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 reviewvideo (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) When NT binds to receptor, ions enter (Door Opens) Receptor molecules have binding sites (Lock)

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? How do drugs affect synaptic transmission? (5 min)

Types of Neurotransmitters 1.Acetylcholine 2.Serotonin 3.GABA 4.Dopamine 5.Norepinephrine 6.Endorphins 7.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 Click on video to 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