Exam 4 (Ch 11-14)
What is the role of calcium in synaptic activity?
Calcium influx into the synaptic terminal causes vesicle fusion.
The primary determinant of the resting membrane potential
K+ permeability
The concentrations of which two ions are highest outside the cell.
Na+ and Cl-
The concentrations of which two ions are highest outside the cell?
Na+ and Cl−
During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?
Na+ is entering the cell.
The Na+-K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped?
Na+ is pumped out of the cell and K+ is pumped into the cell.
Although it plays a role, it is not a primary determinant of the resting membrane potential
Na+ permeability
What prevents the Na+ and K+ gradients from dissipating?
Na+-K+ ATPase
What is the direct role of neurotransmitter at a chemical synapse?
Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane.
Which of the following outcome criteria show that a patient is effectively coping with a stressful problem?
Regular heart beat, unlabored breathing, warm and dry skin, constricted or normal pupils
A patient sustains a ventral horn injury to the lumbar region of the spine. This injury has damaged the cell bodies of several afferent nerves within the region. Predict how the patient's patellar reflex might be affected.
The patient's patellar reflex would be absent or weak
Drugs called beta-blockers ________.
decrease heart and blood pressure
An action potential is self-regenerating because __________.
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
Why would smooth muscle associated with lung bronchioles dilate while smooth muscle associated with arterial walls constricts when stimulated by norepinephrine neurotransmitter?
different receptor types
Cardiovascular effects of the sympathetic division include all of the following EXCEPT ________.
dilation of the blood vessels serving the skin and digestive viscera
Neurotransmitter is released from presynaptic neurons through what mechanism?
exocytosis
Sympathetic nerves may leave the spinal cord at which vertebra?
first thoracic
Control of temperature, endocrine activity, and thirst are functions associated with the ________.
hypothalamus
Emotions influence autonomic reactions primarily through integration in the ________.
hypothalamus
Sympathetic division stimulation causes ________.
increased blood glucose, decreased GI peristalsis, and increased heart rate and blood pressure
A mugger steals your wallet causing all of the following to happen EXCEPT ________.
increased glucose uptake to the liver from blood
Where do most action potentials originate?
initial segment
Raynaud's disease ________.
is characterized by exaggerated vasoconstriction in the extremities
Erection (vasodilation) of the penis or clitoris ________.
is primarily under parasympathetic control
What is the largest danger associated with a blood clot that's lodged in a cerebral artery?
lack of oxygen
Which type of drug would be useful in dilating the pupils for an examination of the retina?
muscarinic receptor inhibitor
A Morton's (plantar) neuroma is a foot condition due to swelling of the common plantar digital nerve. It can cause excruciating pain felt between the third and fourth metatarsal bones when walking. Which of the following would NOT be a factor responsible for this disorder?
nerve thinning
Nasal decongestants phenylephrine and pseudoephedrine act to shrink dilated blood vessels in the nasal passages to relieve congestion. They are called sympathomimetics because they act similar to sympathetic neurotransmitter norepinephrine. Which of the following would be an undesirable side effect associated with their use?
nervousness
Secreted by most postganglionic sympathetic fibers.
norepinephrine
The parasympathetic fibers of the ________ nerves innervate smooth muscles of the eye that cause the lenses to bulge to accommodate close vision.
oculomotor (III)
Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?
resting membrane potential
Which of the following appears to exert the most direct influence over autonomic functions?
reticular formation
In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?
reuptake and degradation
Which target organ receives dual innervation?
small intestine
Preparing the body for the "fight-or-flight" response is the role of the ________.
sympathetic division
The secretions of the adrenal medulla act to supplement the effects of ________.
sympathetic stimulation
Once a sympathetic preganglionic axon reaches a trunk ganglion, it can do all of the following EXCEPT?
synapse with a parasympathetic neuron in the same trunk ganglion
Autonomic ganglia contain ________.
the cell bodies of motor neurons
When calcium ions enter the synaptic terminal,
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
Why would imaging studies such as computed tomography (CT) or magnetic resonance imaging (MRI) be recommended for a patient experiencing sudden aphasia?
to rule out other causes of brain injury
Autonomic ganglia are motor ganglia, containing the cell bodies of motor neurons.
true
The smooth muscle of the digestive viscera is served largely by the ________.
vagus (X) nerves
Visceral reflex arcs differ from somatic in that ________.
visceral arcs involve two motor neurons
Where would you NOT find autonomic ganglia?
within spinal cord
During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?
at the end of the depolarization phase, as the membrane potential approaches its peak value
Where are action potentials regenerated as they propagate along a myelinated axon?
at the nodes of Ranvier
Where in the neuron is an action potential initially generated?
axon hillock
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
If the membrane of a postsynaptic dendrite is setting up a graded potential, what must have happened after neurotransmitter was released by the presynaptic terminal?
bound at postsynaptic receptors to open postsynaptic ion channels
Severe whiplash, or acceleration flexion-extension neck injury, may cause numbness, tingling, or weakness in an accident victim's arms. Most injuries happen in the C_5 and C_6 region. Which nerve plexus would this injury most likely involve?
brachial
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
The mushroom poison muscarine can bind to receptors on ________.
all effector cells stimulated by postganglionic cholinergic fibers
Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential arrives at axon terminal (d) Neurotransmitter is removed from the synaptic cleft (e) Neurotransmitter released into synaptic cleft (f) Graded potential generated in postsynaptic cell
(c) Action potential arrives at axon terminal (a) Voltage-gated calcium channels open (e) Neurotransmitter released into synaptic cleft (b) Neurotransmitter binds to receptors (f) Graded potential generated in postsynaptic cell (d) Neurotransmitter is removed from the synaptic cleft
What is the magnitude (amplitude) of an action potential?
100 mV
Examine the cross section through the lumbar section of the spinal cord and the two patellar reflex pathways shown. What identifies these synapses?
Afferent impulses synapse with motor neurons and interneurons. Pathways will activate one muscle and simultaneously inhibit its antagonist muscle.
Examine and characterize the two motor pathways in the stretch patellar reflex.
Alpha motor neurons send efferent messages to the quadriceps, while parallel efferent messages to the hamstrings are reduced.
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent area
You give Mr. T two ibuprofen for his headache and leave him in the examination room, waiting for the doctor. A little while later, you hear him shouting for help. He says his head is killing him. His face is definitely redder and his eyes more bloodshot. His blood pressure is 230/175 mm Hg, and his heart rate 40 bpm. A more experienced nurse comes into the room. "Check his feet and his catheter. If we don't find a solution there, we'll give him nitroglycerine," she says. Nitroglycerine is a vasodilator that affects both veins and arteries/arterioles. It is commonly used for hypertension (high blood pressure) emergency situations. How would dilating veins and arteries affect blood pressure?`
Dilating veins reduces the stroke volume, and dilating arteries reduces the TPR.`
The concentration of ___ is higher inside than outside the cell.
K+
Mr. T's heart rate is low, but his blood pressure remains high. How could someone develop a high blood pressure without a high heart rate?`
Increased blood volume might have increased his stroke volume. Increased vasoconstriction might have increased his total peripheral resistance.
The ion ___ is crossing the cell's plasma membrane at 1.5 msec.
K+
Which is the true statement about the synapses in the spinal cord in the stretch reflex?
Interneurons make inhibitory synapses with neurons that prevent contraction of the antagonist muscle.
How would an increase in extracellular K+ affect repolarization?
It will decrease the concentration gradient, causing less K+ to flow out of the cell during repolarization.
Predict the possible effect of a drug that totally blocks the neurotransmitter receptor on the postsynaptic membrane. For example, curare is a neurotoxin used by several South American cultures. The primary effect of curare is that acetylcholine, a major neuromuscular neurotransmitter, cannot bind at its receptor because curare is blocking it. Predict the possible effects of curare on the postsynaptic membrane and muscle.
Local graded potential and action potential transmission is blocked, and there is no response by the postsynaptic cell, the muscle.
The EKG is hooked up, and Mr. M's trace looks very abnormal. His heart rate is low. The T wave, which indicates repolarization of the ventricles, is unusually large and pointed and the QRS wave, which indicates the depolarization impulse's passage through the ventricles, is widened or slowed. "That's a classic EKG for hyperkalemia (high blood potassium)!" The doctor gives Mr. M an injection of calcium gluconate. Calcium ions block the Na+ channels on nerve and muscle cells. How will this help counteract the effects of high blood K+?
Mr. M's cells are depolarizing too easily. Blocking Na+ channels will make it harder for them to depolarize, bringing their sensitivity back to normal.
Sympathetic responses generally are widespread because ________.
NE and epinephrine are secreted into the blood as part of the sympathetic response
The concentration of _______ is higher outside than inside the cell.
Na+
Are biogenic amine neurotransmitters such as dopamine considered to be proteins?
No, it simply means that dopamine has at least one amine functional group in its molecular structure.
What characterizes repolarization, the second phase of the action potential?
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
How do action potential propagation speeds compare in myelinated and unmyelinated axons?
Propagation is faster in myelinated axons.
Prozac belongs to a class of drugs known as selective serotonin reuptake inhibitors (SSRIs), which block the removal of serotonin from its receptor, thereby enhancing a patient's mood. What mechanism allows serotonin to remain on its receptors longer?
SSRIs inhibit the reuptake of serotonin back into the presynaptic neuron, which increases the level of serotonin in the synaptic cleft.
You are going to record RMP from a cell using an electrode. You place your electrode and record a resting membrane potential every millisecond. You record an initial value of -70mV; however, over time you notice that your recordings become more and more positive until the RMP reaches 0mV. Assuming that Na+ and K+ are the major determinants of RMP in this cell, which of the following could best explain your results?
The cell's Na+-K+ ATPase pumps have stopped functioning.
Mrs. Oberhaus needs surgery to correct a severe case of Raynaud's disease, affecting one of her hands. What surgical procedure will be performed? After the surgery, will she be more likely to suffer from anhidrosis (lack of sweating) or hyperhidrosis (profuse sweating) in the affected hand?
The doctor will perform a sympathectomy, and the affected hand will suffer from anhidrosis.
The doctor is concerned about Mr. M's weakness. She orders an EKG. Why might an EKG be an appropriate test for this patient?
The heart is a muscle too, so whatever is making his skeletal muscles weak might be affecting it.
A more experienced nurse comes into the room. "Check his feet and his catheter. If we don't find a solution there, we'll give him nitroglycerine," she says. When you take off Mr. T's shoes and socks, you see that his feet are white and cold. You also find that his urinary catheter tube is kinked, and there is very little urine in the catheter bag. When you straighten out the tube, urine immediately starts flowing down into the bag, and Mr. T's blood pressure begins to drop. Mr. T has pale, cold skin below the site of his spinal cord lesion but warm, flushed skin above it. What does this tell you about the sympathetic activity below and above the lesion?
The sympathetic system is active below the lesion, and the parasympathetic system is active above it.
Even though Mr. T's baroreceptor reflex responded to his decreased blood pressure, it did not succeed in raising his blood pressure high enough to prevent him from passing out. Why not? (Hint: remember, this client has a spinal injury that has blocked communication between the brain and the lower half of his body.) Choose the most accurate explanation for Mr. T's problem.
The sympathetic system turned on in the upper half of his body, but it was not activated in the lower half, so the blood vessels in his legs remained dilated, and the blood pooled there. As a result, there wasn't enough blood in the upper half of his body to maintain blood pressure
The plasma membrane is much more permeable to K+ than to Na+. Why?
There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
Select the true statements (more than one) about the characteristics of sensory neurons in the stretch reflex
These sensory neurons transmit afferent impulses toward the spinal cord (CNS). When a stretch activates the muscle spindle, these sensory neurons transmit impulses at a higher frequency.
What type of channel on the postsynaptic membrane binds neurotransmitter?
a chemically gated channel
A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?
a neuron
The velocity of the action potential is fastest in which of the following axons?
a small myelinated axon
Secreted by postganglionic sympathetic fibers to sweat glands.
acetycholine
Secreted by postganglionic parasympathetic fibers.
acetylcholine
Secreted by preganglionic parasympathetic fibers.
acetylcholine
The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned?
acetylcholine
Secreted by preganglionic sympathetic fibers.
aceytlcholine
Which component has a role in the postsynaptic cell during synaptic activity?
chemically gated channels
Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.
chemically gated; postsynaptic
The parasympathetic ganglion that serves the eye is the ________.
ciliary ganglion
What type of conduction takes place in unmyelinated axons?
continuous conduction
Which step of nerve or muscle firing would be directly affected by a change in extracellular K+ ?
repolarization
Which of the following is mismatched?
parasympathetic postganglionic fibers; release NE
The somatic and autonomic nervous systems differ in all of the following EXCEPT ________.
regulation of activity by higher brain centers
Which statement best describes exocytosis?
Membrane organelles fuse with the membrane and release contents out of the cell.
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?
Na+ (sodium)
The figure shows the phases of action potential. The arrow points to the peak potential. What is happening to voltage-gated channels at this point in the action potential?
Na+ channels are inactivating, and K+ channels are opening.
Which of the following best describes the Na+ and K+ concentrations across a neuron's plasma membrane?
The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside.
Imagine that the cell membrane from the previous problem becomes more permeable to Na+. Predict how this will affect the RMP.
The RMP will be more positive.
Tetraethylammonium (TEA) blocks voltage-gated K+ channels such that K+ cannot pass even when the channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron with TEA?
The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time.
Why does the action potential only move away from the cell body?
The areas that have had the action potential are refractory to a new action potential.
The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.
The presence of concentration gradients and leak channels
During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?
The previous axonal segment is in the refractory period.
Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?
The resting membrane potential would become less negative (more positive).
Suppose a drug is developed that blocks K+ leakage channels. The drug prevents ions from passing through those channels. If this drug was applied to a neuron, what would be the most immediate effect on that neuron?
The resting membrane potential would become less negative (more positive).
The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?
The speed of action potential propagation would be slower.
When an action potential arrives at the end of the axon terminal, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. Select the answer that correctly describes the primary stimulus for vesicles to move toward the cell membrane and eventually release their contents.
Voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium.`
What condition will increase the diffusion of molecules, such as neurotransmitters?
an increase in the amount of neurotransmitter exocytized by the presynaptic axon
Binding of the neurotransmitter to its receptor causes the membrane to __________.
either depolarize or hyperpolarize
When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,
ion channels in the plasma membrane of the receiving neuron open.
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
leak channels
What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?
maintaining the concentration gradients for Na+ and K+ across the cell membrane
The resting membrane potential of the cell
membrane potential of -70 mV
The point at which there is no net movement of K+ into or out of the cell
membrane potential of -90 mV
Which of the following would increase the membrane permeability to K+?
more K+ leakage channels
Complete the following sentence. The operation of the Na+−K+ ATPase pump __________.
moves 3 Na+ to the ECF and 2 K+ to the cytoplasm
Saltatory propagation occurs in _________ axons, in which action potentials _________.
myelinated; move from one node of Ranvier to another
A molecule that carries information across a synaptic cleft is a
neurotransmitter
Hyperpolarization results from __________.
slow closing of voltage-gated K+ channels
Which of the following best characterizes depolarization?`
small, consecutive steps of Na+ penetration into the axon along its length
The small space between the sending neuron and the receiving neuron is the
synaptic cleft
If a signal from a sending neuron makes the receiving neuron more negative inside,
the receiving neuron is less likely to generate an action potential.
What is the electrochemical gradient of an ion?
the sum of the electrical and concentration gradients for that ion
The membrane is more permeable to
K+
During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?
K+ channels close. Na+ channels go from an inactivated state to a closed state.
Which of the following is the clearest example of a neuronal membrane's selective permeability?
K+ ions can diffuse across the membrane more easily than Na+ ions.
During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.
K+ ions diffusing through voltage-gated channels
The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.
K+ ions leaving the cell through voltage-gated channels
The resting membrane potential is maintained by Na+-K+ pumps that actively transport _____ into and _____ out of the cell.
K+, Na+
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
K+; Na+
This neuron is most depolarized at ____ mV.
+30
This neuron spends approximately ____ msec in a hyperpolarized state.
2.5
Assume you have a membrane with only potassium leak channels. The RMP is -90mV. Predict the RMP if we add Na+ leak channels. The most likely RMP value of Na+ is __________.
-70 mV
What is the value for the resting membrane potential for most neurons?
-70 mV
This cell reaches threshold at approximately ___ msec.
0.6
Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl− gated channels are suddenly opened.
A more negative RMP would result.
Mr. M is a Type 2 diabetic with diagnoses of (poorly controlled) hypertension and chronic renal failure. He has come in for a routine checkup and claims to be feeling fine, just a little tired. He presents as an overweight 58-year-old man with a sunburn on his cheeks and ears and a BAND-AID® on one cheek (where he says he nicked himself shaving that morning), a heart rate of 66 bpm, blood pressure of 124/80 mm Hg, normal breath and heart sounds, and slightly puffy ankles, face, and hands. His weight has increased by 1.5 lbs since he was last seen eight months ago. Do you see anything to concern you in Mr. M's description? There are several worrying signs in Mr. M's presentation. Can you pick them out?
His blood pressure is low for someone with hypertension. His puffy ankles, face, and hands could indicate fluid retention. His tiredness might indicate worsening of his diseases.
What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?
Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
Why does regeneration of the action potential occur in one direction, rather than in two directions?
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?
The inside surface of the plasma membrane is much more negatively charged than the outside surface.
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
What event triggers the generation of an action potential?
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
What is the function of the myelin sheath?
The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon?
The nodes are more permeable to ions.
Let's consider a scenario in which the resting membrane potential changes from −70 mV to +70 mV, but the concentrations of all ions in the intracellular and extracellular fluids are unchanged. Predict how this change in membrane potential affects the movement of Na+. The electrical gradient for Na+ would tend to move Na+ __________ while the chemical gradient for Na+ would tend to move Na+ __________.
out; in
Which of the following choices best represents synaptic transmission?
presynaptic axon to synapse to dendrite or postsynaptic cell body
In a synapse, neurotransmitters are stored in vesicles located in the __________.
presynaptic neuron
You are working on a new medication to selectively kill cancer cells. You test the drug on a culture of normal neurons to check for any side effects. Despite the presence of the drug, a normal resting membrane potential of −70 mV is maintained. Look at each of the figures below to analyze how the drug might be affecting the neuron. Figure A shows neuron activity under normal, or control, conditions (without the drug). Figure B shows neuron activity that has been altered due to exposure to the drug. Based on these results, the drug is most likely __________.
preventing Na+-gated channels from opening
The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.
saltatory conduction
Imagine you changed the concentration of K+ outside a neuron such that the resting membrane potential changed to -80 mV (from the normal resting value of -70 mV). What have you changed?
the electrical gradient for K+ and the concentration gradient for K+
An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?
the generation of local currents
The repolarization phase of an action potential results from __________.
the opening of voltage-gated K+ channels
Which choice best characterizes K+ leak channels?
transmembrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
voltage-gated Ca2+ channels
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels
The generation of an action potential in a neuron requires the presence what type of membrane channels?
voltage-gated channels