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)