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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 • 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 • Inhibitory message—decreases the likelihood that the postsynaptic neuron will activate. • 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 • • • • • • • Acetylcholine Serotonin Norepinephrine Dopamine Endorphins GABA 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 Click on video to 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 – – – – – 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 • • • • • • Neuron structure Action potentials Synapse Neurotransmitters Receptors and ions Agonists and antagonists