Set 4 (Part II) Flashcards
How do we achieve resting membrane potential after the action potential peaks?
- Opening the K+ channels
- Allowing outward diffusion of K+
What is repolarization?
The opening of K+ channels, which allows the interior of the cell to become more negative
What causes a brief period of hyperpolarization?
K+ channels remain open as the membrane is returning to the RMP
Differentiate the speeds of potassium and sodium channels.
- Potassium channels are slower
- Sodium channels are faster
What are the two options that serve as depolarizing stimulus?
- Chemical (e.g. neurotransmitter)
- Electrical
What must the depolarizing stimulus attain to cause an action potential?
The threshold (-59 mV)
What happens immediately after the depolarizing stimulus reaching the threshold?
- Voltage-gated Na+ channels open quickly, and Na+ enters the cell
- Voltage-gated K+ begin to open slowly
- Potassium is repolarizing and is leaving the cell already (slow-gated channels)
How do cells return to resting membrane potential from hyperpolarization if potassium and sodium channels are closed?
- Sodium/Potassium ATPase pump
- Leak channels
At the resting membrane potential, which gate closes the Na+ channel?
Activation gate
What triggers the opening of the sodium channel’s activation gate?
- Depolarizing stimulus
- Reverse of electrical charges triggers the opening (inside positive, outside negative now)
What stops Na+ entry when the action potential reaches a peak?
Inactivation gate
What happens to the Na+ gates during repolarization caused by K+ leaving the cell?
- Reverse of electrical charges (inside negative, outside positive)
- The activation and inactivation gate reset to their original positions
What is the feedback cycle in terms of action potential?
The reverse of electrical charges along the membrane
What is the absolute refractory period?
- Brief period (half a millisecond)
- A local area of a neuron’s membrane resists restimulation and will not respond to a stimulus, no matter how strong
- When the inactivation gate is in place in the sodium channel
What is the relative refractory period?
- Time during which the membrane is repolarized and is restoring the RMP
- Right after the absolute refractory period
- Membrane will only respond to a VERY strong stimulus
How is an action potential propagated along an axon?
- The reversal in polarity causes electrical current to flow between the site of the action potential and the adjacent regions of membrane
- Triggers voltage-gated Na+ channels in the next segment to open
Why can’t action potentials only move forward (feed-forward mechanism)?
- Because it follows a gradient
- Because the refractory period prevents restimulation
In myelinated fibers, where does action potential occur? What is this called?
- Nodes of Ranvier
- Saltatory conduction, where impulse regeneration leaps from node to node
What do myelin sheaths resist? What are the advantages?
- Ion movement
- Only need to depolarize at the nodes of Ranvier
- Also, K+ does not leak out, so it is easier to depolarize
What are the consequences of demyelinated diseases
- Conduction slows when current leaks out of the previously insulated regions between the nodes
- Eventually, the cell might not even fire
Which disease is characterized by demyelination?
Multiple sclerosis
If the ECF K+ concentration increases from 3mM to 5mM, what happens to the resting membrane potential of cells?
A) It becomes more negative
B) It becomes less negative
C) It doesn’t change
A) It becomes more negative
In your work for a pharmaceutical company, you have just created a neurotransmitter that opens K+ channels in neutrons. A neutron under the influence of this neurotransmitter will:
A) Be more likely to fire an action potential
B) Be less likely to fire an action potential
C) The drug will have no effect on an action potential firing
B) Be less likely to fire an action potential
What causes the repolarization phase of the action potential?
A) Na+ being pumped out of the cell by the ATPase
B) K+ being pumped out of the cell by the ATPase
C) Na+ entering the cell through voltage-gated channels
D) K+ entering the cell through voltage-gated channels
E) None of the above
E) None of the above
K+ leaving the cell for the ECF is the right answer
During the rising phase of the action potential, _____.
A) Voltage-gated potassium channels open
B) There is a decrease in the Na+ permeability
C) Sodium moves down both a concentration and electrical gradient
D) Slow sodium entry depolarizes the cell
E) Sodium permeability is enhanced by a feed-forward/feedback process
F) Three of the above are correct
F) Three of the above are correct
During depolarization of a nerve fiber, ______.
A) K+ leaves the neuron
B) K+ enters the neuron
C) Neither occurs as the finer is in its refractory state
A) K+ leaves the neuron
Which of the following is true about one of the two gates in Na+ channels in axons?
A) The opening of the activation gates stops the depolarization during an activation potential.
B) The closing of the inactivation gate stops the depolarization during an action potential.
B) The closing of the inactivation gate stops the depolarization during an action potential.
Where does an action potential begin?
At the trigger zone
Why do positive charges from the depolarized trigger zone spread to adjacent zones?
Because the K+ is repelled by the Na+, and attracted by the negative charge of the RMP
What are synapses?
Gaps where neurotransmitters are released
When do chemical synapses occur?
Occur where pre-synaptic cells release neurotransmitters across a tiny gap to the post-synaptic cell
The neuromuscular junction is an example of a _______ synapse.
chemical
What are the three structures in which a neuron can terminate?
Muscle, gland, or neuron
What is a synaptic knob?
Tiny bulge at the end of a terminal branch of a pre-synaptic neuron’s axon
What structure contains vesicles housing neurotransmitters?
Synaptic knob
What is the synaptic cleft?
Space between a synaptic knob and the plasma membrane of a post-synaptic neuron
What specialized structure does the plasma membrane of a post-synaptic neuron possess?
Protein molecules that serve as receptors for the neurotransmitters
What does the axon of an axodendritic synapse signal?
- Axon signals post-synaptic dendrite
- Common
What does the axon of an axosomatic synapse signal?
- Axon signals post-synaptic soma
- Common
What does the axon of an axoaxonic synapse signal?
- Axon signals post-synaptic axon
- May regulate action potential of post-synaptic axon
What is required for the fusion of a vesicle containing neurotransmitters to the cell membrane?
Ca2+
Which ion enters the cell at the axon terminal? What is its function?
- Ca2+
- Triggers exocytosis of synaptic vesicle contents
What could the cell response be following the binding of a neurotransmitter to a receptor on a post-synaptic cell?
- Intracellular signaling
- Depolarization
What are the two types of post-synaptic potentials? Which ions are they associated with?
- Excitatory post-synaptic potential (EPSP-Na+)
- Inhibitory post-synaptic potential (IPSP-Cl-)
What produces a post-synaptic potential?
Opening of ion channels
Which diseases are caused by defects/imbalances in neurotransmitters?
- Alzheimer’s
- Depression
- Anxiety
- Schizophrenia
- Parkinson’s
What are the means by which neurons communicate with one another and with muscle cells?
Neurotransmitters
What is the function of a neurotransmitter determined by?
By the post-synaptic receptor
What are the two major types of functional neurotransmitter classifications?
- Excitatory neurotransmitters
- Inhibitory neurotransmitters
What are the two possibilities involved with neurotransmitters binding to receptors?
- Opens a channel directly
- Uses a second messenger mechanism involving G proteins and intracellular signal
Which neurotransmitter effects are context specific? What does this mean?
- Excitatory or inhibitory
- Depends on the location of the receptor
What are the four main chemical classes of neurotransmitters?
- Acetylcholine
- Amines
- Amino acids
- Other small molecules
What are examples of acetylcholine neurotransmitters?
- Junctions with motor effectors (muscles and glands)
- Salivary and sweat
- Autonomic system (fight or flight)
What is an example of amines as neurotransmitters
- Monoamines (serotonin) in the CNS
- Causes inhibitory moods and emotions
What is an example of amino acids as neurotransmitters?
- Glycine
- Spinal cord’s most common inhibitory neurotransmitter
What is an example of other small molecules as neurotransmitters?
Nitric oxide, which maybe a signal from post to pre-synaptic neuron
More Na+ in the cell causes what?
EPSP (excitatory depolarization)
Less K+ out of the cell causes what?
EPSP (excitatory depolarization)
More K+ out of the cell causes what?
IPSP (inhibitory hyperpolarization)
More Cl- in the cell causes what?
IPSP (inhibitory hyperpolarization)
Less Na+ in the cell causes what?
IPSP (inhibitory hyperpolarization)
What is an example of a direct stimulation of a post-synaptic receptor?
A neurotransmitter can bind on an ion channel and directly effect its opening/closing
What is an example of an indirect stimulation of a post-synaptic receptor?
- Neurotransmitters can activate a G protein
- Ex: Norepinephrine binds a GPCR and starts a cAMP mechanism cascade
What are the two ways in which neurotransmitter actions are quickly terminated?
- Transported back into the synaptic knob (re-uptake)
- Metabolized into inactive compounds by enzymes and/or diffused and taken up by nearby glial cells
What is acetylcholine broken down by? Where?
- Acetylcholine esterase
- In the synaptic cleft
What is acetylcholine made from?
Choline and Acetyl-CoA
What family are endogenous opioids neuropeptides apart of?
Neuropeptides
What are the crucial functions of endogenous opioids? How are they most often recognized?
- Motor coordination, learning and memory, GI function, control of seize, hormonal regulation
- Central role in the modulation of pain
Endogenous opioids are often referred to as what?
Endorphins
How do somatic motor neurons binds to muscle fibers?
Through the neuromuscular junction
What is the motor end plate in a neuromuscular junction?
Region of muscle membrane that contains high concentrations of ACh receptors
Explain what happens at the neuromuscular junction.
- Axon potential arrives at the axon terminal, Ca2+ enters the cell, and acetylcholine is released into the synaptic cleft
- Nicotinic cholinergic receptor binds ACh molecules, and allows Na+ to enter the cell, which depolarizes it
What are the two possibilities of graded potentials?
- Graded potentials (excitatory) sum to create a suprathreshold signal (action potential is generated)
- An inhibitory and excitatory neurons sum to create a potential that is below threshold (no action potential generated)
In presynaptic inhibition, activity in the _______ is inhibited by _______.
A) Cell soma; a depolarizing graded potential B) Dendrites; an inhibitory neuron C) Axon; the cell body D) Axon terminal; an inhibitory neuron E) Axon terminal; an EPSP
D) Axon terminal; an inhibitory neuron
An inhibitory neuron can fire, which blocks neurotransmitter release at one synapse
Release of a neurotransmitter requires _______.
A) Action potential B) Ca2+ C) AN ISPS D) A and B E) B and C
D) A and B
If a neuron has receptors for a particular neurotransmitter, it will also ____.
A) Respond in a similar way to an agonist of that neurotransmitters
B) Respond in a similar way to an antagonist of that neurotransmitter
C) Release that same neurotransmitter at its axon terminals
4) Take up that neurotransmitter using active transport
A) Respond in a similar way to an agonist of that neurotransmitters
Which muscles do the somatic and automatic divisions control?
- Somatic: skeletal muscles
- Automatic: smooth and cardiac muscles
What are interneurons?
Neurons that lie entirely within the CNS
What is the difference between a nerve and a neuron?
- Neuron: single nerve cell
- Nerve: bundle of axons from many neurons
Which glial cells support and insulate axons by forming myelin?
- Schwann cells in the PNS
- Oligodendrocytes in the CNS
Would a cell with a resting membrane potential of -70mV depolarize or hyperpolarize in the following cases?
A) Cell becomes more permeable to Ca2+
B) Cell becomes less permeable to K+
C) Small amount of Na+ leaked into the cell
A) Depolarize
B) Depolarize
C) Depolarize
Does a change in the membrane potential from -70 mV to +30 mean that the ion concentration gradients have reversed?
No, since a significant change in membrane potential occurs with the movement of very few ions
Which ion channels spend most of their time in an open state? Why?
- K+ leak channels
- They are the major determinant of resting membrane potential
What are graded potentials?
- Variable-strength signals that travel short distances and lose strength as they travel through the cell
- They reflect stimulus strength
Match each ion's movement with the type of graded potential (depolarization or hyperpolarization) it creates: A) Na+ entry B) Cl- entry C) K+ exit D) Ca2+ entry
A) Depolarization
B) Hyperpolarization
C) Hyperpolarization
D) Depolarization
What is the integrating center of the neuron? What channel does it contain in high concentration?
- The trigger zone
- Voltage-gated Na+ channels
What type of ion channels are required for the conduction of the action potential along the axon?
- Voltage-gated Na+ channels
- Voltage-gated K+ channels
- Some leak channels that help set the resting membrane potential
If you put ouabain, an inhibitor of the Na+-K+ pump, on a neuron and then stimulate the neuron repeatedly, what do you expect to happen to action potentials generated by that neuron?
A) They cease immediately
B) There is no immediate effect, but they diminish with repeated stimulation and eventually disappear
C) They get smaller immediately, then stabilize with smaller amplitude
D) Ouabin has no effect on action potentials
B) There is no immediate effect, but they diminish with repeated stimulation and eventually disappear
If a compound disables the inactivation gates of Na+ channels so that they remain open, what happens to membrane potential?
The membrane potential depolarizes and remains depolarized
When Na+ channel gates are resetting, is the activation gate opening or closing? Is the inactivation gate opening or closing?
The activation gate is closing and the inactivation gate is opening
How do action potentials that fire during the relative refractory period compare to normal? Why?
- They will be smaller
- Na+ entry is offset by K+ loss through still-open K+ channels
Differentiate graded potentials and action potentials.
- Graded potentials can be depolarizing or hyperpolarizing, while action potentials are always depolarizing
- Graded potentials’ membrane potential loses strength over distance (Na+ enters only at the point of stimulus)
- Action potential does not diminish as Na+ channels open along the axon
The opening of Na+ channels follow a ________ feedback loop. How does it stop?
- Positive
- Na+ channel inactivation gate closes
A stimulating electrode placed halfway down an axon artificially depolarizes the cell above threshold. In which direction will an action potential travel: to the axon terminal, the cell body, or both? Explain.
The action potential will go in both directions because the Na+ channels around the stimulation site have not been inactivated by a previous depolarization
What physical features influence the speed of action potential conductance?
- The diameter of the axon
- The resistance of the axon membrane to ion leakage out of the cell
What happens if there is an increase in blood K+?
Shifts the RMP of a neuron closer to threshold, and causes the cells to fire action potentials in response to smaller graded potentials
What happens if there is a decrease in blood K+?
A normal stimulus would not reach the threshold value (shows up as muscle weakness)
What are cholinergic receptors and neurons?
- Neurons that secrete ACh
- Receptors that bind ACh
What do SSRIs do to serotonin activity at the synapse?
SSRIs decrease reuptake of serotonin into the axon terminal, thereby increasing the time serotonin is active in the synapse
Is Na+-dependent neurotransmitter reuptake facilitated diffusion, primary active transport, or secondary-active transport?
- Neurotransmitter uptake is secondary active transport
- It uses energy stored in the Na+ concentration gradient to concentrate neurotransmitter inside the axon terminal
What indicates the strength of the stimulus? What does stronger stimuli cause?
- The frequency of action potential firing
- More neurotransmitter release
What is a divergent pathway?
One presynaptic neuron branches to affect a larger number of postsynaptic neurons
What is a convergent pathway?
Many presynaptic neurons provide input to influence a smaller number of postsynaptic neurons
Fast synaptic responses are always associated with what?
The opening of ion channels
If the inhibitory presynaptic neuron creates an IPSP of -5 mV and two excitatory presynaptic neurons have EPSPs of 10 and 12 mV, will the postsynaptic neuron fire an action potential?
Yes, because the net effect would cause a depolarization (-53 mV)
What is long-term potentiation?
Mechanism by which neurons change the strength of their synaptic connections
Why would depolarization of the membrane drive Mg2+ from the channel into the extracellular fluid?
- Membrane depolarization makes the inside of the membrane more positive than the outside
- Like charges repel one another, so the more positive membrane potential tends to repel Mg2+
An action potential is ______:
A) a reversal of the Na+ and K+ concentrations inside and outside the neuron
B) The same size and shape at the beginning and end of the axon
C) Initiated by inhibitory post-synaptic graded potentials
D) Transmitted to the distal end of a neuron and causes release of neurotransmitter
B) The same size and shape at the beginning and end of the axon
D) Transmitted to the distal end of a neuron and causes release of neurotransmitter
List two factors that enhance conduction speed
Larger axon diameter and the presence of myelin
List three ways neurotransmitters are removed from the synapse.
- Enzymatic degradation
- Absorption
- Diffusion
The presence of myelin allows an axon to (choose all correct answers):
A) produce more frequent action potentials
B) conduct impulses more rapidly
C) produce action potentials of larger amplitude
D) produce action potentials of longer duration
B) conduct impulses more rapidly
The type of synapse that regulates the amount of chemical transmitter that is released is called an _________ synapse.
axoaxonic
Will signals from the parasympathetic nervous system (PNS) cause smooth muscles in the small intestine to increase or decrease contractions?
Increase
Potentiation of a synaptic potential is caused by:
A) increased sodium at the axon or presynaptic terminal.
B) increased calcium entering the axon or presynaptic terminal.
C) an increase in the number of presynaptic neurons.
B) increased calcium entering the axon or presynaptic terminal.
The stimulus for opening ion channels in a synaptic potential is caused by:
A) a change in voltage.
B) the binding of neurotransmitters.
B) the binding of neurotransmitters.
Action potentials are unidirectional. Why do they travel only from the cell body of a neuron to the terminal and never go backward?
A) This statement is false. They do travel backward toward the soma.
B) The sodium channel activation gates close once an action potential passes.
C) The sodium channel inactivation gates close once an action potential passes.
D) Both sodium inactivation gates and potassium gates are closed once an action potential passes.
C) The sodium channel inactivation gates close once an action potential passes.
