BLOCK 3: MPP: (3.1) INTRODUCTION TO THE NERVOUS SYSTEM

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Questions and Answers

What characterizes the threshold potential needed for action potential generation?

A specific amount of neurotransmitter release

A voltage that opens voltage-dependent Na+ channels (correct)

A threshold that stops depolarization

A stable resting membrane potential

Which statement is true regarding the 'all or nothing' principle of action potentials?

Action potentials are graded responses to stimuli.

Once initiated, the action potential cannot be stopped until completion. (correct)

Only a small number of Na+ channels need to open to trigger an action potential.

Action potentials vary in magnitude based on stimulus strength.

What role does axon diameter play in neuronal signaling?

Larger diameter axons typically conduct action potentials more quickly. (correct)

Smaller diameter axons conduct action potentials faster.

Larger diameter axons have lower conduction velocities due to increased resistance.

Axon diameter has no effect on action potential propagation.

What is primarily responsible for the repolarization phase of an action potential?

Efflux of K+ ions through voltage-dependent K+ channels Signup and view all the answers

What effect would a loss of myelination have on an axon?

It would decrease the conduction velocity of the action potential. Signup and view all the answers

What triggers the initiation of an action potential in a neuron?

Sufficient receptor potential reaching a threshold voltage Signup and view all the answers

Which ion's influx is primarily responsible for driving the propagation of action potentials?

Na+ Signup and view all the answers

During the recovery phase of an action potential, what happens to Na+ channels?

They become inactivated due to depolarization Signup and view all the answers

What effect do excitatory postsynaptic potentials (EPSPs) have on the neuron?

They lead to the initial segment of the axon becoming depolarized Signup and view all the answers

Which of the following correctly defines spatial summation in terms of postsynaptic potentials?

Combined effect of multiple EPSPs and IPSPs at different locations Signup and view all the answers

What is the role of calcium ions (Ca++) in neurotransmitter release?

Ca++ influx triggers a Ca++-dependent secretory event Signup and view all the answers

Which neurotransmitter is considered the most widely used in the nervous system?

GABA Signup and view all the answers

What characterizes the action of inhibitory postsynaptic potentials (IPSPs)?

They increase intracellular negativity through K+ efflux or Cl- influx Signup and view all the answers

What is the role of the nodes of Ranvier in action potential propagation?

They localize fast Na+ channels for efficient signaling. Signup and view all the answers

In neurons, how does axon diameter influence signal propagation?

Larger diameters improve the efficiency of action potential propagation. Signup and view all the answers

What characterizes the condition of Multiple Sclerosis?

It involves the degradation of the myelin sheath in CNS neurons. Signup and view all the answers

What may result from disrupted axonal conduction caused by diseases like Multiple Sclerosis?

Symptoms such as weakness and tremors. Signup and view all the answers

Which factor contributes to the speed of action potential propagation along an axon?

The presence and thickness of the myelin sheath. Signup and view all the answers

What clinical feature is NOT typically associated with Multiple Sclerosis?

Deterioration of kidney function. Signup and view all the answers

How does the spacing of nodes of Ranvier affect action potential conduction in large diameter axons?

Closer spacing leads to faster conduction. Signup and view all the answers

What is the current understanding of the cause of Multiple Sclerosis?

It has an unknown cause with a suspected autoimmune component. Signup and view all the answers

What is the primary function of reuptake transporters in neurotransmission?

Recycle neurotransmitters back into the presynaptic nerve Signup and view all the answers

How does calcium play a role at the nerve terminal during neurotransmitter release?

It triggers snap-snare signaling for neurotransmitter release Signup and view all the answers

What role do acetylcholinesterase inhibitors play in neurotransmission?

Prolong the action of acetylcholine in the synaptic cleft Signup and view all the answers

Which consequence is associated with the spillover of neurotransmitters in neuronal signaling?

Diminished signaling due to dilution Signup and view all the answers

What physiological process is directly associated with the action of voltage-gated calcium channels at the nerve terminal?

Promoting neurotransmitter release upon signaling arrival Signup and view all the answers

Which pharmacological approach targets the degradation of neurotransmitters?

Enzyme inhibitors like acetylcholinesterase inhibitors Signup and view all the answers

What is the effect of altering the affinity of reuptake transporters?

Modifies the concentration of neurotransmitters in the synaptic cleft Signup and view all the answers

Which of the following describes a common outcome of calcium's role in neurotransmission?

It supports the release of neurotransmitters through signal transduction mechanisms Signup and view all the answers

What role does calcium play in the process of neurotransmitter release?

It triggers the fusion of synaptic vesicles with the plasma membrane. Signup and view all the answers

What distinguishes ionotropic receptors from metabotropic receptors?

Ionotropic receptors directly open ion channels, while metabotropic receptors activate G proteins. Signup and view all the answers

How does the same neurotransmitter, like acetylcholine, produce different physiological effects in various tissues?

Different receptors in tissues respond differently to the same neurotransmitter. Signup and view all the answers

What is the primary function of calcium ions in neurotransmitter release?

To facilitate the release of neurotransmitters from synaptic vesicles Signup and view all the answers

What is the primary function of the SNARE complex in neurotransmission?

Anchoring synaptic vesicles to the plasma membrane. Signup and view all the answers

Which neurotransmitter is categorized under the cholinergic class?

Acetylcholine Signup and view all the answers

What characterizes a calcium-dependent secretory event in the context of neurotransmitter release?

Calcium activates proteins that promote synaptic vesicle release Signup and view all the answers

Which of the following effects is associated with metabotropic receptors?

Slow and prolonged signal transduction. Signup and view all the answers

What happens when a synaptic vesicle fuses with the plasma membrane?

Neurotransmitters are released into the synaptic cleft. Signup and view all the answers

Which neurotransmitter is primarily associated with the monoamine class discussed?

Serotonin Signup and view all the answers

What type of receptors does glutamate primarily interact with in the nervous system?

Both ionotropic and metabotropic receptors. Signup and view all the answers

What is a common characteristic of the amino acid neurotransmitter group?

Includes glutamate, GABA, and glycine Signup and view all the answers

Which of the following statements best reflects the pharmacological focus regarding neurotransmitters?

Pharmacology primarily focuses on small molecule neurotransmitters Signup and view all the answers

What physiological response can occur due to metabotropic receptor activation by a neurotransmitter?

Muscle relaxation through G protein mediated signaling. Signup and view all the answers

What can be inferred about the release of neurotransmitters in relation to neuron signaling speed?

Neurotransmitter release matches the speed of signal conduction Signup and view all the answers

Why are drugs targeting epinephrine less common compared to other neurotransmitters?

Epinephrine's physiological usage is limited in everyday conditions Signup and view all the answers

Study Notes

Action Potential: Basic Steps & Terms

Threshold Potential (Vth): The voltage required to open enough voltage-dependent Na+ channels to trigger an action potential (AP).
"All or nothing" Principle: When the membrane potential (Vm) surpasses the threshold voltage, voltage-gated Na+ channels open massively, initiating an AP.
Overshoot: The peak of the AP doesn't always reach exactly 0mV; the cell can become positively charged compared to the extracellular fluid (ECF).
Afterpotentials: APs are temporary events. The downstroke is caused by voltage-dependent K+ channels opening, leading to K+ efflux and repolarization of Vm.

Nerve Action Potential: Propagation

Sequential Steps of Neuronal Signaling:
- Excitation
- Initiation
- Propagation
- Recovery
Axon Diameter and Insulation:
- Small Diameter Axons: Action potentials (APs) are propagated through opening fast Na+ channels along the membrane, resulting in relatively slow conduction velocities (0.5 - 2.0 m/s).
- Large Diameter Axons: Fast Na+ channels are localized to nodes of Ranvier (1-2 μm spacing). APs propagate from node-to-node, resulting in faster conduction velocities.

Propagation

Initiation: When the receptor potential is strong enough to cross the threshold potential (Vth), a spike (action potential) is triggered.
Propagation: Driven by the electrochemical gradient for Na+, Na+ flows into the cell, creating an "active current."

Recovery

Na+ Channels: Inactivated by depolarization within milliseconds.
Ion Gradients: Renormalized by ion pumps during recovery.

Postsynaptic Integration

Incoming Messages:
- Excitatory Postsynaptic Potential (EPSP): Rapid influx of Na+, leading to AP initiation in the initial segment of the axon where more Na+ channels are located.
- Inhibitory Postsynaptic Potential (IPSP): Hyperpolarization (increased intracellular negativity) caused by increased permeability to K+ (efflux) or Cl- (influx).

Spatial Summation of Postsynaptic Potentials

Multiple simultaneous inputs from different synapses are combined.

Temporal Summation of Postsynaptic Potentials

Multiple inputs from the same synapse occurring in quick succession are summed.

Neurotransmitter Classes

GABA: The most widely used neurotransmitter.

Synaptic Vesicles and Neurotransmitter Release

Ca++ Influx: Leads to a "Ca++-dependent secretory event."
Ca++ Binding to Synaptotagmin: Activates the SNARE complex.
SNARE Complex: Composed of synaptobrevin, syntaxin, and SNAP-25.

Tissue Specific Receptors

Neurotransmitters bind to specific receptors in different tissues, eliciting various responses.

Clinical Connection: Multiple Sclerosis

Demyelinating Disease of CNS Neurons: Unknown cause(s).
Immune Cells Produce Antibodies: Against myelin sheath components.
Myelin Degradation: Leads to interrupted axonal conduction.
Symptoms: Tremors, visual disturbances, autonomic dysfunction, weakness, and fatigue.
Treatment: No cure, but treatments are available.
Progression: Disease typically progresses over 10 to 20 years.

Synaptic Vesicle and Neurotransmitter Release

Calcium influx is a key component in neurotransmitter release and it binds to snapotagmen, anchored in synaptic vesicles.
Snapotagmen binds to the SNARE complex (made of three subunits) and tethers the synaptic vesicle to the plasma membrane.
When calcium is abundant, it pulls the vesicle, forming a fusion pore and releasing neurotransmitters into the synaptic cleft.
Receptors on the post-synaptic membrane can be ionotropic (ion regulated) or metabotropic (G protein coupled signaling).
The metabotropic receptors are involved in a diverse response, allowing one neurotransmitter to activate a variety of physiological responses.

Neurotransmitter Fates

Glutamate is degraded by astrocytes
Acetylcholine is degraded by acetylcholinesterase
Dopamine, norepinephrine, and serotonin are recycled by reuptake transporters
GABA is taken up by neurons
Glycine is recycled by neurons

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Description

Explore the fundamental concepts of action potentials in neurons, including threshold potential, the all-or-nothing principle, and propagation mechanisms. This quiz covers the basic steps and terms essential for understanding neuronal signaling and the physiological response of nerve cells.