neurotransmission Flashcards
what is a neuromuscular junction?
junctional folds with ACh receptors and cholinesterase enzymes
what are end plate potentials?
Depolarization of skeletal muscle fibres caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction.
Synaptic potentials that you can record across the muscle fibre when you activate the end plate
how does the size of the EPP change as you move towards the end plate?
gets larger
what size EPP can generate an AP?
a large one
what are miniature end plate potentials?
small depolarizations of the postsynaptic membrane caused by the release of a single vesicle into the synaptic cleft
why don’t mEPPs stimulate an AP?
they’re small depolarisations which do not reach the threshold
where can you record mEPPs?
when you’re close to the muscle end plate
what does neurotransmitter release in the CNS cause?
EPSPs and IPSPs in the post synaptic cell
why do membranes have a negative membrane potential?
bc of the distribution of K+ across the membrane –> tendency of K+ to leave the membrane
what receptor does ACh bind to?
nicotinic ACh receptor
how many ACh molecules required for Na+ influx?
2
what effect does ACh have on the membrane?
depolarises it from negative to positive
what is the receptor that is associated with IPSPs?
GABAa receptor
how is an IPSP produced?
GABAa receptor is permeable to Cl-
Cl- moves into the membrane and makes it more negative –> hyperpolarisation
harder to fire an AP
what neurotransmitter do primary sensory neurons use and what type of NTS are they?
glutamate (fast and modulator)
what neurotransmitter do CNS neurons use and what type of NTS are they?
acetylcholine (F+M)
o Amino acids – glutamate, GABA (inhibitory) (both F+M), glycine (inhibitory- F)
o Biogenic amines – noradrenaline (M), 5-HT (F+M), dopamine (M)
describe the reflex arc
• 1a afferent reflex – brought about by patellar ligament tap for example
• AP go through dorsal root into the grey matter
• Monosynaptic connection with a homonymous motor neuron in the ventral horn
oEPSPs excite alpha motor neuron and recruit an AP
•Sends an axon out the ventral root
•Sends AP to the same muscle providing the input
what gives rise to reciprocal antagonism?
inhibitory interneuron which transmits an inhibitory neurotransmitter
what neurotransmitter do inhibitory interneurons use?
glycine
put these in order from fastest to slowest;
neurotrophic factor, neurotransmitter, neuromodulator
neurotransmitter - ms
neuromodulator - s-mins
neurotrophic factor - mins/hours
what receptors do fast neurotransmitters use?
multimeric (pentameric and tetrameric) receptors that incorporate ion channels
what receptors do modulators use?
G-protein coupled receptors
what are the 2 classes of action of neurotransmitters
Fast - direct gating of ion channel
Modulatory – activation of G-protein coupled receptor pathway
what are the mechanisms involved in the termination of transmitter action?
- Transmitter breakdown
2. Reuptake using selective transport mechanisms
how can neurotransmitters be broken down?
acetylcholinesterase - found in the synaptic cleft and cleaves ACh
selective reuptake mechanisms which terminate the action of the transmitter which run off the Na+ gradient
how can acetylcholinesterase be inhibited?
- nerve agents
- medically inhibited by neostigmine, physostigmine etc for treatment of myasthenia gravis
what are examples of neurotransmitter reuptake?
glutamate transporters - glutamate taken up into pre/post synaptic terminals and astrocytes. transporters use energy stored in transmembrane Na+ from Na/K pump to uptake glutamate
GABA reuptake - into presynaptic terminals and astrocytes by GATs
what are the waves of the muscle action potential recorded by electrical stimulation of peripheral nerve?
o M-wave, direct activation of motor units by electrical stimulation
o H-reflex, electrical equivalent to stretch-reflex
o F-wave, antidromic motor nerve action potentials bouncing off the a-motoneurons
what abnormalities can be shown by evoked muscle action potentials?
o Peripheral demyelination
o Carpal tunnel entrapment
o Myasthenia Gravis (neuromuscular disease)
o Lambert-Eaton myasthenic syndrome
