13.4 Nervous transmission Flashcards
what is the resting potential?
the potential when no impulse is being transmitted
-70 mV
what is the charged composition of a membrane under resting potential?
outside of the axoplasm is MORE positively charged than the inside of the axoplasm which makes the membrane polarised
how is a resting potential generated?
Na+ ions are pumped out of the axoplasm
K+ ions are pumped into the axoplasm
Na+ voltage gated channels are closed so Na+ ions cannot diffuse back into the axoplasm
K+ voltage gated channels are opened at resting potential so many K+ ions diffuse out of the axoplasm
means that there are more positive ions outside the axoplasm than inside
therefore the membrane is polarised
how many Na+ ions are pumped OUT?
3
how many K+ ions are pumped IN?
2
how are Na+ and K+ ions pumped in or out?
using a Na/K pump
what are the intrinsic proteins which exist in the axon membrane?
Na+ voltage gated channel
K+ voltage gated channel
K+ channel (leaky channel)
Na/K pump
what is the order of events in generating action potential?
- resting potential
- start of depolarisation
- depolarisation
- end of depolarisation and start of repolarisation
- repolarisation
- hyperpolarisation
- resting potential
what happens between -70mV and -55mV?
stimulus arrives as an electrical impulse which causes Na+ voltage gated channels to open
Na+ ions diffuse INTO the axoplasm down the electrochemical gradient
makes the membrane less polarised
what happens between -55mV and +40mV?
DEPOLARISATION
change in polarisation causes more Na+ voltage gated channels open
this allows more Na+ ions to move INTO the axoplasm down the electrochemical gradient
this causes an increase in the potential difference
what happens between +40mV and -70mV?
REPOLARISATION
the Na+ voltage gated channels close which stops Na+ ions diffusing into the axoplasm
the K+ voltage gated channels open which allows K+ ions to diffuse OUT of the axoplasm which causes a decrease in the potential difference
what happens between -70mV and -90mV?
HYPERPOLARISATION
the K+ channels are still open so more K+ ions move OUT of the axoplasm
potential difference continues to decrease as axoplasm becomes more negative
what happens between -90mV and -70mV?
K+ voltage gated channels are closed
the Na/K pump pumps OUT Na+ ions into the tissue fluid and K+ ions INTO the axoplasm
resting potential is restored
what is the refractory period?
a short period of time when the axon cannot be excited again. the Na+ gated channels are CLOSED which prevents Na+ ions entering the axoplasm meaning an action potential cannot be generated
what does a refractory ensure?
that action potentials don’t overlap and instead pass as discrete impulses
ensures action potentials as unidirectional
what is saltatory conduction?
when an electrical impulse jumps between nodes which makes impulse transmission faster and easier
why does having a myelinated neurone allow for saltatory conduction?
myelinated axons mean there are less places for voltage gated channels to be kept open as only the nodes of Ranvier are exposed to the tissue fluid
why does a non-myelinated neurone transmit impulses slower?
no nodes of ranvier so action potentials need to be generated along the whole axon
makes transmission slower
what factors affect the speed of action potential movement?
- myelination
- axon diameter
- temperature
how does myelination affect the speed of action potential movement?
myelinated neurones allow for saltatory conduction which is faster than in conduction in non-myelinated neurones
how does the axon diameter affect the speed of action potential movement?
bigger the axon diameter, the faster the impulse is transmitted as there is less resistance to the flow of ions
how does the temperature affect the speed of action potential movement?
higher the temp, the faster the nerve impulse due to the kinetic theory. however, once temp has passes optimum, proteins such as the Na/K pump denature which stops the generation of resting potential
what is the all or nothing principle?
a stimulus needs to exceed a threshold value otherwise no response is triggered
what happens with a larger stimulus?
the larger the stimulus the more frequently action potentials are generated
when an action potential is generated when is the Na/K pump active?
ALL THE TIME
why may depolarisation and repolarisation be faster in certain neurones?
presence of more Na+ and K+ voltage gated channels
steeper Na+ gradient
steeper K+ gradient
