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UWL BIO 312 - Exam 2 Study Guide

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Unit 2 Study GuideLecture 8: Nervous System INervous System has 3 main functions:- Sensory receptors- Integrating center- EffectorsBroken up into central nervous system (brain and spinal cord) and peripheral nervous system (motor neurons, skeletal muscle, sympathetic and parasympathetic systems)Nervous tissue histology:- Highly cellular- Composed of 2 types of cellso Neurons: functional units, possess properties of excitability and conductivityo Support cells: not excitable, provide metabolic and physical support to neurons Astrocyte, microglial, ependymal, oligodendrocyte, schwann, satellite- Responsible for reflexes, thought, emotion, personality, behavior- Structural classification:o Unipolar neuron: short singular process that splits into two longer axonso Multipolar neuron: multiple processes- Structure:o Soma: cell bodyo Dendrites: antennas to receive signals from other neuronso Axon hillock: action potential initiationo Axon: (nerve fiber)conduct action potentials, usually myelinatedo Axon terminals: release neurotransmitter onto other neuronso Schwann cells: secrete myelin sheatho Nerve: bundle of many axons in the PNSo Tract: bundle of many axons in the CNSPhysiology of Neurons: all living cells have separation of unlike charge across their membrane- Separation of positive and negative charges across the membranes of two cells is called membrane potential- Membrane potential is much larger in nerve cells which gives properties of excitability and conductivity- In ICF and ECF positive and negative charges exists in form of ions or electrolytes- When oppositely charged particles are separated they have the potential of coming together- The magnitude of charge separation is called the electrical potential difference- In cells the separation of charge is small, units are millivolts (mV)- In cells, the potential difference is called the membrane potential (Em)- Amount of charge that moves across a membrane depends on magnitude of membrane potential and propertiesof the membrane (how much resistance) BIO312 1nd Edition- Neuron at rest has membrane potential is -70mV- Em is always expressed as inside compared to outside- Electrical and chemical gradients both have influence on diffusion of ions across cello Under normal conditions, chemical gradients are generally stronger than electrical gradientsMechanism of the resting membrane potential:- Created by the gradients of sodium and potassium- Differences in permeability allows far more potassium into cell than sodium, steeper gradiento Potassium leaks out faster than sodium leaks in- Gradient maintained by sodium and potassium pumps acting against natural gradient- Electrical Signals in Neuronso Neurons use transient changes in the value of their membrane potential as signals for receiving, processing and transmitting informationo Changes in membrane potential is produced by any stimulus that changes permeability of membrane to Na+, K+, Cl-, or Ca 2+o Terminology for electrical signals in comparison to -70mV resting potential Depolarization: occurs when the membrane potential becomes less negative or more positive Overshoot: inside of cell becomes positive Repolarization: movement back toward the resting potential Hyperpolarization: development of more negative charge than usualo Electrical signals exist in two forms: Graded or local potentials: signal only over short distances Action potentials: utilized for long distance signalsLecture 9Nervous System IIMembrane Potentials- Permeability of membrane to ionso Ions pass through membrane by diffusion only through channel proteins (not through bilayer) Ion channels are ion specific Vast majority are subject to regulation (gated) Several different types of gated ion channels whose opening/closing produce changeso Chemically Gated Ion channels: requires the binding of some specific chemical signal to that ion channel for it to open (neurotransmitter, drug) Involved in graded potentials Four types: cation (Na+, K+), K+, Cl-, Ca +2  Opening of cation channels results in depolarization because gradient for Na is steeper than Ko Voltage Gated ion channels: activated by the voltage of the membrane potential Three types for Na, K and Cao Mechanically Gated ion channels: rely on an outside mechanical force to open Most are cation channels and occur in membrane of certain types of sensory receptorsTypes of electrical signals:- Graded potentials: function is to stimulate or inhibit action potential formationo Occur on the membrane of the sensory receptor in unipolar neurons and on the cell body and axon hillock of multipolar neuronso Only effective at short distances because of decremental conductiono Can be summated temporally or spatially- Action Potential: long distance signals of the nervous system, used by neurons to communicate with other neurons, muscle, and gland cellso Triggered by gated potentialso Triggered at axon hillock, conducted down axon without decremento Large and rapid depolarization of the membrane followed by large and rapid repolarization Entire event lasts only 2-3 milliseconds Amplitude is about 100 mvo Results from large and rapid sequential changes in permeability of membrane first to Na+ then to K+1. Depolarization caused by Na+ permeability being increased and diffusing into the cell down its electrochemical gradient2. Repolarization caused by K permeability being increased and diffusing out of cell down its electrochemical gradient3. Hyperpolarization caused by K permeability being increased for a little longer than necessaryo Voltage gated Na+ channel: two doors open at same time, and close fully in about 0.5 millisecondso Voltage gated K+ channel: one door closed at resting potential, action potential triggers opening of K+ channel but is slower and does not fully open until around the time of peak depolarization (from Na channel being opened)- Triggering of action potential occurs from stimulus causing threshold depolarization of the resting membrane potential, as long as stimulus reaches threshold potential, action potential will always be the same magnitude- Refractory period: period of time during which the membrane is unresponsive to a threshold level stimuluso Caused by time it takes to fully open/close ion channels- Transmission of AP down the axon is a chain reaction of depolarization, will always flow forward because of refractory


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