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Cell Phys > Lec 11: Electrical Signals I > Flashcards

Lec 11: Electrical Signals I Flashcards

1
Q

Cell‐to‐cell communication is absolutely essential for

A

coordinating physiological functions in multicellular organisms

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2
Q

Cell‐to‐cell communication is also used by

A

single celled organisms to signal to other organisms (either “friends” or “foes”)

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3
Q

Several universal mechanisms of cellular regulation because

A

these mechanisms are shared by many types of organisms (since all organisms have a shared evolutionary history)

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4
Q
  • Types of cellular communication: (3)

- Broadly broken down into 2 main classes:

A
  1. ) Direct cell‐to‐cell signaling (via direct contact)
  2. ) Local signaling
  3. ) Long‐distance signaling
  4. ) Chemical signals (Endocrine, paracrine, autocrine)
  5. ) Electrical signals (Action potentials, receptor potentials)
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5
Q

In animals, the _____ ______ utilizes electrical signals to: (3)

A

Nervous System

  1. ) Receive information from either within or outside the body (via various sensory receptors)
    - Sensory or Afferent pathways
    - Photoreceptors, tactile (mechano-) receptors, chemoreceptors (taste, smell, internal), thermoreceptor, electrical receptors
  2. ) Integrate the sensory information [Processing]
    - Central nervous system (CNS): Brain and Spinal Cord
  3. ) Carry out a specific response
    - Motor or Efferent pathways
    - Activation of various effector organs (muscle, glands,…)
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6
Q

Withdrawal Reflex: simple neural circuit (3 Steps)

A
  1. ) Afferent (Sensory) Pathway (input)
  2. ) Integration (Processing)
  3. ) Efferent (Motor) Pathway (output)
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7
Q

2 main categories of cells in the Nervous System:

A
  1. ) Neurons

2. ) Glial cells

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8
Q

Neurons are…
Neurons have the capacity to…
Neurons are the…

A
  • excitable
  • generate and conduct an electrical signal – action potential)
  • functional cells of the NS
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9
Q

3 functions of Neurons:

A
  1. ) Sensory (carry electrical signal to the CNS)
  2. ) Interneurons (mainly in the CNS)
  3. ) Motor (carry the electrical signal away from the CNS to an effector organ)
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10
Q

Glial cells function as…

& 4 types:

A
  • Supporting cells

- Several types: astrocytes, oligodendrocytes, Schwann cells, microglia,…

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11
Q

Review Neuron Structure (Multipolar Neuron)!!!

& name 8 structures of the neuron:

A 
Cell Body (soma)
Dendrites
Axon
Axon Hillock
Axoplasm
Myelin Sheath (nodes of Ranvier)
Terminal Branches
Terminal Bulbs
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12
Q

4 types of neurons:

& how are they different?

A

Bipolar (Interneuron)
Unipolar (Sensory Neuron)
Multipolar (Motoneuron)
Pyrimidial Cell

different anatomically (histologically)

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13
Q

Membrane Potential abbreviations

A

(Vm or Em)

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14
Q

Membrane Potentials are the…

Due to…

A
  • basic Electrochemical Properties of Cells

- an unequal distribution of ions across a cellular membrane each cell will have a Resting Membrane Potential (Vm or Em)

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15
Q

Vm =

A

the quantitative electrical difference across that membrane and is measured as a voltage difference across the membrane (measured in mV, inside with respect to the outside of the cell)

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16
Q

Resting Membrane Potential (Vm) results from…

essentially, is the…

A
  • the separation of charged particles (ions) across the cell membrane.
  • quantitative difference in charge particles inside vs outside.
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17
Q

Due to unequal charge distribution across the membrane:

A

Potential for ions to move across the membrane.

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18
Q

What is potential energy? In a relatable example

A

(a boulder resting on top of hill. It is not moving, but has the “potential energy” to do so if it is nudged off the edge – stored energy)

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19
Q

The membrane potential is…

measured in…

A
  • stored (potential) electrical energy

- millivolts.

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20
Q

Resting Membrane potential in quotes

A

“the potential for electrical current flow”

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21
Q

electrical energy =

A

= electrical current flow = kinetic energy of charge particle movement.

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22
Q

Squids have

A

giant axons to stimulate muscles to contract to forcefully expel water and allow the squid to escape from its predators.

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23
Q

In neurons, the membrane potential is primarily determined by:

A

3 ions (Na+, K+, and Cl-) and negatively charged impermeable ions that reside in the cell

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24
Q

How are resting membrane potentials generated?

Due to combined effects: (4)

A

1.) Diffusion (of substances down a concentration gradient)
2.) Electroneutrality – when ions are in solution they are found in balanced sets (cation and anions), example: NaCl dissociates to Na+ + Cl- in solution
(The charged particles can be separated)
3.) Semipermeable nature of membranes
4.) Na+/K+ ATPase pump

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25
Q

Membrane potentials allow for

A

the generation of electrochemical gradients across the membrane

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26
Q

Electrical potential (voltage) =

A

= the potential tendency for a charged ion to flow across a membrane (potential energy)

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27
Q

Membrane Potential Example (Simplified Donnan Equilibrium)

A

The balance (at equilibrium) between the electrical and chemical differences (electrochemical gradient) across the membrane = equilibrium membrane potential (magnitude of the difference in voltage across the membrane – one side is more positive than the other side)

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28
Q

(Na+/K+ Pump (or ATPase))
1.) ATP transfers…

2.) __ Na+ are pumped out
__ K+ are pumped in

  1. ) This allows…
  2. ) Type of transport?
  3. ) An important aspect of the pump is that…
  4. ) The pump is
  5. ) Which type of ATP pump is this?
A

1.) energy (high energy phosphate bond) to the pump during transport (hence, ATPase).

2.) 3 Na+ are pumped out
2 K+ are pumped in

  1. ) the pump to transport Na+ and K + against their concentration gradients.
  2. ) Direct (Primary) active transport
  3. ) the affinity for Na+ and K+ changes during the cycle.
  4. ) “electrogenic”
  5. ) P class pump
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29
Q

(Steady State (Resting Potential))
Some ion…
Which pumps…
The Na/K pumps helps to…

A
  • leakage occurs (Na+ and K+), countered by the Na/K pump
  • 3 Na+ out and 2 K+ in for every ATP hydrolyzed.
  • “maintain” the resting membrane potential
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30
Q
  • K+ is more concetrated in…
  • so it has a tendency to move…
  • leaving behind…
  • membrane potential becomes more…
A
  • the cytosol
  • out of the cell
  • trapped anions
  • negative
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31
Q
  • Na+ is more concentrated in…
  • so it has a tendency to move…
  • as Na+ enter, they…
  • membrane potential becomes more…
A
  • the outside of the cell
  • into the cell
  • neutralize excess negative charge in the cytosol
  • positive
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32
Q
  • Cl- usually crosses the membrane together with…

- As Cl- enters the cell the membrane potential becomes more…

A
  • a permeable cation (K+)

- negative

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33
Q

Can you quantify the Equilibrium Potential for any individual ion?

A

Yes, by using the equilibrium potential

34
Q

The equilibrium potential for any ion is

A

the electrical potential difference that exactly counterbalances diffusion due to the concentration difference. Sometimes called the reversal potential.

35
Q

In a multi ion system the equilibrium potential is also the

A

voltage difference across the membrane, when the membrane is permeable to only that ion.

36
Q

Nernst Equation function

A

Calculates the equilibrium potential for each individual ion

37
Q

Ex (or Vx) =

A

= equilibrium potential for ion X (voltage)

38
Q

Nernst Equation =

A

Ex = (RT/ZxF)ln([X]o/[X]i)

Ex = equilibrium potential for ion X (voltage)
R = gas constant
T = temperature in kelvin
Zx = ion valence
F = Farraday constant
X = ion
o = outside
i = inside
39
Q

Simplified Nernst Equation =
(fro a monovalent cation @ 37*C)

and its measured in ___ not ____

Thus, for every 10 fold change in the gradient, there is a

A

Ex = (61.5)log([X]o/[X]i)

  • mVolts not Volts
  • 61.5 mV change in E (Equilibrium potential) for that ion
40
Q
  • Multiple ions contribute to the…

- Use the _____ ____ _____ ______ to calculate the steady-state membrane potential

A
  • net resting membrane potential

- GHK (Goldman-Hodgkin-Katz) equation

41
Q 
The GHK (Goldman-Hodgkin-Katz) equation takes into consideration: (2)
& review equation! (screenshot cuz too long lol)
A
  1. ) Multiple ions

2. ) Membrane permeabilities for each ion

42
Q

The resting membrane potential:

Mammals =
Squid Giant Axon =
Skeletal Muscle =

A

Mammals = ~ -70 to -80 mV
Squid Giant Axon = ~ -60 to -70 mV
Skeletal Muscle = ~ -90 mV

43
Q
  • In this state, at rest, the membrane is said to be…
  • This means…
  • At rest, the membrane potential is close to…
A
  • polarized.
  • the cytosolic side is negative with respect to the extracellular side
  • the Eq potentials for K+ and Cl-
44
Q

(Additional Considerations)
- If the membrane permeability for a specific ion is increased, then the…

  • If the membrane permeability for an ion is very high, the…
  • Example:
A
  • membrane potential will ‘move’ towards the Eq potential (Eion) for that ion
  • GHK equation simplifies to the Nernst equation for that ion (the other ions become negligible).
  • Ex: if we dramatically increased the membrane permeability to Na+, then the membrane potential would approach ENa+ (+64 mV) at equilibrium
45
Q

Nernst (Vion) & GHK (Vm) graphical rep

A

screenshot

46
Q

2 Electrical Events in neurons

A
  1. ) Graded Potentials

2. ) Action Potential

47
Q

Graded Potentials =

  • Not…
  • Dissipates with…
A

= A transient electrical signal that occurs due to permeability changes across the membrane, that can be of varying magnitude

  • not “all or none”
  • distance along a membrane (and time)
48
Q

Action Potential =

  • Is…
  • Does it dissipate with distance as it travels along a membrane?
A

= A transient electrical signal that occurs due to permeability changes across a membrane, that has a magnitude that is essentially invariable

  • “All or none”
  • NO
49
Q

Review Graded and Action Potentials graphs

A

screenshot

50
Q

In order for a change in membrane potential to occur (graded or action potential), there needs to be

A

a change in conductance (movement) of some ion (Na+, K+, Cl-, Ca2+) across the membrane.

51
Q

Changes in ion conductance result from

A

changes in permeability for that ion.

52
Q

Generally, ion permeability changes result from

A

the opening or closing of some ion channel.

53
Q

(Ion channels)
The changes in membrane permeability that cause the electrical events (graded potentials and action potentials) result from

A

changes in ion channel conductance (i.e., the open or closed state of an ion channel)

54
Q

Ion channels =

A

Integral membrane proteins (protein complexes) that form ion-conducting pores across the membrane. They are gated.

55
Q

2 Types of gated ion channels:

A
  1. ) Ligand-gated: Will open in response to binding a specific ligand
  2. ) Voltage-gated: Will open in response to a change in membrane potential
56
Q

Ion channels can be studied using

A

patch clamping (whole cell clamping)

57
Q

(Voltage-gated Channels)

  • are specific to…
  • exhibit high
  • due to
  • Channels may have…
  • What allows the channel to open or close?
  • What transiently closes the channel (inactivate) and where?
A
  • ions
  • selectivity (“Selectivity Filter”)
  • amino acid – ion interactions at the pore opening & the size of the central pore
  • multiple gating mechanisms (gates that open and close)
  • Voltage sensor domains
  • Inactivation domains at a second site (multiple gates)
58
Q

(Action Potential (AP))

  • APs are…
  • APs result from…
  • The AP travels…
A
  • rapid (5-6 ms), but large electrical depolarizations & repolarizations of the plasma membrane
  • the opening & closing of voltage-gated Na+ and voltage-gated K+ channels.
  • down the plasma (axonal) membrane via propagation (it essentially reforms at successive regions along the membrane)
59
Q

Each AP occurs in a series of 3 phases:

In order for an AP to occur the membrane potential must reach a threshold voltage (potential)

A
  1. ) Depolarization (“rising”) –opening of Na+ channels
  2. ) Repolarization (“falling”) – opening of K+ channels
  3. ) Hyperpolarization (“undershoot”) - due to prolonged opening of K+ channels
60
Q
  1. ) Depolarization =
    - Becomes…
    - Approaches…
A

= (rising) - opening of Na+ channels

  • positive inside with respect to outside
  • ENa+ (permeability for Na+ is very high)
61
Q
  1. ) Repolarization =
    - Inside…
    - Towards…
A

= (“falling”) – opening of K+ channels

  • returns to negative with respect to outside
  • the EK+ and away from ENa+
62
Q
  1. ) Hyperpolarization =

- Approaches…

A

= (“undershoot”) - due to prolonged opening of K+ channels

- EK+ (Permeability for K+ is very high)

63
Q

The absolute refractory period is caused by

A

Na+ channel inactivation

64
Q

Subthreshold depolarization =

  • At rest, if small positive charges applied to the internal cell membrane (or a small influx of positive ions, like Na+)…
  • Membrane potential will…
  • therefore no
A

= depolarization does not reach threshold

  • the cell will depolarize slightly, but due to the high K+ permeability (conductance), K+ will move out to quickly counter balance the incoming Na+.
  • recover following small depolarizations (sub-threshold graded potentials)
  • no AP
65
Q

What does a Subthreshold depolarization look like?

A

a little bump where depolarization should start

66
Q

If a depolarization reaches a specific threshold voltage (~ -40 mV; usually about 15-25 mV higher than the resting potential), then

A

many voltage-gated Na+ channels will open

67
Q

(Depolarization/Rising Phase)
1.) Depolarization causes…

  1. ) and also causes a…
  2. ) As Na+ enters via the open channels, more…
  3. ) The membrane potential never…
  4. ) At this time (peak of the AP), the channels become…
  5. ) Resulting in…
A
  1. ) the voltage gated Na+ channels to open
  2. ) Huge increase in Na+ permeability (bringing positive charge into the cell)
  3. ) channels (in that region of membrane) are stimulated to open, positive-feedback (Hodgkin Cycle) → large depolarization
  4. ) quite reaches the ENa+, because other channels (K+) are opened before it reaches ENa+
  5. ) inactivated for several milliseconds
  6. ) Absolute refractory period – no stimulus is capable of causing another action potential (because the Na+ channels can’t be opened – they are inactivated)
68
Q

Absolute refractory period =

A

= no stimulus is capable of causing another action potential (because the Na+ channels can’t be opened – they are inactivated)

69
Q

3 main states of Na+ channel:

A

1.) Closed (rest)
2.) Open (depolarization)
3.) Inactivated (end of depolarization and during repolarization)
Changes from Inactivated to Closed (end of repolarization)

70
Q

2 main gates of Na+ channel:

A
  1. ) Activation gate

2. ) Inactivation gate

71
Q

Activation gate details: (4)

A
  • Closed at rest
  • Open during depolarization
  • Open during repolarization
  • Closes at end of repolarization
72
Q

Inactivation gate details: (4)

A
  • Open at rest
  • Open during depolarization
  • Closed during repolarization (absolute refractory period)
  • Opens during end of repolarization and beginning of hyperpolarization (relative refractory period)
73
Q

Memorize 2 main gates of Na+ channel table

A

screenshot

74
Q

What causes the Na+ channel gates to open and close? (2)

A
  1. ) Initial depolarization to threshold causes:
    - Activation gate to open quickly (channel is now open)
    - Inactivation gate to swing closed slowly (~0.5 ms delay) (channel is now inactivated). Thus, for a very short time, both gates are open and Na+ can flow into the cell
  2. ) Repolarization to ~ -40 to -80mV causes both gates to reset (“deinactivation”)
    - Activation gate closes first
    - Inactivation gate opens second
    - Thus, the possibility for another AP is restored
75
Q

(During Repolarization)

  • Na+ channels are…
  • Leading to…
  • Voltage-gated K+ channels are…
  • Efflux of…
A
  • inactivated (not just closed)
  • Absolute refractory period
  • opened
  • K+ repolarizes the membrane towards the resting membrane potential
76
Q

(During Repolarization)
What causes the Voltage-gated K+ channels to open?

Achieve an open state at…

A
  • Depolarization (but they open very slowly)

- ~ +30 mV

77
Q

(Hyperpolarization)

  • Occurs due to…
  • The membrane approaches…
  • Once the membrane approaches ~ -40 to -80 mV…
  • This results in…
  • Eventually…
A
  • the elevated K+ conductance
  • the EK+, which is below (more negative than) the resting potential (“undershoot”)
  • some Na+ channels are returned to their resting state (“deinactivated”)
  • Relative refractory period: An AP can occur, but it is more difficult due to the elevated K+ conductance
  • K+ channels eventually close
78
Q

(Return to resting membrane potential)
1.) Does not require…

  1. ) Only involves…
  2. ) Leaking of…
  3. ) Although there are large changes in membrane potential during the AP, there are only…
  4. ) In fact, even if the Na/K pump is completely inhibited with the inhibitor…
A
  1. ) the Na/K pump
  2. ) ionic movements and changes in gating status (i.e., permeability) of the voltage-gated Na+ and K+ channels
  3. ) some Na+ into the cell
  4. ) negligible changes in total ion concentrations inside and outside of the cell.
  5. ) ouabain, successive APs can continue for prolonged periods.
79
Q

Review Changes in membrane conductance during the AP graph

A

plzzzzz screenshot

80
Q
  • An AP is what kind of event?
  • If threshold is reached, then…
  • But…
A
  • an “all or nothing” event
  • an AP will fire
  • not during the absolute refractory period
81
Q
  • The refractory period prevents
  • Therefore…
  • Thus Channels are either…
A
  • APs from occurring too close together in time
  • APs cannot “summate” (cannot add together)
  • open or closed/inactivated (“all or nothing”)
82
Q
  • An Action Potential is essentially a
  • Thus, the electrical signal (AP) is moved from
  • The electrical signal (AP) allows for
A
  • signal that is carried from one part of a neuron to another (along the axon).
  • one place to another along the axon.
  • communication within the CNS and for communication between the CNS and the effector organs and sensory organs

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