Neurotransmission in the Nervous System Flashcards
what are the 2 classes of molecule that allow neurotransmission
- chemical molecules
- chemically gated receptors
what do end plate potentials do
- it records the potential changes that are occurring across the muscle fibres
if you are close to the end plate….
- If you are close to the end plate then you get a largest end plate potential as you move the voltage further away is gets smaller
what are end plate potentials build up
- EPPs are built of whole numbers of miniEPPs
- Consists with evoked EPPs occurring in multiples of the quantal amplitude
what do miniEPPs do
they occur close to the EPP and can correspond with 1 or 2 vesicles that are released, this gives rise to depolarisation that has a certain amplitude
what can neurotransmitters released in the CNS cause
- EPSPs and IPSPs in the post synaptic cell
how is an EPSP or EPP conducted
- There is an asymmetric complementary distribution of monovalent cations across the membrane
- on the inside there is a lot of potassium whereas on the outside there is a lot of sodium
- Because of this distribution of potassium ions there isa negative membrane potential, this is because the potassium ions are leaving the permeable membrane and this makes it negative
- Nitocinic AcH receptor – 2 acetylcholine receptors bind to the receptor and this opens the receptor
This causes sodium to go in across the membrane in order to depolarise the membrane and gives rise to the EPP or EPSP
How is an IPSP generated
- Chloride moves inwards because ECl is more negative than the resting potential, BUT importantly activating GABAa ALSO makes the membrane more leaky to current
- Makes the hyperpolarise the membrane, makes the membrane leaky at a charge, makes the membrane leakier and shuts down the cell making it less excitable
what is the neurotransmitter in the primary sensory neurones
glutamate
what are the neurotransmitters in the CNS
Acetylcholine
Amino acids:
Glutamate
g-aminobutyric acid (GABA) (inhibitory)
Glycine (inhibitory)
Biogenic Amines:
Noradrenaline
5-HT
Dopamine
What are the inhibitor neurotransmitters in the CNS
GABA and glycine
how does inhibition of a reflex work
- In order to inhibit the activity of the extensor motor neurone need to provide glycine in order to inhibit it ,
- need to have an inhibitory interneurone that is able to provide a glycine input, gives rise to reciprocal antagonist inhibition
What are the excitatory neurotransmitters
- glutamate and acetylcholine
What is an EPSP
An EPSP occurs when an excitatory neuron e.g Ach,
or Glutamate binds it’s respective post synaptic
receptor resulting in an influx of sodium, leading to
to depolarisation
what is an IPSP
An IPSP is essentially the opposite. An inhibitory
neurotransmitter e.g. GABA or Glycine binds its
respective receptor, resulting in Chloride influx
which hyperpolarises the neuron.
describe the fast and modulator effects of glutamate
Has a fast excitatory effect on postsynaptic cells via
AMPAr and a voltage dependent effect via the
NMDAr.
Modulatory effects via the metabotropic G
protein coupled receptors.
describe the fast and modulator effects of acetylcholine
Fast excitatory effect on postsynaptic cells via
nicotinic receptors
a slower modulatory effect
via Muscarinic G protein coupled receptors.
Describe glycine
The glycine receptor is a nicotinoid receptor and
chloride channel. Key inhibitory transmitter in spinal
cord.
describe the fast and modulator effects of GABA
The GABA receptor is the key inhibitory
neurotransmitter of the brain and it has a fast
inhibitory effect via GABAa (a chloride channel)
a slower neuromodulatory action via GABAb
metabotropic receptors.
what neurotransmitters have fast and modulator responses
- Glutamate
- GABA
- 5 HT
- acetylcholine
what neurotransmitters have fast responses
glycine
what neurotransmitters have modulator responses
noradrenaline
dopamine
how does acetylcholine bind to open up a ligand ion channel
- it binds at a C loop, this destabilises the hydrophobic interactions and causes the channels to open
give examples of neuromodulators that are not fast neurotransmitters
• co-transmitter neuropeptide substance P • e.g. inflammatory mediators etc prostaglandin E2 bradykinin
How do you terminate the transmitter
- Transmitter breakdown
* Reuptake using selective transport mechanisms
what happens when you terminate a neurotransmitter
this stops the EPSP, IPSP or end plate
how do you inhibit neurotransmitter breakdown
- acetylcholinesterase can be inhibited by a enrol sagest such as Sarin, or Novicokck this is irreversible
how can you tell if neurotransmitter breakdown has been inhibited
- pin point pupils
- kills you via paralysis of breathing
how do you treat inhibition of a acetylcholinesterase
• medicinally inhibited by neostigmine, physostigmine etc for treatment of myasthenia gravis (pyridostigimine in Gulf War Syndrome)
- these work by binding to the receptors whcih sarin would bind to
what are the waves and reflexes involved in testing muscle action potential
- M wave direct activation of motor units by electrical stimulation
- H-reflex, electrical equivalent to stretch-reflex
- F-wave, antidromic motor nerve action potentials bouncing off the a-motoneurons
what abnormalities might you detect in muscle action potential that is recorded by electrical stimulation of a peripheral nerve
Recorded evoked muscle action potentials
- Peripheral demyelination - - Look for giant motor units (MND/ALS)
- Lambert-Eaton myasthenic syndrome
- Myasthenia Gravis
- Carpal tunnel entrapment
record sensory nerve volley by recording in the digits
- peripheral demyelination
where are glutamate transporters for reputake
- neurones and glia
Glutamate is taken-up into pre and post –synaptic terminals, and into the adjacent glia, terminating its neurotransmitter action
how is GABA reuptaken
GABA reuptake into presynaptic terminals and astrocytes by GATs
how are biogenic amines reuptaked into presynaptic terminals
Biogenic amine reuptake into presynaptic terminals (e.g. for noradrenaline uptake 1 and uptake 2 mechanisms
what do amine and amino acid transporter use for reuptake
- they utilise the energy stored in the sodium gradient
