L3.2 Neural Communication: Synapses Flashcards
define synapse
information from one neuron must be passed to other neurons to be useful. a synapse is the connection between 2 neurons - one presynaptic neuron and one postsynaptic neuron
what are the types of synapses
- electrical (connected by gap junctions)
- chemical (a chemical messenger diffuses across the junction that separates the two neurons)
describe the steps involved in chemical synapses
- action potential arrives along the presynaptic axon at a terminal
- once it arrives, it depolarises the membrane of the terminal
- in the membrane of the terminal there is voltage gated calcium channels- calcium channels open and calcium will enter the terminal
- calcium enters the knob and within the knob there are vesicles of neurotransmitters. the vesicles bind to the membrane and open and release neurotransmitters into the synaptic cleft
- they then diffuse across a cleft and bind onto receptors of the neurotransmitters and there receptors are already sitting in the membrane of the post synaptic neuron (these receptors/neurotransmitters are ion channels in essence). they open the specific channel = action potential in the membrane
fill in the gaps:
presynaptic action potential –> opening of ________ –> increased _______ –> release of neurotransmitter —> ___________ –> NT binds to receptor OR _____ –> from NT binds to receptor: _______
presynaptic action potential –> opening of voltage gated calcium channels –> increased intracellular calcium –> release of neurotransmitter —> diffusion of NT across synaptic cleft –> NT binds to receptor OR breaks down and gets recycled –> from NT binds to receptor: EPSP or IPSP
(see notes for more info)
explain EPSP
EPSP = excitatory postsynaptic potential (i.e. depolarisation)
- becomes less negative = toward threshold
- synapses are excitatory (NT examples: acetylcholine and glutamate)
explain IPSP
IPSP = inhibitory postsynaptic potential (i.e. hyperpolarization)
- becomes more negative = away from threshold
- inhibitory (e.g. glycine and GABA)
explain the ‘graded potential summation’ diagram from the lecture (SEE NOTES)
EX1: synapse excitatory creating EPSP
EX2: also excitatory creating EPSP
IN1: inhibitory creating IPSP
- EX1 by itself: no summation
- EX1 by itself at higher frequency: reaching threshold = temporal summation
- EX1 and EX2 at same time: two graded potential will summate - depolarise enough to reach threshold = spatial summation
- IN1 by itself: hyperpolarisation
- EX1 and IN1 at same time: cancel each other out and nothing happens = EPSP-IPSP cancelation
explain the ‘presynaptic inhibition’ diagram from the lecture (SEE NOTES)
- although A is excitatory on its own, the inhibitory axon B sitting on it cancel its input
- A fires by itself: graded potential
- A and B fire at same time: inhibitory neuron hyperpolarises the membrane of the terminal of synapse A then nothing happens and no neurotransmitters are being released = no changes
- D fires by itself: postsynaptic depolarisation
- D and B fire at same time: graded potential because the inhibitory input of B only has affect on A and not D
what are the types of direct intercellular communication?
- gap junctions: between two adjacent cells
- transient direct link up of cells’ surface markers
what are the types of indirect intracellular communication via extracellular chemical messengers?
- paracrine secretion: secreting cells produce a chemical and binds onto local target cells (only happens in short distances)
- neurotransmitter secretion: synapses between 2 cells. electrical signal travels along the neuron and synapses on local target cell
- hormonal secretion: transported through the bloodstream to target distant cells
- neurohormone secretion: neurotransmitters released into the bloodstream to target distance cell
what are possible synaptic drug actions?
- altering the synthesis, axonal transport, storage or release of a neurotransmitter
- modifying neurotransmitter interaction w/ the postsynaptic receptor
- influencing neurotransmitter reuptake or destruction
- replacing a deficient neurotransmitter w/ a substitute transmitter
