Week 1: Lecture 4
Week 1: Lecture 4 Biol130
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This 4 page Class Notes was uploaded by Alexandria Notetaker on Friday August 19, 2016. The Class Notes belongs to Biol130 at University of California - Santa Cruz taught by Ruben,G.J. in Summer 2016. Since its upload, it has received 11 views. For similar materials see Human Physiology in Biology at University of California - Santa Cruz.
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Date Created: 08/19/16
Lecture 4: The Nervous System: The Action Potential and Synaptic Transmission How can membrane potential be changed in neurons to generate electrical impulses? 1* Leak Channels: always open, unregulated 2 3* Gated Channels: regulate movement of specific ions across the membrane. These channels have an open and closed state that regulate diffusion of ions. This affects permeability. When channel is open, the cell is permeable to the ion and vise versa (channels closed=impermeable). Ion channels can change the membrane potential by allowing ions to move across the membrane 1. Chemically (ligand) gated: Stimulated by chemical messengers or phosphorylation. Remember the structure of protein regulates its function. Conformational change for these channels is induced by the ligand (example: post-synaptic receptors stimulated by neurotransmitters released by presynaptic neuron into the synapse) 2. Mechanically gated: Stimulated by the stretch/ deformation of the cell membrane (example: tendon reflexes) 3. Voltage gated: Stimulated by the change in membrane potential (example: Na voltage gated channels stimulating action potential (AP) propagation) How can the membrane potential be changed in neurons? an example of depolarization caused by a chemical stimulus There are 2 types of changes in membrane potential o Graded potential: localized change in membrane potential that does not reach threshold. It is “graded” because it depends on the strength of the stimulus multiple graded potentials can be “summed” up together to increase magnitude found mostly in the afferent nervous system o Action potential (AP) : large, rapid changes in membrane potential that reach threshold Threshold depolarization results in conduction of the electrical impulse along the length of the neuronal membrane All-or-none (example: like a bullet leaving a gun) Conducted without decrement Magnitude does not reflect strength of stimulus “excitability”- the ability to generate APs In order to generate an action potential, a cell must utilize different types of ion channels o Ligand gated- channels and mechanically gated channels often serve as the initial stimulus for an AP o Voltage gated- give membrane ability to undergo APs by allowing rapid depolarization and repolarization phases of the response + + The AP depends on voltage gated Na and K channels The Action Potential o The transient changes in permeability of the cell membrane to Na and K drive the AP An AP is “all-or-none” o Magnitude of AP does not reflect intensity of stimulus o Intensity of stimulus is translated by frequency of AP generation Membranes are refractory to excitation until they have repolarized o Refractory period limits the number of APs Absolute Refractory Period- during action potential Relative Refractory Period- during repolarization. It requires more intense stimulation to generate an AP of reduced magnitude
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