Neuro 1500 – Neurochemistry

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Synapse
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Zone of connect at which one neuron communicates witch another – Two categories of synapses 1. Chemical 2. Electrical
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Synaptic Transmission steps
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1. relay information from one neuron to another 2. Major Phases 3. Presynaptic Events 4. Postsynaptic Events 5. Postsynaptic Receptors 6. Neurotransmitter fate
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1. Relay information from one neuron to another
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Convert electrical information into chemical information
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2. Major Phases of synaptic transmission
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1. depolarizing of presynaptic membrane 2. Fusing Vesicles 3. Release neurotransmitter into synaptic cleft 4. Binding of neurotransmitters to receptors on postsynaptic membrane 5. Generate EPSP or IPSP 6. Removal of neurotransmitter from synaptic cleft.
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3. Presynaptic Events
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– Neurotransmitter is synthesized in vesicles that are transported to synapse – Depolarization of membrane causes voltage gated Ca2+ channels to open. – Ca2+ causes vesicles to fuses with presynaptic membrane – release vesicles contents into synaptic cleft via exocytosis
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4. Postsynaptic Events
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– Neurotransmitter binds to receptors on postsynaptic membrane – depending on type of neurotransmitter can lead to EPSP or IPSP.
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5. Postsynaptic Receptors
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Two major types of receptors 1. Ionotropic (aka ligand gated ion channels) – direct gating – Faster response 2. Metabotropic (GPCR) – indirect gating – slower response – Can also result in gene expression change
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6. Neurotransmitter Fate
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– Prevent continuous signal transfer – has two major mechanism 1. Reuptake (reused into the presynaptic terminal) 2. Deactivation by enzymes
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ionotropic receptor
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Also called Ligand-gated ion channel. A receptor protein containing an ion channel that opens when the receptors is bound by an agonist.
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Metabotropic receptor
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A receptor protein that does not contain ion channels but may, when activated, use a G protein system to open nearby ion channels or to produce other cellular effects.
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Electrical synapses
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– Two neurons are joined directly together together via gap junction – Connexons are channel in membranes of both presynaptic and postsynaptic membrane. – Depolarization at presynaptic membrane allows for ions to flow through gap junction – Can cause depolarization in postsynaptic membrane Instantaneous signal transmission – Allows for synchronized firing of neurons
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Functional Consequences of Electrical synapse
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Escape response – Extremely fast response by vertebrates to avoid danger – Initially bypasses CNS and mediated by small number of neurons – examples: – Crayfish tail flip – C-star in fish
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Distinguishing between electrical and chemical synapse
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– Electrical has ion current transmission and and chemical is chemical transmitter. – Electrical has cytoplasmic continuity between presynaptic and postsynaptic cells and chemical doesn’t. – Electrical is usually bidirectional and Chemical is unidirectional.
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Neurotransmitters
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Signaling chemical that alters the function of postsynaptic neuron. criteria: – Substance is synthesized in presynaptic neuron and stored in axon terminals. – Is released when action potentials reach axon terminals. – is recognized by receptors on postsynaptic membrane. – Causes changes in the postsynaptic cells – Blocking its release interferes with the effects on the postsynaptic cell.
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4 TYPES of neurotransmitters
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1. Amines 2. Amino Acid 3. Neuropeptides 4. Gases.
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1. Amines
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– Organic compounds that contains nitrogen atom. – Quaternary Amines – Acetylcholine (ACh) -First neurotransmitter described – PNS function – Excitatory motor activity – Inhibitory effect on cardiac muscle – Monoamines – Catecholamines
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Noradrenergic Pathway in the brain
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referring to cells using norepinephrine as a transmitter. – Some function in brain – Alartness – Attention – Mood
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Dopaminergic pathway in the brain
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referring cells that use dopamine as synaptic transmitter. – some functions are – Fine motor function, motivation, pleasure, learning… etc
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Serotonergic pathway in the brain
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referring to cells that use serotonin as their synaptic transmitter. – Some functions are – mood, anxiety, sexual behavior, aggressions…etc
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2. Amino Acid
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– More complex organic compound that contain nitrogen atoms – a neurotransmitter that is itself an amino acid. Example include GABA, glycine, and glutamate. – Glutamate and GABA, both are primarily excitatory and inhibitory effects in CNS.
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3. Neuropeptide
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– More complex organic compound that contain multiple amino acids. – A neurotransmitter consisting of a short chain of amino acids. – some functions are: fluid regulations, social behavior, attachment, aggression, and parental care. – They contains Endorphins, enkephalins, dynorphins.
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4. Gases
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A neurotransmitter that is soluble gas. Examples including nitric oxide and carbon monoxide. – Differs from other transmitters in three ways. 1. Is produced outside axon terminals- mainly in dendrite, and diffuses as soon as it is produced. 2. No receptors involved; it diffuses into the target cells and activates second messengers. 3. Can function as RETROGRADE TRANSMITTER by diffusing from postsynaptic neuron back into the presynaptic neuron.
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Neurotransmitter: GASES
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Example: Nitric OXIDE – can be released as, retrograde transmitter, co-transmitter.
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Acetylcholine (ACh) (In Amines)
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A neurotransmitter found in the autonomic nervous system, motor system, and throughout the brain.
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Dopamine (in Amines)
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a monoamine transmitter found in the midbrain– especially the substaintia nigra– and the basel forebrain.
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Serotonin (5-HT)– In Amines
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a synaptic transmitter that is produced in the raphe nuclei and is active in structure throughout the cerebral hemisphere
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Norepinephrine (NE) –(In Amines)
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a neurotransmitter that is produced and released by sympathetic postganglionic neuron to accelerate organ activity. It is also produce in the brainstem and found in projections through the brain.
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GABA (in amino acid)
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a widely distributed amino acid transmitter, and the main inhibitory transmitter in the mammalian nervous system.
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Glutamate (Amino Acid)
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an amino acid transmitter, the most common excitatory transmitter.
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Opioid Peptide (Neuropeptides)
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A type of endogenous peptide that mimic the effect of morphine in binding to opioid receptors and producing marked analgesia and reward.

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