Lecture 4 (Revised)

Question 1

Types of Synapses?

Answer 1

-Electrical Synapse
-Chemical Synapse

Question 2

Electrical Synapse communication via?

Answer 2

Direct electrical coupling of 2 cells through gap junctions

Question 3

Chemical Synapse communication through?

Answer 3

Release and binding of neurotransmitters

Question 4

Electrical Synapsis - Gap Junctions?

Answer 4

-Several connexions make up 1 connexon
-2 connexons combine to make a gap junction
-Pro: rapid signal transmission
-Con: postsynaptic signal = presynaptic signal

Question 4

Chemical Synapsis - Neurotransmitters?

Answer 4

Types:
1) Acetylcholine
2) Amino Acids
3) Purines
4) Biogenic Amines
5) Gases (NO, CO)
6) Peptides (much larger)
-Pro: postsynaptic signal differs from presynaptic signal
-Con: slow signal transmission

Question 5

(Amino Acid Neurotransmitters) Inhibitory?

Answer 5

1) GABA
2) Glycine
-Primarily responsible for IPSP’s (influx of Cl- ions and/or efflux of K+ ions)
(Become more negative)

Question 6

(Amino Acid Neurotransmitters) Excitatory?

Answer 6

1) Glutamate
2) Acetylcholine
3) Catecholamines (Epi, NE, Dopamine)
4) Serotonin
5) Histamine
6) Aspartate
-Primarily responsible for EPSP’s (influx of Ca2+)
(Become more positive)

Question 7

Biogenic Amines?

Answer 7

-Tyrosine (derived from phenylalanine) is precursor for dopamine, epinephrine, and NE
-Histidine is precursor for Histamine
-Tryptophan is precursor for Serotonin

Question 8

Peptide Neurotransmitters?

Answer 8

-Brain-gut peptides
-Opioid peptides
-Pituitary peptides
-Hypothalamic-releasing peptides
-Miscellaneous peptides

Question 9

Life Cycle of Neurotransmitter?

Answer 9

1) Synthesis
2) Packaging/Transport
3) Docking (Priming)
4) Fusion and Release (Exocytosis)
5) Budding (Endocytosis)
6) Binding
7) Inactivation (Removal)

Question 10

(1) Synthesis (and)
2) Packaging/Transport)
Small-Molecule Transmitters?

Answer 10

1) Enzymes synthesized in cell body and transported to presynaptic
2) Transmitters synthesized at presynaptic
3) Transmitters stored in endosomes, bud off CLEAR CORE vesicles

Question 11

(1) Synthesis (and)
2) Packaging/Transport)
Peptide Transmitters?

Answer 11

1) Large pro-peptide transmitters + enzymes are synthesized in cell body
2) Transmitter + enzymes are packaged in DENSE CORE vesicles which bud off Golgi apparatus
3) Dense core vesicles are transported down axon via microtubules
4) Enzymes process large pro-peptide at presynaptic terminal

Question 12

3) Docking (Priming)?

Answer 12

(Docking is a vesicle so close to pre-synaptic membrane that once AP fires it is ready)
-v-SNAREs (Synaptobrevin) on vesicle membrane
-t-SNAREs (Syntaxin) on target membrane
-Soluble NSF Attachment Protein (SNAP) fuses v-SNARE and t-SNARE

Question 13

4) Fusion and Release (Exocytosis)?

Answer 13

1) AP triggers influx of Ca2+ via voltage-gated Ca2+ channels
2) Synaptotagmin senses and binds Ca2+
3) Ca2+ + Synaptotagmin induces vesicular fusion via interaction with SNAP-25

Question 14

5) Budding (Endocytosis)?

Answer 14

-Clathrin: coats membrane and begins process of endocytosis (lifts it up and bring it back into presynaptic terminal and cleave it off)
-Dynamin: “molecular scissor” which pinches vesicle off membrane

Question 15

6) Binding?

Answer 15

Neurotransmitter binds to postsynaptic receptor and alters postsynaptic membrane potential

Question 16

7) Inactivation?

Answer 16

-Methods:
1) Diffusion of transmitter from synaptic space
2) Cleaving transmitter into inactive constituents
3) Reuptake of transmitter back into presynaptic neuron via transporters

Question 17

Neuromuscular Junction?

Answer 17

1) Voluntary neuronal stimulus form CNS
2) AP leads to alpha-motor neuron stimulation
3) ACh released at postsynaptic membrane in NMJ

Question 18

Nicotinic Acetylcholine Receptor (NAChR)?

Answer 18

1) 2 ACh molecules bind to a single NAChR (pentamer)
2) Receptor opens an ion channel that is equally permeable to Na+ and K+
3) Diffusion of Na+ and K+ across receptor causes depolarization (End Plate Potential)
4) EPP opens voltage-gated Na+ channels, which allows for firing of EPs and muscular contraction

Question 19

Myasthenia Gravis?

Answer 19

-Autoimmune diseaes, where auto-antibodies target nAChR on postsynaptic membrane (make it have nothing to bind to)
-Symptoms:
1) Muscle Weakness
2) Drooping eyelids
3) Fatigue
-Treatment:
1) ACh inhibitors