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Neuronal & Synaptic Transmission.docx

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University of Ottawa
Kenneth Campbell

Psychology Lecture 5 9/20/2012 6:02:00 AM Structure of Neuron  Soma (cell body) o Dendrites o Nucleus  Axon: o Grey & white matter (length of axon) o Terminal ending (bouton endings):  Secrete neurotransmitter substance Myelin Sheath:  Lipid material  Protect the axon  Insulating material  Speeds up transmission Terminal Ending  Synapse/synaptic gap: o Pre- & post synaptic  Transmitter Substance (neurotransmitter): o Excitation or inhibition The Nobel Prize 1906 C. Golgi & S. Ramon y Cajal 3 Catergories of Neurons  Sensory Neurons: transmit impulses received by sensory receptors to Central Nervous System (CNS). Afferents.  Motor Neurons: carry outgoing signals from CNS to muscle & glands. Efferents.  Interneurons:  All neurons are axonated; sensory and motor neurons are typically covered by myelin sheath  Nerve is a bundle (some cases 100’s of thoudsands) of neurons serving the same role Interneurons  Interneuronal communication  Often, far removed from either sensory or motor neurons.  Communication can be excitatory or inhibitory  This allows for flexibility of behavior. Resting Potential  All cells carry an electrical charge (potential)  The charge of the neuron can change  This allows one neuron to communicate with another neuron  An inactive neuron contains an excess of negatively charged ions inside the cell membrane  The charge inside the human neuron is about -70 mVolt (mV).  This is called the resting charge Depolarization  Inside, a surplus of negatively charged molecules (“ions”.)  Mainly because of the buildup of chloride (Cl )- +  Outside, buildup of positively charged ions, largely sodium (Na )  When the dendrite is stimulated (neuron, electrical stimulation)… o cell membrane opens channels; positively charged ions to flow in.  Change in the charge of the neuron (less negativity or more positivity) called depolarization Action Potentials  When the flow of positively charged ions reaches a certain critical threshold (the “threshold of excitation”), the neuron fires.  This called the action potential.  Once the action potential is initiated, it will travel down the length of the axon.  It may then subsequently influence the firing of another neuron.  If the level of excitation is not enough (the critical thresh is reached)…  The depolarization will reverse (the neuron will return to the resting potential)  The depolarization will Psychology Lecture 6 9/20/2012 6:02:00 AM Date: 09/25/12 All-or-None Law  The action potential will travel down (will be propagated) the length of the axon.  The amplitude of the axon potential will not vary. This the all-or- none law.  We either get the action potential or we do no
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