Nerve impulses: transmission 5.3.4
Local currents
During depolarisation, Na+ ions flood into the neurone, which creates local currents in the cytoplasm
1. During action potential, when the channels open, Na+ diffuses into the neurone from high to
low conc
2. Na+ move along the neurone towards areas with low concentrations of Na+ - called a local
current
3. Local current causes slight depolarisation which causes Na+ channels to open and for an
action potential to be created
Action potentials continue to move in one direction due to the high conc of Na+ behind
Saltatory conduction
Na+ ions cannot diffuse through myelin sheath
Ionic movement of action potential happens in nodes of Ranvier
Local currents are elongated and Na+ ions diffuse from one node of Ranvier to the next
Action potential appears to ‘jump’ – a saltatory conduction
Advantages of saltatory conduction
Myelin sheath means action potentials can only occur at the gaps between Schwann cells
SPEEDS UP TRANSMISSION
Frequency of transmission
All action potentials are same intensity - +40mv
Brain detects intensity of stimulus by the frequency of the action potential
Higher frequency means more intense stimulus
Higher frequency means more Na+ channels open
More frequent action potentials
Local currents
During depolarisation, Na+ ions flood into the neurone, which creates local currents in the cytoplasm
1. During action potential, when the channels open, Na+ diffuses into the neurone from high to
low conc
2. Na+ move along the neurone towards areas with low concentrations of Na+ - called a local
current
3. Local current causes slight depolarisation which causes Na+ channels to open and for an
action potential to be created
Action potentials continue to move in one direction due to the high conc of Na+ behind
Saltatory conduction
Na+ ions cannot diffuse through myelin sheath
Ionic movement of action potential happens in nodes of Ranvier
Local currents are elongated and Na+ ions diffuse from one node of Ranvier to the next
Action potential appears to ‘jump’ – a saltatory conduction
Advantages of saltatory conduction
Myelin sheath means action potentials can only occur at the gaps between Schwann cells
SPEEDS UP TRANSMISSION
Frequency of transmission
All action potentials are same intensity - +40mv
Brain detects intensity of stimulus by the frequency of the action potential
Higher frequency means more intense stimulus
Higher frequency means more Na+ channels open
More frequent action potentials
