Transcript 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
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review
(2:00)
Steps to Synaptic Transmission
• Action Potential causes synaptic vesicle to open
• Neurotransmitter (NT) released into synapse
• NT locks onto receptor molecule in postsynaptic
membrane (on receiving dendrite)
• Receptor site opens and allows positive sodium
ions to enter the dendrite triggering action
potential.
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)
• Segment 1A Neural Communication &
excitory & inhibitory responses (3 min)
Locks and Keys
• Neurotransmitter
molecules have specific
shapes
• Receptor molecules have
binding sites
• When NT binds to
receptor, ions enter
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.
Acetylcholine
Serotonin
GABA
Dopamine
Norepinephrine
Endorphins
•
Glutamate
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 = too much ACh
leads to severe 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)
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.
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 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
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–
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difficulty starting and stopping voluntary movements
tremors at rest
stooped posture
rigidity
poor balance
Parkinson’s Disease
• Treatments
– L-dopa
– transplants of fetal dopamine-producing
substantia nigra cells
– adrenal gland transplants
– electrical stimulation of the thalamus has
been used to stop tremors
GABA
• Inhibition (slows down) of brain activity
• Influences anxiety when in low supply.
• Antianxiety medicationss 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
Glutamate
• Major excitatory neurotransmitter
• Too much glutamate (and too little
GABA) associated with epileptic
seizures
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
Summary
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Neuron structure
Action potentials
Synapse
Neurotransmitters
Receptors and ions
Agonists and
antagonists