PSYCH-5-C01Adrian HernandezChapter 2: Synapses I. The Concept of the Synapse Synapse: Specialized gap between neurons. 1.1 Sherrington’s observationsInvestigated how neurons communicate with each other by studying reflexes (automatic muscular responses to stimuli) in a process known as a reflex arcThe Reflexes are slower than conduction along an axon. Several weak stimuli presented at slightly different times or locations produce a stronger reflex than a single stimulus does.He also discovered that if one sets of muscles became excited, the the other set becomes relaxed.2.2 Difference in the Speed Of Conduction Sherrington measured reflex speeds using dogsHe pinched a dog’s foot and observed that the dog flexed the leg after a short delay.Then measured the total distance that the impulse traveled, from the skin receptor to the spinal cord then from the spinal cord back down the legHe observed a rate of 15 meters per secondPrevious research indicated potential nerve velocities of 40 m/sHe concluded that the delay must be caused by one nerve communicating with the other3.3 Temporal Summation: Sherrington observed that repeated stimuli over a short period of time produced a stronger responseRepeated stimuli within a brief time having a cumulative effect. Presynaptic neuron: They are the neurons that deliver the synaptic transmission.Postsynaptic neuron: They are the neuron that receive the message. Graded potentials: Either depolarization (excitatory) or hyperpolarization (inhibitory) of the postsynaptic neuron. A graded depolarization is known as an excitatory postsynaptic potential (EPSP) and occurs when Na+ ions enter the postsynaptic neuron. EPSPs are not action potentials: The EPSP’s magnitude decreases as it moves along the membrane. A.B Spatial Summation, Part 11.1 Spatial summation: Sherrington also noticed that several small stimuli in a similar location produced a reflex when a single stimuli did notFor example, pinching one point does not produce a reflex but pinching two points at once doesThis happens because the two points activated separate sensory neurons, whose axons converged onto a neuron in the spinal cord2.2 Spatial Summation, Part 2Spatial summation is critical to brain Functioning Each neuron receives many incoming axons that frequently produce synchronized responsesTemporal summation and spatial summation ordinarily occur together A neuron could receive input from several axons in succession3.3 Inhibitory postsynaptic potential (IPSP): It is Atemporary hyperpolarization of a postsynaptic cell (this occurs when K+ leaves the cell or Cl- enters the cell after it is stimulated)4.4 Relationship among EPSP, IPSP, and action potentials The more synapses that a response travels through, the longer the response takesThe probability of an action potential on a given neuron depends on the ratio of EPSPs to IPSPs at a given momentSpontaneous firing rate: It the ability to produce action potentials without synaptic input.EPSPs and IPSPs increase or decrease the likelihood of firing action potentials I. II. Module 2.2 Chemical events at the Synapse A.A The Sequence of Chemical Events at the Synapse, Part 1The major sequence of events allowing communication between neurons across the synapse .The major events at a synapse are: Neurons synthesize chemicals that serve as the neurotransmitters.Action potentials travel down the axon At the axon of presynaptic terminal, the action potentials cause calcium to enter the cell, which leads to the release of neurotransmitters from the terminal into the synaptic cleft which is the space between the presynaptic and postsynaptic neuron.Neurotransmitters once released into the synaptic cleft, attach to receptors and alter activity of the postsynaptic neuronThe neurotransmitters will separate from their receptors and (in some cases) are converted into inactive chemicals.The neurotransmitter molecules may be taken back into the presynaptic neuron for recycling or they may diffuse away A.B Types of of neurotransmitters include: Amino acids: Acids containing an amine group (NH2). Neuropeptides: Chains of amino acids. There are also long chains which are called polypeptides.Acetylcholine: A chemical similar to an amino acid, with the NH2 group replaced by an N(CH3)3 group.Monoamines: Neurotransmitters containing an amine group (NH2) formed by a metabolic change of an amino acid.Purines: Adenosine and several of its derivativesGases: includes nitric oxide (NO) and possibly othersA.C Metabotropic Effects and Second Messenger Systems, Part 11.1 A neurotransmitter can have two types of effects when it attaches to the active site of the receptor: ionotropic or metabotropic effects.2.2 Ionotropic effects: Occurs when a neurotransmitter attaches to receptors and immediately opens ion channelsWhen the neurotransmitter attaches, it opens a channe3.3 Metabotropic effects: At other receptors, neurotransmitters exert metabotropic effects by initiating a sequence of metabolic reactions that are slower and longer lasting than ionotropic effectsG-proteins: A protein coupled to the energy-storing molecule guanosine triphosphate (GTP)Second messenger: It is a Chemicals that carries a message to different areas within a postsynaptic cellThe activation of a G-protein inside a cell increases the amount of the second messengerG-Protein Activation- Increases the concentration of a “second-messenger”May open or close ion channels, alter production of activating proteins, or activate chromosomes4.4 Neuromodulators/NeuropeptidesWhereas the neuron synthesizes most other neurotransmitters in the presynaptic terminal, it synthesizes neuropeptides in the cell body and then slowly transports them to other parts of the cell.Whereas the neuron synthesizes most other neurotransmitters in the presynaptic terminal, it synthesizes neuropeptides in the cell body and then slowly transports them to other parts of the cell.IIIA.A Drugs in the body1.1 Stimulant drugs Number 1 Amphetamine and cocaine is known to increase dopamine release from presynaptic terminals which is by reversing the direction of the dopamine transporter which can affect the body sometimes.Number 2 Cocaine/ is a stimulant drug blocks the reuptake of catecholamines and serotonin at the synapse. The behavioral effects of cocaine are believed to be mediated primarily by dopamine and secondarily by serotonin.Stimulate dopamine synapses by increasing the release of dopamine from the presynaptic terminalThese drugs are also known to block the serotonin and norepinephrine transportersMethylphenidate (Ritalin)/is a stimulant drug:Even Though it is known the effect are less intense in Ritalin than cocaine they do act very similar which is by blocking reuptake of dopamine at presynaptic terminalsThe effects of methylphenidate are much longer lasting and less intense as compared to cocaine, yet also come with a risk of addiction2.2 Nicotine- Compound found in tobacco and mostly found in cigars Stimulates the nicotinic receptor (a type of acetylcholine receptor) in both the central nervous system and neuromuscular junction of skeletal musclesCan also increase dopamine release by attaching to neurons that release dopamine in the nucleus accumbensAlso highly addictiveOpiate Drugs: Derived from or similar to those derived from the opium poppy. Similar opiates include:Morphine, heroin, and methadone. Opiate drugs exert their effects by binding to the same receptors as endorphins.
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