Chapter 10 Muscle Tissue and Organization
I. Characteristics of skeletal muscle tissue

1. Produce skeletal movement: pull on tendons, which move bone
2. Maintain posture and body position
3. Support soft tissue
4. Guard entrances and exits
5. Maintain body temperature
6. Store nutrient reserves- contractile proteins broken down, amino acids can be used by the liver to synthesize glucose

II. Connective tissue components Fig.10.1

1. Epimysium- outer layer of dense layer of collagen fibers, connected to the deep fascia
2. Perimysium- divides the skeletal muscle into compartments
a. Fascicle-contain a bundle of muscle fibers
b. Contains blood vessels and nerves to maintain blood flow and innervates the muscle fibers
3. Endomysium- surrounds the individual muscle fibers
Contains:
a. Capillary network that supply blood to the muscle fiber
b. Satellite cells- embryonic stem cells that function in repair of damaged muscle tissue
c. Nerve fibers that control the muscle

III. Muscle attachments Fig.10.2

A. Tendon (Aponeurosis) – collagen fibers of the epimysium, perimysium, and endomysium come together (attach muscle to bone)
B. Origin
C. Insertion

IV. Anatomy of Skeletal muscle Fig.10.3

A. Sarcolemma: cell membrane of muscle fiber surrounds the sarcoplasm
Transverse tubules: pathway for electrical currents to pass through, these impulses are called action potentials

B. Sarcoplasmic reticulum- forms a tubular network around each individual myofibril

C. Terminal cristernae- tubules of SR enlarge, fuse, and form expanded chambers
a. Calcium actively transported into the terminal cristae of SR

D. Myoblasts: groups of embryonic cells fuse forming individual multinucleated skeletal muscle fibers Fig.10.4
b. Unfused myoblasts remain in skeletal muscle tissue as satellite cells

E. Myofibrils: branches of transverse tubules, consists of bundles of protein filaments called myofilaments

V. Sliding Filament Theory

Thin filaments- composed of actin
Thick filaments- composed of myosin

A. Structures Fig.10.6

1. A-bands: dark bands, thick filaments are located here
2. M-line: dark staining proteins help stabilize the position of the thick filaments
3. H-zone: lighter region on either side of the M-line, contains only thick filaments
4. Zone of overlap- 1 thin filament surrounded by three thick filaments, and 1 thick filament surrounded by 6 thin filaments
5. I-bands: contains thin filaments, but no thick filaments, extends from the 6. A-band of 1 sarcomere to the A-band of the next sarcomere
7. Z-lines: Mark the boundary between adjacent sarcomeres
a. Consists of proteins called actinins
b. Titin: Elastic protein extended from the tips of thick filaments to attached sites at the Z-lines

B. Thin Filaments: contains 4 proteins Fig.10.5
1. F actin, nebulin, tropomyosin, and troponin
F actin: twisted strand composed of 2 rows of 300-400 globular molecules of G actin
2. A long strand of nebulin extends along the F actin strand in the cleft between rows of G actin
3. Each G actin molecule contains an active site that can bind to myosin

C. Sarcomere: organized functional myofilaments Fig.10.6
1. 1 myofibril consist of 10, 000 sarcomere, smallest functional units of 2. Muscle fiber contain
1. Thick filament
2. Thin filaments
3. Proteins that stabilize the positions of the thick and thin filaments
4. Proteins that regulate the interactions between thick and thin filaments

D. Sliding filament theory changes with contraction Fig.10.7
1. H zones and I bands get smaller
2. Zones of overlap get larger
3. Z lines move closer together
4. Width of the A band remains constant

VI. Contraction of Skeletal muscle fibers
Steps 1-2 fig.10.9
A. Nueromuscular junction: Intercellular connection where communication between the nervous system and a skeletal muscle fiber occurs Fig.10.8

a. Synaptic Terminal: cytoplasm contains mitochondria and vesicles filled with acetylcholine (neurotransmitter, chemical released by a neuron to change the permeability of another cell membrane)
b. Synaptic cleft: separates the synaptic terminal of the neuron from the opposing sarcolemma surface (motor end plate- contains membrane receptors that bind ACH)
c. Acytlcholinesterase: found in the synaptic cleft and the sarcolemma, breaks down ACH

Steps 1-2 fig.10.9
B. Neuron stimulates muscle fiber: Fig.10.9

1. Arrival of the action potential: electrical stimulus triggers the release of ACH at the synaptic terminal
2. Release of the ACH: exocytosis of Ach into the synaptic cleft
3. ACH binding at the motor end plate: ACH diffuse across synaptic cleft and bind to ACH receptors on the surface of the sarcolemma at the motor end plate. This increases the membrane permeability to sodium ions
4. Appearance of an action potential in the sarcolemma: Sodium influx generates action potential in the sarcolemma
5. Return to initial state: ACH broken down by ACHE

Steps 3-4 fig.10.9
C. Excitation-contraction coupling: link between the generation of an action potential in the sarcolemma and the start of muscle contraction

1. Action potential triggers the release of Ca2+from the cisternae of the SR
2. Troponin keeps active sites inaccessible
3. Troponin has a binding site for calcium; the site is empty when the muscle fiber is at rest
4. Calcium binding weakens the bond between troponin and actin
5. Troponin molecule changes position rolling the tropomyosin strand away from the active sites

Step 4 10.9
D. Contraction cycle

1. Exposure of the active site
2. Formation of cross-bridges: active sites exposed and myosin heads bind to them forming cross-bridges
3. Pivoting of Myosin heads: Myosin head is cocked pointing toward the M-line (energy is obtained from the breaking down of ATP into ADP and a phosphate group)
a. Power stroke: myosin head pivots toward the M-line, ADP and phosphate group are released
4. Detachment of cross-bridge: ATP binds to the myosin head breaking the bond and exposing the active site
5. Reactivation of the Myosin: Free myosin head splits the ATP into the ADP and a phosphate group

Contraction depends on:
1. Duration of stimulation at the neuromuscular junction
2. Presence of free calcium ions in the sarcoplasm
3. Availability of ATP

E. Motor unit: All muscle fibers controlled by a single motor neuron Fig.10.10
I.E. Eye- motor neuron controls 4-6 muscle fibers
Leg- motor neuron controls 1000-2000 muscle fibers

a. Muscle tone: resting tension in a skeletal muscle helps stabilize the positions of bone and joints
b. Isotonic contractions
1. Concentric contractions
2. Eccentric contractions- can exert precise control over the amount of tension produced

c. Isometric contractions: Muscle does not change length tension produced never exceeds the resistance

VII. Types of Skeletal muscle fibers

A. Types Table 10.4

1. Slow fibers: More extensive network of capillaries and high oxygen supply to support mitochondrial activity (Type I fibers)
a. Myoglobin: bind oxygen molecules

2. Intermediate fibers

3. Fast fibers: densely packed myofibrils, large glycogen reserves, and few mitochondria, produce powerful contractions (Type II-B)

4. Fibers and muscle fatigue:
1. Depletion of metabolic reserves within muscle fibers
2. Damage to SR and Sarcolemma
3. Decrease in PH= decrease calcium binding to troponin
4. Low PH and pain in brain

B. Skeletal Muscle fiber organization Table 10.5
1. Circular
2. Parallel
3. Convergent
4. Pennate
a. unipennate
b. bipennate
c. multipennate
C. Exercise and Skeletal muscle
1. Muscle atrophy
2. Muscle hypertrophy

D. Classes of levers Fig.10.13
1. First class levers
2. Second class levers
3. Third class levers
E. Actions of Skeletal Muscles
1. Agonist
2. Antagonist
3. Synergist

VIII. Cardiac Muscle tissue Fig.10.15
A. Cardiac muscle cells include:
1. Has a single centrally placed nucleus
2. T tubules are short and broad and encircle the sarcomeres at the Z lines rather than the zone of overlap
3. SR lacks terminal cisternae and its tubules contact the cell membrane as well as the T-tubules
4. Dependent on aerobic metabolism
5. Intercalated discs: cell membranes of 2 adjacent cardiac muscle cells are intertwined and bound together by gap junctions and desmosomes, creates a direct electrical connection between the 2 cardiac cells

B. Functional characteristics of cardiac muscle tissue:
a. Pacemaker cells: determines the timing of contractions, contract without nueral stimulation
b. Contractions last 10 times as long as skeletal, do not fatigue
c. Cardiac muscle tissue cannot produce titanic contractions
Effects of aging on skeletal muscle