Download Neurons and Neurotransmitters

Neurons and Neurotransmitters
Spinal cord
• Transmits messages from the brain to the
other areas of the body.
– Efferent – away from the brain out to the body
• Produces muscle action
– Afferent – from the periphery to the brain
• Relays information from the sensory organs
Facts About Neurons
There are about 1000 billion
Each can be connected to over 10s of 1000s of
other neurons
What they do
Sensory Neurons – take info from the world
Inter neurons make the connection between motor
and sensory neurons – they do the thinking
makes the connection between sensation
and action
Motor neurons - dictate to the muscles
All or Nothing
Neurons either fire or not. Sensation and action
are graded by number of neurons triggered
and/or frequency
The GAP
Between each neural dendrite and axon there is
a tiny space (about 1/10,000th of a mm).
This gap is called a synapse.
Its a Chemical Thing
When a neuron fires the axon shoots chemicals
through the synapse and they affect the
dendrites.
These chemicals are called neurotransmitters.
Neurotransmitters are contained within a structure
called the presynaptic membrane.
Once released neurotransmitter molecules are
picked up by receptors - structures that appear
on cellular surfaces that pick up molecules that fit
into them like a "lock and key"
Receptors are located in postsynaptic
membrane of another nearby neuron.
Once the neurotransmitter is picked up by
receptors in the postsynaptic membrane, the
molecule is internalized in the neuron and the
impulse continues.
• Each neurotransmitter binds only to specific
receptors on the postsynaptic membrane.
• There are a number of types of receptors for
different neurotransmitters.
• This binding eventually brings about a change
in the electrical state of the postsynaptic cell
either exciting or inhibiting it.
Action of neurotransmitter can be
decreased or neutralized by:
• Glial cells which remove neurotransmitters
from the synaptic cleft
• reuptake, where the chemical is taken back to
the axon that released it
• blocking, whereby the flow by substances that
attach to specific receptors is blocked
For Example:
The release of various neurotransmitters can
excite or inhibit neurons.
This means the understanding of
neurotransmitters is very important to
pharmaceuticals.
Pharmaceuticals
Drugs developed to treat illnesses related to
neurotransmitters are either Agonists or Antagonists.
There are currently at least 50 identified
neurotransmitters.
Agonists – increase the effects of a neurotransmitter,
makes more of it, or stops the minimizing of it
Antagonist – slows down neurotransmitters either
because they destroy or inhibit production, or they
“paste over” dendrites so that neurotransmitters
cannot connect
Specific Neurotransmitters
Acetylcholine
Acetylcholine is linked with learning and
memory formation
A lack of acetylcholine in the brain is thought to
be partly responsible for the symptoms of
Alzheimer's disease.
* See study by Martinez and Kesner, 1991, on
lab mice
Dopamine
Dopamine is concentrated in very specific
groups of neurons collectively called the basal
ganglia.
A decreased brain dopamine concentration is a
contributing factor in Parkinson’s disease.
Increased amounts have other effects.
Serotonin
In addition to mood control, serotonin has been
linked with a wide variety of functions,
including the regulation of sleep, pain
perception, body temperature, blood pressure
and hormonal activity.
* See study by Kasamatsu and Hirai, 1999, on
zen meditation
SSRIs?????
• Selective Serotonin Reuptake Inhibitors
• Used to regulate depression (Prozac, Zoloft,
Paxil)
• High levels = bliss, happiness, hallucinations
• Low levels =sleep disruption, depression,
fatigue, anxiety
Other Drugs?
• Heroin = mimics endorphins by binding to
endorphin receptors
• Morphine = stimulates endorphin production
• Cocaine = Increases dopamine production
(blocks reuptake)
• Marijuana = THC blocks reuptake and normal
functioning of anandamide, dopamine and
serotonin (neurotransmitters)
How neurotransmitters impact
behaviour?