Synapses Flashcards
state what it is meant by the key term - synapse
a synapse is the anatomically specialised junction between two neurones
in essence, what does activity at a synapse do ?
activity at a synapse increases or decreases the likelihood that the post-synaptic neurone will fire action potentials by producing a brief graded potential
what are the two types of synapses ?
excitatory and inhibitory synapses
state what it is meant by the key term - excitatory synapse
the membrane potential off the post-synaptic knob is brought closer to threshold potential (i.e. - depolarisation)
state what it is meant by the key term - inhibitory synapse
the membrane potential of the post-synaptic knob is either driven further from threshold potential (I/e/ - hyperpolarisation) or stabilised at resting potential
state what it is meant by the key term - convergence
hundreds of synapses from Manu different pre-synaptic neurones can affect a single post-synaptic knob
state what it is meant by the key term - divergence
a single pre-synaptic neurone can effect multiple post-synaptic knobs
what does convergence allow for ?
convergence allows for information from many different sources to influence a cells activity
what does divergence allow for ?
allows one information source to affect multiple pathways
finish the sentence:
in an electrical synapse…
in an electrical synapse, the electrical activity of the pre-synaptic neurone affects the electrical activity of the post-synaptic knob via a gap junction
finish the sentence:
in chemical synapses…
in chemical synapses, neurotransmitters release the signal
how and where are neurotransmitters stored ?
neurotransmitters are stored in vesicles within the phospholipid bilayer –> docked on the pre-synaptic membrane in ‘active zones’
what are the two classes of receptors ?
- ionotropic receptors (ion channels)
2. metabotropic receptors (G-protein / second messenger signalling)
what is the synaptic delay, and why ?
0.2 ms, due to the sequence of events
signal termination at a synapse occurs by what 3 mechanisms ?
- diffusion of neurotransmitter from the cleft
- degradation of the transmitter by enzymes
- re-uptake into the pre-synaptic knob for re-use
state the first 5 steps of the synapse mechanism process
- AP arrives at pre-synaptic knob
- causes voltage gated calcium ion channels to open
(Ca2+ diffuses in) - Ca2+ increases fluidity of vesicles containing ACh and they fuse with the membrane
- ACh is released and diffuses across synaptic cleft
- ACh binds to receptor on post-synaptic knob
state the second 6 steps of the synapse mechanism process
- causes SOME voltage-gated Na+ channels to open (Na+ diffuses in)
- positive feedback mechanism causes more voltage gated Na+ channels to open (provided AP threshold isn met)
- an AP is triggered in the post-synaptic neurone
- acetylcholinesterase hydrolyses ACh and terminates the signal
- ACh products are re-absorbed into the pre-synaptic knob and are recycled
state 2 facts about ‘excitatory chemical synapses’
- generates an EPSP (a graded potential)
2. brings membrane potential closer to the threshold potential
state 2 facts about ‘inhibitory chemical synapses’
- generates an IPSP
2. makes membrane potential more negative, making it harder to reach threshold potential
what is the value of a single AP ?
0.5 mV
need 15 mV to reach threshold potential
state what it is meant by the key term - temporal summation
a second potential arrives after the first has died down a bit, the synaptic potentials add together, resulting in greater depolarisation
state what it is meant by the key term - spatial summation
two potentials arrive from two different neurones resulting in summation and greater depolarisation
state 3 ‘pre-synaptic factors’ that determine synaptic strength
- availability of neurotransmitter
- axon terminal membrane potential
- activation of membrane receptors on the pre-synaptic terminal
- axon terminal Ca2+
- certain drugs and diseases, which act via the above mechanisms (1-4)
state 3 ‘post-synaptic factors’ that determine synaptic strength
- immediate past history for electrical state of post-synaptic membrane
- effects of other neurotransmitters or neuromodulators acting on the post-synaptic neurone
- up/down regulation and desensitisation of receptors
- certain drugs or diseases
state 3 ‘general factors’ that determine synaptic strength
- surface area of synaptic contact
- enzyme destruction of neurotransmitters
- geometry of diffusion path
- neurotransmitter re-uptake
