01 - Resting Memb Pot

Question 0

two types of signaling that nerves engage in?

Answer 0

electrical and chemical

Question 1

Define the Resting Membrane Potential

Answer 1

separation of charge between inside and outside of cell.

Question 2

chemical signals of neurons allow what types of functions?

Answer 2

plasticity and integration at synapses

Question 3

electrical signals allow neurons allow what types of functions?

Answer 3

rapid signaling, long-range signaling.

Question 4

what is the voltage of the inside of the cell relative to a saline bath outside of it?

Answer 4

it is 90mV lower than a saline bath: thus RMP (or charge separation) is -90mV

Question 5

the inside of the cell is hyper- or de-polarized with respect to the outside of the cell?

Answer 5

hyper

Question 6

a reduction in charge separation is a depolarization or a hyperpolarization?

Answer 6

depolarization

Question 7

Ohm’s Law?

Answer 7

V = IR
voltage = current * resistance

Question 8

Electrical conductance is represented by what letter? what does it mean?

Answer 8

Conductance = G.

measures the ease of flow of current between two points. in cell, = transmembrane proteins.

Question 9

Resistance means what? what letter? in cell what provides resistance?

Answer 9

reciprocal of conductance. R. represented by transmembrane proteins.

Question 10

capacitance means what? what letter? represented by what in the cell?

Answer 10

means membrane’s ability to separate and store charge. letter = C. represented by lipid bilayer.

Question 11

what types of signaling occur at the synapse?

Answer 11

electrical signal; chemical intermediary to bridge the synapse.

Question 12

what allows the nervous system to do work?

Answer 12

the dissipation of the potential difference (electrical charge going down its gradient).

Question 13

transmembrane channels act as two things using the model of the electrical system - what are they?

Answer 13

both resistors and conductors: because they allow charge to dissipate, but not infinitely (hence offer some resistance).

Question 14

name the 4 classes of ion channels

Answer 14

1. voltage-gated
2. leak channels
3. ligand-gated
4. mechanosensory

Question 15

describe voltage-gated channels

Answer 15

opened by a change in the membrane potential and are critical for the generation of action potentials, allow calcium influx into presynaptic nerve terminals (essential for neurotransmitter release)

Question 16

describe leaky ion channels

Answer 16

have a high probability of being open in the absence of any stimulus, critical for the generation of RMP.
selective for one type of ion.

Question 17

describe ligand-gated ion channels

Answer 17

fundamental mechanism for synaptic transmission. ligand causes conformational change.

Question 18

describe mechanosensory ion channels

Answer 18

channels that give rise to signals from Pacinian corpuscles (aka lamellar corpuscles, sensitive to vibration and pressure), channels found in nerve endings in skin. responsible for sensitivity to pain and pressure.

Question 19

what is the utility of Patch Clamp Recording?

Answer 19

can grab a tiny bit of membrane at the circular end of a glass probe and record the activity of a single membrane protein, in real time. can see how current flows as the protein opens and closes.

Question 20

Convention is to depict an inward flux of + ions into a cell as an upward or downward line on a trace?

Answer 20

inward = down. depicts OPEN channel, entrance of + ions.

Question 21

Describe the generation of the resting membrane potential.

Answer 21

• begin with equal voltage on both sides of membrane
• also begin with unequal concentration of specific ions (ex: K)
• add leak channels; concentration gradient will force out K
• anions cannot follow since they are too big for channels
• K won’t go far since it is attracted to – inside cell
• have buildup of ++ outside cell, – inside cell
• at a certain concentration, electric gradient will oppose concentration gradient and we will have equilibrium
• the voltage at which the system is at equilibrium is described by the Nernst eqn

Question 22

Recall the Nernst equation. Under what conditions might it change?

Answer 22

E(ion) = 61 log [ion(out)/ion(in)]

• If experiment is done at room temp, substitute 58 for 61 (term that includes temp).
• if describing the equilib potential for an ANION, put out/in rather than in/out.

Question 23

what is the definition of equilibrium potential for a species (E)?

Answer 23

the voltage at which the ion is in equilibrium (conc gradient is equal/opposite to electrical gradient)

Question 24

In what cells do we have to consider Cl? in what cells can we ignore Cl?

Answer 24

consider in muscle cells.

ignore in neurons (it passively follows Na)

Question 25

what determines the overall RMP in neurons?

Answer 25

Ek (the equilibrium potential for K).
For most neurons, can ignore the contribution of ECl
Cannot ignore the contribution of ENa, but there are few channels open at rest (very small permeability at rest -> very limited effect).

Question 26

At rest for the overall cell, are K and Na at equilibrium potential?

Answer 26

No, neither. At rest/steady state, the currents of Na and K are equal and opposite. (ie, no net current). This slow leak will eventually dissipate the concentration gradients needed to generate RMP.

Question 27

How does the cell avoid a gradual decline in RMP?

Answer 27

Na/K ATPase to reverse the slow leak of K out and Na in. Pumps 2 K in and 3 Na out.

Question 28

how much of the brain’s energy is used to power the Na/K ATPases?

Answer 28

20-40%. and 70% of energy for an active neuron.

Question 29

define ouabain.

Answer 29

poisonous cardiac glycoside. blocks function of the Na/K ATPase by preventing K from binding.
Yields increased Na inside cell, which causes Na/Ca exchanger to reverse and import Ca.
Result: cell is easier to activate because threshold is already partially reached.

Question 30

At Vrest, is the neuron slightly more or less depolarized than Ek?

Answer 30

slightly more, due to contribution of ENa.

Question 31

describe hyperkalemic periodic paralysis (HYPP)

Answer 31

• mutation in sodium channels, makes them slightly more open than usual.
• if ingestion of K or exercise (both -> extracellular K increase), cell depolarizes (RMP decreases), and open Na channel promotes further K efflux and further depolarization.
• leads to momentary paralysis due to inability to respond to neuro muscular synaptic transmission.

Question 32

Rapid-onset dystonia Parkinsonism: what is the defect?

Answer 32

loss of function mutation in one subunit of the Na/K ATPase.

Question 33

Channelopathy: Myotonia Congenita. Describe what the dysfunction is and what the clinical symptoms are

Answer 33

problem with subunit of Cl channel in skeletal muscle. less chloride coming into muscle fiber to repolarize it after it was depolarized. (usually Cl- counteracts the K that rushes out).
presentation: delayed relaxation of skeletal muscle -> bursts of paralysis.

Question 34

cardiac glysosides like ouabain are therapy for what condition?

Answer 34

therapy for people who need a greater cardiac contraction.