Synapse Learning Objectives1a.Action potential at synaptic knob causes opening of voltage gated Ca channels. Ca diffuses in and causes the release of neurotransmitters into the synaptic cleft. These neurotransmitters bind to receptors on the sub synaptic membrane. This causes chemically gated ion channels to open.1b. Synapse is one way because neurotransmitters go from presynaptic to post synaptic membranes.2a.Acetylcholine (Ach): Is broken down by Acetylcholinesterase- Treat Alzheimer’s by inhibiting this enzyme- This increases levels of AChNorepinepherine: Broken down by monoamine oxidase (MAO)- Depression is treated by inhibiting thisThese neurotransmitters are also removed from synaptic cleft by reuptake (80%)- SSRIs stop reuptake of serotonin and are used to treat depression- Cocaine decrease dopamine reuptakeNeed to terminate signal in order to have a new one3a.EPSP- Excitatory PostSynaptic PotentialIncreases both Na and K permeabilityMore Na in than K out since it has electrical and concentration gradientNeed about 30 to get action potentialIPSP- Inhibatory PostSynaptic PotentialHyperpolarization caused by increased K permeability. Becomes more negative and farther from threshold. 4.1 EPSP will change membrane potential 0.5mvWill change more if the synaptic knob is closer to axon hillock (more ion channels)IPSPs are needed to prevent action potentialsGABA is an inhibitory transmitter7.Temporal Summation: same synaptic knob fires more than onceSpatial Summation: different synaptic knobs fire at same timeIf EPSPs > IPSPs Threshold is achievedIPSPs > EPSPs Threshold is not achieved8. Presynaptic facilitation / inhibition: Axon A can increase/decrease transmitter release from axon B9. Convergence: Many presynaptic knobs synapse with one postsynaptic neuronDivergence: One neuron synapsing with many other neurons10. Gap junctions: tunnels for ions that allow current flow in cardiac and smooth muscleParacrines are local hormonesReflexes and Autonomic Nervous System1a. Afferent Neuron -> CNS -> Can cause motor response1b. Patellar tendon is tapped, muscle is stretched. Causes contraction of the stretched muscle1c. Reflex: automatic response to a stimulusMonosynaptic Reflex: 1 synapsePolysynaptic Reflex: more than one synapse. Interneurons are involved. These are located in the CNS1d. Components of a reflex:- Receptor - Afferent to control center- Integrating center (CNS)- Efferent pathway to the effector muscle- Effector IPSPS to the triceps and EPSPs to the biceps1e. Divergence of the afferent neuron to interneurons on the opposite side of the cord allows you to push away with the other arm. Can also extend leg opposite of tack.2. Somatic reflex effector is skeletal musclesAutonomic reflexes are: stretch receptors, chemoreceptors, osmoreceptorsEffectors for this are smooth and cardiac muscles as well as glands3.Sympathetic – T1 to L2Parasympathetic S2 to S4 and cranial nerve 10, the Vagus3b. Preganglionic fiber (part of the CNS) leaves the CNS and synapses with post ganglionic fiber which then goes to the effector.In somatic nervous system, neurons innervate directly with skeletal muscles. No synapses. Motor neuron = efferent neuronParasympathetic preganglionic fibers are longer than sympathetic preganglionic fibers. 3d. Preganglionics release: AchPostganglionics: Para release Ach, Symp release norepinephrine. Symp release Ach to sweat glandsNitric oxide can be released by non adrenergic or noncholinergic fibers and it can cause an errection. Viagra prolongs the response to nitric oxide3e. Dual intervation = affected by para and sympathetic divisions of the ANSOne is the accelerator, one is the brakes. Both divisions cause secretions in salivary glands. (different)4.Fight or flight is for emergency. Increased glucose levels, heart rate, metablic rate, lung size, pupil size and mental awareness. Also stimulates medulla which releases epinpherine (80%) and norepinephrine (20%) into the blood.Preganglionic reach the medulla but no postganglionic leaveThese hormones reinforce sympathetic effects. They last longer. Can reach all cells in the body.5.Parasympathetic is for rest and digest. Most active when relaxing after a meal.6. SmoothParasympathetic:Sympathetic: Constriction of blood vesselsCardiacParasympathetic: Decreased activitySympathetic: Increased activityGlandsParasympathetic: Thin, watery with enzymes for digestionSympathetic: Thick, lots of mucus, dry7. Adrenergic recptorsAlpha 1:Bloodvessels (contract)Beta 1: HeartBeta 2: AirwaysAgonist mimics the natural chemical, causes stimulusAntagonist blocks receptorsPhenyephrine stimulates alpha receptors and decerases blood flow and then decreases congestionPropranolol is a non-selective beta blockerAtenolol is a B1 antagonist but not B2 (reduce BP)8. ACh ReceptorsMuscarinic: on effector cell membranesNicotinic: at autonomic gangliaAtropine blocks muscarinic receptors on ANS effectors (blocks PS, dilates pupils)Curare blocks nicotinic receptors on skeletal muscle cell membranes (prevent muscle contraction)Hexamethonium blocks nicotinic receptors at ganglia (shuts down ANS)9. Medulla is the CV and Digestive centerHypothalamus acts on medulla to increase heart rate and BPBiofeedback: learn how to control visceral functions with