Week 4: Post-Synaptic Integration & Skeletal Muscle Flashcards
What is convergence in neural circuits?
When many neurons synapse onto a single post-synaptic neuron.
What is divergence in neural signaling?
When one neuron sends signals to many other neurons.
What are transmitter-gated ion channels?
Receptors that open in response to neurotransmitter binding and allow ion flow.
What do excitatory transmitter-gated ion channels do?
Permit Na+ influx and K+ efflux, leading to depolarization.
What do inhibitory transmitter-gated ion channels do?
Permit Cl- influx or K+ efflux, causing hyperpolarization.
How do voltage-gated channels differ from transmitter-gated channels?
Voltage-gated are selective for specific ions; transmitter-gated are selective for charge.
What are EPSPs and IPSPs?
Excitatory or inhibitory post-synaptic potentials that change membrane potential.
What is electrotonic conduction?
Passive spread of current that decreases with distance.
Why are synapses closer to the axon hillock more effective?
Because the signal decays less before reaching the AP initiation zone.
What is spatial summation?
Integration of inputs from multiple synapses at different locations.
What is temporal summation?
Integration of repeated signals from the same synapse over time.
How do fast and slow synaptic inputs differ?
Fast via ion channels; slow via G-proteins and second messengers.
What influences synaptic strength?
Synapse location, presynaptic depolarization, history of activity, and receptor sensitivity.
What is presynaptic facilitation?
Increased transmitter release due to increased Ca2+ influx from another neuron’s influence.
What is presynaptic inhibition?
Reduced transmitter release due to decreased Ca2+ entry.
What is synaptic adaptation?
A decrease in post-synaptic response due to persistent stimulation.
Can one transmitter have both fast and slow effects?
Yes, depending on receptor subtype (ionotropic or metabotropic).
Do EPSPs and IPSPs sum linearly?
Yes, allowing for graded responses in the postsynaptic neuron.
What is the minimum EPSP amplitude to trigger AP at axon hillock?
Enough to reach threshold (~-55 mV) after passive decay.
What is the refractory period in post-synaptic potentials?
There is none; they can sum unlike action potentials.
What determines if a post-synaptic potential will cause an AP?
Its amplitude at the axon hillock and proximity to threshold.
Do inhibitory synapses function better near the axon hillock?
Yes, because they block excitation closest to the AP initiation site.
What is a graded response?
A response that varies in size depending on input strength.
What causes synaptic depression or potentiation?
Changes in recent activity at the synapse affecting its strength.
What defines a successful post-synaptic signal?
If the combined input reaches threshold and triggers an AP.
What is the neuromuscular junction (NMJ)?
The synapse between a motor neuron and a skeletal muscle fiber.
What neurotransmitter is used at the NMJ?
Acetylcholine (ACh).
What type of receptor does ACh bind at the NMJ?
Nicotinic acetylcholine receptors (ionotropic).
What triggers ACh release at the NMJ?
An influx of Ca2+ due to a motor neuron action potential.
How is ACh removed from the synaptic cleft?
Broken down by acetylcholinesterase into choline and acetate.
What is an end plate potential (EPP)?
A large depolarization in muscle due to ACh binding receptors.
Why is transmission at the NMJ one-to-one?
Each motor neuron AP reliably produces a muscle AP due to high safety margin.
What is clathrin-mediated endocytosis?
A process to rapidly recycle synaptic vesicles after ACh release.
How many ACh molecules are in one vesicle?
Approximately 20,000.
How many active zones are in the NMJ?
Roughly 300 per junction.
What percentage of ACh receptors need activation for an AP?
Only about 10%.
What is a motor unit?
One alpha motor neuron and all the muscle fibers it innervates.
What is a motor neuron pool?
All motor neurons that innervate a single muscle.
What types of muscle fibers exist?
Type I (slow oxidative), Type IIa (fast oxidative), Type IIb (fast glycolytic).
What is rate coding in muscles?
Increased firing frequency of motor neurons to increase contraction force.
What is summation in muscle contraction?
Stacking of twitches to produce stronger force due to no refractory period.
What is tetanus in muscle physiology?
Sustained contraction due to high-frequency stimulation.
What is fused tetanus?
Complete fusion of contractions without relaxation phases.
Why is the NMJ considered efficient?
It has high receptor density, fast recycling, and strong depolarization with each AP.
What determines the strength of a muscle contraction?
Motor unit recruitment and firing rate (rate coding).
What causes muscle fatigue?
Sustained high activation of large motor units depleting energy reserves.
What muscle fiber type is fatigue-resistant?
Type I (slow oxidative) fibers.
What muscle fiber type is fast but fatigues quickly?
Type IIb (fast glycolytic) fibers.
What determines motor precision?
The number of muscle fibers per motor neuron (low ratio = high precision).
