Lecture 7 Flashcards
Neural Signalling (20 cards)
What maintains the resting membrane potential (RMP)?
• Na⁺/K⁺ ATPase pump (3 Na⁺ out, 2 K⁺ in)
• K⁺ leakage channels
• RMP ≈ -65 mV
When are ions across a cell membrane at equilibrium?
When chemical and electrical forces counterbalance, stopping net ion flow.
What is equilibrium (Nernst) potential?
The electrical potential difference across a cell membrane that counterbalances the concentration gradient of a specific ion.
What is the Nernst equation used for?
To calculate the equilibrium potential for a single ion.
What is the Goldman equation used for?
To calculate the actual membrane potential considering multiple ions and their permeabilities.
What triggers an action potential?
Membrane depolarization reaching threshold (~ -55 mV)
What are the phases of an action potential?
- Depolarization (Na⁺ influx)
- Repolarization (K⁺ efflux)
- Hyperpolarization (continued K⁺ efflux)
- Return to RMP
What is the Hodgkin cycle?
A positive feedback loop where Na⁺ influx causes further depolarization, opening more VGSCs, leading to an action potential.
What are the three states of voltage-gated Na⁺ channels?
- Closed (at rest)
- Open (depolarized)
- Inactivated (refractory)
What is the role of voltage-gated K⁺ channels?
Open slowly during depolarization to repolarize the membrane; do not inactivate.
What is the absolute refractory period?
No new AP can be generated due to inactivated Na⁺ channels.
What is the relative refractory period?
A stronger-than-normal stimulus is needed to trigger an AP due to hyperpolarization.
What is the axon hillock?
The trigger zone with high VGSC density; initiates action potentials.
How do wider axons speed up conduction?
Reduce resistance but take up space.
How do myelinated axons speed up conduction?
• Prevent ion leakage
• Enable saltatory conduction between nodes of Ranvier
What are the steps of synaptic transmission?
- AP reaches axon terminal
- VGCCs open → Ca²⁺ influx
- Neurotransmitter vesicle fusion
- NT release into synaptic cleft
- NT binds to postsynaptic receptors
What is an excitatory postsynaptic potential (EPSP)?
Depolarisation via ligand-gated cation channels (e.g., glutamate)
What is an inhibitory postsynaptic potential (IPSP)?
Hyperpolarisation via ligand-gated Cl⁻ channels (e.g., GABA)
What is synaptic summation?
The additive effect of multiple EPSPs/IPSPs to reach threshold at the axon hillock.
Where are inhibitory synapses typically located?
On the soma and proximal dendrites (close to axon hillock)
