nerve exam
________ branch from the cell body and receive input from other neurons at specialized junctions called ________. A) Dendrites : synapses B) Somas : synapses C) Dendrites : axon terminals D) Axon hillocks : axon terminals E) Dendrites : cell bodies
A) Dendrites : synapses
What equation is used to calculate the membrane potential based on ion concentration gradients and permeabilities? A) GHK equation B) Fick's equation C) NAD equation D) Nernst equation E) None of the answers is correct.
A) GHK equation
Saxitoxin (STX) is the most well-known paralytic shellfish toxin caused by the phenomenon known as "red tide." Which statement below best describes why this neurotoxin causes paralysis? A) It acts by blocking voltage-gated sodium channels which are needed to generate an action potential. B) It acts on the potassium channels within a neuron, hyperpolarizing the cell membrane; therefore, no action potential can be generated. C) It prevents the synaptic vesicles from migrating to the axon terminal; therefore, no action potentials are generated. D) It blocks ligand-gated channels on the postsynaptic membrane, which blocks signals leaving the central nervous system. E) It acts on the hypothalamus of the brain, shutting down all neurological functions.
A) It acts by blocking voltage-gated sodium channels which are needed to generate an action potential
Which of the following best describes the electrochemical forces acting on sodium and potassium ions at the resting membrane potential? A) The force on sodium ions is to move into the cell, and the force on potassium ions is to move out of the cell. B) The force on sodium ions is to move out of the cell, and the force on potassium ions is to move into the cell. C) Forces on both sodium and potassium ions are to move out of the cell. D) Forces on both sodium and potassium ions are to move into the cell. E) There is no force on either ion to move.
A) The force on sodium ions is to move into the cell, and the force on potassium ions is to move out of the cell.
Which of the following accurately describes afferent neurons? A) They transmit information from the periphery to the CNS. B) They are typically multipolar neurons. C) They are the most abundant class of neurons. D) They transmit information from the CNS to the periphery. E) The cell body is located in the ventral horn of the spinal cord.
A) They transmit information from the periphery to the CNS.
What portion of the peripheral nervous system transmits information from sensory receptors to the central nervous system? A) afferent nervous system B) somatic nervous system C) central nervous system D) efferent nervous system E) autonomic nervous system
A) afferent nervous system
For an unmyelinated axon, conduction velocity is primarily determined by the A) diameter of the axon. B) type of sodium channel activated. C) number of ion channels present on the membrane. D) type of potassium channel activated. E) permeability of the axonal membrane.
A) diameter of the axon.
A group of nerve cell bodies in the peripheral nervous system are referred to as A) ganglia. B) pathways. C) commissures. D) nuclei. E) tracts.
A) ganglia.
Which of the following potentials can sum? A) graded potentials B) threshold potentials C) action potentials D) both graded potentials and action potentials E) neither graded potentials nor action potentials
A) graded potentials
Which of the following potentials dissipate in size as the potential moves away from the site of initiation? A) graded potentials B) threshold potentials C) action potentials D) both graded potentials and action potentials E) neither graded potentials nor action potentials
A) graded potentials
What functional class of neurons accounts for 99 percent of the neurons in the body processing sensory information and carrying out complex functions? A) interneurons B) visceral C) efferent D) bipolar E) afferent
A) interneurons
Which of the following determines the resistance to an ion's movement across a membrane? A) ion channels within the membrane B) receptors on the cell membrane C) the resting membrane potential D) enzymes on the surface of the cell membrane E) the ions present on either side of the membrane
A) ion channels within the membrane
What is the functional unit of the nervous system? A) neurons B) the central nervous system C) the brain D) axons E) glial cells
A) neurons
The all-or-none principle, associated with the action potential, states that A) once membrane potential reaches threshold, an action potential will be generated and that action potential will always be the same magnitude. B) there is a positive feedback loop for sodium channels that results in a rapid membrane depolarization. C) the positive feedback loop for the sodium channel is terminated by the inactivation gate. D) following an action potential, the membrane will be repolarized by the opening of a potassium channel. E) all of the action potentials will be generated from the axon hillock.
A) once membrane potential reaches threshold, an action potential will be generated and that action potential will always be the same magnitude.
During the rapid depolarization phase of an action potential, the plasma membrane is more permeable to which of the following ions? A) sodium (Na+) B) potassium (K+) C) chloride (Cl-) D) calcium (Ca++) E) phosphate (PO4-)
A) sodium (Na+)
Identify the type of summation that is occurring in Figure 7.1 where "S" refers to a stimulus from one source measured in the postsynaptic membrane. A) temporal B) multiplier C) spatial D) suprathreshold E) subthreshold
A) temporal
What limits the maximum number of action potentials on an axon? A) the absolute refractory period B) whether the axon is myelinated or not C) the relative refractory period D) the diameter of the axon E) the concentration of sodium within the cytoplasm of the cell
A) the absolute refractory period
Which statement best describes the events responsible for the phase represented by the letter "A" in Figure 7.1? A) the opening of sodium channels B) the opening and closing of sodium channels C) the opening of potassium channels D) the closing of sodium channels and the opening of potassium channels E) the opening of potassium channels and the closing of sodium channels
A) the opening of sodium channels
Which statement best describes the events responsible for the phase represented by the letter "B" in Figure 7.1? A) the opening of sodium channels B) the opening and closing of sodium channels C) the opening of potassium channels D) the closing of sodium channels and the opening of potassium channels E) the opening of potassium channels and the closing of sodium channels
A) the opening of sodium channels
If the soma of a neuron became more permeable to potassium, which statement below best describes the graded potential that would be generated in the soma? A) Potassium is a cation; therefore, it would cause an excitatory depolarization. B) Potassium would leave the cell, causing the membrane to hyperpolarize. C) Potassium would enter the cell, causing the membrane to depolarize and reach threshold. D) Potassium is an inhibitory second messenger; therefore, it would cause amplification of the graded potential. E) Potassium would reach its equilibrium potential and the voltage inside the cell would not change.
B) Potassium would leave the cell, causing the membrane to hyperpolarize.
As an action potential is propagated away from the axon hillock, why does propagation continue in one direction? A) The region just in front of the action potential is in the relative refractory period. B) The region just behind the action potential is in the absolute refractory period. C) The region just behind the action potential is in the relative refractory period. D) They will travel the path of least resistance. E) The region just in front of the action potential is in the absolute refractory period.
B) The region just behind the action potential is in the absolute refractory period.
On what portion of the neuron do action potentials propagate? A) nucleus B) axon C) cell body D) dendrite E) soma
B) axon
The brain and spinal cord are part of which of the following branches of the nervous system? A) efferent nervous system B) central nervous system C) enteric nervous system D) afferent nervous system E) somatic nervous system
B) central nervous system
What is the inverse of resistance? A) current B) conductance C) impedance D) voltage E) flux
B) conductance
Which of the following changes in membrane potential is considered excitatory? A) hyperpolarization only B) depolarization only C) repolarization only D) both hyperpolarization and depolarization E) both hyperpolarization and repolarization
B) depolarization only
What is the most common neuronal cell type? A) afferent neuron B) efferent neuron C) bipolar neuron D) interneuron E) pseudo-unipolar neuron
B) efferent neuron
At the resting membrane potential, the electrochemical gradient for sodium across the membrane is such that the net flux for sodium movement is directed ________, thereby causing the cell's membrane potential to become more ________. A) at equilibrium : positive B) inward : positive C) outward : positive D) outward : negative E) inward : negative
B) inward : positive
In myelinated axons, sodium and potassium channels would be concentrated in what area? A) axon terminal B) nodes of Ranvier C) axon hillock D) nucleus E) dendrites
B) nodes of Ranvier
The depolarization phase of the action potential is generated by a rapid A) opening of chloride channels. B) opening of sodium channels. C) closure of potassium channels. D) closure of sodium channels. E) opening of potassium channels.
B) opening of sodium channels.
What two divisions of the autonomic nervous system have opposite effects on the organs they innervate? A) somatic and enteric B) parasympathetic and sympathetic C) somatic and motor D) afferent and efferent E) peripheral and central
B) parasympathetic and sympathetic
What portion of the nervous system provides communication between peripheral organs and the brain and spinal cord? A) central nervous system B) peripheral nervous system C) efferent nervous system D) somatic nervous system E) afferent nervous system
B) peripheral nervous system
At rest, the plasma membrane is more permeable to which of the following ions? A) sodium (Na+) B) potassium (K+) C) chloride (Cl-) D) calcium (Ca++) E) phosphate (PO4-)
B) potassium (K+)
Increased permeability to what ion is responsible for the relative refractory period? 98) A) sodium (Na+) B) potassium (K+) C) chloride (Cl-) D) calcium (Ca++) E) phosphate (PO4-)
B) potassium (K+)
The resting membrane potential is close to the equilibrium potential of which of the following ions? A) sodium (Na+) B) potassium (K+) C) chloride (Cl-) D) calcium (Ca++) E) phosphate (PO4-)
B) potassium (K+)
At the resting membrane potential, the membrane is most permeable to ________, which moves ________ the cell due to its electrochemical gradient. A) potassium : into B) potassium : out of C) chloride : into D) sodium : out of E) sodium : into
B) potassium : out of
The jumping of an action potential from node-to-node is called A) nodal conduction. B) saltatory conduction. C) nodal propagation. D) propagation. E) electrotonic conduction.
B) saltatory conduction.
The central nervous system, which is composed of the brain and spinal cord, receives and processes information from both the external environment, known as ________ information and, the internal environment, which refers to ________ information. A) special : somatic B) sensory : visceral C) somatic : autonomic D) somatic : visceral E) peripheral : somatic
B) sensory : visceral
A subthreshold stimulus will not generate an action potential whereas a suprathreshold stimulus does generate an action potential. This is an example of A) positive feedback. B) the all-or-none principle. C) negative feedback. D) a refractory period. E) electrotonic conduction.
B) the all-or-none principle
What is the level of membrane depolarization required to induce the sodium channel's positive feedback loop called? A) suprathreshold B) threshold C) axon hillock D) subthreshold E) axon terminal
B) threshold
Information gathered about our internal environment (i.e., fullness of the stomach, blood pressure, etc.) is called ________ information. A) somatic B) visceral C) afferent D) sensory E) efferent
B) visceral
Which statement best describes how graded potentials determine whether an action potential will be generated or not? A) when the axon hillock is repolarized B) when an excitatory depolarization reaches threshold C) when the neuron is hyperpolarized D) when electrotonic conduction occurs within the soma of the neuron E) when sodium enters the soma of a cell
B) when an excitatory depolarization reaches threshold
What is the only glial cell found outside of the central nervous system? A) oligodendrocytes B) ependymal cells C) astrocytes D) Schwann cell E) microglia
D) Schwann cell
What portion of the efferent nervous system communicates with skeletal muscle? A) afferent nervous system B) central nervous system C) autonomic nervous system D) somatic nervous system E) enteric nervous system
D) somatic nervous system
The direction of change in membrane potential, in response to a stimulus that initiates a graded potential, is dependent upon A) that membrane's threshold potential. B) the gating of sodium channels only. C) the gating of potassium channels only. D) the ion channels that are opened or closed. E) the changes in ion concentration across the membrane.
D) the ion channels that are opened or closed.
What determines the strength of a graded potential? A) the diameter of the axon B) the amount of cytoplasmic resistance within the soma of the neuron C) the amount of voltage-gated channels in the neuron D) the size of the stimulus E) the amount of leak channels open in the neuron
D) the size of the stimulus
The fact that the opening of some sodium channels can induce several other sodium channels to open describes the ________ property of these channels. A) ligand B) all-or-none principle C) refractory D) suprathreshold E) regenerative
E) regenerative
In Figure 7.1, if S2 indicated a stimulus from a different source, and S1 occurred coincident with S2, what type of summation has been generated? A) subthreshold B) temporal C) multiplier D) suprathreshold E) spatial
E) spatial
When a weak stimulus is applied in rapid succession, it will often reach threshold due to A) spatial summation. B) excitatory summation. C) inhibitory summation. D) voltage potential. E) temporal summation.
E) temporal summation.
The magnitude of depolarization at the peak of an action potential is dependent on what factor? A) the length of the refractory period B) the size of the graded potential C) the size of the stimulus D) the concentration of sodium and potassium ions E) the strength of the electrochemical gradient for sodium and potassium ions relative to their permeability to these ions
E) the strength of the electrochemical gradient for sodium and potassium ions relative to their permeability to these ions
What type of ion channels is located along the axon? A) propagation channels B) ligand-gated channels C) mechanical channels D) initiation channels E) voltage-gated channels
E) voltage-gated channels
T/F Afferent neurons are generally bipolar neurons
FALSE
T/F At the resting membrane potential, a cell is at equilibrium.
FALSE
T/F Effector organs act as receptors that detect information about the external environment and transmit that information to the central nervous system.
FALSE
T/F Excitatory graded potentials are those where the stimulus initiates a hyperpolarization of the cell
FALSE
T/F Generation of new neurons (neurogenesis) cannot occur in the brain.
FALSE
T/F Graded potentials are of equal magnitude and travel over long distances along the axon.
FALSE
T/F In temporal summation, stimuli from different sources are applied at the same time such that they overlap and sum.
FALSE
T/F Leak channels are most concentrated in the soma of neurons.
FALSE
T/F Oligodendrocytes are located in the peripheral nervous system, providing the myelin sheath that forms the nodes of Ranvier.
FALSE
T/F The magnitude of the action potential is dependent upon the extent to which the change in membrane potential is above threshold.
FALSE
T/F The membrane potential of a cell is determined exclusively by that cell's sodium and potassium permeability.
FALSE
T/F Under resting conditions, the sodium channel responsible for generating an action potential is closed and incapable of opening.
FALSE
T/F An ion's net electrochemical force will tend to move that ion across the membrane in a direction that will cause membrane potential to move toward that ion's equilibrium potential.
TRUE
T/F Both activation and inactivation gates of a sodium channel are stimulated at the same time by a depolarization with the inactivation gate acting more slowly than the activation gate, thereby allowing sodium to enter the cell.
TRUE
T/F Diabetic neuropathy can affect nerves of the autonomic nervous system
TRUE
T/F During the relative refractory period, the stimulus intensity required to initiate an action potential is elevated.
TRUE
T/F Excitable cells are capable of producing action potentials
TRUE
T/F Once an action potential is generated, it will always depolarize the neighboring membrane above threshold, ensuring the action potential will travel along the axon without interruption.
TRUE
T/F Schwann cells are the only glial cells in the peripheral nervous system
TRUE
T/F The Na+/K+ pump distributes three sodium ions to the outside of the membrane and two potassium ions to the inside of the membrane.
TRUE
T/F The Na+/K+ pump maintains the concentration gradients in a neuron but maintains them.
TRUE
T/F The number of ions whose movement across the membrane creates the resting membrane potential is so few that their movement does not affect that ion's concentration gradient.
TRUE
T/F Tingling can be a sign of diabetic neuropathy.
TRUE
Describe the voltage gating of ion channels and how this plays a role in an action potential.
The action potential is generated by the activity of a specific type of sodium channel that has very unique gating properties. There are two gates on these sodium channels; one is the activation gate and the other is the inactivation gate. At the resting membrane potential, the activation gates are closed and the inactivation gates are open. On depolarization of the membrane to threshold, the activation gates open rapidly creating an open channel. In approximately one millisecond, the inactivation gates close thereby closing the channels. This short duration of time in which the sodium channel remains open is long enough to cause a large change in membrane potential due to the strong electrochemical driving force for sodium to move into the cell. This creates a positive feedback loop where the activation of one sodium channel causes the membrane to depolarize further, thereby opening other sodium channels. This regenerative process in the sodium channel is activated to produce an action potential only if the change in membrane potential is above threshold. At the same time that depolarization activates the sodium channels, there are potassium channels that are sensitive to depolarization and are stimulated to open. These channels are slow-acting as well, with respect to the activation gate of the sodium channel, meaning that the potassium channels open after a short delay. Thus, the action potential is generated by the opening of enough sodium channels, which rapidly depolarizes the membrane. That depolarization is reversed by the closure of the sodium channel's inactivation gate. The potassium channel opens more slowly and remains open for a longer period of time. The delayed opening of the potassium channels increases the rate of repolarization of the membrane following the upstroke of the action potential, and the slow closure results in the after-hyperpolarization of the membrane below resting membrane potential.
Graded potentials develop in the cell body of neurons as well as in sensory receptor cells. In order for sensory information to reach the central nervous system that graded potential must be converted into an action potential. How are graded potentials created, and how are they different from action potentials?
the negative nature of the resting membrane potential is determined by the greater permeability of the membrane to potassium. Any change in membrane potential involves a change in the number of ion channels that are open or closed. For a graded potential to be excitatory, the membrane must depolarize (become more positive), which could occur by more potassium channels closing or more sodium channels opening. For a graded potential to be inhibitory, the membrane must hyperpolarize or be stabilized at a sub-threshold potential. This could occur by more potassium channels opening, chloride channels opening, or more sodium channels closing. These channel-gating events (openings and closings) are created by neurotransmitters binding to receptors at the synapse or by direct activation of an ion channel on a receptor cell. Once created, the graded potential will degrade as it moves along the membrane, further away from the site that was stimulated. The magnitude of the graded potential can be quite variable, depending upon the number and type of channels affected. The magnitude of the graded potential will determine the frequency of action potentials generated. Different ion channels are responsible for an action potential. Voltage-gated sodium channels open and the membrane potential rapidly depolarizes. These channels close and voltage-gated potassium channels open, causing the membrane to repolarize and then hyperpolarize before returning to the resting membrane potential. Action potentials are all-or-none, and once threshold is reached, an action potential will be generated. They are also subject to refractory periods
Describe how an action potential, originating at the axon hillock, is propagated along the axon. Include those factors that can alter conduction velocity.
As an action potential is generated at the axon hillock, the change in membrane potential moves (via electrotonic conduction) along the axon. That electrotonic movement of current along the membrane causes the axonal membrane to depolarize. The extent of depolarization of the axonal membrane downstream from an action potential is always enough to trigger another action potential. This process is repeated multiple times as the action potential moves along the axon. This is the reason for the lack of decay in the action potential as well as the all-or-none property of an action potential, along with the fact that the magnitude of an action potential does not vary from one to the next. In unmyelinated axons, this process continues along the entire axon. The speed with which that action potential can move along the axon is dependent upon the electrical resistance of that axon. The electrical resistance of the axon is determined by the diameter of the axon, with the larger diameter axon having a lower resistance (conduction velocity will be greater) than a smaller diameter axon. In axons that are myelinated, action potentials will occur at discrete points along the axon, known as the nodes of Ranvier. Thus, the action potential jumps from node to node in what has been called saltatory conduction. The resistance of the membrane under the myelin sheath (acting as an insulator) is great enough that there is only a small amount of current lost as it moves between nodes. Because the action potential is jumping from node to node, the speed with which that action potential moves along the axon is greatly increased.
Most neurons have a resting membrane potential of A) -55 mV. B) -5 mV. C) -70 mV. D) +100 mV. E) +30 mV
C) -70 mV.
________ is the mechanism by which action potentials are propagated in unmyelinated axons. A) The all-or-none principle B) After-hyperpolarization C) Electrotonic conduction D) Temporal summation E) The regenerative mechanism
C) Electrotonic conduction
In Figure 7.1, if the direction of event "C" was reversed (hyperpolarization), how would this affect the ability of the postsynaptic membrane to generate an action potential? A) Hyperpolarization only cause refractory periods. B) Hyperpolarization only occur in graded potentials. C) Hyperpolarization will reduce the likelihood that an action potential will be generated. D) Hyperpolarization will cause an equilibrium potential to be reached between the intracellular fluid and the extracellular fluid. E) Hyperpolarization will increase the likelihood that an action potential will be generated.
C) Hyperpolarization will reduce the likelihood that an action potential will be generated.
In the peripheral nervous system, myelin is formed by ________. In the central nervous system, myelin is formed by ________. A) Schwann cells : microglial cells B) Schwann cells : astrocytes C) Schwann cells : oligodendrocytes D) oligodendrocytes : Schwann cells
C) Schwann cells : oligodendrocytes
Which of the following potentials are affected by refractory periods? A) graded potentials B) threshold potentials C) action potentials D) both graded potentials and action potentials E) neither graded potentials nor action potentials
C) action potentials
Which of the following potentials has an all-or-none response? A) graded potentials B) threshold potentials C) action potentials D) both graded potentials and action potentials E) neither graded potentials nor action potentials
C) action potentials
What portion of the efferent branch of the nervous system communicates to glands and cardiac muscle? A) afferent nervous system B) central nervous system C) autonomic nervous system D) enteric nervous system E) somatic nervous system
C) autonomic nervous system
If the graded potential remains above threshold once it reaches the ________, an action potential will be generated. A) nucleus B) dendrite C) axon hillock D) axon E) cell body
C) axon hillock
In a neuron, where is the greatest concentration of voltage-gated sodium and voltage-gated potassium channels? A) soma B) axon terminal C) axon hillock D) axon E) dendrites
C) axon hillock
Toward the end of the relative refractory period, the continued decrease in stimulus intensity required to initiate an action potential is caused by A) decreased sodium permeability. B) increased potassium permeability. C) decreased potassium permeability. D) the number of sodium channels whose inactivation gate has not opened. E) closure of the sodium activation gate.
C) decreased potassium permeability.
Which of the following axons would have the fastest conduction velocity? A) diameter = 5 microns, myelinated B) diameter = 5 microns, unmyelinated C) diameter = 20 microns, myelinated D) diameter = 1 micron, myelinated E) diameter = 20 microns, unmyelinated
C) diameter = 20 microns, myelinated
How can action potentials relay information about the intensity of a stimulus, such as distinguishing between a loud and soft sound? A) due to electrotonic conduction B) due to the magnitude of action potentials C) due to the frequency of action potentials D) due to summation of several action potentials E) due to the decremental properties of graded potentials
C) due to the frequency of action potentials
What type of ion channels in the membrane of neurons open or close in response to a neurotransmitter binding to its receptor? A) leak channels B) synaptic channels C) ligand-gated channels D) voltage-gated channels E) potential-gated channels
C) ligand-gated channels
What type of cell enhances the velocity of electrical transmission of an action potential along an axon in the central nervous system? A) microglia B) Schwann cell C) oligodendrocyte D) astrocyte E) ependymal cell
C) oligodendrocyte
Why do the distributions of sodium and potassium ions across the plasma membrane of neurons not change appreciably, even following hundreds of action potentials? A) The movement of sodium and potassium ions that occurs during an action potential is countered by the passive leak of these ions when a neuron is at rest. B) The movement of sodium and potassium ions that occurs during an action potential is countered by the passive movement of these ions during the repolarization phase. C) The movement of sodium and potassium ions that occurs during an action potential is countered by the passive movement of these ions during the after-hyperpolarization. D) The movement of sodium and potassium ions that occurs during an action potential is countered by the active transport of these ions by the Na+/K+ pump. E) The movement of sodium and potassium ions that occurs during an action potential is countered by counter-transport of potassium with sodium during rest.
D) The movement of sodium and potassium ions that occurs during an action potential is countered by the active transport of these ions by the Na+/K+ pump.
Which statement below best describes why action potentials travel in only one direction? A) The diameter of the axon explains this. B) They have myelinated axons. C) The all-or-none principle explains this. D) They have a refractory period. E) Only sodium- and potassium-gated channels are found on the axon.
D) They have a refractory period.
The movement of synaptic vesicles to the end of the axon terminal involves what type of transport? A) retrograde B) pinocytosis C) passive D) anterograde E) receptor-mediated
D) anterograde
In a neuron, where are voltage-gated calcium channels located? A) soma B) axon hillock C) dendrites D) axon terminal E) axon
D) axon terminal
Which of the following potentials is a result of opening or closing of ion channels? A) graded potentials B) threshold potentials C) action potentials D) both graded potentials and action potentials E) neither graded potentials nor action potentials
D) both graded potentials and action potentials
Which statement best describes how local anesthetics such as Novocaine work in numbing neurons? A) by making the cell membrane more permeable to potassium B) by binding to the enzyme sodiumase C) by blocking voltage-gated potassium channels D) by blocking voltage-gated sodium channels E) by making the cell membrane more permeable to sodium
D) by blocking voltage-gated sodium channels
Which of the following is the correct term for the movement of an electrical charge across a membrane? A) potential difference B) resistance C) capacitance D) current E) transistor
D) current
During which of the following states are the majority of voltage-gated sodium channels closed and incapable of opening? A) during the relative refractory period B) during depolarization C) at the resting membrane potential D) during the absolute refractory period E) during the after-hyperpolarization
D) during the absolute refractory period
What portion of the peripheral nervous system communicates to effector organs? A) afferent nervous system B) central nervous system C) enteric nervous system D) efferent nervous system E) spinothalmic tract
D) efferent nervous system
Once a membrane potential has been developed, the force that drives a particular ion across the membrane is its A) electrical gradient. B) chemical gradient. C) electrogenic pump. D) electrochemical gradient. E) concentration gradient
D) electrochemical gradient.
What is the passive spread of current along a membrane called? A) graded potential B) resistance C) action potential D) electrotonic conduction E) refractory period
D) electrotonic conduction
The opening of sodium channels causes a rapid ________ of sodium that ________ the neuron's membrane. A) influx : hyperpolarizes B) influx : repolarizes C) efflux : hyperpolarizes D) influx : depolarizes E) efflux : depolarizes
D) influx : depolarizes
What type of ion channels in the membrane of neurons allows ions to move across the membrane at rest and thereby contribute to resting membrane potential? A) ligand-gated channels B) voltage-gated channels C) resting channels D) leak channels E) potential-gated channels
D) leak channels
What is the structural classification of a neuron composed of a single axon and a number of dendritic projections from the nerve cell body? A) bipolar B) polar C) pseudo-unipolar D) multipolar E) unipolar
D) multipolar
In myelinated nerve fibers, where do action potentials occur? A) Schwann cell B) cell body C) oligodendrocyte D) nodes of Ranvier E) underlying myelin sheath
D) nodes of Ranvier
Which type of glial cell provides the myelin sheath for many axons in the central nervous system? A) astrocytes B) ependymal cells C) microglia D) oligodendrocytes E) Schwann cell
D) oligodendrocytes
In order to generate an action potential, the magnitude of the inward sodium current must be large enough to overcome which of the following? A) outward calcium current B) inward potassium current C) outward potassium current D) outward sodium current E) inward chloride current
D) outward sodium current
The depolarization of the membrane due to a stimulus is a regenerative mechanism meaning that, once sodium gates begin to open, even more sodium gates will be activated leading to a larger inflow of sodium ions and more depolarization until it is terminated when sodium gates close. This is an example of A) inhibitory graded potentials. B) negative feedback. C) electrotonic conduction. D) positive feedback. E) excitatory graded potentials.
D) positive feedback.
Movement of what ion is responsible for event "D" in Figure 7.1? 84) A) sodium (Na+) B) chloride (Cl-) C) calcium (Ca++) D) potassium (K+) E) phosphate (PO4-)
D) potassium (K+)
Which of the following best describes the function of the myelin sheath? A) increase leakage of ions across the membrane B) decrease ion permeability in the nodes of Ranvier C) decrease axonal conduction velocity D) reduce a membrane's ion permeability E) increase a membrane's ion permeability
D) reduce a membrane's ion permeability
What percentage of people with diabetes develop peripheral neuropathy? A) 5 percent B) 10 percent C) 50 percent D) 20 percent E) 30 percent
E) 30 percent
Which statement best describes the event indicated by the letter "C" in Figure 7.1 and how that event is initiated? A) It is a suprathreshold graded potential resulting from the opening and closing of sodium and potassium channels. B) It is a suprathreshold depolarization representing an action potential. C) It is an excitatory potential that causes the relative refractory period. D) It is a hyperpolarization of the membrane due to the outward movement of potassium ions. E) It is a subthreshold graded potential resulting from the opening of sodium channels, closure of potassium channels, or opening of ion channels for sodium and potassium.
E) It is a subthreshold graded potential resulting from the opening of sodium channels, closure of potassium channels, or opening of ion channels for sodium and potassium.
The ________ maintains the resting membrane potential. A) Na+/H+ antiporter B) equilibrium potential C) Na+/Ca2+ exchanger D) action potential E) Na+/K+ pump
E) Na+/K+ pump
Which of the following is an example of spatial summation? A) A neuron sends out information through collaterals to several target cells. B) Two action potentials occur at the same time and sum. C) Two rapid stimuli from the same source produce graded potentials on the neurons that sum. D) An action potential occurs at the same time as a graded potential, and they sum. E) Two stimuli from two sources produce graded potentials on the same neuron at the same time such that the two potentials sum.
E) Two stimuli from two sources produce graded potentials on the same neuron at the same time such that the two potentials sum.
In the peripheral nervous system, ________ neurons carry sensory and visceral information to the central nervous system, and ________ neurons leave the central nervous system and innervate organs, which are usually muscles or glands . A) sensory : somatic B) sympathetic : parasympathetic C) somatic : sensory D) efferent : afferent E) afferent : efferent
E) afferent : efferent
An action potential originates at the ________ and travels along the axon until it reaches the ________. A) dendrite : axon hillock B) axon hillock : dendrite C) dendrite : axon terminal D) axon terminal : axon hillock E) axon hillock : axon terminal
E) axon hillock : axon terminal
The repolarization phase of the action potential in a neuron is driven by the A) closure of potassium channels. B) opening of calcium channels. C) opening of sodium channels. D) opening of sodium channels and closure of potassium channels. E) closure of sodium channels and opening of potassium channels.
E) closure of sodium channels and opening of potassium channels.
A change in a cell's membrane potential, such that the inside of the cell becomes more positive, is referred to as a ________ whereas if it becomes more negative it is referred to as ________. A) polarization : depolarization B) hypopolarization : repolarization C) hyperpolarization : depolarization D) repolarization : resting membrane potential E) depolarization : hyperpolarization
E) depolarization : hyperpolarization
What nervous system is found in the intestinal tract? A) somatic nervous system B) central nervous system C) afferent nervous system D) efferent nervous system E) enteric nervous system
E) enteric nervous system
A(n) ________ is a subthreshold change in membrane potential within the cell body that decays as it travels away from its point of origin. A) hyperpolarization B) depolarization C) action potential D) polarization E) graded potential
E) graded potential
Which of the following potentials can reach or exceed the sodium equilibrium potential? A) graded potentials B) threshold potentials C) action potentials D) both graded potentials and action potentials E) neither graded potentials nor action potentials
E) neither graded potentials nor action potentials
Which of the following are common symptoms of peripheral neuropathy? A) dizziness, diarrhea, indigestion and impotence B) numbness of the tongue, jaw, and ears C) increased heart rate, excessive sweating, and red skin D) confusion, excessive thirst, dehydration, and frequent urination E) numbness, tingling sensation, or pain in the hands and feet
E) numbness, tingling sensation, or pain in the hands and feet
The fact that a cell has an electrical potential difference across its membrane makes that cell A) polar. B) depolarized. C) hyperpolarized. D) repolarized. E) polarized.
E) polarized.
The repolarization phase of action potentials in neurons is due primarily to A) increased activity of the Na+/K+ pump. B) sodium flow out of the cell. C) sodium flow into the cell. D) potassium flow into the cell. E) potassium flow out of the cell.
E) potassium flow out of the cell.
Describe the structure of a neuron and the important consequences of that arrangement
Neurons are composed of a cell body (or soma), where a majority of their organelles are located, and several projections from the cell body that are classified as dendrites and axons, based upon their function. The cell body itself is incapable of generating an action potential. This inability derives from the absence of voltage-gated sodium channels in the membrane of the cell body that are required for an action potential to be generated. Projecting from the cell body are a number of dendrites that receive synaptic input from axon terminals of other neurons. Another projection from the cell body is a single axon that transmits information from axon hillock to axon terminal in the form of action potentials. Thus, dendrites receive information from other cells while axons transmit that information. At axodendritic synapses, neurotransmitters are released from the axon terminals onto the dendrites to generate a change in membrane potential. The graded change in membrane potential at the dendrite decays as it travels across the cell body from its source. This allows for the integration of numerous synaptic inputs onto one cell body. The final integration occurs at the axon hillock. Within this structure, the voltage-gated sodium channels required for an action potential are present in their greatest concentration. Thus when the axon hillock is depolarized above threshold, an action potential will be generated. Once initiated, the action potential will move along the axon in one direction. That action potential will travel along the axon until it reaches the axon terminal, where a synapse is formed for the transfer of the information on to the next neuron or effector organ.
Amyotrophic lateral sclerosis (ALS), often referred to as "Lou Gehrig's Disease," is a progressive neurodegenerative disease that affects the efferent division, particularly the motor neurons, of the nervous system. People with ALS have normal bodily functions and their ability to think, form memories, and to detect sensations is all normal. However, the progressive nature of this disease can lead to total paralysis. Based on your knowledge of the different divisions of the nervous system and the functioning of neurons, explain the symptoms of ALS.
The efferent division of the nervous system can be subdivided into two main branches: the somatic and autonomic nervous systems. The somatic system consists of motor neurons which regulate skeletal muscle contractions. The autonomic nervous system consists of neurons that regulate the function of internal organs and other structures such as sweat glands and blood vessels that are not under voluntary control. Thus, ALS patients will lose the ability to control their muscles and eventually become paralyzed while most of their involuntary functions remain normal since it is the somatic system which innervates skeletal muscle.
Describe the organization of the nervous system, including a description of the different branches.
The entire nervous system is organized into two main divisions: the central nervous system and the peripheral nervous system. The central nervous system (the brain and spinal cord) receives sensory input from the body, which it integrates to determine whether a response is warranted. Within the central nervous system, learning, memory, emotion, and other complex functions occur. The peripheral nervous system is divided into two main divisions: the afferent and efferent limbs. The afferent limb detects sensory (external) and visceral (internal) information and sends it to the central nervous system. The efferent limb sends information to the effector organ from the central nervous system to initiate a response. The efferent limb can be divided into two branches: the autonomic nervous system and the somatic nervous system. The somatic nervous system transmits information to skeletal muscle, whereas the autonomic nervous system sends information either through the sympathetic or parasympathetic nervous systems, which tend to be counterregulatory (produce the opposite effects). The autonomic nervous system is not under voluntary control. Finally, there is the enteric nervous system in the gastrointestinal tract, involved in digestion, which acts independently of the central and peripheral nervous systems.
Several ions are responsible for the resting membrane potential. Describe the forces that determine resting membrane potential.
The first determinant of the resting membrane potential is the distribution of ions across the membrane. There is a higher concentration of sodium outside the cell, whereas potassium is greater inside the cell. This means that potassium will diffuse out of the cell as sodium diffuses into the cell. This ability of an ion to diffuse across the membrane is determined by the ion channels present on the cell membrane; the more ion channels open, the more a particular ion will be able to move across the membrane. The more an ion moves across the membrane, the greater its effect on membrane potential. Thus, along with the concentration difference, membrane potential is determined by the population of ion channels that remain open under resting conditions. Under resting conditions, most cells have more potassium leak channels open than sodium leak channels. This means that more potassium ions are moving out of the cell than sodium ions are moving in. Thus, the negative charge created by potassium moving out will outweigh the positive charge created by sodium moving in, leaving membrane potential relatively negative. If a channel for a specific ion is open, then membrane potential will tend to move toward the equilibrium potential for that ion (i.e., as those ions are able to move across the membrane, they create an electrical force that tends to pull them in the opposite direction, approaching equilibrium). The channel that is primarily open at rest, potassium, ensures that resting membrane potential is closer to the equilibrium potential for potassium than sodium. However, neither ion ever comes to complete equilibrium. There are several other ions (chloride and calcium) that can play an important role in the resting membrane potential. Their role will vary by cell type.
Describe the types of ion channels that are found in a neuron and how those channels are gated.
There are many types of ion channels that can be characterized by their specificity for an ion as well as their mechanism of gating. This gating refers to the opening and closing of ion channels, either allowing ions through or restricting their access, respectively. There is a population of ion channels that are specific for particular ions like sodium, potassium, calcium, and chloride. Other ion channels are less specific, allowing a number of different ions to traverse the channel. With respect to gating, channels can be leak channels that are open under resting conditions and, on neurons, these channels are most permeable to potassium. Ion channels can also be gated by ligands. These ligand-gated channels act as receptors such that when a ligand (including neurotransmitters) binds to that receptor, ion channels are stimulated to open or close with a greater frequency. These channels tend to be located within the dendrites and cell body of a neuron. Another type of ion channel is the voltage-gated channel, whose gating is determined by membrane potential. There are voltage-gated sodium and potassium channels on the axon that are responsible for the initiation, propagation, and repolarization of an action potential. A voltage-gated calcium channel is present within the axon terminal and is responsible for regulating the release of neurotransmitter.
Once an action potential is generated, there is a delay before another action potential can be generated. Name and describe the basis for the two refractory periods.
he refractory period is broken into two components: the absolute and relative refractory periods. The absolute refractory period is, as the name suggests, a duration of time following the initiation of an action potential in which a second action potential cannot be generated. The absolute refractory period spans all of the depolarization phase of the action potential, as well as most of the repolarization phase (1-2 msec). During this period, a second action potential cannot be generated regardless of stimulus activity. The cause is two-fold: 1) once rapid depolarization is initiated, it must continue to its conclusion, and 2) at the beginning of the repolarization phase, the inactivation gates of the sodium channel are closed and cannot be opened by a second stimulus. Those channels can be found in three different states: 1) closed but capable of opening, 2) open, and 3) closed yet incapable of opening. After the activation gate has opened (the inactivation gate is already open under resting conditions), the inactivation gate closes. The channel cannot be opened again until the inactivation gate has opened. The remainder of the repolarization and after-hyperpolarization phases is part of the relative refractory period. A second stimulus can initiate an action potential, but that stimulus must be suprathreshold. The relative refractory period is reflective of two changes: 1) increased potassium permeability of the membrane, and 2) opening of the inactivation gate in a portion of the sodium channels. From the beginning to the end of the relative refractory period, the amplitude of the suprathreshold stimulus required to initiate an action potential is reduced as potassium permeability declines and more inactivation gates open. Early in the relative refractory period, all of the sodium channels have not returned to the resting state. At the same time, the cell must overcome a greater potassium current created by the number of open potassium channels that are repolarizing the cell. Thus, a greater depolarization is required.
