Transcript Module 9: Synaptic Transmission

Synaptic Transmission
•How a neuron communicates with
another neuron and the effects of
drugs on this process.
•Types of Neurotransmitters
Neuron to Neuron
• Axons branch out and end near dendrites of
neighboring cells
• Axon terminals are
the tips of the axon’s branches
• A gap separates the axon terminals from
dendrites
• Gap is the Synapse
Click on video to
review
(2:00)
Steps to Synaptic Transmission
1. Action Potential causes synaptic
vesicle to open
2. Neurotransmitter (NT) released
into synapse
3. NT locks onto receptor molecule in
postsynaptic membrane (on
receiving dendrite)
4. Receptor site opens and allows
positive sodium ions to enter the
dendrite triggering action potential.
5. Remaining NT either dissolved by
enzymes or “recycled” to sending
neuron through Reuptake
NT Cause
Excitatory and Inhibitory
Messages
• Excitatory message — increases the
likelihood that the postsynaptic neuron will
activate (allows + ions to enter)
• Inhibitory message — decreases the
likelihood that the postsynaptic neuron will
activate. (allows – ions to enter)
Locks and Keys
• Neurotransmitter
molecules have specific
shapes (Key)
• Receptor molecules have
binding sites (Lock)
• When NT binds to
receptor, ions enter
(Door Opens)
Neurotransmitters Bonding at a
Receptor Site
Drugs Impact on Synaptic Transmission
Some Drugs Work on Receptor Sites
• Some Drugs are
shaped extremely
similar to a NT and
like a copy of a key
unlock the receptor
site
• Agonists: fit receptor
well and mimic the
NT causing Action
Potential
– e.g., nicotine
Some Drugs Work on Receptor Sites
• Some drugs are shaped
like neurotransmitters but
do NOT unlock the
receptor site thus blocking
it from receiving natural
NT.
• Antagonists: fit the
receptor but poorly and
block the NT stopping the
action potential message
– e.g., beta blockers
Natural Neurotransmitters are like a key to a lock.
They bond to the receptor site “unlocking” it
Antagonist Drugs block the receptor site. Like
a key in the wrong lock, they won’t open the
door/receptor site.
Agonist drugs mimic neurotransmitters and
open the receptor site
just like a copied key will unlock a door.
Addiction
How do drugs affect synaptic transmission? (5 min)
Types of Neurotransmitters
1.
2.
3.
4.
5.
6.
7.
Acetylcholine
Serotonin
GABA
Dopamine
Norepinephrine
Endorphins
Glutamate
Function of a NT depends on which part of the brain it acts upon:
•Brainstem – Breathing & Heartbeat
•Midbrain – Memory & Emotion
•Cortex – Memory Integration, Problem Solving, Perception
Acetylcholine (Ach)
• Excitory neurotransmitter found in
neuromuscular junctions
• Involved in muscle contractions
• Involved in learning and memory
Disruption of
Acetylcholine Functioning
• Curare—blocks ACh receptors
– paralysis results
• Nerve gases and Black Widow
spider venom; mimics Ach
• - muscle spasms and possible death
Disruptions in ACh Functioning
• Cigarettes—nicotine works on ACh
receptors by mimicking ACh
– can artificially stimulate skeletal muscles,
leading to slight trembling movements
Alzheimer’s Disease
• Deterioration of memory, reasoning,
and language skills
• Low levels of Ach found in those with
Alzheimer’s disease
• Symptoms may be due to loss of ACh
neurons
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view (7 min)
Dopamine
• Involved in movement, attention and
learning. Also pleasure & rewarding
sensations.
• Too much Dopamine involved in
schizophrenia. Thorazine blocks it.
• Drugs like cocaine and nicotine mimic
dopamine
• Loss of dopamine-producing neurons in substantia
nigra cells is cause of Parkinson’s disease.
• Give L-Dopa (converts to dopamine) to combat this.
Parkinson’s Disease
• Results from loss of dopamine-producing
neurons in the substantia nigra
• Symptoms include
– difficulty starting and stopping voluntary
movements
– tremors at rest
– stooped posture
– rigidity
– poor balance
Serotonin
• Involved in mood, hunger,
sleep
• Low levels involved in
depression
– Prozac works by keeping serotonin
in the synapse longer, giving it more
time to exert an effect (re-uptake
inhibitor)
Norepinephrine
• Arousal, learning & memory
• “Fight or flight” response
• Low levels found in those with
depression.
GABA
• Inhibition (slows down) of brain activity
• Influences anxiety when in low supply.
• Antianxiety medications Valium & Xanax
increase GABA activity slowing down the
brain.
• Alcohol mimics GABA
• Plays a dual role in sleep: day – excites the
brain, night – slows down the brain.
• Huntington’s disease involves loss of
neurons in striatum that utilize GABA
– Symptoms:
• jerky involuntary movements
• mental deterioration
Endorphins
• Control pain and pleasure by blocking the
neurotransmitter Substance P which transmits pain
messages to the brain.
• Released in response to pain
• Morphine and codeine work on endorphin receptors;
involved in healing effects of acupuncture
• Runner’s high— feeling of pleasure after a long run is
due to heavy endorphin release
Glutamate
• Major excitatory neurotransmitter
• Too much glutamate (and too little GABA)
associated with epileptic seizures &
migraines
• Associated with Mania of Bipolar Disorder