100s of 1000s pounds of puffer fish (fugu) are consumed in japan (oct-march). 100-200 people die from the effects of tetrodotoxin (ttx). Ttx blocks the formation and transmission of electrical signals (action potentials) within nerve cells. It blocks the movement of na+ across the cell membrane that makes signaling possible. Puffer fish are not poisoned by ttx (by its own ttx or by consumption of other ttx species) since its sodium channel has specific adaptations. Glia (glue): support activities of neurons; 10-50 glia per neuron. 5 nanometers thick (1 nm= 1 billionth of a meter or 10-9m) Permeability is controlled by suspended protein structures: ion channels- ions move passively, selective. E. g. voltage-dependent channels- open/close in response to the electrical status of adjacent areas of the membrane. Ligand gated channels- open when in contact with specific chemicals: ion pumps- requires energy, selective. Maintain differences in chemical composition between intra-and-extra-cellular fluids. 3 na+ out and 2 k+ in.