Potential Test Questions Comp Phys
Which of the following statements best describes what is occurring in the bottom panel?
In this section of membrane, there are two acetylcholine channels that, in the presence of increasing neurotransmitter concentration, have an increasing probability of being open at the same time.
Which of the following is the best explanation for the absolute refractory period of the action potential?
Inactivated voltage-gated sodium channels
What is the mechanistic explanation for sensitization?
Increase in calcium flux
Which of the following could not be the postsynaptic membrane mechanism during an inhibitory postsynaptic potential?
Increase in the permeability to Na+
Fast IPSPs result mainly from a(n) _______ in permeability to _______.
Increase; Cl-
Which of the following best describes long-term potentiation?
Increased synaptic response occurs with increased numbers of AMPA receptors.
Excitatory inputs from the cerebral cortex to the striatum will lead to what effects on corresponding neurons downstream in the direct pathway of the basal ganglia?
Inhibition in the globus pallidus and excitation in the thalamus
Most of the neurons in the basal ganglia are inhibitory. How can an inhibitory synapse be involved in generating a movement?
Inhibition of a tonically active inhibitory neuron results in disinhibition of its target neuron.
Which of the following could increase the force produced by a smooth muscle cell?
Inhibition of myosin light-chain phosphatase
Which second messenger acts directly to mediate the release of Ca2+ from the endoplasmic reticulum?
Inositol triphosphate (IP3)
Compare and contrast ionotropic and metabotropic receptors.
Ionotropic and metabotropic receptors are both found on the postsynaptic membrane of a chemical synapse and respond to the binding of a neurotransmitter. When bound to a neurotransmitter, ionotropic receptors directly alter permeability to ions, whereas metabotropic receptors trigger a signaling cascade of second messengers.
The plasma membrane of a resting neuron is most permeable to which of the following ions?
K+
Which of the following is not one of the likely factors affecting the various velocities at which axons conduct action potentials?
Length
Which of the following occurrences in the synapse is not likely to be involved in the formation of long-term memories?
Long-lasting neurotransmitter release
Compare and contrast electrical synapses with chemical synapses, including advantages and disadvantages for each.
Both electrical and chemical synapses can rapidly change the membrane potential of a postsynaptic cell. In electrical synapses, there is a direct electrical coupling that allows current flow to flow between cells with only negligible delay. While this provides a speed and synchronization advantage, there is low plasticity and directionality within these synapses. In chemical synapses, on the other hand, a presynaptic neuron releases a neurotransmitter, which diffuses across a synapse and binds to the postsynaptic receptor, causing a postsynaptic potential. While generally slower than the electrical synapse, the advantage of chemical synapses is their high plasticity, which gives them the ability to integrate neuronal functions.
Muscle A has a volume of 200 cm3, a length of 10 cm, and a cross-sectional area of 20 cm2. Muscle B has a volume of 100 cm3, a length of 5 cm, and a cross-sectional area of 20 cm2. Which of the following statements about the muscles is true?
Both muscles can exert the same force, but one can shorten more quickly than the other.
Muscle A has a volume of 200 cm3, a length of 20 cm, and a cross-sectional area of 10 cm2. Muscle B has a volume of 200 cm3, a length of 10 cm, and a cross-sectional area of 20 cm2. Which of the following statements about these muscles is true?
Both muscles can produce the same power, but they will shorten at different speeds.
Compare and contrast the techniques of patch clamping and voltage clamping
Both patch clamping and voltage clamping provide experimental information about membrane currents, especially during an action potential. The patch-clamp technique uses a micropipette to record single channel currents, whereas the voltage-clamp technique shows whole cell ionic currents.
Which arrow best represents the point where the voltage-gated sodium channels are inactivated?
C and D
. Calmodulin binds to _______ and becomes activated.
Ca+2
What is entering the cell at the first stage of this event?
Ca+2
Which of the following is most directly responsible for exocytosis of synaptic vesicles?
Ca+2
During the latent period of an isometric twitch,
Ca2+ binds to troponin C.
Which of the following is true of most arthropod and vertebrate skeletal muscle?
Ca2+ is released from the sarcoplasmic reticulum in response to depolarization of the fiber.
Cross-bridges generate force in a skeletal muscle cell any time
Ca2+ levels in the cytoplasm are high.
Which of the following statements best describes the fusion process in exocytotic release of neurotransmitter?
Calcium interacts with synaptotagmin.
Which of the following is not a factor in the Nernst Equation?
Capacitance
How are central pattern generators and peripheral reflexes thought to interact in normal locomotion?
Central pattern generators initiate and maintain locomotion and reflexes correct and fine-tune motion.
Neuromodulators of the stomatogastric ganglion of a decapod crustacean would be least likely to do which of the following?
Change the order in which the neurons of the pyloric circuit contract
Why do the channels at B of the figure stay open longer than those at label A?
Channels at A become inactivated, whereas channels at B close due to membrane voltage.
In a typical neuron, which of the following ions is in passive equilibrium across the cell membrane?
Cl-
Which of the following is not found in the structure of the chemical synapse?
Connexons
Which term best describes the movement of ions across a membrane?
Current
What is occurring on the postsynaptic membrane?
Depolarization
What is occurring at the membrane?
Depolarization and Redistribution of charges during a current pulse
What experimental evidence indicates that the decision to perform a voluntary movement originates in the association cortex?
Diffuse readiness potentials can be recorded over most of the cortical surface prior to the localized potentials that precede movement.
Explain why a muscle always works by shortening and cannot actively increase its length unless an external force pulls on it.
During the cross-bridge cycle, myosin goes through a characteristic sequence of conformational changes and interactions with actin. The power-stroke of the myosin head can only pull the actin-containing thin filament in one direction, so the muscle always works by shortening. However, external forces from other muscles or loads external to the body can act on the muscle to lengthen it.
Considering the cycle of an action potential, when is the permeability to K+ at its greatest?
During the falling phase of the action potential
Which of the following illustrates the principle of convergence?
Each motor neuron receives input from thousands of synapses.
Which of the following transmits information the fastest?
Electrical synapse
One reason that fast glycolytic muscle fibers fatigue more rapidly than slow oxidative muscle fibers is that
FG fibers use ATP more rapidly than SO fibers.
Evaluate the following statement: "A neuron's output is the same as its input."
False
Briefly explain why fast glycolytic muscle fibers fatigue more rapidly than slow-twitch muscle fibers.
Fast glycolytic muscle fibers use ATP much more rapidly than slow-twitch fibers. At first, they can produce ATP very rapidly through phosphagen breakdown and anaerobic glycolysis. However, these pathways are limited by the quantity of phosphagen and the build up of end products, including inorganic phosphate, pyruvate, and lactate. FG fibers have fewer mitochondria per unit volume to generate ATP by aerobic mechanisms. Therefore, as the ATP supply declines below ATP demand, fatigue sets in. Slow-twitch fibers use ATP more slowly and have a higher capacity for sustained ATP production via aerobic pathways
Describe how observations on human patients or animals with lesions of the nervous system have contributed to our understanding of normal motor control. Include relevant examples and relate them to general experimental principles.
Functional deficits observed in an animal with a lesion may indicate that the site of the lesion is important to the function. However, some deficits may be related to more general impairment or reduced connectivity of the nervous system. Proper controls need to be included in the experimental design in order to determine the specificity of the lesion.
What are glial cells and how do they aid in the function of the nervous system?
Glial cells are the support cells of the nervous system. They function in forming myelination, which increases action potential velocity. They surround capillaries and act as metabolic intermediaries between neurons and their circulatory supply. They also serve immune and scavenging functions in order to protect surrounding neurons.
Which of the following is not known to be a neurotransmitter?
Glycogen
Discuss some of the areas of scientific uncertainty regarding the control of voluntary movement by vertebrate animals. Speculate on some experimental techniques (either current or still to be developed) and possible experimental results that might help to refine our models of motor control.
Important areas of uncertainty include how decisions are made to generate a voluntary motion, how neurons in the central nervous system interact to generate a voluntary motion, and the number of neurons that are involved in a simple motion. While relevant areas of the brain have been identified, scientists lack "wiring diagrams" for the generation of voluntary motions. High resolution functional imaging (both spatial and temporal) may help to improve our models of motor control.
Which of the following statements regarding postsynaptic potentials is false?
In a CNS neural synapse, K+ is the main ion producing the EPSP.
Which of the following statements about membrane capacitance is false?
In a cell, the membrane separates only similarly charged ions
Which of the following statements regarding the action potential is false?
In an extremely long axon, the action potential eventually will degrade.
Vertebrate skeletal muscle is characterized by thin-filament regulation of contraction while smooth muscle is characterized by thick-filament regulation. Explain the distinction between thin-filament and thick-filament regulation.
In skeletal muscle, actin and myosin are able to interact and generate force when calcium binds to troponin C, which is part of the thin filament. In smooth muscle, actin and myosin are able to interact when calcium triggers phosphorylation of myosin light chains by myosin light-chain kinase.
Which of the following statements regarding vertebrate neurotransmitters is false?
In the CNS, many receptors for biogenic amines mediate fast ionic responses.
Suppose that each cross-bridge cycle moves the thin filament 10 nanometers relative to the thick filament. If myosin in a particular muscle can go through the cross-bridge cycle at 250 cycles per second, what is the rate at which a muscle that is 30 cm long can shorten?
0.60 m/s
Where is depolarizing temporal summation occurring?
1
If a muscle contains 10,000 sarcomeres in a series (i.e., end-to-end along its length), each sarcomere is ~2.5 µm in length, and each sarcomere can shorten by 2.5 µm/s, how fast can the muscle shorten?
2.5 cm/s
How many separate current pulses cause the membrane potential to reach the threshold?
3
Where is hyperpolarizing spatial summation occurring?
3
Put the following steps in neuromuscular junction synaptic transmission and EC-coupling in chronological order. 1. Myosin heads hydrolyze ATP during the cross-bridge cycle. 2. An EPSP is generated in the muscle cell. 3. An action potential is conducted along the sarcolemma. 4. Voltage-gated Na+ channels open in sarcolemma. 5. Ca2+ rises in the muscle cell cytoplasm. 6. Vesicles containing acetylcholine fuse with axon terminal membrane. 7. Tropomyosin rotates into groove of thin filament. 8. Ca2+ dissociates from troponin. 9. Motoneuron axon terminal are depolarized. 10. RyRs open. 11. Acetylcholine receptors open and conduct ions. 12. Ca2+ binds to troponin C.
9-6-11-2-4-3-10-5-12-7-1-8
Which arrow best represents the point where the permeability to sodium is the highest?
A
Contrast the mechanisms by which cellular oscillators and network oscillators generate patterns of rhythmic motion.
A cell that acts as a cellular oscillator has a combination of ion channels or other cellular mechanisms that cause its membrane potential to oscillate spontaneously. It may or may not fire action potentials when its membrane potential is depolarized in the cycle. A network oscillator can generate rhythmic output without any single cell that oscillates spontaneously. Network oscillators typically involve networks of cells that activate or inhibit one another sequentially. If the cells inhibit one another, some or all of them may be tonically active in the absence of inhibition. If the cells are tonically active and/or activate one another, they are likely to have some intrinsic mechanism of fatigue or synaptic antifacilitation to prevent indefinite activation.
According to the Nernst equation, which of the following will depolarize Vm, the membrane potential?
A decrease in the concentration of anions inside the membrane
Which of the following factors would increase the stimulation frequency at which a muscle shifts from twitch to tetanic contractions?
A larger number of SR Ca2+-ATPase proteins
During presynaptic inhibition, which of the following is true?
A metabotropic response reduces the amount of calcium entering the nerve terminus
Which of the following muscles can generate the most power per cubic centimeter of muscle?
A muscle containing mostly fast glycolytic fibers contracting against a moderate load
Which of the following statements about the stomatogastric ganglion of a crayfish (which functions as a hybrid oscillator) is true?
A rhythm generated by a cellular oscillator is reinforced and stabilized by network properties.
Which of the following illustrates the principle of divergence?
A single muscle spindle afferent stimulates many motor neurons.
In the absence of _______, muscle can contract but cannot relax
ATP
Compare and contrast the central control hypothesis and peripheral control hypothesis as they relate to insect flight
According to the central control hypothesis, a central pattern generator sends alternating output that produces alternating contractions of depressor and levator muscles. According to the peripheral control hypothesis, stretch of a muscle (or other sensory feedback) activates receptors and neural pathways leading to contraction of that muscle. Alternating stretch and contraction leads to rhythmic motion.
Which of the following neurotransmitters elicits responses of both ionotropic and metabotropic receptors?
Acetylcholine and Glutamate
What is occurring at A?
Acetylcholine is being broken down
How does the acetylcholine receptor respond to prolonged exposure to acetylcholine?
Acetylcholine will remain bound to the receptor, but the channel will close
Which of the following is not directly mediated by a G protein?
Activating cAMP-dependent protein kinase
In a cell, the difference in ion concentration between the intracellular and extracellular fluids results from
Active ion transport and the passive diffusion of ions
Neurons that relay sensory signals to integrative centers of the CNS are called
Afferent neurons
Draw a diagram of a network oscillator involving multiple neurons and label each synapse as excitatory or inhibitory. Graph the membrane potential of each of the neurons in the oscillator as a function of time on a single x-axis and add a paragraph describing how the network works and the pattern of output that it generates.
All synapses in the circuit are excitatory and each neuron fires a brief burst of action potentials before fatiguing. The circuit is activated by a burst of action potentials from the command neuron (C) and then continues oscillating through many cycles. Synaptic transmission and axonal transmission are slow enough so that neuron #1 recovers before it is re-excited by neuron #3. The output of the entire network corresponds to the activity of neuron #3. The circuit could stop sending output by one of several means. For example, any of the 3 numbered neurons could be inhibited by a neuron that is not shown in the diagram. Alternately, neuron #1 could depend on low-level tonic output from the command neuron to remain sensitive to excitation from neuron #3.
What are the similarities and differences among the channels in the voltage-gated channel superfamily?
All the voltage-gated channels have principal subunits with extensive sequence homology and thus are evolutionarily related. Voltage-gated Na+ and Ca2+ channels have four domains, whereas the voltage-gated K+ channel has one domain that is homologous to one of the domains on the Na+ channel.
If Na+ and K+ move in opposite directions through the acetylcholine receptor (which has similar permeability to both ions) when it is bound to acetylcholine, why is there an overall depolarization instead of no change in the membrane potential?
Although the acetylcholine channel has similar permeabilities to Na+ and K+, most of the synaptic current underlying the EPSP is created by Na+ movement. This is because the driving force for Na+ to enter the cell is far greater than the driving force for K+ to leave the cell.
What would likely occur if stimulus 3 and 6 were performed simultaneously?
An action potential would likely not occur
Sketch and give a written description of how the nervous system plans, programs, and executes a voluntary movement. Include a sentence describing the role of each of at least four different brain areas.
An example includes something similar to Figure 19.17: The sensory association cortex (as well as other cortical areas) funnels activity to premotor cortical areas, including loops through the basal ganglia and the cerebrocerebellum, in the planning and programming of the movement. Activity passes to the primary motor cortex for executing the movement, with correction from a cerebellar loop through the spinocerebellum. Inputs to the cerebral cortex pass through the thalamus
Which of the following experimental results would demonstrate that central pattern generators are involved in generating the muscle contractions involved in rhythmic movement?
An insect in which sensory afferents from the wings have been cut can fly
Why is the latent period of an isotonic twitch different from that of an isometric twitch?
An isotonic twitch does not begin until the muscle develops enough force to lift the load.
Fast glycolytic muscle fibers dependent on carbohydrate as a fuel, whereas slow oxidative fibers are capable of metabolizing carbohydrates, lipids, or amino acids. What is the physiological reason for this difference?
Anaerobic glycolysis can produce ATP from glucose much more quickly than lipid or amino acid oxidation can take place.
Which of the following statements about a local circuit in an axon is false?
Anions migrate into the membrane interior.
Which of the following statements about a voltage clamp of a neuron to 0 mV is false?
Apart from the initial current shift from the clamp, no other current is produced.
. A 52-year-old woman has difficulty initiating voluntary movements. She can clearly state what she intends to do, describe exactly how she would do it, and picture herself doing it easily. When she is able to begin the motion, she can complete it smoothly and accurately, but she has difficulty beginning the motion. If the difficulty arises from a defect in one particular area of the nervous system, which area is most likely to be involved?
Basal ganglia
Which of the following cannot modulate force production in smooth muscle?
Binding of Ca2+ to troponin C
According to the peripheral control model of insect flight,
sensory detection of wing depression stimulates motor neurons innervating the levator muscles.
The primary site of behavioral plasticity is at the ______ synapse
sensory-to-motor neuron
Studies of the circuitry and function of the vertebrate cerebellum have resulted in
several competing models of how the cerebellum might work to coordinate movement.
The force‒velocity relationship for skeletal muscle indicates that a muscle
shortens at maximum velocity when contracting against no load.
Modeling experiments on walking and swimming in robotic salamanders suggest that a. each type of repetitive motion that an animal performs is controlled by a distinct central pattern generator.
simple changes in the coordination of central pattern generators can produce different locomotor patterns.
In tonic smooth muscle that contracts continuously for long periods, the highly efficient "latch state" depends on
slow release of Ca2+ by troponin C
ATP use is lower in smooth muscle than in skeletal muscle in part because
smooth muscle myosin completes the cross-bridge cycle more slowly than skeletal muscle myosin does.
The limiting factor in the synthesis of acetylcholine is the
speed at which choline is recycled
The action potentials that directly trigger muscle contractions of walking movements in a vertebrate animal are initiated by neurons whose cell bodies are located in the
spinal cord.
In the network of central pattern generators that governs walking and swimming in salamanders,
stronger stimulation causes trunk oscillation to prevail over limb movements.
A specialized site of contact of one neuron with another neuron (or effector) is known as a
synapse
Output from the primary motor cortex consists mostly of action potentials that are transmitted to
synapses with interneurons in the spinal cord.
The _______ is the flow of ions through all the channels that open in response to release of a neurotransmitter.
synaptic current
The protein responsible for triggering the actual release of neurotransmitter at the synapse is
synaptotagmin
In striated muscle, _______ before the sarcomere can generate force
the SR calcium channel must open
In the lower panel, the difference between the dashed line and the observed red line is due to
the difference in applied current pulses
A muscle produces less force during a twitch than during a tetanic contraction because during a twitch
the elastic components of the muscle are not fully stretched.
When you are walking barefoot and your left foot lands on a marble,
the extensors of your right leg contract.
In an electrical synapse, the main structure responsible for transmission of an impulse from one cell to the next is
the gap junction
Long-term potentiation has been extensively studied in
the hippocampus.
If you voluntarily lift an object and have correctly judged its weight,
the intrafusal muscle fibers shorten at a rate that maintains constant tension on the stretch receptor
During an eccentric muscle contraction,
the muscle produces force and its length increases.
If you voluntarily lift an object and have underestimated its weight,
the muscle spindle afferents fire a rapid burst of action potentials.
In striated muscle, phosphate is released from the myosin head at the same instant that
the myosin head starts the power stroke.
In the figure, _______in the center of the cell.
the overall charge neutrality would be maintained independently of the membrane potential
The induction of long-term potentiation occurs in
the postsynaptic neuron.
Synaptic efficacy is
the relative amplitude of the postsynaptic potential in response to the presynaptic action potential.
During an isometric tetanic contraction,
the sarcomeres generate force and stretch the elastic component of the muscle, but they cannot move the load.
During an isometric tetanic contraction,
the sarcomeres shorten, but the elastic components lengthen.
When you step on a tack, excitation of sensory afferents leads to excitation of motor neurons innervating one set of muscles and inhibition of motor neurons innervating another set of muscles. The stimulus produces opposite responses in different motor neurons because
the signals reach some motor neurons via excitatory interneurons but they reach other motor neurons via inhibitory interneurons.
The stomatogastric ganglion of decapod crustaceans has received extensive study because
the stomatogastric ganglion generates a variety of rhythmic output with a small number of neurons.
If stimulating current pulse 9 (not shown) was both stronger and longer than stimulating current pulse 8, then
the train of action potentials would continue for the length of the stimulating current
Oscillatory networks based on the half-center model are unstable unless
there is a fatigue mechanism so that the first neuron that fires action potentials stops firing action potentials.
In resting skeletal muscle, contraction does not occur because
there is very little calcium in the cytoplasm.
According to the sliding filament theory of muscle contraction, myosin heads pull on _______ filaments and _______.
thin; move the z-lines together
In skeletal muscle cells, cytoplasmic Ca2+ is bound by
troponin
A cellular oscillator in a central pattern generator is a cell
whose membrane potential goes through regular cycles of depolarization and repolarization.
The sarcomeres of vertebrate skeletal muscles are all about the same length, but squid have different sarcomere lengths in different muscles in the body. If all other factors are equal, the muscle with shorter sarcomeres
will shorten more rapidly.
If you accidentally grab a very hot frying pan with your right hand, _______ will _______ action potential frequency.
α motor neurons innervating the right elbow flexors; increase
When you voluntarily pick up an object such as a glass of milk,
α motor neurons stimulate extrafusal muscle fibers to contract, while γ motor neurons stimulate the ends of intrafusal muscle fibers to contract.
How were extracellular ion concentrations manipulated in the experiments supporting the theory of quantal release of neurotransmitters?
Mg2+ replaced Ca2+ in the extracellular fluid so that action potentials would release few vesicles.
When a superior cervical ganglion is heavily stimulated, how does it keep from running out of acetylcholine?
More choline is produced in the cleft and taken back up into the cell to create more acetylcholine.
Which of the following statements best describes long-term potentiation?
More sodium entering the postsynaptic membrane per presynaptic action potential
Which statement best reflects the evolutionary history of the ligand-gated channel?
Most kinds of ligand-gated channels appear to have evolved from a common ancestor.
How do most second messengers go on to affect the membrane potential?
Most second messengers activate protein kinases, which phosphorylate proteins such as ion channels and change their permeability, which then alters the membrane potential.
What is the best description of B?
Muscle fiber action potential
Explain why muscles such as rattlesnake tail-shaker muscles, which are capable of very fast activation and relaxation, tend to produce lower forces than other skeletal muscles.
Muscles that contract and relax very rapidly require small myofibrils surrounded by extensive sarcoplasmic reticulum. This arrangement minimizes the distance over which Ca2+ must diffuse to reach each thin filament within the myofibrils, speeding both contraction and relaxation. Rapid Ca2+ pumping by the SR Ca2+ ATPase requires a large amount of ATP, so mitochondria and glycogen granules tend to be abundant as well. If the SR, mitochondria and glycogen take up more of each muscle cell's volume, there is less space available for myofibrils containing actin and myosin, so fewer cross-bridges can form and the muscle cell cannot produce as much force as a typical skeletal muscle. (In fact, in tail-shaker muscle, only a third of the cell volume is devoted to myofibrils compared to about 85% in the body muscle.)
Describe the significance of myelination.
Myelination greatly increases conduction velocity of an axon by increasing the membrane resistance while decreasing the membrane capacitance. In other words, conduction velocity is increased by increasing the length constant without increasing the time constant. Action potentials occur only at the nodes of Ranvier, in a process that is called saltatory conduction.
What happens when Ca2+ increases in the cytoplasm of a striated muscle cell?
Myosin binding sites on actin are exposed, allowing cross-bridge cycles to occur until Ca2+ drops again.
Identify the two major uses of ATP in skeletal muscle cells that are involved in contraction and relaxation, and explain why each process uses ATP more rapidly in fast-twitch muscles than in slow-twitch muscles.
Myosin hydrolyzes ATP as part of the cross-bridge cycle that generates force and causes the muscle to shorten. The myosin isoforms in fast-twitch muscle go through the cross-bridge cycle more quickly than the isoforms in slow-twitch muscle, so ATP is broken down more rapidly. The SR Ca2+-ATPase uses ATP to pump Ca2+ into the SR during relaxation. Fast-twitch muscle has more sarcoplasmic reticulum containing more SR Ca2+-ATPase and more ryanodine receptors than slow-twitch muscle. Therefore, Ca2+ is released more rapidly and taken up more quickly in response to each action potential, requiring more ATP.
The main ion responsible for the EPSP is
Na+
Which is the principal ion moving?
Na+
Ligand-gated channels on the postsynaptic membrane open and K+ and Na+ both move through these channels in opposite directions. Why then do we measure depolarization on the postsynaptic membrane?
Na+ has a much stronger driving force into the cell.
Which of the following statements regarding the ions in intracellular and extracellular fluids is false?
Na+ leaks into the cell rapidly because its electrochemical gradient is large.
Which of the following statements about ion permeability as shown in the figure is true?
Na+ permeability is at its highest very close to the membrane potential peak.
Compare and contrast nervous systems and endocrine systems.
Neural and endocrine systems are both systems for communication within the body. Nervous systems are faster and capable of much finer temporal and spatial control, whereas endocrine systems typically control more widespread and prolonged activities.
Which of the following is not a type of glial cell?
Neurocytes
The properties shown in the figure can be measured in which of the following
Neurons, Muscle cells, and pacemaker cells
Which of the following statements about an animal's nervous system is false?
Neurotransmitter is released throughout the body via the blood.
Which of the following is a shared characteristic between a spiking neuron and a nonspiking neuron?
Neurotransmitter secretion based on a change in membrane potential
The phrase "like a chicken with its head cut off" refers to a person rushing around frantically or carelessly. Explain how a chicken might be able to run (briefly) when its brain has been disconnected from the rest of its body.
Once initiated, rhythmic contractions of the limbs can be sustained by a spinal central pattern generator. Neurons descending from the brain to the spinal cord may be depolarized by physical contact when the chicken's head is detached. Because the cerebellum and other portions of the brain are disconnected, normal quality control of movement patterns will be absent and movements are likely to be poorly coordinated
Which of the following statements about a network oscillator is true?
One or more neurons receive input that turns the network on, and then neurons interact to generate a rhythmic output pattern.
In myelinated axons, action potentials occur
Only at the nodes of Ranvier
The diffusion rate of which factor best explains why vertebrates evolved to have slow oxidative muscle fibers that are smaller in diameter than fast glycolytic fibers?
Oxygen
Which of the following is the most likely explanation for the data shown in the figure?
PD/AB is a cellular oscillator that inhibits both LP and PY, which are autoactive.
Write a paragraph describing the mechanism that causes you to withdraw your right hand very rapidly when you reach out and touch a hot frying pan by mistake.
Painful stimuli activate flexion-reflex afferents that synapse on spinal interneurons. These interneurons excite motor neurons leading to the ipsilateral flexor muscles as well as interneurons that inhibit motor neurons leading to the ipsilateral extensors. They also activate the crossed extensor reflex by exciting interneurons that activate motor neurons of the contralateral extensors and inhibitory interneurons leading to the contralateral flexors
What are the best titles for Panel 1 and Panel 2?
Panel 1 = Motor-neuron EPSP; Panel 2 = Gill withdrawal
Which human pathology has been linked to degeneration of the basal ganglia?
Parkinson's disease
What technique is being used to collect the data presented?
Patch clamp
Which technique was used to collect the data in the bottom panel?
Patch-clamp
Explain why α‒γ coactivation is important for quality control of voluntary motions.
When extrafusal muscle fibers contract, the entire muscle shortens, including the portion surrounding the intrafusal fibers that contain the muscle spindles. If the contractile portion of the intrafusal fiber is not activated to contract, the normal baseline tension on the muscle spindles will be released and the action potential frequency of the spindle afferents will decrease or stop entirely. α‒γ coactivation ensures that the intrafusal fiber contracts at a rate that corresponds to the expected rate of shortening of the entire muscle. If the muscle shortens at the expected rate, the tension on the spindle remains constant, resulting in a constant rate of action potentials in the 1a afferent fibers. If the muscle shortens more slowly than expected, the tension on the spindle increases, resulting in a higher action potential frequency in the 1a afferents. If the muscle shortens too quickly, the tension on the spindle decreases, resulting in a lower action potential frequency in the 1a afferents.
Which of the following contributes to the length‒tension relationship observed in skeletal muscle?
When sarcomere lengths are long, thick and thin filaments do not overlap optimally.
Explain why it is the receptor and not the neurotransmitter that determines whether the postsynaptic membrane produces an EPSP or an IPSP.
Whether the PSP is excitatory or inhibitory depends on what kinds of ions flow through the ion channels when the channels open. A particular neurotransmitter can act at different receptors, and they may produce similar effects or different effects.
Which of the following proteins cannot contact a G protein directly?
Protein kinase C
Which of the following statements best describes the mechanism of sensitization?
Protein kinase phosphorylates K+ channels and decreases the K+ current that normally terminates the action potential, which leads to an increase in Ca2+ influx.
Output from the cerebellar cortex is sent by
Purkinje cells.
Which of the following would not be considered synaptic plasticity?
Reducing voltage gated Na+ channels on the neuron
The power stroke of the myosin head occurs in conjunction with what other event of the cross-bridge cycle?
Release of inorganic phosphate from the myosin head
Which of the following experimental results would demonstrate most strongly that sensory feedback is important in the control of rhythmic movement?
Repetitive stimulation of sensory afferents can alter the frequency of wingbeats in a tethered insect.
Which of the following factors best explains why vertebrates evolved to have FG muscle fibers that are larger than SO fibers?
SO fibers rely on aerobic metabolism, whereas FG fibers rely on anaerobic metabolism.
Running mice are capable of moving their legs back and forth much more quickly than
SR Ca2+-ATPase.
Smooth muscle cells possess which of the following components?
Sarcoplasmic reticulum
Which of the following glial cells are found int he peripheral nervous system
Schwann Cells
Which of the following is most uniquely associated with a metabotropic receptor?
Second messenger
Which of the following statements about the startle response of the cockroach is false
Sensory neurons synapse with and excite the dorsal hollow spinal cord
In two sentences, explain the overall mechanism of presynaptic facilitation (sensitization) in Aplysia.
Serotonin acts via a G protein to upregulate cAMP, which activates cAMP-dependent protein kinases to phosphorylate the K+ channel. This leads to a decrease in the repolarizing K+ current, allowing Ca2+ channels to stay open longer, mediating a greater release of neurotransmitter per action potential.
_______ are responsible for extending the time of the cardiac action potential relative to a neural action potential.
Slow Ca+ channels
A 66-year-old man has difficulty controlling voluntary movements. He can clearly state what he intends to do, describe how he would do it, and initiate or stop the movement. However, he has poor coordination and often misses his target. If his difficulty arises from a defect in one particular area of the central nervous system, which area is most likely to be involved?
Spinocerebellum
What is the difference between synaptic facilitation and behavioral sensitization?
Synaptic facilitation underlies behavioral sensitization.
Which of the following is not likely to affect the conduction velocity of an action potential?
Temperature
What effect would injecting a leg muscle with a drug that binds to and disables acetylcholinesterase have on that leg?
Tetany once the leg muscle was contracted
Suppose that you contract your biceps brachii muscle to toss a juggling pin into the air and find that it is much lighter than you expected. Which of the following will happen in compensation?
The action potential frequency in the α motor neurons to the biceps brachii will be decreased reflexively.
Explain in mechanistic terms how the action potential is an all-or-none phenomenon.
The action potential is initiated only when a threshold depolarization is reached near the axon hillock. That is, a certain critical number of voltage-gated Na+ channels have to open in order to cause a depolarization that is strong enough to initiate the Hodgkin cycle and, by definition, perpetuate the further opening of voltage-gated Na+ channels via their own depolarization. If the threshold is not reached, there will be no Hodgkin cycle or action potential.
What is the mechanism explaining Panel 1?
The amount of neurotransmitter per presynaptic impulse changes.
Movement disorders such as Parkinson's disease and Huntington's disease are associated with degeneration in what areas of the central nervous system?
The basal ganglia
If a current pulse is generated on the membrane and creates a passive potential, which of the following will be true?
The change in the membrane potential will decrease as the distance from the current pulse increases.
Which of the following statements regarding the structure of the voltage-gated Na+ channels is false?
The channel protein changes its primary structure in response to membrane depolarization.
Since the bulk solutions that make up the intracellular and extracellular fluids maintain charge neutrality, how does the cell produce membrane potentials?
The charge separation producing the membrane potential is an extraordinarily local phenomenon. According to textbook Figure 12.11, in a small 1 µm3 section around each side of the membrane, of the 110,000 cations and 110,000 anions in each fluid compartment, only six pairs of ions need to sit on the membrane and charge its capacitance to produce a membrane potential of -90 mV.
Describe the startle response in the cockroach.
The cockroach's startle response is a reflex. Sound waves or air vibrate the filiform hair receptors, which generate impulses in sensory neurons. The sensory neurons excite the giant interneurons that synapse with leg motor neurons. Once excited, the leg motor neurons activate the leg muscles.
Which of the following would not occur if ouabain was used to block Na+-K+-ATPase pumps?
The concentration of K+ would be equal on both sides of the membrane
Some crabs have giant skeletal muscle fibers that are much larger in diameter than other muscle fibers found in most other animals. What fiber type are these fibers likely to be and why?
The giant fibers are fast glycolytic fibers (FG). Oxidative fibers rely on continuous diffusion of oxygen from outside the cell to the mitochondria in order to generate ATP, so they can work effectively only if the fiber diameter (i.e., the diffusion distance for oxygen) is relatively small. Glycolytic fibers can generate ATP using substrates contained within the cell. Metabolic byproducts can then diffuse out of the cell slowly before the muscle is used again.
On the same set of axes, graph the relationship of velocity to force in two muscles of equal mass from the same animal. Muscle A contains predominantly fast glycolytic fibers, while muscle B contains predominantly slow oxidative fibers.
The graph should show that both muscles produce the same maximum force, but muscle A has a faster maximum shortening velocity when force is zero, and shortens more quickly at any given force/load.
_______ prevents bidirectional propagation of action potentials.
The inactivation of Na+ channels
Which one of the following statements regarding neurotransmitters (NTs) is true?
The inactivation of small molecule NTs can occur via reuptake or via enzymes
How does the indirect pathway of synaptic transmission in the basal ganglia help to fine tune voluntary movement?
The indirect pathway inhibits thalamic neurons, thereby suppressing movements that may compete with the intended movement
Which of the following statements about glial cells is false?
The intergrate cell membrane potentials to enhance of inhibit action potentials.
How do we account for the two hypotheses of vesicular fusion and retrieval?
The kiss-and-run pathway is likely used at lower rates of NT release while the classical pathway predominates at higher rates of NT release.
Which of the following is the best explanation for the difference between the middle panel and the lower panel?
The membrane voltage measured in the lower panel is farther away from the current pulse.
How can summation of skeletal muscle twitches occur if the motor neuron's refractory period prevents multiple action potentials from being transmitted to the neuromuscular junction at the same time?
The motor neuron's absolute refractory period is much shorter than the time it takes for calcium release and reuptake from the SR.
Compare and contrast current and voltage with respect to the cell membrane.
The net movement of charge constitutes an electric current. The separation of positive and negative charges constitutes a voltage. In terms of the cell membrane, the current would be a flow of ions through channels in the membrane, whereas the voltage would be the separation of charges across the membrane.
How would the trace on the right look if the neuron was soaking in TEA?
The outward ionic current would disappear.
Which of the following statements regarding cardiac pacemaker cells is false?
The pacemaker cells are modified neural tissue
Briefly explain the patch clamp technique and why it is important.
The patch clamp technique uses a fine glass microelectrode sealed the membrane with suction. The patch of membrane is then pulled from the cell and the researcher has the ability to alter the solution on either side of the membrane, as well as measure the receptor channel current. Because of its small size, researchers are able to measure the current on isolated receptors, which has been invaluable in advancing the field of receptor physiology and pharmacology
Which of the following distinguishes a standard neuromuscular EPSP from a miniature EPSP (mEPSP)?
The postsynaptic response to the release of the contents of one synaptic vesicle.
Two sets of axons carry stimuli near the axonal hillock. One set produces an IPSP and the other set produces an EPSP. If both sets produce action potentials at the same time, what is the likely effect at the axonal hillock?
The potentials created will cancel each other out
. In what ways do mirror neurons in the premotor areas of the cerebral cortex highlight the complexity of motor pathways?
The premotor area is involved in planning and organizing voluntary motor patterns. Experiments on primates indicate that particular mirror neurons are activated when an animal generates a particular movement, initially suggesting a simple correspondence of neurons in the cortex to particular patterns of muscle contraction. However, these neurons are also activated when an animal observes another animal making the same movement. Thus the neurons cannot be immediately responsible for causing the movement, and must operate at a higher level of motor programming.
Which of the following statements about the neuromuscular junction acetylcholine (Ach) receptor is false?
The probability that an ACh channel will open depends on membrane voltage
Which of the following does not contribute to the passive electrical properties of a cell?
The resting membrane current
Explain in mechanistic terms why the action potential can travel a great distance along an axon without degrading.
The same mechanism that is responsible for the rising phase of the action potential also aids in its perpetuation along the axon without degradation. The action potential on one location on the axon can itself initiate an action potential at a neighboring location, and the induced action potential will have the same all-or-none amplitude as the original.
Why does a skeletal muscle twitch last longer than a skeletal muscle action potential?
The twitch begins with the action potential but also requires opening of ryanodine receptors, diffusion of Ca2+ from the interior of the SR to the myofibrils, Ca2+ binding to troponin, configuration changes in tropomyosin, cross-bridge cycling, release of Ca2+ from troponin, and removal of Ca2+ from the cytoplasm. Many fewer ions are moved by pumps per unit time than occurs with fluxes of ions through channels. Each of these events takes time, so the twitch lasts substantially longer than the action potential that produces it.
Which of the following is the most likely explanation for the differing patterns of innervation in arthropod skeletal muscle (polyneuronal) and vertebrate skeletal muscle (single innervation)?
The two patterns are products of the evolutionary history of the two taxa and each one allows effective control of muscle contraction.
Why were the terms nicotinic and muscarinic both used as names for the acetylcholine receptor?
The two types of acetylcholine receptors were first characterized many years ago by their pharmacological response. The acetylcholine receptor in skeletal muscle is stimulated by nicotine and was hence named a nicotinic receptor. The acetylcholine receptor on the heart muscle is stimulated by muscarine and was thus named a muscarinic receptor.
How does the G protein activate adenylyl cyclase?
The α subunit of the G protein, with GTP, diffuses laterally in the membrane and binds to adenylyl cyclase to activate it.
Which of the following statements about slow oxidative and fast glycolytic muscle fibers is false?
Their thick and thin filaments are arranged differently.
How do nonspiking neurons function even though their depolarization signal significantly degrades with distance?
These neurons are very short, so there is no major signal decrement.
Which of the following statements regarding metabotropic receptors is false?
They can directly open or close ion channels.
Which of the following best describes of the mechanistic uniqueness of the Doogie mouse strain?
They have longer-opening NMDA receptors compared to standard lab mice.
Which of the following statements about skeletal muscle is true?
Which of the following statements about skeletal muscle is true?
Which of the following statements regarding the ligand-gated channel at the vertebrate neuromuscular junction is false?
Two acetylcholine molecules need to bind to the intracellular side of the receptor
What is the best explanation for the plateau shown in the figure?
Volatage gated Na+ channels remain open, and voltage gated K+ channels delay opening
Which technique was used to collect the data shown in the figure?
Voltage-clamp
_______ channels govern the generation of an action potential.
Voltage-gated Na+
Which of the following is most responsible for the all-or-none property of the action potential?
Voltage-gated Na+ channels
What allows the action potential to return to a repolarized state?
Voltage-gated Na+ channels become inactivated.
What occurs when the membrane is clamped at -100 mV?
Voltage-gated ion channels do not open at all.
_______ channels are responsible for the undershoot at point D of the figure.
Voltage-gated potassium
Modeling experiments on walking and swimming in robotic salamanders have yielded which of the following conclusions?
Walking or swimming movements can be generated automatically by a network of central pattern generators responding to the intensity of the central command.
A readiness potential is
a broad wave of electrical activity in the cerebral cortex that precedes a voluntary movement.
If you voluntarily lift an object and have underestimated its weight,
a burst of action potentials from the muscle spindle afferents causes the contracting muscles to contract more forcefully.
The extraocular muscles that move the mammalian eyeball can contract and relax at much higher frequencies than the muscles of the limbs, but they produce relatively low force as they rotate the eye. These characteristics tell us that extraocular muscles have
a high volume fraction of sarcoplasmic reticulum.
Suppose that muscle A is long with a narrow diameter and muscle B is short with a large diameter. Compared to muscle A, muscle B is capable of producing _______ maximum force and _______ maximum velocity.
a higher; a lower
A vertebrate motor unit consists of
a single motor neuron and all of the muscle fibers that it innervates.
The seperation of positive and negative charges constitutes
a voltage
List three specific changes in the synapse that would be categorized as synaptic plasticity.
a) Number of receptors on the postsynaptic membrane b) Amount of neurotransmitter released per action potential c) The effectiveness of the uptake or breakdown of the neurotransmitter once released into the synapse
Which of the following regarding the mechanism of vesicular docking and release is false?
a. Targeted vesicles move to active zones where they attach reversibly. b. Docking is mediated by the formation of a SNARE complex. c. The v-SNAREs and t-SNARES interact to hold the vesicle at the release site. d. Fusion is triggered by the binding of Ca2+ to synaptotagmin. All of the above are true; none is false
Conduction velocity shows a(n) _______ axon diameter.
a. proportional relationship to b. proportional relationship to the square root of c. exponential relationship to d. Either a or b, depending on the type of axon e. Either a or b, depending on the type of axon
In skeletal muscle, an unfused tetanus results from
action potentials arriving at a rate fast enough for sarcomeres to generate force while the elastic components of the muscle are still stretched.
Evidence for the role of the primary motor cortex comes from experiments that show that
activity of some neurons of the motor cortex correlates with the force or direction of a movement.
According to the principle of reciprocity, when a muscle is stimulated to contract, its
agonists contract while its antagonists relax
On the plateau of the length‒tension curve,
all myosin heads are in proximity to actin.
The involvement of the cerebellum in motor learning is demonstrated by the observation that patients with cerebellar lesions
are capable of voluntary movements but are clumsy and uncoordinated
The involvement of the cerebellum in preprogramming voluntary movements is demonstrated by the observation that many patients with cerebellar lesions
are capable of voluntary movements but must think about each step in complex movements individually.
Lengthening of a muscle occurs
as a result of an external load that acts on the muscle.
When your family physician taps your left patellar tendon with a mallet, stretch is sensed by sensory receptors
associated with intrafusal fibers in the quadriceps
In vertebrates, the highest-level planning of voluntary movement, such as deciding whether or not to make a movement, begins in the
association cortex
According to the current general model describing planning and execution of a voluntary movement, decisions generated in the _______ cortex are passed to the _______ via the _______.
association; motor cortex; basal ganglia
Initiation of the action potential usually occurs _______of the neuron
at the axon initial segment
The treatment difference between the membranes shown in the graphs is that the membrane on the left is _______, while the membrane on the right is being _______.
being hyperpolarized; depolarized
Experiments in which cats with transected spinal cords are able to walk on treadmills demonstrate that the
brain does not control the timing of repetitive limb movements in cats.
The figure depicts a
cardiac action potential
In the closed-loop network depicted in the figure, stimulation from outside the network would cause
cell 3 to fire action potentials until it is inhibited by cell 1
In a vertebrate skeletal muscle cell, depolarization of the t-tubule membrane causes dihydropyridine receptors to
change conformation and interact with ryanodine receptors.
The motor cortex sends output to the cerebellum as movements are initiated, and the cerebellum
compares sensory feedback to the initial motor output to detect errors
Slow oxidative fibers in skeletal muscle are used
constantly, for postural activities such as standing and sitting.
A hypothetical skeletal muscle cell with no t-tubules would probably
contract and relax more slowly during twitch contractions
A quantum is a
count of the number of acetylcholine molecules in a vesicle
When muscle is suddenly activated to perform contractions at a rapid rate, most of the ATP to fuel the first 3‒5 seconds of exercise comes from
creatine phosphate hydrolysis.
A decrease in the absolute value of the membrane potential toward zero is called
depolarization
Which of the following does not contribute to the cell's membrane potential?
depolarization.
Calcium enters the cytoplasm of a smooth muscle cell by
diffusion from the extracellular space and the sarcoplasmic reticulum.
In the stretch reflex, a signal from a sensory neuron that detects stretch in a muscle reaches a motor neuron innervating the stretched muscle via
direct sensory-to-motor-neuron synapses as well as excitatory spinal interneurons.
In relaxed skeletal muscle, myosin heads are
dissociated from actin with ADP and phosphate bound.
Epinephrine is
either excitatory or inhibitory.
Mammalian cardiac muscle cells are stimulated to contract by
electrical signals transmitted through gap junctions from other autorhythmic cardiac muscle cells.
The primary motor cortex contains neurons that
encode the force and/or direction of movements.
A skeletal muscle fiber with high myosin ATPase activity, a high rate of Ca2+ reuptake by the SR, and large number of mitochondria would be classified as a
fast oxidative glycolytic fiber.
The figure shows that membrane potential results
from relatively few charges sitting on the membrane.
The muscle fibers in a muscle spindle
function to maintain tension on spindle stretch receptors
The major excitatory neuromuscular junction neurotransmitter in a moth is
glutamate
In the figure, the _____ decreases with distance
graded potential
Compared to a typical avian leg muscle, hummingbird flight muscle
has an exceptionally high volume fraction of mitochondria.
Single-unit smooth muscle differs from multiunit smooth muscle in that multiunit smooth muscle
has cells that function as independent units.
Muscles of the larynx that help mammals to produce complex sounds can contract and relax at much higher frequencies than the muscles of the limbs, but they produce relatively low force as they act on the vocal cords. Based on these characteristics, one would predict that laryngeal muscles have
high levels of parvalbumin
In Aplysia, the result of sensitization at the synapse is a(n)
increase in the amount of neurotransmitter per impulse.
Myelination by Schwann cells increases the velocity of action potential propagation by
increasing the resistance and decreasing the capacitance, allowing the action potential to "jump" over the myelinated area.
Antidepressants, such as Prozac, work by
inhibiting the reuptake of serotonin.
The Purkinje cells of the cerebellum send _______ output from the cerebellar cortex to _______.
inhibitory; the cerebellar nuclei
Electrical recordings from human volunteers indicate that the decision to move a body part and the signals generating that movement arise from
interactions of multiple cortical regions.
Voluntary movements of a vertebrate animal are generated by
interactions of several regions
Fast oxidative-glycolytic fibers in skeletal muscle are used
intermittently, for activities requiring more force output than the SO fibers alone can produce.
When your family physician taps your left patellar tendon with a mallet, motor neurons innervating the flexors of the left knee are inhibited by _______ in the _______.
interneurons; spinal cord
If only α motor neurons were activated during a voluntary movement, the muscle spindle would be unable to transmit information to correct the rate of the movement because the
intrafusal fibers would be slack.
In order to function effectively as an oscillatory network, the half-center model depicted in the figure must
involve a mechanism for the activated neuron to stop signaling.
Label A of the figure represents _______ currents through voltage-gated _______ channels.
inward; Na+
Once acetylcholine is released into the synapse it
is broken down by acetylcholineesterase
Tonic muscle
is found primarily in postural muscles
Experiments in which sensory afferent fibers in the hindlimbs of cats are transected show that sensory feedback from the limbs
is not necessary to maintain repetitive movements.
According to the Goldman equation, the contribution of each ion to the membrane potential depends the most on
its membrane permeability
When your family physician taps your left patellar tendon with a mallet, motor neurons innervating the _______ are excited and motor neurons innervating the _______ are inhibited.
left knee extensors; left knee flexors
The 1a afferent fibers associated with muscle spindles increase their action potential frequency only when the muscle
lengthens involuntarily or shortens less than expected during a voluntary contraction.
During an isotonic muscle twitch, the presence of elastic elements causes the latent period to be _______ than during an isometric twitch, and the peak force transmitted through the tendon to be _______.
longer; lower
Slow oxidative fibers in skeletal muscle have
low levels of glycolytic enzymes but high levels of oxidative enzymes.
Compared to the neural circuits responsible for reflexes of invertebrates, the circuits of vertebrates involve
many more individual neurons to complete the same steps
When your family physician taps your left patellar tendon with a mallet
many motor neurons innervating your left quadriceps are excited by 1a afferent fibers.
Compared to the repetitive motor patterns of locomotion, more complex motor behaviors
may be composed of simple patterns linked by CNS commands and responses to sensory feedback
Ultimately, it is the _______ that determines whether the postsynaptic membrane produces an inhibitory postsynaptic potential (IPSP) or an excitatory postsynaptic potential (EPSP).
movement of ions
Injections of the norepinephrine precursor L-dopa can enable spinally transected cats to walk on a treadmill. The most likely explanation for this result is that
norepinephrine activates the central pattern generator that causes rhythmic stepping motions.
The force that a particular vertebrate skeletal muscle produces can be changed by a change in the
number of motor units recruited
Invertebrates have often been used in motor control studies because
only a few neurons are often involved in a particular step in an invertebrate motor control pathway.
For an axon at resting membrane potential, the K+ leak channel is _______, the voltage-gated Na+ channel is _______, and the voltage-gated K+ channel is _______.
open; closed; closed
During the falling phase of an action potential, the K+ leak channel on the axon is _______, the voltage-gated Na+ channel is _______, and the voltage-gated K+ channel is _______.
open; inactivated; open
The small diameter of slow oxidative muscle fibers is particularly advantageous for minimizing the distance over which
oxygen diffuses from the sarcolemma to the mitochondria.
When the cell membrane of a vertebrate skeletal muscle is depolarized, ryanodine receptors change configuration and permit passage of Ca2+
passively, from the sarcoplasmic reticulum to the cytoplasm
The frontal cortex contains areas that are involved in
planning and organizing movement.
The neuron converts an electrical signal to a chemical signal in the
presynaptic terminal
A stimulating depolarizing current that depolarizes the axon hillock just slightly negative to the threshold will
produce a temporary graded potential
The main role of the cerebellum is to
provide feedback to correct errors as a voluntary movement is performed.
In the primary motor cortex, the neurons most responsible for sending motor output to spinal motor neurons are the
pyramidal cells
For a hormone to elicit a specific response from a cell, the cell must possess
receptor protiens specfic to the hormone
The time constant (τ) depends on the
resistance and capacitance of the membrane.
The smallest unit of a skeletal muscle that shortens during a muscle contraction is the
sarcomere.
For contraction to occur in smooth muscle
myosin light chains must be phosphorylated.
In rhythmic behavior such as human walking, each muscle contraction occurs in response to
nerve action potentials originating in the CNS.
Pyramidal cells are
neurons in the primary motor cortex that send output to activate spinal motor neurons.
Describe two mechanisms by which the human nervous system can voluntarily alter the force and velocity of a contraction of the biceps muscle of the arm.
1. Varying numbers of motor units can be recruited. 2. Variation of action potential frequency can generate twitches, unfused tetani, or fused tetanic contractions.
Briefly describe the mechanism of docking and fusion in the release of neurotransmitters.
Docking is mediated by the formation of a SNARE complex; the v-SNAREs and t-SNAREs interact to hold the vesicle at the release site. Following priming, Ca2+ entry through voltage-gated Ca2+ channels triggers fusion by the binding of Ca2+ to the vesicular protein synaptotagmin. The Ca2+-synaptotagmin complex changes conformation to fuse the vesicular and terminal membranes.
List four factors that could allow a leg muscle in one animal to activate and relax more quickly than a leg muscle in another animal.
Possible factors include (1) higher levels of parvalbumin, (2) larger quantities of sarcoplasmic reticulum, (3) greater quantities of SR Ca2+-ATPase, and (4) troponins that change configuration more quickly
Which of the following statements regarding chemical synapses is false?
Pre- and postsynaptic currents are always similar.
In chemical synapses, neurotransmitters are released by
calcium-dependent exocytosis
In smooth muscle, calcium must bind to _______ to initiate contraction.
calmodulin
In contrast to skeletal muscle, nervous signaling to smooth muscle cells
can be excitatory or inhibitory.
Lactate produced by muscle cells
can be exported into the bloodstream and used by other cells
Lactate produced by muscle cells
can be exported into the bloodstream and used by other cells.
Agonists are
muscles that work together to generate a given motion.
The elastic component of the gastrocnemius
must be fully stretched in order for the muscle to exert maximum tetanic force.
A striated muscle fiber is made up of many parallel _______, each containing a series of _______.
myofibrils; sarcomeres
