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111A Lecture 1
January 5, 09
38
Physiology
Undergraduate 3
01/11/2009

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Term
The membrane is a highly selective filter that...
Definition
1. maintains unequal concentrations of ions
2. allows nutrients to enter and waste the cell
Term
What does a membrane consist of?
Definition
1. phosholipid bilayer
2. proteins
Term
What are the three different classes of phospholipids?
Definition
1. phosphoglycerides
2. sphingolipids
3. sterols
Term
What is a phosphoglyceride?
Definition
Amphipatic (polar head, apolar tail) molecule with a glyceride backbone
Term
What is a sphingolipid?
Definition
Amphipatic molecule with a sphingosine backbone
Term
What is a sterol
Definition
Nonpolar molecule
Term
What is our phospholipid bilayer referred to as?
Definition
Singer-Nicolson Fluid Mosaic Model
Term
What is the purpose of having proteins in the membrane?
Definition
To allow the passage of ions since the membrane is impermeable to them
Term
What are some functions of proteins?
Definition
1. enzymes
2. receptors for hormones
3. passive channels/pores
4. pumps for active transport
5. carriers for passive transport
6. recognition of molecules
Term
What are the two main functions of the membrane?
Definition
1. To control solute concentrations
2. To store energy to do work
Term
How does the membrane set up a membrane potential?
Definition
1. By establishing a concentration (electrochemical) gradient using chemical energy
2. By establishing charge separation using electrical energy
Term
What is permeation?
Definition
The passive diffusion of solutes across a barrier
Term
What is Fick's Law of Diffusion?
Definition
dS/dt=Px(C1-C2)
Term
What does Fick's Law tell us?
Definition
That the amount of a substance crossing a unit area per time is equal to the product of the permeability constant and the change in concentration across the membrane
Term
Does every cell carry a membrane potential?
Definition
Yes, but only excitable cells can modify it
Term
What is the permeability constant (Px)?
Definition
Depends on how soluble a solute is in the membrane
Term
How does the permeability constant apply to nonpolar substances?
Definition
Nonpolar substances have a higher permeability constant therefore they are more permeable
Term
What is the equation for permeability?
Definition
Px=(DK)/a where D is the diffusion coefficient, K is the partition coefficient, and a is the membrane thickness (usually ~70A
Term
What does the partition coefficient mean?
Definition
It is the ratio of the concentration of a solute in oil and water (oil:water), thus the higher the K the more soluble it is in oil and the more nonpolar it is
Term
What does the diffusion coefficient say?
Definition
As viscosity and molecular size increase, D decreases
Term
Who was Santiago Ramon Y Cajal?
Definition
Spanish neuroscientist who discovered that the nervous system is made up of neurons, discrete signaling elements ("Neuron Doctrine")
Term
Who was Camillo Golgi?
Definition
Italian neuroscientist who discovered histological staining techniques by impregnating the cell with silver grains
Term
How much charge can a capacitor store?
Definition
C=EA/d where E is the dielectric constant, A is the area of the plates, and d is the distance between the plates
Term
What does a capacitor do?
Definition
Although DC current cannot flow through a capacitor, it can store charge and such charge buildup can push charges to circulate
Term
How does capacitance relate to the plasma membrane?
Definition
The plasma membrane is like a capacitor because it can store charge and channels could be seen as resistors
Term
What kind of channels are there?
Definition
1. Open (leakage) channels
2. Gated channels (voltage gated, ligand gated, mechanosensory)
Term
What is meant by active transport?
Definition
Requires ATP (energy) to sustain pumps that will maintain the voltage inside (eg: Na/K ATPase pumps 2K in and 3Na out)
Term
What could block the active transport mechanism of the pumps?
Definition
Cardiac glycosides (eg: those found in some toad poisons)
Term
How is a membrane potential measured?
Definition
As the difference in voltage across the membrane; the potential of the inside relative to the outside (~70mV)
Term
At resting potential what is the state of the K and Na ions?
Definition
There is more K in than out and more Na out than in
Term
What does the Nernst equation say?
Definition
At equilibrium, the chemical force of an ion equals its electrical force
Term
What is the equation for the chemical force?
Definition
Fc=RTln([Kout]/[Kin])
Term
What is the equation for electrical force?
Definition
Fe=zFV
Term
What are the equilibrium potentials for a cell only permeable to K or Na, respectively?
Definition
K: -90mV, Na: +63mV
Term
What is the relationship between resting potential and temperature?
Definition
RP is directly proportional to temperature
Term
What did Baker, Hodgkin, and Shaw discover in 1961?
Definition
When they switch the axoplasm of a squid giant axon with its extracellular fluid, the voltage across the membrane reversed to ~+90mV
Term
How much capacitance is usually found across a membrane per square cm?
Definition
1 microF (10^-6) per square cm
Term
What is the Goldman equation (Constant-Field equation)?
Definition
It takes into account the permeability of the membrane to more than one (monovalent) ion (an expansion of the Nernst equation
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