Anterior pituitary, posterior pituitary, thyroid, parathyroid, adrenal cortex, adrenal medulla, pancreas, thymus (neck), pineal (brain), ovaries, and testes. RESTING POTENTIAL: An unstimulated neuron is polarized, with a membrane potential of about -70mV. In order for the nerve to fire, a stimulus must be strong enough to overcome the resting potential.
ACTION POTENTIAL: An action potential/impulse can only be generated in the axon of a neuron. Once it is stimulated over the threshold, the permeability of a region of the membrane suddenly changes. Sodium channels open and sodium floods the cell, down the concentration gradient, while potassium floods out of the cell. This wave of depolarization reverses the polarity and is called the action potential. The neuron becomes repolarized during the refractory period with the help of the sodium-potassium pump. During this short time, the neuron cannot respond to another stimulus. The first action potential causes a chain reaction, triggering others down the line.
THE SYNAPSE: When the impulse changes an axon electrically, it is also crosses a synapse chemically. The terminal branch of the neuron contains neurotransmitter filled vesicles. The depolarization of the presynaptic membrane causes an increase in Ca++ ions, stimulating the vesicles to fuse with the membrane and release the neurotransmitters by exocytosis, which sets up the action potential in the next cell.
1. Filtration: occurs by diffusion, passive and nonselective. Glucose, salts, vitamins, wastes, and other small molecules travel through Bowman's capsule, the loop of Henle, the tubule, and then into the ureter and the urinary bladder for temporary storage and then to the urethra and out of the body.
2. Secretion: active, selective uptake of molecules that did not get filtered into Bowman's capsule. Occurs in the tubules.
3. Reabsorption: the process by which water and solutes that entered the tubule during filtration are transported back into the capillaries. This takes place in the tubule, the loop of Henle, and the collecting the tubule.
4. Excretion: removal of wastes, excreted from body.