Lecture 2 - Neurophysiology Flashcards
1. Be able to describe how different ions contribute to the resting membrane potential of neurons and glial cells 2. Explain how the distribution of ions result in a negative charge inside neurons 3. List the sequence of ions flows that underlies an important neuronal signal called an action potential 4. Describe how specialized ion channels propagate the action potential from the start of an axon to the tips of its every branch 5. Contrast the way the action potentials spread down myelinate
What is Neurophysiology?
the study of electrical and chemical processes in neurons
Electrochemical signaling
information flowing WITHIN neurons is via electrical signaling (inside the neuron)
information passing BETWEEN two neurons is chemical signaling (can sometimes be electrical too)
2 fundamental neuronal signals
- Synaptic Transmission - processes information
- Action Potential - makes the decision
Both are dependent on electrical properties of neurons
The Membrane Potential
potential energy that is waiting to happen. The membrane acts as a barrier from forming that potential
Cells all have electrical charges. The inside is more… (negative or positive?)
negative
Ions
Electrically charged molecules
Anions
specifically, negatively charge molecules
Cations
specifically, positively charged molecules
Diffusion
ions flowing from an area of high concentration to low concentration (moving down the concentration gradient)
Electrostatic Pressure
Like charges repel each other, opposite charges attract each other
Entropy
from an ordered state to disordered state
Lipid Bilayer
- a membrane
- separates 2 conducting solutions (the cytoplasm and the extracellular fluid)
- has charged ions on the inside and ouside of the cell
Membrane Potential
- there is a voltage difference across the membrane
- flow of anion/cations change the membrane potential
- charged particles always travel to the path of least resistance
The membrane potential formula
Vm = V in - V out
Voltage membrane = the difference of the voltage inside and outside the cell
Vm is usually -65 mV
Equilibrium Potential for
1. Glial Cells
- Glial Cells: -75 mV
Major Ions
1. K+
2. Na+
3. Cl-
Permeable:
K+ (potassium)
Na+ (sodium)
Non-permeable:
Cl- (chlorine/chloride)
Nernst Equation
purpose: predicts the equilibrium potential
Ex = RT/zF 1n [X]○/[X]i
Ex = 58mV/z log [X]○/[X]i
[X]○ is voltage outside
[X]i is voltage inside
Sodium-Potassium pump uses how much energy ?
- uses 1/3rd of the body’s enegry to keep the pump going
- also accounts for 1/2 of neurons energy
ATP vs ADP
ATP: Adenosine Triphosphate
ADP: Adenosine Diphosphate
Resting Membrane Potential
1. K+
2. Na+
3. Cl-
K+ and glial cells (-75mV)
Na+ (-70 mV)
Cl- (-70 mV)
usually -65 mV
Hyperpolarized
away from 0mV membrane potential
Action Potential
- Energy that allows a constant push for electrical signals to reach the end of a neuron
- Relies of voltage-gated ion channels
Voltage-gated ion channels
- has 3 modes: Resting, Activated, and Inactive
- Resting
- VG is closed
- extracellular side is positive
- cytoplasmic side is negative - Activated (caused by potential change)
- VG is open + activation gate is open
- Inactivation gate is closing (slow) - Inactivated
- channel closed by inactivation gate
- Refractory Period: cannot fire another action potential
Activation Gate (VG)
Closes and opens VG’s due to its own positive charge. Its positive charge repels the other positively charged ions (cations like Na+) causing the gate to open.
Consideration of Ohms Law
V= Voltage/volts
I= Current (amperes) is flow of charge/ions
R= Resistance (Ohms) stuff blocking the signal
G= Conductance (Siemens) G=1/R
Insulators - separate electrical conductors, really good resistors (blocks flow of current)
Formula: △V= IR
Hodgkin and Huxley Model: Needs
- Healthy cells: in vitro (culture/expression), ex vivo (an acute slice), in vivo (an alive animal)
- Microscope, fine electrodes, noise reduction (grounding wires, faraday cages, vibration dampening)
Signal acquisition device: amplifier, digitizer, computer software
