6.5 Synaptic transmission Flashcards
what is a synapse
junction between neuron and another neuron or neuron and an effector cell
synaptic cleft
gap between cells at a synapse
synaptic knob
swelling in presynaptic neuron
where are synaptic vesicles found
synaptic knob
what do synaptic vesicles contain
neurotransmitters
what happens when an action potential reaches the end of a neuron
neurotransmitters are real eased into synaptic cleft
what happens after neurotransmitters are released
diffuse across to postsynaptic membrane and bind to specific receptors
what happens when neurotransmitters bind to receptors
action potential
muscle contraction
hormone secretion
what does acetylcholine bind to
cholinergic receptors
why are impulses unidirectional
receptors are only on post synaptic membrane so can only travel in one direction
how is nerve impulse sent across a cholonergix synapse
- action potential at synaptic onob of presynaptic neuron triggers voltage gated CA2+ channel to open
- Ca2+ diffuses into synaptic onob
- causes synaptic vesicles to fuse with presynaptic membrane
- vesicles release acetylcholine into synaptic cleft (exocytosis)
- acetylcholine diffuses across synaptic cleft, binds to specific cholinergic receptors on postsynaptic membrane
- Na+ channels in postsynaptic open, influx of Na+ causes depolarisation
- if threshold reached > action potential generated
- acetylcholine hydrolysed by acetylcholinesterase
- acetate and choline reabsorbed imto presynaptic neuron and used to make more ACH
do the calcium ions move into or out of synaptic knob
INTO
what is exocytosis
processes by which a vesicle inside a cell moves to
the cell-surface membrane, fuses with the membrane and releases its
contents outside the cell
what do excitatory neurotransmitters do
depolarise the postsynaptic membrane
> action potential fired if threshold is reached
is acetylcholine excitatory or inhibitory
excitatory (in cholinergic synapses in CNS and neuromuscular junctions)
what is GABA
Inhibitatory neurotransmetteurs
what do inhibitory neurotransmitters do
hyperpolarise post synaptic membrane preventing it from firing an action potential
what does GABA do
when it
binds to its receptors it causes potassium ion
channels to open on the postsynaptic membrane,
hyperpolarising the neurone.
when can acetylcholine act as an inhibitory
cholinergic synapses in the
heart.
> can cause
potassium ion channels to open on the
postsynaptic membrane, hyperpolarising it
what is an inhibitory synapse
synapse where inhibitatory neurotransmitters are released from presynaptic membranes
what is summation
Effect of neurotransmitters released from many neurons is added together
___ sum of total lots of smaller impulses triggers an action potential fired
two types of summation
spatial
temporal
what is spatial summation
two or more presynaptic neurons release their neurotransmitters at the same time onto the same post synaptic neuron
— small amount can be enough to reach threshold in postsynaptic and trigger an action potential
what happens if some neurons release an inhibitory neurotransmitter
total effect of all neurotransmitters may be no action potential
what is temporal
where two or more nerve impulses arrive in quick succession from the same presynaptic neuron
- makes action potential more likely as neurotransmitter released into synaptic cleft
why do impulses have to follow eachother quickly
neurotransmitter will be removed from the cleft before it’s reached threshold lebel to trigger action potential
what is a neuromuscular junction
specialised cholinergic synapse between a motor neuron and a muscular cell
what do neuromuscular junctions use
acetylcholine which binds to nicotinic cholinergic receptors
compare cholinergic and neuromuscular
neromuscular : motor neuron and muscle fibre, main function is to stimulate muscle contraction
cholinergic : between two neurons, used to transmit signals for various functions
differences between neuromuscular junction and cholinergic
in neuromuscular
- postsynaptic membrane has clefts which store acetylcholinesterase
- postsynaptic has more receptors
- acetylcholine is always excitatory
similarities between neuromuscular and cholinergic
- both release acetylcholine from vesicles in the presynaptic membrane
- then diffuses across the synaptic cleft and binds to cholinergic
receptors on postsynaptic membrane, this triggers an action
potential if the threshold is reached - acetylcholine broken down by acetylcholinesterase in both
how do agonists affect synapses
same shape as neurotransmitters so they mimic their action at receptors
- more receptors are activated
how do antagonists affect synapses
block receptors so they can’t be activated by neurotransmitters so fewer receptors can be activated
what do drugs that inhibit the enzyme that breaks down neurotransmitters do
more neurotransmitters in synaptic cleft to bind to receptors and they are there for longer
what do drugs that stimulate the release of neurotransmitters do
more receptors activated
what do drigs that inhibit the release of neurotransmitters
fewer receptors activated
what is endogenous
produced naturally by the body
what is an autoimmune disease
persons immune system mistakes their own cells for for pathogens so it starts to attack them
