communication within and between neurones (2) Flashcards
how long can axons be
a few cm
signals need to travel from - to end of -
cell body, axon
why is communication not via diffusion of chemicals
we can respond to stimuli very quickly especially in reflexes- communication is fast,
diffusion of chemicals would be far too slow
what type of signal occurs in neurones
electrical
what type of state is the resting membrane potential
an unstable state
what happens while a neurone is in it’s passive state
energy is expended to maintain the unstable state of the resting membrane potential
what happens upon a trigger to a neurone
because the neurone is in an unstable state, stored energy is then released
what is the release of energy upon trigger of a neurone called
an action potential
what is the membrane of a neurone
a phospholipid bilayer
what type of ion does the lipid bilayer prevent passing through?
charged molecules/ ions
how does the lipid bilayer create an unstable resting membrane potential
membrane creates barrier between inside and outside of neurone, creating a disparity between composition of liquid inside compared to inside
what is embedded within the barrier
proteins with various roles
what does the sodium/potassium exchange transporter do
moves sodium ions outside of the neurone and moves potassium ions into the neurone
do the exchange transporters move more sodium out or more potassium ions in?
more sodium ions out
sodium and potassium are both cations, meaning…
they each carry a single positive charge
because transporter moves more sodium ions out of the cell than it does potassium ions into the cell, the charge is…
more negative inside the cell, as there is an accumulation of positively charged ions outside of the cell
chloride is an…
anion, holds negative charge
what is the difference in charges between the inside and outside of a neurone cell?
-70mV (minus as the charge inside of the cell is more negative)
what is caused by the difference in charges between the inside and outside of a neurone cell
electrostatic pressure
what is electrostatic pressure
the idea that positively charged ions want to move to an area of negative charge
what does a transporter do
moves specific ions using energy
what forces push sodium back into the cell
electrostatic pressure AND diffusion
why does sodium not move back into the cell despite electrostatic pressure and diffusion
it can’t move through the phospholipid bilayer
why does a little sodium get back into the cell and what happens to it then
because the lipid membrane is leaky, transporters push them back in
what forces act to push K out of the cell
diffusion
what forces act to keep K in the cell
electrostatic pressure
why does K stay in the cell
the forces of diffusion balance out the force of electrostatic pressure
describe the neurone cell at resting state
more sodium outside and more potassium inside, charge more positive outside cell and more negative inside cell, cell has electrical excitability (electrically charged ions would move if we let them), energy is being used by the sodium/ potassium transporter
what happens in stage 1 of an action potential
the membrane depolarises
why is the membrane said to be polarised when at rest
because there is differential charge inside and outside the cell
what does depolarisation refer to
anything that brings the membrane closer to a charge of 0
at what point to voltage-gated sodium channels open
-55mV
what happens when voltage-gated sodium channels open
the membrane is much more permeable to sodium, and sodium moves into the cell via diffusion and because of electrostatic pressure
what happens as sodium moves into the cell
the cell becomes less negatively charged
what happens when the cell becomes positively charged
electrostatic pressure works against sodium moving into the cell, however diffusion overcomes this pressure
what 2 channels open in stage 1 of an action potential
sodium and potassium
what happens in stage 2 of an action potential
the membrane potential gets more positive as cations flood in
what ion leaves the cell in stage 2 of an action potential
potassium, as the channels are open and there is no electrostatic pressure opposing them
when do voltage-gated sodium channels close again
+40mV
what happens in action potential stage 3
membrane repolarisation
why does the membrane depolarise in stage 3
sodium ions and potassium leave the cell, so the cell starts becoming negatively charged again
what happens in stage 4
membrane hyperpolarisation
what is hyperpolarisation and why does it occur in stage 4
it is where the cell membrane becomes extremely negatively charged, it occurs becomes positively charged potassium cations continue to leave the cell
what happens in stage 5
potassium channels close and other processes return the balance to resting membrane potential
after an action potential is generated, what happens
the action potential is regenerated further down the membrane
what makes up the myelin sheath
oligodendrocytes
what do glia do
wrap around the neurone forming an insulating layer where an action potential can’t form, forming nodes
what do nodes do
force action potentials to jump between nodes
what happens to the action potential as it travels underneath the myelin sheath
it decreases, and then is regenerated at the nodes to save energy
are action potentials always the same size
yes
what is a chemical synapse
a physical gap between the neurones which is around 20nm
what is in the terminal of presynaptic neurones
vesicles containing chemicals called neurotransmitters
what are the 2 types of post synaptic potentials
excitatory and inhibitory
what happens in an EPSP
they make it more likely that an action potential will fire because it brings the membrane potential closer to the threshold
what causes an EPSP
Generally happens if we are opening cation channels (positive ion)
what causes IPSP
open anion (negatively charged ion) channels
what happens in an IPSP
As the membrane becomes less negative it creates less electrostatic pressure, so more chloride will move in- overall makes an action potential less likely to occur
what are the 2 types of synapses
chemical and electrical (also called gap junctions)
describe an electrical synapse
2 neurones are fused together by a single channel so that ions can move directly from 1 neurone to another
when can an electrical charge move in both directions
in an electrical synapse
