A&P chapter 11: Nervous Tissue
Which area of the graph occurs when there is a sudden inrush of sodium ions?
2: depolarization
The myelin sheath that covers many CNS axons is formed by A) astrocytes. B) satellite cells. C) oligodendrocytes. D) microglia. E) ependymal cells.
C) oligodendrocytes.
After acetylcholinesterase acts, the synaptic knob A) reabsorbs the acetylcholine. B) reabsorbs the acetate. C) reabsorbs the choline. D) degrades the acetate. E) degrades the choline.
C) reabsorbs the choline.
The period during which an excitable membrane can respond again, but only if the stimulus is greater than the threshold stimulus, is the A) refractory period. B) depolarization. C) relative refractory period. D) repolarization. E) absolute refractory period.
C) relative refractory period.
Which of the following is important in emotional states? A) glutamate B) gamma aminobutyric acid C) serotonin D) noradrenalin E) glycine
C) serotonin
The minimum stimulus required to trigger an action potential is known as the A) graded potential. B) resting potential. C) threshold. D) refractory period. E) membrane potential.
C) threshold.
Regions of the CNS with an abundance of myelinated axons constitute the ________ matter. A) white B) grey C) clear D) dark E) yellow
A) white
The buildup of depolarization when EPSPs arrive at several places on the neuron is called ________ summation. A) threshold B) spatial C) temporal D) chemical E) electrical
B) spatial
When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what occurs? A) spatial summation B) temporal summation C) inhibition of the impulse D) hyperpolarization E) decrease in speed of impulse transmission
B) temporal summation
Neurons in which dendritic and axonal processes are continuous and the soma lies off to one side are called A) anaxonic. B) unipolar. C) bipolar. D) tripolar. E) multipolar.
B) unipolar.
________ provide information about the external environment. A) Proprioceptors B) Interoceptors C) Exteroceptors D) Somatic sensory receptors E) Interneurons
C) Exteroceptors
The buildup of depolarization when EPSPs arrive in rapid succession is called ________ summation. A) threshold B) spatial C) temporal D) chemical E) electrical
C) temporal
In a(n) ________ neuron, the dendrites and axon are continuous or fused. A) multipolar B) anaxonic C) unipolar D) bipolar E) pseudopolar
C) unipolar
Neurotransmitter for release is stored in synaptic A) telodendria. B) knobs. C) vesicles. D) mitochondria. E) neurosomes.
C) vesicles.
Identify the three types of gated ion channels, and state the conditions under which each operates.
Chemically gated ion channels operate when they bind specific chemicals (such as ACh); voltage-gated ion channels operate in response to changes in the membrane potential; and mechanically gated ion channels operate in response to physical distortion of the membrane surface.
Define continuous propagation and salutatory propagation.
Continuous propagation is the propagation of an action potential along an unmyelinated axon, where the action potential affects every portion of the membrane surface. Saltatory propagation is the relatively rapid propagation of an action potential between successive nodes of a myelinated axon.
The Na-K ion exchange pump actively transports A) 1 intracellular sodium ion for 2 extracellular potassium ions. B) 2 intracellular sodium ions for 1 extracellular potassium ion. C) 3 intracellular sodium ions for 1 extracellular potassium ion. D) 3 intracellular sodium ions for 2 extracellular potassium ions. E) 3 extracellular sodium ions for 2 intracellular potassium ions.
D) 3 intracellular sodium ions for 2 extracellular potassium ions.
Describe a synapse. (Module 11.2B) A) A synapse is the connection between the dendrites and the cell body. B) A synapse is where the axon joins the cell body. C) A synapse is where multiple dendrites join an axon. D) A synapse is where one neuron communicates with another cell. E) A synapse is where the neuronal organelles are housed.
D) A synapse is where one neuron communicates with another cell.
Define gated ion channels. (Module 11.8A) A) Gated ion channels are pumps in the plasma membrane for specific ions. B) Gated ion channels allow water to pass through the plasma membrane for osmotic balance. C) Gated ion channels allow all ions to enter a cell but do not allow any ions to exit a cell. D) Gated ion channels do not allow any ions to enter a cell but allow all ions to exit a cell. E) Gated ion channels are channels that open or close in response to specific stimuli.
E) Gated ion channels are channels that open or close in response to specific stimuli.
________ are the most numerous type of neuron in the CNS. A) Sensory neurons B) Motor neurons C) Unipolar neurons D) Bipolar neurons E) Interneurons
E) Interneurons
Which glial cell protects the CNS from chemicals and hormones circulating in the blood? (Module 11.4C) A) ependymal cells B) satellite cells C) microglia D) astrocytes E) oligodendrocytes
D) astrocytes
Which part(s) of the neuron can conduct an action potential? A) dendrites B) dendrites and cell body C) cell body and axon D) axon and telodendria E) dendrites and telodendria
D) axon and telodendria
The axon is connected to the cell body at the A) telodendria. B) synaptic knobs. C) collateral branches. D) axon hillock. E) synapse.
D) axon hillock.
Name the structural components of a typical neuron. (Module 11.2A) A) cell body, cilia, and a basement membrane B) neurofilaments, neurofibrils, and axolemma C) neurilemma, neurofibrils, and dendrites D) cell body, axon, and dendrites E) cell body, flagellum, and synaptic cleft
D) cell body, axon, and dendrites
The site of intercellular communication between neurons is the A) telodendria. B) synaptic knob. C) collateral branch. D) hillock. E) synapse.
E) synapse.
The effect that a neurotransmitter has on the postsynaptic membrane does not depend on the A) frequency of neurotransmitter release. B) nature of the neurotransmitter. C) characteristics of the receptors. D) quantity of neurotransmitters released. E) the strength of the action potential.
E) the strength of the action potential.
Which type of membrane channels are found in axons? A) voltage-gated Na+ channels B) voltage-gated K+ channels C) chemically gated Na+ and K+ channels D) voltage-gated Ca2+ channels E) voltage-gated Na+ and K+ channels
E) voltage-gated Na+ and K+ channels
In the process of continuous propagation, all of the following are true except A) the action potential is triggered by graded depolarization of the initial segment. B) at threshold, sodium channels begin to open rapidly. C) local currents depolarize the region just adjacent to the active zone. D) depolarization of the axonal membrane only occurs at nodes. E) each step takes about one millisecond.
D) depolarization of the axonal membrane only occurs at nodes.
Which of the following is not a function of the nervous system? A) sense the internal and external environments B) integrate sensory information C) coordinate voluntary and involuntary activities D) direct long-term functions, such as growth E) control peripheral effectors
D) direct long-term functions, such as growth
EPSPs (excitatory postsynaptic potentials) occur when A) more potassium ions than usual leak out of a cell. B) more calcium ions than usual leak out of a cell. C) chloride ions enter a cell. D) extra sodium ions enter a cell. E) hyperpolarizations occur.
D) extra sodium ions enter a cell.
After a stroke, what type of glial cell accumulates within the affected brain region? A) Schwann cells B) satellite cells C) oligodendrocytes D) microglia E) ependymal cells
D) microglia
Small, wandering cells that engulf cell debris and pathogens in the CNS are called A) astrocytes. B) satellite cells. C) oligodendrocytes. D) microglia. E) ependymal cells.
D) microglia.
Which of the following does not influence the time necessary for a nerve impulse to be transmitted? A) length of the axon B) presence or absence of a myelin sheath C) diameter of the axon D) presence or absence of nodes E) whether or not the impulse begins in the CNS
E) whether or not the impulse begins in the CNS
The tiny gaps between adjacent Schwann cells are called A) gap junctions. B) synapses. C) myelinated. D) nodes. E) internodes.
D) nodes.
Which of the following is not associated with the cytoskeleton of the perikaryon? A) neurofilaments B) axon C) dendrite D) nucleus E) neurofibrils
D) nucleus
Active neurons need ATP to support all of the following except the A) movement of materials to the soma by axoplasmic transport. B) synthesis of neurotransmitter molecules. C) movement of materials from the soma by axoplasmic transport. D) opening of voltage-gated channels. E) recovery from action potentials.
D) opening of voltage-gated channels.
Which of the following is not a recognized structural classification for neurons? A) anaxonic B) bipolar C) multipolar D) pseudopolar E) unipolar
D) pseudopolar
The ________ nervous system controls the skeletal muscles. A) sympathetic B) parasympathetic C) afferent D) somatic E) autonomic
D) somatic
List the events involved in the generation of an action potential.
The events involved in the generation of an action potential are (1) depolarization to threshold, (2) activation of voltage-gated sodium ion channels and rapid depolarization, (3) inactivation of voltage-gated sodium ion channels and activation of voltage-gated potassium ion channels, and (4) closing of voltage-gated potassium ion
Which point of the graph shows when potassium ion outflow exceeds sodium ion inflow?
3: re-polarization
Which area of the graph shows the membrane potential if potassium ions were freely permeability to the plasma membrane?
4: hyper polarization
When is the neuron in the relative refractory period?
4: re-polarization
The equilibrium potential for potassium ions occurs at approximately A) -90 mV. B) -70 mV. C) +66 mV. D) 0 mV. E) -55 mV.
A) -90 mV.
Define action potential. (Module 11.10A) A) An action potential is the propagated change in membrane potential of an excitable cell. B) An action potential is the membrane potential of an unstimulated cell. C) An action potential is a temporary, localized change in the potential of a cell. D) An action potential is the minimum ability of a cell to generate electrical impulses. E) An action potential is the resting speed a cell can propagate electrical impulses.
A) An action potential is the propagated change in membrane potential of an excitable cell.
Describe depolarization, repolarization, and hyperpolarization. A) Depolarization is a shift in membrane potential toward a more positive value; repolarization is the return of the membrane potential to resting; and hyperpolarization is a shift in membrane potential toward a more negative value. B) Depolarization is a shift in membrane potential toward a more negative value; repolarization is the return of the membrane potential to resting; and hyperpolarization is a shift in membrane potential toward a more positive value. C) Depolarization is the return of the membrane potential to resting; repolarization is a shift of the membrane potential toward a more positive value; and hyperpolarization is a shift in membrane potential toward a more negative value. D) Depolarization is the return of the membrane potential to resting; repolarization is a shift of the membrane potential toward a more negative value; and hyperpolarization is a shift in membrane potential toward a more positive value. E) Depolarization is a shift in membrane potential toward a more negative value; repolarization is a shift of the membrane potential toward a more negative value; and hyperpolarization is the return of the membrane potential to resting.
A) Depolarization is a shift in membrane potential toward a more positive value; repolarization is the return of the membrane potential to resting; and hyperpolarization is a shift in membrane potential toward a more negative value.
How would the absolute refractory period be affected if voltage-regulated sodium channels failed to inactivate? A) It would last indefinitely. B) It would be much briefer. C) It would be basically unaffected.
A) It would last indefinitely.
________ neurons are the most common class in the CNS. A) Multipolar B) Anaxonic C) Unipolar D) Bipolar E) Pseudopolar
A) Multipolar
Classify neurons based on their function. (Module 11.3B) A) Neurons are classified functionally as sensory, interneurons, or motor neurons. B) Neurons are classified functionally as central, peripheral, or enteric neurons. C) Neurons are classified functionally as anaxonic, bipolar, unipolar, or multipolar. D) Neurons are classified functionally as anaxonic or axonic. E) Neurons are classified functionally as sympathetic or parasympathetic neurons.
A) Neurons are classified functionally as sensory, interneurons, or motor neurons.
_______ monitor the position of skeletal muscles and joints. A) Proprioceptors B) Interoceptors C) Exteroceptors D) Somatic sensory receptors E) Special sensory receptors
A) Proprioceptors
Identify the neuroglia of the PNS. (Module 11.5A) A) Schwann cells and satellite cells B) ependymal cells, microglia, astrocytes, oligodendrocytes C) Kuppfer cells, dendritic cells, astrocytes D) mast cells, microglia, satellite cells E) dendritic cells, axonal cells, oligodendrocytes
A) Schwann cells and satellite cells
Describe synaptic fatigue. (Module 11.12C) A) Synaptic fatigue occurs in an axon terminal when neurotransmitters are released into the synaptic cleft faster than they can be reabsorbed or recycled. B) Synaptic fatigue occurs when not enough ATP is present to cause the release of neurotransmitters out of the axon terminal. C) Synaptic fatigue occurs during oxygen deficiency and the synapse fails to bind neurotransmitters. D) Synaptic fatigue occurs during starvation and not enough neurotransmitters are synthesized for normal synaptic function. E) Synaptic fatigue occurs when the axon terminal can no longer receive action potentials from the axon hillock due to overstimulation.
A) Synaptic fatigue occurs in an axon terminal when neurotransmitters are released into the synaptic cleft faster than they can be reabsorbed or recycled.
Which of the following statements about the action potential is false? A) The rapid depolarization phase is caused by the entry of potassium ions. B) During the repolarization phase, sodium channels close and potassium channels open. C) During the depolarization phase, membrane potential becomes positive. D) In the hyperpolarization phase, membrane potential approaches the potassium equilibrium potential. E) The rapid depolarization phase is caused by the entry of sodium ions.
A) The rapid depolarization phase is caused by the entry of potassium ions.
What happens at the sodium-potassium exchange pump? (Module 11.7B) A) The sodium-potassium exchange pump maintains the resting membrane potential of the cell by ejecting 3 sodium ions for every 2 potassium ions entering the cell. B) The sodium-potassium exchange pump maintains the resting membrane potential of the cell by ejecting 2 sodium ions for every 3 potassium ions entering the cell. C) The sodium-potassium exchange pump maintains the resting membrane potential of the cell by ejecting 3 potassium ions for every 2 sodium ions entering the cell. D) The sodium-potassium exchange pump maintains the resting membrane potential of the cell by ejecting 2 potassium ions for every 3 sodium ions entering the cell. E) The sodium-potassium exchange pump maintains the resting membrane potential of the cell by ejecting 1 sodium ions for every 6 potassium ions entering the cell.
A) The sodium-potassium exchange pump maintains the resting membrane potential of the cell by ejecting 3 sodium ions for every 2 potassium ions entering the cell.
Neurons that are rare, small, and lack features that distinguish dendrites from axons are called A) anaxonic. B) unipolar. C) bipolar. D) tripolar. E) multipolar.
A) anaxonic.
All of the following are true of IPSPs (inhibitory postsynaptic potentials) except A) are graded depolarizations. B) are graded hyperpolarizations. C) increase membrane permeability to chloride ions. D) increase the efflux of potassium ions. E) increase the efflux of calcium ions.
A) are graded depolarizations.
The glial cells in the central nervous system that form scar tissue after central nervous system injury are the A) astrocytes. B) satellite cells. C) oligodendrocytes. D) microglia. E) ependymal cells.
A) astrocytes.
The largest and most numerous neuroglia in the CNS that absorb and recycle neurotransmitters are the A) astrocytes. B) ependymocytes. C) microglia. D) oligodendrocytes. E) tanycytes.
A) astrocytes.
Which type of synapse is most common in the nervous system? A) chemical B) electrical C) mechanical D) processing E) radiative
A) chemical
A shift of the resting transmembrane potential toward 0 mV is called A) depolarization. B) repolarization. C) hyperpolarization. D) non-polarization. E) hypopolarization.
A) depolarization.
Raising the potassium ion concentration in the extracellular fluid surrounding a nerve cell will have which effect? A) depolarize the membrane potential B) hyperpolarize the membrane potential C) increase the magnitude of the potassium equilibrium potential D) repolarize the membrane potential E) increase the magnitude of the sodium equilibrium potential
A) depolarize the membrane potential
In a(n) ________ synapse, current flows directly between cells. A) electrical B) chemical C) electrochemical D) ionic E) charged
A) electrical
Integral membrane proteins that connect electrical synapses are called A) gap junctions. B) receptors. C) desmosomes. D) sodium channels. E) leak channels.
A) gap junctions.
Which of the following is the most important excitatory neurotransmitter in the brain? A) glutamate B) gamma aminobutyric acid C) serotonin D) noradrenaline E) glycine
A) glutamate
The greater the degree of sustained depolarization at the axon hillock, the ________ (higher or lower) the frequency of action potentials generated. (Module 11.14C) A) higher B) lower
A) higher
If the sodium-potassium pumps in the plasma membrane fail to function, all of the following occur except that the A) intracellular concentration of potassium ions will increase. B) neuron will slowly depolarize. C) membrane will slowly lose its capacity to generate action potentials. D) inside of the membrane will have a resting potential that is more positive than normal. E) intracellular concentration of sodium ions will increase.
A) intracellular concentration of potassium ions will increase.
The resting membrane potential exists mainly due to passive ________ channels. A) leak B) active C) chemically gated D) voltage-gated E) mechanically-gated
A) leak
The same ________ can have different effects depending on the properties of the ________. A) neurotransmitter; receptor B) receptor; neurotransmitter C) substrate; receptor D) hormone; neurotransmitter E) propagation; neurotransmitter
A) neurotransmitter; receptor
Which division of the PNS brings information to the CNS? (Module 11.1B) A) sensory B) motor C) efferent D) parasympathetic E) enteric
A) sensory
Are unipolar neurons in a tissue sample of the PNS more likely to have a sensory or a motor function? (Module 11.3C) A) sensory function B) motor function
A) sensory function
Which of the following activities or sensations is not monitored by interoceptors? A) sight B) joint movement C) activities of the digestive system D) cardiovascular activities E) urinary activities
A) sight
When cholinergic receptors are stimulated with acetylcholine, A) sodium ions enter the postsynaptic neuron. B) sodium ions leave the postsynaptic neuron. C) chloride ions enter the postsynaptic neuron. D) chloride ions leave the postsynaptic neuron. E) potassium ions leave the postsynaptic neuron.
A) sodium ions enter the postsynaptic neuron.
Summation that results from the cumulative effect of multiple synapses at multiple places on the neuron is designated A) spatial summation. B) temporal summation. C) inhibition of the impulse. D) hyperpolarization. E) impulse transmission.
A) spatial summation.
If the chemically gated sodium channels in the postsynaptic membrane were completely blocked, A) synaptic transmission would fail. B) release of neurotransmitter would stop. C) smaller action potentials would result. D) repolarization of the cell would stop. E) more action potentials would occur.
A) synaptic transmission would fail.
Axons terminate in a series of fine extensions known as A) telodendria. B) knobs. C) collateral branches. D) dendrites. E) synapses.
A) telodendria.
Compare the effects of the neurotransmitters acetylcholine and serotonin on ion channels.
Acetylcholine has a direct effect on ion channels through its binding to chemically gated ion channels. The effect of the neurotransmitter serotonin has an indirect effect on ion channels. It acts as a first messenger by binding to membrane receptors coupled with G proteins. The activated G protein produces or releases a second messenger that then affects ion channels, altering conditions or activities of the postsynaptic cell.
The following are the steps involved in transmission at a cholinergic synapse. 1. Chemically gated sodium channels on the postsynaptic membrane are activated. 2. Calcium ions enter the synaptic knob. 3. Acetylcholinesterase hydrolyzes acetylcholine. 4. An action potential depolarizes the synaptic knob at the presynaptic membrane. 5. The synaptic knob reabsorbs choline. 6. Acetylcholine is released from storage vesicles by exocytosis. 7. Acetylcholine binds to receptors on the postsynaptic membrane. 8. Calcium ions are removed from the cytoplasm of the synaptic knob. What is the proper sequence of these events? A) 4, 2, 6, 7, 8, 5, 3, 1 B) 4, 2, 6, 7, 1, 8, 3, 5 C) 2,4,6,7,1,8,3,5 D) 2, 5, 4, 6, 7, 1, 8, 3 E) 6, 4, 2, 7, 1, 8, 3, 5
B) 4, 2, 6, 7, 1, 8, 3, 5
The following are the main steps in the generation of an action potential. 1. Sodium channels are inactivated. 2. Voltage-gated potassium channels open and potassium moves out of the cell, initiating repolarization. 3. Sodium channels regain their normal properties. 4. A graded depolarization brings an area of an excitable membrane to threshold. 5. A temporary hyperpolarization occurs. 6. Sodium channel activation occurs. 7. Sodium ions enter the cell and depolarization occurs. ***What is the proper sequence of these events?** A) 4, 6, 7, 3, 2, 5, 1 B) 4, 6, 7, 1, 2, 3, 5 C) 6,7,4,1,2,3,5 D) 2, 4, 6, 7, 1, 3, 5 E) 4, 2, 5, 6, 7, 3, 1
B) 4, 6, 7, 1, 2, 3, 5
Describe the all-or-none principle. (Module 11.10B) A) All stimuli will generate an action potential or none will. B) All stimuli that bring the membrane to threshold will generate identical action potentials. C) Stimuli that bring the membrane to threshold will generate a larger or smaller action potential depending on the size of the stimuli. D) Stimuli that bring the membrane to threshold will generate a longer or shorter action potential depending on the timing of the stimuli. E) Stimuli that do not bring the membrane to threshold can still generate an action potential if the stimuli are strong enough.
B) All stimuli that bring the membrane to threshold will generate identical action potentials.
________ neurons are small and have no anatomical features that distinguish dendrites from axons. A) Multipolar B) Anaxonic C) Unipolar D) Bipolar E) Pseudopolar
B) Anaxonic
Which of the following interactions between electrical and chemical gradients does not lead to the establishment of a neuronʹs resting potential? A) Chemical and electrical forces both favor sodium ions entering the cell. B) Electrical forces push sodium ions out of the cell. C) Chemical forces tend to drive potassium ions out of the cell. D) Potassium ions are attracted to the negative charges inside the cell. E) Potassium ions are repulsed by positive charges outside the cell.
B) Electrical forces push sodium ions out of the cell.
_______ monitor the digestive, respiratory, cardiovascular, urinary, and reproductive systems. A) Proprioceptors B) Interoceptors C) Exteroceptors D) Somatic sensory receptors E) Special sense receptors
B) Interoceptors
________ monitor the internal environment. A) Endoceptors B) Interoceptors C) Exteroceptors D) Special sensory receptors E) Sensory ganglia
B) Interoceptors
If a single EPSP depolarizes the initial segment from a resting membrane potential of -70 mV to -65 mV, and threshold is at -60 mV, will an action potential be generated? Explain your answer. (Module 11.13C) A) Yes, because depolarization reached threshold. B) No, because depolarization did not reach threshold. C) Yes, because depolarization did not reach threshold. D) No, because depolarization reached threshold. E) Yes, because all stimuli to a resting membrane will cause an action potential.
B) No, because depolarization did not reach threshold.
Define resting membrane potential. (Module 11.7A) A) Resting membrane potential is the change in charge across the inner and outer membrane of a cell. B) Resting membrane potential is the membrane potential of an unstimulated cell. C) Resting membrane potential is a temporary, localized change in the potential of a cell. D) Resting membrane potential is the minimum ability of a cell to generate electrical impulses. E) Resting membrane potential is the resting speed a cell can propagate electrical impulses.
B) Resting membrane potential is the membrane potential of an unstimulated cell.
ompare the central and peripheral nervous system. (Module 11.1A) A) The central nervous system consists of the brain and it integrates, processes, and coordinates sensory data and motor commands. The peripheral nervous system consists of the spinal cord, and sensory and motor divisions. B) The central nervous system consists of the brain and spinal cord and it integrates, processes, and coordinates sensory data and motor commands. The peripheral nervous system consists of all the nervous tissue outside the central and enteric nervous systems. C) The central nervous system consists of the spinal cord and all the nervous tissue outside the enteric nervous system. The peripheral nervous system consists of the brain and it integrates, processes, and coordinates sensory data and motor commands. D) The central nervous system consists of all the nervous tissue outside the enteric nervous system. The peripheral nervous system consists of the brain and spinal cord and it integrates, processes, and coordinates sensory data and motor commands. E) The central nervous system consists of the sensory and motor division in the axial region of the body. The peripheral nervous system consists of the sensory and motor division in the appendicular region of the body.
B) The central nervous system consists of the brain and spinal cord and it integrates, processes, and coordinates sensory data and motor commands. The peripheral nervous system consists of all the nervous tissue outside the central and enteric nervous systems.
If the potassium permeability of a resting neuron increases above the resting permeability, what effect will this have on the transmembrane potential? A) The inside of the membrane will become more positive. B) The inside of the membrane will become more negative. C) There will be almost no effect on transmembrane potential. D) The membrane will become depolarized. E) The outside of the membrane will become more positive.
B) The inside of the membrane will become more negative.
The most abundant class of neuron in the central nervous system is A) anaxonic. B) bipolar. C) multipolar. D) pseudopolar. E) unipolar.
C) multipolar.
What effect would decreasing the concentration of extracellular potassium ions have on the resting membrane potential of a neuron? (Module 11.7C) A) The resting membrane potential would become more positive because more potassium ions would leave the cell through potassium leak channels. B) The resting membrane potential would become more negative because more potassium ions would leave the cell through potassium leak channels. C) The resting membrane potential would become more positive because more potassium ions would enter the cell through potassium leak channels. D) The resting membrane potential would become more negative because more potassium ions would enter the cell through potassium leak channels. E) The resting membrane potential would not change because it is controlled by the movement of sodium ions not potassium ions.
B) The resting membrane potential would become more negative because more potassium ions would leave the cell through potassium leak channels.
The period from when an action potential begins until another action potential could be initiated is known as the ________ period. A) depolarization B) absolute refractory C) relative refractory D) repolarization E) hyperpolarization
B) absolute refractory
The all-or-none principle states that A) all stimuli will produce identical action potentials. B) all stimuli great enough to bring the membrane to threshold will produce identical action potentials. C) the greater the magnitude of the stimuli, the greater the magnitude of the action potential. D) only sensory stimuli can activate action potentials. E) only motor stimuli can activate action potentials.
B) all stimuli great enough to bring the membrane to threshold will produce identical action potentials.
The ________ principle states that the size and speed of an action potential are independent of the stimulus strength. A) threshold B) all-or-none C) graded potential D) saltatory propagation E) summation
B) all-or-none
The ________ nervous system provides involuntary regulation of smooth muscle, cardiac muscle, and glandular activity. A) somatic B) autonomic C) sensory division of the peripheral D) automatic E) special sensory
B) autonomic
At a(n) ________ synapse, a neurotransmitter is released to stimulate the postsynaptic membrane. A) electrical B) chemical C) electrochemical D) ionic E) charged
B) chemical
Functions of astrocytes include all of the following except A) maintaining the blood-brain barrier. B) conducting action potentials. C) absorbing excess neurotransmitter. D) responding to neural tissue damage. E) forming a three-dimensional framework for the CNS.
B) conducting action potentials.
Name the neuroglia of the CNS. (Module 11.4A) A) Schwann cells and satellite cells B) ependymal cells, microglia, astrocytes, oligodendrocytes C) Kuppfer cells, dendritic cells, astrocytes D) mast cells, microglia, satellite cells E) dendritic cells, axonal cells, oligodendrocytes
B) ependymal cells, microglia, astrocytes, oligodendrocytes
Damage to ependymal cells would most likely affect the A) formation of myelin sheaths. B) formation of cerebrospinal fluid. C) formation of ganglia. D) repair of axons. E) transport of neurotransmitters within axons.
B) formation of cerebrospinal fluid.
Neuron cell bodies in the PNS are clustered together in masses called A) nerves. B) ganglia. C) the spinal cord. D) peripheral nerves. E) nuclei.
B) ganglia.
Regions of the CNS where neuron cell bodies dominate constitute the ________ matter. A) white B) grey C) clear D) dark E) yellow
B) grey
Which of the following is not a function of the neuroglia? A) support B) memory C) secretion of cerebrospinal fluid D) maintenance of blood-brain barrier E) phagocytosis
B) memory
The separation of plus and negative charges across the membrane creates a ________ difference, or voltage. A) kinetic B) potential C) concentration D) gradient E) graded
B) potential
Which of the following is a type of glial cell found in the peripheral nervous system? A) astrocytes B) satellite cells C) oligodendrocytes D) microglia E) ependymal cells
B) satellite cells
Glial cells that surround the neurons in ganglia are A) astrocytes. B) satellite cells. C) oligodendrocytes. D) microglia. E) ependymal cells.
B) satellite cells.
Many medications introduced into the bloodstream cannot directly affect the neurons of the CNS because A) oligodendrocytes form a continuous myelin sheath around the axons. B) the astrocytes isolate the CNS by forming a blood-brain barrier. C) the neurilemma is impermeable to most molecules. D) ependymal cells restrict the flow of interstitial fluid between the capillaries and the neurons. E) Schwann cells form a capsule around neurons.
B) the astrocytes isolate the CNS by forming a blood-brain barrier.
If the axon terminal of a motor neuron suddenly became permeable to calcium ions, A) the neuron will fire an action potential. B) the motor end plate will be depolarized. C) the motor end plate will be hyperpolarized. D) neurotransmitter release will be blocked. E) the neuron will become unable to stimulate the muscle cell.
B) the motor end plate will be depolarized.
Sensory neurons of the PNS are A) anaxonic. B) unipolar. C) bipolar. D) tripolar. E) multipolar.
B) unipolar.
A gated channel that responds to changes in transmembrane potential is called a(n) ________ channel. A) leak-gated B) voltage-gated C) chemically gated D) mechanically gated E) ATP
B) voltage-gated
Most CNS neurons lack centrioles. This observation explains A) why CNS neurons grow such long axons. B) why CNS neurons cannot divide. C) the ability of neurons to generate an action potential. D) the ability of neurons to communicate with each other. E) the ability of neurons to produce a resting potential.
B) why CNS neurons cannot divide.
________ channels open or close in response to binding specific molecules. A) Leak B) Activated C) Chemically gated D) Voltage-gated E) Mechanically-gated
C) Chemically gated
Define graded potential. (Module 11.9A) A) Graded potential is the change in charge across the inner and outer membrane of a cell. B) Graded potential is the membrane potential of an unstimulated cell. C) Graded potential is a temporary, localized change in the potential of a cell. D) Graded potential is the minimum ability of a cell to generate electrical impulses. E) Graded potential is the resting speed a cell can propagate electrical impulses.
C) Graded potential is a temporary, localized change in the potential of a cell.
Which of the following is not involved in creating the resting potential of a neuron? A) diffusion of potassium ions out of the cell B) diffusion of sodium ions into the cell C) Membrane permeability for sodium ions is greater than for potassium ions. D) Membrane permeability for potassium ions is greater than for sodium ions. E) The interior of the plasma membrane has an excess of negative charges.
C) Membrane permeability for sodium ions is greater than for potassium ions.
________ account for roughly half of the volume of the nervous system. A) Axons B) Dendrites C) Neuroglia D) Synapses E) Efferent fibers
C) Neuroglia
Classify neurons based on their structure. (Module 11.3A) A) Neurons are classified structurally as sensory, interneurons, or motor neurons. B) Neurons are classified structurally as central, peripheral, or enteric neurons. C) Neurons are classified structurally as anaxonic, bipolar, unipolar, or multipolar. D) Neurons are classified structurally as anaxonic or axonic. E) Neurons are classified structurally as sympathetic or parasympathetic neurons.
C) Neurons are classified structurally as anaxonic, bipolar, unipolar, or multipolar.
Compare presynaptic and postsynaptic cells. (Module 11.2C) A) Presynaptic cells are sensory neurons and postsynaptic cells are motor neurons. B) Presynaptic cells are motor neurons and presynaptic cells are sensory neurons. C) Presynaptic cells are usually neurons and postsynaptic cells can be a neuron or another type of cell, such as skeletal muscle fiber or a gland cell. D) Presynaptic cells can be a neuron or another type of cell, such as a skeletal muscle fiber or a gland cell and postsynaptic cells are usually neurons. E) Presynaptic cells are usually found in the peripheral nervous system and postsynaptic cells are usually found in the central nervous system.
C) Presynaptic cells are usually neurons and postsynaptic cells can be a neuron or another type of cell, such as skeletal muscle fiber or a gland cell.
What determines the frequency of action potential generation? (Module 11.14B) A) The size of the synaptic cleft determines the frequency of action potentials. B) The distance between the presynaptic cell and postsynaptic cell determines the frequency of action potentials. C) The degree of sustained depolarization at the axon hillock determines the frequency of action potentials. D) The number of postsynaptic cells that a presynaptic cell is communicating with determines the frequency of action potentials. E) The length of the presynaptic cell axon determines the frequency of action potentials.
C) The degree of sustained depolarization at the axon hillock determines the frequency of action potentials.
What factors account for the local currents associated with graded potentials? (Module 11.9C) A) The movement of negative charges parallel to the inner surface of the cell. B) The movement of negative charges parallel to the outer surface of the cell. C) The movement of sodium ions parallel to the inner and outer surfaces of the cell. D) The movement of extracellular fluid parallel to the outer surface of the cell. E) The movement of intracellular fluid parallel to the inner surface of the cell.
C) The movement of sodium ions parallel to the inner and outer surfaces of the cell.
What is the relationship between myelin and the propagation speed of action potentials? (Module 11.11B) A) The presence of myelin slows the propagation speed of action potentials. B) The presence of myelin speeds up the graded depolarization but does not affect the propagation speed of action potentials. C) The presence of myelin increases the propagation speed of action potentials. D) The presence of myelin does not affect the speed of action potentials. E) The presence of myelin blocks the propagation of action potentials.
C) The presence of myelin increases the propagation speed of action potentials.
The plasma membrane of an axon is called the A) axon hillock. B) axoplasm. C) axolemma. D) axon terminal. E) axokaryon.
C) axolemma.
The site in the neuron where EPSPs and IPSPs are integrated is the A) chemical synapse. B) electrical synapse. C) axon hillock. D) dendritic membrane. E) synaptic knob.
C) axon hillock.
In which part of a neuron does Wallerian degeneration occur? (Module 11.5B) A) cell bodies of CNS neurons B) cell bodies of PNS neurons C) axons of PNS neurons D) axons of CNS neurons E) dendrites of the PNS neurons
C) axons of PNS neurons
Neurons that have one axon and one dendrite, with the soma in between, are called A) anaxonic. B) unipolar. C) bipolar. D) tripolar. E) multipolar.
C) bipolar.
The ion that triggers the release of acetylcholine into the synaptic cleft is A) sodium. B) potassium. C) calcium. D) chloride. E) magnesium.
C) calcium.
Name the effectors of the ANS. (Module 11.1C) A) skeletal muscle, cardiac muscle, and smooth muscle B) skeletal muscle only C) cardiac muscle, smooth muscle, glands, and adipose tissue D) cardiac muscle and smooth muscle E) glands and adipose tissue
C) cardiac muscle, smooth muscle, glands, and adipose tissue
The ________ nervous system is composed of the brain and spinal cord. A) autonomic B) peripheral C) central D) efferent E) afferent
C) central
Branches that may occur along an axon are called A) dendrites. B) synaptic knobs. C) collateral branches. D) hillocks. E) synapses.
C) collateral branches.
An action potential traveling along the entire length of an axon demonstrates ________ propagation. A) relative B) saltatory C) continuous D) graded E) degraded
C) continuous
In the peripheral nervous system, Schwann cells participate in the repair of damaged nerves by A) producing new axons. B) regenerating cell bodies for the neurons. C) forming a cellular cord that directs axonal regrowth. D) clearing away cellular debris. E) producing more satellite cells that fuse to form new axons.
C) forming a cellular cord that directs axonal regrowth.
Voltage-gated channels are present A) at the motor end plate. B) on the surface of dendrites. C) in the membrane that covers axons. D) on the soma of neurons. E) along the perikaryon of neurons.
C) in the membrane that covers axons.
Ion channels that are always open are called ________ channels. A) active B) gated C) leak D) regulated E) local
C) leak
Graded potentials A) produce an effect that increases with distance from the point of stimulation. B) produce an effect that spreads actively across the membrane surface without diminishing. C) may be either a depolarization or a hyperpolarization. D) are often all-or-none. E) always cause repolarization.
C) may be either a depolarization or a hyperpolarization.
Which neuroglia appear in increased numbers in a person with a brain infection? (Module 11.4B) A) ependymal cells B) satellite cells C) microglia D) astrocytes E) oligodendrocytes
C) microglia
The smallest neuroglia of the CNS that act as phagocytes are the A) astrocytes. B) ependymocytes. C) microglia. D) oligodendrocytes. E) tanycytes.
C) microglia.
The sodium-potassium ion exchange pump A) is not involved in producing the resting membrane potential. B) transports sodium ions into the cell during depolarization. C) transports potassium ions out of the cell during repolarization. D) moves sodium and potassium opposite to the direction of their electrochemical gradients. E) depends on a hydrogen gradient for energy.
D) moves sodium and potassium opposite to the direction of their electrochemical gradients.
Define excitatory postsynaptic potential (EPSP) and inhibitory postsynaptic potential (IPSP). (Module 11.13A) A) An excitatory postsynaptic potential is a graded hyperpolarization by the postsynaptic cell and an inhibitory postsynaptic potential is a graded repolarization by the postsynaptic cell. B) An excitatory postsynaptic potential is a graded repolarization by the postsynaptic cell and an inhibitory postsynaptic potential is a graded hyperpolarization by the postsynaptic cell. C) An excitatory postsynaptic potential is a graded hyperpolarization by the postsynaptic cell and an inhibitory postsynaptic potential is a graded depolarization by the postsynaptic cell. D) An excitatory postsynaptic potential is a graded depolarization by the postsynaptic cell and an inhibitory postsynaptic potential is a graded hyperpolarization by the postsynaptic cell. E) An excitatory postsynaptic potential is a graded depolarization by the postsynaptic cell and an inhibitory postsynaptic potential is a graded repolarization by the postsynaptic cell.
D) An excitatory postsynaptic potential is a graded depolarization by the postsynaptic cell and an inhibitory postsynaptic potential is a graded hyperpolarization by the postsynaptic cell.
________ neurons are short, with a cell body between dendrite and axon, and occur in special sense organs. A) Multipolar B) Anaxonic C) Unipolar D) Bipolar E) Pseudopolar
D) Bipolar
Compare the absolute refractory period with the relative refractory period. (Module 11.10C) A) During the absolute refractory period the membrane can respond only to a larger-than-normal stimulus. During the relative refractory period the membrane cannot respond to further stimulation. B) During the absolute refractory period the membrane cannot respond to further stimulation. During the relative refractory period the membrane can respond to any stimulus. C) During the absolute refractory period the membrane is highly responsive to stimuli. During the relative refractory period the membrane is unresponsive to stimuli. D) During the absolute refractory period the membrane cannot respond to further stimulation. During the relative refractory period the membrane can respond only to a larger-than-normal stimulus. E) During the absolute refractory period the membrane is highly responsive to stimuli. During the relative refractory period the membrane can respond only to a larger-than-normal stimulus.
D) During the absolute refractory period the membrane cannot respond to further stimulation. During the relative refractory period the membrane can respond only to a larger-than-normal stimulus.
Define information processing. (Module 11.6C) A) Information processing is the change in charge across the inner and outer membrane of a cell. B) Information processing is a temporary, localized change in the resting membrane potential of a cell. C) Information processing involves the release of neurotransmitters by the presynaptic cell. D) Information processing is the integration of stimuli by an individual cell. E) Information processing is transfer of neurotransmitters from the presynaptic cell to an effector cell.
D) Information processing is the integration of stimuli by an individual cell.
________ channels open or close in response to physical distortion of the membrane surface. A) Voltage-gated B) Chemically gated C) Active D) Mechanically gated E) Leak
D) Mechanically gated
Clusters of RER and free ribosomes in neurons are called A) neurofilaments. B) neurofibrils. C) perikaryon. D) Nissl bodies. E) microglia.
D) Nissl bodies.
Which of the following statement is false when comparing neurons and muscle tissue? A) Muscle tissue and nerves are both excitable. B) Muscle tissue and neurons both have a resting membrane potential. C) Muscle tissue and neurons both have refractory periods. D) Resting membrane potentials are greater (more positive) in muscle compare to neurons. E) Action potentials last longer in muscle tissues compared to neurons.
D) Resting membrane potentials are greater (more positive) in muscle compare to neurons.
Puffer fish poison blocks voltage-gated sodium channels like a cork. What effect would this neurotoxin have on the function of neurons? A) Neurons would depolarize more rapidly. B) Action potentials would lack a repolarization phase. C) The absolute refractory period would be shorter than normal. D) The axon would be unable to generate action potentials. E) None, because the chemically gated sodium channels would still function.
D) The axon would be unable to generate action potentials.
What event must occur in the postsynaptic cell before it generates an action potential? (Module 11.12B) A) The postsynaptic cell must fuse to the presynaptic cell membrane to generate an action potential. B) The postsynaptic cell receive passage of ions through the gap junctions between the two cells in order to generate an action potential. C) The postsynaptic cell must release neurotransmitters to generate an action potential. D) The postsynaptic cell membrane must reach threshold to generate an action potential. E) The postsynaptic cell membrane must hyperpolarize to generate an action potential.
D) The postsynaptic cell membrane must reach threshold to generate an action potential.
Which is not true of voltage-gated sodium channels? A) They have both an activation gate and an inactivation gate that work independent of each other. B) They open and close in response to changes in the membrane potential. C) They are found on excitable membranes. D) They have both an activation gate and an inactivation gate that work dependent of each other. E) None of these is false.
D) They have both an activation gate and an inactivation gate that work dependent of each other.
Deteriorating changes in the distal segment of an axon as a result of a break between it and the soma is called ________ degeneration. A) neural B) central C) peripheral D) Wallerian E) conduction
D) Wallerian
Contrast the white matter and gray matter in the CNS. (Module 11.4D) A) White matter of the CNS is dominated by glial cells. Gray matter is dominated by myelinated axons. B) White matter of the CNS is dominated by myelinated axons. Gray matter is dominated by glial cells. C) White matter of the CNS is dominated by neuron cell bodies, dendrites, and unmyelinated axons. Gray matter is dominated by myelinated axons. D) White matter of the CNS is dominated by myelinated axons. Gray matter of the CNS is dominated by neuron cell bodies, dendrites, and unmyelinated axons. E) White matter of the CNS is dominated by unmyelinated axons. Gray matter of the CNS is dominated by glial cells.
D) White matter of the CNS is dominated by myelinated axons. Gray matter of the CNS is dominated by neuron cell bodies, dendrites, and unmyelinated axons.
Cholinergic synapses release the neurotransmitter A) norepinephrine. B) epinephrine. C) serotonin. D) acetylcholine. E) GABA.
D) acetylcholine.
Describe the components of a chemical synapse. (Module 11.12A) A) A presynaptic cell and a postsynaptic cell locked together by gap junctions B) A presynaptic cell and a postsynaptic cell locked together by tight junctions C) A presynaptic cell and a postsynaptic cell with fused plasma membranes D) A presynaptic cell and a postsynaptic cell whose plasma membranes are separated by a narrow synovial cavity E) A presynaptic cell and a postsynaptic cell whose plasma membranes are separated by a narrow synaptic cleft
E) A presynaptic cell and a postsynaptic cell whose plasma membranes are separated by a narrow synaptic cleft
________ line the brain ventricles and spinal canal. A) Astrocytes B) Satellite cells C) Oligodendrocytes D) Microglia E) Ependymal cells
E) Ependymal cells
Define membrane potential. (Module 11.6A) A) Membrane potential is the ability of a cell to become excitable. B) Membrane potential is the maximum ability of a cell to generate electrical impulses. C) Membrane potential is the maximum speed a cell can propagate electrical impulses. D) Membrane potential is the maximum times a cell can be stimulated by electrical impulses. E) Membrane potential is the unequal charge distribution between the inner and outer surfaces of the plasma membrane.
E) Membrane potential is the unequal charge distribution between the inner and outer surfaces of the plasma membrane.
Why is a CNS neuron not usually replaced after it is injured? (Module 11.2D) A) Most CNS neurons are not replaced because we have an abundance of neurons and it is not necessary to replace any that are injured. B) Most CNS neurons are not replaced because the PNS neurons just take over the functions of any injured CNS neurons. C) Most CNS neurons are not replaced because it is not possible to replace any injured cell in the body. D) Most CNS neurons are not replaced because they contain Nissl bodies which prevents the cell from undergoing cellular division. E) Most CNS neurons are not replaced because they lack centrioles so they cannot divide.
E) Most CNS neurons are not replaced because they lack centrioles so they cannot divide.
Which of the following is not contained in the axoplasm of the axon? A) neurotubules B) mitochondria C) vesicles D) neurofibrils E) Nissl bodies
E) Nissl bodies
Describe the role of regulatory neurons. (Module 11.14A) A) Regulatory neurons act as part of the defense system to protect the presynaptic neurons from pathogens. B) Regulatory neurons block presynaptic neurons from drugs and other chemicals in the blood. C) Regulatory neurons assist in the repair of injured neurons. D) Regulatory neurons speed the propagation of action potentials between presynaptic neurons and postsynaptic neurons. E) Regulatory neurons facilitate or inhibit the activities of presynaptic neurons by affecting the membrane of the cell body or by altering the sensitivity of axon terminals.
E) Regulatory neurons facilitate or inhibit the activities of presynaptic neurons by affecting the membrane of the cell body or by altering the sensitivity of axon terminals.
The neurilemma of axons in the peripheral nervous system is formed by A) astrocytes. B) satellite cells. C) oligodendrocytes. D) microglia. E) Schwann cells.
E) Schwann cells.
What effect would a chemical that blocks voltage-gated sodium ion channels in a neuronʹs plasma membrane have on its membrane potential? (Module 11.8C) A) The membrane potential would become more positive because more sodium ions would leave the cell. B) The membrane potential would become more negative because more sodium ions would leave the cell. C) The membrane potential would become more positive because more sodium ions would enter the cell. D) The membrane potential would become more negative because more sodium ions would enter the cell. E) The membrane potential would not change because sodium could not enter the cell.
E) The membrane potential would not change because sodium could not enter the cell.
The period during which an excitable membrane cannot respond to further stimulation is the A) hyperpolarization. B) depolarization. C) relative refractory period. D) repolarization. E) absolute refractory period.
E) absolute refractory period.
If the permeability of sodium ions increases in an axon, A) the membrane potential will depolarize. B) the membrane potential will hyperpolarize. C) inward movement of sodium ions will increase. D) outward movement of sodium ions will decrease. E) both the inward movement of sodium ions will increase and the membrane potential will depolarize.
E) both the inward movement of sodium ions will increase and the membrane potential will depolarize.
Opening of sodium channels in the axon membrane causes A) hyperpolarization and decreased positive charge inside the membrane. B) repolarization and increased positive charge inside the membrane. C) hyperpolarization and increased negative charge inside the membrane. D) depolarization and increased negative change inside the membrane. E) depolarization and increased positive charge inside the membrane.
E) depolarization and increased positive charge inside the membrane.
Ions can move across the plasma membrane in all of the following ways except A) through voltage-gated channels along the axolemma. B) through passive or leak channels. C) by ATP-dependent ion pumps like the sodium-potassium exchange pump. D) through chemically-gated channels as in neuromuscular transmission. E) diffusion directly through the plasma membrane.
E) diffusion directly through the plasma membrane.
The sum of the electrical and chemical forces acting on an ion is known as its ________ gradient. A) osmotic B) chemiosmotic C) concentration D) potential E) electrochemical
E) electrochemical
Opening of each of the following types of channels will contribute toward a graded potential except A) closed voltage-gated sodium channel. B) chemically gated acetylcholine receptor. C) sodium leak channel. D) mechanically gated sodium channel. E) inactivated voltage-gated sodium channel.
E) inactivated voltage-gated sodium channel.
Which of the following would not have an effect on synaptic function? A) interfering with neurotransmitter synthesis B) interfering with neurotransmitter reuptake C) preventing neurotransmitter inactivation D) interfering with chemically gated sodium channels E) interfering with voltage-gated sodium channels
E) interfering with voltage-gated sodium channels
Which of the following are not types of neuroglia? A) ependymal cells B) microglia C) astrocytes D) oligodendrocytes E) interneurons
E) interneurons
Neurons that have several dendrites and a single axon are called A) anaxonic. B) unipolar. C) bipolar. D) tripolar. E) multipolar.
E) multipolar.
The basic functional unit of the nervous system is the A) brain. B) spinal cord. C) nerve. D) glial cell. E) neuron.
E) neuron.
The cytoplasm that surrounds the nucleus of a neuron is called the A) protoplasm. B) nucleoplasm. C) sarcoplasm. D) neuroplasm. E) perikaryon.
E) perikaryon.
Extensive damage to oligodendrocytes in the CNS could result in A) loss of the structural framework of the brain. B) a breakdown of the blood-brain barrier. C) inability to produce scar tissue at the site of an injury. D) decreased production of cerebrospinal fluid. E) reduced speed of nerve impulses.
E) reduced speed of nerve impulses.
Compare a graded potential with an action potential.
Graded potentials are temporary, localized changes in resting membrane potentials that decrease with distance away from the stimulus. In response to sufficiently large graded potentials, action potentials are generated. Action potentials begin in one location and spread along the surface of an axon toward the axon terminals.
Contrast an electrical synapse with a chemical synapse
In chemical synapses, a neurotransmitter crosses a narrow synaptic cleft. In electrical synapses, the membranes of the presynaptic and postsynaptic cells are joined together by gap junctions.
A drug that blocks ATP production is introduced into an isolated axon preparation. The axon is then repeatedly stimulated, and recordings are made of the response. What effects would you expect to observe?
Initially, the recording would show normal action potentials in response to the repetitive stimulation. After 50,000 to 100,000 action potentials have passed, the recording would start to indicate less responsiveness from the axon; ultimately, the axon would fail to respond. Because very few ions actually move across the membrane during an action potential, axons can carry thousands of action potentials before the concentrations of sodium and potassium ions must be reestablished by the sodium-potassium pump. Without ATP production, the supply of ATP would be consumed, the pump would shut down, and so the cell could not restore the sodium and potassium ion gradients. The resulting slow depolarization would inactivate voltage-gated sodium channels, leading to a persistent absolute refractory state. The loss of the electrochemical gradients denies the axons their means of generating an action potential, and transmission would stop.
Compare temporal summation with spatial summation.
Temporal summation is the addition of a rapid succession of stimuli occurring at a single synapse. Spatial summation involves the addition of simultaneous stimuli applied at different locations; that is, it involves multiple synapses that are active all at the same time.
Describe the neurilemma of a myelinating and nonmyelinating Schwann cell.
The neurilemma of a myelinating Schwann cell is the outer surface of the myelin sheath covering an internode of one axon. The neurilemma of a nonmyelinating Schwann cell is folded separately around multiple axons.
The myelination of central and peripheral axons occurs rapidly through the first few years of life. How can this developmental process explain the improved motor abilities of infants and toddlers?
Without full myelination, information about limb movement and body position moves slowly to the CNS, and motor commands move slowly and erratically to the muscles. By the time the brain is aware of movement or position and can issue a motor command, the limb has already moved. When the motor command reaches the skeletal muscle, the response is no longer appropriate. As the neurons become fully myelinated, information processing speeds up, so we observe improved balance, coordination, and movement.