CBIO 2200 1nd Edition Lecture 19 Outline of Last Lecture I Overview of the Nervous System II Subdivisions of the Nervous System III Nervous Tissue IV Classes of Neurons V Types of CNS Neuroglia VI Types of PNS Neuroglia VII Myelin VIII Regeneration of PNS Nerve Fibers IX Electrophysiology of Neurons Outline of Current Lecture I The Refractory Period II Chemical Synapses III Memory and Synaptic Plasticity IV Common Degenerative Disorders of the Brain Current Lecture I The Refractory Period a Two phases of the refractory period i Absolute refractory period no matter the strength of the stimulus you cannot generate another action potential ii Relative refractory period can generate another action potential but the stimulus would have to be extremely strong b Action potential propagation called These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II i Continuous conduction in un myelinated fiber ii Saltatory conduction in myelinated fiber at nodes of Ranvier Chemical Synapses a Synapse between two neurons i First neuron in the signal path is the presynaptic neuron ii Second neuron is postsynaptic neuron b Neurotransmitters and synaptic delay i Neurotransmitters 1 Fall into four major categories according to chemical compositions a Acetylcholine acetic acid and choline b Amin acid neurotransmitters e g glycine glutamate aspartate and GABA c Monoamines synthesized from amino acids with carboxyl group removed i catecholamines norepinephrine epinephrine and dopamines ii Seratonin and histamine d Neuropeptides act in the brain cholecystokin and substance P ii Synaptic delay of a millisecond for neurotransmitters to cross synaptic clef iii Types of synapses with different modes of action 1 Excitatory cholinergic synapse a employs acetylcholine as neurotransmitter b excitatory in skeletal muscle but inhibitory in cardiac muscle 2 Inhibitory GABA ergic synapse a Employs aminobutyric acid as its neurotransmitter b When released crosses synaptic clef and binds to GABA receptors which are also chloride channels c Chlorine cause hyperpolarization 3 Excitatory adrenergic synapse a Employs norepinephrine as neurotransmitter b Receptor is a trans membrane protein associated with G protein activates adenylate cyclase which activates cyclic AMP c Act through second messenger systems d Enzyme amplification one molecule has multiple effects iv Stopping synaptic transmission 1 Two steps a Stop adding neurotransmitter b Get rid of that which is already there i Diffusion ii Reuptake into synaptic know monoamine oxidase iii Degradation of neurotransmitter in clef and acetylcholinesterase breaks down acetylcholine and then choline is reabsorbed III IV c Postsynaptic potentials i Excitatory postsynaptic potential EPP may or may not cause local depolarization 1 Glutamate and aspartate are excitatory brain neurotransmitter that produce EPP s ii Inhibitory postsynaptic potential IPSP causes hyperpolarization 1 Glycine and GABA produce IPSPs are inhibitory d Summation i Process of adding up postsynaptic potentials and responding to their net effect ii Occurs in the trigger zone axon hillock iii Temporal summation 1 Repeated release of excitatory neurotransmitter from a single presynaptic neuron 2 Stimulus occurs at same location at different times iv Spatial summation 1 EPSP s generated from multiple presynaptic neurons at same time e Facilitation i One neuron increases the amount of neurotransmitter released by another neuron thereby enhancing the effect ii Ex serotonin f Presynaptic Inhibition i Process in which one presynaptic neuron suppresses the firing of another ii Ex GABA Memory and Synaptic Plasticity a Memory trace actual physical basis of our memory or engram i Synaptic plasticity ii Synaptic potentiation one form of synaptic plasticity iii Kinds of memory 1 Immediate short and long term memory b Stages of memory i Encoding ii Storage can t happen with cramming iii Retrieval Common Degenerative Disorders of the Brain a Alzheimer s disease i Generally among elderly ii Diagnosis confirmed at autopsy 1 Atrophy of gyri folds in cerebral cortex 2 Accumulation of beta amyloid plaque and neurofibrillary tangles iii Most common cause of dementia loss of cognitive function b Parkinson disease i Progressive loss of motor function beginning in 50s or 60s ii Degeneration of dopamine releasing neurons c Huntington s disease i Accumulation of Huntington protein ii Affects hippocampus purkinje cells and cerebellum