Membrane transport proteins - pores, gated channels and pumps

• a Three different types of membrane ion transport proteins are required to produce and carry electrical signals: • Pores • Gated channels • Na+/ K+ pump • Pores are always open and allow the diffusion of Na+ and K+ ions across the membrane, down their concentration gradients. • Gated channels are also ion specific. • Gated channels open or close depending on the stimulus affecting the membrane. 1. Chemicals (igands) 2. Voltage changes 3. Mechanical deformation ▪ Ligand gated channels, located at the dendrites and cell bodies, open or close when chemicals, including hormones and neurotransmitters, bind to them. ▪ Voltage gated channels, located on a neuron's axon, are used in the generation and propagation of action potentials. • Mechanically gated channels open or close when the shape of the membrane is stretched due to vibrations or pressure. These channels are located on the dendrites of sensory neurons or in sensory receptor cells. • The third type of membrane protein, the Na'/K' pump, actively transports three Na+ ions out of the cell for every two K+ ions pumped into the cell. • The action of the pump compensates for the flow of ions through the other membrane proteins. • The Na+/K+ pump helps maintain an ionic imbalance across the membrane known as a resting membrane potential.

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