Chapter 11 Muscular Tissue ehow.com

Objectives Know the microanatomy of skeletal muscle and what a sarcomere is Understand the relationship between the somatic nervous system and muscle cells Understand how the sliding filament mechanism works Know how to interpret a myogram Know some characteristics of cardiac and smooth muscles

Structure Macro to micro Epimysium Fascicles Muscle fibers (cells) Wrapped by perimysium Muscle fibers (cells) Wrapped by endomysium Myofibrils Contractile element training.seer.cancer.gov faculty.etsu.edu

Microanatomy of Myofibril Dark band A band Light band I band H zone Z disc Sarcomere Titin Largest protein in body Stabilizes thick fillaments Gives muscle elasticity http://legacy.owensboro.kctcs.edu/gcaplan/anat/images/Image286.gif

The Sarcomere Functional unit Microfilaments Actin Myosin Troponin Tropomyosin Myosin Heads contain two binding sites Actin and ATPase scioly.org people.eku.edu

Somatic Nervous System Motor neurons supply skeletal muscle Single neuron with cell bodies in ventral horn of spinal cord Release acetylcholine Only excitatory

Neuromuscular Junction Junction of motor axon with a muscle cell Only one junction per muscle cell Motor end plate Specialized area on muscle cell for synapse High concentration of cholinergic receptors Open nonspecific ion channels Na+ rushes in producing an end-plate potential Action potential on muscle cell EPP opens ion channels in adjacent membrane Threshold is reached and an action potential propagates away from the motor end plate adinstruments.com

Acetylcholinesterase Enzyme that inactivate Ach Ensures that muscles only contract when needed Please look at chemicals and disease associated with the neuromuscular junction

Muscular Contraction What needs to happen in order for a muscular contraction to begin?

Sliding Filament Theory Proposed by Hugh Huxley in 1954 Mechanism by which sarcomeres contract Involves formation of cross-bridges between actin and myosin Thin filaments slide over thick filaments Greater overlap between filaments

Sliding Filament Mechanism Calcium released from sarcoplasmic reticulum Foot proteins stimulated by dihydropyridine receptors of T tubules Calcium binds to troponin Troponin–tropomysin complex shifts position Myosin binding site exposed Myosin heads form cross-bridges with actin Actin filaments pulled toward center of sarcomere

Calcium Initiates the Sliding Filament Mechanism (cont.) Figure 6.7

Role of ATP octc.kctcs.edu

Sliding Filament Mechanism http://youtu.be/WRxsOMenNQM

Muscle Relaxation Nerve activation ends, contraction ends Calcium pumped back into sarcoplasmic reticulum Ca2+ - ATPase pump Calcium removed from troponin Myosin-binding site covered No calcium = no cross-bridges

Energy Required for Muscle Activity Principle source of energy: ATP ATP replenished by variety of means: Creatine phosphate Stored glycogen Aerobic metabolism of glucose, fatty acids, and other high-energy molecules

Activity of Muscles Can Vary Isotonic contractions: muscle tension remains constant as muscle changes length Concentric – muscle shortens Eccentric – muscle stretched, but still contracting Isometric contractions: muscle prevented from shortening, tension develops at constant muscle length Degree of nerve activation influences force Terms to know: Motor unit Muscle tension All-or-none principle

Muscle Contraction: Myogram Latent period Contraction Relaxation Summation vs. tetanus

Types of Muscle Fibers Slow-twitch Fast-twitch Slow oxidative (type I) Red fibers Low myosin ATPase activity Slow twitch: endurance, long duration contraction : Jogging, swimming, biking Fast-oxidative (type IIa) Red fibers High myosin ATPase activity Intermediate Fast-glycolytic (typeIIb) White fibers Fast twitch: strength, white muscle, short duration contraction: Sprinting, weight lifting

Features of Cardiac and Smooth Muscles Activation of cardiac and smooth muscles: Involuntary Specialized adaptations in each Cardiac pacemaker cells Dense bodies Calcium binds to calmodulin Activates myosin light-chain kinase Speed and sustainability of contractions Arrangement of myosin and actin filaments