Neurophysiology - Cells AQ Flashcards
(121 cards)
1
Q
What are the two divisions of the CNS?
A
The brain and the spinal cord.
2
Q
What are the two divisions of the PNS?
A
The cranial nerves and the spinal nerves.
3
Q
In which division would sensory receptors be appropriately categorized and what is your rationale?
A
Sensory receptors would be categorized into the PNS because sensory organs are the most peripheral extensions of sensory neurons.
4
Q
How is it that brain cancer is fairly common, yet neurons do not mitotically divide?
A
Brain cancer is typically caused by glial cells, not neurons. Glial cells rapidly divide in the brain and they are more abundant then neurons.
5
Q
What are the major differences between oligodendrocytes and Schwann cells?
A
Oligodendrocytes are found in the CNS and can myelinate several axons. Schwann cells are found in the PNS and can myelinate one segment of an axon at a time.
6
Q
What glial cell in the PNS has a similar function to the astrocyte in the CNS?
A
Satellite cells
7
Q
What is a node of Ranvier, and are they found in the CNS, PNS, or both?
A
The node of Ranvier is the region of an axon between myelinated regions (i.e., internodes), and they are found both in the CNS and the PNS.
8
Q
Comparing a neuron (specifically the axon portion) to the charging cord for your cell phone, what biological material surrounding the axon would be analogous to the plastic/rubber coating surrounding the wire of the cord itself?
A
Myelin sheath surrounds our ‘wires’ (axons).
9
Q
What is the purpose of this material surrounding axons in humans?
A
To insulate the neurons and increase action potential velocity.
9
Q
What percentage of all neurons are interneurons and where are they located?
A
99% of all CNS neurons are interneurons and they are located in the brain and the spinal cord.
10
Q
Can you draw out and label a typical motor neuron?
A
*See Question 6 on AQ sheet
11
Q
What are dendritic spines?
A
Dendritic spines are elevations on dendrites where presynaptic neurons form a synapse.
12
Q
What is a soma?
A
A soma is the cell body of a neuron.
13
Q
What are synaptic knobs?
A
Synaptic knobs are the terminal ends of axons where neurotransmitters are stored and released.
14
Q
What are the three components of a synapse?
A
Presynaptic cell - synaptic cleft - postsynaptic cell.
15
Q
The synaptic cleft is nothing more than what?
A
Interstitial fluid (i.e., ISF).
16
Q
How is information transferred from the presynaptic cell to the postsynaptic cell?
A
Information is transferred in the form of neurotransmitters.
17
Q
In an axo-dendritic synapse, where an axon of one neuron synapses with the dendrite of another, what are the presynaptic and postsynaptic cells?
A
The presynaptic cell is the axon terminal and the postsynaptic cell is the dendrite.
17
Q
What portion(s) of a neuron do other neurons form synapses with?
A
Cell body and dendrites.
18
Q
Which MAP transports recycled vesicles from the terminal knob to the soma? Is this in the positive or negative direction?
A
Dynein is the MAP that goes from the terminal knob to the soma and it travels in a negative direction.
19
Q
Which MAP transports secretory vesicles from the soma to the terminal knob? Is this in the positive or negative direction?
A
Kinesis is the MAP that goes from the soma to the terminal knob and it travels in a positive direction.
19
Q
Which of the three components of the cytoskeleton do these MAPs “walk” along?
A
MAPs walk along the microtubules.
20
Q
What is an equilibrium potential?
A
The equilibrium potential is the membrane potential at which an ion is in equilibrium across the plasma membrane.
21
Q
How do these equilibrium potentials relate to the RMP? In other words, how did we experimentally determine that K+ is the ion primarily responsible for the establishment of an RMP?
A
If the only ions across the cell membrane are K+ ions, the resultant membrane potential will be -90 mV, very close to the actual RMP of the neuron (-70 mV).
22
What is the equilibrium potential value for Na+ and for K+?
The equilibrium potential for Na is +60 mV and the equilibrium potential for K is -90 mV.
23
In which portion(s) of a neuron does a resting membrane potential (RMP) exist?
It runs through the entirety of the neuron.
24
In which portion(s) of a neuron do graded (local) potentials occur?
Graded potentials occur in the cell body, dendrite, axon hillock, internode, and terminal knob.
25
What type of gated channels would you find in the locations where a graded potential can occur?
Ligand-gated and mechanically-gated channels.
26
In which portion(s) of a neuron do action potentials occur?
Action potentials occur in the initial segment of axon and the node of Ranvier.
26
What type of gated channels would you find in the locations where an action potential can occur?
Voltage-gated channels.
27
What is the primary mechanism responsible for establishing a RMP?
K+ leak channels.
28
Hypothetically, how would your cells’ RMP be affected if this mechanism went offline (i.e., stopped working)?
If K+ leak channels stopped working, the RMP would become more positive, as the K+ would build up in the cell via the action of the Na+/K+ pump.
29
What is the most abundant intracellular cation?
he most abundant intracellular cation is potassium.
30
What is the most abundant extracellular cation?
The most abundant extracellular cation is sodium.
31
What cation has the steepest concentration gradient across the plasma membrane?
Calcium has the steepest concentration gradient across the plasma membrane
31
Why is it crucial that there is a 1 milli-osmolar difference in plasma solute concentration between our blood plasma and interstitial fluid (ISF)?
It is crucial to have a difference in plasma solute concentration between our blood plasma and ISF so that water will go into our bloodstream to keep the blood volume and blood pressure up.
32
If a cell at rest is -70 mV, what happens when sodium enters it?
The cell becomes more positive, or depolarized.
32
If a cell at rest is -70 mV, what happens when potassium leaves it?
The cell becomes more negative, or hyperpolarized.
33
If a cell at rest is -70 mV, what happens when chloride enters it?
The cell becomes more negative, or hyperpolarized.
34
If a cell goes from -70 mV to -60 mV, is that a reduction or increase in membrane potential? Why?
Reduction occurs when the cell goes from -70 to -60 millivolts. The cell is becoming less negative, so the polarity is being reduced.
35
What is a depolarization and how can it be achieved?
A depolarization is a decrease in membrane potential; the membrane potential is becoming less negative or more positive. This can occur by a cation entering the cell or an anion leaving the cell.
36
What is a hyperpolarization and how can it be achieved?
Hyperpolarization is an increase in membrane potential. The membrane potential is becoming more negative. This can occur by an anion entering the cell or a cation leaving the cell.
37
What is a repolarization and how does this term relate to depolarization, hyperpolarization and resting membrane potential?
Repolarization is the return to RMP. During an action potential, a neuron becomes depolarized to its maximum amplitude, is repolarized, reaches RMP, and is hyperpolarized shortly after.
38
Graded potentials are also referred to as local potentials. Why are these potentials referred to as “graded” potentials or “local” potentials?
Graded potentials are referred to as graded because the change in membrane potential is directly proportional to the magnitude of the stimulus. In addition to this, graded potentials are referred to as local potentials because they only occur over small regions of the plasma membrane.
39
What does it mean that the change in membrane potential is directly proportional to the size of the stimulus?
If there is a greater stimulus (i.e., more ions entering the cell) there will be a greater change in membrane potential. Therefore, the change in membrane potential is directly proportional to the stimulus.
40
What does it mean that graded potentials are distance-limited?
They are distance-limited because diffusion is distance-limited.
41
For a patient with hyper-neuronal activity (e.g., anxiety or PTSD), what could you inhibit/block to stop their neurons from generating the graded potentials thereby preventing their neurons from firing (i.e., undergoing action potentials)?
You could block receptors in the neuron that, when opened, lead to a depolarization.
42
What does it mean that action potentials are variable in frequency?
The frequency of APs along an axon is a major way in which information in coded. In general, a strong stimulus would have a greater AP frequency than a weak one.
43
What does it mean that action potentials are fixed in magnitude?
The amplitude of an AP is fixed so the amplitude will stay the same regardless of the stimulus strength (all-or-nothing response)
44
Can you compare and contrast the major differences between graded potentials and action potentials?
Graded potentials may be depolarizing or hyperpolarizing depending on the stimuli, whereas APs always initiate with a depolarization. In graded potentials, the amplitude is proportional to the stimuli, whereas in APs, the amplitude is fixed.
44
What is the RMP value of a typical neuron?
The RMP of a typical neuron is -70 mV.
45
What is a threshold potential (TP)?
A threshold potential, which must be achieved in the axon hillock, is the potential at which the neuron will fire an action potential.
46
What is the peak amplitude (in mV) of a typical neuron?
The peak amplitude of a typical neuron is +30 mV.
46
What is a TP value for a typical neuron?
The typical TP of a neuron is -60 mV.
47
Can a cell fire a second AP after the threshold has been met but the TMP has not yet reached +30 millivolts, why or why not?
No, the cell cannot fire a second AP because voltage-gated sodium channels would still be open from the first AP.
48
Can a cell fire a second AP after the threshold has been met, during the relative refractory period, why or why not?
Potentially, yes, but the stimulus would have to be greater than normal as the cell is becoming hyperpolarized during this period.
49
Why is it important that the heart’s AP frequency is about 1 AP per 200 milliseconds versus skeletal muscle, which has a frequency of about 1 AP per 5 milliseconds?
Heart cell AP frequency is markedly decreased, making it impossible for the summation of muscle tension. Therefore, the heart cannot undergo a sustained contraction.
50
Action potential (AP) propagation along a myelinated neuron can be described as a series of successively regenerated APs linked by a series of successively regenerated graded potentials. Starting with a neuron reaching a threshold in the axon hillock, can you provide a more detailed explanation of how an AP arises in the initial segment and then how the signal is propagated along a neuron? Is the same AP that is generated in the initial segment of axon the signal that is propagated along the entire axon?
An AP arises in the initial segment when enough Na+ comes into the cell to bring it from -70 mV to -60mV. Voltage-gated Na+ channels open, and Na+ flows in until the cell reaches +30 mV, where voltage-gated Na+ channels inactivate and voltage-gated K+ channels open. K+ leaves the cell until it reaches -90 mV, where voltage-gated K+ channels close and the cell returns to its normal state. This process repeats itself as AP propagation continues. New APs are generated at each node, so no, the initial AP generated in the initial segment of axon is not the same AP that is propagated along the axon.
51
What is an excitatory postsynaptic potential (EPSP)?
An EPSP is an excitatory stimulus that causes a depolarization in the postsynaptic cell.
51
In general, what types of potentials are EPSPs and IPSPs?
In general, EPSPs and IPSPs are graded potentials.
52
What is an inhibitory postsynaptic potential (IPSP)?
An IPSP is an inhibitory stimulus that causes hyperpolarization in the postsynaptic cell.
53
What type of channels, neurotransmitters, and ions are involved in EPSPs?
The channel involved in an EPSP is ligand-gated. A typical neurotransmitter involved in an EPSP is glutamate, as it is the most abundant excitatory neurotransmitter in the CNS. The ions involved in an EPSP are typically cations, such a Na+.
53
What type of channels, neurotransmitters, and ions are involved in IPSPs?
The channel involved in an IPSP is ligand-gated. A typical neurotransmitter involved in an IPSP is GABA. The ions involved in an IPSP are typically anions, such a Cl-.
54
What are the two regions of the spike initiation zone of a neuron?
The axon hillock and the initial segment of axon.
55
What types of channels are located in each area?
The axon hillock has ligand-gated and mechanically-gated channels. The initial segment has voltage-gated channels.
56
What type of potentials (action or graded) occurs in each area?
The axon hillock undergoes graded potentials and the initial segment of axon undergoes action potentials.
57
Where does an action potential (AP) first occur in a neuron?
The initial segment of the axon.
58
What are the events that lead up to an AP occurring?
If the current reaching the axon hillock changes the membrane potential to -60 mV, current will spread to the initial segment of axon and open voltage-gated Na+ channels at -60 mV. An action potential will then ensue.
59
If a postsynaptic cell synapses with 32 different EPSPs totaling 42 mV, and one IPSP of -32 mV, would the initial segment of the axon fire an AP? Why or why not?
Yes, because spatial summation is occurring, so you have more EPSPs firing than IPSPs thus causing depolarization of the neuron. 42 mV - 32 mV = +10 mV change in voltage. -70 mV (i.e., RMP) + 10 mV = -60 mv (i.e., threshold). An action potential will ensue.
60
What channels are involved in an AP?
Voltage-gated Na+ channels and voltage-gated K+ channels.
61
At which voltages (in mV) do they open, inactivate, and close?
Voltage-gated sodium channels open at -60 mV, inactivate at +30 mV, and fully close at -90 mV. Voltage-gated potassium channels open at +30 mV, and close at -90 mV.
62
During depolarization in an AP, what channel is open and what channel is closed?
During depolarization, voltage-gated sodium channels are open and voltage-gated potassium channels are closed.
63
During a minor hand surgery, a local anesthetic (e.g., lidocaine) is used to numb the patient’s hand. What is the mechanism by which this drug works?
Lidocaine inhibits voltage-gated Na+ channels. Neurons are still active, but the voltage-gated Na+ channels can’t open, so there are no APs and no signal propagation. Therefore, the perception of pain never occurs in the brain.
64
During repolarization in an AP, what channel is open and what channel is closed?
During repolarization, voltage-gated potassium channels are open and voltage-gated sodium channels are inactivated.
65
Where are voltage-gated sodium and potassium channels found in myelinated axons versus unmyelinated?
In myelinated axons, they are found in the nodes of Ranvier. In unmyelinated axons, they occur continuously down the axon.
66
What other structure must be present in the axolemma for AP formation and propagation?
The sodium-potassium pump.
67
What type of conduction occurs in myelinated and unmyelinated nerve fibers, and what are the relative speeds of conduction?
A myelinated axon does saltatory conduction, which propagates action potentials at about 100 meters per second, while an unmyelinated axon does continuous conduction which propagates action potentials at about 1 meter per second.
68
Nerve fibers are much like electrical wires. Current in electrical wires is generated by the flow of electrons. What is flowing in nerve fibers that creates the current of your neurons?
The potassium flowing through the axons creates the current for the neurons.
69
What are the factors that increase the velocity of an action potential?
An increased axon diameter leads to less resistance in the axon, thus increasing velocity of signal travel; myelination (by reducing the number of APs to occur along the axon via saltatory conduction, by insulating the axolemma, and by reducing the charges at the internodes).
70
In a disease like multiple sclerosis (MS) where the immune system attacks myelin-synthesizing cells, which property or properties of neurons would be affected? How is this so?
The conduction and velocity of action potentials would be affected.
In demyelinating disorders like MS, there is damage to the myelin sheath and the axolemma since the immune system attacks oligodendrocytes. Current can leak out of the axon, meaning cations will no longer be able to depolarize the neuron to reach threshold. Thus, the signal can be lost due to insufficient action potential propagation.
71
A friend explains to you that multiple sclerosis (MS) is analogous to having a phone charging cord that has a broken coating and is frayed. He also explains how some electricity from the outlet is lost through these frayed spots on its way to charge the phone. In other words, there is a short in the wire. How do you compare this to a neuron that is damaged due to multiple sclerosis?
This is analogous to MS since the myelin sheath is attacked by the immune system. The myelin sheath acts as the rubber coating to a wire, and when this sheath is attacked by the immune system, it breaks down over time. Without this sheath, information/current in the form of potassium will leak out of our cells, thus creating a ‘short’ in our wires.
72
You are creating a human-like android. You want to create an android that can react, move and think faster than yourself. How would you construct neurons for your android so that they propagate APs with a greater velocity than your own neurons?
Construct the nodes of Ranvier closer together.
73
The internodes of an axon are a defined length. What is the reason they evolved to be the length that they are?
Diffusion is distance-limited. If the nodes were any further apart, the graded potentials in the internodes would be too weak to reach the nodes.
74
The internodes of an axon are a defined length. What would happen if axons were longer?
The AP initiated in the initial segment could not be regenerated along the axon.
75
What kind of potential occurs in a terminal knob?
A graded potential
76
This change in membrane potential in the synaptic terminal leads to the opening of what type of channel?
A change in membrane potential in the synaptic terminal leads to the opening of the voltage-gated calcium channels.
77
In a synapse, we often say that information is communicated from one neuron to the next in the following way: electrical to chemical to electrical. Can you explain what this means in neurophysiological terms?
The presynaptic neuron undergoes action potentials (electrical) and releases neurotransmitters (chemical) that simulate the postsynaptic neuron to undergo action potentials (electrical).
77
What happens as the result of the influx of these ions into the terminal knob?
As a result of the influx of these irons into the terminal knob, synaptic vesicles undergo exocytosis.
78
What is a ligand?
A ligand is an ion/molecule that binds to a receptor.
79
What is an agonist?
An agonist is an ion/molecule that binds to a receptor and enhances that receptor's activity or response.
80
What is an antagonist?
An antagonist is an ion/molecule that binds to a receptor and resists that receptor's activity or response.
81
What is a cholinergic synapse and what is/are the ligand(s) present in this synapse?
A cholinergic synapse contains acetylcholine (ACh), a ligand, and uses this ligand as a neurotransmitter. They may be excitatory or inhibitory. These are abundant in the brain and neuromuscular junctions. Nicotine and muscarine can also act as agonists to their respective receptor.
82
What are the different types of cholinergic receptors?
Nicotinic and muscarinic. Nicotinic receptors are ionotropic, which means they are permissive to ions, and muscarinic receptors are metabotropic, which means they are altered through metabolic changes.
82
Can you provide an example of an excitatory cholinergic synapse and explain how it works?
An example of an excitatory cholinergic synapse is the neuromuscular junction of skeletal muscle. Acetylcholine binds to nicotinic receptors on muscle cells and opens these receptors, allowing Na+ to depolarize the cell.
83
Can you provide an example of an inhibitory cholinergic synapse and explain how it works?
An example of an inhibitory cholinergic synapse is the sinoatrial node on the heart. Acetylcholine binds to muscarinic receptors on the SA node and ultimately decreases cAMP levels, decreasing activity and thus slowing heart rate.
84
What would happen if acetylcholine was not tonically dripped on the heart’s sinoatrial node?
If acetylcholine stopped dripping on the SA node, our heart rate would increase.
85
What would happen if epinephrine (adrenaline) was dripped on the sinoatrial node instead of acetylcholine?
If epinephrine was dripped on the SA node, our heart rate would increase dramatically since it speeds up the rate of APs.
86
Would heart rate (HR) increase or decrease if cAMP levels in the sinoatrial node increased?
If cAMP levels increased in the SA node, heart rate would increase.
87
What is an adrenergic synapse and what is/are the ligand(s) that are used in this synapse?
An adrenergic synapse is a nerve fiber that releases the catecholamines norepinephrine and epinephrine at the synapse. They may be excitatory or inhibitory.
88
What is a catecholamine?
A catecholamine is a hormone that is created by your adrenal glands.
89
What are the different types of adrenergic receptors?
The different types of adrenergic receptors include α1, α2, β1, and β2 adrenergic receptors.
90
What is the Gs signaling pathway?
This is a stimulatory pathway. The neurotransmitter binds to a receptor attached to Gs and activates Gs. This will activate adenylyl cyclase, which converts ATP to cAMP, increasing cellular activity. Protein kinase A will activate, which phosphorylates proteins inside the cell and changes the cell’s metabolism.
91
What is the Gi signaling pathway?
This is an inhibitory pathway. The neurotransmitter binds to a receptor attached to Gi and activates Gi. This will inhibit the activity of adenylyl cyclase, inhibiting production of cAMP. cAMP will be further degraded by cAMP PDE. Protein kinase A will not activate, thus inhibiting protein phosphorylation.
92
What is the Gq signaling pathway?
Activation of Gq activates phospholipase C, which produces diacylglycerol (DAG) and IP3. DAG activates protein kinase C, which phosphorylates proteins inside the cell and changes the cell's metabolism. IP3 increases calcium levels.
93
What is a GABAergic synapse and what is/are the ligand(s) that are used in this synapse?
A GABAergic synapse contains γ-aminobutyric acid (GABA) which is an inhibitory neurotransmitter in the brain. This is exclusively inhibitory.
94
What are the different types of GABAergic receptors?
GABAA and GABAB.
95
Which one is ionotropic, and which is metabotropic? For the receptor that is ionotropic, which ion is the receptor permissible to?
GABAA is ionotropic and GABAB is metabotropic. GABAA is permissible to Cl-.
96
Is diazepam (Valium) an agonist or antagonist, and for which receptor?
Diazepam is an agonist for the GABAA receptor.
97
What is a glutamatergic synapse and what is/are the ligand(s) that are used in this synapse?
A glutamatergic synapse contains the neurotransmitter glutamate. This is exclusively excitatory. It is the most abundant excitatory neurotransmitter in the CNS.
97
What are the different types of glutamatergic receptors?
NMDA and AMPA.
98
How are AMPA and NMDA gated?
AMPA is a ligand-gated and NMDA is a ligand-gated and voltage-gated.
99
Are these receptors metabotropic or ionotropic? For the receptor(s) that is/are ionotropic, which ion is the receptor permissible to?
Both receptors are ionotropic. AMPA is a ligand-gated Na+ channel, and NMDA is a ligand-gated Ca2+ channel.
100
Can you describe how the AMPA and NMDA receptors work together to mediate the postsynaptic response?
Na+ entering AMPA depolarizes the cell, which ejects the Mg2+ ion in the center of the NMDA.
101
Is ketamine an agonist or antagonist, and for which receptor?
Ketamine antagonizes the NMDA receptor
102
What type of channels would you target to treat depression and anxiety?
One mechanism to treat depression would be to inhibit serotonin reuptake. One mechanism to treat anxiety would be to hold GABAA channels open
103
What are the various mechanisms involved in the cessation of a nerve signal?
The presynaptic neuron can stop firing signals; ligands binding to receptors is only temporary, and the signal can stop when ligands unbind; neurotransmitters can diffuse out of synaptic cleft; neurotransmitters can be degraded in the synaptic cleft; presynaptic knob can reabsorb neurotransmitters and their degraded constituents.
104
What is acetylcholinesterase and what is its function?
Acetylcholinesterase is an enzyme that degrades acetylcholine to acetate and choline; this can be resynthesized in the terminal knob.
105
What is the function of MAOIs?
MAO degrades the catecholamines (dopamine, norepinephrine, and epinephrine). MAOIs inhibit the degradation of these catecholamines. By preventing the degradation of chemicals like dopamine, this can be utilized as an antidepressant.
106
What is a selective serotonin reuptake inhibitor (SSRI) and what is it used to treat?
Selective serotonin reuptake receptors reabsorb serotonin back into the presynaptic terminals. SSRI’s treat depression by limiting serotonin reabsorption into presynaptic cells, thereby increasing serotonin levels in the cleft. Thus, more can bind to the postsynaptic receptors.
107
Of the three structural classes of neurons, which are sensory and which are motor?
Special sensory neurons are bipolar, somatic sensory neurons are unipolar, and motor neurons are multipolar.
108
Explain how temporal and spatial summation affect the threshold potential?
Temporal summation is when the same presynaptic neuron is fired repeatedly over time. Spatial summation is when several presynaptic neurons fire simultaneously. In either case, many ions accumulate in the postsynaptic cell. Positive charge pushes K+ towards the axon hillock. Negative charge draws K+ away from the axon hillock
