Neurochemistry

Question 1

What is an EPSP?

Answer 1

Communication with dendrites from other neurons can bring positive ions into the cell
Positive ions produce a small depolarisation- an Excitatory Post Synaptic Potential Small EPSPs are not enough to produce an action potential
If enough positive charge arrives, the post synaptic cell will fire
The summation of EPSP’s (total charge) plus IPSPs will determine if an action Potential will occur: neural integration at the axon hillock

Question 2

What is an IPSP?

Answer 2

Communication with dendrites from other neurons can bring negative ions into the cell
Negative ions produce a small hyperpolarisation- an Inhibitory Post Synaptic Potential IPSPs will not produce an action potential (pushes potential down)
Large IPSPs are due to many negative ions entering the cell.
The integration of charge at the axon hillock can’t reach the excitation threshold. An action potential can not occur

Question 3

How does one cell talk to another?

Answer 3

Electrical communication: Gap junctions (electrical synapses)
Chemical communication: Synaptic cleft (chemical synapses)

Question 4

What are gap junctions?

Answer 4

*Rarely seen between neurons, but seen between glial cells
*Instead of using chemical messengers they transfer ions between the plasma wall of neuritesvia connexons
*The junction is specialisedso that it is only a small distance (3.5 nm) between cells (usually around 20 nm gap)

Question 5

What are chemical synapses?

Answer 5

Chemical synapses are commonly formed between a terminal button and a dendritic spine
Chemical synapses use neurotransmitters to convey messages
Neurotransmitters are packaged in synaptic vesicles - ready for release into the synapse

Question 6

What does an action potential produce?

Answer 6

Action potential produces “exocytosis” of neurotransmitter from vesicles
The action potential increases [Ca2+] in the terminal bouton
Vesicles are moved to the membrane by trafficking proteins (SNARE)
Once docked, exocytosis occurs to empty vesicle contents into synapse

Question 7

How are neurotransmitters recycled?

Answer 7

Neurotransmitter recycle back into terminal “endocytosis”
After binding to receptors, some neurotransmitters are recycled
Letftover NT are taken back up by the cell by endocytosis to be recycled or metabolised (inactivated)
Metabolism may occur presynaptically or in the synapse