Physiology Module: Action Potential and Muscle Contraction

Compiled Module: Guyton Special

• This module is a compilation of specifics from Guyton and Hall's Textbook of Medical Physiology, Twelfth Edition.

Action Potential and Sodium Channels

• The explosive development of an action potential begins at a threshold of -65 millivolts.
• Sodium channels have activation and inactivation gates.
• Sodium channels activate from -90 mV to +35 mV.
• Sodium channels inactivate from +35 mV to -90 mV, with a delay.
• Sodium channels will not reopen until the membrane potential returns to resting levels.
• Sodium channels play a role in nerve fiber repolarisation.

Neuromuscular Junction

• Acetylcholine is released from synaptic vesicles at the neural membrane of the neuromuscular junction.
• Acetylcholine receptors are located close to release sites on the muscle membrane.
• Acetylcholine activates voltage-gated sodium channels, initiating muscle contraction.

Muscle Contraction

• The "walk-along" mechanism describes muscle contraction.
• Myosin filaments move along actin filaments.
• The process is activated by calcium ions.
• Calcium release is triggered by the electrical signal (action potential).
• Intracellular calcium concentration increases for muscle contraction.

Cell Membrane

• The cell membrane, or plasma membrane, is a thin, pliable, elastic structure, about 7.5-10 nanometers thick.
• It consists mainly of proteins and lipids (55%, 25%, respectively).
• Other components include cholesterol (13%), other lipids (4%), and carbohydrates (3%).

Extracellular and Intracellular Fluid

• The composition of extracellular and intracellular fluids includes various ions (Na+, K+, Ca++, Mg++, Cl-, HCO3).
• Glucose, amino acids, phosphates, and cholesterol are also present in different concentrations.

Proopiomelanocortin (POMC)

• POMC is processed by enzymes, prohormone convertase 1 (PC1), and PC2.
• Different tissues express PC1 and PC2, producing varying peptides.
• Tissue-specific expression leads to the synthesis of hormones like ACTH, B-lipotropin, and MSH.

Feeding Regulation Neural Control

• Neurons in the arcuate nuclei regulate food intake; POMC neurons/α-MSH decrease feeding, and AGRP/NPY neurons increase feeding.
• Hormones like Leptin, Insulin, CCK, and Ghrelin influence feeding signals.

Membrane Potential and Smooth Muscle

• Slow waves, spikes, depolarization, and hyperpolarization are different potential states in intestinal smooth muscle.
• Different physiological conditions influence these states.

Salivary Gland and Formation

• The daily volume and pH of saliva, gastric secretions, pancreatic secretions, bile, and bowel secretions vary.

Active and Passive Transport

• Primary active transport depends on ATP or other high-energy phosphate compounds for energy.
• Secondary active transport uses energy stored due to ionic concentration differences established by primary active transport.

Mechanism of Activation of G Protein-Coupled Receptor

• Hormones activate receptors, triggering an exchange of GDP for GTP on the alpha subunit of the G protein.
• This leads to dissociation of the alpha subunit, activating a target protein (enzyme).
• Intracellular signals are initiated.

Body Temperature Regulation

• Maintaining body temperature involves mechanisms like vasoconstriction, piloerection, shivering and sweating.
• Hypothalamus plays a key role in body temperature control.

Glandular Cells

• Glandular cells are responsible for producing enzymes and other secretory substances.
• Secretion involves various organelles including mitochondria, ribosomes, and the endoplasmic reticulum.

Decompression Sickness

• Gas bubbles blocking blood vessels in tissues.
• Symptoms include pain in joints and muscles, dizziness, and in extreme cases, paralysis and death.
• Prolonged space missions can cause similar effects such as a decrease in blood volume, cardiac output, etc..

Glomerular Filtration Rate

• The glomerular filtration rate is affected by various substances in the blood plasma.
• Chronic renal failure can cause alterations in plasma levels.

Renal Tubule Fluid

• Levels of different substances in the renal tubules change relative to their plasma levels.
• Substances are either reabsorbed or secreted into the tubules.

Urine Formation

• Antidiuretic hormone (ADH) influences the concentration of urine.
• Urine is dilute or concentrated based on ADH levels

Cardiovascular System

• Baroreceptors and their innervation play roles in controlling arterial pressure.
• Signals are sent to the medulla for regulation.

Electrocardiograms

• Lead voltages sum to equal voltages in other leads.
• Bipolar electrocardiograms are recorded.

Arterial Pressure Pulses

• Patterns of aortic pressure pulses can indicate conditions including arteriosclerosis, aortic stenosis, patent ductus arteriosus, and aortic regurgitation.

Capillary Pressure

• Mean aortic pressure, capillary pressure, and right atrial pressure can change depending on cardiac output.
• Changes in these pressures can lead to conditions like peripheral edema.

Blood Flow through Lungs

• Blood flow occurs primarily through the bottom part of the lungs in a resting state.
• Blood flow increases in the top of the lungs during exercise.

Este quiz explora conceptos claves de la Fisiologia Medica, incluindo potencial de accion, canais de sodio e a uniao neuromuscular. Avalie seu conhecimento sobre como esses mecanismos funcionam e suas implicacoes na contracao muscular.