Neuron Ion Channels and Membrane Potential

Ion Channels and Membrane Potential

• Ion channels in the membrane are selective and allow some ions to pass more easily.
• The direction and size of ion movement depends on the concentration gradient and the voltage difference of the membrane.
• Leak potassium channel is responsible for the resting membrane potential.
• Potassium ions diffuse out of the cell along the concentration gradient and leave behind negative charges within the cell.
• Potassium equilibrium potential is the membrane potential at which the net movement of K+ ceases.

Types of Ion Channels

• Some ion channels are “gated”: Open and close under certain conditions.
• Voltage-gated channels respond to change in voltage across the membrane.
• Chemically-gated channels depend on molecules that bind or alter channel protein.
• Mechanically-gated channels respond to force applied to the membrane.

Graded Changes and Ion Transport

• Graded membrane potentials are changes from the resting potential.
• Ion transporters and channels generate membrane potential.
• Ion channels and ion transporters in the membrane create the membrane, resting and action potentials.

Electrical Properties of Neurons

• Membrane potential is a charge difference across the membrane, with the inside of the cell negative relative to the outside.
• Resting potential is the steady state membrane potential of a resting neuron.
• Action potential, or nerve impulse, is a rapid, large change in membrane potential.

Sodium-Potassium Pump

• Sodium-potassium pump—moves Na+ ions from inside, exchanges for K+ from outside.
• Establishes concentration gradients.
• The Na+-K+ pump is an antiporter, or sodium-potassium ATPase, as it requires ATP.

Electrical Synapses

• Electrical synapses couple neurons electrically through gap junctions.
• Characteristics of electrical synapses include:
• Fast transmission
• No synaptic cleft
• No synaptic vesicles
• No possibility of IPSPs

Chemical Synapses

• Chemical synapses involve the release of neurotransmitters from the presynaptic neuron.
• Characteristics of chemical synapses include:
• Slower transmission
• Presence of synaptic cleft
• Presence of synaptic vesicles
• Possibility of IPSPs

Neuromuscular Junction

• The neuromuscular junction is a chemical synapse between motor neurons and skeletal muscle cells.
• ACh receptor is a ligand-gated, non-selective cationic channel.

Postsynaptic Potentials

• Postsynaptic cell sums the excitatory and inhibitory input.
• EPSP – excitatory synapse
• IPSP – inhibitory synapse

Neurotransmitters and Receptors

• Major neurotransmitters of the nervous system include:
• Acetylcholine
• Dopamine
• Norepinephrine
• Serotonin
• Glutamate
• GABA
• Glycine
• Ionotropic receptors are ion channels, whereas metabotropic receptors are not ion channels.
• Examples of ionotropic receptors include glutamate receptors, GABAA, and glycine receptors.
• Examples of metabotropic receptors include glutamate receptors and GABAB receptors.