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What is the primary function of dendrites in a neuron?
What is the principle followed by neurons in transmitting electrical signals?
What is the typical membrane potential of a neuron?
What is the purpose of glass micropipettes in recording membrane potential?
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What is the name of the Nobel laureates who developed the technique of intracellular recording?
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What is the main difference between one type of neuron and another?
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What is the purpose of the axon hillock in a neuron?
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What is the term for the combination of dynamic polarization and connectional specificity in neurons?
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What is the primary function of the Na+/K+ -ATPase pump in neurons?
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Which of the following factors does NOT contribute to changes in membrane potential?
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Graded potentials are primarily associated with which type of ion channels?
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In the Goldman-Hodgkin-Katz Equation, which ion has the highest permeability in the example provided?
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What is the effect of opening voltage-gated ion channels in response to a graded potential?
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What type of ion channel opens in response to physical deformation, such as pressure or stretch?
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The resting membrane potential of a neuron is primarily influenced by which of the following?
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How does a blockade of the Na+/K+ pump affect the membrane resting potential?
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What primarily determines the membrane potential (Vm) in neurons?
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Which ions have a higher concentration extracellularly compared to intracellularly?
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What is the equilibrium potential (ENa+) for sodium ions calculated using the Nernst equation?
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Which of the following ions has the highest intracellular concentration according to the provided data?
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Why does the membrane potential (Vm) in neurons tend to be closer to the equilibrium potential of potassium (EK+)?
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What role do ion pumps such as Na+/K+ ATPase play in neuronal function?
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Which ion has the second highest extracellular concentration compared to others listed?
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Which of these ionic species is most critical in establishing the resting membrane potential?
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What is the primary consequence of a blockade of the Na+/K+ pump on the membrane resting potential?
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What determines the net flux of ions across the cell membrane?
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What is the purpose of the Nernst equation in the context of membrane potential?
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What is the name of the equation that takes into account the permeability of multiple ions when calculating the membrane potential?
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What is the primary effect of the electrogenic Na+/K+ pump on the membrane resting potential?
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What type of ion channel is responsible for the opening of channels in response to synaptic input from other neurons?
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What is the primary function of the Na+/K+ pump in maintaining the electrochemical gradient?
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What is the main reason why the resting membrane potential (Vm) is closer to the equilibrium potential of potassium (EK+)?
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What is the relationship between the electro-chemical gradients and the ionic channels in the membrane?
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What is the effect of the Na+/K+ pump on the membrane resting potential?
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What is the effect of the Na+/K+ pump on the concentration gradients of sodium and potassium ions?
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What type of ion channels are responsible for the generation of graded potentials?
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What is the primary mechanism by which the Na+/K+ pump maintains the electrochemical gradient?
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What is the effect of a change in the permeability of K+ ions on the membrane resting potential?
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What is the primary reason for the difference in concentration of sodium ions across the neuronal membrane?
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According to the Nernst equation, what is the equilibrium potential for sodium ions?
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What is the primary function of the electrogenic Na+/K+ pump in maintaining the membrane resting potential?
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Why does the membrane potential of a neuron tend to be closer to the equilibrium potential of potassium ions?
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What would be the effect on the membrane resting potential if the Na+/K+ ATPase pump were blocked?
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What is the primary factor that determines the resting membrane potential of a neuron?
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What is the effect of an increase in permeability of the membrane to sodium ions on the resting membrane potential?
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What is the role of the electrogenic Na+/K+ pump in maintaining the electrochemical gradient across the neuronal membrane?
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Study Notes
Nervous System Overview
- Neurons are fundamental units of the nervous system, as described in the Neuron Doctrine by Ramon y Cajal in the early 1900s.
- Dendrites have extensive branching and process a high number of synaptic inputs (4,000 to over 100,000, particularly in Purkinje cells).
- The cell body (~50 μm) serves as the metabolic center and includes the axon hillock.
- Axons transmit electrical signals over distances ranging from 0.1 mm to 2 m, connecting with up to 1000 other neurons.
Principles of Neuron Function
- Neurons operate based on two principles:
- Dynamic Polarization: Electrical signals travel in one direction.
- Connectional Specificity: Neurons connect in specific patterns, not randomly.
- These principles form the basis of the modern connectionist approach in neuroscience.
Neuron Morphology and Physiology
- Neurons can be distinguished by their form, specifically the number of processes (dendrites and axons) extending from the cell body.
- Electrical and chemical signals are essential for neuron communication.
- The membrane potential of neurons is typically around -70 mV, a critical aspect of their function.
Membrane Potential and Recording Techniques
- The differential electrical potential across the neuronal membrane is a key feature; intracellular recording techniques were pioneered in the late 1940s by Hodgkin, Huxley, and Eccles, who won the Nobel Prize in 1963.
- Glass micropipettes filled with saline solution are used as electrodes for measuring membrane potential.
- The Na+/K+ pump creates and maintains concentration gradients by transporting 3 Na+ ions out of the cell and 2 K+ ions in.
Ion Channels and Their Classification
- Ion channels are membrane proteins that regulate the passage of specific ions, e.g., channels that permit K+ but not Na+ or Cl-.
- Types of ion channels include:
- Voltage-gated: Open based on membrane voltage changes.
- Chemically-gated: Open in response to chemical binding.
- Mechanically-gated: Responsive to pressure or stretch.
Neuronal Membrane Dynamics
- The neuronal membrane can be represented with the following components:
- Transmembrane electrochemical potential (Ex).
- Conductance of ion channels (gx).
- Electrical capacitance due to the phospholipid bilayer (Cm).
- The Goldman-Hodgkin-Katz equation calculates membrane potential based on ion permeability.
Graded Potentials
- Graded potentials signify local changes in membrane potential due to synaptic inputs via chemically-gated channels at synapses.
- These local changes can open voltage-gated channels, resulting in depolarization or hyperpolarization.
Ion Concentrations Inside and Outside Neurons
- Typical ionic concentrations:
- Sodium (Na+): 15 mM intracellular, 145 mM extracellular.
- Potassium (K+): 150 mM intracellular, 4 mM extracellular.
- Calcium (Ca2+): 70 nM intracellular, 2 mM extracellular.
- Chloride (Cl−): 10 mM intracellular, 110 mM extracellular.
- Total ion concentration gradients created by pumps like Na+/K+ ATPase impact neural activity.
Equilibrium Potential Calculations
- The Nernst equation for sodium (Na+) gives an equilibrium potential of approximately +60 mV, calculated using the ratio of external to internal concentrations.
- Most neurons maintain a membrane potential closer to EK+ due to higher permeability for potassium compared to sodium and chloride.
Role of Pumps and Transporters
- Pumps and transporters are crucial in maintaining the chemical gradients of key ions (Na+, K+, Ca2+, Cl−) that directly influence neuronal excitability and signaling.
Ion Transport Mechanisms
- Na+/K+-ATPase pump transports 3 Na+ ions out and 2 K+ ions into the cell, crucial for maintaining concentration gradients.
- This pump is termed an electrogenic pump due to its contribution to the membrane's resting potential.
- Inhibition of the Na+/K+ pump can result in a 10 mV change in membrane resting potential.
Ion Channels
- Membrane proteins function as ion channels, selectively allowing specific ions to pass (e.g., potassium but not sodium or chloride).
Classification of Ion Channels
- Voltage-gated channels: Open based on the membrane's voltage.
- Chemically-gated channels: Open in response to chemical binding.
- Mechanically-gated channels: Respond to mechanical pressure or stretch.
Membrane Potential
- Membrane potential (Vm) is influenced by the permeability of various ions within the cell.
- The Nernst equation and Goldman-Hodgkin-Katz equation (GHK) are used to calculate Vm by considering the concentration gradient and permeability of ions.
Example of Ion Permeability
- Example permeability values for potassium (PK = 1), sodium (PNa = 0.04), and chloride (PCl = 0.45) yield a calculated Vm of approximately -70 mV.
Graded Potentials
- Graded potentials are local changes in membrane potential initiated by synaptic input from other neurons affecting chemically-gated channels.
- These local changes can lead to the opening of voltage-gated channels, resulting in either depolarization or hyperpolarization.
Ionic Concentrations and Membrane Potential
- Sodium (Na+) and potassium (K+) concentrations vary significantly between intracellular (15 mM Na+, 150 mM K+) and extracellular environments (145 mM Na+, 4 mM K+).
- Other ions such as Mg2+, Ca2+, Cl-, and HCO3- also contribute to the overall membrane potential.
Equilibrium Potential
- The equilibrium potential for sodium (ENa) can be calculated using the Nernst equation: ENa = 61 log(145/15) = +60 mV.
- K+ typically produces a membrane potential near its equilibrium due to higher permeability relative to Na+ and Cl-.
Factors Affecting Resting Potential
- The resting membrane potential (Vm) is established by the electrogenic nature of the Na+/K+ pump and the relative permeability of the membrane to various ions.
- The cell membrane acts as a barrier, exchanging ions through channels to maintain electrochemical gradients.
Electrophysiology of Neurons
- A neuron can be viewed as a charged liquid-filled compartment with a lipid bilayer that restricts ion movement.
- The net ion flow across the membrane is dependent on established electrochemical gradients.
- At equilibrium, electrical and chemical forces balance, creating no net ion flux. The voltage across the membrane at this state is termed the equilibrium potential.
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Description
This quiz covers the basics of the nervous system, including the neuron doctrine, dendrites, cell body, axon, and electrical signals. It is based on chapters 2, 6, 7, 8, and 10 of a physiology textbook.
