Ion_Channels_and_Membrane_Potential.pptx

The resting membrane potential is the voltage difference across the plasma membrane of a resting (non-excited) cell. In neurons, it is typically around -70 mV (inside is negative relative to outside).

1. Ion Channels and Membrane Potential Resting Membrane Potential and Action Potential Voltage-Gated, Ligand-Gated, Leak, and Chloride Channels

2. Resting Membrane Potential (RMP) • The RMP is the voltage difference across a resting cell membrane (~ -70 mV) • Maintained by: – High K⁺ inside and high Na⁺ outside – K⁺ leak channels (K⁺ moves out) – Na⁺/K⁺ pump (3 Na⁺ out, 2 K⁺ in) • Inside becomes negative due to K⁺ efflux • Essential for nerve impulse and muscle contraction

3. Action Potential (AP) • Rapid and temporary change in membrane potential • Phases: 1. Resting (-70 mV) – Na⁺ and K⁺ channels closed 2. Depolarization – Na⁺ channels open, Na⁺ enters 3. Repolarization – K⁺ channels open, K⁺ leaves 4. Hyperpolarization – K⁺ channels stay open briefly • All-or-none response • Responsible for transmitting nerve impulses

4. Voltage-Gated Channels • Open/close in response to changes in membrane potential • Types: – Na⁺ channels → depolarization – K⁺ channels → repolarization – Ca²⁺ channels → neurotransmitter release • Important for generating and propagating action potentials

5. Ligand-Gated Channels • Open when a chemical (ligand) binds to receptor • Example: Acetylcholine binds to nicotinic receptor → Na⁺ influx • Found at synapses • Involved in neurotransmission • Example channels: – Nicotinic ACh receptor (Na⁺, K⁺) – GABA_A receptor (Cl⁻)

6. Leak Channels • Always open (no gating mechanism) • Allow ions to passively diffuse according to their gradient • K⁺ leak channels play a major role in setting RMP • Small Na⁺ leak slightly depolarizes cell • Important for maintaining stable resting potential

7. Chloride Channels • Selective for Cl⁻ ions • Types: – Voltage-gated Cl⁻ channels → stabilize potential – Ligand-gated Cl⁻ channels → inhibition (e.g., GABA_A) – CFTR channel → regulates fluid balance • Function: – Helps maintain membrane potential – Provides inhibitory control in neurons

8. Comparison of Ion Channels • Voltage-Gated: Respond to voltage → Action potential • Ligand-Gated: Respond to neurotransmitters → Synaptic signaling • Leak: Always open → Maintain RMP • Chloride: Voltage or ligand controlled → Stabilize or inhibit