Study Guide: Nervous System Physiology and Muscle Contraction (ANP)

Q1. Explain how muscle fibers are stimulated to contract by describing the events that occur at the neuromuscular junction.

Background

Topic: Neuromuscular Junction & Muscle Contraction

This question tests your understanding of how a nerve impulse leads to muscle contraction, focusing on the communication between a motor neuron and a muscle fiber.

Key Terms and Concepts:

• Neuromuscular junction (NMJ)

• Motor neuron

• Synaptic cleft

• Acetylcholine (ACh)

• Muscle action potential

Step-by-Step Guidance

1. When an action potential reaches the axon terminal of a motor neuron, voltage-gated calcium channels open, allowing $\mathrm{Ca^{2+}}$ to enter the terminal.

2. The influx of $\mathrm{Ca^{2+}}$ causes synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine (ACh) into the synaptic cleft.

3. ACh diffuses across the synaptic cleft and binds to receptors on the motor end plate of the muscle fiber.

4. This binding opens chemically gated ion channels, allowing $\mathrm{Na^+}$ to enter the muscle cell, generating an end plate potential.

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Q2. Describe end plate potential.

Background

Topic: Synaptic Transmission at the NMJ

This question focuses on the electrical changes that occur in the muscle fiber membrane after ACh binds to its receptors.

Key Terms:

• End plate potential (EPP)

• Depolarization

• Ion movement ($\mathrm{Na^+}$ influx, $\mathrm{K^+}$ efflux)

Step-by-Step Guidance

1. When ACh binds to its receptors, chemically gated channels open, allowing $\mathrm{Na^+}$ to flow in and $\mathrm{K^+}$ to flow out.

2. The influx of $\mathrm{Na^+}$ is greater than the efflux of $\mathrm{K^+}$, causing a local depolarization called the end plate potential.

3. If the EPP reaches threshold, it triggers an action potential in the muscle fiber.

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Q3. Which voltage-gated channel is found along the axon terminal of a motor neuron?

Background

Topic: Synaptic Transmission

This question tests your knowledge of the types of ion channels involved in neurotransmitter release at the NMJ.

Key Terms:

• Voltage-gated calcium channels

• Axon terminal

Step-by-Step Guidance

1. Recall that neurotransmitter release is triggered by an influx of a specific ion when an action potential arrives at the axon terminal.

2. Identify which voltage-gated channel allows this ion to enter the terminal, leading to vesicle fusion and neurotransmitter release.

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Q4. Which neurotransmitter is found in the synaptic cleft of a motor neuron?

Background

Topic: Neurotransmitters at the NMJ

This question asks you to recall the main neurotransmitter responsible for muscle contraction at the neuromuscular junction.

Key Terms:

• Acetylcholine (ACh)

• Synaptic cleft

Step-by-Step Guidance

1. Think about the neurotransmitter released by motor neurons to stimulate skeletal muscle fibers.

2. Recall the name of the molecule that binds to receptors on the muscle cell membrane.

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Q5. Identify the types of membrane ion channels, their role, and where they are found in a neuron.

Background

Topic: Neuronal Membrane Channels

This question tests your understanding of the different types of ion channels in neurons and their specific locations and functions.

Key Terms and Types:

• Voltage-gated channels (Na+, K+, Ca2+)

• Chemically gated (ligand-gated) channels

• Leak channels

• Na+/K+ pump

Step-by-Step Guidance

1. List the main types of ion channels found in neurons and describe their general function (e.g., initiating action potentials, maintaining resting potential).

2. Identify where each type is typically located (e.g., dendrites, axon hillock, axon, axon terminal).

3. Explain the role of each channel in neuronal signaling.

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Q6. Define resting membrane potential and describe how it is generated.

Background

Topic: Resting Membrane Potential

This question focuses on the electrical charge difference across the neuronal membrane at rest and the mechanisms that establish it.

Key Terms and Formulas:

• Resting membrane potential (RMP)

• Na+/K+ ATPase pump

• Leak channels

• Typical value: $-70$ mV

Step-by-Step Guidance

1. Define what is meant by the resting membrane potential and its typical value in neurons.

2. Describe the role of the Na+/K+ pump in maintaining ion gradients across the membrane.

3. Explain how leak channels contribute to the resting potential, especially for K+.

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Q7. Explain the differences in ionic composition of a neuron cell body. Where is Na+ and K+ heavily concentrated?

Background

Topic: Ionic Gradients in Neurons

This question tests your understanding of the distribution of major ions inside and outside the neuron.

Key Terms:

• Na+ (sodium)

• K+ (potassium)

• Intracellular vs. extracellular concentration

Step-by-Step Guidance

1. Recall which ion is more concentrated inside the neuron and which is more concentrated outside.

2. Explain how the Na+/K+ pump helps maintain these gradients.

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Q8. List the channels/pumps that maintain resting membrane potential.

Background

Topic: Maintenance of Resting Potential

This question asks you to identify the specific proteins responsible for maintaining the resting membrane potential in neurons.

Key Terms:

• Na+/K+ ATPase pump

• K+ leak channels

• Na+ leak channels

Step-by-Step Guidance

1. List the main channels and pumps involved in maintaining the resting membrane potential.

2. Briefly describe the function of each (e.g., which ions they move and in which direction).

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Q9. For an open channel, what factors determine in which direction ions will move through that channel?

Background

Topic: Ion Movement Across Membranes

This question tests your understanding of the forces that drive ion movement across the neuronal membrane.

Key Terms:

• Electrochemical gradient

• Concentration gradient

• Electrical gradient

Step-by-Step Guidance

1. Define the two main forces that influence ion movement: concentration gradient and electrical gradient.

2. Explain how the combination of these forces (the electrochemical gradient) determines the direction of ion flow.

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Q10. Compare and contrast graded potentials and action potentials.

Background

Topic: Types of Electrical Signals in Neurons

This question asks you to distinguish between two types of changes in membrane potential.

Key Terms:

• Graded potential

• Action potential

• Amplitude, duration, propagation

Step-by-Step Guidance

1. Define graded potentials and action potentials, including where they occur in the neuron.

2. Compare their characteristics: amplitude, duration, ability to propagate, and whether they are all-or-none.

3. Explain how one can trigger the other.

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Q11. Describe depolarization and hyperpolarization.

Background

Topic: Changes in Membrane Potential

This question focuses on the meaning of these two terms and what causes them in neurons.

Key Terms:

• Depolarization

• Hyperpolarization

• Ion movement

Step-by-Step Guidance

1. Define depolarization and describe what happens to the membrane potential during this process.

2. Define hyperpolarization and describe how it differs from depolarization.

3. Identify which ions are typically involved in each process.

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Q12. What determines the size of a graded potential?

Background

Topic: Graded Potentials

This question tests your understanding of what factors influence the magnitude of graded potentials in neurons.

Key Terms:

• Stimulus strength

• Ion channel opening

Step-by-Step Guidance

1. Explain how the strength of the stimulus affects the size of the graded potential.

2. Discuss the role of the number of open ion channels.

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Q13. Explain how action potentials are generated and propagated along neurons. (include which gates are used and when they are open/closed, the direction of flow of ions, and threshold voltage)

Background

Topic: Action Potential Generation and Propagation

This question asks you to describe the sequence of events during an action potential and how it travels along the axon.

Key Terms and Steps:

• Threshold voltage (about $-55$ mV)

• Voltage-gated Na+ and K+ channels

• Depolarization, repolarization, hyperpolarization

Step-by-Step Guidance

1. When the membrane potential reaches threshold, voltage-gated Na+ channels open, allowing Na+ to rush into the cell (depolarization).

2. At the peak, Na+ channels inactivate and voltage-gated K+ channels open, allowing K+ to exit the cell (repolarization).

3. Hyperpolarization occurs as K+ channels remain open briefly after repolarization.

4. The action potential propagates as the depolarization triggers adjacent voltage-gated Na+ channels to open.

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Q14. Define absolute and relative refractory periods.

Background

Topic: Action Potential Refractory Periods

This question tests your understanding of the periods during which a neuron cannot or is less likely to fire another action potential.

Key Terms:

• Absolute refractory period

• Relative refractory period

Step-by-Step Guidance

1. Define the absolute refractory period and explain why no action potential can be generated during this time.

2. Define the relative refractory period and describe what is required to generate another action potential during this phase.

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Q15. List the factors that contribute to conduction velocity.

Background

Topic: Action Potential Conduction

This question asks you to identify what influences the speed at which action potentials travel along axons.

Key Terms:

• Axon diameter

• Myelination

• Temperature

Step-by-Step Guidance

1. List the main factors that affect conduction velocity in neurons.

2. Explain how each factor influences the speed of action potential propagation.

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Q16. Define saltatory conduction and explain how it differs from continuous conduction.

Background

Topic: Action Potential Propagation

This question focuses on the difference between how action potentials travel in myelinated vs. unmyelinated axons.

Key Terms:

• Saltatory conduction

• Nodes of Ranvier

• Continuous conduction

Step-by-Step Guidance

1. Define saltatory conduction and describe how action potentials "jump" from node to node in myelinated axons.

2. Contrast this with continuous conduction in unmyelinated axons.

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