Structure and Function - Week 4 Neurotransmission

Question 1

What is neurotransmission? (2)

Answer 1

Communication within the nervous system and of the nervous system with other systems

Question 2

Describe synaptic transmission (3)

Answer 2

AP arrives at pre synaptic terminal
Triggers entry of Ca2+ through voltage gated Ca2+ channel
Causes synaptic vesicles to release neurotransmitters across synaptic cleft
Neurotransmitter diffuse and bind to post synaptic receptors causing a post synaptic response

Question 3

What could the post synaptic responses be? (4)

Answer 3

Depolarization
Hyperpolarization
Changes to biochemical cascade
Change to gene expression

Question 4

What are the two types of transmission? (2)

Answer 4

Transmission can be extra-synaptic and non-synaptic too (volume transmission).

Question 5

Describe electrical synapse (3)

Answer 5

Allow physical connection to exist between neurons through gap junctions
Gap junctions - made of connexin subunits (called connexon channels) - allow ions and other substances to transfer between 2 cells

Question 6

Describe characteristics of chemical synapses (4)

Answer 6

Slow, has gain, diverse postsynaptic response, unidirectional release

Question 7

Describe characteristics of electrical synapses (4)

Answer 7

Fast, lack gain, limited postsynaptic response, mostly bidirectional

Question 8

Give examples of how could you assess electrical coupling between two neurons? (2)

Answer 8

Dual electrode recording
Cell traces

Question 9

What are the 3 components of chemical synapses (3)

Answer 9

Presynaptic terminal
Synaptic cleft
Postsynaptic terminal

Question 10

What is a bouton? (2)

Answer 10

Another name for axon terminals
Terminal enlargements on the axon where it forms a synapse

Question 11

What are the different synapse locations (4)

Answer 11

Axon to soma
Axon to dendrite / spine
Axon to axon
Dendrite to dendrite

Question 12

Describe axo-dendritic synapse (3)

Answer 12

Axon to dendritic shaft or spine
Spines are protrusions that increase surface area
Often excitatory

Question 13

Describe Axo-Somatic synapse (3)

Answer 13

Axon to soma (cell body)
If synapse is at the axon hillock, large influence on firing
Often inhibitory

Question 14

Describe Axo-Axonic synapse (3)

Answer 14

Modulatory - can be excitatory or inhibitory
Increased calcium current in presynaptic terminal = increase in transmitter release
Decreased calcium current in presynaptic terminal = decrease in transmitter release

Question 15

What are the different types of vesicles? (2)

Answer 15

Small clear core vesicles
Large dense core vesicles

Question 16

How do non-peptide neurotransmitters get inside synaptic vesicles at axon terminal? (1)

Answer 16

Use transporters - vesicle transporters

Question 17

Describe how vesicle transporters work? (3)

Answer 17

H+ gradient is established by a V-type H+-ATPase. 2H+ exchanged for the positively charged neurotransmitter.

Question 18

What are the methods of calcium clearance? (3)

Answer 18

Buffering
Removal
Active transport

Question 19

Describe buffering as a method of calcium clearance (2)

Answer 19

Buffering by cytoplasmic Ca2+ binding proteins (Ca-B)

Question 20

Describe buffering as a method of calcium clearance (2)

Answer 20

Removal from the presynaptic terminal (e.g. Na-Ca exchangers, Ca-ATPases).

Question 21

Describe active transport as a method of calcium clearance (2)

Answer 21

Active transport to endoplasmic reticulum via Ca-ATPase pump.

Question 22

Describe vesicle recycling (2)

Answer 22

Synaptic vesicles fuse to early endosomes (an organelle)
This is where new vesicles bud from after processing (e.g. clathrin coat)

Look at lecture

Question 23

Describe dense core vesicles (2)

Answer 23

Dense core vesicles often released from extra-synaptic sites and slowly diffuse to their target

Question 24

What can happen to neurotransmitters in synaptic cleft? (4)

Answer 24

Be taken back up by a neuron
Be taken up by a glial cell
Be broken down by an enzyme
Diffuse away from the cleft

Question 25

Describe Botulinum Toxin (4)

Answer 25

Primarily affects neuromuscular junction, causing paralysis Use in cosmetics and chronic pain Cleaves SNARE proteins so SNARE complex does not form and neurotransmitter is not released at neuromuscular junction Lead to muscle paralysis

Question 26

Describe Tetatnus Toxin (3)

Answer 26

Primarily affects inhibitory interneurons of the spinal cord (GABA, glycine). Loss of inhibition to motor neurons = muscle spasms (painful, constant contraction of muscles).

Question 27

Describe post synaptic density (2)

Answer 27

Proteins for anchoring and trafficking neurotransmitter receptors, just below postsynaptic membrane

Question 28

Describe the classifications of synapses (2)

Answer 28

Asymmetric (type I) synapses Symmetric (type II) synapses

Question 29

Describe Asymmetric (type I) synapses (2)

Answer 29

Thicker postsynaptic density (PSD). Typically excitatory

Question 30

Describe Symmetric (type II) synapses (2)

Answer 30

PSD similar width to presynaptic component Typically inhibitory

Question 31

What are the two neurotransmitter receptors (2)

Answer 31

Ionotropic Metabotropic

Question 32

Describe metabotropic receptors (2)

Answer 32

May interact with G-protein-gated ion channels AND/OR enzymes which generate second messengers

Question 33

What are EPSPs? (2)

Answer 33

Excitatory postsynaptic potential A transient depolarisation Net influx of positive ions depolarise and bring closer to firing threshold

Question 34

What are IPSPs? (2)

Answer 34

Net influx of negative ions hyperpolarise and move further from firing threshold. IPSP = inhibitory postsynaptic potential. A transient hyperpolarisation.

Question 35

Describe PSPs (3)

Answer 35

Graded Decay over distance

Question 36

What is integration? (2)

Answer 36

Integration (decision making) occurs at the axon – to fire or not to fire.

Question 37

What is temporal summation? (2)

Answer 37

Temporal summation as a result of one input receiving multiple stimuli close in time. A single neuron can therefore exhibit temporal and spatial summation at the same time

Question 38

What are neural circuits? (4)

Answer 38

Divergence Convergence Serial Processing Parallel processing

Question 39

Describe divergence (2)

Answer 39

Look at week 4 notes for structure and function