Movement of Information Within Neurons

Flashcards testing knowledge of neural conduction, membrane potentials, ion channels, action potentials, and laws of neural communication based on lecture notes.

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What is electric potential?

The relative difference in electric charge between two places, such as between the inside and outside of a cell membrane.

What is the typical resting membrane potential of a neuron?

Approximately $-60\text{ to }-70\text{ mV}$ inside relative to outside (or $+60\text{ to }+70\text{ mV}$ outside relative to inside).

What are the relative ion concentrations inside versus outside a neuron at resting potential?

There is $10 \times$ more $\text{Na}^+$ and $40 \times$ more $\text{Cl}^-$ outside the cell, and $50 \times$ more $\text{K}^+$ inside the cell, along with trapped organic anions.

What is electrostatic pressure?

The force exerted by ions on each other, where like charges repel each other and opposite charges attract each other.

How does diffusion influence ion movement across the membrane?

Particles randomly move from areas of higher concentration to areas of lower concentration down their concentration gradient until concentration is equalized.

What is the function of the sodium-potassium ($\text{Na}^+/\text{K}^+$) pump?

It uses ATP to continuously move $3\text{ Na}^+$ ions out of the cell and $2\text{ K}^+$ ions into the cell, maintaining concentration gradients.

How do leak channels contribute to establishing the resting membrane potential?

Many $\text{K}^+$ leak channels allow $\text{K}^+$ to leak out (driving potential toward $-90\text{ mV}$), while a few $\text{Na}^+$ leak channels allow a little $\text{Na}^+$ in, bringing the potential to about $-70\text{ mV}$.

What are the roles of the three types of ion channels found in neural membranes?

Leak channels establish resting membrane potential; voltage-gated channels generate and propagate action potentials; ligand-gated channels mediate synaptic transmission.

Why do organic anions ($\text{A}^-$) remain inside the cell?

They are large, polar, or charged proteins made inside the neuron that cannot pass through the membrane.

Where on a neuron does an action potential initiate?

At the axon hillock.

Why do action potentials not occur on the dendrites or soma?

Dendrites and soma lack voltage-gated $\text{Na}^+$ channels and only contain neurotransmitter-dependent (ligand-gated) channels.

According to this step-by-step diagram, what happens at Step 1 of the action potential?

Voltage-gated $\text{Na}^+$ channels open when the threshold of excitation is reached, allowing $\text{Na}^+$ to flood into the cell.

What are the three structural states of a voltage-gated sodium ($\text{Na}^+$) channel shown in this image?

1. Closed (impermeable to $\text{Na}^+$), 2. Open (permeable to $\text{Na}^+$), and 3. Inactivated (impermeable to $\text{Na}^+$).

What triggers a voltage-gated sodium channel to transition from open to inactivated?

Further depolarization reaching the peak of the action potential (around $+30\text{ to }+40\text{ mV}$).

What is the absolute refractory period?

The period during which another action potential cannot be triggered at the same spot because voltage-gated $\text{Na}^+$ channels are inactivated and cannot open until reset.

What is the relative refractory period?

The period following an action potential where a new action potential can be triggered, but requires greater depolarization to offset hyperpolarization and reach the threshold.

What occurs under the myelin sheath during saltatory conduction as shown in this diagram?

Decremental passive conduction of voltage changes occurs under the myelin sheath, while the action potential is regenerated at each node of Ranvier.

What are the two components of the All-or-None Law?

1. All action potentials are the same amplitude (size). 2. Once triggered, an action potential propagates all the way to the end of the axon and all of its branches.

What is the Rate Law in neural communication?

The principle stating that information about stimulus or response strength is represented by the rate of action potential firing (number of APs per unit of time), rather than the size of individual action potentials.