Excitable Cell Membranes and Action Potential

Question 1

Lipid Bilayer

Answer 1

•	 Intracellular space 
   o	cytosol
•	Extracellular space
   o	Outside of cell
•	At body temperature, interior of bilayer is fluid

Question 2

Transmembrane/Integral Proteins

Answer 2

o Span membrane

o Signal, channel proteins

Question 3

Peripheral Membrane Proteins

Answer 3

o On either side of membrane, doesn’t go through
o Usually enzymes
o Facilitate functions of transmembrane proteins

Question 4

Charges Near the Cell Membrane:

Answer 4

Na, K, Cl, negatively charged proteins
o Na and Cl more concentrated outside cell
o Called physiological saline
o K and Proteins more concentrated inside cell
o Overall more negative inside than outside
o Mainly because of negatively charged proteins

Question 5

Membrane Potential

Answer 5

o Difference in electrical charge between inside and outside of cell

Question 6

Permeability of Cell Membrane:

Answer 6

o Impermeable to electrically charged proteins
o Not very permeable to Na
o Relatively permeable to K
o Very permeable to Cl (therefore Cl is in equilibrium)

Question 7

Hodgkin and Huxley Experiment

Answer 7

o Calculated electrostatic charge needed to keep various ions from equilibrium (at rest, with the exception of Cl)
o Potassium
o 90 mV acting to move K out of neuron
o Sodium
o 120 mV of force pushing Na into neuron
o 70 mV attracted Na into cell, 50 mV pushing Na in, adds to 120

Question 8

Sodium-Potassium Pump:

Answer 8

o Active Co-transport mechanism
o Used energy (ATP)
o 3 Na ions move out, 2 K ions move in, maintains uneven distribution of Na and K ions
o Phosphate binds to pump, allows Na to bind, Na moves out of cell, K moves in, Phosphate comes off pump

Question 9

EPSP

Answer 9

o Na channels open, Na enters cell, causes depolarization

o 120 mV of pressure acting on Na to move, when channels open, Na very readily moves into cell

Question 10

IPSP

Answer 10

o Cl enters cell, causes hyper polarization

Inhibatory Poste Synaptic Potential

Question 11

Spatial/Temporal Summation

Answer 11

o Each EPSP/IPSP only causes a small change in membrane potential (only measurable in location where it is occurring). Therefore rely on spatial and temporal summation
o Same time, different locations, rapid succession at the same synapse

Question 12

Graded Response

Answer 12

EPSP/IPSP vary in magnitude

Question 13

Decremental Conclusion

Answer 13

o Signal getting smaller because ion are dispersing within neuron
o By the time it reaches the axon, it is not large enough to cause action potential

Question 14

Action Potential

Answer 14

o Fires at around -65 mV, membrane potential changes from -65 to +50 mV
o All or none principle- it either fires or it doesn’t
o Occurs in axon membrane adjacent to axon hillock
o Travels down axon, non-decremental (doesn’t lose strength)

Question 15

Process of Action Potential

Answer 15

Na channels open (voltage gated)
Na enters, cell depolarizes causing K channels to open (voltage gated)
K ions exit cell
membrane reaches +50 mV
Na channels close
K ions still exit cell due to electrostatic pressure, membrane starts depolarizing
K channels close gradually, hyperpolarization, refractory period

Question 16

o Absolute Refractory Period

Answer 16

o Can’t initiate action potential while it is firing

o ~1 millisecond

Question 17

o Relative Refractory Period

Answer 17

o Can initiate action potential, but it takes larger EPSP to initiate new action potential
o Occurs after hyperpolarization

Question 18

o Orthodromic Conduction

Answer 18

o Normal direction, from axon hillock towards axon terminal

Question 19

o Antidromic conduction

Answer 19

o Opposite direction, action potential travels from axon terminal towards axon hillock

Question 20

Neuronal Firing Rate

Answer 20

o Related to stimulus intensity
o High intensity-> firing rate set by absolute refractory period
o Low intensity-> firing rate set by relative refractory period
o Low intensity might not produce strong enough EPSP for action potential to occur

Question 21

Myelination:

Answer 21

o Na and K channels are on nodes de ranvier (no myeline), boosts signal back up
o Myelination increases transmission speed, decremental conduction
o Non myelinated axons found in local circuits because the signal doesn’t have to go far
o SLOW-> fast->fast->fast-SLOW->fast ->fast….etc

Question 22

Measuring Neuronal Activity:

Answer 22

o Normal electrode measure activity of an area
o Micro electrode measure activity of single neuron
o Place cells
o Neurons in hippocampus that respond to a specific location in a specific environment, creates map of environment based on firing of cells