Synapses, Neurotransmitters and Neuromodulators

Question 1

state what it is meant by the key term ‘synapse’

Answer 1

a synapse is an anatomically specialised junction between two neurones, at which the electrical activity in a presynaptic neurone influences the electrical activity in a postsynaptic neurone

Question 2

state what it is meant by the key term ‘excitatory synapse’

Answer 2

an excitatory synapse is where the membrane potential of a postsynaptic neurons is brought closer to threshold (depolarised)

Question 3

state what it is meant by the key term ‘inhibitory synapse’

Answer 3

an inhibitory synapse is where the membrane potential of a postsynaptic neurone is either driven further away from threshold (hyperpolarised) or stabilised at resting potential

Question 4

what can activity at synapses cause

Answer 4

activity at synapses can inc^ or dec^ the likelihood that the postsynaptic neurone will fire action potentials by producing a brief graded potential

Question 5

state what it is meant by an ‘electrical synapse’

Answer 5

an electrical synapse is where the pre and post synaptic neurones are connected by gap junctions

Question 6

state what it is meant by a ‘chemical synapse’

Answer 6

a chemical synapse is where the presynaptic neurones release chemical neurotransmitters from their axon terminals

Question 7

state 2 facts about electrical synapses

Answer 7

1. AP flow directly across junction depolarising the second neurone to threshold continuing AP propagation
2. communication via eléctrical synapses is rapid

Question 8

state what it is meant by the key term ‘postsynaptic density’

Answer 8

postsynaptic density refers to the membrane on the postsynaptic neurone which has a high density of neurotransmitter receptor proteins

Question 9

state what it is meant by the key term ‘cotransmitter’

Answer 9

sometimes, more than one neurotransmitter is released from the presynaptic neurone, in such cases, the second neurotransmitter is called a cotransmitter

Question 10

once neurotransmitters are released from the presynaptic membrane, they diffuse across the synaptic cleft and bind to receptors. these receptors are one of two receptors called…

Answer 10

1. ionotropic receptors - ion channels

2. metabotropic receptors - G protein/second messenger signalling

Question 11

state the 3 ways in which neurotransmitters are removed

Answer 11

1. diffusion of the neurotransmitter from the cleft
2. degradation of the neurotransmitter by enzymes
3. re-uptake into the presynaptic neurone for reuse

Question 12

mechanisms of neurotransmitter release: describe step 1

Answer 12

action potential depolarises axon terminal opening Ca2+ channels and Ca2+ diffuses into axon down it’s electrochemical gradient

Question 13

mechanisms of neurotransmitter release: describe step 2

Answer 13

Ca2+ associate with synaptotagmins triggering conformational shape change in SNARE complex leading to vesicle fusion with neurone membrane and neurotransmitter release

Question 14

state what it is meant by the key term ‘SNARE proteins’

Answer 14

proteins which dock vesicles in the active zones in the neurone

Question 15

state what 2 possible outcomes occur to vesicles after they release their neurotransmitters into the synapse

Answer 15

1. completely fuse with membrane and are re absorbed by endocytosis later
2. can only be momentarily fused to release contents and then withdraw again where frequencies are high

Question 16

what do neurotransmitters do on the postsynaptic membrane

Answer 16

bind to either ionotropic or metabotropic receptors which cause opening/closing of specific ion channels changing membrane potential in that neurone

Question 17

what is the effect of an ‘excitatory chemical synapse’ (2 things)

Answer 17

1. excitatory chemical synapses generate an excitatory postsynaptic potential (EPSP) which is a graded potential
2. EPSP’s serve to bring the membrane potential closer to threshold for generating an action potential

Question 18

what is the effect of an ‘inhibitory chemical synapse’

Answer 18

1. inhibitory chemical synapses generate inhibitory postsynaptic potential (IPSP)
2. IPSP’s make the cell membrane more negative, making it harder to generate an action potential

Question 19

state what it is meant by the key term ‘temporal summation’

Answer 19

temporal summation a second synaptic potential (from the same presynaptic neurone) adds onto the first synaptic potential creating a greater depolarisation of the postsynaptic neurone

Question 20

state what it is meant by the key term ‘spatial summation’

Answer 20

spatial summation is where neurotransmitters add together from different presynaptic neurones to act on the postsynaptic neurone

Question 21

what is the effect of both temporal and spatial summation

Answer 21

the interaction of EPSP’s through spatial and temporal summation increase the inward flow of positive ions and bring the postsynaptic membrane to threshold so AP’s are initiated

Question 22

state 2 mechanisms which effect the effectiveness/strength of the synapse

Answer 22

1. presynaptic neurone doesn’t release a constant amount of neurotransmitter each time
2. neurotransmitter output is altered by activation of membrane receptors on the axon terminals themselves

Question 23

explain how not releasing the same amount of neurotransmitter each time effects the strength of a synapse (2 things)

Answer 23

1. if Ca2+ removal doesn’t equal entry then neurotransmitter release will be greater than usual
2. more neurotransmitter means greater amplitude of IPSP or EPSP in postsynaptic neurone

Question 24

explain how neurotransmitter output is altered by membrane receptors on axon terminals themselves effects the strength of synapses (3 things)

Answer 24

1. presynaptic receptors may be associated with a second synaptic ending known as an ‘axo-axonic synapse’
2. eg - neurotransmitter released from A binds to receptor on B resulting in change in neurotransmitter released from B
3. can result in pre-synaptic inhibition/facilitation

Question 25

state what it is meant by the key term ‘axon-axonic synapse’

Answer 25

an axo-axonic synapse is where the axon terminal of one neurone ends on the axon terminal of another neurone

Question 26

state what it is meant by the key term ‘receptor densetization’

Answer 26

receptor densetization refers to a receptor responding normally to a neurotransmitter when first exposed to the neurotransmitter but eventually fails to respond despite the continued presence of the receptor’s neurotransmitter

Question 27

state 3 effects a drug may have on synaptic transmission

Answer 27

1. inc^ leakage of neurotransmitter from vesicle into cytoplasm allowing enzyme breakdown
2. inc^ neurotransmitter release into cleft
3. block transmitter release
4. block transmitter re-uptake
5. block cleft enzymes that hydrolyse transmitter
6. bind to receptor on postsynaptic neurone to block (antagonise) or mimic (agonist) transmitters actions
7. inhibit or stimulate 2nd messenger activity within postsynaptic neurone

Question 28

state what it is meant by the key term ‘neuromodulators’

Answer 28

neuromodulators cause complex responses that cam’t simply be described as EPSP’s or IPSP’s

Question 29

state 2 functions of neuromodulators

Answer 29

1. modify postsynaptic neurone’s response to specific neurotransmitters, amplifying or dampening the effectiveness of ongoing synaptic activity
2. change presynaptic’s synthesis, release, re-uptake or metabolism of a transmitter

Question 30

what do neuromodulator receptors do

Answer 30

usually bring about changes in metabolic processes in neurones, often via G-proteins coupled to a second messenger

Question 31

are neuromodulators actions fast or slow

Answer 31

neuromodulator action is associated with slower events such as learning, development and motivational states

Question 32

state what it is meant by the key term ‘cholinergic neurnes’

Answer 32

neurones which release AcetylCholine (ACh) are called cholinergic neurones

Question 33

state the enzyme responsible for the hydrolysis of ACh

Answer 33

acetylcholinesterase

Question 34

what can inhibit acetylcholinesterase

Answer 34

acetylcholinesterase action can be inhibited by chemical weapons, such as nerve gas Sarin, which leads to a build up of ACh in the synaptic cleft

Question 35

state what it is meant by the key term ‘nicotinic receptors’

Answer 35

nicotinic receptors are receptors which respond to the binding on both ACh as well as Nicotine

Question 36

state what it is meant by the key term ‘muscarinic receptors’

Answer 36

muscarinic receptors are receptors which are stimulated by ACh as well as the mushroom poison muscarine

Question 37

state the 2 types of cholinergic receptors in the body

Answer 37

1. nicotinic receptors

2. muscarinic receptors

Question 38

state what it is meant by the key term ‘biogenic amines’

Answer 38

biogenic amines are small, charged molecules that are synthesised from amino acids and contain an amino group (R – NH2)

Question 39

state what the 3 Biogenic Amines are

Answer 39

1. catecholamines (dopamine, norepinephrine and epinephrine)
2. seretonin
3. histamine

Question 40

what are the 2 types of amino acid neurotransmitters/neuromodulators

Answer 40

1. excitatory amino acids (eg - glutamine)

2. inhibitory amino acids (eg - gammons-aminobutyric acid - GABA - and glycine)

Question 41

state what the neuropeptide neurotransmitters/neuromodulators are

Answer 41

eg - endogenous opioids, oxytocin and tachykinins

Question 42

state what the gases are that act as neurotransmitters/neuromodulators

Answer 42

nitric oxide, carbon monoxide, hydrogen sulfide

Question 43

state what the purines are in relation to neurotransmitters/neuromodulators

Answer 43

adenosine, ATP