Integrated Physiology: Action Potential & ANS
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Questions and Answers

What primarily generates the resting membrane potential in neurons?

  • Selective K+ permeability (correct)
  • Calcium channels
  • Chloride ion concentration
  • Sodium permeability

Which ion channel is responsible for the depolarization phase of the action potential?

  • Ca2+ channels
  • Cl- channels
  • K+ channels
  • Na+ channels (correct)

During which phase of the action potential do Na+ channels become inactivated?

  • Refractory period
  • Resting potential
  • Repolarization (correct)
  • Threshold potential

What is the value of the typical resting membrane potential for neurons?

<p>-70mV (B)</p> Signup and view all the answers

What does the Nernst equation predict?

<p>The equilibrium potential for a single ion species (B)</p> Signup and view all the answers

What occurs during the absolute refractory period?

<p>Na+ channels cannot be stimulated (B)</p> Signup and view all the answers

Which ion has the highest permeability during the repolarization phase?

<p>K+ (D)</p> Signup and view all the answers

What is the role of the myelin sheath in axonal conduction?

<p>Facilitating faster action potential generation (D)</p> Signup and view all the answers

What is a compound action potential?

<p>The sum of multiple axon action potentials measured together (D)</p> Signup and view all the answers

Which part of the neuron receives incoming signals?

<p>Dendrite (B)</p> Signup and view all the answers

Which fiber type transmits information about pain and temperature?

<p>Aδ (B)</p> Signup and view all the answers

Which fiber type is responsible for motor control to muscle spindles?

<p>Aγ (B)</p> Signup and view all the answers

Which of the following is NOT a benefit of myelination?

<p>Increases membrane permeability (B)</p> Signup and view all the answers

In demyelination, which of the following occurs?

<p>Increased membrane capacitance (A)</p> Signup and view all the answers

What is the primary reason for the increased conduction velocity in myelinated axons?

<p>Both A and B (B)</p> Signup and view all the answers

Which of the following is TRUE about the nodes of Ranvier?

<p>Both A and B (C)</p> Signup and view all the answers

What is 'saltatory conduction'?

<p>The jumping of action potentials from one node of Ranvier to the next (D)</p> Signup and view all the answers

What is the main function of the B fibers?

<p>Preganglionic autonomic (A)</p> Signup and view all the answers

What is the primary function of the inactivation gate in a Na+ channel?

<p>To ensure that the action potential only travels in one direction by preventing the opening of Na+ channels in the direction from which the action potential has already traveled. (A)</p> Signup and view all the answers

What is the main characteristic that distinguishes the relative refractory period from the absolute refractory period?

<p>The relative refractory period is a period of reduced excitability but still allows for the generation of action potentials with a strong enough stimulus. (B)</p> Signup and view all the answers

Why is the 'all-or-none' principle important for action potential propagation?

<p>It allows the nervous system to encode stimulus intensity by altering the frequency of action potentials rather than the amplitude. (C)</p> Signup and view all the answers

Based on the analogy of a toilet flushing, what would correspond to the 'absolute refractory period'?

<p>The period when the bowl is full and the cistern is empty. (B)</p> Signup and view all the answers

Which of the following is NOT a property of action potentials?

<p>They are graded potentials, meaning their amplitude can vary with stimulus strength. (A)</p> Signup and view all the answers

Which of the following factors contributes to the faster conduction velocity of action potentials?

<p>Both A and B. (D)</p> Signup and view all the answers

What is the primary role of the sodium-potassium pump in the context of action potentials?

<p>To establish the electrochemical gradient that drives the movement of ions during action potentials. (D)</p> Signup and view all the answers

What is the significance of the "undershoot" phase during an action potential?

<p>It is the phase where the neuron is hyperpolarized and less likely to fire another action potential. (B)</p> Signup and view all the answers

Flashcards

Resting membrane potential

The potential difference across the neuronal membrane when the neuron is at rest.

K+ permeability

Selectively permeable channels in the neuronal membrane that allow potassium ions (K+) to pass through more easily than other ions.

Depolarization

The movement of ions across the neuronal membrane, causing a change in the electrical potential.

Repolarization

The movement of ions across the neuronal membrane, bringing the electrical potential back to its resting state.

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Absolute refractory period

The brief period after an action potential during which a neuron cannot be stimulated to produce another action potential.

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Action potential

The rapid change in electrical potential across the neuronal membrane, caused by the opening and closing of ion channels.

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Threshold potential

The point at which a neuron must be depolarized to initiate an action potential.

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Sodium influx

The process by which sodium ions (Na+) flow rapidly into the neuron, causing depolarization during an action potential.

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Potassium efflux

The process by which potassium ions (K+) flow rapidly out of the neuron, causing repolarization during an action potential.

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Axon hillock

A specialized region at the beginning of the axon where action potentials are initiated.

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Relative Refractory Period

The period during which a neuron can generate another action potential, but only with a stronger than usual stimulus. This occurs because the sodium channels are starting to recover from inactivation, but not yet fully functional.

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Self-propagation of action potentials

The process by which an action potential travels down the axon without losing strength. The depolarization of one section of the axon triggers the opening of sodium channels in the next section, causing a new action potential to occur.

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Self-propagation of an action potential

The action potential travels along the axon, spreading from one segment to the next. Imagine a line of dominoes falling.

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Frequency coding of action potential

The strength of the stimulus is encoded in the frequency of action potentials, not their amplitude. A stronger stimulus will cause more action potentials to occur in a given time period.

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Refractory Period

The time period following an action potential during which another action potential is either impossible (absolute) or more difficult (relative) to generate. This helps to limit the rate of action potentials.

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Axon

A long, thin extension of a neuron that transmits action potentials from the cell body to other neurons or target cells

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Myelin

A fatty sheath that surrounds many axons, improving the speed of conduction of action potentials.

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Aα Fiber

A type of nerve fiber characterized by its large diameter, thick myelin sheath, and fast conduction velocity. It is responsible for transmitting signals related to motor control and proprioception.

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Aβ Fiber

A type of nerve fiber with a moderate diameter, myelin sheath, and conduction velocity. It carries signals related to touch and pressure.

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Aγ Fiber

A type of nerve fiber that is responsible for transmitting motor signals to muscle spindles, which sense muscle length and tension.

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Aδ Fiber

A type of nerve fiber with a thin myelin sheath and slower conduction velocity. It carries signals related to pain, temperature, and light touch.

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B Fiber

A type of nerve fiber that transmits preganglionic autonomic signals, which control involuntary functions like heart rate and digestion.

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C Fiber

A type of nerve fiber lacking a myelin sheath and having the slowest conduction velocity. It transmits pain and reflex signals, as well as postganglionic sympathetic signals.

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Saltatory Conduction

The process by which nerve impulses jump from one node of Ranvier to the next along a myelinated axon, significantly increasing conduction velocity.

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Demyelination

The loss or damage of the myelin sheath surrounding nerve fibers, leading to impaired nerve impulse transmission.

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Study Notes

Course Information

  • Course title: Integrated Physiology
  • Course code: PH2130
  • Instructor: Stuart Cruickshank

Presentation Topics

  • Action Potential
  • Neurotransmitters
  • Autonomic Nervous System

Why Emphasize the ANS?

  • Vasovagal syncope is an example
  • [YouTube Video Link]

Neuron Structure

  • Cell body (soma)
  • Dendrites
  • Axon hillock (initial segment)
  • Axon
  • Axon collaterals
  • Myelin sheath
  • Nodes of Ranvier
  • Terminal branches/axon terminals (synaptic knobs)
  • Presynaptic terminals

Axonal Conduction

  • Resting membrane potential
  • Ion channels generating action potential
  • Speeding up action potentials
  • Compound action potentials

Resting Membrane Potential

  • Generated by selective potassium (K+) permeability of the membrane
  • Ion distribution across the membrane (diagrammed)

Nernst Equation

  • Predicts equilibrium potential for a single ion species
  • Formula and variables (R, T, z, F) are defined

Electrophysiology Summary

  • Short description of electrophysiology, with relevant ions(Na+, Ca2+, Cl-) and membrane potential(-70mV)

Action Potential Permeability Changes

  • Graph showing permeability changes of Na+, K+ during an Action Potential

Action Potential Summary

  • Depolarization phase
  • Repolarization phase
  • Resting membrane potential
  • Threshold potential
  • Diagrams showing ion movement during different phases of the Action Potential

Refractory Periods

  • Absolute Refractory Period
    • Na+ channels cannot be stimulated again until inactivation gate resets
  • Relative Refractory Period
    • Requires a stronger-than-usual stimulus to create another AP

Self-propagation of Action Potentials

  • Diagram showing sequential activation of Na+ channels along an axon, leading to propagation down the axon

Properties of Action Potentials

  • Voltage-gated channels mediate action potentials
  • All-or-none response to stimulus
  • Signalled through frequency changes, not amplitude
  • Refractory periods prevent overlapping action potentials
  • Self-propagating for long-distance signaling
  • Conduction velocity improved by large axons or myelination

Nerve Fiber Types

  • Classification based on myelination and conduction velocity
  • Different classes of nerve fibers and their associated functions

Myelination

  • Speeds up action potential transmission
  • Diagram demonstrating myelinated vs. unmyelinated axons
  • Saltatory conduction
  • Increased membrane resistance during myelination

Demyelination

  • Opposite effect to myelination
  • Diagram showing effect of demyelination, which slows conduction significantly

Key Concepts

  • Important concepts related to resting/action potentials, affecting velocity, myelination and de-myelination, refractory periods.

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Description

This quiz covers key topics in Integrated Physiology, focusing on the Action Potential and the Autonomic Nervous System. Delve into concepts like resting membrane potential, ion channels, and neuron structure. Enhance your understanding of essential electrophysiological principles and their applications.

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