electrical synapses

Question 1

what are gap junctions?

Answer 1

an array of intracellular channels for direct cell-to-cell communication but may also connect with the extracellular space as hemichannels

Question 2

what are gap junctions composed of

Answer 2

connexins

Question 3

how many connexins are there

Answer 3

21

Question 4

what are connexins expressed by

Answer 4

most cell types - other than fused muscles

Question 5

what are innexins

Answer 5

the same as connexins, but present in invertebrates

Question 6

what do gap junctions do

Answer 6

they very strongly coordinate the biochemical and electrical activities of coupled populations in a cell to cell fashion
(basicallu pass materials from cell-cell within a whole network so that every cell has a ‘taste’ of every other cell)

Question 7

what are gap junctions permeable to

Answer 7

inorganic compounds, small organic (signalling) molecules, dyes and metabolites

Question 8

what do gap junctions do within neurons

Answer 8

they do not generate current fluxes de novo, but pass current-bearing ions from one cell to another along the ECG

Question 9

intercellular channels at gap junctions are ___ ___

Answer 9

densely packed

Question 10

gap junctions are ____

Answer 10

ubiquitous

Question 11

what ensures the generation of cell-specific assemblies

Answer 11

the targeted arrangement of gap junctions and connexin subunits

Question 12

where od gap junctions mediate bidirectional signalling

Answer 12

between oocytes and granulosa cells
also between epithelial cells of the gut

Question 13

what connexin mutations are reposnsible for cataracts

Answer 13

Cx46, Cx50

Question 14

what connexin mutations are responsible for hearing impairments

Answer 14

Cx26, Cx30 and Cx31

Question 15

what connexin mutation is responsible for CMTX

Answer 15

Cx32

Question 16

where and when were synapses discovered

Answer 16

in crayfish in 1957, and in shrimp in 1958

Question 17

what are electrical synapses in the brain composed of

Answer 17

Cx36

Question 18

what is the difference between electrical synapses and chemical synapses

Answer 18

chemical synapses require a transmitter, and electrical do not

Question 19

what is the coupling coefficient

Answer 19

the ratio between the voltage change observed in the non-injected and injected neurons

Question 20

explain electrical synapse transmission

Answer 20

• can pass subthreshold current
• APs result in strongly attenuated postsynaptic responses called spikelets
• they are bidirectional
• show no preference for depolarizing or hyperpolarizing responses
• are sign preserving

Question 21

excitatory postsynaptic potential (EPSP) is

Answer 21

sign preserving

Question 22

inhibitory postsynaptic potential (IPSP) is

Answer 22

sign reserving

Question 23

structural difference between C and E synapses

Answer 23

close opposition of membranes required for E

Question 24

what is the activation speed of C vs E synapses

Answer 24

E activate faster than C (may have synaptic delay)

Question 25

what kind of current do C and E synapses possess

Answer 25

E = ionic current
C = requires neurotransmitter binding and release

Question 26

directionality of C and E synapses

Answer 26

E synapses are bidirectional, C are not

Question 27

specificity of C and E synpases

Answer 27

C = de/hyperpolarizing
E = no specificity

Question 28

preservation of C and E synapses

Answer 28

E = preserving
C = not

Question 29

reliability of C and E synpases

Answer 29

E = reliable
C = reliability varies

Question 30

strenth of synapses

Answer 30

both show modifiable strength

Question 31

properties of electrical synapses

Answer 31

• bidirectionality
• shorter synaptic delay
• sign preservation
• mediates both hyper and depoalrizing responses
• facilitates synchrony (both, sub- and supra-threshold) and promotes APs
• coordinates activity is cell-to-cell fashion in a large population

Question 32

electrical synapses create a network of ___

Answer 32

synchronously coactive neurons

Question 33

Cx36 can create multiple groups of

Answer 33

coupled interneurons

Question 34

in many brain regions, Cx36 expression is restricted to

Answer 34

interneurons (which comprise many different subtypes)

Question 35

what does Cx36 typically couple

Answer 35

similar interneuron subtypes

Question 36

what do electrical synapses create

Answer 36

electrically couples homocellular assemblies

Question 37

what does the specificity in Cx36 assembly create

Answer 37

multiple networks of synchronously coactive neurons

Question 38

what happens if you eliminate electrical synapses in the brain

Answer 38

• retinal deficits
• impairment of fine motor control
• EEG abnormalities
• impairment in more ‘complex’ motor learning tasks, object mememory, and habituation
• deficits of circadian behaviour

Question 39

why does motor impairment occur when there is a lack of Cx36?

Answer 39

electrical synapses are important in neural circuits related to the cerebellum
- neurons in the inferior olive nucleus generate subthreshold rhythms, which occasionally trigger APs, which send signals to the cerebellum
- when Cx36 is absent, olivary neurons can no longer synchronize, when olivary neurons cannot synchronize, coordination of muscle contractions is impaired “ataxia”