L5 & L6 - Neurons Flashcards
Hodgkin and Huxley
1940
giant squid axon experiments which showed mechanism of action potential
Homogenizing forces
forces that act to evenly distribute ions equally throughout intracellular and extracellular fluid
- random motion and conc grad
- electrostatic pressure1
What forces counteract the homogenising forces?
~ different permeability of ions
~ sodium-potassium pump
Levels on ions inside the cell at resting potential.
~ low Na+ and Cl-
~ high K+
(outside cell is opposite)
What is the membranes resting potential?
-70mV
Why is the refractory period important?
~ AP only travel in one direction
~ rate of firing relative to intensity of stimulus
~ 1-2ms
Saltatory conduction
conduction of AP hops between nodes of Ranvier
How is acetylchloline made?
choline + acetyle CoA = acetylcholine
choline acetyltransferase needed
Presynaptic transporters
inactivation of neurotransmitters by reuptake
How is acetylcholine removed from receptors?
Actylecholinesterase breaks down ACh to acetate and choline
What affects can neurotransmitters have on neurones?
Depolaisation - increase likely hood of firing
Hyperpolaristion - decrease likelihood of firing
Temporal summation
several impulses from one neurone over time
Spatial summation
several impulses from different neurons at the same time
How can drugs affect synapses? (5)
- increase no. of impulses
- release NT from vesicles with or w/o impulse
- block reuptake/receptors
- produce more/less NT
- prevent vesicles from releasing NT
Agonistic drug
facilitates normal postsynaptic effect of NT
Antagonistic drug
blocks/inhibits normal postsynaptic effects of NT
Which three drugs affect NTs?
Methamphetamine
Nicotine
Alcohol
Methamphetamine
~ enters dopamine vesicles causing release of NT
~ blocks dopamine transporters from pumping dopamine back into the transmitting neuron
= more dopamine in synaptic cleft = euphoric feeling
Problems with taking methamphetamine.
~ euphoric feeling ‘crashes’ and won’t return until the drug is taken
~ long term use can cause cons to die
Cocaine
blocks dopamine and works in a similar manner to methamphetamine
Nicotine
similar to dopamine release into synapse like methamphetamine
~ BUT binds to receptors on postsynaptic neuron (diff. mechanism)
Alcohol
~ alters neurone membranes, ion channels, enzymes and receptors
~ binds directly to receptors for acetylcholine, serotonin, GABA and glutamate
GABA
~ inhibitory neurotransmitter
~ binding allows Cl- ions to pass into neurone
~ causes hyperpolarisation of neurone = inhibits impulse transmission
GABA + Alcholol
~ alcohol binds to GABA receptors = increased hyperpolarisation of neurone
~ neurone activity diminished
~ responsible for sedative effects
Threshold level
-55mV
neurone will only send impulse if signal reaches this level of depolarisation
