CoverModule 1.0. Homeostasis, Membranes, Electrophysiology and ANS1.1. Homeostasis1.1.1. Homeostasis Defined1.1.2. Homeostatic Control Systems1.1.3. Feedback Response Loop1.2. Cell Transport; Water & Solutes1.2.1. Fluid Compartments1.2.2. Osmosis1.2.3. Diffusion of Solutes1.2.4. Active Transport1.2.5. Bulk Transport1.3. Electrophysiology1.3.1. Ions and Cell Membranes1.3.2. Membrane Potentials1.3.3. Graded Potential1.3.4. Action Potentials1.3.5. Refractory Periods1.3.6. Propagation of an Action Potential1.4. The Synapse1.5. The Autonomic Nervous System1.5.1. Organization of the Nervous System1.5.2. Structural Organization of the ANS1.5.3. The SNS and the PNS1.5.4. The Enteric Nervous System1.5.5. Physiology of the ANS1.5.6. Neurotransmitters of the ANS1.5.7. Receptors of the ANS1.5.8. Actions of the Autonomic Nervous System1.5.9. Table of Actions for the SNS and PNS and Some Common DrugsModule 2.0. Skeletal Muscle and Special Senses2.1. Structural Organization of Skeletal Muscle2.2.1. Neuromuscular Junction, Excitation-Contraction Coupling2.2.2. Muscle Contractures and Cramps2.3. Whole Muscle Contraction, Fiber Type, Fatigue and Muscle Pharmacology2.3.1. Motor Units2.3.2. Factors that Influence the Force of Contraction2.3.2. Factors that Influence the Force of Muscle Contraction2.3.3. Energy Source for Muscle Contraction2.3.4. Skeletal Muscle Fiber Types2.3.5. Fatigue2.3.6. Muscle Pharmacology2.4. Smooth Muscle2.4.1. Smooth Muscle Contraction2.5. Control of Body Movement2.5.1. Voluntary Control of Muscle2.5.2. Reflexes2.6. Taste and Smell2.6.1. Taste2.6.2. The Sense of Smell2.7. Vision2.7.1. Structure of the Eye2.7.2. Focusing Light on the Retina2.7.3. Converting Light to Action Potentials2.7.4. The Retina2.7.5. Phototransduction2.7.6. Receptive Fields2.8. Hearing and Equilibrium2.8.1. The Nature of Sound2.8.2. The Hearing Apparatus2.8.3. Sound Vibrations to Action Potentials2.8.4. The Sense of Balance and EquilibriumModule 3.0. Cardiovascular System3.1. Structure of the Heart3.1.1. Chambers and Circulation3.2. Cardiac Cell Action Potentials3.2.1. Action Potentials in Cardiac Muscle Cells3.2.2. Action Potentials in Cardiac Autorhythmic cells3.2.3. Cellular Mechanisms of Inotropy and Chronotropy3.3. Electrophysiology of Heart Muscle3.3.1. Heart Conduction System3.3.2. Electrocardiogram (ECG)3.3.3. Abnormal ECG - Current of Injury3.4. The Cardiac Cycle3.4.1. Cardiac cycle3.4.2. Cardiac Measurements and Pressure Volume Loops3.5. Blood vessels and Blood Pressure3.5.1. Arteries and Veins3.5.2. Capillaries3.5.3. Blood Pressure Regulation and Shock3.5.4. Capillary Exchange3.5.5. Myogenic and Paracrine Regulation of Vasoconstriction and Vasodilation3.6. Blood3.6.1. Composition of Blood3.6.2. Hematopoeisis3.6.3. Breaking Down Red Blood Cells3.6.4. HemostasisModule 4.0. Urinary and Respiratory Systems4.1. Function and Structure of the Kidney4.1.1. Urinary System Function4.1.2. Functional Anatomy of the Urinary System4.1.3. The Nephron: Functional Unit of the Kidney4.1.4. The Renal Corpuscle: Bowman's Capsule4.2. Physiology of Urine Production4.2.1. Filtration4.2.2. Renal Clearance4.2.3. Tubular Reabsorption4.2.4. Urine Concentration and Dilution4.2.5. Hormonal Regulation of Urine Production4.3. Acid/Base Balance4.3.1. Buffers4.3.2. Acid/Base Disturbances4.4. The Respiratory System4.4.1. Respiratory System Structure and Function4.4.2. Respiratory Membrane4.4.3. Respiratory pressures and Inspriation/Expiration4.4.4. Alveoli and Surfactant4.4.5. Pneumothorax4.4.6. Pressure-Volume Loops and the Work of Breathing4.5. Gas Exchange and Transport4.5.1. Gas Laws4.5.2. Partial Pressure Gradients in the Lung4.5.3. Alveolar Gas Equation4.5.4. Oxygen and Carbon Dioxide Transport in the Blood4.5.5. Alveolar Ventilation4.5.6. Ventilation/Perfusion Ratio4.6. Chronic Bronchitis and Emphysema4.6.1. Respiratory Control by the Medulla Oblongata4.6.2. Chemicals that Regulate VentilationModule 5.0. Digestive, Endocrine and Reproductive Systems5.1. Functional Anatomy of the Digestive System5.1.1. Layers of the Digestive Tract5.1.2. Enteric Nervous System5.1.3. Organs of the Digestive System5.2. Digestion5.2.1. Carbohydrates5.2.2. Proteins5.2.3. Lipids5.2.4. Lipoproteins5.3. Regulation of Digestive Secretions5.4. Endocrine System5.4.1. Overview of the Endocrine System5.4.2. Hormone Receptors5.4.3. Hormones of the Body5.4.4. Other Hormones: Melatonin and Pheromones5.5. The Hypothalamus and Pituitary Gland5.5.1. Structure and Function of the Hypothalamus and Pituitary Gland5.5.2. The Posterior Pituitary5.5.3. The Anterior Pituitary5.5.4. Growth Hormone5.5.5. Prolactin5.5.6. Thyroid Hormones5.5.7. Adrenal Hormones5.6. Pancreas5.6.1. Insulin and Glucagon5.6.2. Diabetes Mellitus5.7. Reproductive System Anatomy5.7.1. Female Reproductive Anatomy5.7.2. Male Reproductive Anatomy5.7.3. Sexual Development at Puberty5.7.4. Male Reproductive Endocrine Axis5.7.5. Spermatogenesis5.7.6. Female Reproductive System: Oogenesis5.7.7. Ovulation and Fertilization5.7.8. The Ovarian Cycle5.7.9. The Uterine Cycle5.7.10. PregnancyAppendix A. GenderAppendix B. The Placebo EffectB.2.1. The Placebo EffectB.2.2. Examples of the Placebo EffectB.2.3. How do Placebos Work?B.2.4. Are Placebos Ethical?B.2.5. How do we validate actual effectiveness of placebosB.2.6. Tips for evaluating scientific evidenceB.2.7. What about Faith Healings

Receptors of the ANS

Usually, a particular receptor subtype for each division of the ANS will dominate in a certain gland or organ. In general, activation of some receptor subtypes leads to stimulation of the effector and activation of others to inhibition of the effector. Even numbered subtypes are usually inhibitory and odd numbered subtypes are usually excitatory, but there are no hard and fast rules. Ultimately, the relative amounts of each receptor subtype expressed in the tissue will determine the overall effect (stimulation or inhibition) on the particular gland or organ. Similar to how neurons can be classified by the neurotransmitter they release, receptors can be classified by the type of neurotransmitter they receive. Cholinergic receptors receive acetylcholine and adrenergic receptors bind to catecholamines. This can get confusing at times because it is possible that a adrenergic neuron (one that releases norepinephrine) will have cholinergic receptors. This would be the case for most of the post ganglionic neurons in the sympathetic nervous system.

Cholinergic Receptors

As mentioned, preganglionic neurons of both sympathetic and parasympathetic divisions produce and release ACH. The receptors for ACH are known as cholinergic receptors. There are two main subtypes of cholinergic receptors; nicotinic and muscarinic. They are named after alkaloids found in tobacco and certain mushrooms respectively. The alkaloid nicotine specifically activates nicotinic cholinergic receptors, while muscarin activates muscarinic cholinergic receptors, and ACH activates both types. The cell bodies of postganglionic neurons for both sympathetic and parasympathetic nervous systems express nicotinic receptors (see figure above). To distinguish nicotinic receptors in neurons from nicotinic receptors found in the neuromuscular junction, we use the terms nicotinic (N1 or N2) cholinergic receptors. N1 are located in the neuromuscular junction and N2 are used in the ANS. Similar to the neuromuscular junction, stimulation of nicotinic type II (N2) channels results in the entry of Na+ which depolarizes the post synaptic neuron.

Muscarinic receptors (M) are located on cells of all parasympathetic effectors and on cells of some sweat glands innervated by the sympathetic nervous system. There are several subtypes of muscarinic receptors (M1-M5) which may be stimulatory (depolarization) or inhibitory (hyperpolarization)

Adrenergic Receptors

As mentioned, neurons that produce and release the neurotransmitter NE are known as adrenergic neurons. NE is secreted by postganglionic neurons of the sympathetic nervous system and binds to adrenergic receptors expressed on effector cells. Epinephrine (EPI) released by the adrenal gland also binds to adrenergic receptors expressed on effectors (see figure above). There are two main types of adrenergic receptors, namely, alpha and beta which have several subtypes. For our purposes, we will focus on the following five subtypes: alpha 1, 2, and beta 1, 2, and 3. Activation of adrenergic receptors expressed on effectors by NE or EPI may result in stimulation or inhibition of the effector depending on the tissue involved. Odd subtypes of adrenergic receptors (alpha 1, and beta 1, and 3) generally have stimulatory effects and even subtypes (alpha 2 and beta 2) have inhibitory effects. NE has a stronger affinity for alpha 1 receptors than EPI and EPI has a stronger affinity for Beta-2 receptors than NE. Below is a table that summarizes the receptor types and the second messenger system involved with stimulation of that receptor. 


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