Neuroscience - Neural Signaling, Action Potentials & Synapses Flashcards

Question 1

What is the typical resting membrane potential (RMP) of a neuron?

Accepted Answer

The typical RMP of a neuron is approximately $-70 	ext{ mV}$. This negative charge inside the cell relative to the outside is crucial for neuronal excitability.

Question 2

How does the $Na^+/K^+$ ATPase contribute to the resting membrane potential?

Accepted Answer

The $Na^+/K^+$ ATPase actively pumps $3 	ext{ Na}^+$ ions out of the cell and $2 	ext{ K}^+$ ions into the cell against their concentration gradients. This maintains the electrochemical gradients necessary for the RMP and consumes ATP.

Question 3

What is the primary role of $K^+$ leak channels in establishing the resting membrane potential?

Accepted Answer

Neuronal membranes are much more permeable to $K^+$ than $Na^+$ at rest due to $K^+$ leak channels. $K^+$ ions flow out of the cell down their concentration gradient, making the inside of the cell more negative and contributing significantly to the RMP.

Question 4

State the Nernst equation and explain its purpose.

Accepted Answer

The Nernst equation calculates the equilibrium potential for a single ion: $E_{ion} = rac{RT}{zF} \ln rac{[ion]_{out}}{[ion]_{in}}$. It determines the membrane potential at which the net flow of a specific ion across the membrane is zero, given its concentration gradient.

Question 5

What is the 'threshold potential' in the context of an action potential?

Accepted Answer

The threshold potential is the critical membrane potential (typically around $-55 	ext{ mV}$) that must be reached to trigger an action potential. It causes a rapid, regenerative opening of voltage-gated $Na^+$ channels.

Question 6

Describe the depolarization phase of an action potential.

Accepted Answer

Upon reaching threshold, voltage-gated $Na^+$ channels rapidly open, causing a massive influx of $Na^+$ ions into the cell. This makes the inside of the membrane rapidly become more positive, rising to about $+30 	ext{ mV}$.

Question 7

Describe the repolarization phase of an action potential.

Accepted Answer

During repolarization, voltage-gated $Na^+$ channels inactivate, and slower-opening voltage-gated $K^+$ channels open. $K^+$ ions flow out of the cell, restoring the negative charge inside the membrane.

Question 8

What causes the 'undershoot' or hyperpolarization phase during an action potential?

Accepted Answer

The undershoot occurs because voltage-gated $K^+$ channels are slow to close, leading to an excess efflux of $K^+$ ions. This causes the membrane potential to become transiently more negative than the resting potential before returning to rest.

Question 9

Differentiate between the absolute and relative refractory periods.

Accepted Answer

**Absolute Refractory Period:** No new action potential can be generated, regardless of stimulus strength, because voltage-gated $Na^+$ channels are inactivated.
**Relative Refractory Period:** A stronger-than-normal stimulus can generate an action potential because some $Na^+$ channels have reset, but $K^+$ channels are still open, making it harder to depolarize.

Question 10

What are the three main states of voltage-gated $Na^+$ channels?

Accepted Answer

1. **Closed:** At resting potential, ready to open.
2. **Open:** Upon depolarization to threshold, allowing $Na^+$ influx.
3. **Inactivated:** During repolarization, a ball-and-chain mechanism blocks the pore, preventing further $Na^+$ influx.

Question 11

Briefly describe the process of chemical synaptic transmission.

Accepted Answer

An action potential arrives at the presynaptic terminal, triggering voltage-gated $Ca^{2+}$ channels to open. $Ca^{2+}$ influx causes neurotransmitter vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft. These bind to receptors on the postsynaptic membrane, causing a response.

Question 12

What is an Excitatory Postsynaptic Potential (EPSP)?

Accepted Answer

An EPSP is a transient depolarization of the postsynaptic membrane caused by the influx of positive ions (e.g., $Na^+$ or $Ca^{2+}$) when an excitatory neurotransmitter binds to its receptor. It makes the postsynaptic neuron more likely to fire an action potential.

Question 13

What is an Inhibitory Postsynaptic Potential (IPSP)?

Accepted Answer

An IPSP is a transient hyperpolarization or stabilization of the postsynaptic membrane caused by the influx of negative ions (e.g., $Cl^-$) or efflux of positive ions (e.g., $K^+$) when an inhibitory neurotransmitter binds. It makes the postsynaptic neuron less likely to fire an action potential.

Question 14

Explain spatial summation in synaptic integration.

Accepted Answer

Spatial summation is the integration of postsynaptic potentials (EPSPs or IPSPs) that originate from different presynaptic terminals simultaneously. If enough EPSPs arrive at different locations at the same time, their combined effect can reach threshold.

Question 15

Explain temporal summation in synaptic integration.

Accepted Answer

Temporal summation is the integration of postsynaptic potentials (EPSPs or IPSPs) that occur at the same synapse in rapid succession. If a presynaptic neuron fires repeatedly and quickly, the individual postsynaptic potentials can add up to reach threshold.

Question 16

What is the primary excitatory neurotransmitter in the CNS?

Accepted Answer

**Glutamate**. It mediates fast synaptic transmission and is crucial for learning and memory. Its receptors include AMPA, NMDA, and kainate receptors.

Question 17

What is the primary inhibitory neurotransmitter in the CNS?

Accepted Answer

**GABA** (gamma-aminobutyric acid). It typically binds to $GABA_A$ receptors (ionotropic $Cl^-$ channels) or $GABA_B$ receptors (metabotropic $K^+$ channels), leading to hyperpolarization or stabilization of the membrane.

Question 18

What is the main function of Acetylcholine (ACh) at the neuromuscular junction and in the CNS?

Accepted Answer

At the **neuromuscular junction**, ACh is the primary neurotransmitter, causing muscle contraction. In the **CNS**, it plays roles in attention, learning, memory, and arousal.

Question 19

What are some key functions of Dopamine in the brain?

Accepted Answer

Dopamine is involved in reward and motivation, pleasure, motor control, executive functions, and arousal. Dysregulation is implicated in Parkinson's disease (loss of dopaminergic neurons) and schizophrenia.

Question 20

Define Long-Term Potentiation (LTP).

Accepted Answer

LTP is a persistent strengthening of synapses based on recent patterns of activity. It is a widely accepted cellular mechanism underlying learning and memory, where repeated high-frequency stimulation of a presynaptic neuron leads to an enhanced postsynaptic response.

Question 21

Which two glutamate receptors are critically involved in the induction phase of many forms of LTP?

Accepted Answer

**AMPA receptors** (ionotropic, mediate fast EPSPs) and **NMDA receptors** (ionotropic, voltage- and ligand-gated, allow $Ca^{2+}$ influx, crucial for LTP induction).

Question 22

Briefly describe the role of $Ca^{2+}$ influx through NMDA receptors in LTP induction.

Accepted Answer

During strong stimulation, sufficient depolarization removes the $Mg^{2+}$ block from NMDA receptors. Glutamate binding then allows $Ca^{2+}$ to enter the postsynaptic neuron. This $Ca^{2+}$ influx activates intracellular signaling cascades (e.g., protein kinases) that lead to the insertion of more AMPA receptors into the postsynaptic membrane, strengthening the synapse.

Neuroscience - Neural Signaling, Action Potentials & Synapses

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