Cells and Action Potentials PDF

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Summary

The teacher was Amber Lacrosse. The class was PY-204 Psychological Psych....

Description

I.

Cell Membrane: a. Outside: Na+, Cl-, and Ca2+ b. Inside: K+ c. Action Potential (nerve impulse): i. Electrical message transmitted down the axon of a neuron 1. Resting potential (polarized) a. Stimulus b. Threshold of excitation 2. Depolarization 3. Repolarization 4. Refractory Period 5. Return to resting potential state d. The Resting Potential (polarization) i. The membrane of a neuron maintains an electrical gradient. 1. A difference in the electrical charge inside and outside of the cell. ii. The resting potential is the state prior to an action potential. 1. At rest the inside of the membrane is slightly negative. iii. The membrane is selectively permeable. 1. What does that mean? Protein channels 2. Main ions: Sodium (Na+) and Potassium (K+) iv. Electrical gradient: Difference in electrical charge v. Concentration gradient: Difference in ion distribution vi. Diffusion: Movement of ions from areas of high concentration to low concentration e. Polarization of the Membrane i. The resting potential is stable until the neuron is stimulated. ii. The threshold of excitement is the point at which a stimulus produces massive depolarization. iii. Depolarization: Decreased polarization towards zero iv. Hyperpolarization: Increased polarization (difference in electrical charge btw the inside/outside of cell) f. The Action Potential i. An action potential is a rapid depolarization of the neuron. 1. FYI, the action potential threshold varies from one neuron to another. ii. Stimulation of the neuron past the threshold of excitation triggers an action potential. iii. Voltage-activated channels are membrane channels whose permeability depends upon the voltage difference across the membrane. 1. There are voltage activated sodium (Na+) and potassium (K+) ion channels. iv. When sodium channels are opened, positively charged sodium ions rush in v. Voltage Gated Na+ Channel

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1. Open following stimulus 2. Stays open for about 1ms 3. Cannot be opened until the membrane returns to threshold vi. Voltage Gated K+ Channel 1. Opening is delayed: delayed rectifier; delayed restoration of the membrane potential. vii. Phases of the AP 1. Resting Potential 2. Rising Phase a. Depolarization, Na+ influx b. Overshoot (+ charge) 3. Falling Phase a. Repolarization, K+ efflux b. Undershoot (- charge) viii. Movement of Na+ and K+ During AP 1. Na+ cross during the peak of the action potential (depolarization) 2. K+ cross later in the opposite direction, returning the membrane to its original polarization (repolarization) ix. Spike-initiation Zone 1. The axon hillock contains voltage gated Na+ channels. a. Location of action potential. b. A swelling where the axon exits the soma. x. After an AP 1. Sodium channels are quickly closed. 2. The neuron return to its resting state by the opening of potassium channels. a. Potassium ions flow out due to the concentration gradient and take with them their positive charge. 3. The sodium-potassium pump later restores the original distribution of ions. xi. Sodium-Potassium Pump 1. Protein complex that continually pumps 3 sodium ions out of the cell while drawing 2 potassium ions into the cells. a. Helps to maintain the electrical gradient b. Uses ATP Refractory Periods a. After an action potential, a neuron has a refractory period during which time the neuron resists the production of another action potential. b. Absolute refractory period i. The first part of the period in which the membrane cannot produce an action potential. c. Relative refractory period

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i. The second part where it takes a stronger stimulus to trigger an action potential. ii. The undershoot is the relative refractory period. d. The All-or-None Law: i. States that the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it. ii. Action potentials are equal in intensity and speed within a given neuron. e. Propagation of the AP i. The action potential begins at the axon hillock and propagates or regenerates down the axon. f. Propagation of the action potential i. Describes the transmission of the action potential down the axon. 1. Does not directly travel down the axon g. The Myelin Sheath i. Myelin sheath of axons are interrupted by short unmyelinated sections called nodes of Ranvier. 1. Myelin is an insulating material composed of fats and proteins. ii. At each node of Ranvier, the action potential is regenerated by a chain of positively charged ion pushed along by the previous segment. h. Saltatory Conduction i. Used to describe the “jumping” of the action potential from node to node. 1. Provides rapid conduction of impulses 2. Conserves energy for the cell Local Neurons a. Not all neurons have lengthy axons. b. Local neurons i. Have short axons, exchange information with only close neighbors, and do not produce action potentials. ii. Depolarizes or hyperpolarizes in proportion to the simulation. iii. When stimulated, local neurons produce graded potentials, which are membrane potentials that vary in magnitude and do not follow the all-ornone law....