulting increase in the diameter and size of muscle fibers
An increase in the size of the whole muscle that follows exercise and subjecting of the skeletal muscle to a load occurs mainly as a result of an increase in the number of muscle filaments (myosin and actin) resulting in the thickening of the muscle fiber (increased diameter). There is no increase in the number of muscle fibers. Muscle fiber production occurs mainly during early development and formation of the skeletal muscle.
Which of the following is NOT required in the regulation of contraction in smooth muscle? A) Calcium B) Calmodulin C) Troponin D) Myosin light chain kinase
C) Troponin
Smooth muscle contraction occurs when cytosolic calcium levels rise. Calcium binds to the regulatory protein, calmodulin, which is similar in structure to troponin. The calcium-calmodulin complex then binds to and activates the enzyme myosin light chain kinase. This kinase phosphorylates the myosin light chains on the globular head of myosin. This phosphorylation activates the myosin allowing cross-bridges to form. Troponin itself plays no role in the regulation of contraction in smooth muscle.
Which of the following comparisons of skeletal and smooth muscle contraction is correct?
A) Skeletal muscle contraction requires the influx of extracellular Ca++, whereas smooth muscle contraction does not
B) Skeletal muscle contraction involves interactions between thick and thin filaments, whereas smooth muscle contraction does not
C) Skeletal muscle contraction results from cross-bridge cycling, whereas smooth muscle contraction does not
D) Smooth muscle contraction requires release of Ca++ from sarcoplasmic reticulum, whereas skeletal muscle contraction does not
E) The site of calcium regulation of skeletal muscle contraction is on the thin filament, whereas in smooth muscle contraction calcium regulation involves the thick filament
E) The site of calcium regulation of skeletal muscle contraction is on the thin filament, whereas in smooth muscle contraction calcium regulation involves the thick filament
The site of calcium regulation is very different in the two types of muscle. In skeletal muscle, calcium binds to troponin, a regulatory protein, allowing actin (thin filament) and myosin to interact. In smooth muscle, calcium promotes the phosphorylation of myosin (thick filament), activating the myosin. Contraction of both skeletal muscle and smooth muscle involves the interaction of thin and thick filaments in the cross-bridge cycles. In both muscle types the activity of the cross-bridge cycle is regulated by cytosolic calcium levels, but the source of the increase in cytosolic calcium differs. In skeletal muscle, the calcium that initiates contraction comes from the sarcoplasmic reticulum, whereas in the smooth muscle, calcium also comes from the extracellular fluid.
Which of the following comparisons between smooth and skeletal muscle fibers is true?
A) Nervous stimulation of smooth muscle is always excitatory, whereas nervous stimulation of skeletal muscle may be excitatory or inhibitory.
B) The contractile activity of smooth muscle may be affected by hormones, whereas the contractile activity of skeletal muscle is not
C) Smooth muscle may be innervated by both the autonomic system and the somatic motor system, whereas skeletal muscle may be innervated by the somatic motor system only
D) In the smooth muscle action potential, depolarization is due to the influx of Na++, whereas in the skeletal muscle action potential, depolarization is due to the influx of Ca++
B) The contractile activity of smooth muscle may be affected by hormones, whereas the contractile activity of skeletal muscle is not
Smooth muscle plasma membranes contain receptors for a variety of hormones and neurotransmitters, the binding of which can lead to either membrane excitation or inhibition. In contrast, skeletal muscle fibers receive input from somatic motor nerves only, and it is always excitatory. Smooth muscle may be innervated by both divisions of the autonomic nervous system (i.e. sympathetic and/or parasympathetic), but skeletal muscles can only be innervated by the somatic motor system. In action potentials, the influx of Ca++ depolarizes smooth muscle cells while the influx of Na+ depolarizes skeletal muscle cells.
Which of the following statements concerning smooth muscle activation is NOT correct?
A) Smooth muscle cells are activated by the autonomic nervous system
B) Neurotransmitter is released from swollen regions of neurons called varicosities
C) Some neurotransmitters increase smooth muscle contraction, while other neurotransmitters decrease smooth muscle contraction
D) Smooth muscles have a very high rate of fatigue
D) Smooth muscles have a very high rate of fatigue
Smooth muscles have a slow rate of fatigue. Low ATPase activity generally prevents smooth muscle from running out of ATP. This prevents fatigue and allows smooth muscles to contract for longer periods of time than skeletal muscles. All other statements regarding smooth muscle are true.
Which of the following statements concerning cardiac muscle cells is correct?
A) Dihydropyridine receptors act as calcium channels in the sarcoplasmic reticulum
B) Most of the calcium required for contraction is extracellular calcium that enters the cell through voltage gated calcium channels
C) Unlike a twitch in skeletal muscle fibers, a twitch in cardiac muscle fibers only releases enough calcium to expose about 30% of the cross-bridge attachment sites on the actin filaments
D) Tetanic contractions are possible in cardiac muscle cells because they have a much shorter absolute refractory period than skeletal muscle cells
C) Unlike a twitch in skeletal muscle fibers, a twitch in cardiac muscle fibers only releases enough calcium to expose about 30% of the cross-bridge attachment sites on the actin filaments
A twitch in cardiac muscle fibers only releases enough calcium to expose about 30% of the cross-bridge attachment sites on the actin filaments. By modifying the amount of calcium released into the cytosol, the strength of a cardiac muscle fiber contraction can be varied. Most of the calcium required for contraction is released from the sarcoplasmic reticulum. Modified ryanodine receptors are the calcium channels of the sarcoplasmic reticulum. Cardiac muscle fibers do not experience tetanus due to a long absolute refractory period. The cardiac muscle fiber must relax at least partially before the absolute refractory period is over.
Which of the following corresponds to the state of myosin under resting conditions and rigor mortis?
a. Myosin + ATP
b. Myosin + ADP + Pi
c. Actin + Myosin + ADP +Pi
d. Actin + Myosin
b. Myosin + ADP + Pi
ATP is required to detach myosin from actin.
If the transverse tubules of a skeletal muscle are disconnected from the plasma membrane, will action potentials trigger a contraction?
No. The transverse tubules conduct the muscle action potential from the plasma membrane into the interior of the fiber, where it can trigger the release of Ca from the SR. If the transverse tubules were not attached to the plasma membrane, an action potential could not be conducted to the SR and there would be no release of Ca to initiate a contraction.
What conditions will produce the maximum tension in a skeletal muscle fiber?
Max tension is produced when:
a. the fiber is stimulated by an action potential frequency that is high enough to produce a maximal tetanic tension.
b. at its optimum length, where the thick and thin filaments have greatest overlap and create the most cross-bridges.
If the blood flow to a skeletal muscle were markedly decreased, which types of motor units would most rapidly undergo a severe reduction in their ability to produce ATP for contraction?
The oxidative motor units, fast and slow, will be affected first by the decrease in blood flow because they depend on blood flow to provide both the fuel -glucose and fatty acids- and the oxygen required to metabolize the fuel. The fast-glycolytic motor units will be affected more slowly because they rely predominantly on internal stores of glycogen which is anaerobically metabolized.
In the lab, will an isolated skeletal muscle contract when it is placed in a solution with no calcium ions and stimulated: a) by directly depolarizing its membrane, b) stimulating the nerve to the muscle? What would happen if it were smooth muscle?
In the absence of extracellular Ca, skeletal muscle contracts normally because the Ca required comes from the SR within the fibers.
If the motor neuron to the muscle is stimulated in a Ca-free medium- the muscle will NOT contract because the influx of Ca from the ECF is needed to trigger release of ACh to trigger the action potential.
Smooth muscle: in a Ca free solution do not contract either way because Ca must enter the cell to cause a contraction or Ca release from SR.
An endocrine tumor secretes a hormone that leads to elevation of extracellular fluid Ca concentrations. How might this affect cardiac muscle?
a. Elevation of extracellular Ca would increase the amount of Ca entering the cytosol via L-type Ca channels.
b. This creates a greater depolarization and would increase the strength of the contraction via release of more Ca through the ryanodine receptor channels.
Doubling the radius of an artery would \_\_\_\_\_\_\_ the resistance in that artery by \_\_\_\_\_\_\_. A) Decrease; two B) Decrease; four C) Decrease; sixteen D) Increase; two E) Increase; four
C) Decrease; sixteen
Resistance = 1/radius4. Therefore, doubling the radius would decrease the resistance by sixteen.
The valve that separates the left atrium and the left ventricle is called the A) Tricuspid valve B) Bicuspid valve C) Left semilunar valve D) Right semilunar valve
B) Bicuspid valve
The bicuspid valve separates the left atrium and ventricle. This valve is also called the left atrioventricular (AV) valve. The tricuspid valve separates the right atrium and ventricle. The left semilunar valve is also known as the aortic valve, and it separates the left ventricle and the aorta. The right semilunar valve is also known as the pulmonary valve, and it separates the right ventricle and the pulmonary trunk.
What part of the conductive system of the heart directly delivers the action potential to the ventricular muscle cells or fibers? A) Purkinje fibers B) Bundles of His C) Gap junctions D) Pacemaker cells E) AV node
A) Purkinje fibers
The best answer here is the Purkinje fibers. Once the pacemaker cells fire, the excitation reaches the AV node and from there it proceeds down the two branches of the bundle of His (left and right branches) and finally to the Purkinje system of conductive cells (fibers). These cells make contact with cardiac muscle cells of the ventricle and excite them to discharge and contract. Note also that not every cardiac muscle cell is innervated by the Purkinje cells. Cardiac muscle cells have gap junctions, which allow the direct transfer of electrical excitation from one muscle cell to another.
The action potential in myocardial cells is prolonged compared to skeletal muscle cells due to the presence of \_\_\_\_\_\_\_ in myocardial cells. A) L-type calcium channels B) F-type sodium channels C) T-type calcium channels D) Voltage-gated potassium channels
A) L-type calcium channels
Long-lasting (L-type) calcium channels in myocardial cells open in response to the initial depolarization of these cells. These channels allow calcium ions to enter the cell from the extracellular fluid. Because these channels remain open longer than other voltage-gated ion channels, they allow the membrane to remain depolarized for a longer period of time. F-type sodium channels and T-type calcium channels are important in the pacemaker cells of the SA node. Voltage-gated potassium channels are responsible for the repolarization phase of the action potential in both myocardial cells and skeletal muscle cells.
Which of the following statements regarding the pacemaker activity of the heart is true?
A) The pacemaker of the heart is normally in the AV node
B) Heart rate is increased when adrenergic receptors on the pacemaker cells are activated
C) The pacemaker potential is caused by a spontaneous decrease in membrane permeability to sodium
D) F-type sodium channels open at threshold
E) T-type calcium channels open at threshold
B) Heart rate is increased when adrenergic receptors on the pacemaker cells are activated
The heart rate would be increased when adrenergic receptors on the pacemaker cells are activated. The heart is innervated by both sympathetic and parasympathetic nerve fibers. The sympathetic postganglionic fibers release primarily norepinephrine, which acts on beta-adrenergic receptors. Heart rate will increase when these receptors are activated. The SA node is the normal pacemaker for the heart, not the AV node. The pacemaker potential, or slow depolarization in SA cells, is due to a decrease in potassium efflux, an increase in sodium influx through F-type channels, and a transient increase in calcium influx through T-type channels.
The type of ion channel important in the oscillation of spontaneous discharges in pacemaker cells of the SA node is the T-type calcium channel.
A) True B) False
A) True
This statement is true. T-type calcium channels are very critical for pacemaker cell function. These channels require a low voltage for their activation and allow calcium to enter the cells at a membrane potential below threshold. This influx of calcium brings the cell membrane potential to threshold level. In pacemaker cells an L-type calcium channel opens at threshold resulting in the depolarization phase of the action potential. In cardiac muscle cells, the L-type calcium channel is important in allowing calcium to enter the heart after depolarization and thereby prolonging the repolarization phase and refractory period of the action potential.
Tetanic contractions in cardiac muscle do not occur due to the long absolute refractory period.
A) True.
B) False.
A) True.
This statement is true. The long absolute refractory period in cardiac muscle occurs due to the prolonged open time of the L-type calcium channels. Relaxation of the cardiac muscle cell begins before the absolute refractory period has ended. As a result, the cardiac muscle cannot develop tetanus.
Which of the following statements regarding the cardiac cycle is true?
A) The AV valves are open during most of diastole (mainly ventricular diastole)
B) The aortic valve is closed throughout the interval between the QRS and T waves
C) The first heart sound is the opening of the AV valves
D) The ventricular pressure is greater than the aortic pressure during isovolumetric contraction
E) SL valves open when pressure in the ventricles is less than pressure in the great arteries
A) The AV valves are open during most of diastole (mainly ventricular diastole)
During the cardiac cycle, AV valves are open during ventricular diastole, and blood is passing from the atria to ventricles through the AV valves. The first heart sound, or lub, is made by the closing of the AV valves, not their opening. Ventricular pressure is less than aortic pressure during isovolumetric contraction, and SL valves are closed. The time between the QRS and T waves is when the ventricle is contracting (ventricular systole) and pushing the blood through the open aortic valve into the aorta.
Which of the following statements concerning the period of isovolumetric ventricular contraction is true?
A) Pressure in the ventricles is decreasing
B) The volume of blood in the ventricles is decreasing
C) The ventricles are completely closed chambers
D) The blood in the atria is moving into the ventricles
C) The ventricles are completely closed chambers
During isovolumetric ventricular contraction, ventricular systole produces an increase in ventricular pressure. This increase in pressure is great enough to close the AV valves, but it is not great enough to open the SL valves. As a result, the ventricles are closed chambers and the volume of blood in them does not change. This period ends when pressure in the ventricle becomes greater than the pressure in the great arteries and the SL valves open and blood begins to leave the ventricles.
The majority of ventricular filling occurs while
A) Both the atria and ventricles are in systole
B) The atria are in diastole and the ventricles are in systole
C) Both the atria and ventricles are in diastole
D) The atria are in systole and the ventricles are in diastole
C) Both the atria and ventricles are in diastole
Approximately 80% of ventricular filling occurs while the heart is completely at rest. This period of passive filling is followed by atrial systole which adds the final 20% of blood to the ventricles (still in diastole) to achieve the end diastolic volume (EDV).
The left ventricle ejects a larger volume of blood during systole than does the right ventricle because the left ventricular pressure is greater than the right.
A) True
B) False
B) False
Although during systole the left ventricular pressure is higher than the right ventricular pressure, the two ventricles pump the same volume of blood.
Which of the following statements concerning the cardiac output in a resting, average adult human is true?
A) It is the amount of blood delivered by one of the heart’s ventricles in one hour
B) It is approximately 5 liters per min
C) It is equal to [HR] X [EDV]
D) It is the sum of blood pumped by both left and right ventricles in one minute
B) It is approximately 5 liters per min
Since at resting condition, the average heart rate is about 72 beats per minute and since in the average adult person, the stroke volume is about 70 ml, the product of these two values is 5000 ml or 5 liters per minute. Cardiac output is the amount of blood delivered by either of the ventricles in one minute. It is defined by HR (heart rate) X SV (stroke volume). Note that during exercise cardiac output increases markedly to supply blood to the exercising muscles.
