3: Physiology - Excitatory and inhibitory neurotransmission in the CNS Flashcards
Given that nerve cells depolarise to cause an action potential, are their resting membrane potentials positive or negative?
Negative
Which ion channels open to cause a depolarisation?
Na+
Ca2+
i.e positively charged ions
Which ion channels open to cause a hyperpolarisation?
C- (flows inwards, makes cell more negative)
K+ (flows outwards, makes cell more negative)
In which directions do
a) sodium
b) calcium
c) chloride
d) potassium
ions flow to cause a/b) depolarisation and c/d) hyperpolarisation?
a) Inwards
b) Inwards
c) Inwards
d) outwards
What type of nerve transmission is triggered by a depolarisation?
Excitation
What type of nerve transmission is triggered by a hyperpolarisation?
Inhibition
Given that sodium influx causes a cell to depolarise, what effect do
a) sodium channel agonists
b) sodium channel antagonists
have on nerve cells?
a) Excitatory
b) Inhibitory
Given that potassium efflux causes a cell to hyperpolarise, what effects do
a) K+ channel agonists
b) K+ channel antagonists
have on nerve cells?
a) Inhibition
b) Excitation
What is the difference between an axon and a dendrite?
Both are projections of a neuron
Axons carry outputs to other neurons
Dendrites receive inputs from other neurons
Neurons have many dendrites but only one axon
What is the space between a pre-synaptic cell and a post-synaptic cell called?
Synaptic cleft
Which ion is essential in triggering the release of neurotransmitters across a synaptic cleft?
Ca2+
What releases neurotransmitters into the synaptic cleft?
What transport process is this an example of?
Synaptic vesicle
Exocytosis
By which three means are neurotransmitters cleared from the synaptic cleft?
1. Recycling into axon terminal or glial cell
2. Deactivation by enzymes
3. Diffusion out of synaptic cleft
Which types of receptors
a) directly
b) indirectly
activate ion channels as a result of the binding of neurotransmitters?
a) Direct receptors for ligand-gated channels
b) G-protein coupled receptors
What is faster, direct or indirect gating of ion channels?
direct gating
ligand binds to receptor, response
where as indirect gating involves proteins and metabolites which have to react and change confirmation etc etc
What is the main excitatory neurotransmitter?
Glutamate
What are the main inhibitory neurotransmitters?
GABA
Glycine
Molecules called AMPA and NMDA are sometimes found bound to glutamate (excitatory) receptors.
What happens to the speed of the neurotransmision when NMDA is bound?
Slows down - “slow component”
What happens to the speed of neurotransmission at a glutamate (excitatory) receptor when AMPA is bound?
Speeds up - rapid transmission
What are the main inhibitory neurotransmitters?
GABA
Glycine
What are ionotropic and metabotropic receptors?
Ionotropic - directly gated by ions which bind to them to cause a response e.g channel opening
Metabotropic - indirectly gated - binding by a ligand causes a chemical reaction / protein release etc. etc. which eventually opens the channel
Which type of receptor is faster acting - ionotropic or metabotropic?
Ionotropic
Ionotropic receptors are often responsible for ___ an action potential at the post-synaptic terminal.
triggering
Because metabotropic receptors are slower acting than ionotropic receptors, which role do they have in a synapse?
Alter PROPERTIES of action potential e.g firing rate, amplitude
Alter neurotransmitter release
In general, ionotropic receptors trigger (fast / slow) action potentials.
ionotropic - fast action potentials
In general metabotropic receptors trigger (fast / slow) action potentials.
metabotropic - slow action potentials
What is the name of the action potential triggered by neurotransmitters in the neuron FOLLOWING a synapse?
Post-synaptic potential
What must the post-synaptic potential overcome to trigger an action potential?
Threshold potential
In terms of threshold potential, what is meant by an excitatory or inhibitory post-synaptic potential?
Excitatory - depolarises the neuron and brings it closer to the threshold potential required for an AP
Inhibitory - hyperpolarises the neuron and brings it further away from threshold
What variable determines the amplitude of an AP generated by sensory neurons?
Stimulus intensity
What is meant by the term graded potential?
A gradual change in membrane potential rather than a sharp jump
Why does the graded potential of a neuron decrease?
Time - ion channels open and close
Distance - charge leaks away
If a graded potential overcomes threshold, what does it become?
Action potential
What neurotransmitters cause depolarisation of the post-synaptic neuron?
Glutamate - excitatory neurotransmitter
Which neurotransmitters cause hyperpolarisation of the post-synaptic neuron?
GABA
Glycine
What is an interneuron?
Which neurotransmitter does it secrete?
An independent neuron which processes local information
GABA (inhibitory)
What is a quanta of neurotransmitter?
The volume secreted from ONE synaptic vesicle
What influences the number of quanta of neurotransmitter secreted by a synaptic vesicle?
Stimulus intensity
From other lectures, what is
a) spatial summation
b) temporal summation?
a) Whether a neuron fires or not depends on all the excitatory and inhibitory synapses connected to it
b) Whether a neuron fires or not depends on the number of excitatory / inhibitory signals and the sequence they’re received in
