,L1 Electrical signals
Neuron signaling: based on the flow of ions across the membrane = electrical signaling (needed for brain function)
Micro electrodes record:
• receptor potentials in skin touch receptors
• synaptic potential upon activation single synapse
• AP (action potential) when threshold is reached
Resting potential = -65 Plasma membrane: hydrophobic core
Negative current —> hyperpolarization
Positive current —> Depolarization
Threshold (-50) —> Action Potential } all or none, stimulus intensity is encoded in AP frequency
Membranes selectively permeable to ions
Action potentials: carry information (AP frequency) and allow long range signal transduction
• passive conduction decays over distance
• active conduction is constant over distance = action potential
Ion transport is allowed by proteins in the membrane
• active transport: 2 K+ ions in, 3 Na+ ions out
• Ion channels: concentration gradient } open/close upon changes in membrane potential
• K+ en Na+ channels
, V = 0 no electrical potential
At rest: K+ channels are open, Na+ channels are closed
Concentration of ions is evenly distributed
• K+ diffuses outside (negative potential inside)
• electrical force pushes them back inside - at rest no net movement of k+ = equilibrium potential
Diffusion force (outside) - Electrical force (Inside)
Equilibrium potential:
• at rest: Goldman equation = Nernst equation for K+ V-
• during AP: Goldman equation = Nernst equation for Na+ V+ AP results from rise in Na+
permeability
Voltage Clamp to control and measure membrane potential
• one internal electrode measures membrane potential (Vm) and is connected to the voltage clamp amplifier
• Voltage clamp amplifier compares membrane potential to the desired potential
Current flow when an AP is induced
1. Inward fast & short lived current
2. Outward slow & lasting current
Blocking sodium channels: TTX (neurotoxin)
1. early influx of sodium Na+ (fast & early) - Inward current
2. delayed efflux of potassium K+ (slow & later) - Outward current
Patch Clam method: current resulting from opening of ion channels (more channels open = stronger current)
= to record ion currents
, What happens during an AP:
1. Resting potential
1. Na+ channels open 2. rising phase
3. overshoot phase
2. Na+ enters the cell - more concentrated on the outside 4. falling phase
3. Membrane potential depolarized 5. undershoot phase
6. recovery
4. Electrochemical driving force for Na+ diminishes
5. K+ channels open + Na+ current inactivates
6. K+ exits the cell
Myelinated axon: faster (nodes of Ranvier)
Glutamate receptors: NMDA, AMPA receptors
Glutamate (synapse), receptors (postsynaptic)
—> glutamate bindings gives way for Na+
Neuron signaling: based on the flow of ions across the membrane = electrical signaling (needed for brain function)
Micro electrodes record:
• receptor potentials in skin touch receptors
• synaptic potential upon activation single synapse
• AP (action potential) when threshold is reached
Resting potential = -65 Plasma membrane: hydrophobic core
Negative current —> hyperpolarization
Positive current —> Depolarization
Threshold (-50) —> Action Potential } all or none, stimulus intensity is encoded in AP frequency
Membranes selectively permeable to ions
Action potentials: carry information (AP frequency) and allow long range signal transduction
• passive conduction decays over distance
• active conduction is constant over distance = action potential
Ion transport is allowed by proteins in the membrane
• active transport: 2 K+ ions in, 3 Na+ ions out
• Ion channels: concentration gradient } open/close upon changes in membrane potential
• K+ en Na+ channels
, V = 0 no electrical potential
At rest: K+ channels are open, Na+ channels are closed
Concentration of ions is evenly distributed
• K+ diffuses outside (negative potential inside)
• electrical force pushes them back inside - at rest no net movement of k+ = equilibrium potential
Diffusion force (outside) - Electrical force (Inside)
Equilibrium potential:
• at rest: Goldman equation = Nernst equation for K+ V-
• during AP: Goldman equation = Nernst equation for Na+ V+ AP results from rise in Na+
permeability
Voltage Clamp to control and measure membrane potential
• one internal electrode measures membrane potential (Vm) and is connected to the voltage clamp amplifier
• Voltage clamp amplifier compares membrane potential to the desired potential
Current flow when an AP is induced
1. Inward fast & short lived current
2. Outward slow & lasting current
Blocking sodium channels: TTX (neurotoxin)
1. early influx of sodium Na+ (fast & early) - Inward current
2. delayed efflux of potassium K+ (slow & later) - Outward current
Patch Clam method: current resulting from opening of ion channels (more channels open = stronger current)
= to record ion currents
, What happens during an AP:
1. Resting potential
1. Na+ channels open 2. rising phase
3. overshoot phase
2. Na+ enters the cell - more concentrated on the outside 4. falling phase
3. Membrane potential depolarized 5. undershoot phase
6. recovery
4. Electrochemical driving force for Na+ diminishes
5. K+ channels open + Na+ current inactivates
6. K+ exits the cell
Myelinated axon: faster (nodes of Ranvier)
Glutamate receptors: NMDA, AMPA receptors
Glutamate (synapse), receptors (postsynaptic)
—> glutamate bindings gives way for Na+
