Neuronal responses Flashcards
where are the synapses located and name some axons
- Axosecteroy – axon terminal secretes directly into the blood stream
- Axoaxonic – axon terminal secretes into another axon
- Axodendritive – axon terminal ends on a dendrite spine – most common
- Axoextracellular – axon with no connection secretes into extracellular fluid
- Axosomatic – axon terminal ends on soma
- Axosynaptic – axon terminal ends on another axon terminal
describe basically what happens when the action potential arrives at the axon terminal
- Action potential arrive at the axon terminal
- Causes a change in the membrane charge
- This causes voltage gated calcium ion channels to open
- Calcium enters the cell
- Calcium signals to the vesicles
- Vesicles move to the membrane
- Docked vesicles release neurotransmitter by exocytosis
- Neurotransmitter diffuses across the synaptic cleft and binds to receptors
- The response depends on what receptor that the neurotransmitter binds to
what does the response to neurotransmitters depend on
depends on the receptor type
what does the action potential generated depend on
- depends if the receptor is inhibitor or excitatory
- depends in the neurotransmitter is inhibitor or excitatory
what does the release of ACh at neuromuscular junctions cause
it always gives an excitatory response
- all nicotinic acetylcholine responses are excitatory
what happens at most synapses
excitatory or inhibitory response
what kind of receptor type is the ligand gated sodium channel
nicotinic acetylcholine receptor
what has to happen for the action potential to be trigger
• For an action potential to be triggered the sum of all the inputs msut be above the threshold value
- action potential is only produced in the sum of all inputs is enough to depolarise the neurone above the threshold
what is an example of an EPSP
- Increases membrane Na+ permeability causing depolarisation
- E.g. nicotinic ACh receptor open cation channel leading to influx of sodium ions
what is an example of IPSP
- Increases K+ permeability (moves out making outside more positive) or increase Cl- permeability (moves in so makes inside more negative) causing hyperpolarisation so that more sodium is required for the threshold value to be reached
- E.g. muscarinic ACh receptor opens K+ channel g protein coupled acting by a 2nd messenger – M2 receptor on the heart
- E.g. GABAA receptor directly open the Cl- channel this causes hyper polarisation and makes it more difficult get an excitatory post synaptic potential
what does an excitatory post synaptic potential do
increase sodium permeability
what does an inhibitor post synaptic potential do
increase potassium or chloride permeability
what happens in sub-threshold stimuli
• For sub-threshold stimuli no action potential will be generated if they do not overlap
what happens in temporal summation
- rapid firing of a single input
- second EPSP occurs before the first has died away
- reaches threshold
- post-synaptic neurone fires an action potential
what happens in spatial summation
- stimulus activation from two inputs
- the sum of the two EPSPs reaches threshold
- post synaptic neurone fires an action potential
ISPSs can…
can cancel out ESPSs meaning no change in membrane potential and therefore no action potential is generated
describe the ligand gated ion channel
- opens when ligand(neurotransmitter or drug) binds to it and opens the channel
- ionotropic meaning it allows the ion directly in
- response is in milliseconds
describe an example of a ligand gated ion channel
• E.g. nicotininc ACh (requires 2 ACh molecules - permits na+ movement from synaptic cleft to post synaptic neurone),
- Glutamate NMDA and non-NMDA receptors, GABAA - inhibitory - glutamate binds to these receptors one the channel and allow for sodium and calcium to enter therefore it is excitatory
• Gaba – benzodiazepines for sleep and reducing anxiety cl- moves through channels on binding and hyperpolarises the neurone. Sedative, sleep inducing no action potentials as threshold isnnt reached and shuts off cns = calming effect and prevents overstimulation
the benzodiazepines bind to the GABAa receptor and cause the structural change
describe the G protein coupled receptors
- Metabotropic – needs some sort of energy
- Activates a second message using the G protein (with or without using an enzyme such as adenylate cyclase for cAMP)
- 7 transmembrane segments
How do G protein coupled receptors respond to neurotransmitters
- Ligand binds to receptor, activatesg protein- enzyme- 2nd messenger – phosphorylation events( protein kinase)
- 2nd messengers transmit+ amplify signals from receptors to downstream target molecules – one messsenger can therefore lead to phosphorylation of many proteins
- 3 different types of 2nd messnegers
- Hydrophillia]ic water soluble – cAMP, cGMP, Ca2+
- Hydrophobic water soluble – DAG and PIP3
- Gases – NO, CO, ROS
- Response in seconds
what is an example of G protein receptor
Catalytic receptors enzyme linked – tyrosine kinase – ligands activate intrinsic intracellular enzyme activity, minutes for dimerisation, phosphorylation, 2nd messengers to occur
Name what the intracellular receptors do
o Steriods, thyroid hormones, growth hormones- bind to receptor and form complex
o Bind to dna
o Affect dna transcription rates, changes production of functionally relevant proteins
o Slow responses
What does adaptation do
prevents signal overload
what does X mean
- no adaption
- slow adaption
- rapid adaption
- No adaptation – maintains initial potential – e.g. otoliths detecting head position
- Slow adaptation – olfactory system (smells), Ruffini endings (stretching of the skin), Merkel cells (pressure texture)
- Rapid adaptation – Pacician corpuscle (vibration and mechanical pressure), Meissner corpuscles (light touch – e.g. with clothes) notice start and end not in between
