Cell Physics

Question 1

What makes the cell a good electrical circuit?

Answer 1

-The lipid bilayer is a good capacitor b/c it is an excellent insulator and the intra/extracellular fluid allows for the flow of ions
- Ion channels are good resistors or conductors depending on if they’re open or not

Question 2

Define hyperpolarization

Answer 2

change in the cell membrane potential that makes it more negative

Question 3

Define depolarization

Answer 3

change in the cell membrane potential that makes it more positive

Question 4

How are membrane potentials measured?

Answer 4

measured as the difference between inside and outside of the cell. Always measured relative to the inside of the cell

Question 5

What are the main ionic species involved in setting and modifying membrane potential

Answer 5

K, NA, Cl, Ca

Question 6

What are the types of channels involved in setting and changing membrane potential?

Answer 6

-Leak channels
-voltage gated
-ligand gated
-mechanical

Question 7

How does membrane permeability to select ions affect the membrane potential?

Answer 7

The resting membrane potential will be closer to the ion type with higher permeability

Question 8

Resting membrane potential depends on what?

Answer 8

-Electrical potential difference
-Ion concentration gradient
-Active transport mechanisms

Question 9

Which equation includes permeability?

Answer 9

Goldman-Hodgkin-Katz

Question 10

Describe the role of the Na/K ATPase pump in maintaining membrane potential

Answer 10

-Needed to offset the continuous leakage of ions accross the membrane
-works against both the concentration and electrical gradient
-Maintains the low concentration of intracellular Na

Question 11

What would happen without the Na/K ATPase pump?

Answer 11

Overtime intracellular Na would increase, and the cell would become depolarized, which would open more voltage gated Na gates bringing in more Na. In an effort to dilute, water enters cell causing it to swell and lyse

Question 12

Whats the difference between graded and action potentials?

Answer 12

-Graded are small fluctuations in membrane potential that can either be inhibitory or excitatory. amplitude depends on strength of stimulus
-Action potential is a rapid substantial but transient increase in the membrane potential that is propagated. Amplitude does NOT depend on stimulus strength

Question 13

What aspect of action potentials is depended on strength of stimulus?

Answer 13

frequency. NEVER AMPLITUDE

Question 14

What are the 3 phases of an action potential initiation?Describe them

Answer 14

-Depolarization: voltage threshold is reached causing voltage gated Na channels to open, which will be self propagating until all Na channels are open.
-Repolarization: Increase in voltage due to Na channels opening causes voltage gated K channels to open, causing K to leave.
-Hyper polarization: The vast exit of K trying to reach its equilibrium potential causes the membrane potential to become more negative than resting, causing K channels to close

Question 15

What restores the cell back to resting potential after the hyper polarization phase of action potential initiation?

Answer 15

Na/K ATPase pump

Question 16

Define absolute refractory period

Answer 16

occurs immediately after the initiation of the action potential during which time another action potential CANNOT be generated

Question 17

Define relative refractory period

Answer 17

Occurs after absolute, corresponds to hyper polarization and an action potential can be generated but needs a stronger stimulus

Question 18

What are the similarities of action potentials across all cell types? (3)

Answer 18

-Very rapid depolarization
-all-or-nothing
-amplitude is independent of the stimulus strength

Question 19

Describe action potential propagation in neurons

Answer 19

-Initiated at the axon hillock
-Wave of depolarization travels toward the axon terminal
-This depolarization continues through opening of Na channels
-Immediately after depolarization, K channels open, which re-polarizes the axon. This prevents the potential from moving backwards

Question 20

How does axon myelination modulate action potential propogation?

Answer 20

Myelin makes it move faster by reducing membrane capacitance and increasing membrane resistance

Question 21

How does axon diameter affect conductance velocity?

Answer 21

Increased axon diameter increases conductance velocity

Question 22

Describe an electrical synapse

Answer 22

-utilizes gap junctions
-bidirectional signal
-no significant synaptic delay
-found in cardiac and smooth muscle

Question 23

Describe a chemical synapse

Answer 23

-most common
-unidirectional
-utilizes vesicles/ ligand gated ion channels

Question 24

Describe signal transmission at a chemical synapse

Answer 24

-Action potential depolarizes the axon terminal
-the depolarization opens voltage gated Ca channels and Ca enters the cell
-Ca entry triggers exocytosis of vesicles
-Neurotransmitter diffuses across the synaptic cleft and binds with receptors which triggers a response in postsynaptic cell

Question 25

What are the roles of kinesin and dynein in synaptic transmission?

Answer 25

Kinesin moves cargo toward the synapse
Dynein moves cargo away from synapse
*cargo can include small molecules, mitochondria, ribosomes, lysosomes, etc

Question 26

What is the difference between ionotropic and metabotropic receptors?

Answer 26

Ionotropic are channels and result in fast neurotransmitter transmission, while metabotropic are usually slower and are g-coupled receptors

Question 27

Describe presynaptic inhibition

Answer 27

a modulatory neuron synapses on one collateral of the presynaptic neuron and selectively inhibits target

Question 28

Describe postsynaptic inhibition

Answer 28

no action potential triggered in postsynaptic neuron. all triggers are inhibited equally

Question 29

Describe the process of neuroplasticity

Answer 29

-involves NMDA receptors which allow influx of Ca, Ca alters receptor trafficking to membrane. also changes dendrite shape and release of regulating chemicals

Question 30

Describe the process of neurotoxicity

Answer 30

If glutamate is too high, intracellular ca will be high which can lead to cell death.

Question 31

What factors can lend a cell more vulnerable to neurotoxicity?

Answer 31

high concentration of NMDA and Ca permeable AMPA receptors

Question 32

What are the two major excitatory neurotransmittors

Answer 32

Glutamate and Aspartate

Question 33

What are the two major inhibitory neurotransmittors

Answer 33

Glycine and GABA

Question 34

What are the modulatory neurotransmitters? (can do both)

Answer 34

Biogenic amines (catecholamines, serotonin, histamine)