Psych 115 Week 3 Study Questions and Correct Answers
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Course
PSYC 115
Institution
PSYC 115
Phospholipid Made up of a glycerol backbone (3 carbons), hydro-carbon tail, and phosphate (negative) choline (positive) head group
Have two hydrophobic hydrocarbon (oily) tails Hydrophilic phosphate head
How the phospholipid layers form? The hydrophobic fatty acid tails and hydrophilic polar head...
Psych 115 Week 3 Study Questions and
Correct Answers
Phospholipid ✅Made up of a glycerol backbone (3 carbons), hydro-carbon tail, and
phosphate (negative) choline (positive) head group
Have two hydrophobic hydrocarbon (oily) tails
Hydrophilic phosphate head
How the phospholipid layers form? ✅The hydrophobic fatty acid tails and hydrophilic
polar heads are part of the lipid bilayer. The tails repel water, so they are always facing
the inside of the membrane. The polar heads love it, so they face the outside of the
membrane.
tails -> away from water
head -> associate with water
oily tails toward center and hydrophilic head groups face outside
phopholipid bilayer ✅Two layers of phospholipids -> two molecules thick
head groups directed outward and interacts with surrounding water and tails packed into
the interior
What can pass the phospholipid bilayer? ✅only hydrophobic small molecules
5 concepts of electrophysiology ✅1. Diffusion of uncharged species
2. Diffusion of an ion
3. Equilibrium potential
4. Membrane potential
5. Action potential
How long does action potential take? ✅About 1-2 milliseconds
What used to study action potential? ✅Giant Axon of a squid
Diffusion ✅molecules move from high to low concentration
Why does diffusion occur? ✅Random thermal motion where things end up moving
from region of high concentration to low concentration
, Concentration of Na+, K+, Cl-, Ca2+, and Proteins inside and outside cell ✅Na+ ->
more outside than inside
K+ -> more inside than outside
Cl- -> more outside than inside
Ca2+ -> more outside than inside
proteins -> more inside than outside (ions of K+ roughly equal inside cell due to the
proteins)
+ and - outside are equal to inside
Equilibrium potential of the outside of the cell ✅By convention outside is always
assigned the value 0
Equilibrium Potential ✅Consider sodium ions. [Na+]out > [Na+]in
1.If the membrane is permeable to Na+, then more Na+ enters from the outside than
leaves from the inside.
2.The inside develops a net excess of + charge over - charge.
3.The excess + charge inside acts like 'pressure' against the entry of more + ions,
including Na+. This electric pressure is measured in millivolts (mV), positive inside with
respect to outside. (By convention, the outside is always assigned the value 0.)
4.The excess of + charge inside (and the positive voltage it generates) increases up to
the point that the rate of the efflux of Na+ (due to the positive voltage) from the interior
equals the rate of influx (due to the concentration gradient) into the interior.
5.The potential across the membrane at this point is called the equilibrium potential for
sodium (ENa). If the interior became even more positive, then more Na+ would leave
than would enter, and the potential across the membrane would respond by falling back
to the equilibrium potential for sodium (ENa).
rate of entry equals rate of exit -> equilibrium
the point at which the movement of ions across the cell membrane is balanced, as the
electrostatic pressure pulling ions in one direction is offset by the diffusion force pushing
them in the opposite direction
Inside of equilibrium potential for sodium ✅Inside will be positive and outside 0
Inside of equilibrium potential for potassium ✅K+ moves out of cell so inside becomes
negative and outside zero
How do the ions move? ✅Na+ into the cell (inside becomes positive)
K+ out of the cell (inside becomes negative)
Cl- into the cell (inside becomes negative)
Nerst Equation ✅Calculates equilibrium potential:
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