Cell Physics Flashcards
What makes the cell a good electrical circuit?
-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
Define hyperpolarization
change in the cell membrane potential that makes it more negative
Define depolarization
change in the cell membrane potential that makes it more positive
How are membrane potentials measured?
measured as the difference between inside and outside of the cell. Always measured relative to the inside of the cell
What are the main ionic species involved in setting and modifying membrane potential
K, NA, Cl, Ca
What are the types of channels involved in setting and changing membrane potential?
-Leak channels
-voltage gated
-ligand gated
-mechanical
How does membrane permeability to select ions affect the membrane potential?
The resting membrane potential will be closer to the ion type with higher permeability
Resting membrane potential depends on what?
-Electrical potential difference
-Ion concentration gradient
-Active transport mechanisms
Which equation includes permeability?
Goldman-Hodgkin-Katz
Describe the role of the Na/K ATPase pump in maintaining membrane potential
-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
What would happen without the Na/K ATPase pump?
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
Whats the difference between graded and action potentials?
-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
What aspect of action potentials is depended on strength of stimulus?
frequency. NEVER AMPLITUDE
What are the 3 phases of an action potential initiation?Describe them
-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
What restores the cell back to resting potential after the hyper polarization phase of action potential initiation?
Na/K ATPase pump
Define absolute refractory period
occurs immediately after the initiation of the action potential during which time another action potential CANNOT be generated
Define relative refractory period
Occurs after absolute, corresponds to hyper polarization and an action potential can be generated but needs a stronger stimulus
What are the similarities of action potentials across all cell types? (3)
-Very rapid depolarization
-all-or-nothing
-amplitude is independent of the stimulus strength
Describe action potential propagation in neurons
-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
How does axon myelination modulate action potential propogation?
Myelin makes it move faster by reducing membrane capacitance and increasing membrane resistance
How does axon diameter affect conductance velocity?
Increased axon diameter increases conductance velocity
Describe an electrical synapse
-utilizes gap junctions
-bidirectional signal
-no significant synaptic delay
-found in cardiac and smooth muscle
Describe a chemical synapse
-most common
-unidirectional
-utilizes vesicles/ ligand gated ion channels
Describe signal transmission at a chemical synapse
-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
What are the roles of kinesin and dynein in synaptic transmission?
Kinesin moves cargo toward the synapse
Dynein moves cargo away from synapse
*cargo can include small molecules, mitochondria, ribosomes, lysosomes, etc
What is the difference between ionotropic and metabotropic receptors?
Ionotropic are channels and result in fast neurotransmitter transmission, while metabotropic are usually slower and are g-coupled receptors
Describe presynaptic inhibition
a modulatory neuron synapses on one collateral of the presynaptic neuron and selectively inhibits target
Describe postsynaptic inhibition
no action potential triggered in postsynaptic neuron. all triggers are inhibited equally
Describe the process of neuroplasticity
-involves NMDA receptors which allow influx of Ca, Ca alters receptor trafficking to membrane. also changes dendrite shape and release of regulating chemicals
Describe the process of neurotoxicity
If glutamate is too high, intracellular ca will be high which can lead to cell death.
What factors can lend a cell more vulnerable to neurotoxicity?
high concentration of NMDA and Ca permeable AMPA receptors
What are the two major excitatory neurotransmittors
Glutamate and Aspartate
What are the two major inhibitory neurotransmittors
Glycine and GABA
What are the modulatory neurotransmitters? (can do both)
Biogenic amines (catecholamines, serotonin, histamine)
