Lecture 03 Membrane Potentials & Action Potentials Flashcards
Which of the type of neuron would transmit an action potential the fastest?
Large Diameter and myelinated
Saltatory conduction is characteristic of which part of a typical neruon?
Axon
Selectivity Filter with carbonyl oxygen is associated with what ion channel
K+
Restin potential for a typical neuron, like motor neuron is represented by how many mV?
-90mV
What is a cell body of a neuron?
Houses the nucleus and oter typical cell organelles. Has local potentials and voltage-gated ion channels are NOT characteristic of the cell body membrane
How does the cell body differ from the axon?
conducts a different type of potential
Define Dendrites
Cellular extensions of the neuron. Have ligand gated ion channels. Local potentials
Define axons
Extension of the cell body. Covered by the plasma membrane. Voltage - gated ion channels for action potentials. Membrane bound vesicles with neurotransmitters
What is an axolemma
Plasma membrane that coveres the axon
What causes a diffusion potential?
Caused by an ion concentration difference on either side of a membrane
Define Nerst potential
The Nernst potential is the diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through a membrane. How much energy is needed to keep an ion from diffusing across a membrane
How does one measure membrane potential?
Electrode outside the cell membrane in the extracellular fluid. Micropipette electrode is placed inside the cell. Inside the cell at rest is negative. Reference from inside the cell
What represents an electrical dipole layer?
The distribution of ions immediately on either side of the membrane is mostly positive or mostly negative. A voltage change area
The ions immediately on either side of a membrane is mostly positive or mostly negative is what type of distribution?
Dichotomous distribution
Describe the graph
A: Recording electrode is in the extracellular fluid
B: Recording electrode pierces cell membrane
C: recording electrde pierces other side of membrane and is in the extracellular fluid again
The Nernst equation can measure the potential for how many ions?
Only one ion at a time
What equation is used to measure the potential for more than one ion at a time?
Goldman’s equation
What are the three assumptions that must be made when using the Nernst equation?
- Only be used for one ion at at time
- Membrane must be completely permeable to that ion
- Ion must be at equilibrium
Define the following equation
E = 2.3 RT/F log Co/Ci
E = Nernst potential
R = Universal gas constant
T = Absolute temperature
F = Faraday’s constant
Ci = Concentration of ions inside the membrane
Co= Concentration of ions outside the membrane
What is the Nernst equation equal to EMF
EMF = Eion = z(61.5) x log ([ion]outside/[ion]inside
What are the characteristics of action potential
Its all-or-none.
Self-propagating = Each region of depolarization serves to generate action potentials on either side
Non-decremental: does not decrease in strength
What is local potential
Conducted at the dentrites and the cell body. Potential that involves ligan gated channel. It can become less negative or more negative. Can be an inhibitory or excititory potential. Very quickly phases out. If you can keep it strong enough until it gets to axon hillock it can generate an axon potential
What do ligand gated channels require?
Attachment of a chemical messenger such as a neurotransmitter to a receptor
What is the molecular structure of a voltage - gated sodium channel
4 domains in a cylindrical configuration. Each domain has 6 hydrophobic transmembrane segments. S4 has a high positive charge. Inactivation gate associated with intracellular hydrophilic linkage between domains 3 and 4
Voltage-gated sodium channels have how many gates?
2 gates. Activation gate and inactivation gate
Describe the activation steps in voltage-gated sodium channels
- Resting potential: Activation gate is closed and the inactivation gate is opened at -90mV
- Depolarization: Activation gate opens asa voltage reaches -7-mV to -50mV
- Repolarization: Activation gate is opened and the inactivation gate is cosed at +35mV to -90mV
Describe the K+ gate
K+ has one gate
- Gate is closed at resting potential of -90mV
- Slow activation opens the gate from +35 to -90mV
What are the steps in the generation of an action potential on a neuron axon memebrane?
- Resting Stage -90mV
- Deplarization state-Membrane suddenly becomes permeale to sodium ions, membrane potentail may overshoot fr large axons
- Replarization stage - Sodium channels close, K+ channels open more than normal.
What is hyperpoloraization
When repolarization exceeds -90
What propagates the increased speed at which the action potential travels?
Increase of diameter=larger cross-sectional area to internal flow of current
Wrapping axon with layers of insulation (myelin sheeths)
How does myelin sheath create a capacitor effect?
Capacitor consists of two conducting plates sparated by an insulating barrier.
Intracellular and extracellular fluids = plates
Lipid membrane layer = insulating barrier
What is capacitor’s capacitance?
Directly proportional to the area of the plates - bigger plates can store more charge
Inversely proportional to the distance separating the plates
How do myelinatd axons increase the speed of conduction?
Current flows at points of least resistance, therefore potential flow jumps from one node to the next greatly increasing the speed.
What is the jumping from node to node referred to as?
saltatory conduction
What is the threshold point at which a local potential will elicit an action potential
-65mV
What is the direction of propagation?
Action potential travels in all idrections from the point of stimulation
What are the two directions of propagation?
Orthodromic direction: Towards distal end of axon
Antidromic direction: Towards the axon hillock/neuron cell body
Why do action potential typically travel in the orthodromic direction?
We always start the action potential on the axon hillock in our nervous system. In a lab situation we could have it go either way
What is sphingomyelin
Principle lipid found in myelin sheath
What are schwann cells?
Cells that form the myelin sheaths in peripheral axons
What is absolute refractory period?
Period during which a second action potential cannot be elicitd even with a strong stimulus. And energy is derived directly from breakdown of ATP
What is relative refractory period
Stronger than normal stimulus can cause action potential
