Nerve Conduction and Action Potentials

Nerve Conduction and Synapses

• Nerve cells generate electrical signals using ion flow across their membranes.
• Neurons create a resting membrane potential, which is a negative potential.
• Action potentials temporarily remove the negative resting potential, making the transmembrane potential positive.
• The resting membrane potential is not zero.
• Action potentials propagate along axons; these are the fundamental signals for information transmission in the nervous system.
• These signals arise from ion fluxes across nerve cell membranes, which are selectively permeable and have uneven ion distributions.

Action Potential

• Action potentials involve a rapid depolarization (upstroke) followed by repolarization of the membrane potential.
• Opening Na+ channels causes depolarization (sodium influx).
• Opening K+ channels causes repolarization (potassium efflux).
• The action potential has a threshold.
• Failed action potential initiations can occur if the stimulus does not reach the threshold.
• The "all-or-none" response means that once an action potential begins, it will complete its course or not occur at all.
• Depolarization lessens the membrane potential, hyperpolarization increases it.
• Overshoot is when the membrane potential becomes positive inside the cell.

Velocity of Action Potential

• Action potential speed depends on fiber diameter (larger is faster) and myelination (myelinated nerves are faster).
• Myelin allows for "saltatory conduction," where the action potential jumps between Nodes of Ranvier, making it faster than continuous conduction.
• Myelinated neurons are faster than unmyelinated ones.

Synapses

• Synapses are junctions connecting neurons or between a neuron and another cell type, like muscle.
• Most synapses are chemical, using neurotransmitters to relay signals.
• Some synapses are electrical, using direct connections.
• At chemical synapses, neurotransmitters are released at the presynaptic terminal, cross the synaptic gap, and bind to receptors on the postsynaptic neuron.
• Neurotransmitters can be excitatory or inhibitory; their effect depends on the type of receptor.

Different Types of Synapses

• Chemical synapses release neurotransmitters, which either cause depolarization (excitation) or hyperpolarization (inhibition) in the postsynaptic neuron.
• The influx of Ca2+ in the axon terminal triggers neurotransmitter release.
• Voltage-gated Ca2+ channels open when an action potential reaches the axon terminal.
• Neurotransmitters diffuse across the synaptic cleft to bind to receptors on the postsynaptic cell membrane, which can be excitatory (Na+ influx) or inhibitory (Cl- influx).
• Glutamate is a common excitatory neurotransmitter.
• GABA is a common inhibitory neurotransmitter.

Functions of the Synapse

• Summation of EPSPs (excitatory postsynaptic potentials) and IPSPs (inhibitory postsynaptic potentials) determines whether an action potential occurs in the postsynaptic neuron.
• If the sum of EPSPs is large enough to reach the threshold, an action potential occurs.
• The summed inhibitory potentials push the membrane away from the firing threshold.

Multiple Sclerosis

• Multiple sclerosis is an autoimmune disease affecting the myelin sheath.
• It leads to damaged myelin, forming scar tissue, which slows the conduction of action potentials.

Explore the fascinating world of nerve conduction and action potentials. This quiz covers the generation of electrical signals in nerve cells, explaining how resting membrane potential and action potentials work in the transmission of information within the nervous system.