Synapses, Neurotransmitters and Neuromodulators Flashcards
state what it is meant by the key term ‘synapse’
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
state what it is meant by the key term ‘excitatory synapse’
an excitatory synapse is where the membrane potential of a postsynaptic neurons is brought closer to threshold (depolarised)
state what it is meant by the key term ‘inhibitory synapse’
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
what can activity at synapses cause
activity at synapses can inc^ or dec^ the likelihood that the postsynaptic neurone will fire action potentials by producing a brief graded potential
state what it is meant by an ‘electrical synapse’
an electrical synapse is where the pre and post synaptic neurones are connected by gap junctions
state what it is meant by a ‘chemical synapse’
a chemical synapse is where the presynaptic neurones release chemical neurotransmitters from their axon terminals
state 2 facts about electrical synapses
- AP flow directly across junction depolarising the second neurone to threshold continuing AP propagation
- communication via eléctrical synapses is rapid
state what it is meant by the key term ‘postsynaptic density’
postsynaptic density refers to the membrane on the postsynaptic neurone which has a high density of neurotransmitter receptor proteins
state what it is meant by the key term ‘cotransmitter’
sometimes, more than one neurotransmitter is released from the presynaptic neurone, in such cases, the second neurotransmitter is called a cotransmitter
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…
- ionotropic receptors - ion channels
2. metabotropic receptors - G protein/second messenger signalling
state the 3 ways in which neurotransmitters are removed
- diffusion of the neurotransmitter from the cleft
- degradation of the neurotransmitter by enzymes
- re-uptake into the presynaptic neurone for reuse
mechanisms of neurotransmitter release: describe step 1
action potential depolarises axon terminal opening Ca2+ channels and Ca2+ diffuses into axon down it’s electrochemical gradient
mechanisms of neurotransmitter release: describe step 2
Ca2+ associate with synaptotagmins triggering conformational shape change in SNARE complex leading to vesicle fusion with neurone membrane and neurotransmitter release
state what it is meant by the key term ‘SNARE proteins’
proteins which dock vesicles in the active zones in the neurone
state what 2 possible outcomes occur to vesicles after they release their neurotransmitters into the synapse
- completely fuse with membrane and are re absorbed by endocytosis later
- can only be momentarily fused to release contents and then withdraw again where frequencies are high
what do neurotransmitters do on the postsynaptic membrane
bind to either ionotropic or metabotropic receptors which cause opening/closing of specific ion channels changing membrane potential in that neurone
what is the effect of an ‘excitatory chemical synapse’ (2 things)
- excitatory chemical synapses generate an excitatory postsynaptic potential (EPSP) which is a graded potential
- EPSP’s serve to bring the membrane potential closer to threshold for generating an action potential
what is the effect of an ‘inhibitory chemical synapse’
- inhibitory chemical synapses generate inhibitory postsynaptic potential (IPSP)
- IPSP’s make the cell membrane more negative, making it harder to generate an action potential
state what it is meant by the key term ‘temporal summation’
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
state what it is meant by the key term ‘spatial summation’
spatial summation is where neurotransmitters add together from different presynaptic neurones to act on the postsynaptic neurone
what is the effect of both temporal and spatial summation
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
state 2 mechanisms which effect the effectiveness/strength of the synapse
- presynaptic neurone doesn’t release a constant amount of neurotransmitter each time
- neurotransmitter output is altered by activation of membrane receptors on the axon terminals themselves
explain how not releasing the same amount of neurotransmitter each time effects the strength of a synapse (2 things)
- if Ca2+ removal doesn’t equal entry then neurotransmitter release will be greater than usual
- more neurotransmitter means greater amplitude of IPSP or EPSP in postsynaptic neurone
explain how neurotransmitter output is altered by membrane receptors on axon terminals themselves effects the strength of synapses (3 things)
- presynaptic receptors may be associated with a second synaptic ending known as an ‘axo-axonic synapse’
- eg - neurotransmitter released from A binds to receptor on B resulting in change in neurotransmitter released from B
- can result in pre-synaptic inhibition/facilitation
state what it is meant by the key term ‘axon-axonic synapse’
an axo-axonic synapse is where the axon terminal of one neurone ends on the axon terminal of another neurone
state what it is meant by the key term ‘receptor densetization’
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
state 3 effects a drug may have on synaptic transmission
- inc^ leakage of neurotransmitter from vesicle into cytoplasm allowing enzyme breakdown
- inc^ neurotransmitter release into cleft
- block transmitter release
- block transmitter re-uptake
- block cleft enzymes that hydrolyse transmitter
- bind to receptor on postsynaptic neurone to block (antagonise) or mimic (agonist) transmitters actions
- inhibit or stimulate 2nd messenger activity within postsynaptic neurone
state what it is meant by the key term ‘neuromodulators’
neuromodulators cause complex responses that cam’t simply be described as EPSP’s or IPSP’s
state 2 functions of neuromodulators
- modify postsynaptic neurone’s response to specific neurotransmitters, amplifying or dampening the effectiveness of ongoing synaptic activity
- change presynaptic’s synthesis, release, re-uptake or metabolism of a transmitter
what do neuromodulator receptors do
usually bring about changes in metabolic processes in neurones, often via G-proteins coupled to a second messenger
are neuromodulators actions fast or slow
neuromodulator action is associated with slower events such as learning, development and motivational states
state what it is meant by the key term ‘cholinergic neurnes’
neurones which release AcetylCholine (ACh) are called cholinergic neurones
state the enzyme responsible for the hydrolysis of ACh
acetylcholinesterase
what can inhibit acetylcholinesterase
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
state what it is meant by the key term ‘nicotinic receptors’
nicotinic receptors are receptors which respond to the binding on both ACh as well as Nicotine
state what it is meant by the key term ‘muscarinic receptors’
muscarinic receptors are receptors which are stimulated by ACh as well as the mushroom poison muscarine
state the 2 types of cholinergic receptors in the body
- nicotinic receptors
2. muscarinic receptors
state what it is meant by the key term ‘biogenic amines’
biogenic amines are small, charged molecules that are synthesised from amino acids and contain an amino group (R – NH2)
state what the 3 Biogenic Amines are
- catecholamines (dopamine, norepinephrine and epinephrine)
- seretonin
- histamine
what are the 2 types of amino acid neurotransmitters/neuromodulators
- excitatory amino acids (eg - glutamine)
2. inhibitory amino acids (eg - gammons-aminobutyric acid - GABA - and glycine)
state what the neuropeptide neurotransmitters/neuromodulators are
eg - endogenous opioids, oxytocin and tachykinins
state what the gases are that act as neurotransmitters/neuromodulators
nitric oxide, carbon monoxide, hydrogen sulfide
state what the purines are in relation to neurotransmitters/neuromodulators
adenosine, ATP
