PSYCH 240 Lecture Notes - Lecture 2: Magnetic Resonance Imaging, Central Nervous System, Pituitary Gland
Document Summary
Our neural system is basically made up of nerve cells or neurons. Each neuron is composed of dendrites ~ message receiving fibers and axons. ~ message sending fibers which are insulated by the myelin sheath ~ fatty cells that help \speed up impulses. Impulses or action potential is a brief electrical charge that travels down the axon as it becomes depolarized due to the movement of positively charged ions entering the axon. After the transmission, the axon becomes polarized as positive ions are pumped out during the. The intensity of a stimulus is called the threshold. A stimulus must exceed the threshold in order for a transmission to occur. The neuron will either fire or it won"t. Much like a gun, the neuron either fires or it doesn"t, there are no half-fires. This is called the all-or-none-response; if a stimulus is really strong, only the number of neurons firing will increase, not their speed.
