lecture 6.dr hameed alsarraf
DESCRIPTION
skeleton musleTRANSCRIPT
![Page 1: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/1.jpg)
• Structure and action of skeletal muscle
• Mechanisms of contraction
• Neural control of skeletal muscle contraction
• Cardiac and smooth muscle
CHAPTER 12
![Page 2: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/2.jpg)
Types of Muscle in the BodyMuscle is involved in all movements of parts of our body. Muscle create movements by converting chemical energy to mechanical energy.
- Skeletal muscle:muscle mainly attached to the skeleton and used for movement.
“muscle of locomotion and exercise”
- Smooth muscle:muscle mainly lining internal organs of the body, such as blood vessels, gut, urinary bladder, etc.
“muscle of regulatory movements, closure & opening, constriction & dilation”
- Cardiac muscle:muscle of the heart. Its contraction and relaxation causes pumping action of the heart.
![Page 3: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/3.jpg)
Types of Muscle in the Body
Skeletal Cardiac Smooth
![Page 4: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/4.jpg)
Skeletal Muscle Movements
![Page 5: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/5.jpg)
Skeletal Muscle Structure
![Page 6: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/6.jpg)
Skeletal Muscle Structure- A single muscle cell is called muscle fiber.- Each muscle fiber contains several hundreds to several thousands of structures called
myofibrils. - Diameter of a muscle fiber ranges from 10-80 m, but the length may extend the entire
length of the muscle (e.g the thigh muscle fiber is about 35 cm long).- Plasma membrane of muscle fiber is called sarcolemma.- Each muscle fiber is ultimately attached to a bone via a hard connective tissue called
tendon.- Cytoplasm of muscle fiber is called sarcoplsam.- The endoplasmic reticulum is called sarcoplasmic reticulum (storage site for calcium).- Transverse tubules are structures that:
- pass laterally through the muscle fiber,- Transmit nerve signals closer to individual myofibrils,- Provide access of oxygen and glucose to inner parts of muscle fiber.
![Page 7: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/7.jpg)
Skeletal Muscle
Structure
![Page 8: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/8.jpg)
Skeletal Muscle Contraction
• Contraction (shortening in length) of a muscle fiber is due to sliding of thick and thin filaments against each other at opposite directions. This is called sliding filament theory.
• The size of filament remains the same but they slide against each other resulting in shortening of sarcomere.
• The sliding occurs by formation of cross bridges between the filaments.
• During the shortening of the sarcomere the A band remain the same length while the H and I bands shorten causing the Z discs to come closer to each other.
![Page 9: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/9.jpg)
![Page 10: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/10.jpg)
Actin
![Page 11: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/11.jpg)
Molecular Basis of Contraction
![Page 12: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/12.jpg)
Molecular Basis of Contraction
![Page 13: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/13.jpg)
Molecular Basis of Contraction
![Page 14: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/14.jpg)
Excitation-Contraction Coupling• When a nerve impulse is received by a muscle fiber this leads to its contraction.
The sequences which lead to contraction are as follow:
1- Nerve impulse causes the release of Ach from axon terminal into the neuromuscular junction.
2- The ACh binds with a receptor on the muscle fiber and generates action potential on the muscle fiber.
3- The action potential spreads over the sarcolemma as well as the T tubuls.
4- Depolarization of the T tubuls cause release of calcium from the sarcoplasmic reticulum into the sarcoplasm.
5- Calcium binds to troponin which leads to muscle contraction.
As long as the level of calcium in sarcoplasm is above 1 M the contractionwill continue. For the contraction to stop (relaxation) the calcium in the
Sarcoplasm is actively removed back into sarcoplasmic reticulum and storedthere for next contraction.
![Page 15: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/15.jpg)
Excitation-Contraction Coupling
![Page 16: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/16.jpg)
Motor Unit
Each somatic motor neuron with all its musclefibers that it innervates is called motor unit.
![Page 17: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/17.jpg)
Properties of Skeletal Muscle• Skeletal muscle can be studied in vitro: e.g Gastronemius muscle of frog.• This muscle can be stimulated with electric shock and contraction can be recorded by force transducer. Using this preparation, the followings can be studied:
• Muscle twitch : applying a single electric shock causes the muscle to contract and relax.
• Summation : if a second electric shock immediately follows the first, another muscle twitch will be produced which will ride on the first one.
• Tetanus : high frequency stimulation of the muscle causes continuous contractions which fuse together.
• Series-Elastic Component : connective tissue and tendons show elasticity (resist distension). This helps in muscle relaxation.
![Page 18: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/18.jpg)
![Page 19: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/19.jpg)
Types of Skeletal Muscle ContractionsIsotonic contraction:a type of contraction that results in muscle shortening. In this type of contraction the tension on the muscle fibers remain constant.
iso = same, tonic = strength
Isometric contraction:
when a muscle remains the same length
during contraction while the tension
changes.
iso = same, metric = length
![Page 20: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/20.jpg)
Smooth Muscle
• The arrangement of the actin and myosin filaments is different. Therefore showing no striation.
• Fibers are smaller than skeletal muscle fibers.
• Same chemical substances (actin and myosin) cause contraction. Sliding filament mechanism applies here.
• Smooth muscle has slower rate of contraction and relaxation than skeletal and cardiac muscle.
• Less energy is required for smooth muscle contractions.
• Smooth muscle can contract without action potential, using local factors.
• Level of cytoplasmic Ca++ is crucial for contraction, however the Ca ++ mainly comes from outside the cell (has less developed SR).
![Page 21: Lecture 6.dr hameed alsarraf](https://reader035.vdocuments.net/reader035/viewer/2022062404/55493eccb4c905144d8b508b/html5/thumbnails/21.jpg)
Cardiac Muscle
• Like skeletal muscle the cardiac muscle is striated.
• Is contracted by the sliding filament mechanism.
• Unlike skeletal muscle, the cardiac muscle cells are interconnected by gap junctions.
• The cells are joined electrically, this is called myocardium (single functional unit).
• Contractility (ability to contract) is increased by epinephrine and stretch.
• Can produce action potential automatically.