A bundle of axons from different neurons is called a nerve. In appearance, nerves actually look a lot like blood vessels, in part because of the white color imparted by the myelin sheath surrounding each neuron. The myelin sheath is a layer of lipid produced by Schwann cells that serves to insulate the nerve and help in propagating nerve impulses. Interneurons relay and integrate messages between nerve cells. Networks of neurons are required to carry out complex behavior.
Motor neurons carry signals from brain or spinal cord to muscles or secretory glands.
In this state, the inside of the cell has a greater concentration of negatively charged ions than the outside, and a potential difference of -70 mV is created. A nerve impulse, called an action potential , is a sudden and rapid reverse in charge across a portion of the neuron membrane as a result in a change in membrane permeability. Followed by brief refractory period to restore the resting polarized condition and then the neuron is ready for another impulse. Bell s Palsy. Neurotransmitters - special chemicals in the brain, far more common among vertebrates.