Neurons & Neurotransmitters A typical neuron

Neurons & Neurotransmitters
Neurons: cells specialized for processing
information
A typical neuron
Dendrites
INPUT END
Signals
received
(neurotransmitters)
Cell body
Axon
Axon
branches
&
terminal
buttons
OUTPUT END
(Signals
transmittedneurotransmitters)

Some brief points about neurons
1) Functioning of neurons involves electrical
activity within “axon”
Axon
Under certain circumstances, a neuron will become active
generate wave of activity similar to electrical current
Neuron is “firing”
(generating nerve
impulse)

Other important point about neurons:
• they communicate with and influence each each
other through release of specialized chemicals =
neurotransmitters

How this enables one part of brain to influence another
Locus
coeruleus
• Tiny structure, consists of ~ 12,000 neurons
• But they project to wide areas of brain lying above
• Each neuron can influence thousands of other
neurons
by releasing neurotransmitter, norepinephrine

• Norepinephrine has effect of sensitizing the neurons
(prepares them to become active)
• e.g., Neurons in prefrontal cortex may be required to make
decision- if sensitized, can react more quickly
• Sequence of events may have begun with amygdala
detecting a threat >> stimulates locus coeruleus >>
stimulates prefrontal cortex (and other areas)

How neurotransmitters influence neurons
1 2
receptor
[Figure 1 shows two adjacent neurons.
Although terminal buttons of neuron on left appears to be touching
neuron on right, there is actually a small gap between them (=
synapse; see Figure 2)
Neurotransmitters (NTs) are being released from terminal buttons
of neuron on left into synapse (= presynaptic neuron) (
~ neuron sending messages)
Neuron on other side of synapse = postsynaptic neuron. (~
neuron that receives the messages) contains structures
(receptors) which can be influenced by the NTs

• Receptors can have various features
• Common feature = binding site
• Neurotransmitter molecule
can briefly attach (bind) to
binding site
• But only if one important
condition met:
“Shape” (structure) of
binding site must match
shape of
neurotransmitter
[simplified representation here,
more realistic >>>

[NT has complex
3–dimensional
structure; binding site
has to have
corresponding 3-D
structure to allow NT
to attach]

• Over 50 different neurotransmitters used for
communication within brain
• Each has specific shape (molecular structure)

• Binding sites on receptors also have shapes
• Match shape of one- and only one- type of
neurotransmitter- I.e. are sensitive to only this
neurotransmitter
• e.g., some receptors are responsive only to
GABA
• major “inhibitory” NT in brain
• Reduces activity in neurons
• E.g., plays major role in keeping amygdala
from becoming overactive
• GABA is the neurotransmitter
predominantly used by PFC to inhibit
activity in amygdala

• Other receptors are responsive only to the NT
dopamine
• Plays major role in brain’s reward
(“pleasure”) system >>

The importance of binding sites on receptors
By attaching to receptor binding sites
N-Ts cause structures in walls of the
axon to open (gates or “ion channels””)
allows electrically charged particles (ions) to flow
into neuron >> alters electrical activity in neuron
Positively charged particles stimulate neuron
(moved towards firing)
Negatively charged particles inhibit it (prevent
it from firing)
[Neurotransmitter
molecule attaching
here is what causes
ion channel to open]

look-ahead
Why do psychoactive drugs have effects
on psychological functioning?
• [on how we feel, thinking, memory, etc.]
• affect neurological functioning, usually at
level of neurotransmitter systems
• E.g., Simplest basis for drug effects >>>>>>

• A drug can have a chemical structure so
similar to that of a NT that it attaches to
binding sites for that NT
• If the NT has effect of stimulating (exciting)
neurons in certain brain areas,
• the drug will excite those neurons and cause
them to become active
• The drug is “mimicking” the NT
• [briefly discuss opiates ~ endorphins
cannabis ~ endocannabinoids]