How does cocaine affect neurotransmitter levels in the synaptic cleft?
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Cocaine prevents the uptake of epinephrine, leading to increased levels in the synaptic cleft.
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How does cocaine affect neurotransmitter levels in the synaptic cleft?
Cocaine prevents the uptake of epinephrine, leading to increased levels in the synaptic cleft.
What are the two types of receptors for Acetylcholine?
Muscarinic and nicotinic receptors.
Is binding to receptors a major pathway for neurotransmitter elimination?
No, because the transmitter can dissociate from the postsynaptic receptor after a while.
What triggers the release of neurotransmitters at the axon terminal?
The influx of calcium ions through voltage-gated calcium channels triggers the release of neurotransmitters.
What type of neurotransmitter is glycine and what effect does it have?
Glycine is a small-molecule neurotransmitter that opens inhibitory postsynaptic potentials (IPSP), similar to GABA.
What is the primary function of the cell body in a neuron?
The cell body is considered the metabolic control center, acting as a manufacturing and recycling plant for the neuron.
What happens when open mechanosensitive channels allow Na+ influx?
It leads to depolarization and suprathreshold depolarization.
What occurs after depolarization in terms of voltage-gated sodium channels?
Voltage-gated sodium channels open, resulting in an action potential.
How is the effect of neurotransmitters terminated?
Through various mechanisms that can include reuptake, degradation, or diffusion.
What motor protein is involved in anterograde transport?
Kinesin motor protein.
What happens to the membrane potential when the receptor potential is larger?
The membrane potential reaches the threshold earlier, resulting in a shorter time period between action potentials and a larger action potential frequency.
What role do synaptic vesicles play in synaptic transmission?
Synaptic vesicles are responsible for the release of neurotransmitters during synaptic transmission.
What are sensory receptors and their function?
Sensory receptors are specialized nerve endings that detect different stimuli and provide electrical signals sent into the CNS.
What happens to the mechanosensitive ion channel under resting conditions?
The mechanosensitive ion channel is closed under resting conditions.
What is the relationship between small maintained summed EPSP and action potential frequency?
Small maintained summed EPSP results in low action potential frequency.
What type of neuron is characterized by having the fastest conduction speed?
A-alpha neurons are the fastest.
What happens to the receptor potential when a small mechanical stimulus is applied?
It results in a small depolarization due to the opening of few mechano-sensitive channels, leading to a smaller current.
What is the function of pseudounipolar sensory neurons?
They have a receptor potential and their cell body is located in the dorsal root ganglion or trigeminal ganglion.
What type of receptors respond to ATP?
Purinergic receptors.
What is electrotonic depolarization?
Electrotonic depolarization occurs when the large sodium current in a region causes depolarization in the next region of the membrane, activating sodium channels there.
What effect does lidocaine have on action potential generation?
It blocks voltage-gated sodium channels, preventing action potential generation and pain sensation.
What happens with a subthreshold mechanical stimulus?
It produces a small receptor potential that decays, and no action potential is generated.
What are the two categories of electrical signals in neurons?
The two categories of electrical signals are electrotonic potentials and action potentials.
What occurs when the mechanical stimulus is maintained?
The membrane potential depolarizes again to the threshold of voltage-gated sodium channels, allowing another action potential.
What is the effect of large maintained EPSP on action potential frequency?
Large maintained EPSP leads to high action potential frequency.
What are the basic regions of an idealized neuron?
An idealized neuron has four basic regions: cell body (soma), dendrites, axon, and axon terminals.
What is the function of AMPA receptors?
AMPA receptors are permeable to 'one-charge' cations, primarily allowing sodium influx into the cell.
What happens when an action potential arrives at the axon terminal?
Depolarization occurs, leading to the opening of N/P type calcium channels.
What is the effect of metabotropic receptors on the postsynaptic membrane?
Metabotropic receptors cause small hyperpolarization (IPSP) for milliseconds, stabilizing the membrane potential at negative values.
What role do G-protein coupled receptors play in neurotransmitter signaling?
G-protein coupled receptors activate heterotrimeric G-proteins, which induce signaling changes in the postsynaptic cell, affecting the activity of ion channels and potentially causing depolarization or hyperpolarization.
What is the process by which neurotransmitters are transported from the cell body to the axon terminal?
Axonal transport, specifically anterograde transport.
What is the frequent inhibitory neurotransmitter mentioned?
GABA (gamma amino-butyric acid)
What role does Acetylcholinesterase play in neurotransmitter elimination?
It breaks down Acetylcholine in the synaptic cleft.
What is electrotonic depolarization caused by?
Open mechanosensitive channels.
How does action potential propagate along a neuron?
Action potential propagates as a regenerating response, developing at one region of the cell and inducing action potential at another location, spreading without decrement.
What triggers the activation of action potential in a neuron?
The activation of action potential is triggered by voltage-gated sodium channels, leading to a large influx of sodium ions.
What is the role of calcium in the axon terminal?
Calcium enters the axon terminal, triggering exocytosis and the release of neurotransmitters.
What causes an IPSP in the postsynaptic neuron?
An IPSP is caused by the opening of ligand-gated chloride channels and sometimes potassium channels, leading to small hyperpolarization.
What functions do mitochondria serve in the axon terminal?
Mitochondria pump out calcium, operate the Na+/K+ pump, and fill synaptic vesicles with neurotransmitters, all requiring ATP.
What is the effect of axoplasm on current flow in the axon?
Axoplasm has high resistance, leading to a major percentage of current leaving and less current entering the cytoplasm of the axon.
What is spatial summation in the context of action potentials?
Spatial summation occurs when action potentials at fibers A and B lead to a larger depolarizing effect than stimulation of one alone.
What neurotransmitter do excitatory fibers release?
Excitatory fibers release glutamate, which binds to AMPA receptors.
What is the role of action potentials in sensory signal transmission?
Action potentials propagate electrical signals rapidly along nerve fibers to the CNS for processing.
What is the function of gap junctions in neurons?
They allow synchronization of depolarization between connected neurons.
What is the output of the CNS after processing sensory information?
The output of the CNS includes effectors such as muscles, vessels, and glands, leading to effects like muscle contraction and glandular secretion.
What is the role of dendrites in a neuron?
Dendrites receive incoming signals from other neurons.
What causes the opening of voltage-gated K+ channels?
A large depolarization causes voltage-gated K+ channels to open while voltage-gated sodium channels inactivate.
What occurs if a mechanical stimulus is maintained?
There can be many successive action potentials generated one after another.
How does current flow in an electrical synapse?
Current flows through the lumen of gap junctions, allowing for instant flow between cells.
What types of synapses exist between neurons?
There are axodendritic synapses, where the axon terminal connects to the dendrite of another neuron, and axosomatic synapses, where the axon terminal forms a synapse with the cell body of another neuron.
How do NMDA receptors operate?
NMDA receptors are permeable to sodium and calcium, requiring glutamate binding and depolarization to open, expelling a magnesium plug.
What is the synaptic cleft?
The gap between the presynaptic and postsynaptic membranes, approximately 20-50 nm wide.
What characterizes electrodens vesicles in the axon terminal?
They contain peptide transmitters, are not in a docked position, and are released upon repeated stimulation by action potentials.
What types of GABA receptors are ligand-gated chloride channels?
GABA A and GABA C receptors
What are the three main pathways for the elimination of neurotransmitters from the synaptic cleft?
Transmitter diffusion away, uptake by presynaptic terminal, and enzymatic breakdown.
What are the types of glutamate receptors on the postsynaptic membrane?
The types of glutamate receptors are ionotropic receptors (like AMPA and NMDA) and metabotropic receptors (G-protein coupled receptors).
How does the amplitude of the signal change with distance from the channel?
The amplitude of the signal decreases with distance, leading to a decay in space.
What is the relationship between mechanical stimulus strength and receptor potential?
A large mechanical stimulus results in a large depolarization, while a small stimulus results in a small depolarization.
What protein is involved in the attachment of synaptic vesicles to the cytoskeleton?
Synapsin I.
What triggers the fusion of synaptic vesicles to the plasma membrane?
A calcium signal (Ca2+).
What are the two main types of synapses?
What is the effect of stimulating fiber C?
Stimulating fiber C results in a small hyperpolarization, leading to an inhibitory postsynaptic potential (IPSP).
What is the effect of the beta/gamma subunit of the Gi protein?
It activates the opening of K+ channels, leading to a rapid outflow of K+ and resulting in hyperpolarization (IPSP).
What is the role of transmembrane proteins in synaptic vesicles?
They facilitate the association of the vesicle to the active cytoskeleton.
Which type of neuron is the slowest and unmyelinated?
C fibers are the slowest and unmyelinated.
What is the effect of sodium influx through ligand-gated channels on the postsynaptic cell?
The influx of sodium through ligand-gated channels causes a small depolarization of the postsynaptic cell, resulting in an excitatory postsynaptic potential (EPSP).
What occurs when chloride channels open in response to neurotransmitter binding?
When chloride channels open, chloride ions move into the postsynaptic cell, making it more negative and resulting in hyperpolarization, which is an inhibitory postsynaptic potential (IPSP).
What happens when a neurotransmitter binds to its receptor on the postsynaptic neuron?
The binding of the neurotransmitter should evoke an effect on the postsynaptic neuron, resulting in either an excitatory postsynaptic potential (EPSP) or an inhibitory postsynaptic potential (IPSP).
What is the nature of action potential in terms of response?
Action potential is an all or none response, meaning it either develops fully or not at all.
What is the amplitude range of an action potential?
The amplitude of an action potential is several times 10mV, typically reaching +20 or +30mV.
How does the electrochemical gradient of H+ affect neurotransmitter accumulation?
The electrochemical gradient of H+ allows for the accumulation of high concentrations of neurotransmitter in the vesicle, facilitating rapid release when the vesicle fuses with the plasma membrane.
What are the criteria for a substance to be classified as a neurotransmitter?
What occurs if depolarization reaches the threshold of voltage-gated sodium channels?
The channel opens, leading to action potential generation.
How do neurotransmitters affect postsynaptic receptors?
Neurotransmitters bind to postsynaptic receptors, which are often ligand-gated, leading to excitatory or inhibitory postsynaptic potentials.
What happens when two action potentials occur rapidly one after another in fiber A?
It results in two EPSPs, with the new one riding on the back of the first, leading to a higher amplitude.
What are the properties of electrotonic potentials?
Electrotonic potentials are graded, have low amplitude (about 1/10 mV), are localized, decay in space, and decay in time if no current is present.
Which motor protein is responsible for retrograde transport?
Dynein motor protein.
What is the typical duration of synaptic delay in neurotransmitter release?
~1-5 ms (milliseconds)
What forms the gap junction between two neurons?
Connexin subunits form connexons, creating hemichannels.
What happens to receptor potential during depolarization?
It spreads with decrement.
Where does depolarization arrive with the highest density of voltage-gated sodium channels?
Around the first myelin sheath.
What neurotransmitter do inhibitory fibers release and which receptors do they bind to?
Inhibitory fibers release GABA and bind to GABA-A receptors.
What is the result of a small amount of glutamate being released in the stimulation of A fiber?
It leads to the opening of AMPA receptors and a small depolarization, resulting in an excitatory postsynaptic potential (EPSP).
What is the result of a suprathreshold stimulus?
It causes electrotonic depolarization that reaches the threshold of voltage-gated sodium channels, resulting in action potential.
What is the effect of a weak suprathreshold stimulus on action potential firing frequency?
A weak suprathreshold stimulus results in low frequency action potential firing.
What characterizes an electrical synapse?
Gap junctions between neighboring neurons that interconnect cytoplasm, allowing bidirectional transmission with no delays.
What types of synapses are formed on the cell body of a neuron?
There are axodendritic, axosomatic, and axoaxonic synapses.
What is a key feature of chemical synapses?
The presence of neurotransmitters that are released from the axon terminal to evoke effects on the postsynaptic membrane.
Is there any flow of information in the opposite direction in chemical synapses?
Typically no, except in some special cases known as retrograde signaling.
What is the role of the V-type proton pump in neurotransmitter storage?
The V-type proton pump uses ATP to pump protons into the lumen of the vesicle, acidifying it and creating a high concentration of H+, which drives the uptake of neurotransmitters as a secondary active transport process.
Where is glycine primarily found?
In the spinal cord and other areas.
Where is the cell body of primary sensory neurons located?
In the dorsal root ganglion or trigeminal ganglion.
What is the role of catecholamines in neurotransmission?
Catecholamines act on noradrenergic receptors.
How does the thickness of an axon affect the velocity of action potential propagation?
Thick fibers have a larger velocity of propagation than thin fibers because the current in thin fibers rapidly leaves the axon through the plasma membrane, spreading less.
What is the function of axon terminals?
Axon terminals form synapses where outgoing signals pass to the dendrite or another neuron.
What is the speed range of fast anterograde transport?
50-400 mm/day.
What is the maximum speed of action potential conduction?
100 - 120 m/s
How are small molecule neurotransmitters filled into vesicles?
They are filled into vesicles in the axon terminal.
What protein is responsible for the uptake of neurotransmitters into synaptic vesicles?
Neurotransmitter-proton exchanger protein.
What happens to the vesicle membrane after neurotransmitter release?
The vesicle membrane may become part of the plasma membrane, but in the Kiss&Run mechanism, the vesicle opens to release neurotransmitter and then closes again to move back into the axon terminal.
What is the role of synaptic vesicles in chemical synapses?
They contain neurotransmitter molecules and are involved in neurotransmitter release.
What structures are contained within the cell body of a neuron?
The cell body contains the nucleus, endoplasmic reticulum (ER), Golgi apparatus, and is responsible for synthesizing most proteins of the neuron.
What type of neuron runs to the skin and is mechano-sensitive?
The peripheral axon of primary sensory neurons runs to the skin and is mechano-sensitive.
How many axons does a typical neuron have?
Typically, a neuron has one axon.
What is required for an action potential to be evoked in the postsynaptic neuron?
The postsynaptic potential needs to reach the threshold, which is -60 mV.
What is an EPSP and how is it generated?
An EPSP is a small depolarization lasting milliseconds, typically caused by the opening of ligand-gated non-selective cation channels, often involving glutamate.
What happens when GABA binds to the GABA A receptor?
The GABA-A channel opens, allowing chloride to flow into the postsynaptic cell, resulting in hyperpolarization and an inhibitory postsynaptic potential (IPSP).
How do voltage-gated sodium channels affect the propagation of action potentials in thick fibers?
Voltage-gated sodium channels in thick fibers allow for a larger range, resulting in a higher velocity of propagation compared to thin fibers.
What is an axospinous synapse?
An axospinous synapse is where the axon terminal attaches to the dendritic spines, which are small compartments on the dendrites.
What type of fibers are typically found at the axon hillock?
A & B fibers, which are excitatory and attach to dendrites.
What occurs to the receptor potential when the mechanical stimulus is removed?
There is a decay in time of the receptor potential.
Why is it important for the receptor potential to evoke an action potential?
Because the receptor potential decays in space and may not reach the CNS, it needs to evoke an action potential to transmit the signal.
What occurs when a mechanical stimulus is applied to a mechanosensitive neuron?
The mechanosensitive ion channel opens, allowing mostly sodium to flow into the nerve ending, causing a small depolarization.
What happens to inactive sodium channels after depolarization?
Inactive sodium channels can return to a closed state.
What type of transport occurs from the axon terminal back to the cell body?
Retrograde transport.
What type of receptor is GABA B and what protein is it coupled to?
GABA B is a 7 TM receptor coupled to Gi protein.
Where are electrical synapses commonly found?
In smooth muscle and heart muscle tissues.
Describe the flow of information in a chemical synapse.
The flow is unidirectional from presynaptic to postsynaptic, typically from the axon terminal to the dendrite or cell body of the next neuron.
What is the effect of opening voltage-gated K+ channels?
It hyperpolarizes the membrane potential below the threshold line.
What determines the frequency of action potentials in a series?
The frequency of action potentials depends on the amplitude of electrotonic depolarization.
What must occur for the postsynaptic cell to fire?
The summed postsynaptic potential must reach depolarization at the threshold.
Why can't an action potential reverse direction?
Because the region of origin has inactive voltage-gated sodium channels and activated voltage-gated potassium channels.
How does the electrical resistance of thick fibers compare to thin fibers?
Thick fibers have much less electrical resistance in their interior, allowing a higher percentage of current to enter the axis of the axon and a smaller percentage to leave.
What is the relationship between fiber thickness and electrotonic potential decay?
In thick fibers, the electrotonic potential decays less in space due to a larger space constant.
What are the constituents of a synaptic vesicle?
Neurotransmitter and proteins involved in exocytosis.
What is the function of the myelin sheath in relation to current flow?
The myelin sheath acts as an electrical insulator, preventing current from leaving the axon in the regions covered by myelin, forcing it to travel inside the axon.
What type of synapse does the C fiber form?
The C fiber forms an axo-somatic synapse and is inhibitory.
What is the process called when an action potential jumps from one node of Ranvier to the next?
SALTATORY CONDUCTION
How is stimulus intensity encoded in action potentials?
Stimulus intensity is encoded in action potential frequency, where a weak stimulus evokes low frequency and a strong stimulus evokes high frequency.
What ensures that action potentials are loss-free, error-free, and distortion-free?
The action potential produced at one end will always reach the other end without loss, errors, or distortion.
What happens to neurotransmitter vesicles in a chemical synapse?
The vesicles fuse to the plasma membrane, releasing neurotransmitter molecules.
How does a strong stimulus affect action potential firing?
A strong stimulus leads to high frequency action potential firing, with the neuron capable of producing up to 500 action potentials per second.
What is the outcome when both excitatory fiber A and inhibitory fiber C are stimulated?
The result is an IPSP and EPSP that can cancel each other out, depending on their summed effects.
What happens to the voltage-gated potassium channels after a mechanical stimulus is maintained?
The voltage-gated potassium channels gradually close since there is no further depolarization to trigger them, closing after some time.
What happens to the electrotonic potential between nodes of Ranvier?
It spreads rapidly and reaches the threshold at the next node without activating voltage-gated sodium channels in between.
What happens when the mechanical stimulus finishes?
No further depolarization occurs, and the membrane potential will return to resting level after the activation of voltage-gated K+ channels.
How does the conduction speed of myelinated axons compare to unmyelinated axons?
Myelinated axons conduct faster due to saltatory conduction.
What direction does an action potential propagate?
Unidirectional (anterograde, orthodromic)
What factors affect the speed of action potential conduction?
The thickness of the fiber and whether the axon is myelinated or unmyelinated.
How does incoming information through synapses affect neuronal activity?
The neuron decides whether to fire an action potential based on the incoming action potentials propagating along the fiber.
What role does myelination play in the velocity of action potential propagation?
Myelination of the axon is a major determinant of the velocity of propagation, resulting in very rapid propagation of action potentials.
What does a large space constant indicate about electrotonic potential?
A large space constant indicates that the electrotonic potential decays slower.
What is the role of voltage-gated potassium channels during action potential firing?
Voltage-gated potassium channels open during depolarization, leading to a hyperpolarizing effect as K+ ions move outward, affecting the membrane potential.
Where is the membrane potential measured for synaptic integration?
At the axon hillock, which is the initial segment of the axon.
What are benzodiazepines and barbiturates in relation to GABA A?
They are activators of GABA A, acting as tranquilizers that induce sleepiness and relaxation.
What pump extends the uptake of neurotransmitters?
V-type proton pump.