membrane physiology - phys.szote.u-szeged.hu
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Membrane physiology
Zoltán Lelkes
Learning objectives 2-7.
Structure of the cell membrane
Channel Carrier
Passage though the membrane
Water channel Ion channel
Some of the ion channels can be opened or closed by potential changes (voltage gated channels), chemical substances (ligands, ligand gated channels) or by mechanical effects.
Carrier mediated transports
UniportCotransport
Symport Antiport
Carrier
Energetically passive Diffusion Facilitated diffusion
Energetically active Active transport
Channel
Osmosis
Simple diffusion
Facilitated diffusion
Rate of transport
The Na+/K+ pump
Active transport
Primary active transport:ATP is splitted on the site of the
transport.
Secondary, tercier etc. active transport :ATP is splitted not on the site of the transport.
(The energy is provided by a concentration gradient produced by an other active transport.)
Secondary active transportsymport
Secondary active transport antiport
Direction Need for extraenergy (ATP)
Need for carrier
Diffusion Downhill to the concentration and potential gradient
No No
Facilitateddiffusion
Downhill to the concentration and potential gradient
No Yes Saturation,competitiveinhibition
Active transport Uphill to the concentration and potential gradient
Yes Yes Saturation,competitiveinhibition
Membrane transports
Primary active transport: ATP is splitted on the site of the transportSecondary active transport : ATP is splitted not on the site of the transport
(The energy is provided by a concentration gradient producedby an other, primary, active transport.)
Endocytosis and exocytosis
Endocytosis Exocytosis
Resting potencial and depolarisation
The origine of the resting potential
1. Diffusion potential
2. Na+/K+ pump
The Na+/K+ pump
Goldmann-Hodgkin-Katz (GHK) equation:
Nernst equation:
The action potential
Threshold
Refractory period
Absolute Relative
Refractory periodAbsolute Relative
Threshold
DEPOLARIZATION
Inactivation of sodium channels
Action potential Electrotonic potential
Evoking stimulus Only depolarization Various
Threshold Yes No
Sign of potential change Always depolarizing Depolarizing or hyperpolarizing
Amplitude Constant (all or non rule) graded
Propagation Without decrement With decrement
Refractory period Yes No
Summation No Yes (spatial, temporal)
Duration Constant Various (depending on the stimulus)