structure and function of muscle ansc 3404 objectives: study the structures of muscle and the...
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Structure and Function of Muscle
ANSC 3404
Objectives: Study the structures of muscle and the mechanism of muscle contraction.
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SKELETAL SMOOTH CARDIAC
METHOD OF CONTROL VOLUNTARY INVOLUNTARY INVOLUNTARY
BANDING PATTERN STRIATED NON-STRIATED STRIATED
NUCLEI/CELL MULTI SINGLE SINGLE
Muscle Types
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Cardiac Muscle
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Smooth Muscle
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Skeletal Muscle
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Muscle Cross Sections Showing Bundles of Myofibers
FAT CELL
BLOOD VESSEL
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Cross Section of Muscle Fibers
NUCLEI
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Myofiber
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Red and White Fibers in Muscle
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Fiber types
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The Blood Supply for Myofibers
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Connective Tissues
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Position of Mysiums in Muscle
ENDO = within PERI = aroundEPI = upon
Endomysium
Perimysium
Epimysium
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• Endomysium from muscle not aged
• Endomysium after cooler aging (28 D At 4oC)
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The Sarcoplasmic Reticulum
• Sarcoplasmic reticulum – T-tubule
• Calcium Storage
• Required for contraction
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Structure of Muscle
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Structure of Muscle (Cont)
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Sarcomere• Functional unit of a muscle
• Runs from z-line to z-line– Actin– Myosin
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Myosin Filament
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Actin Filament
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Muscle Structure
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Critical Contractile Proteins
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REVIEW
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Fat Structures
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ADIPOSE TISSUE
BLOOD VESSEL
ADIPOCYTE
ADIPOCYTES
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Fat Layers and Depots
I.F. = Inter-fasicular or intramucular (marbling)
I.M. = Intermuscular (seam fat)
PR. = Perinephric or Peri-renal (fat around the kidneys)
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FAT CELLS
Adipoblasts develop at widely varying rates in different parts of the body.
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Adipogenesis
• Adipoblasts– 20 microns in diameter
• Adipocytes– 120 micron in diameter– 300 micron in obese
• Cellular make-up– 95% of cytoplasm is lipid– Remainder primarily nucleus
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ADIPOCYTE
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HOW ARE ADIPOCYTES FORMED?
ONCE RECRUITED & FILLED, AN ADIPOCYTE IS EASIER TO FILL
AGAIN THAN IF NOT FILLED BEFORE
Adipose cells begin to accumulate
When filled with lipid, it is a mature adipocyte
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Muscle Contraction
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Introduction
• Overall structure of muscle is designed for contraction and relaxation, which leads to movement and locomotion.
• The ability to contract and relax is lost during the transformation of muscle to meat.
• Events surrounding this conversion greatly impact meat palatability
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Introduction
• The biochemical processes that provide energy to the living muscle cause the accumulation of metabolites during harvest– Affects color, WHC, pH, others
• An understanding of muscle contraction is necessary to understand these processes
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Contraction
• Begins with stimuli that arrive at the surface of the muscle fiber at the sarcolemma
• Nerve impulse starts in the brain and is transmitted via nerves to the muscle
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Transmembrane Potentials
• Under resting conditions, an electric potential exists between the inside and outside of the cell– Fluids inside are negative– Fluids outside are positive– Results in a resting membrane potential
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Transmembrane Potentials
• Extracellular – Na+ and Cl-• Intracellular – K+ and A-• Na+ and K+ gradient maintained by a sodium-
potassium pump.
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Action Potential
• Transmits electric impulse to muscle• Travels along the membrane surface of the nerve
fiber by depolarization– Initiated by a dramatic increase in the permeability of
Na+– Na+ rushes into cell to establish equilibrium;
however K+ stays in cell causing a change in the net charge inside the cell to positive• Lasts only a millisecond (0.5 to 1 millisecond) before the
permeability to Na+ is changed to resting state
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Myoneural Junction
• Action potential is not strong enough to elicit a response alone
• Uses a chemical transmitter called acetylcholine to be released.– Acetylcholinesterase is quickly released to
neutralize the acetylcholine
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Muscle Action Potentials
• Same as the action potential for nerve fibers• Communicated to the inner muscle cell via the
T-tubule system– Action potential transverse a muscle fiber via the t-
tubules and are ultimately responsible for the release of calcium from the SR
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Sarcomere - Basic contractile unit of the muscle
1. Myosin
2. Actina) Tropomyosin
b) Troponin
3. Z lines
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Elements required for muscle contraction and relaxation
1. Acetylcholine and Acetylcholinesterase
2. Calcium
3. Adenosine 5'-triphosphate (ATP)a) Derived from aerobic and anaerobic
metabolism
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Sources of Energy for Muscle Contraction and Relaxation
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Energy
• Aerobic– Glycolysis– TCA cycle– Electron transport chain
• Anerobic– Excess Hydrogen is used to reduce pyruvic
acid to lactic acid, which permits glycolysis to proceed at a rapid rate
– Easily fatigued
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Contraction Phase1. Nerve pulse/impulse transmitted through
action potential
2. Acetylcholine is released at neural juncture
3. Action potential transmitted to muscle fiber via the T-tubles to the sarcoplasmic reticulum
(SR)
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Contraction phase4. Calcium is released from SR into
sarcoplasm
5. Calcium binds to troponin
6. ATP is hydrolyzed (burned)
7. Energy causes a shift in tropomyosin and actin binding site is exposed
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Contraction phase8. Actin-myosin cross bridge forms (cross
bridge is termed actomyosin)
9. ATP hydrolyzed
10. Myosin head rotates
11. Repeated over and over; filaments slide causing shortening of sarcomere
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Contraction
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A sarcomere contracting
Notice that neither filament changes length
ACTIN MYOSIN
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http://www.unmc.edu/Physiology/Mann/mann14.htmlhttp://www.blackwellpublishing.com/matthews/myosin.htmlhttp://entochem.tamu.edu/musclestruccontractswf/index.html
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Relaxation phase1. Acetylcholinesterase is released (neutralizes
acetylcholine)
2. Calcium pump activated by SR to sequester calcium
3. Actin-myosin cross bridge terminated
4. Tropomyosin shifts covering the binding site
on actin
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Relaxation phase
5. Passive sliding of filaments
6. Sarcomere returns to resting state
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Be Able To:
• Draw a sarcomere showing:
Myosin
Actin
Z Line
A Band
I Band
H Zone
M Line
• Explain how a muscle contracts and relaxes– starting with a nerve impulse and including the SR role
• Explain the role of ATP in muscle contraction and relaxation•(See p.889-900 In The Meat We Eat)