Neurotransmission: Presynaptic and Postsynaptic Phases with Refractory Periods

list all the steps of the presynaptic phase

-The action potential travels down the axon to the presynaptic neuron

-The charge becomes more positive as VG sodium channels open( depolarization)(sodium ions flood in because solutes move from high concentration to low)

-Neurotransmitter vesicles are created

-Voltage gated calcium ion channels open and activate an enzyme to help the vesicles release from synapsin(branches)

-Snare protein helps vesicle dock and bind to the presynaptic membrane

-NT's are released in to the synaptic cleft either by kiss and run or full fusion

-Kiss and run( give a little bit of NT and leave)

Full fusion( expel all NTs)

list all the steps of postsynaptic phase

1. The NT's bind to receptors on the Post synaptic neuron

Positive potassium channels open and flow out of the presynaptic neuron(repolarization)

2.The outside of the presynaptic neuron becomes more positive than the inside which makes the inside more negative

3.because sodium gates are closed temporarily in the presynaptic neuron, it enters an Absolute refractory period: The brief time after an action potential during which a neuron cannot fire another action potential, regardless of stimulus strength

Absolute refractory period

The brief time after an action potential during which a neuron cannot fire another action potential, regardless of stimulus strength

Snare protein

helps vesicle dock and bind to the axon terminal(botulism cleaves this causing issues with acetycholine release)

Threshold for action potential

-55mv

Kiss and run

a small bit of the neurotransmitters in a vesicle is released in to the synaptic cleft

Full fusion

expelling all neurotransmitters

Clean up phase (3 ways)

1.Some Nt's float out of synaptic cleft

2.Enzymes can break down leftover NT's and put them in the PreSN to reuse

3.Transport protein attached to the PreSN can grab leftover NTs

depolarization

The process during the action potential when sodium is rushes into the cell causing the interior to become more positive. (causes action potential to become positive)

repolarization

Return of the cell to resting state -70mv, as potassium channels open and potassium floods out of the cell because there is less potassium outside the cell

inhibitory postsynaptic potential (IPSP)

an inhibitory hyperpolarization of the postsynaptic membrane of a synapse caused by the binding of GABA to the postsynaptic receptors

chlorine ions flood in to the postsynaptic neuron causing hyperpolarization

hyperpolarization

membrane potential becomes more negative than resting state

excitatory postsynaptic potential (EPSP)

Excitation of more action potentials

Triggered by glutamate NT

Depolarization (make charge more positive)

Ligand gated sodium channels open (NA+ ions)

spatial summation

Inputs of glutamate from Multiple synaptic neurons in to multiple synapses

Occurs on different synapses on the postsynaptic neuron

Depends on the amount of presynaptic neurons

Better at reaching a action potential

Temporal summation

Multiple neurotransmitters from one synaptic neuron

Occurs at the same synapse

Acquire multiple inputs by the rapid firing of inputs

Likely to reach the threshold potential