Lecture 3 - Neurophysiology: Neural Signals Flashcards
Membrane potential
The electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell.
Inside the cell is usually more ____ charged than outside the cell, especially at rest
(-)ly
Axons have two basic electrical potentials:
- Resting membrane potential
2. Action potential
Resting membrane potential
The membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials.
Action potential
The brief electrical impulse that provides the basis for conduction of information along an axon.
How do we know if it is a squid axon?
- huge
- visible by the naked eye
- often used in petri dishs
When we insert our electrode into the axon, we get…
a straight line — the resting potential
How the membrane potential can change:
- Hyperpolarization
- Depolarization
- Threshold of excitation
Hyperpolarization
An increase in the membrane potential of a cell, relative to the normal resting potential. (further from 0)
Depolarization
Reduction (toward zero) of the membrane potential of a cell from its normal resting potential.
Threshold of excitation
The value of the membrane potential that must be reached to produce an action potential.
Changing membrane potential is…
creating unrest!
Neurons – resting and action potentials.
- Resting potential ≈ -70 mV
- Threshold ≈ -55 mV
- Action Potential ≈ +40 mV and Hyperpolarization ≈ -90 mV
Takes approximately 2 msec!
How long does an AP take?
~ 2 msec
AP’s are…
All-or-none & the same everytime
Diffusion gradient
Movement of molecules from a region of high concentration to regions of low concentration. (e.g. sugar dissolving in water)
Electrostatic gradient
Molecules can carry charge (ions)
Cations (+ charge)
Anions (- charge)
Move towards areas of unlike charge (opposites attract)
Dynamic equilibrium
Gradients can balance one another.
Where are these ions?
- Intracellular fluid
- Extracellular fluid
Intracellular fluid
The fluid contained within a cell.
Extracellular fluid
Body fluids located outside the cell.
Membrane Equilibrium
when there’s certains ions inside & outside the cell
A– = protein K+ = potassium Na+ = sodium Cl– = chloride
What is happening inside of cell?
- anions cannot leave cell
K+ is achieving dynamic equilibrium as the force of diffusion and electrostatic pressure balance each other out
- normally can free float inside & outside the cell b/c those 2 pressures are working against each other forming an equil.
What is happening outside of cell?
- low concentration of K+
High concentration of:
- Cl- is achieving dynamic equilibrium as force of diffusion and electrostatic pressure balance each other out
- Na+ is being forced into the cell as force of diffusion and electrostatic pressure are both pushing that direction
- but Na+ has to wait for a Na+ channel to open & the opening of that channel is the basis & start of an A