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Membrane Physiology Flashcards

1
Q

Define the “reference state” of medicine

A

Physiology is the normal condition: the HOMEOSTATIC CONDITION

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2
Q

Why was Claude Bernard defined the ‘father of physiology’?

A

He was the first to describe the relationship between environments in the body:

  • milieu exterieur
  • milieu interieur: EXTRACELLULAR FLUID
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3
Q

What is HOMEOSTASIS?

A

The control of vital parameters through Negative-feedback mechanism.
It is a dynamic equilibrium

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4
Q

Which are the parameters for homeostasis?

A
  • SET-POINT: Desired value
  • PRESENT VALUE
  • ERROR: Difference between present value and set-point
  • PERTURBATION: Stimulus that moves present value from set point
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5
Q

What is POSITIVE FEEDBACK?

A

Intensification of the change in body’s physiological condition

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6
Q

What is NEGATIVE FEEDBACK?

A

Any response which oppose the source and direction of perturbation

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7
Q

What is SELECTIVE PERMEABILITY?

A

The property of biological membranes that allows only certain molecules to enter or exit the cell

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8
Q

Which are the type of transport?

A

SIMPLE DIFFUSION, PASSIVE TRANSPORT and ACTIVE TRANSPORT

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9
Q

FICK’S LAW

A

Flux= (D x A x C)/(Dx)

The flux of simple diffusion is proportional to surface area and gradient concentration, and inversely proportional to thickness of the membrane.
For biological membrane we have to take into account Permeability:
Flux= P x A x C

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10
Q

TRUE OR FALSE
The diffusion of a molecule across the plasma membrane is:
-Inversely proportional to membrane surface
-Requires consumption of energy
-Inversely proportional to membrane thickness
-Depends on its concentration gradient
-Inversely proportional to membrane permeability
-Faster for an ion than for water because ions are smaller

A
  • F
  • F
  • T
  • T
  • F
  • F
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11
Q

Characteristics of channels?

A
  • Open on both sides of membrane
  • No binding site for the transported molecule
  • High selectivity, only for a certain molecule or generally for cations/ions
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12
Q

What is the electrochemical gradient?

A

The combination of chemical gradient, which is based on the concentration of ions on both sides of the membrane, and electrical gradient, which is based on the gradient of charges across the membrane.
Charged ions are usually driven by the chemical one.

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13
Q

What is the ION FLUX?

A

The diffusion of ions according to electrochemical gradient.

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14
Q

Properties of channels

A
  • GATING: Governs the transition from a closed to an open state and viceversa
  • SELECTIVITY
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15
Q

What are the different kinds of gating?

A
  • VOLTAGE GATED channels
  • LIGAND-GATED channels
  • MECHANICAL STRESS channels
  • TEMPERATURE GATED channels
  • LIGHT-GATED channels
  • NON-GATED channels (leaky channels)
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16
Q

How are non-gated channels different from pores?

A

Non-gated channels only allow the passage of ions, while pores do not allow passage of ions

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17
Q

What are the characteristics of carriers?

A
  • Not open simultaneously on both sides
  • Has a binding site for the transported molecule
  • The transported molecule changes the conformation of the carrier binding to it
  • Highly selective
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18
Q

What are the two type of Active transport?

A
  • PRIMARY ACTIVE TRANSPORT, which directly use the energy obtained from ATP hydrolysis, also called Pumps because move the molecule against gradient
  • SECONDARY ACTIVE TRANSPORT, which doesn’t directly use the energy from ATP hydrolysis but depends on the primary active transport
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19
Q

What are different kinds of active transport?

A
  • UNIPORT

- COTRANSPORT, divided in SYMPORT and ANTIPORT

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20
Q

Which is an antagonist of the sodium potassium pump?

A

OUABAIN, which causes the pump to remain stuck and become non-functional. Causes the accumulation of potassium outside the cell and of sodium inside the cell.
Also DIGITOXIN and DIGOXIN.

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21
Q

How can we classify secondary active transport?

A
  • Based on whether they depend on Na+ as the motor ion or not
  • Based on the transported molecule which can be organic or an ion.
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22
Q

Define SATURATION

A

Saturation is when all the binding sites of transporters are occupied by the molecules. It is the relationship between transport speed and concentration gradient.

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23
Q

TRUE OR FALSE

Transporters are always faster than simple diffusion

A

-T

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24
Q

What is Vmax of transport?

A

The amount of time it takes the molecule to change the carrier state conformation, specific for each carrier and depends on saturation.

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25
What is the binding constant Km?
The concentration of molecule when the transport rate is at half Vmax
26
How do COMPETITIVE and NON-COMPETITIVE INHIBITOR change the saturation?
- Competitive inhibitors change the Km, therefore we need a higher concentration of substrate to reach the Vmax - Non-competitive inhibitors change the Vmax.
27
How is the membrane potential maintained?
Through the difference in net charges across the external and internal sides of the membrane
28
What is the formula for Vm?
Vm= Vin -Vout
29
What determines charges separation on the sides of the membrane?
The three main determinants are SELECTIVE PERMEABILITY, ION CHANNELS (which move along electrochemical gradient) and PUMPS (which restore the gradient dissipated by channels)
30
How are charges distributed on the sides of the membrane?
There is a relative excess of positive charges outside and negative charges inside
31
Depolarization and Hyperpolarization
- DEPOLARIZATION: A reduction of charges separation | - HYPERPOLARIZATION: An increase of charges separation
32
What is Nernst equation for?
Nernst equation is for the membrane potential for a membrane permeable only for one ion.
33
Nernst’s equation
Ek= ((RT)/(zF))ln((Kout)/(Kin))
34
Is the membrane potential of the cell the same value of Ek calculated by Nernst’s equation?
No, it is similar, but not exactly the same; it is slightly more positive, demonstrating the contribution of other ions, specifically sodium ones
35
Goldman’s Equation
See on book for verification
36
MICHAELIS-MENTEN EQUATION
V=Vmax((S)/(Km + S))
37
Michaelis-Menten Equation with Competitive and Non-competitive inhibitors
-See on the book to verify
38
Which are the three main ions for membrane potential?
SODIUM, POTASSIUM and CHLORINE
39
Why doesn’t the resting potential reach zero, even with leaky potassium channels?
Because of the sodium potassium pump which contributes to maintaining membrane potential
40
What is the distinctive feature of excitable cells?
They can communicate with other cells through manipulation of membrane potential
41
What is the signal transmitted by excitable cells by the change in membrane potential?
ACTION POTENTIAL
42
What is the membrane potential of a resting neuron?
Roughly 70 mV
43
How can we produce an action potential?
Through a strong enough depolarization which can surpass the threshold value, which is roughly -50 mV
44
TRUE or FALSE - The amplitude of the action potential is proportional to amplitude of stimulus - The amplitude of a graded/electrotonic potential is proportional to the stimulus
- False; after they surpass threshold value, it doesn’t matter the amount of stimulus; because it depends on the characteristics of sodium channels and concentration. - True.
45
Which ions mainly cause action potential?
Sodium and potassium with their channels
46
Describe the steps after the threshold value is surpassed and action potential is activated
The first step is the opening of the sodium voltage gated channels, after reaching -50 mV; this causes an inflow of sodium in the cell and a further depolarization. Then the sodium channels close, which causes the cell to lack sodium conductance, and potassium ones open in delay, allowing positive charges to flow out of the cell, causing a sudden hyperpolarization towards its own value of -97mV. Finally then the potassium channels shut, causing the cell to go back to the membrane resting potential.
47
Connect the toxin and the channels it blocks - TETRODOTOXIN -SODIUM - SAXITOXIN - TETRAETHYLAMMONIUM -POTASSIUM - OUBAIN -CALCIUM
- TETRODOTOXIN: Sodium - SAXITOXIN: Sodium - TETRAETHYLAMMONIUM: Potassium - OUBAIN: Sodium and Calcium
48
What is the difference in action between tetrodotoxin and saxitoxin?
Tetrodotoxin causes an irreversible block of sodium channels; Saxitoxin causes a reversible block.
49
What are the properties of Action potential in neurons?
- Need for a TRIGGER: depolarization - Need to surpass the THRESHOLD POTENTIAL - LOCATION of the action potential generations: Axon hillock in efferent neurons - ALL or NOTHING: once you pass the threshold value all stimuli are the same, if they do not reach the value the action potential is not generated
50
What is the refractory period?
The period during which, after peak action potential, sodium channels shut temporarily
51
What is the difference between ABSOLUTE REFRACTORY PERIOD and RELATIVE REFRACTORY PERIOD?
- Absolute refractory period begins right after the peak of the action potential and shuts and inactivates all sodium channels; therefore even with a further depolarization, we cannot get another action potential - Relative refractory period begins when the potassium channels are halfway through closing, and some sodium channels start being close but active again; therefore we can reach another action potential, but the depolarization needs to be much stronger since some channels are still deactivated. In addition it won’t reach its maximum value for the same reason.
52
What is ANTEROGRADE SIGNALING?
The ability of the action potential to propagate its signal in only one direction, away from the nucleus, in order to induce synaptic transmission. The presence of a refractory period impedes the conduction of the action potential in the opposite way by hindering the back diffusion of depolarization.
53
What is the MAXIMUM FIRING FREQUENCY?
It is the action potential frequency of a neuron, defined by the absolute refractory period. The stronger the stimulus the faster the AP frequency.
54
What is the function of the MYELIN SHEATH?
- Reduces leakiness of the axon - Increases the speed of conduction through SALTATORY PROPAGATION - Protection from damage and inflammation
55
Which are faster, myelinated axons or unmyelinated axons? Why?
-Myelinated axons; to avoid leaking ions and loosing amplitude during AP propagation, unmyelinated axons have to activate every spot on the membrane which takes time. Myelinated axons, thanks to insulation provided by myelin, only have to activate an AP on the nodes of Ranvier, resulting faster thanks to Saltatory propagation.
56
What are some strategies to improve conduction properties of nerve fibers?
- Myelinating the fibers (seen in mammals) | - Increasing the axon’s diameter (seen in squids for example)
57
TRUE or FALSE - Membranes act like CAPACITORS - Membranes act like RESISTORS - Membranes cannot form RC CIRCUITS
- TRUE: An insulated bilayer with accumulated ions and charges on the two sides - TRUE: Specifically channels, as they let ions flow in and out of the cell, generating a current and its respective resistance - FALSE: The membrane circuit is exactly an RC circuit
58
Cell Capacitance Formula
C= (e x A)/d | Measured in Farads
59
Resistance formula
R= (ro x L)/A
60
What is time constant and its formula?
Tau is the time it takes for the cell to respond to the current by increasing V of 63% -Tau= R x C
61
What is the length constant and its formula?
The length constant lambda is the lenght from the initial point of stimulus it takes to lower the Vm to 37% of initial potential -Lambda = radice quadrata di (Rm/Ra)
62
How is the perfect neuron in relation to tau and lambda?
It has an infinitely high lambda, and a very small tau

Physiology (2 decks)

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