Nervous System I – Neurons, Neurotransmitters & Nerve Impulse Propagation

These Q&A flashcards cover key points from the lecture: membrane potentials, ion pumps, gated channels, graded vs action potentials, propagation mechanisms, refractory period, synapses, and specific details of cholinergic transmission.

What general study rule links anatomy with physiology?

Always try to link structure to function.

What is the typical resting membrane potential of most neurons?

Approximately –60 to –70 mV.

Which pump actively maintains the resting membrane potential?

The sodium-potassium (Na⁺/K⁺) ATPase pump.

How many Na⁺ and K⁺ ions are moved per cycle of the Na⁺/K⁺ pump?

3 Na⁺ are pumped out and 2 K⁺ are pumped in, using 1 ATP.

Name the two passive forces acting across a neuronal membrane.

Chemical (concentration) gradients and electrical gradients.

Why do extracellular and intracellular fluids differ greatly in ionic composition?

Because cell membranes are selectively permeable and permeability varies by ion.

What is the equilibrium potential of potassium (Eₖ) if the membrane were freely permeable to K⁺?

About –90 mV.

What is the equilibrium potential of sodium (Eₙₐ) if the membrane were freely permeable to Na⁺?

About +66 mV.

What immediate event can trigger a change in resting potential?

Opening or closing of specific gated ion channels.

List the three functional states of a gated ion channel.

Closed, Open, Inactive.

Name the three classes of gated channels.

Chemically (ligand)-gated, voltage-gated, and mechanically-gated channels.

Where do graded potentials usually occur in a neuron?

In dendrites and the cell body.

Give two key characteristics of graded potentials.

They are small, variable, decremental changes in membrane potential that can summate.

Where are action potentials generated and propagated?

Generated at the axon hillock (trigger zone) and propagated along the axon.

What principle states that an action potential either occurs fully or not at all?

The All-or-None Principle.

What membrane potential change marks threshold for most neurons?

Depolarization to roughly –60 to –55 mV.

Step 1 of an action potential involves what key event?

Depolarization to threshold at the axon hillock, opening voltage-gated Na⁺ channels.

During Step 2 of an action potential, what happens to the membrane polarity?

Rapid depolarization: the inside becomes positive as Na⁺ rushes in.

Which ion channels open during Step 3 of an action potential?

Voltage-gated K⁺ channels open while Na⁺ channels become inactivated.

What restores resting permeability in Step 4 of an action potential?

Closing of K⁺ channels, reopening of Na⁺ inactivation gates, and continued pump/leak action.

Define the refractory period.

The time from initiation of an action potential until return to resting state when the membrane cannot normally respond to another stimulus.

Differentiate continuous and saltatory propagation.

Continuous occurs along unmyelinated axons (slow, ~1 m/s); saltatory jumps between nodes on myelinated axons (up to 50× faster, energy-efficient).

What property of myelin allows saltatory conduction to be faster?

Myelin lowers membrane capacitance and insulates the axon, restricting depolarization to nodes of Ranvier.

List the five main membrane processes involved in neural signaling.

Resting potential, graded potential, action potential, synaptic activity, and information processing.

Which type of synapse is most common in the nervous system?

Chemical synapse.

What two factors determine whether an action potential is propagated at a chemical synapse?

Amount of neurotransmitter released and sensitivity (receptor number/threshold) of the postsynaptic cell.

In chemical synapses, what determines whether the effect is EPSP or IPSP?

The type of receptor on the postsynaptic membrane, not the neurotransmitter itself.

Define a cholinergic synapse.

A synapse that releases the neurotransmitter acetylcholine (ACh).

Give three locations where cholinergic synapses are found.

All neuromuscular junctions with skeletal muscle, many CNS synapses, and nearly all neuron-to-neuron synapses in the PNS.

What ion triggers exocytosis of ACh in the presynaptic terminal?

Calcium ions (Ca²⁺).

What enzyme degrades ACh in the synaptic cleft?

Acetylcholinesterase (AChE).

Name the four sequential events at a cholinergic synapse.

1) AP arrives and depolarizes terminal; 2) Ca²⁺ influx triggers ACh exocytosis; 3) ACh binds receptors and depolarizes postsynaptic membrane; 4) ACh is broken down by AChE.

What happens to choline after ACh is degraded?

It is taken back up into the presynaptic terminal for recycling.

Besides acetylcholine, list four broad categories of other neurotransmitters.

Biogenic amines, amino acids, neuropeptides, and dissolved gases.