General Physiology Dr. Tony Serino Cell Membrane General Physiology Dr. Tony Serino

The Cell: Components Cell Membrane Cytoplasm Organelles

Membrane Components Hydrophobic area

Membrane Protein Functions

Movement through the membrane

Diffusion -is the movement of substances from areas of high concentration to areas of lower concentration until an equilibrium is reached. The movement of these substances is provided by the heat of the system (thermokinetic energy). Increasing the heat, increases the rate of diffusion; decreasing the heat has the opposite effect. (Diffusion ceases at absolute zero (0oK or –273 oC)

Diffusion Only particles that are not charged and relatively small can pass through the membrane by diffusing. Water*, Oxygen, Carbon dioxide, and lipids can move freely.

Facilitated Diffusion

Active Transport

(solvent diffusion)

Osmosis Less solute Equal solute More solute swells same shrinks Hypotonic Isotonic Hypertonic Crenates

Exocytosis Endocytosis

Membrane Potentials Produced by the unequal distribution of ions across a selectively permeable membrane The inside of the cell is called negative by convention The intensity of the ion difference is expressed as voltage (measured in millivolts (mV))

Measuring Membrane Potentials

Resting Membrane Potential Parameters necessary to create a resting membrane potential: A semi-permeable membrane Distribution of ions across membrane Presence of large non-diffusible anions in interior Na-K pump (3 Na+ out for every 2 K+ in)