L1 Synaptic Transmission

Question 1

What is a synapse?

Answer 1

Specialised junction where one part of a neurone contacts another neurone, muscle of glandular cell.

Question 2

How common are chemical synapses?

Answer 2

Majority of synapses in the adult brain are chemical.

Question 3

How is an electrical synapse different to chemical?

Answer 3

Simpler structure and function
Faster
Passive signal transmission (can’t amplify)
Bidirectional

Question 4

How common are electrical synapses?

Answer 4

Minority but common in development and the retina..

Question 5

What do electrical synapses allow for?

Answer 5

Synchronised electrical activity among populations of neurones.

Question 6

How is a drug different to hormones?

Answer 6

Must be exogenously administered rather than released endogenously. Hormones can be drugs when intentionally administered.

Question 7

What are psychoactive drugs?

Answer 7

Cross blood brain barrier and act on the CNS, changing brain function.

Question 8

What is an axodendritic synapse?

Answer 8

Axon of the presynaptic neurone -> dendrite of the postsynaptic neurone.

Question 9

What is an axosomatic synapse?

Answer 9

Axon of the presynaptic neurone -> soma of the postsynaptic neurone.

Question 10

What is a axoaxonic neurone?

Answer 10

Axon of the presynaptic neurone -> Another presynaptic neurone axon -> the postsynaptic neurone

Question 11

How does location of the synapse affect function?

Answer 11

Axodendritic= many inputs Axosomatic= powerful synaptic weight 
Axoaxonic= may cancel out if one is excitatory and the other is inhibitory (signal integration) to the final target

Question 12

What is the synaptic bouton?

Answer 12

Presynaptic element (axon terminal).

Question 13

What structures are in the presynaptic terminal?

Answer 13

Mitochondria, vesicles, secretory granules (chemicals), cytoskeleton.

Question 14

What is the active zone?

Answer 14

Membrane differentiations of the pre and postsynaptic terminals, allowing communication.

Question 15

What is the synaptic cleft?

Answer 15

Gap between the active zone and the postsynaptic densitY. Larger in chemical synapses.

Question 16

How does a neuromuscular junction differ in structure from a chemical synapse?

Answer 16

The postsynaptic membrane is called the motor end plate and contains folds to increase SA.

Question 17

What is direct neurotransmission?

Answer 17

Excitatory or inhibitory, the membrane of the next cell is either slight hyper or depolarised.
On or off switch.

Question 18

What is neuromodulation?

Answer 18

Alters the presynaptic cell’s ability to release more NT or the postsynaptic cell’s ability to respond.
Wide range of possibilities.

Question 19

Why is neuromodulation important?

Answer 19

Development, learning and memory, allowing for changes to synapses as they are created or removed when no longer used.

Question 20

What defines a neurotransmitter?

Answer 20

Synthesised in neurone
Released from presynaptic terminal in an amount enough to cause a defined effect on a postsynaptic neurone/organ
Exogenously administered drug mimics endogenous NT
Specific mechanism to remove from cleft

Question 21

How is a chemical synapse transmission signalled?

Answer 21

AP depolarises the presynaptic terminal and opens voltage gated Ca2+ channels.

Question 22

How does Ca2+ affect vesicles?

Answer 22

Causes vesicles to fuse with the presynaptic membrane, releasing the NT.

Question 23

How does the neurotransmitter affect the postsynaptic membrane?

Answer 23

Binds to receptors and either opens or closes channels causing an excitatory or inhibitory current that changes excitability of the cell.

Question 24

How is neurotransmitter removed from the cleft?

Answer 24

Glial uptake or enzymatic degradation.

Question 25

How are vesicles anchored?

Answer 25

In pools above the AZ, to the cytoskeleton by synapsin.

Question 26

How are vesicles released?

Answer 26

Ca2+ influx activates Calcium calmodulin activated kinase II (CaMKII) which phosphorylates synapsin. P-synapsin can no longer bind to the cytoskeleton.

Question 27

What are SNARE complexes?

Answer 27

Allow vesicles to fuse and communicate with the membrane, NT can't be released without.

Question 28

What are the two types of SNARE?

Answer 28

v-SNARE: vesicle t-SNARE: target They come together to allow exocytosis of the NT.

Question 29

What catalyses membrane fusion?

Answer 29

Ca2+ binding to synaptotagmin which then binds to the SNAREs and plasma membrane.

Question 30

How are vesicles recycled?

Answer 30

The membrane is rapidly recovered by endocytosis, new vesicles bud off and are refilled with the NT.

Question 31

What is priming?

Answer 31

Docked vesicles are not ready for fusion as the SNARE complexes must be assembled to allow rapid response to Ca2+ concentration.

Question 32

What is the affect of Botulinum?

Answer 32

Proteolysis of amino acids in SNARE prevents neuromuscular transmission of acetylcholine causing constant relaxation and paralysis.

Question 33

What is the affect of Tetanus?

Answer 33

Proteolysis of AAs in SNARE preventing the release of inhibitory GABA and Gly in interneurones at the spinal cord. This causes permanent muscle contraction due to dis-inhibition of cholinergic neurones.

Question 34

What diseases affect the presynaptic terminal?

Answer 34

Congenital myasthenia syndromes: imparted vesicle recycling Latrotoxin: extreme and constant vesicle fusion (similar to Botox and Tet) Cognitive disorders: impair transsynaptic signalling LEMS: attacks presynaptic Ca2+ channels

Question 35

What are vesicular transporters?

Answer 35

Powered by proton gradient, ATPase proton pump loads vesicles with H+ making them acidic and then are traded with glutamate (counter transport). Mainly allow transport into the vesicles.

Question 36

What are plasma membrane transporters?

Answer 36

Powered by electrochemical gradient, Glutamate is co-transported with Na+ as there's a higher conc outside. Mainly allow transport into the presynaptic terminal.

Question 37

What do membrane transporters mainly transport?

Answer 37

Amino acids, amines and acetylcholine.

Question 38

What site allows the action of a number of drugs?

Answer 38

Membrane transporters.

Question 39

What are astrocytes?

Answer 39

A form of glial cell that wrap around synapses that receive the NT, causing as Ca2+ increase and release their own NT that can enhance or inhibit synaptic activity. Tri-partite synapse.

Question 40

Why are glia important?

Answer 40

Control synapse formation, function, plasticity and elimination. Crucial during development, learning, memory and disease.

Question 41

Which diseases are glia linked to?

Answer 41

Reactive gloss following an injury (CNS regeneration potential) Aberrant synapse formation (epilepsy and neuropathic pain) Brain cancer HIV-induced dementia Neuroinflammatory response of depression Neurodegenerative diseases (Alzheimer's, glaucoma, prion disease) through aberrant synaptic stripping