Lecture 1 Synaptic transmission

Question 1

what is a synapse

Answer 1

a specialised junction where part of a neuron contacts and communicates with another neuron or cell type (muscle or glandular)

Question 2

what are the two main categories of synapses

Answer 2

chemical (majority) and electrical (minority)

Question 3

how do electrical; synapses compare to chemical

Answer 3

simpler structure and function
faster
passive signal transmission
bidirectional 
minority (common in development)
allow synchronised electrical activity among populations of neurons

Question 4

how do chemical synapses work simply

Answer 4

Arrives as electrical and converted to chemical and back to electrical in chemical synapses

Question 5

what is a drug

Answer 5

a chemical substance, which when administered to a living organism, produces a biological effect
drugs affect how signals are communicated at a synapse
eg caffeine
affects learning and memory

Question 6

what are the types of synapse

Answer 6

axodendritic
axosomatic
axoaxonic

Question 7

what is the presynaptic element

Answer 7

upstream neuron, source of current

Question 8

what is the postsynaptic element

Answer 8

downstream neuron, into which current flows

Question 9

how does synapse location link to function

Answer 9

where they are affected how strongly they affect the postsynaptic neuron

Question 10

what is an axodendritic synapse

Answer 10

presynaptic axon to dendrite in postsynaptic neuron

Question 11

what is an axosomatic synapse

Answer 11

presynaptic contact to postsynaptic soma (more synaptic weight)

Question 12

what is an axoaxonic synapse

Answer 12

presynaptic axon contacts axon of another cell before attaching to postsynaptic soma, affects communication as can cancel each other out (signal integration to determine excitation/inhibition)

Question 13

what is the chemical synapse

Answer 13

synaptic bouton - presynaptic element
cytoskeleton - aid function and passing signals
mitochondria
synaptic vesicles - cont nt
synaptic granules ^
active zone - membrane of presynaptic cell to optimise conditions of membrane for communication
synaptic cleft - gap btwn AZ and postsynaptic cell

Question 14

what is the neuromuscular junction

Answer 14

similar to chemical synapse
one synapse innervates many muscle fibres
vesicles contain Ach, received by muscle fibres converted to electricity for contraction

Question 15

what is the postsynaptic membrane at the neuromuscular junction called

Answer 15

motor end-plate

folds to inc SA for more powerful reception of signals

Question 16

how does synaptic transmission occur

Answer 16

as an action potential reaches the synaptic terminal, nt molecules are released from presynaptic neuron and diffuse across cleft to post synaptic membrane

Question 17

what do receptors on the postsynaptic membrane recognise

Answer 17

specific neurotransmitters to initiate a response

Question 18

what are the types of responses

Answer 18

direct excitatory or inhibitory (on or off) neurotransmission

neuromodulation - lots of possible effects (dynamic so important in development and memory)

Question 19

what is direct excitatory or inhibitory transmission

Answer 19

the membrane of the next cell becomes slightly depolarised (ex) or hyperpolarised (in)

Question 20

what is neuromodulation

Answer 20

alters the presynaptic cell’s ability to release more transmitter or the postsynaptic cell’s ability to respond

Question 21

how much transmitter is released

Answer 21

released in specific packages (quanta)

Question 22

what criteria define a neurotransmitter

Answer 22

synthesised in the neuron
present in presynaptic terminal and released to exert a defined effect on postsynaptic neuron or effector organ
administered exogenously it mimics action of endogenously released transmitter
specific mechanism exists to remove it from cleft

Question 23

what is the first step of typical chemical synapse transmission

Answer 23

transmitter synthesised then stored in vesicles

Question 24

what is the 2nd step of typical chemical synapse transmission

Answer 24

action potential invades the presynaptic terminal

Question 25

what is the 3rd step of typical chemical synapse transmission

Answer 25

presynaptic. terminal depolarises causes opening voltage gated ca2+ channels

Question 26

what is the 4th and 5th step of typical chemical synapse transmission

Answer 26

influx of Ca2+ causing vesicles to fuse with presynaptic membrane

Question 27

what is the 6th and 7th step of typical chemical synapse transmission

Answer 27

transmitter released int synaptic cleft by exocytosis | binds to receptor molecules in postsynaptic membrane

Question 28

what is the 8th and 9th step of typical chemical synapse transmission

Answer 28

opening or closing of postsynaptic channels | postsynaptic current causes ex or in potential that changes the excitability of the postsynaptic cell

Question 29

what is the 10th and 11th step of typical chemical synapse transmission

Answer 29

remove nt by glial uptake or enzymatic degradation | retrieve vesicular membrane from plasma membrane

Question 30

where and how are vesicles anchored in the presynaptic cell

Answer 30

pool of vesicles anchored to cytoskeleton by synapsin

Question 31

how does action potential flow through the cell

Answer 31

action potential to presynaptic terminal, voltage gated ca2+ channels open so ca2+ flows to cytoplasm activate calmodulin activated kinase II (CaMKII) which phos synapsin

Question 32

How are synaptic vesicles released and recycled

Answer 32

activates calmodulin activated kinase II (CaMKII) which phos synapsin P-synapsin can no longer bind to cytoskeleton, allows vesicles to dock to active zone to start fusion/exocytosis vesicles reused

Question 33

what is a SNARE complex

Answer 33

at active zone | enzyme (ATPase) docks vesicles to plasma membrane as a helical protein with v and t SNAREs

Question 34

what are the mechanisms of exocytosis during neurotransmitter release

Answer 34

vesicle docks entering Ca2+ allows binding to membrane SNARE complex form to pull membranes together entering Ca2+ binds to synaptotagmin ca2+ bound synapto catalyses membrane fusion by binding SNAREs to plasma membrane

Question 35

how are vesicles recycled

Answer 35

rapidly recovered by endocytosis (10-20 sec), new vesicles bud off and refilled with transmitter whole cycle about 1min

Question 36

how are SNARE proteins affected by clostridial toxins

Answer 36

sites of proteolysis blocking nt release target amino acids in SNAREs botox and tetanus prevent transmission release

Question 37

how does botulinum toxin affect SNAREs

Answer 37

stops neuromuscular transmission of Ach - paralysis by relaxation (treatment for muscle paralysis)

Question 38

how does tetanus toxin affect SNAREd

Answer 38

interneurons at spinal cord, GABA/gly to stop inhibitors - permanent contraction

Question 39

where are botulinum and tetanus toxins from

Answer 39

from bacteria Clostridium botulinum and tetani respectively

Question 40

what diseases affect the presynaptic terminal

Answer 40

cong myasthenia syndromes - impaired vesicle recycling latrotoxin - trigger vesicle fusion botox and tetanus cog disorders impair transsynaptic signalling LEMS attacks presynaptic Ca2+ channels

Question 41

how are vesicular transporters powered

Answer 41

proton gradient ATPase proton pump loads up vesicles with H+ to make acidic (pH 5.5 comp to cytoplasm 7.2) eg 1 glut traded for 1 H+ (counter transport)

Question 42

how are plasma membrane transporters powered

Answer 42

by electrochemical gradient Na+ higher outside and K+ inside eg glut co transported in with 2 Na+

Question 43

what do glia do

Answer 43

part of tri-partite synapse - support and regulate support synaptic transmission express nt receptors (can respond to synaptic activity by changing intracellular Ca2+) coordinate synapse formation and elimination with secreted and cell surface associated signals

Question 44

what do glia control

Answer 44

``` synapse formation function plasticity elimination crucial in development, learning, memory and disease ```

Question 45

how do glia link to disease

Answer 45

reactive gliosis post injury (relevant to CNS regeneration) aberrant synapse formation (link to epilepsy and neuropathic pain) brain cancer HIV induced dementia neuroinflammatory response (depression) neurodegernative diseases (Alzheimers, glaucoma, prion disease through aberrant synaptic stripping)