PSYCH LECTURE 3
Modules 4-6, 11, 18, 20-22
Two Requirements for Interacting with the Environment
In order to operate in our world. One thing we have to do is sense and perceive the world around
us, the environment. Secondly, we must respond to that environment of ours, to act upon it, to
have some effectiveness of that world. This describes afferent processes – related to inbound
process, coming inward. Efferent processes- process exiting, emitting or going outward. At this
level, sensation is an afferent process – taking info in.
Three Parts: Cell Body, Dendrites, Axon
The real building block of the brain is the neuron. It consists of three parts. Neurons have an
amazing range of variety in shape and size. Some are entire length of cell. Others are three or
four feet long. The longest ones we have is the from the base of our spine to our toes. The three
parts are the cell body also known as soma (its brain center), branch like things called dendrites
that operate of afferent process, and axon. Info comes in by dendrites, interpretation by cell
body, then the longer part called the axon is the efferent component that will send a response out
of the cell. Axons vary in size.
Three Kinds: Sensory, Motor and Interneuron’s
First: Sensory neurons – bring info from external world into our brain
As a result, they are working their dendrites must be outside the central nervous system in order
to bring the info into the central nervous system. All of our sensory equipment has neurons to
traduce info into our brain. Eyes interpret light energy. Being transported by optic nerve that
consists of neurons that bring info into brain for processing. There are 2-3 million sensory
neurons. Afferent process.
Second: Motor neurons get messages from the brain to various aspects that are going to act on
the world. Ex. Muscles. For me to take a drink of water, I need messages, I need all of my
muscles to operate. Messages sent to muscles come from inside CNS. Dendrites for motor
neurons are INSIDE the CNS, and axons exit the CNS to send message to muscles and glands. 2-
3 million. Efferent direction. These have a great variety of size.
Third: Interneuron’s they are entirely in CNS and brain. They are contained entirely within,
dendrites and axons inside. They communicate with other neurons. There are 10-100 billion.
They are crammed inside between our two ears. Brain Numbers
100 billions neurons = number of humans who have ever lived
100 trillion connections b/w neurons = number of emails sent worldwide in past year
621 000 kilometers of neurons = moon and back, then around the earth 6 times.
The Electrical Component
Electrical current/impulse from neuron to neuron. In order to support electrical theory – Luigi
Galvani – Italian scientist. Galvani’s experiment attaches cords to legs of dead frog, electrical
current goes on and the frog legs start moving. He used this to interpret to say once you inserted
the current into the system its like the cells communicating with one another and brought the frog
legs back to life. His experiments with reanimating dead tissue became popular and news spread
– may have lead to idea of Frankenstein.
There is in fact an electrical component – in the axon part, an electrical msg moves along the
axon from the cell body.
The Chemical Component
Even if there is an electrical component, something is inadequate. There has to be something else
happening. The opposing theory is the chemical theory. Otto Loewi believed there were
chemicals involved. He worked for 18 years until the answer occurred to him in a dream. He did
an experiment on a frog’s heart. Attach an electrode to the heart, like the legs, the heart would
come to life and beat. The difference here is that Lewi had distilled water in the beaker
containing the heart. After running Galvani’s experiment, he pours the water from the first heart
into another beaker with a heart attached to no electrode. The second heart started to beat. He
had in fact discovered first discovery of a neurotransmitter.
The Hodkin-Huxley Model
They presented the modern theory, received nobel prize. Within neuron communication is
electrical. We have a weak electrical current that moves down length of axon. This works by
gates that open and close. The interior of axon is slightly negative charged. These gates open
with an electrical difference, the ions move, there is depolarization of the axon. These gates open
and close like a wave around a football stadium standing up and sitting down. As it depolorizes
(exchange of ions when its turning neutral) you can send more than one pulse. These electrical
messages sent down to end of axon. Takes milliseconds for that one msg to move along. In the
axon, there are little hot dog sections called mylin sheath – axon is mylinated – what happens
here is the depolarization repolarization happens in all the gates simultaneously in each
mylinated section. When the electrical impulse comes down to end, little branches at end of
axon, electrical comes to point on branches, it becomes a chemical component now. The cell body has a firing coat, base on what is being received by dendrites, can fire again and
When it reaches the terminal end, there are little sacs that contain a chemical molecule called
neurotransmitter, those molecules migrate to surface and then rupture into the gap. This chemical
when released into the gap…
Neurotransmitter being released goes to receptor sites. The dendrites of one neuron will start
reaching for axon of other neurons and we start to form a neuronal pathway.
There are a couple of possibilities. We can have an agonist – molecular structure or molecule
going around a synaptic gap that binds to dendrite, it mimics the neurotransmitter that should be
Or there can be an antagonist – neurotransmitter cannot get in and activate receptor site.
1) Decomposed by specific enzyme - When molecules are sent into synaptic gap, several
things can happen to them. One thing, we have specific enzymes that can be released that
break down certain neurotransmitters. If its released it goes around like pacman and gulps
down colleague molecules. It allows that in a heartbeat we can release these enzymes and
decrease the number