Nervous System: Graded and Action Potentials

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Questions and Answers

What primarily results in the membrane potential of a neuron?

Constant membrane permeability for all ions

Equal distribution of ions across the membrane

Uneven distribution of ions across the membrane (correct)

Presence of myelin sheath around the neuron

How are graded potentials primarily formed in the neuron?

From the uneven ion distribution along the axon

Due to the influx of neurotransmitters at the dendrites (correct)

By rapid firing of action potentials

Through the activation of voltage-gated channels

At which location is the action potential generated in a neuron?

Axon terminal

Synaptic cleft

Dendritic region

Axon hillock (correct)

What determines the propagation of an action potential along the axon?

The presence of gated ion channels Signup and view all the answers

Which of the following is a key factor in cell-to-cell communication in the nervous system?

Chemical signaling via neurotransmitters Signup and view all the answers

What is the process called when a channel opens to allow ion flow?

Channel activation Signup and view all the answers

Which types of ions typically flow into the cell during activation of ion channels?

Cl- Signup and view all the answers

Which term describes the flow of electrical charge carried by an ion during channel activation?

Ionic current (Iion) Signup and view all the answers

What occurs during channel inactivation?

The channel remains open despite a stimulus. Signup and view all the answers

Which category of gated channels responds primarily to changes in membrane voltage?

Voltage-gated channels Signup and view all the answers

What type of potential occurs as a result of excitatory stimuli in neurons?

Depolarization Signup and view all the answers

What is positively correlated to the amplitude of the graded potential generated?

Strength of the stimulus Signup and view all the answers

Where do graded potentials most frequently occur in neurons?

Soma and dendrites Signup and view all the answers

What structure forms a conductive link in electrical synapses?

Gap junctions Signup and view all the answers

Which of the following is NOT an advantage of electrical synapses?

Chemical modification of signals Signup and view all the answers

What is the primary role of neurotransmitters in chemical synapses?

To convert electrical signals into chemical signals Signup and view all the answers

Which neurotransmitter is primarily associated with the parasympathetic nervous system?

Acetylcholine Signup and view all the answers

Which amino acid is primarily known as an inhibitory neurotransmitter in the CNS?

GABA Signup and view all the answers

How are biogenic amines formed?

By decarboxylating amino acids Signup and view all the answers

Which neurotransmitter is linked to the sensation of pleasure and reward?

Dopamine Signup and view all the answers

In the context of neurotransmitters, what function do receptors provide?

Bind neurotransmitters and elicit a response Signup and view all the answers

What is responsible for the maintenance of constant amplitude of an action potential as it propagates along an axon?

High density of voltage gated Na+ channels at the Node of Ranvier Signup and view all the answers

When does the action potential fire?

Once the threshold is reached Signup and view all the answers

Which of the following biogenic amines primarily affects the sympathetic nervous system?

Epinephrine Signup and view all the answers

How can neurotransmitters affect the postsynaptic cell's membrane potential?

By opening or closing ion channels Signup and view all the answers

What occurs during point #4 of the action potential generation?

Massive Na+ influx occurs leading to full depolarization Signup and view all the answers

What happens to the membrane potential during K+ efflux?

It returns to its resting state Signup and view all the answers

What triggers the activation of voltage gated Na+ channels sequentially along the axon?

Threshold being reached at the Nodes of Ranvier Signup and view all the answers

What is the role of Na+/K+-ATPase in relation to action potentials?

It sets and maintains the resting membrane potential Signup and view all the answers

What is the behavior of action potentials as they conduct down an axon?

They behave like a wave of electrical energy with constant amplitude Signup and view all the answers

What occurs at point #5 in the sequence of ionic events for an action potential?

Activation of K+ channels leading to K+ efflux Signup and view all the answers

Which of the following statements is true about purines?

Adenosine diphosphate (ADP) is a type of purine. Signup and view all the answers

What is the primary function of nitric oxide (NO) in the body?

It causes vasodilation of smooth muscles. Signup and view all the answers

Which of the following describes neuropeptides?

They consist of chains of amino acids linked by peptide bonds. Signup and view all the answers

What is the role of endorphins in the body?

They act as the body's natural painkillers. Signup and view all the answers

Which neurotransmitter is classified as a gasotransmitter alongside nitric oxide?

Carbon monoxide (CO) Signup and view all the answers

What characteristic distinguishes the action of purines in the nervous system?

They function as excitatory neurotransmitters. Signup and view all the answers

Which of the following neurotransmitters is best known as an endogenous painkiller?

Endorphins Signup and view all the answers

Which statement about gasotransmitters is false?

Gasotransmitters are always inhibitory. Signup and view all the answers

What is the primary function of the nodes of Ranvier in an axon?

To increase the speed of conduction via saltatory conduction Signup and view all the answers

What happens to action potential propagation in the presence of a damaged myelin sheath?

It slows down or may not occur due to current leaks Signup and view all the answers

In the synapse, what is the presynaptic axon terminal primarily responsible for?

Releasing neurotransmitters to the postsynaptic neuron Signup and view all the answers

What are the two main components of a synapse?

Presynaptic axon terminal and postsynaptic membrane Signup and view all the answers

How do simultaneous recordings along an axon illustrate the phases of an action potential?

They demonstrate that different sections experience varying phases simultaneously Signup and view all the answers

What is the role of the myelin sheath in the conduction of action potentials?

To insulate the axon and speed up conduction Signup and view all the answers

What is a characteristic feature of saltatory conduction?

It allows the action potential to jump from node to node Signup and view all the answers

What distinguishes axodendritic synapses from axosomatic synapses?

Where the presynaptic neuron contacts the postsynaptic neuron Signup and view all the answers

What effect does a depolarization phase have during an action potential?

It causes sodium ions to flood into the neuron, raising the membrane potential Signup and view all the answers

What role do dendrites play in a neuron’s function?

Integrating signals and receiving input from other neurons Signup and view all the answers

Study Notes

Nervous System: Generation and Propagation of Graded and Action Potentials

Neurons are cells with a membrane
Membrane potential is a direct result of uneven ion distributions and differing membrane permeabilities for these ions
Concentration gradients and membrane permeability are involved in forming the electrical signals in neurons
Ion permeability is a function of the channels that transport the ion
Channels can change due to changes in their environmental condition
Most channels are gated ion channels that open or close in response to a stimulus
Gated channels are categorized into mechanically gated, chemically gated, and voltage-gated channels
Channel conductance (G) is the ease of ion flow through a channel
Channel activation is channel opening to allow ion flow
Channel inactivation is channel closing even with continued activation
Ions like Na+, Cl-, and Ca2+ usually flow into the cell (influx) while K+ ions usually flow out (efflux)
The excitable characteristic of a neuron, created by the activation and inactivation of the gated channels, allows for the generation of nerve impulses (action potentials) which enable the neuron to communicate between various regions of the body and regulate body functions

Graded Potentials in Neurons

Graded potentials are events of depolarization (excitatory) or hyperpolarization (inhibitory) that occur in dendrites and soma
Less frequent near axon terminals
Occur in dendrites and soma frequently
Chemical stimuli (e.g., neurotransmitters) and mechanical stimuli (e.g., pressure receptor) can cause graded potentials
Strength of the stimulus is positively correlated to the amplitude of the graded potential
Amplitude of the graded potential reflects the number of gated ion channels opened
Graded potentials are degraded (decrease in amplitude) along the cytoplasmic space of dendrites and soma because of current leak and cytoplasmic resistance
The sensory neurons' graded potentials are formed from the ionic flow caused by mechanically gated or chemically gated channels
Graded potentials may occur when an open ion channel becomes close
Graded potential begins when stimulus opens Na+ gated channels allowing for influx of Na+ and spreading the depolarization wave, or local current flow
Strength of the stimulus determines the number of Na+ channels activated which correlates with the amplitude of the graded potential
It spreads from the stimulation site but decays over distance

Action Potentials

If the sum of graded potentials is above threshold at trigger zone, an electrical signal (action potential) is initiated and propagated along the axon
The trigger zone is typically the axon hillock that is located between the cell body and the axon
In sensory neurons, the trigger zone lies adjacent to the receptor
The graded potentials, summed at the trigger zone, will trigger an action potential if it exceeds the threshold value
A typical mammalian neuron's threshold for action potential generation is about -55 mV
An action potential is generated when the cumulative graded potential is equal to or above the threshold.
Action potentials have a uniform strength and do not decay

Propagation of Action Potentials

Action potentials are all-or-none phenomena; their amplitude is the same along the axon regardless of the strength of the graded potential, as long as the graded potential is equal to or greater than the threshold
Conduction of action potentials is consistent in amplitude and like a wave of electrical energy travelling down the axon
The ability to maintain constant amplitude during propagation is due to voltage-gated Na+ ion channels present in high density within the Node of Ranvier along the axon and triggering sequential activation at the nodes
High density of voltage-gated Na+ channels are located in neuron trigger zones and Node of Ranvier allowing action potential (minimal decay)
Myelin sheaths composed of Schwann cells insulate the axon, minimizing current leak and reducing decay of electrical signal through the gaps (Node of Ranvier)
During demyelinating diseases, conduction will either be slow or absent due to current leakage from damaged regions

Neural Communication

Neural communication happens between neurons through chemical synapses or electrical synapses
The two main components of a synapse are a presynaptic axon terminal and the postsynaptic cell membrane
The synapses happen either between dendrites and cell bodies (axodendritic or axosomatic)
It can also be between a neuron and a non-neuronal cell, such as a motor unit
Electrical synapses connect directly, allowing ionic currents to easily pass through connexon channels
Electrical synapses are characterized by faster communication via a direct transmission of ions across the synapse
Chemical synapses use neurotransmitters to transfer signals
Neurotransmitters bind to receptors, causing a change in postsynaptic membrane potential
Neurotransmitters include acetylcholine, amino acids, and biogenic amines; others are neuropeptides, nitric oxide, and carbon monoxide

Neurotransmitters

Neurocrines are secreted by neurons which bind to neurotransmitter receptors
Neurotransmitter types include acetylcholine, amino acids, biogenic amines, neuropeptides, nitric oxide, and carbon monoxide, and other purines

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Description

Explore the mechanisms behind graded and action potentials in neurons. This quiz delves into membrane potentials, ion distributions, and the role of various channel types. Test your understanding of how these electrical signals are generated and propagated in the nervous system.