Lecture 8:
Muscle Tissue
Lecture
Lab: Muscles
Figures: Muscular System & Elbow
Terms for Muscular Quiz
Video Questions
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Chapter Questions: Muscular System
Crossword - Skeletal Muscles
Lab Slide: Muscles - Draw Neuromuscular Junction
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Students know the cellular and molecular basis of muscle contraction, including
the roles of actin, myosin, Ca+2, and ATP. |
I.
Introduction:
1. Motion is an essential body function resulting from contracting and relaxing of muscles. Muscles provide force. Bones act as levers.
2. Muscle tissue constitutes 40 to 50% of body weight.
3. Myology is the study of muscles.
II. Characteristics
1. Excitability: Ability of muscles to receive and respond to stimuli. Stimulus is a change in the internal or external environment. Stimulus must be strong enough to create an action potential - nerve impulse. Response is the body's reaction to a stimulus.
2. Contractility: Ability to shorten and thicken.
3. Extensibility: Ability to be stretched (extended). Many skeletal muscles are in opposing pairs: extensor/contractor.
4. Elasticity: Ability to return to original shape after contraction or extension.
III. Functions:
1. Motion: obvious- whole body walking, or grabbing. Less obvious - heart, stomach, intestines, urinary bladder.
2. Maintenance of Posture: Muscle tone.
3. Heat production: 85% of all body heat is generated by muscles.
IV. Types
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Skeletal |
Cardiac |
Smooth |
1. Skeletal: Striated, bandlike structures which are perpendicular to long axes of cells. Voluntary muscles - conscious control.
Cylindrical cells,
striated fibers with several peripheral nuclei.
Attached to
bones.
2. Cardiac: Heart, striated, involuntary
Quadrangular,
branching, striated with one central nucleus.
Bands are called intercalated
discs. This is a thickening of sarcolemma (cell
membrane) which separates cells and makes tissue strong.
3. Smooth Muscle: Involved in processes of homeostasis. Involuntary
Spindle shaped,
non-striated, one central nucleus.
Located in walls
of hollow internal structures, such as, blood vessels, stomach, intestines.
V. Skeletal Muscle Tissue
A. Connective Tissue
1. Facia: Sheet or broad band of fibrous connective tissue. Located beneath skin or around muscles and organs of body.
2. Superficial Facia (subcutaneous layer of skin) Composed of adipose and loose connective tissue. Functions:
Storehouse of
water and fat: is location of fat in overweight people.
Layer of
insulation against heat loss.
Mechanical
protection from blows.
Pathway for
nerves and blood vessels.
3. Deep Fascia: Dense connective tissue lines body wall and extremities and holds muscles together. Separates them into functioning groups. Allows free movement of muscles, carries nerves and blood and lymph vessels, provides origin for muscles.
4. Deep Fascia is subdivided into groups, which separate muscles into functioning groups. All are extensions of deep fascia and contain collagenous fibers.
Epimysium--
surrounds entire muscle.
Perimysium -envagination of epimysium, which surrounds fascicles or fasciculi.
Endomysium- further envaginations,
which surrounds and separates muscle fibers (muscle cells or myofibers).
5. All three extend beyond muscle to form tendon. Tendon attaches to periosteum of bone.
6. Certain tendons, especially wrist and ankle are enclosed by tubes of fibrous tissue. The inner layer is visceral layer-attached to tendon. Parietal layer is outer layer. Between is synovial fluid. Allows tendons to slide smoothly.
7. Tendonitis or tenosynovitisis inflammation of tendon sheath and synovial membrane around joints (wrists, shoulders, and elbows-tennis elbow). Causes pain and swelling.
VI. Nerve and Blood Supply
1. Innervation and vascularization are directly related to contraction.
2. An artery and one or two veins accompany each nerve that penetrates a skeletal muscle.
3. Capillaries branch through the edomysium. Each muscle fiber is in contact with one or two capillaries.
4. Each skeletal muscle fiber makes contact with a nerve's synaptic end bulb.
VII. Histology
1. Muscle fibers, myofibers-lie parallel and are 10-100um in diameter. Some as long as 30cm. Each muscle has 1000's cells.
2. Sarcolemma - plasma membrane
3. Sarcoplasm - cytoplasm
4. Multinucleated - peripheral
5. Within sarcoplasm are smaller fibers called myofibrils - 1-2um in diameter (100's to 1000's in myofiber)
6. Myofibrils are further divided or composed of myofiliments: thick and thin.
7. Myofilaments do not extend length of fiber and are arranged in compartments called sarcomeres (z line to z line)
8. Sarcoplasmic reticulum - endoplasmic reticulum
9. Transverse tubules (T tubes) run perpendicular to and extend from reticulum to outside.
10. Triad - a transverse tubule and segments of sarcoplasmic reticulum on either side.
11. Myofilaments are arranged in compartments called sarcomeres.
12. A band - anisotropic band. Length of thick myofilament. Darkness is from overlapping of thin and thick myofilaments. (changes with contractions).
13. I band - Isotropic band is less dense and is thin myofilaments, only.
14. Alternating of dark A and light I gives striations.
15. H zone is thick myofilaments, only.
16. Actin - protein in thin myofilaments.
16. Myosin - protein in thick myofilaments.
17. M line in center of H zone, series of thin threads which attach to and line up thick filaments.
18. Z lines anchor thin myofilaments, which project in both directions.
19. Cross bridges extend out from thick filaments like paddles.
VIII. Muscle Contraction - sliding filament theory.
1. Myosin cross bridges pull on thin myofliaments, causing them to slide inward to H zone.
2. Sarcomere shortens.
3. Myofilaments do not change size.
4. H zone thins out and may disappear. Thin filaments may overlap. (Show animation on Body Works).
5. Z line drawn towards each other and sarcomere is shortened.
IX. Neuromuscluar junction.
1. Motor neuron activates muscle.
2. May be 3 ft long.
3. Axon of neuron branches into telondendria which contact sarcolemma.
4. Neuromuscular junction is axon terminal with portion of sarcolemma. See Figure10-6.
5. At end of terminal is synaptic end bulb which store neurotransmitters such as acetylcholine. Passes impulse to muscle, nerve, or gland.
6. After impulse, acetylcholinesterase decomposes acetylcholine.
X. Physiology of Contraction
1. Ca++ ions are stored in sarcoplasmic reticulum.
2. ATP in relaxed muscle fiber is high.
3. ATP is attached to cross bridges.
4. Impulse reaches axon terminal. Ach is secreted and crosses cleft to sarcolemma.
5. Ach causes change in sarcolemma. Impulse spreads across it and into transverse tubules.
6. Ca++ is released into surrounding myofilamnets.
7. Attaches to spots on myosin. ATP is release from ATP binding sites. Head of Myosin cross bridge is exposed and a "power stroke" results, pulling myosin along actin fibers.
Result is contraction.