### substance | fiber:

Axon
* All axons start off unmyelinated.
* Every axon contains neurotransmitters at their end.
* Many axons make up a myelin sheath
  - nerve
* Most axons eventually regrow, over a variable period of time
  - form many branches as they extend away from the soma
* Most axons have lower resistance
  - motile structures
  - myelin sheaths
* Some axons are part of brains
  - cortexes
  - neocortexs
  - neurons
  - can extend up to one meter or more while others extend as little as one millimeter
  - pass from one hemisphere to the other in bundles such as the large corpus callosum
* Some axons penetrate dorsal nuclei
* actively navigate to their targets by reading chemical cues in their environments.
* are fibers that interconnect the cells
  - generally straight, non-branching processes of uniform diameter
  - like cables that carry messages throughout the nervous system
  - long , thin and tendril-like
  - much like a highly developed dendrite
  - nerve fiber
  - ordinarily longer than dendrites although there is usually only one axon per neuron
  - part of nerve cells
  - single, extended fibers
  - spiny extensions of neurons that carry brain impulses
* are the cable-like processes of neurons that carry impulses from one region to another
  - long extensions of nerve cells that make up nerve fibers
  - long, thin arms that link one nerve cell to another
  - primary transmission lines of the nervous system , and as bundles they form nerves
  - structures which transmit a signal from one neuron to another cell
  - telephone lines of the nervous system, carrying a nerve impulse to a target cell
  - unique extension from the neuronal cell body
* arising from the phrenic nucleus comprise the phrenic nerve that innervates the diaphragm
  - the phrenic nerve, which innervates the diaphragm
* can be several feet long, can go down the spine and across the hemispheres of the brain.
* carry electrical signals from a neuron to the dendrite of another neuron
  - electro-chemical impulses away from cell bodies
  - messages to and from the brain
  - signals to and from the neurons and are covered by a protective sheath called myelin
* conduct impulses away from the cell body
  - nerve impulses between neurons
* cross to the opposite side of the brain at the medulla, travel to the thalamus.
* end at junctions known as synapses.
* extend for as long as four feet in humans.
* form the oculomotor nerve.
* grow from the trigeminal to the cuneate nucleus in adult monkeys following deafferentations
  - into the limb buds before any recognizable structures are present
  - selectively along their respective pathways
  - slowly, probably no faster than our hair grows, at about a mm a day at fastest
* includes cell membranes
  - chromosomes
  - corpi
  - cytoskeletons
  - lobes
  - nerve endings
  - plasma membranes
  - sections
  - vacuoles
* invariably acquire sheaths along their course.
  - fibre
* leave the olfactory receptors and synapse in the olfactory bulb.
* send information to other neurons, to muscle cells, or to gland cells
  - target cells, while dendrites are the sites for receiving information
* showing homotypic collateral sprouting can grow for long distances for over a year.
* take information 'away from' the cell body.
* terminate widely throughout the brain.
* transmit signals to other neurons by means of specialized junctions called synapses.
* vary in length from a few millimeters to a meter or more
  - micrometers to over a meter
+ Nerve, Nerve Structure: Anatomy of the nervous system
  * Nervous system contains neurons and cells called glia. Glia cells keep the neurons safe and healthy. Neurons take messages to and from the CNS to the rest. The dendrite and axon are fibers that go out from the cell body. Axons take information 'away from' the cell body. Dendrites take information to the cell body.
  * The 'axon' is the part of a neuron that sends the signal. Axons are long, thin and tendril-like.