C) GABA

Explanation: Inhibitory fibers release GABA (gamma-aminobutyric acid), which binds to GABA-A receptors, playing a crucial role in inhibitory neurotransmission.

C) It leads to high frequency action potential firing

Explanation: A strong stimulus results in high frequency action potential firing, demonstrating that the intensity of the stimulus correlates with the frequency of action potentials produced.

B) Muscarinic & Nicotinic

Explanation: Acetylcholine is known to bind to two types of receptors: muscarinic and nicotinic, which play crucial roles in various physiological functions.

B) Arrival of action potential

Explanation: The arrival of an action potential at the axon terminal leads to the opening of voltage-gated calcium channels, allowing calcium ions to enter the terminal and trigger neurotransmitter release.

B) Unmyelinated and slow

Explanation: C fibers are characterized as the slowest nerve fibers and are unmyelinated, which contributes to their slower conduction velocity.

C) EPSP

Explanation: The small amount of glutamate released leads to the opening of AMPA receptors, causing a small depolarization, which is classified as an excitatory postsynaptic potential (EPSP).

C) Depolarization

Explanation: NMDA receptors require both the binding of glutamate and depolarization of the postsynaptic membrane to open, allowing sodium and calcium to enter the neuron.

C) Through the lumen of gap junctions

Explanation: In electrical synapses, the current flows through the lumen of gap junctions, allowing for bidirectional transmission without delays.

B) It spreads without decrement

Explanation: An action potential propagates without decrement, meaning its amplitude remains constant as it travels along the neuron, allowing for effective signal transmission.

C) Transmembrane proteins and phospholipid bilayers

Explanation: The cell body contains organelles like the ER and Golgi apparatus, which are responsible for producing transmembrane proteins and phospholipid bilayers, including those found in synaptic vesicles.

B) Ionotropic receptors

Explanation: AMPA and NMDA receptors are classified as ionotropic receptors, which are ligand-gated ion channels that respond to the binding of glutamate.

B) To pump protons into the vesicle lumen

Explanation: 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 is crucial for the uptake of neurotransmitters through secondary active transport.

B) Because receptor potentials decay and do not reach the CNS

Explanation: Receptor potentials decay over distance and time, so they must evoke an action potential to ensure that the signal can effectively reach the central nervous system.

B) Opening of voltage-gated K+ potassium channels

Explanation: The opening of voltage-gated K+ potassium channels leads to hyperpolarization, which occurs after the large depolarization phase of the action potential.

C) Electrical and Chemical

Explanation: The two main types of synapses are electrical and chemical, each with distinct mechanisms and characteristics that facilitate neuronal communication.

C) It leads to a small depolarization

Explanation: A small mechanical stimulus results in a small depolarization of the receptor potential, demonstrating the graded nature of the electrotonic potential in sensory receptors.

C) Opens IPSP

Explanation: Glycine functions to open inhibitory postsynaptic potentials (IPSP), similar to GABA, and is primarily found in the spinal cord, contributing to inhibitory neurotransmission.

D) Sodium

Explanation: AMPA receptors are permeable to 'one-charge' cations, primarily allowing sodium ions to influx into the postsynaptic neuron.

A) Reuptake by presynaptic neurons

Explanation: One common method for terminating the effect of neurotransmitters is through reuptake by presynaptic neurons, which helps to clear neurotransmitters from the synaptic cleft and terminate their action.

B) Voltage-gated sodium channels open

Explanation: Following the initial depolarization, voltage-gated sodium channels open, leading to the rapid rise of the action potential.

B) Temporal summation

Explanation: When two action potentials arrive rapidly in fiber A, they lead to temporal summation, resulting in a higher amplitude of EPSP as the second potential rides on the back of the first.

C) ATP

Explanation: ATP is known to interact with purinergic receptors, which can respond to ATP and play roles in various physiological processes.

B) Exocytosis

Explanation: The rapid release of neurotransmitters into the synaptic cleft occurs through exocytosis, where vesicles fuse with the plasma membrane to release their contents.

B) It becomes part of the plasma membrane

Explanation: After neurotransmitter release, the vesicle membrane may become part of the plasma membrane, but through the Kiss & Run mechanism, the vesicle can close again and be refilled with neurotransmitter.

B) Ligand-gated channel

Explanation: The receptors on the postsynaptic membrane are ligand-gated channels that open in response to the binding of neurotransmitters, allowing ions to flow into the cell.

C) GABA

Explanation: GABA (gamma amino-butyric acid) is identified as the frequent inhibitory neurotransmitter, playing a crucial role in inhibitory synaptic transmission.

C) Gap junctions between neighboring neurons

Explanation: Electrical synapses are characterized by gap junctions that interconnect the cytoplasm of two neurons, allowing for direct electrical conduction.

C) Noradrenergic

Explanation: Catecholamines, such as norepinephrine, primarily interact with noradrenergic receptors, which are involved in the body's response to stress and other functions.

B) To detect stimuli

Explanation: Sensory receptors are specialized nerve endings that are designed specifically for the detection of different stimuli, playing a crucial role in the sensory system.

B) They can diffuse away

Explanation: One of the methods for neurotransmitter elimination from the synaptic cleft is diffusion away from the synapse, allowing them to disperse into the surrounding area.

C) A higher percentage enters

Explanation: In thick fibers, a higher percentage of current enters the axis of the axon, which contributes to the propagation of electrical signals.

C) It increases the amount of epinephrine remaining in the synaptic cleft

Explanation: Cocaine can inhibit the reuptake of neurotransmitters like epinephrine, leading to an accumulation of these substances in the synaptic cleft.

B) Larger

Explanation: The space constant is larger in thick fibers, meaning that the electrotonic potential decays slower, allowing for more effective signal propagation.

A) Transport from axon terminal to cell body

Explanation: Retrograde transport refers to the movement of materials from the axon terminal back to the cell body, which is essential for recycling and signaling.

B) Opening of mechanosensitive channels

Explanation: Electrotonic depolarization is initiated by the opening of mechanosensitive channels, which allows ions to flow and cause a change in membrane potential.

C) Non-selective cation channel opens, mostly sodium flows in

Explanation: When the mechanosensitive ion channel opens, it allows sodium ions to flow into the nerve ending, leading to a small depolarization.

B) Action potentials will always reach the other end without being lost

Explanation: 'Loss-free' conduction means that once an action potential is generated, it will always reach the other end of the axon without being lost.

B) Connexons

Explanation: Connexons, formed by connexin subunits, create the gap junctions that interconnect the cytoplasms of two neurons, allowing for direct electrical communication.

C) Low frequency action potential firing

Explanation: A weak suprathreshold stimulus results in low frequency action potential firing, indicating that the intensity of the stimulus is encoded in the frequency of action potentials.

C) Several times 10 mV, around +20 to +30 mV

Explanation: The action potential has a high amplitude, typically several times 10 mV, reaching around +20 to +30 mV, which is crucial for its propagation.

C) It decays over time

Explanation: When the mechanical stimulus is removed, the receptor potential undergoes a gradual decay in time, indicating that the potential is not permanent and diminishes after the stimulus is no longer present.

D) EPSP + IPSP

Explanation: Stimulating both excitatory fiber A (producing EPSP) and inhibitory fiber C (producing IPSP) results in the cancellation of their effects, leading to a summed postsynaptic potential that may or may not reach the threshold.

B) It breaks down Acetylcholine in the synaptic cleft

Explanation: Acetylcholinesterase is an enzyme located in the synaptic cleft that specifically breaks down Acetylcholine, facilitating the termination of its action.

C) It increases the velocity

Explanation: The myelin sheath acts as an electrical insulator, resulting in very rapid propagation of action potentials and significantly increasing the velocity of propagation.

C) Forming synapses with other neurons

Explanation: Axon terminals are responsible for forming synapses, where outgoing signals are transmitted to the dendrites of other neurons.

C) They allow for a larger range, increasing velocity

Explanation: Voltage-gated sodium channels in thick fibers provide a larger range for action potentials, which contributes to a larger velocity of propagation compared to thin fibers.

C) It is closed

Explanation: Under resting conditions, the mechanosensitive ion channel is closed, meaning that there is no mechanical stimulus to trigger its opening.

B) It is coupled to a Gi protein

Explanation: The GABA B receptor is described as a 7 TM receptor that is coupled to a Gi protein, which is involved in inhibitory signaling.

B) The channel opens

Explanation: If depolarization reaches the threshold of voltage-gated sodium channels, the channels open, leading to the generation of an action potential.

C) Slow change in postsynaptic cell

Explanation: Peptide transmitters released from electrodense vesicles result in a slow change in the postsynaptic cell, often referred to as a neuromodulator effect, rather than rapid signaling.

B) It either fully develops or does not develop at all

Explanation: The 'all or none response' indicates that an action potential either occurs fully or not at all, emphasizing the binary nature of action potential generation.

C) Metabolic control center for manufacturing and recycling

Explanation: The cell body is considered the metabolic control center of the neuron, responsible for synthesizing proteins and recycling materials necessary for neuronal function.

C) Unidirectional from presynaptic to postsynaptic

Explanation: In chemical synapses, the flow of information is typically unidirectional, moving from the presynaptic neuron to the postsynaptic neuron.

C) They gradually close

Explanation: After a mechanical stimulus is maintained, the voltage-gated potassium channels gradually close since there is no further depolarization to trigger their opening, affecting the action potential firing rate.

B) They allow current to spread more efficiently

Explanation: Thick fibers allow the current coming in through voltage-gated sodium channels to spread more efficiently, resulting in a larger velocity of propagation compared to thin fibers.

B) They stabilize the membrane potential at negative values

Explanation: Metabotropic receptors cause small hyperpolarizations (IPSPs) that stabilize the membrane potential at negative values without significantly changing it.

C) It dissociates from the receptor after a while

Explanation: When a neurotransmitter binds to a postsynaptic receptor, it does not permanently bind; instead, it eventually dissociates, allowing for the possibility of further signaling.

C) Saltatory conduction

Explanation: The jumping of action potentials from one node of Ranvier to the next is known as saltatory conduction, which increases the speed of propagation significantly compared to continuous conduction.

C) They are responsible for the uptake of neurotransmitters into synaptic vesicles

Explanation: V-type proton pumps are involved in the uptake of neurotransmitters into synaptic vesicles, helping to maintain the necessary concentration for effective synaptic transmission.

D) Glutamate

Explanation: Excitatory fibers release glutamate, which binds to AMPA receptors, facilitating excitatory synaptic transmission.

C) 500 APs

Explanation: A neuron can produce up to 500 action potentials per second, which highlights the neuron's capacity for rapid signaling in response to stimuli.

C) They cause hyperpolarization

Explanation: Voltage-gated potassium channels open during the action potential, allowing K+ to flow outward, which hyperpolarizes the membrane potential following depolarization.

B) Activation of voltage-gated sodium channels

Explanation: The action potential is initiated by the activation of voltage-gated sodium channels, leading to a large influx of sodium ions and subsequent depolarization.

B) Electrochemical gradient of H+

Explanation: The electrochemical gradient created by the high concentration of H+ ions drives the uptake of neurotransmitters into vesicles as a secondary active transport process.

B) To transport materials from the cell body to the axon terminal

Explanation: Axonal transport is crucial for moving synthesized materials, such as neurotransmitters, from the cell body to the axon terminal, ensuring proper neuronal function.

B) Kinesin

Explanation: Kinesin is the motor protein that facilitates anterograde transport, moving materials from the cell body to the axon terminal at speeds of 50-400 mm/day.

C) It increases AP frequency

Explanation: A large maintained EPSP results in a high frequency of action potentials, demonstrating that stronger excitatory signals can lead to increased neuronal firing rates.

C) Hyperpolarization

Explanation: When a chloride channel opens, chloride ions move into the cell, making the inside of the postsynaptic cell more negative, resulting in hyperpolarization and an inhibitory postsynaptic potential (IPSP).

B) They activate GABA A receptors

Explanation: Benzodiazepines and barbiturates are activators of GABA A receptors, leading to increased chloride influx and resulting in sedative effects such as relaxation and sleepiness.

C) Axodendritic

Explanation: An axodendritic synapse is characterized by the axon terminal of one neuron attaching to the dendrites of another neuron, facilitating communication between the two.

B) A threshold of -60 mV

Explanation: The postsynaptic neuron needs to reach a threshold of -60 mV to evoke an action potential, which is not achieved by a single EPSP.

B) One

Explanation: A typical neuron has one axon, which is responsible for transmitting outgoing signals to axon terminals.

B) Cell body, dendrites, and axon

Explanation: An idealized neuron consists of four basic regions: the cell body (soma), dendrites for receiving information, a single axon (which may be myelinated or unmyelinated), and axon terminals for forming synapses.

C) Depolarization

Explanation: The influx of sodium ions through ligand-gated channels causes a small depolarization of the postsynaptic cell, leading to an excitatory postsynaptic potential (EPSP).

B) Inactive voltage-gated sodium channels

Explanation: Action potentials are unidirectional because the region where the action potential originated has inactive voltage-gated sodium channels, preventing it from reversing direction.

B) It blocks action potential generation

Explanation: Lidocaine blocks voltage-gated sodium channels, preventing the generation of action potentials and thus blocking pain sensation.

B) To attach synaptic vesicles to the actin cytoskeleton

Explanation: Synapsin I is involved in the attachment of synaptic vesicles to the actin cytoskeleton, facilitating their movement and release during neurotransmission.

C) Axoaxonic

Explanation: An axoaxonic synapse occurs when the axon of one neuron connects with the axon of another neuron, influencing the transmission of signals between them.

C) Neurotransmitter release

Explanation: Chemical synapses operate primarily through the release of neurotransmitters from the presynaptic neuron, which then evoke effects on the postsynaptic membrane.

B) High resistance

Explanation: Axoplasm is characterized by high resistance, which affects the flow of electrical current within the axon.

C) It decreases the amplitude

Explanation: The amplitude of the receptor potential signal decreases with distance from the channel, leading to a decay in space, which affects how the signal is transmitted to the central nervous system.

C) Dendrites

Explanation: Dendrites are the parts of the neuron that receive information from other neurons or sensory receptors, making them crucial for signal reception.

B) Axosomatic synapse

Explanation: An axosomatic synapse is formed when an axon terminal connects directly to the cell body (soma) of another neuron, facilitating communication between neurons.

B) No further depolarization

Explanation: When the mechanical stimulus is finished, there is no further depolarization, leading to the closure of voltage-gated potassium channels and a return to the resting membrane potential.

C) 100-120 m/s

Explanation: The conduction speed of action potentials in myelinated fibers can reach a maximum of 100-120 m/s, making it very rapid compared to unmyelinated fibers.

C) It spreads with decrement

Explanation: The receptor potential spreads with decrement, meaning that its amplitude decreases as it moves away from the site of depolarization.

B) It produces a small receptor potential that decays

Explanation: A subthreshold mechanical stimulus results in a small receptor potential that does not reach the threshold for action potential generation, leading to decay without signal transmission.

B) The amplitude of electrotonic depolarization

Explanation: The frequency of action potentials is influenced by the amplitude of electrotonic depolarization, meaning that a larger depolarization can lead to a higher frequency of action potentials.

C) Larger stimuli cause larger depolarization

Explanation: The receptor potential is graded, meaning that a larger mechanical stimulus results in a larger depolarization, reflecting the strength of the stimulus.

B) To propagate electrical signals rapidly to the CNS

Explanation: Action potentials are essential for the rapid propagation of electrical signals along nerve fibers to the central nervous system (CNS) for processing.

B) Opening of mechanosensitive channels and Na+ influx

Explanation: The process begins with the opening of mechanosensitive channels, allowing Na+ sodium influx, which leads to depolarization and potentially a suprathreshold depolarization.

C) A-alpha fibers

Explanation: A-alpha fibers are identified as the fastest nerve fibers, which are crucial for rapid signal transmission in the nervous system.

C) Chloride channels

Explanation: IPSPs are primarily caused by the opening of ligand-gated chloride channels, which allow chloride ions to enter the postsynaptic cell, leading to small hyperpolarization.

C) Binding to postsynaptic receptors

Explanation: While binding to postsynaptic receptors occurs, it is not considered a major pathway for neurotransmitter elimination, as the neurotransmitter will eventually dissociate from the receptor.

C) Around the first myelin sheath

Explanation: The region with the highest density of voltage-gated sodium channels is located around the first myelin sheath, which is crucial for the generation of action potentials.

B) 1-5 ms

Explanation: The synaptic delay, which is the time it takes for the release of neurotransmitters to affect the postsynaptic membrane, typically ranges from 1 to 5 milliseconds.

C) Receive incoming signals from other neurons

Explanation: Dendrites are specialized structures that receive incoming signals from other neurons, allowing for communication within the nervous system.

B) Neurotransmitter is released rapidly

Explanation: When the vesicle fuses with the plasma membrane, the neurotransmitter is released rapidly into the synaptic cleft, primarily through diffusion due to the high concentration in the vesicle.

C) Small EPSP leads to low AP frequency

Explanation: A small maintained excitatory postsynaptic potential (EPSP) results in a low frequency of action potentials (AP), indicating that the strength of the EPSP directly influences the firing rate of the neuron.

B) Pseudounipolar sensory neuron

Explanation: Pseudounipolar sensory neurons are described as mechano-sensitive, as they respond to mechanical stimuli through their peripheral axons that run to the skin.

B) GABA A and C

Explanation: GABA A and C receptors are specified as ligand-gated chloride channels, which facilitate the flow of chloride ions into the postsynaptic cell, leading to hyperpolarization.

B) N/P type calcium channels open

Explanation: During depolarization, N/P type calcium channels open, allowing calcium ions to enter the axon terminal, which is crucial for neurotransmitter release.

B) To synchronize the depolarization of connected neurons

Explanation: Electrical synapses allow for rapid communication between neurons, enabling synchronization of depolarization when multiple neurons need to activate simultaneously.

B) Small compartments on dendrites

Explanation: Dendritic spines are small compartments found on dendrites that can form synapses, specifically referred to as axospinous synapses, enhancing synaptic connectivity.

C) It must be present in the postsynaptic neuron

Explanation: While a neurotransmitter must bind to a specific receptor on the postsynaptic cell to evoke an effect, it does not need to be present in the postsynaptic neuron itself; rather, it must be released from the presynaptic neuron.

B) Electrotonic and action potential

Explanation: Electrical signals in neurons can be categorized into electrotonic potentials and action potentials, each with distinct properties and functions.

C) It helps return the membrane potential to resting state

Explanation: The repolarizing effect is crucial for returning the membrane potential to its resting state after an action potential, allowing the neuron to be ready for subsequent firing.

B) Causes hyperpolarization and inhibition

Explanation: Activation of GABA A receptors leads to the opening of chloride channels, resulting in chloride influx, hyperpolarization, and inhibition of neuronal activity.

C) It leads to a series of action potentials

Explanation: A suprathreshold stimulus generates an electrotonic depolarization that reaches the threshold for voltage-gated sodium channels, resulting in a series of action potentials if the mechanical stimulus is maintained.

B) In the dorsal root ganglion or trigeminal ganglion

Explanation: The cell bodies of primary sensory neurons are located in the dorsal root ganglion or trigeminal ganglion, which is essential for sensory signal processing.

C) Continuous mechanical stimulus maintaining sodium influx

Explanation: As long as the mechanical stimulus is maintained, the membrane potential can depolarize again to the threshold of voltage-gated sodium channels, allowing for the generation of another action potential.

A) Storing neurotransmitters

Explanation: Synaptic vesicles are responsible for storing neurotransmitters, which are released into the synaptic cleft to transmit signals between neurons.

D) Thick myelinated axon

Explanation: Thick myelinated axons conduct action potentials faster than thin or unmyelinated axons due to the presence of saltatory conduction.

B) To produce ATP for energy

Explanation: Mitochondria in the axon terminal produce ATP, which is necessary for various energy-dependent processes, including pumping out calcium and filling synaptic vesicles with neurotransmitters.

C) Calcium signal (Ca2+)

Explanation: The influx of calcium ions (Ca2+) is crucial for the docking proteins to fuse the synaptic vesicles with the presynaptic membrane, allowing for rapid neurotransmitter release.

B) It can evoke either EPSP or IPSP

Explanation: The binding of a neurotransmitter to its receptor on the postsynaptic neuron can lead to either excitatory postsynaptic potentials (EPSP) or inhibitory postsynaptic potentials (IPSP), depending on the nature of the neurotransmitter and the receptor.

C) They decay in space and time

Explanation: Electrotonic potentials are characterized by their graded nature, low amplitude, and the fact that they decay both in space and time when the current ceases.

A) Action potential arrives

Explanation: The arrival of an action potential at the axon terminal triggers the opening of calcium channels, leading to the influx of calcium ions and subsequent exocytosis of neurotransmitters.

C) Excitatory postsynaptic potential (EPSP)

Explanation: When neurotransmitters bind to ligand-gated channels, they can generate an excitatory postsynaptic potential (EPSP), which is a small depolarization that occurs for milliseconds.

B) Based on incoming action potentials

Explanation: A neuron decides to fire an action potential based on the incoming action potentials that propagate along the fiber, which may or may not lead to the generation of an action potential.

B) 50-400 mm/day

Explanation: Fast anterograde transport occurs at speeds ranging from 50 to 400 mm/day, allowing synaptic vesicles to travel significant distances to reach the axon terminal.

C) Axon hillock

Explanation: The axon hillock is noted for having the highest concentration of voltage-gated sodium channels, making it the site where action potentials are typically generated.

C) It reaches the threshold earlier

Explanation: A larger receptor potential, resulting from more mechanosensitive channels being opened, allows the membrane potential to reach the threshold sooner, leading to a shorter time period between action potentials.