Synapses and Neurotransmitters

Question 1

How is neurotransmitter released at chemical synapses

Answer 1

1) depolarization down the axon reaches Voltage Gated Ca2+ channel at axon terminal and opens them
2) Ca2+ rushes in and activates synaptotagmin sensor protein
3) sensor protein activates v and t SNARE proteins, which tether vesicles to pre-synaptic membrane 4) vesicles dump contents into the synapse

Question 2

Excitatory vs Inhibitory neurotransmittors in the CNS

Answer 2

Excitatory:

• Glutamate
• Achetylcholine

Inhibitory:

• GABA
• Glycine

Question 3

Describe what EPSP’s/IPSP’s are and what they do

Answer 3

Excitatory Post Synaptic Potential:

Results from an excitatory neurotransmittor binding and positive ions coming in, it pushes the sum of charges at the axon hillock closer threshold.

Inhibitory Post Synaptic Potential:

Results from an inhibitory neurotransmittor binding and negative ions coming in; it pushes the sum of charges at the axon hillock further away from threshold.

Question 4

Ionotropic vs Metabotropic Receptors

Answer 4

Ionotropic: [FAST] ligand gated, something binds and channel opens

Metabotropic: [SLOW] linked to GPCR. Although it is slower, secondary messengers can result in a wider range of responses.

Question 5

Mechanisms of Neurotransmitter Clearance in the Chemical Synapse

Answer 5

Taken up into Glia Cells: GABA, glycine, glutamate

Achetylcholinesterase: takes up Acethycholine

COMT in cleft and MAO: take up Biogenic Amines (e.g. epinephrine, dopamine, seretonin, histamine, etc.)

• Peptide Neurotransmitters either diffuse or are broken down by proteases.

Question 6

Describe how temporal and spatial summation of synaptic potentials affect postsynaptic responses.

Answer 6

Each post synaptic potential is small, so to reach threshold you will need a collection of potentials to sum.

• Temporal: multiple back to back activations at the same synapse can get you over threshold
• Spatial: simulatenous potentials at different locations can get you over threshold.

In reality, most of the time it is a combination of these two factors that determine whether or not you have an action potential.

Question 7

Chemical vs Electrical Synapses

Answer 7

Chemical Synapses: [SLOW]

• The model neuron. Releases neurotransmitter into a synapse to bind post-synaptic receptors on dendrites.

Electrical: [instantaneous and bidirectional]:

• GAP junctions. Very fast. Direct connection between cytoplasm of adjacent cells allows ions to flow from one cell to another, and back again.