The neuron Flashcards
Define the characteristics of a neurotransmitter.
- They are very variable (shape and size, responses, functions, modifiability)
- Fast
- inexpensive: only need small amounts of signalling molecule
- Directional: signals are sent to specific targets, often over long distances (synapse–> dendrite–> soma–> axon–> synapse)
- selective: signals are small, discrete and targeted
Ohm’s law
the rate of movement of a charged particle (i) depends on the force moving it (V) and the ease with which it can move (g)
I=gV
R=1/g
I=current Amperes A. pico A = 10^-12 A
V= voltage (volts) milli V= 10^-3 V
g= conductance (S) nano S=10^-9S
R= resistance (Ohms) mega ohm = 10^6 ohmss
What is resting membrane potential based on
ion channels permeable to Na+, K+ and Cl-
flow through ion channels depends on concentration and electrical gradients across the membrane
measurement of resting membrane potential shows that— inside of membrane is… compared with outside
negative
-90 to -45mV
What is ionic equilibrium potential / when does it occur
occurs when forces exerted on an ion by concentration and electrical differences across membrane are equal and opposite, so net flow of ion ceases
is electrical potential which exactly counterbalances force of ionic concentration gradient
What is the typical distribution of ions across neurone membrane.
K+ 5mM outside 100mM inside
Na+ 150mM outside 15mM inside
Cl- 150mM outside 13mM inside
Ca2+ 2mM outside 0.0002mM inside
What is a major pump maintaining RMP
Na-K ATPase
moving 3Na+ out every 2K+ in using alot of ATP
Ca pump also used ATP to move Ca out of cell cytoplasm into internal stores or out of cell.
Where is decision to dire in neurons made
Axon initial segment
What ion causes depolarisation
Na+
drives rising phase of AP
Definition of a neurotransmitter
chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell
- must be synthesized endogenously, that is, within the presynaptic neuron
- is available in sufficient quantity in the presynaptic neuron to exert an effect on the postsynaptic neuron
- its effects mimic the endogenously released substance if externally administered
- a biochemical mechanism for inactivation must be present
RPM Is a balance between
flux and pump activities
constant flux of K+, Na+ and Cl- through non-voltage gated dependent ion channels
Ion flux opposed by ion exchanger pumps (Na/K ATPase- 3 Na out/ 2 K in
K/Cl pumps Cl out K in
Membrane acts like a capacitor results in
potential changes more slowly than current as capacitor transiently ‘absorbs’ some current
what is RMP predominantly determined by
why
K+ distribution across the membrane
because K+ permeability is high, and the ration os K+ concentration across the membrane is high
Increasing Extracellular K+ levels will strongly
depolarise RMP
change concentration of K+ outside
- change the gradient- slow down outflow of K+ from cell - less outflow = depolarisation because more stays in
- increase in membrane potential opens some sodium channels- letting +ve ions in– depolarising
deceasing extracellular K+ will
hyperpolarise RMP
