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Chapter 4

Chapter 4 Definitions.docx

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Paul Mallet

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Chapter 4: Neural Conduction and Synaptic Transmission 4.1 Resting Membrane Potentials Membrane Potential: The difference in electrical charge between the inside and outside of a cell Microelectrodes: Extremely fine recording electrodes, which are used for intracellular recording Resting Potential: The steady membrane potential of a neuron at rest, usually about -70 mV Ions: Positively or negatively charged particles Ion Channels: Pores in neural membranes through which specific ions pass. Sodium(out)-potassium(in) pumps: Active transport pumps that pump NA+ out of neurons and K+ ions in Transporters: Mechanisms in the membrane of a cell that actively transports ions or molecules across the membrane. 4.2 Generation and Conduction of Postsynaptic Potentials Depolarize: To decrease the resting membrane potential Hyperpolarize: to increase the resting membrane potential Excitatory Postsynaptic potentials (EPSPs): Postsynaptic depolarizations, increase the likelihood that the neuron will fire Inhibitory postsynaptic potentials (IPSPs): Postsynaptic hyperpolarizations, decrease the likelihood that the neuron will fire Graded Responses: (Both EPSPs and IPSPs are graded responses) the amplitudes of EPSPs and IPSPs are proportional to the signals that elicit them. 4.3 Integration of Post synaptic Potentials and Generation of Action Potentials: Axon Hillock: The conical structure at the junction between the axon and cell body Threshold of excitation: The level of depolarization necessary to generate an action potential, generally -65mV. Action Potential (AP): A massive, but momentary-lasting about 1 millisecond- reversal of the membrane potential from -70 to +50mV. Follows the All or-non principal All-or-none responses: Either fire completely or do not fire at all. Integration: Neurons integrate incoming signals in two ways: over space and over time. Spatial summation: The integration of signals that occur on different sites of the neuron’s membrane. Temporal Summation: The integration of neural signals that occur at different times at the same synapse. 4.4 Conduction of Action Potentials Voltage-activated Ion Channels: Ion channels that open and close in response to changes in the level of membrane potential Absolute refractory period: A brief period (typically 1 to 2 milliseconds) after the initiation of an action potential in the same neuron Relative refractory period: A period after the absolute refractor period during which a higher-than- normal amount of stimulation is necessary to make a neuron fire. Antidromic Conduction: Axonal conduction opposite to the normal direction; conduction from axon terminals back towards the cell body. Orthodromic conduction: Axonal conduction in the normal direction-from the cell body toward the terminal buttons Nodes of Ranvier: The gaps between adjacent myelin segments on an axon Saltatory conduction: Conduction of an action potential from one node of Ranvier to the next along a myelinated axon 4.5 Synaptic Transmission: Chemical Transmissions of signals among Neurons Dendritic Spines: The tiny nodules of various shapes that are located the surfaces of many dendrites and the sites of the most excitatory synapses in the mature mammalian brain Directed synapses: Synapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximal distance Nondirected synapses: Synapses at which the sites of neurotransmitter release and neurotransmitter reception are not close together Neuropeptide transmitters: Peptides that function as neurotransmitters, of which about 100 have been identified; also called neuropeptides Synaptic Vesicles: Small spherical membranes that store neurotransmitter molecules and release them into the synaptic cleft. Golgi complex: Structures in the cell bodies and terminal buttons of neurons that package neurotransmitters and other molecules in vesicles Coexistence: The presence of more than one neurotransmitter in the same neuron Exocytosis: The process of releasing a neurotransmitter Receptors: Cells that are specialized to receive chemical, mechanical, or radiant signals from the environment; also proteins that contain binding sites for particular neurotransmitters Ligand: A molecule that binds to another molecule; neurotransmitters are ligands of their receptors Receptor subtypes: The different types of receptors to which a particular neurotransmitter can bind Ionoitropic receptors: Receptors that are associated with ligand-activated channel proteins Metabolic Receptors: Receptors that are associated with signal proteins and G proteins G Proteins: Proteins t
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