1.  A synapse divides at least 2 (usually more) neurons by ~20nm.  Presynaptic Neurons: carry impulses to the synapse  Postsynaptic Neurons: carry impulses away from synapse 1

2. 2  The action potential will not move across the synapse  More synapses= slower transmission. (reflex arc has little synapses) Neuro-transmitters (chemicals) brave the gap: Released by the end plate of presynaptic neuron to the receptor sites of postsynaptic neuron. Move by diffusion -See fig 11.18 pg379

3. 3  Excitatory: triggers receptor proteins in post synaptic cleft to allow positive ions in (ex. sodium)  Depolarization! & lowered threshold level!  Inhibitory: triggers potassium channels to open  hyperpolarization! (increased threshold level)

4.  The greater the # of synapses, the slower the speed of transmission over a specified distance  Transmitter chemical  Acetylcholine Acetylcholine  Can act as an excitatory transmitter chemical on many postsynaptic neurons by opening Na+ channels  Cause depolarization 4

5.  However, acetylcholine presents a problem  Postsynaptic neuron would remain in a constant state of depolarization cholinesterase  Release of enzyme cholinesterase follows acetylcholine and destroys it  Na channels are closed - neuron begins recovery phase  Insecticides - block cholinesterase  Insect's heart responds to nerve message by contracting, but it never relaxes 5

6.  Acetylcholine may also act as an inhibitory transmitter chemical on a diff. postsynaptic membrane  By opening more K gates, K+ on inside of neuron follow concentration gradient and diffuse out of neuron  Rush of K+ out of cell increases # of + ions on outside of cell relative to # found on inside  Neurons are hyperpolarized since resting membrane is even more “–”  More Na channels must now be opened to achieve depolarization and an a.p.  Inhibitory transmitter chemicals prevent postsynaptic neurons from becoming over active 6

7. 7 NeurotransmitterFunctionEffects of abnormal production dopamineEffects the brain synapses in the control of body movements; is linked to sensations of pleasure, such as eating Excessive production linked to schizophrenia; inadequate production linked to Parkinson’s disease (progressive disorder that destroys neurons) serotoninRegulates temperature and sensory perception; is involved in mood control Inadequate amounts in the brain synapses is linked to depression endorphinsAct as natural painkillers in synapses in the brain; also affects emotional areas of the brain Deficiency linked to an increased risk of alcoholism norepinehrineUsed by brain and some autonomic neurons; complements actions of the hormone epinephrine, which readies the body to respond to danger or other stressful situations Overproduction linked to high blood pressure, anxiety, and insomnia; deficiency linked to hunger cravings and exhaustion

8. 8 1.Action potential reaches end plate 2.Ca 2+ gates open influx of + ions 3.Build-up of Ca 2+ causes release of acetylcholine 4.Acetylcholine released 5.Acetylcholine binds with Na+ channels opening them (postsynaptic receptor sites) 6.Na+ ions rush in causing depolariazation. 7.Action potential continues through dendrite of post synaptic neuron. 8.Presynaptic endplate membrane releases cholinsterase (enzyme) which destroys acetylcholine 9.Na+ gates close, recovery phase begins Chemical synapse videos : http://highered.mcgrawhill.com/olc/dl/120107/anim0015.swf http://highered.mcgrawhill.com/olc/dl/120107/anim0015.swf http://bcs.whfreeman.com/thelifewire/content/chp44/4402003.html http://itc.gsw.edu/faculty/gfisk/anim/neurotransmission.swf http://www.mind.ilstu.edu/flash/synapse_1.swf

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10. 10 Summation: -effect produced by the accumulation of transmitter chemical from two or more neurons. -can be inhibitory or excitatory Quit messing with my synapses!

11.  Serotonindopamine  Serotonin and dopamine affect sleep, mood, attention, and learning  Serotonin – generally inhibitory  Decreased levels associated with depression  Medication or ↑ exercise  Dopamine – excitatory and inhibitory, depending on sites  Released as rewarding of a behavior 11

12.  GABA – inhibitory - As a drug, calms the body  Glutamic acid  Glutamic acid – excitatory - Memory  Endorphins  Endorphins – inhibitory (reduce pain perception)  Norepinephrine  Norepinephrine (noradrenaline) is found in both CNS and PNS  In the PNS - Excitatory  In the CNS - Excitatory or inhibitory 12

13. 2) Disorders  Various disorders have been associated with transmitter chemicals  Parkinson's disease  Parkinson's disease - involuntary muscle contractions and tremors - inadequate production of dopamine  Schizophrenia  Schizophrenia – excess dopamine Schizophrenia  Alzheimer's disease  Alzheimer's disease - deterioration of memory and mental capacity - related to decreased production of acetylcholine 13