Neurotransmission 2 - synapses Flashcards
1
Q
What are the 6 types of synapses?
A
- axosecretory
- axoaxonic
- axodendritic
- axoextracellular
- axosomatic
- axosynaptic
2
Q
What is an axosecretory synapse?
A
- axon terminal secretes directly into bloodstream
3
Q
What is an axoaxonic synapse?
A
- axon terminal secretes into another axon
4
Q
What is an axodendritic synapse?
A
- axon terminal ends on a dendrite spine
5
Q
What is an axoextracellular synapse?
A
- axon with no connection secretes into extracellular fluid
6
Q
What is an axosomatic synapse?
A
- axon terminal ends on soma
7
Q
What is an axosynaptic synapse?
A
- axon terminal ends in another axon terminal
8
Q
How can substances be transported along an axon?
A
- anterograde = NTs over microtubules
- Retrograde = lysosomes, viruses and neurotrophic factors
9
Q
What are acetylcholine receptors?
A
- they are ligand-gated ionic channels that specifically bind Ach
10
Q
Acetylcholine receptors are composed of five types of subunit - What are these?
A
- alpha (a1- a10)
- beta (b2-b5)
- delta
- epsilon
- gamma
11
Q
What receptor is most important at the neuromuscular junction?
A
- the N1 (or Nm) nicotinic cholinergic receptor is more important
12
Q
What receptor is the most important at the autonomic ganglia?
A
- N2 (or NN)
13
Q
What does the activation of the acetylcholine receptor lead to?
A
- activation leads to net influx of Na+
14
Q
What are the two types of acetylcholine receptors?
A
- nicotinic
- muscarinic
15
Q
Where are nicotinic receptors found?
A
- found in the NMJ and ANS pre-ganglionic neurons
16
Q
Where are muscarinic acetylcholine receptors found?
A
- found in post-ganglionic neurons of parasympathetic
17
Q
Where are alpha 1 and 2 adrenergic receptors found?
A
alpha 1 = vascular smooth muscle, iris, uterus, salivary glands, bladder = higher affinity for noradrenaline
alpha 2 = presynaptic, vascular smooth muscle, gut, brain
18
Q
Where are beta 1,2,3 adrenergic receptors found?
A
- B1 = heart
- B2 = uterus, airway smooth muscle, vascular smooth muscle
- B3 = adipose tissue
19
Q
What are neurotransmitters mainly made up of or derived from?
A
- NTs are mainly peptides
- or derived from amino acids
20
Q
What are the three types of NTs?
A
- excitatory
- inhibitory
- modulatory
21
Q
Where are NTs synthesised and transported to be stored?
A
- NTs are synthesised in the nerve cell body and transported along the axon to the pre-synaptic terminal where they are stored in vesicles
22
Q
What determines the effects of the NT?
A
- their receptors (on the post-synaptic membrane)
23
Q
What are examples of NTs?
A
- acetylcholine
- catecholamines
- glutamate
- glycine
- gamma-aminobutyric acid (GABA)
- Gamma
- Others (serotonin, gases, neuropeptides)
24
Q
What is acetylcholine?
A
- released at neuromuscular junction (motor end plate) - also in ANS
- its receptors are either nicotinic or muscarinic (M receptors)
25
What is an example of catecholamines and what does it do?
- norepinephrine (noradrenaline) = acts on adrenoceptors (a1, a2, B1, B2), dopamine
26
What does glutamate do?
- excitatory within the brain
27
What does glycine do?
- inhibitory within spinal cord
28
What does Gamma-aminobutyric acid (GABA) do?
- inhibitory within CNS
29
Where is Acetylcholine a NT?
- NT in NMJ
- NT in parasympathetic fibres (pre and post)
- NT in preganglionic of sympathetic
30
Where is norepinephrine a NT?
- NT in sympathetic postganglionic
31
Where can other peptide transmitters be produced and what are examples of these?
- some cells in ganglia supplying postganglionic fibres to the gut produce peptide transmitters
- such as somatostatin, substance P and enkephaline
32
What are the 8 stages in neurotransmission?
1. Nerve action potential
2. Calcium entry into the pre-synaptic terminus
3. Release of Ach quanta due to flood of calcium
4. Diffusion of Ach across cleft
5. Binding of Ach on post synaptic receptors
6. Ach breakdown by acetylcholinesterase
7. Opening of Na+/K+ channels
8. Post-synaptic membrane depolarisation
33
What are agonists and antagonists?
- substances (non-neurotransmitters) that effect neurotransmission
34
What do agonists do?
- make transmission of nerve impulses more likely. they prevent reuptake of NT (e.g., Prozac and cocaine)
35
How to agonists do their job?
1. triggering the receptor themselves (nicotine)
2. making the receptor more responsive (anti-anxiety drugs)
36
What do antagonists do?
- interfere with nerve transmission across synapse
37
How do antagonists do their job?
1. blocking receptor sites (spider and snake venom)
2. preventing release of the neurotransmitter from the presynaptic terminal (many anti-psychotic drugs)
38
What are examples of neurotransmitter blockers?
- drugs
- toxins
- chemicals
- alcohol, opiates (heroine, morphine), cocaine, nicotine, caffeine, amphetamines, cannabis, ecstasy, benzodiazepines
39
How are non-depolarising blocking agents reversed?
- reversed by acetylcholinesterase inhibitors since they are competitive antagonists at the Ach receptor
40
What are the two types of non-depolarising agents and what do they not do?
- Tubocurarine (active agent in curare)
- pancuronium neuromuscular blockers
- do not depolarise the motor end plate
41
Non-depolarising blocking agents are widely used clinically - as what?
- muscle relaxants
- used adjunctively to anaesthetics to produce paralyses for surgeries
42
What are the side-effects of non-depolarising agents?
- hypotension
- tachycardia
43
What is tubocurarine?
- is a nicotinic acetylcholine receptor antagonist
44
How do depolarising blocking agents work?
- work by depolarising the plasma membrane of the muscle fibre, similar to acetylcholine
45
How can depolarisation blocking agents persistently depolarise the muscle fibres?
- are more resistant to degradation by acetylcholinesterase so can be more persistent
46
How do depolarising blocking agents differ from acetylcholine?
- acetylcholine is rapidly degraded and only transiently depolarises the muscle
47
What is an example of a depolarising agent?
- succinylcholine
48
There are two phases to the depolarising block - What happens during phase 1 - the depolarising phase?
- they cause muscular fasciculations (muscle twitches) while they are depolarising the muscle fibres.
- eventually after sufficient depolarisation has occurred phase 2 begins
49
What happens during stage 2 the desensitising phase in depolarisation blocking agents?
- the desensitising phase sets in and the muscle is no lo ger responsive to acetylcholine released by the motoneurons
