week 4: neurobiology: action potential and autonomic nervous system Flashcards
neurones at rest
transmembrane potential
outisde:
Na+ =150mM
K+ = 4mM
inside:
Na+= 15mM
K+= 140mM
difference in inside and outside neurone concentrations at rest due to the
sodium potassium pump
Sodium/ potassium ATP pump
uses energy from ATP
ATP>ADP
uses energy to pump Na ut and K in
why can sodium and K not cross membrane unless transported
charged ions
inside of cell has very …. charge compared to outside
negative
how can we measure potential difference between outside and inside of cell
using electrodes
can be inserted inside neurons
resting potential of cell
-65mV
electrochemical force
electrical driving force and chemical driving force combines
electrical driving force of a neurone ???
inside of a cell is - and attracts +
+ > - ?????
chemical driving force of a neurone
conc gradient
high conc Na+ outside, low conc inside
equilibrium potential
membrane potential where electrical force is equal and opposite to the clinical force
can be worked out for any ion
equilibrium potential
membrane potential of cell in which there is no movement of ions
eg
electrical force (driving in) = chemical force (driving out)
Nernst equation Ex=
(RT/zF) x (ln[X]o/[X]i)
R=gas constant
(8.314472 JK-1mol-1)
T= absolute temp
z= charge of ion
F= faradays constant
(9.6485309 X10^4 Cmol-1)
[X]o= conc of ion outside cell
[X]i = conc of ion inside cell
simplified Nernst equation
Ex=
58 x log ([X]O/[X]i)
when does the simplified Nernst equation work
monocovalent cations at room temp
at equilibrium potential, electrical gradient =
same magnitude but in opposite direction to chemical gradient
ligand gated ion channels
on post synaptic membrane
neurotransmitter binds to receptor
conformational change to receptor
ion channel opens
inside of cell becomes less negative
are channels directional
no
electrochemical force of ion sets direction of travel
acetylcholine binds to receptor on post synaptic membrane
channel opens
lots of Na+ enters
small amount of K+ leaves
depolarisation occurs ‘inside of cell becomes more +
how are neurotransmitters released at a synaptic terminal
exocytosis
AP 1 - neurotransmitters bind to cell
membrane depolarised
AP 2- membrane depolarisation reaches threshold potential
voltage-gated Na+ open
large influx of Na+
overshoot: membrane potential becomes +
AP 3- Na+ channels become deactivated…
voltage gated K+ channels open
K+ moves out of cell
repolarisation occurs
AP 4- afterhyperpolarisation/ undershoot
resets using sodium-potassium ATP pump
absolute refractory period
time where cant inject more current and get a second AP
sodium channels inactivated
no ions can flow through even when they are open
relative refractory period
still possible to get a second AP
larger stimulus can result in AP
membrane potential is more negative than resting potential
what does the absolute refractory period ensure
action potential propagation is unidirectional
why does AP only propagate in one direction
sodium channels become inactivated after a while
cant maintain depolarisation
when inactivation is lost, membrane is repolarised so channel is no longer open
where are sodium and potassium channels present in myelinated neurones
at nodes of Ranvier
saltory conduction
action potentials jump from node to node
electrical synapses
no neurotransmitter release
protein channels- gap junction channels
couple cytoplasm of two cells
allows ions and small molecules to flow through
change in pre-synaptic neurone fed immediately through to post-synaptic neurone
direct and quick signal trasmission
chemical synapses
use neurotransmitters
most of synapses in brain
