quantum Flashcards
What is the quantum hypothesis of neurotransmitter release?
Neurotransmitter is released from presynaptic nerve terminals in discrete packages called quanta
Quanta refer to the smallest quantity of neurotransmitter that can be released, typically contained within a single synaptic vesicle.
What are spontaneous miniature EPPs (MEPPs)?
Tiny increments in membrane potential that occur in the absence of presynaptic stimulation
What are evoked EPPs?
Larger depolarization of the membrane caused by stimulation of the axon of a motor neuron
How does presynaptic stimulation affect quanta release?
It causes the synchronous release of some quanta from a pool of stored quanta
What role does Ca2+ play in neurotransmitter release?
Ca2+ controls the probability of a given quantum being released
What happens when Ca2+ levels are reduced?
The EPP magnitude is reduced to MEPP size
What is the function of synapsin?
Formation of reserve pool by anchoring vesicles to each other
What are the roles of SNAPs and NSFs?
Primary coating proteins involved in synaptic vesicle cycling
What are SNAREs and their components?
Proteins involved in docking, priming, and fusion steps, including:
* Synaptobrevin
* Syntaxin
* SNAP-25
* Synaptotagmin
What are the steps of neurotransmitter release via exocytosis?
1) Complex formation (Synaptobrevin coils around syntaxin and SNAP-25.
- Synaptotagmin binds to this SNARE complex)
2) Synaptotagmin binds Ca2+
3) Fusion of membranes leads to exocytosis
What is the role of clathrin in synaptic vesicle exocytosis?
Important for endocytotic budding and forms a coated pit
What proteins are involved in the uncoating of vesicles?
Hsc70, auxillin, and synaptojanin
Fill in the blank: Ca2+ dependent neurotransmitter release leads to receptor binding to _______.
[ionotropic or metabotropic] receptors
What are the outcomes of postsynaptic potential changes?
Postsynaptic cells can be excited or inhibited, resulting in EPSP or IPSP
What occurs after neurotransmitter release in the postsynaptic cell?
Change in ion permeability leads to change in current flow
What is the function of dynamin in synaptic vesicle exocytosis?
Forms a ring-like coil that pinches off the membrane
What is the overall process of post-synaptic signaling?
Binding of neurotransmitter to receptor -> changes in ion channel state -> changes in postsynaptic membrane potential
Neurotransmitter release (Ca2+ dependent) -> receptor binding (inotropic, metabotropic) -> ion channels open or close (depends on type of receptor ionotropic or metabotropic) -> change in permeability which causes change in current flow -> postsynaptic potential changes - > postsynaptic cells excited or inhibited ( EPSP or IPSP)
What neurotransmitter binds to Ach receptors at neuromuscular synapses?
Acetylcholine (Ach)
Ach is crucial for muscle contraction at the neuromuscular junction.
What type of Ach receptors are found in muscle?
Nicotinic; ionotropic
These receptors are responsible for mediating fast synaptic transmission.
What ions are Ach nicotinic receptors permeable to?
Na+ and K+
This permeability is essential for generating the end plate current.
What is the result of many Ach receptors being opened at the neuromuscular synapse?
End Plate Current (EPC)
EPC leads to depolarization of the muscle membrane.
What does EPC cause in the muscle cell?
End Plate Potential (EPP)
EPP is the depolarization due to the influx of Na+ and K+.
How is EPC calculated?
EPC = gAch (Vm - Erev)
gAch is the conductance of Ach receptors, Vm is the membrane potential, and Erev is the reversal potential.
What is the reversal potential (Erev)?
The voltage at which the direction of the current changes
It indicates the balance point for ion flow through the channel.
What determines the magnitude and polarity of EPP?
The electrochemical driving force on the permeant ions
This force is influenced by ion concentration gradients and membrane potential.
What is the goal of studying EPP without the influence of action potentials (AP)?
To isolate EPP by bathing in TTx and TEA
TTx blocks Na+ channels, and TEA blocks K+ channels, preventing APs.
Does the membrane ever reach 0 mV during EPP?
No, it never reaches 0 mV
The value is still above threshold for generating an action potential.
What determines whether an EPSP or IPSP fires?
Reversal potentials and threshold potentials
The receptor type and associated channel influence this outcome.
What is an excitatory postsynaptic potential (EPSP)?
A potential caused by Na+ influx
Glutamate is an example of a neurotransmitter that induces EPSPs.
What is an inhibitory postsynaptic potential (IPSP)?
A potential caused by Cl- influx or K+ efflux
GABA is an example of a neurotransmitter that induces IPSPs.
What is signal summation?
Convergence of inputs leading to summation across space and time
This is critical for determining whether an action potential is fired.
What determines whether an action potential is fired at the axon hillock?
Net Vm change
This change must reach the action potential threshold.
How do IPSPs of equal strength affect EPSPs?
They can cancel out an EPSP
This illustrates the integration of excitatory and inhibitory signals.
What happens if the combined postsynaptic potentials reach threshold?
An action potential is fired down the axon
This is the final outcome of successful summation of inputs.
