Neuroscience Action Potentials

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Questions and Answers

What initiates the action potential in sensory neurons?

A wave of depolarization caused by a stimulus (correct)

Sustained chemical stimulation from the environment

The movement of Na+ ions into the neuron

Increased concentration of K+ ions outside the neuron

What is the resting membrane potential of a neuron?

-70 mV (correct)

+70 mV

-40 mV

0 mV

What does the term 'all-or-none response' refer to in sensory neurons?

The neuron can fire at varying strengths depending on the stimulus.

Sensory responses are graded based on the type of receptor activated.

Sensory neurons only respond to strong stimuli.

The neuron fires only if the threshold level is reached or exceeded. (correct)

Which ions are primarily involved in creating the wave of depolarization in a neuron?

Na+ and K+ Signup and view all the answers

What must occur for a neuron to fire an impulse?

A minimum level of stimulus must be reached. Signup and view all the answers

What is the primary function of neurotransmitters?

To bind to receptors on the post-synaptic membrane Signup and view all the answers

Which statement correctly describes excitatory neurotransmitters?

They open Na+ channels in the post-synaptic membrane Signup and view all the answers

What happens to acetylcholine after it has exerted its action at the neuromuscular junction?

It is degraded by acetylcholinesterase Signup and view all the answers

Which of the following neurotransmitters is classified as excitatory?

Glutamate Signup and view all the answers

In the context of muscle movement, what role do inhibitory neurotransmitters play?

They relax opposing muscles to facilitate movement Signup and view all the answers

How many different types of neurotransmitters are approximately known?

One hundred Signup and view all the answers

What is a potential consequence of substances that interfere with cholinergic systems?

Convulsions and paralysis Signup and view all the answers

Which of the following neurotransmitters can act as both excitatory and inhibitory?

Acetylcholine Signup and view all the answers

What is the primary ion that rushes into the axon during depolarization?

Sodium (Na+) Signup and view all the answers

What occurs immediately after depolarization in a neuron?

Na+ channels close and K+ channels open Signup and view all the answers

What role does the sodium-potassium pump play in the depolarization and repolarization process?

It actively transports ions to restore resting membrane potential. Signup and view all the answers

During which phase of an action potential does the membrane potential reach approximately +30 mV?

Depolarization Signup and view all the answers

What is the refractory period in the context of neuron activity?

The time in between action potentials when the membrane cannot be reactivated. Signup and view all the answers

How does the strength of the action potential change as it travels along the neuron?

It remains constant throughout the length of the neuron. Signup and view all the answers

What happens to the Na+ and K+ concentrations during the repolarization phase?

Na+ is actively transported out and K+ flows out of the axon. Signup and view all the answers

What initiates the action potential in a neuron?

An external stimulus triggering Na+ channels to open. Signup and view all the answers

Study Notes

Action Potentials

Nerve response to stimuli
Sensory neurons have receptors on their ends, often linked to collagen fibers and ion channels.
These sensory receptors detect environmental changes, triggering a depolarization wave called an action potential.
Action potentials are electrochemical messages transmitted through nerve fibers.
Action potentials travel in one direction along the axon.
The axon sends a wave of depolarization along its length.
The wave of depolarization is primarily the movement of Na+ and K+ ions across the axon's membrane.

Receptors in Skin

Free nerve endings (pain, temperature), Merkel's disc (touch), Meissner's corpuscle (touch), hair follicle receptor (touch), Pacinian (or lamellated) corpuscle (vibration and pressure), Ruffini's ending (stretch) are types of receptors.

Synaptic Transmission

Tiny gaps between neurons are called synapses; they span 20 nm.
Messages are carried from the presynaptic neuron to the postsynaptic neuron across the synapse.

Neurotransmitters

Chemicals released by nerve endings that diffuse across synaptic clefts.
Neurotransmitters bind to receptors on post-synaptic membranes.
Neurotransmitters are contained in spherical, membrane-bound vesicles.
Approximately 100 types; many are amino acid derivatives or peptides (e.g., glutamate, endorphins).
Neurotransmitters can be excitatory or inhibitory.
Excitatory neurotransmitters cause Na⁺ channels to open.
Inhibitory neurotransmitters prevent action potentials by opening K⁺ channels.
Some neurotransmitters can both excite or inhibit, depending on the receptor they bind to.

Acetylcholine

An excitatory neurotransmitter used at neuromuscular junctions
Motor neurons release acetylcholine to activate muscles.
Degraded by acetylcholinesterase.
Drugs that interfere with cholinergic systems can cause dangerous effects (e.g., convulsions, paralysis)

Depolarization

When a nerve cell is excited (by a stimulus), Na⁺ channels open and Na⁺ rushes into the axon.
K⁺ channels remain closed (during depolarization), resulting in charge reversal.
Membrane potential becomes approximately +30 mV.
This process is called depolarization.
Depolarization of one part of the axon causes neighboring Na⁺ channels to open, continuing along the axon.

Repolarization

Immediately after depolarization, Na⁺ channels close.
K⁺ channels open, allowing K⁺ to move outside the axon.
This process restores the membrane to its resting potential.
A sodium-potassium pump actively transports 3Na⁺ out of the axon for every 2K⁺ in.
The time between impulses when the membrane is repolarizing is the refractory period.

All-or-None Response

Sensory neurons can be stimulated by chemicals, light, heat, membrane disruption or electricity.
A minimum stimulus level (threshold level) must be reached before a neuron fires an impulse.
Once the threshold level is reached, the strength of the response is uniform along the axon.
This strong response is called the all-or-none response; there are no mild or strong responses.

How to distinguish warm from hot

The more intense a stimulus, the greater the frequency of impulses.
Warm stimuli have slower frequencies, while hot stimuli have higher frequencies.
Each neuron has a threshold level, and more neurons fire when the stimulus is more intense, leading to a greater intensity of the response from the brain.

The Neuron at Rest

The outside of the neuron is more positively charged than the inside.
(Outside: ↑Na⁺, K⁺; Inside: ↓Na⁺, ↑K⁺).
A resting membrane potential of -70 mV exists.
The uneven concentrations of Na⁺ and K⁺ on either side of the neuron membrane maintain an external positive charge.

Homework Questions

Read section 9.2 and answer questions #1-8 and #10 on page 426.

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Description

Explore the mechanisms of action potentials and synaptic transmission in this quiz. Understand how sensory receptors detect stimuli and the role of ion movement in depolarization waves. Test your knowledge of nerve response and receptor types in the skin.