Principles of Synaptic Transmission

Question 1

What are the two specialised junctions signals can be transferred at?

Answer 1

Neuron-neuron= synapse
Neuron-muscle= neuromucular junction

Question 2

What are the two types of synapses?

Answer 2

Chemical

Electrical

Question 3

What is a chemical synapse?

Answer 3

Chemical neurotransmitters

Question 4

What is electrical synapses?

Answer 4

Flow of current

Question 5

Who first found evidence for chemical transmission?

Answer 5

Otto Lowei during a dream

Question 6

What is Lowei’s experiment?

Answer 6

2 isolated frog hearts (still beating)
Reservoir of physiological solution
Perfused the first heart and went into the second heart
Stimulated a nerve on first heart connected to various pointers
When stimulated the vagus nerve, the first heart slowed down
After time the heartbeat of the second heart also slowed down
Conclusion: chemical slowed the heart beat

Question 7

Who discovered acetylcholine?

Answer 7

Henry Dale

Question 8

How is pharmacological evidence used as evidence for chemical transmission?

Answer 8

Drugs used to study neuromuscular junction (NMJ)

Question 9

What does NMJ release?

Answer 9

Acetylcholine

Question 10

What are agonists?

Answer 10

Drugs that mimic the actions of the natural transmitter

Question 11

Give an example of an agonist?

Answer 11

Nicotine- nicotinic acetylcholine receptors

Question 12

What are antagonists?

Answer 12

Drugs that block the actions of the neurotransmitter, bind to receptor (high affinity, low efficacy)

Question 13

What is curare?

Answer 13

Antagonist at nicotinic receptors, paralyse at neuromuscular

Question 14

What was the experiment at NMJ with curare?

Answer 14

Competitive antagonist
Clock with curare
Inactivate acetylcholine with serine
More acetylcholine is available- overcomes the action of curare

Question 15

What can be used to show the morphological evidence of chemical transmission?

Answer 15

Electron microscopes

Question 16

What can electron microscopes show about chemical transmission?

Answer 16

Presynpatic element- axon terminal

Postsynaptic element- dendrite

Question 17

What are the key features of the synapse?

Answer 17

Synaptic cleft- space between the element (20-30nm in width)
In pre-synaptic element there is the axon terminals which contain vesicles- transmitter diffuses across the synaptic cleft- synaptic delay (.5 of millisecond)
Postsynaptic density (Psd)- collection of proteins- scaffold proteins etc.

Question 18

What are the two actions of synapses?

Answer 18

Excitation

Inhibition

Question 19

What is excitation?

Answer 19

Depolarisation of the postsynaptic membrane, i.e. less negative
Excitatory postsynaptic potentials (EPSPs)

Question 20

How are action potentials generated?

Answer 20

Summation

Question 21

What are the two types of summation?

Answer 21

Spatial summation

Temporal summation

Question 22

What is spatial summation?

Answer 22

Several synapses generate EPSPs simultaneously

Question 23

What is temporal summation?

Answer 23

Same synapse generates EPSPs rapidly

Question 24

What is inhibition?

Answer 24

Hyperpolarisation of the postsynaptic membrane, i.e. more negative
Inhibitory postsynaptic potentials

Question 25

What are the locations of inhibitory and excitatory synapses?

Answer 25

Inhibitory synapses on the cell body and axon hillock | Excitatory synapses on the dendritic tree

Question 26

Where is presynaptic inhibition?

Answer 26

Spinal cord and brainstem

Question 27

Where are the inhibitory synapses on the axon terminals?

Answer 27

Axo-axonic synapses

Question 28

What effects Ca channels?

Answer 28

Reduce the amount of transmitter released from axon terminals

Question 29

What is electrical synapses?

Answer 29

Direct flow of current across a low resistance junction

Question 30

What is shown when you inject current into presynaptic neuron and record from target neuron?

Answer 30

Small voltages with same signs | Very short latencies- no synaptic delay

Question 31

How is electrical transmission shown by gap junctions?

Answer 31

Gap junctions do not have vesicles associated with them Membranes are closely apposed but are separated by a small gap of 2-3nm An array of tubes or connexons are responsible for communication

Question 32

What is the basis of the low resistance junction?

Answer 32

Connexons- responsible for communication | Large enough to allow charge power ions i.e. K+ ions

Question 33

What are the functions of electrical synapses?

Answer 33

No synaptic delay Escape mechanisms Synchronising neuronal activity