Lecture 19: Synaptic Transmission Flashcards
What is the first stage of the chemical synapse?
Calcium ions, Ca2+, enter the cell through voltage-gated calcium channels found on the terminal axon end of the presynaptic neuron.
What is a chemically gated ion channel?
A type of ion channel which closes and opens in response to chemicals.
What is the second stage of the chemical synapse?
The introduction of Ca2+ causes the vesicles containing AcetylCholine to bind to the plasma membrane of the terminal axon resulting in exocytosis of ACh. ACh then diffuses across the synaptic cleft / synaptic gap.
What is the third stage of the chemical synapse?
On the membrane of the postsynaptic neuron are chemically gated sodium ion channels which change shape and open when ACh binds to the protein. This results in Na+ flooding the Intracellular fluid of the postsynaptic neuron leading to graded depolarisation / local depolarisation / Excitatory postsynaptic potential. If the depolarisation exceeds the action potential threshold an action potential is created.
what is the fourth stage of the chemical synapse?
AcetylCholine is released from the protein causing the chemically gated sodium ion channels to close. Ending the depolarization. This allows an enzyme Acetylcholinesterase to come in and break down ACh. Choline then goes back into the presynaptic neuron and can be reused for more ACh.
What is the concentration of calcium in the ECM?
2-2.5 mmol /L
What is an EPSP? What neurotransmitter is used?
Excitatory Post Synaptic Potential. Creates a depolarisation through the opening of chemically gated sodium ion channels. Acetyl Choline is used as the neurotransmitter.
What is an IPSP? What neurotransmitter is used?
Inhibitory Post Synaptic Potential. Creates a hyperpolarisation through the opening of chemically gated potassium ion channels.
Explain summation
The sum of EPSP + IPSP. If both are one then no action potential is created. EPSP > Threshold > IPSP for action potential to be created.
What type of synapse has no absolute or refractory period?
The neuromuscular junction.
What is the relative summation of two EPSP?
If each EPSP represents one then the summation of these is greater than 2.
What are the two types of summation?
Temporal Summation and Spatial Summation
Temporal Summation
Time between EPSP in the same position. Not in the absolute refractory period so that they summate to overcome the threshold. When the threshold is reach an action potential is propagated along the axon.
Spatial Summation
Two EPSP produced at different locations summate to overcome threshold.
