Neuroscience: Nernst Equation and Ion Gradients

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Questions and Answers

What happens when the chemical and electrical gradients reach equilibrium?

The system can change direction.

The Nernst equation is applied. (correct)

The membrane becomes impermeable to ions.

The concentration of ions inside the membrane increases.

What is the primary role of the Nernst equation in this context?

To determine membrane potential at equilibrium. (correct)

To measure the volume of the cell.

To establish ion permeability of the membrane.

To calculate ion concentrations outside the cell.

What would likely occur if the chemical gradient of K+ was greater than the electrical gradient?

K+ would move into the cell, increasing the electrical potential.

K+ would lead to cell depolarization immediately.

K+ would move out of the cell until equilibrium is reached. (correct)

K+ would remain static, as gradients do not affect motion.

Which ion is primarily referenced for establishing the Nernst equation in the content?

K+ (C) Signup and view all the answers

What describes the relationship between the concentration gradient and electrical gradient at equilibrium?

They are equal and opposite. (B) Signup and view all the answers

What is the primary factor contributing to the negative charge inside the neuronal membrane at rest?

Presence of impermeant negatively charged ions (A-) (C) Signup and view all the answers

Which ion has the highest concentration outside the neuronal membrane at rest?

Na+ (C) Signup and view all the answers

At rest, which ion is the neuronal membrane most permeable to?

K+ (A) Signup and view all the answers

What happens to K+ ions as a result of their concentration gradient?

They leak out of the cell (D) Signup and view all the answers

What is the K+ concentration inside the neuronal cell at rest?

140 mM (B) Signup and view all the answers

What effect does the permeability of the neuronal membrane have on the distribution of Cl- ions?

Cl- ions cannot diffuse across the membrane (A) Signup and view all the answers

What is the Na+ concentration outside the neuronal membrane at rest?

145 mM (B) Signup and view all the answers

How do the impermeant negatively charged ions (A-) affect membrane potential?

They contribute to the resting membrane potential being negative (A) Signup and view all the answers

What initiates the activation of sodium channels in the membrane?

Depolarization of the membrane to threshold (D) Signup and view all the answers

What is the membrane potential at which 60% of sodium channels are reported to open?

-70 mV (A) Signup and view all the answers

Which of the following best describes the resultant effect when sodium channels open?

Membrane undergoes further depolarization (B) Signup and view all the answers

What pattern describes the opening of sodium channels upon reaching threshold?

Positive feedback loop (B) Signup and view all the answers

What is the typical value of the resting membrane potential?

-70 mV (A) Signup and view all the answers

What is the primary ion involved in the depolarization process described?

Sodium ions (Na+) (B) Signup and view all the answers

What primarily causes the resting membrane potential?

A small excess of negatively charged ions inside the cell (D) Signup and view all the answers

Which ion's gradient is most significant for establishing resting membrane potential?

Potassium ions (D) Signup and view all the answers

How does the excess of negatively charged ions affect resting membrane potential?

It creates a negative voltage within the cell (A) Signup and view all the answers

In terms of ion distribution, what occurs at resting membrane potential?

Higher concentration of potassium ions inside the cell (D) Signup and view all the answers

What is the role of ion concentration gradients at resting membrane potential?

They stabilize the electrical charge across the membrane (B) Signup and view all the answers

Which statement is true about the resting membrane potential?

It reflects the balance of ionic charge inside and outside the cell (A) Signup and view all the answers

What happens to the resting membrane potential when sodium permeability increases?

The potential becomes more positive (A) Signup and view all the answers

Which ion's concentration is usually lower inside the cell compared to outside at resting membrane potential?

Sodium ions (B) Signup and view all the answers

Which ions contribute to the establishment of the resting membrane potential?

Potassium and sodium ions (A) Signup and view all the answers

What characterizes the absolute refractory period in neuronal activity?

Sodium channels are inactive and the membrane is completely unexcitable. (C) Signup and view all the answers

Which of the following statements is correct regarding action potentials?

They exhibit a frequency that conveys information. (A) Signup and view all the answers

How do neurotoxins like tetrodotoxin and batrachotoxin affect sodium channels?

They inhibit the activity of sodium channels. (D) Signup and view all the answers

What is the primary mechanism by which action potentials propagate along an axon?

By spreading electrotonic currents from the action potential site. (C) Signup and view all the answers

During which period is the membrane potential overshooting its resting level due to open voltage-gated potassium channels?

Relative refractory period. (C) Signup and view all the answers

What is the equilibrium potential for K+ ions typically characterized as?

Approximately $-90 mV$. (B) Signup and view all the answers

How do sodium channels affect neuronal excitability after an action potential?

They become inactive temporarily, promoting unexcitable states. (C) Signup and view all the answers

What role does the frequency of action potentials play in neuronal signaling?

It dictates the response level of the neuron to stimuli. (C) Signup and view all the answers

What is the primary function of metabotropic glutamate receptors (mGluRs)?

To relay a chemical signal inside the postsynaptic neuron (A) Signup and view all the answers

Which of the following neurotransmitters primarily interacts with metabotropic receptors?

Glutamate (C) Signup and view all the answers

What type of signaling molecule is generated inside the postsynaptic spine upon activation of mGluRs?

Second messenger (D) Signup and view all the answers

What role do second messengers play in neuronal signaling?

They activate cellular proteins such as kinases and transcription factors (A) Signup and view all the answers

Which of the following is NOT a feature of ionotropic receptors?

They relay signals via G-proteins (D) Signup and view all the answers

Which protein type is specifically activated by second messengers?

Protein kinases (D) Signup and view all the answers

What distinguishes metabotropic receptors from ionotropic receptors?

Metabotropic receptors initiate signaling cascades involving second messengers (C) Signup and view all the answers

What is the effect of activating GABAB receptors in the synaptic environment?

Generates a second messenger cascade within the postsynaptic neuron (C) Signup and view all the answers

Study Notes

Course Information

Course name: PHGY 209
Course topic: Introduction to the Nervous System
Instructor: David Ragsdale
Affiliation: Montreal Neurological Institute
Email: [email protected]

Remembering Past Events

Students are asked to recall past events
A picture of a group of people at a skating rink is displayed

Quote on the Mind

"Our mind is the pattern of information processing running on a special kind of machine: our brain. ... Its information processing all the way down and all the way up."
Author: Read Montague

Organization of the Nervous System

The nervous system is divided into central and peripheral systems
The central nervous system consists of the brain and spinal cord
The peripheral nervous system includes afferent (sensory) fibers, efferent (motor) fibers, and the autonomic and enteric nervous systems
Afferent fibers carry sensory information to the central nervous system to the CNS
Efferent fibers carry motor information from the central nervous system to muscles and glands
The autonomic nervous system controls involuntary functions
The enteric nervous system controls the gastrointestinal tract

Neurons

The nervous system includes approximately 100 billion neurons
Neurons communicate with each other at specialized sites called synapses
The human nervous system comprises hundreds of trillions of synapses
Neurons show a wide range of shapes and sizes

Neuron Structure

Neurons have a cell body (soma), branching dendrites, and an axon
Axons can range in length from a few millimeters to more than a meter
Dendrites receive information
Axons transmit information
Presynaptic terminals transmit information to the next neuron

Electrical Properties of Neurons

Resting Membrane Potential

The inside of a typical neuron is -60 to -70 mV compared to the outside
This resting membrane potential is caused by a slight excess of negatively charged ions inside the cell
The resting membrane potential is created by concentration gradients for ions like Na+, K+, Cl- and A-

Concentration/Permeability gradients

Na+ : outside = 145mM, inside = 10mM
K+ : outside = 5mM, inside = 150mM
Cl- : outside = 100mM, inside = 5mM
A- : outside = 50mM, inside = 155mM
The neuronal membrane is highly permeable to K+ but much less permeable to other ions.
K+ ions leak out of the cell down the concentration gradient, leaving negatively charged ions inside, creating an electrical gradient that pulls K+ ions back in
The equilibrium state of the concentration and electrical gradients is described by the Nernst Equation.

Nernst Equation

Eion = 2.3RT/ZF * log [ion]out/[ion]in
The equilibrium potential for potassium (EK) plays a significant role in the resting membrane potential (approximate -90 mV)
The actual resting membrane potential is slightly closer to –70 mV due to some sodium leakage through the membrane.
Resting permeability to K+ is caused by leak channels
Leak channels are proteins that form K+ selective pores through the membrane.
The channels are open at rest.

Action Potential

Action potential is a short, rapid change in the electrical potential across a neuron’s membrane. An all-or-none event
Action potentials usually start at the initial segment of the axon and propagate along the axon to the presynaptic terminals
The rising phase (depolarization) of the action potential is caused by sodium ions flowing into the cell. Voltage-gated sodium channels
The falling phase (repolarization) is caused by potassium ions flowing out of the cell . Voltage-gated potassium channels.
The action potential is initiated when the membrane potential depolarizes to a threshold level.
The threshold is determined by the properties of voltage-gated sodium channels.
Sodium channels have three critical properties: Closed at resting potential, open when the membrane depolarizes, selective for Na+, open channel rapidly inactivates, stopping the flow of Na+ ions.
The density of voltage-gated sodium channels in the axon membrane is much higher than the density of leak potassium channels.
Action Potential Propagation
Action potential propagation is caused by spread of electrotonic currents from the site of the action potential.

Refractory Periods

Absolute refractory period: A brief period after an action potential where the membrane cannot be re-excited. Sodium channels are inactivated
Relative refractory period: A somewhat longer period after the absolute refractory period where the membrane is less excitable. Voltage-gated potassium channels are open

Synaptic Transmission

Synapses are specialized junctions between neurons or between neurons and other cells
Different types of synapses
Axodendritic
Axosomatic
Axoaxonic
Spine synapses
Shaft synapses
Presynaptic terminal
Postsynaptic terminal

Summary of LTP (Long-Term Potentiation)

High-frequency activity in active synapses increases the strength of synapses.
Involved opening of NMDA receptors enabling Calcium influx.
This strengthens the synapse.
This can impact neuron survival and play a significant role in neurodegenerative and stroke related diseases.

Other important factors

Excitotoxicity: High glutamate concentrations are toxic. Calcium influx through NMDA receptors causes this toxicity
Neuromodulators: Dopamine, serotonin, norepinephrine and neuropeptides do not directly transmit neural information, but influence global neural conditions such as alertnes, attention and mood.
Multiple sclerosis: A disease resulting from loss of myelin
Types of synapses: Excitatory and Inhibitory
Main neurotransmitter for excitatory synapses: Glutamate
Main neurotransmitter for inhibitory synapses: GABA

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Description

Explore the dynamics of neuronal ion gradients and the role of the Nernst equation in this quiz. Discover how electrical and chemical gradients interact at equilibrium and the significance of various ions in maintaining resting membrane potential. Perfect for students studying neurobiology and biophysics.