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Contraction and Rigor Mortis

Contraction and Rigor Mortis - Contraction and Rigor Mortis...

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Unformatted text preview: Contraction and Rigor Mortis Contraction Sensory Neurons • Afferent fibers – Gathers external information. – Sends information to the “center” • Efferent neurons – Carries nerve impulses to the “effectors” – When connected to muscle- a “motor When unit” unit” – Each muscle fiber has one Impulse Transmission • Every skeletal muscle fiber is innervated Every by a terminal branch of a motor axon. motor • Total time 0.5 – 1 millisecond • Neuromuscular Juncture- at sarcolemma Impulse Transmission • Action potential reaches the axon Action terminal causing acetylcholine (ACH) release. (ACH) Impulse Transmission • Acetylcholine binds receptors on the Acetylcholine sarcolemma. sarcolemma. • Begins depolarization of muscle fiber • Acetylcholinesterase breaks down Acetylcholinesterase ACH preventing further stimulation. ACH Wave of Depolarization Transverse Tubules (T-tubules) Originate from sarcolemma Sarcoplasmic Reticulum (SR) (SR) Where Ca is Where stored & released from released ATPase Cycle of Myosin ATPase Cycle of Myosin S1 tightly binds ATP & myosin dissociates from G-actin ATPase Cycle of Myosin ATP hydrolysis (ADP•Pi); myosin head “cocks” Mg serves as a cofactor ATPase Cycle of Myosin Non-force generating, weak bond Ca binds Troponin-C exposing myosin binding site ATPase Cycle of Myosin Pi release generates power stroke ATPase Cycle of Myosin Release of ADP from Actin-Myosin forms strong rigor bond Actin Myosin Crossbridge www.sci.sdsu.edu/movies/actin_myosin.html Rigor Mortis • General – There is an alteration of muscle’s biochemical and physical properties. – This improves the keeping quality and acceptability of the subsequent food product. At physiological death… • Cessation of blood circulation – Cessation of oxidative phosphorylation – Cannot clear waste products of metabolism • Energy derived from muscle stores – ATP & CP – Glycogen → glucose – Use energy available at the time circulation stopped Biochemical • Energy (fuel) – Dietary fat – Dietary carbohydrate • high concentrate ration • Converting muscle to meat depends on synthesis, degradation, & availability of high-energy phosphate compounds – ATP & ADP/ CP Biochemical • ATP is necessary for muscles to contract. • ATP can be produced from carbohydrate. – Glucose – Stored in muscle as glycogen • Two pathways of muscle glucose metabolism – Aerobic (oxygen present) – Anaerobic (oxygen absent) • Lactic acid accumulation Biochemical Liver Liver Blood Glucose Muscle Glycogen Pi + ADP Glycogenol ysis & ysis ATP glycolysis glycolysis Biochemical Liver Liver Blood Glucose Muscle Glycogen Pi + ADP Glycogenol ysis & ysis ATP glycolysis glycolysis Lactate Biochemical Liver Liver Blood Glucose Muscle Glycogen Pi + ADP Glycogenol Lactate Lactate & ysis ysis Lactate ATP Lactate glycolysis glycolysis Lactate Lactate Biochemical Liver Liver Blood Glucose Muscle Glycogen Pi + ADP Glycogenol Lactate Lactate & ysis ysis ATP Lactate Lactate Lactate glycolysis Lactate Lactate glycolysis Lactate Lactate Lactate Lactate Lactate Pi + ADP Biochemical Liver Liver Blood Glucose Muscle Glycogen Pi + ADP Glycogenol ysis & ysis ATP glycolysis glycolysis Lactate Lactate Biochemical Liver Liver Glucose Blood Glucose Muscle Glycogen gluconeogen esis Lactate Pi + ADP Glycogenol ysis & ysis ATP glycolysis glycolysis Lactate Biochemical Liver Liver Glucose Blood Glucose Muscle Glycogen ADP+GDP +Pi gluconeogen esis ATP+GTP Lactate Pi + ADP Glycogenol ysis & ysis ATP glycolysis glycolysis Lactate Biochemical Liver Liver Blood Glucose Muscle Glycogen Pi + ADP Glycogenol Lactate Lactate & ysis ysis ATP Lactate Lactate Lactate glycolysis Lactate Lactate glycolysis Lactate Lactate Lactate Lactate Lactate Pi + ADP ⇓ Intramuscular pH Intramuscular Biochemical • Anaerobic metabolism continues postmortem – Glycogen → glucose → lactic acid – ATP produced from anaerobic glycolysis & ADP/ CP Biochemical • Muscle pH decline (most important for conversion of muscle to meat) – Glycogen → glucose → lactic acid continues lowering pH until glycogen and (or) ATP are depleted OR contractile proteins cease to function Molecular Calcium • In living muscle, regulates contraction. Sarcoplasmic Reticulum (SR) (SR) Structural • Influence on meat tenderness – Resolution of rigor ...
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