1. If some of the postsynaptic receptors are blocked, what would be the effect o
ID: 3518002 • Letter: 1
Question
1. If some of the postsynaptic receptors are blocked, what would be the effect on quantum content and quantum size? Explain.
2. If the postsynaptic receptor produced only an increase in Na+ conductance would you expect it to be an inhibitory or excitatory synapse? Explain
3. If the reversal potential for a synapse is -80 would you expect it to be an excitatory synapse or inhibitory synapse?
4. How would the amplitude of the EPSP be affected by an increase in the membrane resistance of the postsynaptic cell? (Assume the synaptic current remains constant.)
5. If the EPSP amplitude doubles and the miniature EPSP amplitude remains constant, what is the change in quantum content?
Explanation / Answer
ANSWER:
1.POSTSYNAPTIC RECEPTORS:The postsynaptic receptors are
Post synaptic inhibition is called direct inhibition.This occurs due to the release of an inhibitory neurotransmitter from presynaptic terminal instead of excitatory neurotransmitter substance.
GABA(GAMMA AMINO BUTYRIC ACID) is the most inhibitory neurotransmitter. and it acts on the postsynaptic membrane by binding with the receptor.
The transmitter receptor complex opens the ligand gated potassium channels instead opening the sodium channels.Nowthe potassium ions pass out of the synapse in the extracellular fluid.Chloride channels also open followed by the influx of chloride ions inside.
The exit of potassium ions and influx of chloride ions cause more negativity inside leading to hyperpolarization.
ANSWER 2.
VOLTAGE GATED SODIUM CHANNELS:These channels are closed under resting conditions.Membrane depolarization is the signal that causes these channels to qickly open and then close.
This time dependent property is called Inactivation.Once they close they will not respond to a second stimulus untill the cell almost completely repolarizes.
Closure of sodium channels is essential for the rapid repolarization phase of action potential.
Voltage gated sodium channels are required for the depolarization phase and thus the generation of an action potential in neurons and skeletal muscle.Preventing the opening of these channels in response to depolarization will prevent the development of an action potential.
ANSWER 3. If the reversal potential of a synapse is -80 then it would be an inhibitory synapse because the synapse is monophasic.
ANSWER 4.The neurotransmitter receptor complex increases the permeability of the postsynaptic membrane for sodium i.e. this complex causes opening of ligand gated sodium channels.The sodium ions from extracellular fluid enters the soma.As the sodium ions are positively charged the resting membrane potential inside the soma is altered and depolarization or EPSP is developed.
EPSP is confined only to a synapse .It differs from the action potential and is similar to receptor potential and end plate potential, and its properties are
1.It is non - propagative
2. It is monophasic
3.It does obey all or none law.
EPSP is not transmitted in to the axon of postsynaptic neuron.It causes development of action potential in the axon.
When EPSP is strong , it causes the opening of voltage gated sodium channels in the initial segment of axon.Now due to the entrance of sodium ions the depolarization occurs in the initial segment of axon and thus ,the action potential develops and from here the action potential spreads to the other segment of the axon.
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