Membrane Structure and Functions, Overview of Membrane Transport, Membrane Potential

1. MEMBRANE
PHYSIOLOGY

2. The plasma membrane is a fluid lipid
bilayer embedded with proteins.

3. Three views of a Cell Membrane
An electron micrograph of a plasma membrane seen in cross-section.
These drawings show two-dimensional and three-dimensional views of a
cell membrane and the general disposition of its lipid and protein
constituents.

4. Overview of Membrane Transport
Transport pathways through the cell membrane, and the basic mechanisms of
transport.

5. Diffusion
is the spontaneous movement of a substance
down its concentration or electrochemical gradient, from a
region where it is more concentrated to a region where it is less
concentrated.
Simple diffusion, channel-mediated facilitated diffusion, & carrier-mediated facilitated
diffusion

6. Facilitated Diffusion
is the passage of molecules/ions down
their electrochemical gradient across a biological membrane with the help
of specific transmembrane transport proteins, requiring no energy
expenditure.

7. Active transport
is carrier-mediated transport that uses energy and
moves a substance against its concentration gradient.

8. Primary Active Transport
EXTRACELLULAR [Na] high
FLUID
[K] low
Na
Na
Na
Na
Na
Na
Na
Na
CYTOPLASM Na
1
[Na] low
[K] high
P
ADP
2
ATP
P
3
Na+-K+ Pump
K
K
K
6
K
K
K
5
4
P
Pi

9. In secondary active transport, the energy stored in a Na+ or
H+ concentration gradient is used to drive other substances across
the membrane against their own concentration gradients.

10. Bulk transport across the plasma membrane occurs by Exocytosis and
Endocytosis.
Endocytosis
Movement of substances
into a cell in vesicles.
Exocytosis
Movement of materials out
of a cell via membranous
vesicles.
Transcytosis
Movement of a substance
through a cell as a result of
endocytosis on one side
and exocytosis on opposite
side.

11. Ion channels in the Plasma Membrane
1) Leakage channels randomly open and close.
2) A chemical stimulus opens a ligand-gated channel.

12. Ion channels in the Plasma Membrane
3) A mechanical stimulus opens a mechanically gated channel.
4) A change in membrane potential opens voltage-gated channels.

13. Chemical compositions of Extracellular & Intracellular
fluids
A comparison of ion concentrations inside & outside a typical mammalian
cell.

14. Resting
Potential

15. Action Potential

16. Key
Na
K
Membrane potential
(mV)
Action
potential
OUTSIDE OF CELL
100
Sodium
channel
3
0
50
2 Depolarization
4 Falling phase of the action potential
50
3 Rising phase of the action potential
Threshold
2
1
4
5
Resting potential
Time
Potassium
channel
INSIDE OF CELL
Inactivation loop
1 Resting state
5 Undershoot
1

17. Propagation of Action Potentials