Chapter 45 Action potential

Chapter 45 Action potential - Dendrite and soma 1....

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1. Dendrite/diversity Site where signals are received Receptors for neurotransmitters Postsynaptic structure Dendritic spines 2. Soma Nucleus House-keeping Transcription Protein synthesis Golgi apparatus Dendrite and soma
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Axon and terminal 3. Axons Axon hillock “Electrical” cable Myelin sheath Transport 4. Terminal/diversity Site where signals are sent to next cell Release of neurotransmitters Pre-synaptic ending
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CNS and PNS CNS : Central nervous system Encased in bone Brain and spinal cord PNS : Peripheral nervous system Not encased in bone Spinal nerves (motor and sensory) Cranial nerves (motor and sensory Autonomic nervous system (sympathetic and parasympathetic)
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Three types of glia in the central nervous system (CNS) 1. Astrocytes – K+, glutamate, synapse isolation, blood-brain barrier, supply of 3C molecules 3. Microglia macrophages 2. Oligodendrocytes – myelin nodes of Ranvier
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One type in the PNS In peripheral nervous system ( PNS ) Schwann cells – myelin
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Cell membranes Phospholipids Hydrophilic head group Hydrophobic (hydrocarbon) tails Membranes: phospholipid bilayer Impermeable to ions Na + , K + , Ca ++ , Cl -
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Electrophysiology 1. Diffusion of an uncharged species 2. Diffusion of an ion 3. Equilibrium potential 4. Membrane potential 5. Action potential
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1. Diffusion
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2. Diffusion of an ion
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3. Equilibrium potential for sodium (E Na )
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Equilibrium potential for potassium (E K )
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Chloride equilibrium potential
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4. Membrane potential (V m )
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Resting potential The resting membrane is negative because the resting membrane is permeable mainly to K + , the result of leakage channels.
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Terminology: Depolarization 1. The membrane potential (V m ) refers to the electrical potential of the cell’s interior relative to the exterior (which by convention is assigned the value zero). 2. The resting potential is negative, about –70 mV. The cell is said to polarized . 3. The net entry of + ions (e.g., Na + ) causes a positive change in the electrical potential of the interior, making it less negative or depolarizing ” it. With a net entry of a large number of + ions, V m may even become positive; this is still called depolarization. 4. Return to resting potential is called repolarization .
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Description based on electrical current When Na + channels open, more Na + enters the cell, and V m rises from –70 mV to a less negative ( depolarized ) value. The flow of Na + into the cell is called a sodium current . By convention, the direction of current flow is the direction of movement of positive charge. Since the positive (sodium) current flows into the cell, it is also called an inward current .
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Description based on permeability If membrane permeability to Na + (P Na ) increases, more Na + enters the cell, and V m rises from –70 mV to a less negative ( depolarized ) value. For
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Chapter 45 Action potential - Dendrite and soma 1....

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