What portion of the neuron is an outgrowth of the cell body, and is the "beginning" of the axon?
What is "special" about the axon hillock?
It is where the individual A.P.s are "summed" before transmission down the axon.
What are not typically found in the PM of the cell body?
Voltage gated channels (Why not?)
The f(x) of telodendria
To propagate action potentials to other neurons/muscle, or to release neurotransmitters.
What type of gated channels are found on dendrites?
Voltage gated ion channels are primarily located on what portion of the neuron?
Where is the "telodendria?"
The presynaptic end of the neuron
Where are dendrites found?
On the cell body
Neurotransmitters terminal boutons use what type of gated channel?
Typically voltage gated (usually Ca2+)
What is the diffusion potential?
The electrical E* that directly opposes the flow of ions down their concentration gradient
What are the "assumptions" of the Nernst equation?
1) only one ion studied at a time 2) ion is at equilibrium regarding [ion]in to [ion]out 3) the P.M. must be completely permeable to the ion in question
E=z(61.5) x log([ion]o/[ion]i) z= valence or "charge" on ion
What is the "all-or-none" response in A.P. propagation?
The membrane reaches a threshold where it WILL fire (all). That MUST be reached. Sub-threshold changes will NOT fire an A.P. (none)
What is the principle of "self-generation?"
Depolarization of an area of the cell will result in other depolarizations ("new A.P.s" on either side)
What portion of the neuron contains the nucleus, organelles, etc.?
What is assumed in the Nernst equation?
That the plasma membrane is permeable to only ONE ion at any given time. Therefore, the Nernst equation can only tell you about the potential of one ion, not all the ions used in establishing the resting membrane potential.
What are the characteristics of action potential propagation?
1) All-or-none: sub-threshold depolarization will NOT fire an A.P. 2) Self-propagating: depolarization will occur on either side of the local A.P. 3) Non-decremental: the A.P. does not decrease in strength over time or distance
What is the f(x) of the S4 segment of the Na+ channel?
It "drives" Na+ through due to it's highly (+) AA charge; basically "repels" Na+ through the channel
Describe the Na+ channel activation gate (i.e. when is it closed/open?)
It is open from -90mV to +35 mV (allows for depolarization) Closed from +35mV to -90mV
Describe the Na+ channel inactivation gate
Closed from +35mV to -90mV Open at -90mV
Describe the Na+ "selectivity filter."
The hydrophobic domains of the Na+ channel contain carbonyl groups. These groups H-bond with the water around Na+, thereby freeing it, allowing the "naked" Na+ to flow into the cell.
Why doesn't Na+ pass through the K+ channel?
Due to the K+ selectivity filter.
Describe Fig. 5-3
Fit. 5-3 describes an electrode as it passes through a cell (L to right in both the cell diagram and voltage).
While in the same medium on the left, voltage is '0 mV.' As the electrode pierces the cell, it reads the -mV produced by the (-) charges on the cell interior. It remains level throughout the cell as there is an even distribution of charges. As it passes through the other side of the cell, it returns to '0 mV.'
Describe the difference in K+ vs Na+ selectivity
Describe K selectivity
The K+ channel is line with (-) AA residues. As a result, it "pulls" the K away from its hydrating molecules. It is smaller than Na, so Na cannot move through the channel.
Capacitance is equal to?
(Area of capacitors/distance between them)
What can be done to increase the speed of an action potential?
Increase resistance (via myelination) and increase neuron cross section
How do action potentials move around myelin?
Saltatory (jumping) conduction
What it's the typical neurons threshold for promoting sodium influx?
Period where a stimulus, no matter how large, will not produce another stimulus
Absolute refractory period
What is the mechanism for absolute refractory period?
Lack of ATP to run Na/K/ATPAse results in inability to reset RMP.
What is the refractory period where a larger than normal stimulus can creat an action potential?
Relative refractory period
What is the mechanism of Relative refractory period?
Increased K+ conductance has resulted in some depolarization of the cell.
What is the mechanism behind the relative refractory period?
As K leaves the cell (increased conductance of K) during repolarization, a new stimulus will cause the generation of an action potential.
In other words, the cell has become just repolarized enough that a new stimulus will depolarize it.