Psychology Lecture 5 9/20/2012 6:02:00 AM
Structure of Neuron
Soma (cell body)
o Grey & white matter (length of axon)
o Terminal ending (bouton endings):
Secrete neurotransmitter substance
Protect the axon
Speeds up transmission
o Pre- & post synaptic
Transmitter Substance (neurotransmitter):
o Excitation or inhibition
The Nobel Prize 1906
C. Golgi & S. Ramon y Cajal
3 Catergories of Neurons
Sensory Neurons: transmit impulses received by sensory receptors
to Central Nervous System (CNS). Afferents.
Motor Neurons: carry outgoing signals from CNS to muscle &
All neurons are axonated; sensory and motor neurons are typically
covered by myelin sheath
Nerve is a bundle (some cases 100’s of thoudsands) of neurons
serving the same role
Interneurons Interneuronal communication
Often, far removed from either sensory or motor neurons.
Communication can be excitatory or inhibitory
This allows for flexibility of behavior.
All cells carry an electrical charge (potential)
The charge of the neuron can change
This allows one neuron to communicate with another neuron
An inactive neuron contains an excess of negatively charged ions
inside the cell membrane
The charge inside the human neuron is about -70 mVolt (mV).
This is called the resting charge
Inside, a surplus of negatively charged molecules (“ions”.)
Mainly because of the buildup of chloride (Cl )-
Outside, buildup of positively charged ions, largely sodium (Na )
When the dendrite is stimulated (neuron, electrical stimulation)…
o cell membrane opens channels; positively charged ions to
Change in the charge of the neuron (less negativity or more
positivity) called depolarization
When the flow of positively charged ions reaches a certain critical
threshold (the “threshold of excitation”), the neuron fires.
This called the action potential.
Once the action potential is initiated, it will travel down the length
of the axon.
It may then subsequently influence the firing of another neuron.
If the level of excitation is not enough (the critical thresh is
The depolarization will reverse (the neuron will return to the resting
The depolarization will Psychology Lecture 6 9/20/2012 6:02:00 AM
The action potential will travel down (will be propagated) the length
of the axon.
The amplitude of the axon potential will not vary. This the all-or-
We either get the action potential or we do no