Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
78 Cards in this Set
- Front
- Back
|
Define afferent neuron, interneuron, efferent neuron, neuronal circuit.
|
Afferent: axon of sensory neuron, conducts signal to brain; Interneuron: most numerous, lie w/in CNS and located between neurons; Efferent: causes the effector to act, completing the Neuronal Circuit.
|
|
|
What makes up the CNS?
|
- brain and spine |
|
|
What are ganglia?
|
group of soma that control a local part of the body |
|
|
What are glial cells? Name two types.
|
Glial cells act as support for neurons. Oligodendrocytes (CNS) and Schwann cells (PNS) wrap axon in myelin sheath |
|
|
Starting from a receptor, describe how signal is passed onto the next neuron. |
A signal causes graded potential in the first section of the sensory receptor, this graded potential spreads passively to the soma; if it is high enough, it will cause an all-or-none action potential through the axon. At the terminal, NT are released, causing another graded potential to the next neuron. |
|
|
What is resting potential or Vrest?
|
- cytoplasm has uniform potential |
|
|
Define E=V/d
|
The strength of an electric field (E) is voltage divided by the membrane thickness (d) in metres
|
|
|
By convention, what direction does current flow?
|
Positive to negative (flow of cations) |
|
|
What is hyperpolarization? |
When cytosol becomes even more negative due to the exit of more cations or addition of anions (current exits) |
|
|
What is depolarization?
|
current adds a positive charge to cytosol; this may cause VG ion channels to open and illicit an AP |
|
|
What are the two passive electrical properties of membranes?
|
Capacitance and conductance |
|
|
How does the membrane have capacitance and conductance?
|
The cytosol and ECF are saline solutions and act like conductors, separated by the membrane (insulator). This separation allows for a capacitor to form. The ion channels allow ions to travel through membrane, thus, conductance. |
|
|
Define electrical resistance (R) and conductance (g). How are they related? |
They explain how readily charges move in circuit. R=1/g; the lower the R, the greater the g, the better charges can move
|
|
|
What is Ohm's Law?
|
V=IR; where V is change in voltage across membrane, I is the current across membrane, R is the resistance of the membrane |
|
|
What is input resistance? |
The total resistance encountered by a current. The more surface area, the more channels (conductance), the less the resistance; also the more dense the channels, the less resistance. |
|
|
What is the formula gx = Ix/emfx
|
gx is the membrane conductance for ion X. Ix is the current of ionx and emfx is the electromotive force active on X. When no channels or no ions are present, Ix= 0 and automatically, gx=0. |
|
|
How do capacitors work?
|
If we add voltage across membrane, the excess cations go towards the cathode (negative side). Despite the space, they interact with the other plate, causing the cations on the other side to be repelled and anions to accumulate. The movement of ions causes a current. |
|
|
What factors affect capacitance? |
1) The thickness of the insulator 2) The dielectric constant: the ability of insulating material to store charges |
|
|
How does current move across a membrane acting as a capacitor? |
Initially, current moves easier through capacitor (so Ic is high); eventually, the voltage in capacitor opposes anymore charge accumulation and current is forced to travel through the channels (which act like resistors), so Ir now increases and Ic decreases. Ir + Ic = Itotal |
|
|
What does Vt = Vinf (1-e^[-t/RC]) mean? |
|
|
|
What factors affect electrochemical potentials?
|
1) The concentration of an ion differ across membranes 2) Ion channels are selectively permeable to ions. |
|
|
Scenario: You have two solutions: 0.1M KCl and 0.01M KCl, separated by a selectively-permeable membrane for K+. What happens?
|
Because of the concentration difference, K+ and Cl- will want to move from compartment 1 to 2. However, it is only K+ that can go to 2. Eventually, K+ starts building up in 2 and incoming K+ get repelled. The Cl- buildup in 1 also attracts K+ back. The electromotive force wants K+ to go back to 1. A balance between the emf and the concentration gradient eventually occurs and equilibrium potential is achieved. |
|
|
What is steady state? Provide a scenario as an example.
|
We have the same scenario as previous question but we have a battery that balances the electrochemical potential of K+ by making an artificial emf and equilibrium potential. This state of balance is the steady state. |
|
|
What voltage clamping?
|
An experimental method where voltage is held constant. |
|
|
How does voltage clamping work? |
|
|
|
What is patch clamping?
|
- we use needle and apply gentle suction to create a seal around one ion channel - we can study the current passing through that one specific channel - the sum of current of all channels is equal to the value in voltage clamping |
|
|
What are the structural classes of neurons?
|
2) Bipolar: has a dendrite and axon attached to soma 3) Multipolar: has many dendrites and one axon attached |
|
|
What are the fast NTs?
|
fast, excitatory: ACh, glutamate fast, inhibitory: GABA, glycine |
|
|
What are the slow NTs?
|
slow, excitatory: NE, dopamine, serotonin slow, inhibitory: NE, serotonin, ACh, glutamate, GABA |
|
|
What are NTs? Neurohormones? Neuropeptides? Neuromodulators?
|
NTs: affect synapses; Neurohormones: get released in the blood Neuropeptides: most abundant; seen as neurochemical in brain/gut and acts as hormone in blood; Neuromodulators: affect close-by neurons |
|
|
What are the units of capacitance?
|
Farad (F)
|
|
|
What are the units of electrical charge (Q)?
|
Coulombs (Q); 1C is the charge of a current per second (1C=A/sec); the excess charge on capacitor of one farad charged to potential difference of 1V (1C=1Fx1V) |
|
|
In a series resistor, how is sum of resistance found?
|
Rtotal = R1 + R2 |
|
|
In parallel resistor, how do you calculate sum of resistance?
|
- the ion channels in a membrane are in parallel; so the more channels, the less input resistance |
|
|
What is the Faraday (F)?
|
The charge of one mole of electron. 1 Faraday = 96,500C/mol |
|
|
When does the capacitor stop charging?
|
When the potential different between plates equals emf or voltage of the battery |
|
|
What principles does a resting cell obey?
|
Principle of Equimolality: the cocn of osmotically-active particles on both sides should be equal. Principle of Neutrality: the concentration of extracellular anions equal extracellular cations. Same intracellularly. |
|
|
If the principles are observed by a resting cell, why is resting potential not 0V?
|
- small concentration imbalance has great effects |
|
|
In mmol/L, what are the concentrations of Na+ inside and outside the cell?
|
Inside: 15 mmol/L |
|
|
In mmol/L, what are the concentrations of K+ inside and outside the cell?
|
Inside: 150 mmol/L |
|
|
In mmol/L, what are the concentrations of Cl- inside and outside the cell?
|
Inside: 7 mmol/L |
|
|
Study Nernst Equation.
|
OK. It is used to calculate equilibrium potential for one ion (Eion). |
|
|
Study Goldman Equation.
|
- calculates steady state |
|
|
How do you calculate Vm?
|
Vm = Vin-Vout, with Vout=0mV. |
|
|
Scenario: You have 0.15M NaCl and 0.15M KCl separated by Na/K selective membrane. What happens?
|
Cl- concentration balanced on both sides (it can't diffuse also). The K+ and Na+ both diffuse to other side until they balance. In the end, both sides have 0.15MCl, 0.075M K+, and 0.075M Na+. |
|
|
How many osmol/L are there in 0.15M Cl-, 0.15M KCl, and 0.15M NaCl?
|
In 0.15M Cl-, there are 0.15osmol/L. In the 0.15M NaCl and KCl, they both have 0.15osmol Na or K/L + 0.15osmol Cl/L = 0.3osmol/L |
|
|
Does the cell ever equilibriate with the ECF?
|
No. The Na+/K+ pump maintains steady state.
|
|
|
In a cell with only K+ channels, what does it mean when Vm = EK?
|
There is no net flow in or out. The concentration gradient is balanced by the electric gradient.
|
|
|
If EK=-88mV. What happens when Vm=-100mV?
|
- the negative charge wants to keep K+ in - net flow is inwards. |
|
|
If EK=-88mV. What happens when Vm=-12mV?
|
- the negative charge wants to keep K+ in - however, knowing the EK, this negative charge must be relatively weak and is overpowered by the concn gradient - net flow in out. - RECALL: only in the EK, does the direction of flow change. |
|
|
How do you calculate electromotive force?
|
emf=Vm-Eion |
|
|
How does the Na+ channel physically work?
|
- at depolarization, it opens - when K+ channels open, it is opened and inactivated. |
|
|
How does the K+ channel physically work?
|
- closed at rest; open at depolarization |
|
|
What factors affect Vm?
|
1) Action potential is the rapid reversal of Vm 2) The most permeable ion's Eion affects Vm the most. 3) Ion channels dictate permeability. |
|
|
If you hit the funny bone in the middle of the axon, where does the signal travel?
|
- signal will run in both directions - if large enough, may cause NT release - the one going to the soma dies down |
|
|
Why is active transport used in the membrane?
|
- if no pump (3 Na+ out, 3K+ in), Na+ will accumulate inside as cocn gradient favours it and Nernst equation says it is favourite electicaly also - K+ will leak out due to Na+ repulsion - the Vm is highly influenced by permeability of K+. If more K+ outside, Vm decreases to 0. - ensures we have a resting potential, from which we can generate an AP |
|
|
In an action potential curve, what is overshoot?
|
Anytime the Vm goes above 0 (turns positive)
|
|
|
What is accommodation?
|
When you continuously apply sub-threshold depolarization, the threshold keeps on increasing until such time, it is so high you can't reach it. |
|
|
What are the two ways neurons accommodate?
|
- Tonic: causes continuous firing of AP throughout stimuli; low accommodation |
|
|
What is adaptation?
|
In the tonic response, the AP start weakening eventually and the less frequent they become. The cell is adapting to the stimulus. |
|
|
What does Ix = gx(Vm-Ex) mean? |
- at AP, the conductance has greater effect as cocn of ions don't change much |
|
|
Describe Hodgkin's experiment.
|
He used voltage-clamping on a squid axon. With Vm constant, Ex known, Ix measured, gx can be calculated using Ix = gx(Vm-Eion) |
|
|
What is the effect of Tetradotoxin (TTX)? |
TTX blocks Na+ channels (no current for Na+) |
|
|
What factors affect permeability?
|
- size, charge, ease of dehydration (ions only pass when water shell around them can be replaced by functional group in the pores) |
|
|
What is Hodgkin's Cycle?
|
- interrupted when channels are inactivated or when Vm cannot be changed (no depolarization due to voltage clamping) |
|
|
In an AP, what does the curve of gK look like versus gNa?
|
gK starts increasing when gNa starts decreasing; then decreases after hyperpolarization and going close to EK |
|
|
What happens in a relative refractory period?
|
- some K+ channels still open, opposing the work of Na+ channels |
|
|
What's the structure of VG-K+ channels?
|
- S4 senses voltage |
|
|
What is the structure of VG-Na+ channels?
|
An alpha subunit made of 4 domains; surrounds a pore and has beta subunits associated
|
|
|
What is the function of Ca2+ channels? What activates them
|
They are activated by depolarization caused by Na+. They further polarize the membrane, helping in AP propagation. Ca2+ act as signals (ex. releasing NT) |
|
|
What happens once a lot of Ca2+ (excess) are inside?
|
- they activated Ca2+-activated K+ channels, causing K+ to exit and charges to balance out |
|
|
What is the effect of TEA?
|
Extra and intracellularly binds VG-K+ channels, preventing rapid repolarization (makes repolarization take longer) |
|
|
In terms of INa and IK, when is threshold reached?
|
When the current of Na+ in overcome current of K+ out |
|
|
At rest, why is gK higher than gNa? |
Leak channels |
|
|
What does the EMF mean/interpret?
|
The eagerness of current to travel a direction. |
|
|
Passive vs. Active Conduction
|
Active: depends on VG-ion channels allowing ions through membranes |
|
|
What do positive, negative, and zero electromotive force mean for a cation such as Na+/K+?
|
-: influx in 0: equilibrium potential, no flux |
|
|
What do positive, negative, and zero electromotive force mean for an anion such as Cl-/HCO3-?
|
-: efflux out 0: equilibrium potential |
