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ContentHomeostasis, Membranes, Electrophysiology and ANS Homeostasis Homeostasis Defined Homeostatic Control Systems Feedback Response Loop Cell Transport; Water & Solutes Fluid Compartments Osmosis Diffusion of Solutes Active Transport Bulk Transport Electrophysiology Ions and Cell Membranes Membrane Potentials Graded Potential Action Potentials Refractory Periods Propagation of an Action Potential The Synapse The Autonomic Nervous System Organization of the Nervous System Structural Organization of the ANS The SNS and the PNS The Enteric Nervous System Physiology of the ANS Neurotransmitters of the ANS Receptors of the ANS Actions of the Autonomic Nervous System Table of Actions for the SNS and PNS and Some Common Drugs Skeletal Muscle and Special Senses Structural Organization of Skeletal Muscle Neuromuscular Junction, Excitation-Contraction Coupling Muscle Contractures and Cramps Whole Muscle Contraction, Fiber Type, Fatigue and Muscle Pharmacology Motor Units Factors that Influence the Force of Contraction Energy Source for Muscle Contraction Skeletal Muscle Fiber Types Fatigue Muscle Pharmacology Smooth Muscle Smooth Muscle Contraction Control of Body Movement Voluntary Control of Muscle Reflexes Taste and Smell Taste The Sense of Smell Vision Structure of the Eye Focusing Light on the Retina Converting Light to Action Potentials The Retina Phototransduction Receptive Fields Hearing and Equilibrium The Nature of Sound The Hearing Apparatus Sound Vibrations to Action Potentials The Sense of Balance and Equilibrium Cardiovascular System Structure of the Heart Chambers and Circulation Cardiac Cell Action Potentials Action Potentials in Cardiac Muscle Cells Action Potentials in Cardiac Autorhythmic cells Cellular Mechanisms of Inotropy and Chronotropy Electrophysiology of Heart Muscle Heart Conduction System Electrocardiogram (ECG) Abnormal ECG - Current of Injury The Cardiac Cycle Cardiac cycle Cardiac Measurements and Pressure Volume Loops Blood vessels and Blood Pressure Arteries and Veins Capillaries Blood Pressure Regulation and Shock Capillary Exchange Myogenic and Paracrine Regulation of Vasoconstriction and Vasodilation Blood Composition of Blood Hematopoeisis Breaking Down Red Blood Cells Hemostasis Urinary and Respiratory Systems Function and Structure of the Kidney Urinary System Function Functional Anatomy of the Urinary System The Nephron: Functional Unit of the Kidney The Renal Corpuscle: Bowman's Capsule Physiology of Urine Production Filtration Renal Clearance Tubular Reabsorption Urine Concentration and Dilution Hormonal Regulation of Urine Production Acid/Base Balance Buffers Acid/Base Disturbances The Respiratory System Respiratory System Structure and Function Respiratory Membrane Respiratory pressures and Inspriation/Expiration Alveoli and Surfactant Pneumothorax Pressure-Volume Loops and the Work of Breathing Gas Exchange and Transport Gas Laws Partial Pressure Gradients in the Lung Alveolar Gas Equation Oxygen and Carbon Dioxide Transport in the Blood Alveolar Ventilation Ventilation/Perfusion Ratio Chronic Bronchitis and Emphysema Respiratory Control by the Medulla Oblongata Chemicals that Regulate Ventilation Digestive, Endocrine and Reproductive Systems Functional Anatomy of the Digestive System Layers of the Digestive Tract Enteric Nervous System Organs of the Digestive System Digestion Carbohydrates Proteins Lipids Lipoproteins Regulation of Digestive Secretions Endocrine System Overview of the Endocrine System Hormone Receptors Hormones of the Body Other Hormones: Melatonin and Pheromones The Hypothalamus and Pituitary Gland Structure and Function of the Hypothalamus and Pituitary Gland The Posterior Pituitary The Anterior Pituitary Growth Hormone Prolactin Thyroid Hormones Adrenal Hormones Pancreas Insulin and Glucagon Diabetes Mellitus Reproductive System Anatomy Female Reproductive Anatomy Male Reproductive Anatomy Sexual Development at Puberty Male Reproductive Endocrine Axis Spermatogenesis Female Reproductive System: Oogenesis Ovulation and Fertilization The Ovarian Cycle The Uterine Cycle Pregnancy Gender The Placebo Effect The Placebo Effect Examples of the Placebo Effect How do Placebos Work? Are Placebos Ethical? How do we validate actual effectiveness of placebos Tips for evaluating scientific evidence What about Faith Healings
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The motor neurons that innervate skeletal muscle fibers are called alpha motor neurons. As the alpha motor neuron enters a muscle, it divides into several branches, each innervating a muscle fiber (note this in the image above). One alpha motor neuron, along with all of the muscle fibers it innervates, is a motor unit. The size of the motor unit correlates with the function of the muscle. In muscles involved with fine, coordinated control, the motor units are very small with 3–5 muscle fibers per motor neuron. Muscles that control eye movement and muscles in our hands have relatively small motor units. On the other hand, in muscles involved with more powerful but less coordinated actions, like the muscles of the legs and back, the motor units are large with thousands of muscle fibers per motor neuron.
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