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Chapter 03: Synaptic Communications


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How the synapse works and the chemicals of synaptic communications.

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Chapter 03: Synaptic Communications

  1. 1. The Concept of The Synapse
  2. 2. Properties of the Synapses <ul><li>Gaps Between Neurons </li></ul><ul><li>First deduced by Sherington </li></ul><ul><li>Graded Potentials </li></ul><ul><li>Either Depolarization (Excitation) or Hyperpolerization (Inhibition) of the Postsynaptic Neuron </li></ul><ul><li>Graded depolarization is known as Excitatory Postsynaptic Potential (ESPS) & occurs when Sodium (Na + ) ions enter the postsynaptic neuron </li></ul>
  3. 3. Summation <ul><li>Temporal Summation </li></ul><ul><li>Repeated stimulation of one Presynaptic Neuron occurring within a brief period of time that has a cumulative effect on the Postsynaptic Neuron </li></ul><ul><li>Spatial Summation </li></ul><ul><li>Several synaptic inputs originating from separate locations exerting a cumulative effect on a postsynaptic neuron </li></ul><ul><li>Inhibitory Postsynaptic Potential (IPSP) </li></ul><ul><li>When Potassium (K +) leaves the cell or chloride enters the cell after stimulation </li></ul><ul><li>Spontaneous Firing Rate </li></ul><ul><li>The ability to produce Action Potentials without synaptic input </li></ul>
  4. 4. Synaptic Transmission <ul><li>Events at the Synapse </li></ul><ul><li>Action Potentials cause Calcium to enter the cell leading to the release of Neurotransmitters </li></ul><ul><li>Released Neurotransmitters attach to Receptor sites altering the activity of the Postsynaptic Neuron </li></ul><ul><li>Neurotransmitters will separate from their Receptors & are at times converted into Inactive Chemicals </li></ul><ul><li>Reuptake occurs in some cells recycling Neurotransmitters </li></ul><ul><li>In some cells empty Synaptic Vesicles are returned to the cell body </li></ul>
  5. 5. Types of Neurotransmitters <ul><li>Amino Acids: Acids containing an amine group </li></ul><ul><li>Peptides: Chains of amino acids </li></ul><ul><li>Acetylcholine: A chemical similar to an amino acid </li></ul><ul><li>Monoamines: Nonacidic neurotransmitters containing an amine group & formed by a metabolic change in an amino acid </li></ul><ul><li>Purines: Adenosine & several of its derivatives </li></ul><ul><li>Gasses: Includes nitric oxide & possibly others </li></ul>
  6. 6. Neurotransmitters <ul><li>Synthesized from Precursors derived from Food </li></ul><ul><li>Phenylalanine & Tyrosine precursors for the Catecholimines </li></ul><ul><li>Catecholimines: Dopamine, Epinephrine, & Norepinephrine </li></ul><ul><li>Choline is the precursor for acetylcholine found in foods containing lecithin </li></ul><ul><li>Tryptophan is the precursor for serotonin </li></ul><ul><li>Transport of Neurotransmitters </li></ul><ul><li>Certain Neurotransmitters (e.g. acetylcholine) synthesized in the Presynaptic Terminal </li></ul><ul><li>Larger Neurotransmitters synthesized in the cell body & transported down to the axon terminal </li></ul><ul><li>Transporting of Neurotransmitters can take hours or days for long axons </li></ul>
  7. 7. Neurotransmitter Release <ul><li>Stored in Synaptic Vesicles </li></ul><ul><li>Depolarization occurs when Action Potential reaches the Axon Terminal </li></ul><ul><li>After release, there is diffusion across Synaptic Cleft </li></ul><ul><li>Brain uses dozens of Neurotransmitters </li></ul>
  8. 8. Effects of Neurotransmitters <ul><li>Ionotropic Effect </li></ul><ul><li>Neurotransmitter attaches to the receptor causing the immediate opening of an Ion Gate </li></ul><ul><li>Metabotropic Effect </li></ul><ul><li>Neurotransmitter attaches to a receptor & initiates a cascade of metabolic processes </li></ul><ul><li>Neuromodulators </li></ul><ul><li>Mainly peptides, that do not excite or inhibit neurons but alter the effects of a neurotransmitter </li></ul>
  9. 9. Inactivation & Reuptake <ul><li>Inactivation </li></ul><ul><li>Inactivation occurs shortly after binding to Postsynaptic Receptors </li></ul><ul><li>Neurotransmitter activation occurs in different ways </li></ul><ul><li>Acetylcholinesterase breaks down Acetylcholine after release from the receptor </li></ul><ul><li>Rapid series of Action Potentials can release neurotransmitters faster than a presynaptic cell can synthesize it bringing transmission to a stop </li></ul><ul><li>Reuptake </li></ul><ul><li>Serotonin & Catecholamines go through reuptake after leaving Postsynaptic Receptor </li></ul><ul><li>Reuptake occurs through specialized proteins called Transporters </li></ul><ul><li>Some Serotonin & Catecholamine molecules converted into inactive chemicals by Enzymes </li></ul>
  10. 10. Drugs’ Affects on Synapses <ul><li>Antagonist </li></ul><ul><li>A drug that blocks the effects of Neurotransmitters </li></ul><ul><li>Agonist </li></ul><ul><li>A drug that mimics a Neurotransmitter </li></ul><ul><li>Drugs’ influence Synaptic activity: </li></ul><ul><li>1. Alters synthesis of Neurotransmitter </li></ul><ul><li>2. Disrupts the Vesicles </li></ul><ul><li>3. Increases the release of Neurotransmitter </li></ul><ul><li>4. Decreases Reuptake </li></ul><ul><li>5. Blocks Neurotransmitter breakdown into an inactive chemical </li></ul><ul><li>6. Directly stimulates the blocking of Post-synaptic Receptors </li></ul><ul><li>Affinity </li></ul><ul><li>Efficacy </li></ul>
  11. 11. Synapses & Personality <ul><li>Important in Almost All Behavior </li></ul><ul><li>Variance of Receptor Levels may be a genetic marker of Personality </li></ul><ul><li>Weak correlations found for certain types of behavior & Dopamine Receptors </li></ul><ul><li>D 2 Receptor implicated in risky behaviors, D 4 Receptor associated with “novelty-seeking personality </li></ul>