Lecture 21. Electrical Properties of Neurons Flashcards
What is the membrane potential at rest?
~-70 mV
What is it called when the membrane potential becomes more negative?
Hyperpolarisation
What is it called when the membrane potential becomes more positive?
Depolarisation
What does the resting membrane potential require?
- Intact cell (semi-permeable) membrane
- Ionic concentration gradients and ionic permeabilities (particularly K+ ions)
- Over the long term: metabolic processes
What are the intracellular concentration gradients?
12 mM Na⁺
125mM K⁺
5 mM Cl⁻
108 mM anions⁻
What are the extracellular concentration gradients?
120 mM Na⁺
5 mM K⁺
125 mM Cl⁻
What is the ideal plasma membrane?
Impermeable to Na⁺ ions
Changing Na⁺ concentration will not affect resting potential
What occurs at equilibrium in the plasma membrane?
There is a balance between K⁺ ions moving in and out of the cell this occurs at the resting potential
In reality, why is the membrane potential usually less negative than Eₖ?
Cell membrane not completely impermeable to Na⁺ (Na⁺ moves in) and there is K⁺ leakage (K⁺ moves out) Na⁺ and K⁺ movements will change the membrane potential
What is the action potential?
Major mechanism of neuronal communication
Travels down axon to terminals
Does not decrement
Trigger transmitter release
What are voltage gated channels?
Transmembrane proteins
Activated by changes in voltage (depolarisation)
Selective for ionic species eg Na⁺, K⁺, Ca²⁺ etc
When do the Na⁺ channels open?
When resting membrane potential - -30 mV
What initially depolarises neurones to open the voltage-gated Na⁺ channels?
- Synaptic transmission: excitatory postsynaptic potentials EPSPs
- Generator (receptor) potentials (sensory neurones)
- Intrinsic properties (eg pacemaker activity in heart)
- Experimental (eg electrical stimulation)
What two things contribute to repolarisation?
1) Na⁺ channels close (inactivate)
2) Voltage-gated K⁺ channels open (after a delay)
What initiates the action potentials?
Axon hillock
