PHGY 209: Introduction to the Nervous System

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What triggers the activation of sodium channels in the initial segment of the membrane?

Inhibition of potassium channels

Hyperpolarization of the membrane potential

Decrease in calcium ion concentration

Depolarization of the membrane to threshold (correct)

What is the consequence of the initial opening of sodium channels?

Activation of potassium channels

Hyperpolarization of the membrane

Increased sodium current leading to further depolarization (correct)

Inhibition of neurotransmitter release

At what membrane potential does the sodium current initially activate sodium channels?

+50 mV

-50 mV

0 mV

-70 mV (correct)

What effect does the depolarization have on sodium channel activation?

It activates a small fraction of sodium channels Signup and view all the answers

What happens to sodium channels during the rising phase of the action potential?

Sodium channels open in a regenerative manner. Signup and view all the answers

At what membrane potential (in mV) does the action potential peak due to sodium channel activation?

+50 mV Signup and view all the answers

Which state of sodium channels is characterized by the inability to allow Na+ influx?

Inactivated state Signup and view all the answers

What proportion of sodium channels are open at -50 mV during the action potential?

10% Signup and view all the answers

What is the role of sodium current during the rising phase of the action potential?

It contributes to the regenerative process. Signup and view all the answers

What happens during the absolute refractory period?

The sodium channels are inactivated, making the membrane unexcitable. Signup and view all the answers

What is the primary ion contributing to the resting membrane potential?

Potassium (K+) Signup and view all the answers

What does the frequency and pattern of action potentials indicate?

The strength of the stimulus. Signup and view all the answers

How does the sodium-potassium pump maintain ion gradients?

By hydrolyzing ATP to transport sodium out and potassium in Signup and view all the answers

Which ion is primarily responsible for depolarization during an action potential?

Na+ Signup and view all the answers

Which membrane potential is closest to the equilibrium potential for potassium (EK)?

-90 mV Signup and view all the answers

Which toxin is produced by puffer fish and affects sodium channels?

Tetrodotoxin Signup and view all the answers

Which factor primarily determines the membrane potential?

Permeability to different physiological ions Signup and view all the answers

What occurs during the relative refractory period?

The membrane potential overshoots its resting level. Signup and view all the answers

What occurs to the membrane potential if the permeability to sodium (Na+) dramatically increases?

It will approach the equilibrium potential for sodium (+70 mV) Signup and view all the answers

What is the resting membrane potential typically around in neurons?

-70 mV Signup and view all the answers

What happens to the concentration gradients of sodium and potassium at rest?

They remain relatively stable Signup and view all the answers

How do action potentials propagate along an axon?

By spread of electrotonic currents from the action potential site. Signup and view all the answers

What is the value of ERest as mentioned in the content?

-70 mV Signup and view all the answers

Which of the following statements about sodium channels is INCORECT?

Sodium channels remain open after the peak of the action potential. Signup and view all the answers

Which of the following statements is true about the dominant ion at rest?

Potassium ions move freely, maintaining a negative potential Signup and view all the answers

What is the role of AMPA receptors in synaptic transmission?

They are responsible for the 'fast' excitatory postsynaptic potential (EPSP). Signup and view all the answers

How does the depolarization caused by a single EPSP compare to the threshold needed to initiate an action potential?

It is too small to reach the action potential threshold. Signup and view all the answers

What is the typical duration of an EPSP at brain synapses?

20 msec Signup and view all the answers

What must occur for an action potential to initiate at the axon initial segment?

Between 50 to 100 EPSPs must sum to threshold. Signup and view all the answers

Which of the following statements regarding NMDA receptors is true?

They are ionotropic receptors that require additional signals for activation. Signup and view all the answers

What does the depolarization observed during an EPSP typically reach?

-58 mV Signup and view all the answers

Which neurotransmitter is primarily associated with AMPA receptor activation?

Glutamate Signup and view all the answers

What is the primary function of EPSPs in neuronal communication?

To transiently depolarize the postsynaptic membrane. Signup and view all the answers

What triggers neurotransmitter release at the presynaptic terminal?

Calcium influx into the terminal Signup and view all the answers

Which type of neurotransmitter response results in depolarization of the postsynaptic membrane?

Excitatory postsynaptic potential (EPSP) Signup and view all the answers

Which neurotransmitter is primarily responsible for excitatory transmission in the brain?

Glutamate Signup and view all the answers

What are the two types of ionotropic glutamate receptors involved in rapid excitatory transmission?

AMPA and NMDA receptors Signup and view all the answers

What occurs when neurotransmitter binds to a postsynaptic receptor?

It can result in an EPSP or IPSP in the postsynaptic neuron Signup and view all the answers

What is the significance of the active zone in synaptic transmission?

It is the site of synaptic vesicle fusion and neurotransmitter release Signup and view all the answers

What characterizes the postsynaptic density in a synapse?

It is rich in neurotransmitter receptors and signaling proteins Signup and view all the answers

How does an inhibitory postsynaptic potential (IPSP) affect the postsynaptic neuron?

It hyperpolarizes the postsynaptic membrane Signup and view all the answers

Study Notes

Course Information

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

Nervous System Overview

The nervous system consists of approximately 100 billion neurons.
The brain is part of the central nervous system.
The peripheral nervous system includes afferent (sensory) and efferent (motor) fibers.
Information processing in the brain occurs throughout the entire system.
Neurons are electrical cells.
Neurons communicate with each other at specialized sites called synapses.
Neurons have diverse shapes and sizes.
Basic neuron structure includes soma (cell body), dendrites, and axon.

Electrical Properties of Neurons

The neuron's interior is typically -60 to -70 mV compared to the outside.
This resting membrane potential is due to differences in ion concentrations (Na+, K+, Cl-, and A-) inside and outside the cell.
The resting membrane potential is primarily determined by the permeability of the membrane to K+ ions.
K+ ions leak out of the cell, creating a negative internal charge.
Membrane permeability to Na+, and other ions is much lower.
The sodium-potassium pump maintains ion gradients; pumping Na+ out of the cell and K+ in.

Action Potential

Electrical impulses are action potentials.
The signal originates at the initial segment of the axon, and moves down the axon toward the presynaptic terminal.
These action potentials begin at the initial segment when voltage-gated sodium channels are activated and Na+ ions rush inside.
The action potential triggers voltage-gated potassium channels to open, allowing K+ ions to flow outside of the cell.
The peak of the action potential is determined by Na+.
Inactivation of the Na+ channels determines the falling phase of the action potential.
Sodium channels are targets for naturally-occurring neurotoxins.
Sodium channels are also blocked by therapeutically important drugs (e.g. local anesthetics & antiepileptics).
Action potential propagation is faster in axons with larger diameters.
Myelination, consisting of Schwann cells (PNS) or oligodendrocytes (CNS), acts as an insulator accelerating the transmission of signals.
Saltatory conduction occurs along these insulated regions.
Nodes of Ranvier are the gaps in myelination where voltage gated sodium channels concentrate and regenerate action potentials.
Unmyelinated axons have a slower conduction velocity.

Synaptic Transmission

A synapse is the region of communication between two neurons.
There are three main types of synapses: Axodendritic, Axosomatic, Axoaxonic.
Neurotransmitters are released into the synaptic cleft, which are received by postsynaptic receptors, potentially leading to an excitatory or inhibitory postsynaptic potential.
Excitatory postsynaptic potential (EPSP) increase the likelihood of postsynaptic firing.
Inhibitory postsynaptic potential (IPSP) decrease the likelihood of postsynaptic firing.
Glutamate is a main excitatory neurotransmitter in the brain.

Receptors

Ionotropic and metabotropic receptors exist.
AMPA receptors are ionotropic receptors and are responsible for the “fast” EPSPs.
NMDA receptors are highly permeable to calcium.
Metabotropic glutamate receptor (mGluRs) and GABAB receptors are involved in modulation.

Synaptic Integration

Action potentials arise when the sum of EPSP's and IPSPs reaches or exceeds threshold.
High frequency activity leads to synaptic plasticity, strengthening the synapse strength over time.
Long-term potentiation (LTP) and other forms of synaptic plasticity contribute to the learning and memory mechanisms.

Neurotoxins

Puffer fish make tetrodotoxin which blocks sodium channels.
Phyllobates frogs secrete batrachotoxin which activates sodium channels.

Excitotoxicity

High concentrations of glutamate can be toxic to neurons.
Excitotoxicity results from calcium influx through NMDA receptors.
Excitotoxicity is related to neurodegenerative diseases after a stroke, and in other cases of neuronal damage.

Inhibitory Synapses

GABA is a primary inhibitory neurotransmitter.
GABAA receptors trigger Cl- influx, generating IPSPs.

Neuromodulators

Dopamine, serotonin, norepinephrine interact mostly or entirely with metabotropic receptors.
Neuromodulators modulate the overall state of the neurons, such as mood, alertness, and attention.

Additional Information

Multiple sclerosis is caused by myelin loss.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz tests your understanding of the nervous system, including its structure, function, and the electrical properties of neurons. You'll explore topics such as neuron communication, synapses, and the roles of the central and peripheral nervous systems.