5 - Synaptic Transmission & Integration

Question 1

What’s saltatory conduction?

Answer 1

AP leaping from one node of ranvier to the next

Question 2

T/F - it’s faster for AP to occur at every point in axon than passive diffusion

Answer 2

False - faster for passive diffusion to occur between Nodes than for AP to occur at every pt in axon

Question 3

Is the Na/K-ATPase pump involved in changing mempot during an AP?

Answer 3

NO

Question 4

What does the Na/K-ATPase pump help with then?

Answer 4

Helps reset Na and K+ concentrations after AP

Question 5

What are the 2 classes of synapses?

Answer 5

1. Electrical

2. Chemical

Question 6

Electrical synapses

Answer 6

Direct electrical coupling between cytosol of 2 neurons

Question 7

Chemical synapses

Answer 7

Electrical signals converted into chemical signal

Question 8

Gap junctions used in which synapses?

Answer 8

Electrical - connect cytosol of 2 neurons so changes in Vm of one immediately affect the other

Question 9

How many subunits form cone on in each cell membrane with a gap junction?

Answer 9

6

Question 10

Are gap junctions selective?

Answer 10

No - allow ions and small molecules through

Question 11

Gap junctions electrically….

Answer 11

Couple neurons

Question 12

Cytosol connections are limited by what?

Answer 12

Number of ions that can pass through gap junctions

Question 13

Are gap junctions unidirectional?

Answer 13

No - bidirectional; change in Vm in post-synaptic neuron reflected in pre-synaptic and vice versa

Question 14

T/F - chemical synapses are fast but weak

Answer 14

False - slow but powerful

Question 15

Pre-synaptic active zones

Answer 15

Location of specialised proteins that bind vesicles, releasing neurotransmitter

Question 16

What are the different types of chemical synapses based on axon location?

Answer 16

Axo-dendritic
Axo-somatic
Axo-axonic

Question 17

Axo-dendritic

Answer 17

Most common; axon-dendrite connection on dendrite spines or shaft

Question 18

Axo-somatic

Answer 18

Axon-soma connection; commonly inhibitory

Question 19

Axo-axonic

Answer 19

Axon-axon connection; can module signal before transmission

Question 20

Different types of chemical synapses based on microscopic structure

Answer 20

Gray’s type I and Gray’s type II

Question 21

Gray’s type I

Answer 21

• asymmetrical
• round vesicles
• e- dense
• usually excitatory
• contact dendritic spines

Question 22

Gray’s type II

Answer 22

• symmetrical
• oval vesicles
• less e- dense
• usually inhibitory
• contact dendritic shaft/soma

Question 23

What does number & size of synapses connecting 2 neurons indicate?

Answer 23

Strength and importance of the signalling

Question 24

4 criteria of a neurotransmitter

Answer 24

1. Synthesised in pre-synaptic neuron
2. Defined action on post-synaptic neuron/effect after release
3. Exogenous administration mimics actions of endogenous transmitter
4. Specific mechanism exists for removing substance from synaptic cleft

Question 25

What are the 3 types of neurotransmitters?

Answer 25

Amino acids Amines Peptides

Question 26

Amino acids

Answer 26

Small organic molecules | Eg: glutamate (excitatory - opens cation channels), GABA (usually opens Cl- channels)

Question 27

Amines

Answer 27

Small organic molecules | Eg: dopamine, acetylcholine

Question 28

Peptides

Answer 28

Short amino acid chains stored in and released from secretory granules

Question 29

Neuromuscular junction

Answer 29

Special synapse in periphery connecting moto neurons to muscle fibres

Question 30

What are the steps for communication via a chemical synapse?

Answer 30

1. Neurotransmitter synthesis 2. Neurotransmitter loading into synaptic vesicles 3. Vesicles fuse w/ pre-synaptic terminal 4. Neurotransmitter binds post-synaptic receptors 5. Post-synaptic response 6. Removal of neurotransmitter from synaptic cleft

Question 31

1. Neurotransmitter synthesis

Answer 31

Must be synthesised in neuron from which it will be released Most neurons only release one type A) simple amino acids available in all cells B) GABA & amines need special enzymes for synthesis C) peptides packaged into secretory granules in nucleus then transported to terminal

Question 32

2. Neurotransmitter loading into vesicles

Answer 32

Vesicles from phospholipid bilayer, approximately all same size and contain similar amounts of neurotransmitter

Question 33

Are secretory granules smaller than vesicles?

Answer 33

Nope - larger

Question 34

3. Vesicles binding & neurotransmitter release

Answer 34

Exocytosis to release vesicle contents & endocytosis to recover vesicle membrane & reuse When AP reaches axon terminal, Cav channels in active zone open. Intracellular Ca2+ triggers fusion of synaptic vesicle w/ membrane, releasing neurotransmitter into cleft

Question 35

4. Neurotransmitter binding to post-synaptic receptors What are the 2 mechanisms of neurotransmitter action at post-synaptic membrane?

Answer 35

1. Ionotropic | 2. Metabotropic

Question 36

Ionotropic

Answer 36

Ion channel gated by ligand (neurotransmitter), fast & brief

Question 37

Metabotropic

Answer 37

Receptor indirectly linked w/ ion channel, need signalling cascade, slower and longer action, broader effects

Question 38

5. Response to neurotransmitter

Answer 38

Post-synaptic potential

Question 39

Post-synaptic potential (PSP)

Answer 39

Transient change in mempot due to neurotransmitter-mediated channel opening

Question 40

Excitatory PSP

Answer 40

Transient depolarisation (eg: Na+ channels opened)

Question 41

Inhibitory PSP

Answer 41

Transient hyperpolarisation (eg: Cl- channels opened)

Question 42

Size of PSP depends on what?

Answer 42

Amount of neurotransmitter released, no. Binding sites that can receive it, no. Neurotransmitter molecules that successfully bind

Question 43

6. Recycling the neurotransmitter

Answer 43

Signal turned off by diffusion, reuptake or enzymatic destruction

Question 44

How do we get Ca+2 out of axon terminal?

Answer 44

Na/Ca exchanger (NCX) moves 3 Na+ into cell & 1 Ca+2 out) uses [Na+] gradient

Question 45

Dendrites ___________ inputs from each synapse

Answer 45

Integrate

Question 46

Spatial summation

Answer 46

Summation across input from many axons

Question 47

Temporal summation

Answer 47

Summation across time from single axon