1. Chapter 11
Muscular Tissue
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2. 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

3. Structure Macro to micro Epimysium Fascicles Muscle fibers (cells)
Wrapped by perimysium
Muscle fibers (cells)
Wrapped by endomysium
Myofibrils
Contractile element
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4. 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

5. The Sarcomere Functional unit Microfilaments Actin Myosin Troponin
Tropomyosin
Myosin
Heads contain two binding sites
Actin and ATPase
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6. Somatic Nervous System
Motor neurons supply skeletal muscle
Single neuron with cell bodies in ventral horn of spinal cord
Release acetylcholine
Only excitatory

7. 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
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8. Acetylcholinesterase
Enzyme that inactivate Ach
Ensures that muscles only contract when needed
Please look at chemicals and disease associated with the neuromuscular junction

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

10. 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

11. 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

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

13. Role of ATP
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14. Sliding Filament Mechanism

15. 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

16. 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

17. 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

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

19. 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

20. 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