Download axon - the long extension of a neuron that carries nerve impulses

The Neuron
__________________________ - the long extension of a neuron that carries nerve
impulses away from the body of the cell.
__________________________ - the hair-like ends of the axon
__________________________ - the cell body of the neuron; it contains the nucleus
(also called the soma)
__________________________ - the branching structure of a neuron that receives
messages (attached to the cell body)
__________________________ - the fatty substance that surrounds and protects some
nerve fibers
node of Ranvier - one of the many gaps in the myelin sheath - this is where the action
potential occurs during saltatory conduction along the axon
Nucleus - the organelle in the cell body of the neuron that contains the genetic material of
the cell
Schwann Cell - cells that produce myelin - they are located within the myelin sheath.
I. Nervous System Notes
1. General information: passage of information occurs in two ways:
Nerves - process and send information fast (eg. stepping on a tack)
Hormones - process and send information slowly (eg. growth hormone etc)
2. Major components of the nervous system: Two major divisions
The central nervous system (CNS) - made up of the spinal cord and brain
The peripheral nervous system (PNS) - made up of the cranial and spinal
nerves
Central Nervous System
Peripheral Nervous System
axon - the long extension of a
neuron that carries nerve impulses
away from the body of the cell.
myelin sheath - the fatty substance that surrounds
and protects some nerve fibers
node of Ranvier - one of the many gaps in the
axon terminals - the hair-like ends myelin sheath - this is where the action potential
of the axon
occurs during saltatory conduction along the axon
cell body - the cell body of the
nucleus - the organelle in the cell body of the
neuron; it contains the nucleus (also neuron that contains the genetic material of the cell
called the soma)
Schwann's cells - cells that produce myelin - they
dendrites - the branching structure are located within the myelin sheath.
of a neuron that receives messages
(attached to the cell body)
The Neuron
Very Special(ized) Cells
Your nervous system is composed of specialized cells called neurons. The structure of a
neuron can give you a clue to its function. Each has a compact cell body and long,
slender processes - a little like antennae. The processes that pick up messages are called
dendrites. Those that conduct messages to the next cell are called axons.
Let's see how a message travels down an axon. The neuron has the special ability to build
up a charge - much like a battery - across its membrane. More sodium ions (Na+) and
potassium ions (K+) build up outside the membrane, so the inside of the cell is more
negative. If you could put a microscopic meter on each side of the membrane, you could
measure the potential energy (about -70 millivolts), like a tiny battery.
When the neuron is stimulated, sodium ions can enter the cell. The potential energy
(voltage) across the membrane drops. Even though the cell membrane quickly begins to
restore the ions to their proper position, this change, in turn, affects the membrane next to
it. Like fire along a fuse, the electrical change moves down the axon. By the time the
membrane restores the charge across the membrane at one point, the signal is moving
ahead.
Axons are the longest parts of any cell. A single axon can be only a few micrometers or
as long as a meter. But eventually the electrical signal reaches the end. The axon of one
neuron doesn't touch the dendrites of the next neuron. Instead there is a tiny gap called a
synapse. A chemical neurotransmitter is released from the end of the axon, which jumps
the gap and starts the process all over again, stimulating the next nerve cell.
How fast does this occur? Don't be confused by the word "electric." Unlike electrons in a
conductor (which move at nearly the speed of light) the messages that are sent by
movement of charged ions move at about 100 m/second.
How the Neuron Works
Vocabulary
Action potential
Synapse
Neurotransmitter
Terminal endings