-A neuron is made up of three parts: a cell body that houses the chromosomes with the organisms
DNA and maintains the health of the cell; dendrites that receive information from other neurons; and an
axon that transmits information to other neurons, muscles, and glands.
Dendrites- Receive info from
other neuron and relay to cell
Axon- transmits info from other
neurons muscles or glands.
Myelin Sheath- insulating layer
of fatty material (glial cells)
around axon. The Myelin helps
the axon work more efficiently.
in diseases like multiple
sclerosis the sheath breaks
down slowing the transfer of
Cajal found that dendrites and
axons do not touch each other.
There is a small gap between
called the Synapse.
The Synapse is the junction
between axon of one neuron
the dendrite or cell body of
another. (Neurons dont touch
synaptic gap) between axon
dendrite. Three major types of Neurons-
1) Sensory Neurons receive info from external world and convey it to brain via spinal cord.
ie. Signals for light, south, taste, touch, smell.
2) Motor Neurons carry signal from spinal cord to muscles to produce movement.
ie. Neurons with long axons to stretch out to muscles.
3) Interneruons- connect sensory, motor or other neurons together.
ie. Brings info from nervous system to sensory, nervous to motor, etc.
1) Purkinje Cells- a type of interneuron that carries info from cerebellum to rest of brain and spinal cord
2) Pyramidal Cells- found in cerebral cortex (brain)
3) Bipolar Cells- type of sensory neuron found in eye.
Communiciation between two neurons has 2 stages, conduction and transmission. First stage is the
conduction of an electric signal within neurons from dentrites to cell body then through axon. Second
stage is transmission of electric signal between neurons over the synapse.
K is closed during resting potential, for action potential K channels briefly shut down,
and other channels that allow the flow of a positively charged ion, Na , are opened.
Na is typically much more concentrated outside the axon than inside. When the
Na channels open, those positively charged ions flow inside, increasing the positive
charge inside the axon relative to that outside.
This flow of Na into the axon triggers the action potential
After the action potential comes, the membrane channels return to their original state, and
K flows out until the axon returns to its resting potential. + +
This leaves a lot of extra Na ions inside the axon and a lot of extra K ions outside the
axon. During this period where the ions are imbalanced, the neuron cannot initiate
another action potential, so it is said to be in a refractory period, the time following an
action potential during which a new action potential cannot be initiated. The imbalance
in ions eventually is reversed by an active chemical pump in the cell membrane that
moves Na outside the axon and moves K inside the axon (the pump does not operate
during the action potential)
(action potential- an electric signal conducted along length of neurons axon to synapse)
Nodes of Ranvier- breaks in the myelin sheath
How does action potential (electric signal) travel along axon? When an electric signal passes
down length of a myelinated axon the charge jumps from each node to node rather than
through the entire axon. This process is called Saltatory Conduction which helps speed the flow
of information down the axon.
Axons end in terminal buttons (top
part of left figure). They are filled with tiny
vesicles (bags) that contain
neurotransmitters (chemicals that transmit
information from synapse to dendrite) The
dendrites of the other neuron contain
receptors that receive neurotransmitters.
As K+ and Na+ flow across cell membrane
they trigger a change from resting to action
potential which travels down the length of
axon to the terminal button. This will
release neurotransmitters from vesicles
into synapse. They will bind onto receptor
sites on a nearby dendrite of receiving
neuron which starts a new process (called
The neurotransmittors will be
either 4) 5) or 6) happen to them.