Neuro 4: Synapse Structure

Front 1

what are the two types of junctions that signal transmission can occur through

Back 1

1. bridged/gap juctions-electrical transmission through hemi-channel (connexon), can be bidirectional 2. Unbridged junction (synaptic cleft)-discretely separate membranes, chemical transmission, unidirectional

Front 2

Describe the structure of gap junctions.

Back 2

3.5 nm wide gap that eletrically couples (low resistance, high conductance) adjacent cells. Each cell contriubtes a hemi-channel called a connexon which combine to form an ion channel, each connexon is made up of 6 connexins

Front 3

Describe speed,nd synchronization of gap jucntiosn

Back 3

no synaptic delay, transmission between two or more coupled nuerons is syncrhonous

Front 4

Describe the mechanisms of inhibition and modulation of eletrically coupled neurons

Back 4

there is no mechanism for inhibition or long lasting changes. Electrical synapses are involved in all or none behaviors so if one fires, they all fire.

Front 5

List four types of CNS chemical synapses

Back 5

1. Greys I (asymetric) 2. Grey's II (symmetric) 3. Monoamingeric (dense core vesciles) 4.Peptidergic (large dense core veiscles)

Front 6

Describe the unique features of Gray's type I CNS chemical synapses

Back 6

aka asymmetric synapse, rouund vesicles and a wider cleft with more prominent postsynaptic densitive s than type II

Front 7

Describe the unique features of Grey's type II synapses

Back 7

aka symmetric synapse, flat or pelomorphic vesicles, narrower cleft, less prominent porssynaptic densities

Front 8

Describe the unique features of monoaminergic CNS chemical syanpses

Back 8

dense-core vesicles, axonal varicosities, wide synatic cleft, no prominent densities

Front 9

Describe the unique features of peptidergic CNS chemical synapses

Back 9

large dense-core vesicles containing neuropeptides

Front 10

Describe how vesicles are prepared for docking in the acive zone (how are they released from cytoskeletal proteins)

Back 10

Dephosphorylated synapsin I anchors the vesicles to the cytoskeletal proteins during transport. Synapsin I is phosphosphorylated in a Calcium dependent manor and the veiscle is released from the cytoskeleton. Rab 3A proteins then help propel the vesicle toward the active zone

Front 11

Which proteins are invovled in vesicle docking and release at the active zone? Which membranes are they located on

Back 11

VAMP and synaptotagmin are v-snares that are located on the vesicle membrane these interact with syntaxins (t-snare) and neurexinson the target plasma membrane to dock the vesicle. After docking, phosphorylation of synaptophysin by tyrosine kinases may regulate release

Front 12

What is the role of NSF in chemical transmission at the active zone.

Back 12

The SNAREs that mediate vesicle docking are receptors for SNAP, SNAP binds NSF which utilizes ATP to unravel the SNARE assembly to allow for vesicle recycling.

Front 13

Zinc endoproteases produced by bacteria can interfere with vesicle trafficking and release at the active zone. Give four examples of toxins and their targets. Describe the effect these toxins have

Back 13

1. Tetanus-cleaves VAMP (v-SNARE) 2. Botulinum A-cleaves SNAP-25 (t-SNARE) 3. Botulinum B- Cleaves VAMP 4. Botulinum C- cleaves syntaxin (t-SNARE)., These toxins prevent association of v-SNARE with t-SNARE which impairs Ach release at the neuromuscular junction. This impairs synaptic transmission

Front 14

A-latrotoxin is a spider to that binds to neurexin in the presynaptic membrance. What is the effect of this

Back 14

induces massive relase of NTs which depelets the supply

Front 15

What is the role of Ca in fusion of the vesicle membrane with the presynaptic membrane

Back 15

Ca binds to synaptotagmin and triggers rapid fusion

Front 16

List four ways in which the action of a neurotransmitter can be terminated

Back 16

1. diffusion 2. enzymatic hydrolysis 3. binding to and activation of presynaptic autoreceptors (negative feedback) 4. reputake into the presynaptic terminal

Front 17

Compare and contrast direct and indirect gating of postsynaptic membrane ion channels that repond to chemical transmission in terms of speed and mechanism of opening

Back 17

Direct gating-fast time domain, mediated by a recepotor that is part of the ion channel moelcule iteself (ionotropic receptor) Indirect gating-slow time domain, mediated by a receptor coupled to G proteins and second messenger cascade (metabotropic)

Front 18

Expalin how nitric oxide synthase is activated

Back 18

Glutamate is released from the presynaptic terminal an dbinds to NMDA receptors. Ca enters through the receptors and activates NOS via its calmodulin binding site. NOS the produces NO while converting arginine to citrulline.

Front 19

What are the downstream affects of NO

Back 19

NO binds to iron in a heme moiety attached to soluble guanylate cyclase. The bindng activates the cyclase and produces cGMP activating cGMP dependent protein kinase. These molecuels then alter the gating of ion channels in the postsynaptic membrane.

Front 20

Rank the three types of synapses in order of smallest to largest gap between membranes

Back 20

smallest= electrical <chemical<gaseous

Front 21

Which of the three types of synapses exhibit cytoplasmic continuity between pre and post membranes

Back 21

eletrical only

Front 22

What is the "agent of transmission" for each of the three types of syanpses

Back 22

electrical=ion current, chemical=chemical transmitter molecule, gaseous=gas-like transmitter

Front 23

Compare the synaptic delay of each of the three types of synapses

Back 23

electrical= virtually absent, chemical and gaseous=significant

Front 24

Compare the direction of transmission for each of the three types of synpases

Back 24

eletrical= usually bidirectional, chemical= unidirectional, gaseous=unidirectional, can be bidirectional