Neurophysiology Part II: Synapses and Receptors

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Questions and Answers

What is the name of the gap between the presynaptic neuron and the postsynaptic neuron?

  • Myelin sheath
  • Synaptic cleft (correct)
  • Axon terminal
  • Node of Ranvier

What is the function of the myelin sheath?

  • To produce neurotransmitters
  • To generate action potentials
  • To receive signals from other neurons
  • To increase the speed of action potential propagation (correct)

What happens to the axon terminal when the action potential arrives?

  • It becomes hyperpolarized
  • It increases the thickness of the myelin sheath
  • It releases neurotransmitters (correct)
  • It generates a new action potential

What is the approximate width of the synaptic cleft?

<p>20-50 nanometers (A)</p> Signup and view all the answers

Which of the following is NOT found in the axon terminal?

<p>Nucleus (C)</p> Signup and view all the answers

Which of these is NOT a characteristic of ionotropic receptors?

<p>They have a longer-lasting effect than metabotropic receptors. (D)</p> Signup and view all the answers

Which type of receptor is typically involved in the transmission of sensory information, such as taste or smell?

<p>Metabotropic receptors (B)</p> Signup and view all the answers

Which neurotransmitter is commonly associated with inhibitory ionotropic synapses?

<p>GABA (A)</p> Signup and view all the answers

What is the primary function of metabotropic receptors?

<p>Relaying information within the cell using a series of proteins (D)</p> Signup and view all the answers

What is one way that metabotropic receptors can influence cellular activity?

<p>Activating enzymes that produce second messengers (D)</p> Signup and view all the answers

What is the approximate size of a small vesicle containing neurotransmitters?

<p>20-30 nm (D)</p> Signup and view all the answers

Which of the following proteins is involved in the fusion of synaptic vesicles with the presynaptic membrane during neurotransmitter release?

<p>Synaptotagmin (D)</p> Signup and view all the answers

What is the role of calcium ions in synaptic transmission?

<p>Calcium ions promote exocytosis of neurotransmitters from the presynaptic terminal. (B)</p> Signup and view all the answers

Which of the following statements about synaptic vesicles is TRUE?

<p>Synaptic vesicles can be produced both at the presynaptic terminal and in the soma. (D)</p> Signup and view all the answers

What is the role of the postsynaptic density (PSD) in synaptic transmission?

<p>The PSD contains receptors that bind to neurotransmitters and initiate signaling in the postsynaptic neuron. (A)</p> Signup and view all the answers

Which of the following describes the process by which small molecule neurotransmitters are packaged into vesicles?

<p>Small molecule neurotransmitters are synthesized in the cytoplasm and then packaged into vesicles by the Golgi apparatus. (A)</p> Signup and view all the answers

What is the function of SNARE proteins in synaptic transmission?

<p>SNARE proteins act as tethers that help to dock synaptic vesicles to the presynaptic membrane. (D)</p> Signup and view all the answers

What is the fate of synaptic vesicles that have released their neurotransmitter into the synaptic cleft?

<p>Synaptic vesicles are recycled back to the presynaptic terminal and refilled with neurotransmitter. (B)</p> Signup and view all the answers

What are the three main ways vesicles release neurotransmitters?

<p>Kiss and run, merge and recycle, bulk endocytosis (B)</p> Signup and view all the answers

In which of the following ways does a vesicle release a neurotransmitter, reseal, and then moves away from the presynaptic membrane?

<p>Kiss and run (A)</p> Signup and view all the answers

What is the difference between small-molecule neurotransmitter release and large-molecule neurotransmitter release?

<p>Small-molecule transmitters are released quickly, while large-molecule transmitters are released gradually. (B)</p> Signup and view all the answers

Which of the following statements about neurotransmitter release is TRUE?

<p>Small-molecule neurotransmitters are released after a single action potential, while large-molecule neurotransmitters are released after multiple action potentials. (B)</p> Signup and view all the answers

What is the role of the receptors in the synapse?

<p>Receptors are responsible for binding neurotransmitters and initiating a response in the postsynaptic cell. (C)</p> Signup and view all the answers

What is the name for receptors that open ion channels when bound by a neurotransmitter?

<p>Ionotropic receptors (B)</p> Signup and view all the answers

Which type of receptor uses a series of proteins to cause a cascade of effects within the cell?

<p>Metabotropic receptors (A)</p> Signup and view all the answers

What is the key difference between ionotropic and metabotropic receptors?

<p>Ionotropic receptors directly open ion channels, while metabotropic receptors indirectly affect ion channels through a signaling cascade. (D)</p> Signup and view all the answers

What is the role of the second messenger in the metabotropic signaling pathway?

<p>The second messenger amplifies the effects of the G protein, leading to a wider and longer-lasting response. (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of neurotransmitters?

<p>Neurotransmitters are always excitatory, meaning they increase the likelihood of an action potential. (C)</p> Signup and view all the answers

Which of the following methods of neurotransmitter removal is NOT directly involved in the rapid termination of synaptic transmission?

<p>Retrograde signaling (A)</p> Signup and view all the answers

Which of the following is a characteristic of nondirected synapses?

<p>They are characterized by the diffusion of neurotransmitters from axonal varicosities. (D)</p> Signup and view all the answers

What is the main function of autoreceptors?

<p>To regulate the production and release of neurotransmitters from the presynaptic neuron. (A)</p> Signup and view all the answers

Which of the following accurately describes the mechanism of electrical synapses?

<p>Action potentials directly jump from one neuron to another via specialized channels called connexons. (C)</p> Signup and view all the answers

Which of the following is an example of a neurotransmitter that is typically removed from the synapse by enzymatic degradation?

<p>Acetylcholine (C)</p> Signup and view all the answers

What is the primary function of glial cells in the removal of neurotransmitters from the synaptic cleft?

<p>They absorb and recycle neurotransmitters that have diffused away from the synapse. (B)</p> Signup and view all the answers

Which of the following is true about retrograde synapses?

<p>They involve the release of neurotransmitters from the postsynaptic neuron to the presynaptic neuron. (D)</p> Signup and view all the answers

Which of the following best describes the role of electrical synapses in the nervous system?

<p>To allow for the rapid and synchronous activity of groups of neurons. (B)</p> Signup and view all the answers

What is the effect of an excitatory postsynaptic potential (EPSP) on a neuron?

<p>Depolarizes the neuron (B)</p> Signup and view all the answers

Which of the following is NOT a mechanism for removing neurotransmitters from the synaptic cleft?

<p>Up-regulation of receptors (A)</p> Signup and view all the answers

Which of the following is an example of an exogenous agonist for acetylcholine receptors?

<p>Muscarine (C)</p> Signup and view all the answers

What is the primary effect of an inhibitory postsynaptic potential (IPSP) on the postsynaptic neuron?

<p>Decreases the likelihood of the neuron firing an action potential (C)</p> Signup and view all the answers

What is the role of receptors in synaptic transmission?

<p>To bind neurotransmitters and trigger a postsynaptic response (A)</p> Signup and view all the answers

Which of the following is an example of a neurotransmitter that is degraded in the synaptic cleft?

<p>Acetylcholine (A)</p> Signup and view all the answers

Which of the following is an example of how the number of receptors in a neuron can vary?

<p>All of the above (D)</p> Signup and view all the answers

Which of the following statements about acetylcholine receptors is TRUE?

<p>They can be either excitatory or inhibitory. (B)</p> Signup and view all the answers

Flashcards

Action Potential

An electrical signal that travels along the axon, triggering synaptic transmission.

Axon Terminal

The end of the axon where neurotransmitters are released into the synapse.

Synaptic Cleft

The tiny gap (20-50nm wide) between two neurons where neurotransmitters cross.

Depolarization

A process where the axon terminal becomes more positive, triggering neurotransmitter release.

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Synaptic Transmission

The process of transmitting signals from one neuron to another via neurotransmitters.

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Small vesicles

Contain small molecule neurotransmitters; made in cytoplasm and packaged by Golgi apparatus.

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Large dense-core vesicles

Contain peptides, made in soma by ribosomes and transported by microtubules.

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Synapse

The junction between pre-synaptic and post-synaptic neurons where neurotransmission occurs.

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Post synaptic density (PSD)

A structure at the postsynaptic side that organizes proteins for synaptic function.

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Voltage-gated calcium channels

Membrane proteins that open in response to depolarization, allowing Ca2+ ions to enter the terminal.

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Exocytosis

Process where vesicles fuse with the presynaptic membrane to release neurotransmitters into the synaptic cleft.

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Neurotransmitter release

Release of neurotransmitters into the synaptic cleft, facilitated by specialized proteins like SNAREs and synaptotagmin.

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Excitatory Post-Synaptic Potential (EPSP)

A change that depolarizes the neuron, making it less negative.

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Inhibitory Post-Synaptic Potential (IPSP)

A change that hyperpolarizes the neuron, making it more negative.

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Threshold Potential

The level of depolarization needed to trigger an action potential.

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Summation

The process of combining EPSPs and IPSPs to determine if the neuron fires.

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Cholinergic Receptors

Receptors that respond specifically to acetylcholine (ACh).

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Agonist

A substance that mimics the action of a neurotransmitter at a receptor.

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Antagonist

A substance that blocks or dampens the action of a neurotransmitter.

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Receptor Regulation

Changes in the number of receptors due to various factors (up or down).

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Kiss and run

Vesicle releases neurotransmitter, reseals, and leaves.

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Merge and recycle

Vesicle fuses with presynaptic membrane and is incorporated.

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Bulk endocytosis

Formation of new vesicles from the presynaptic membrane.

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Small-molecule transmitters

Released with each action potential at the terminal.

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Large-molecule transmitters

Released gradually in response to multiple action potentials.

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Ligands

Substances that bind to receptors to activate or block them.

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Ionotropic receptors

Open upon binding with a neurotransmitter, allowing ion flow.

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Metabotropic receptors

Relay information within the cell via a series of proteins.

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Second messenger

Molecules that amplify the effects of a neurotransmitter.

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Ligand-gated Ion Channels

Channels that open when a neurotransmitter binds, allowing ion flow and altering cell charge.

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Time to Onset of Effects

Time it takes for receptor effects to occur; fast for ionotropic (1 ms) and slow for metabotropic (30 ms+).

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Diffusion

Movement of neurotransmitters down their concentration gradient out of the synapse.

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Reuptake

Transport of neurotransmitters back into the original cell after synaptic transmission.

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Enzymatic Degradation

Process where enzymes break down neurotransmitters for reuse, like acetylcholine by acetylcholinesterase.

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Autoreceptors

Receptors on the presynaptic membrane that bind transmitters and provide feedback about neurotransmitter concentration.

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Retrograde Synapses

Synapses that allow gases like nitric oxide to diffuse from postsynaptic to presynaptic neurons, signaling transmitter release.

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Nondirected Synapses

A type of synapse where neurotransmitters are released widely rather than at a specific target, common with monoamines.

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Electrical Synapses

Connections (gap junctions) that allow direct ion flow between neurons without chemical signals.

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Gap Junctions

Protein channels that connect the cytoplasm of adjacent cells, facilitating ion exchange.

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Study Notes

Neurophysiology (part II): Synapses and Receptors

  • Synapses are the connections between neurons, crucial for information transfer.
  • Neurotransmitters are chemical messengers that facilitate communication across synapses.
  • When an action potential reaches the axon terminal, depolarization occurs, triggering neurotransmitter release.
  • Terminals house mitochondria, vesicles, and proteins.
  • Small vesicles hold small molecule neurotransmitters, produced in the cytoplasm and packaged by the Golgi.
  • Large dense-core vesicles contain peptides, synthesized in the soma and transported to the terminal.
  • The synaptic cleft is a narrow gap (~20-50nm) between neurons.
  • Synaptic transmission involves specialized proteins (SNAREs, synaptotagmin) for exocytosis (neurotransmitter release).
  • Neurotransmitter release is fast due to the presence of readily available vesicles ("docked" or "release-ready").
  • Different neurotransmitters have different fates: some are broken down (degradation), diffuse, or are reabsorbed (reuptake).
  • Autoreceptors on the pre-synaptic membrane regulate neurotransmitter release.
  • Retrograde synapses involve feedback from the postsynaptic side to the presynaptic neuron (e.g., nitric oxide).
  • Non-directed synapses involve wider dispersal of neurotransmitters from varicosities (windows) on the axon.
  • Electrical synapses (gap junctions) enable direct ion flow between neurons without chemical messengers, making communication extremely rapid.
  • Neural circuits involve interconnected neurons and synapses.
  • The knee-jerk reflex is an example of a simple neural circuit composed of sensory, and motor neurons.
  • Visual systems exhibit convergence (multiple cells signal one) and divergence (one cell signals multiple).
  • Number of receptors can change through up- or down-regulation.
  • Different receptor subtypes (ionotropic and metabotropic) mediate various responses and have diverse durations.

Synaptic Transmission - Receptors

  • Ligands fit receptors to activate or block them.
  • Excitatory postsynaptic potential (EPSP) depolarizes the neuron, and inhibitory postsynaptic potential (IPSP) hyperpolarizes the neuron.
  • Neurotransmitters bind to specific receptors.
  • Receptors include ionotropic and metabotropic types.
  • Ionotropic receptors are ligand-gated ion channels that cause quick, short-lasting effects.
  • Metabotropic receptors are G-protein coupled receptors and cause longer, more complex effects.
  • Neurotransmitters can cause the activation or deactivation of downstream chemical pathways, influencing the postsynaptic cell's long-term function.
  • Synaptic activity can lead to the production of a threshold at the axon hillock.
  • Different types of neuroreceptors that respond to neurotransmitters are excitatory or inhibitory.
  • Ion flow creates EPSP or IPSP, and if the EPSP reaches a threshold, it leads to the generation of an action potential.
  • Neurotransmitters are removed from the synaptic cleft or deactivated via enzymatic degradation and diffusion.

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