Muscles and Muscle Tissue

Muscular Tissue

1. Characteristics1. Excitability: tissue is able to respond to a

stimulus2. Extensibility: tissue is able to be stretched3. Elasticity: tissue is able to return to normal

after stretching.4. Contractibility: tissue is able to shorten and

thicken

2. Functions:1. Motion- both reflex and voluntary2. Maintenance of posture and organ volume3. Thermogenesis- heat production4. Joint Stability- allows for motion and

maintenance of posture.

Muscle Fiber Types

3 Types of Muscle- 1. Smooth2. Cardiac3. Skeletal/Striated

Skeletal Muscle

1. Fascia: sheets or broad bands of fibrous connective tissue located beneath skin or around muscle or body organs.

1. Categories of Fascia:1. Superficial Fascia-

Structure: contains adipose, blood vessels, nervesFunctions: stores fat, provides insulation, protects from injury

1. Categories of Fascia (cont):2. Deep Fascia: no fat

1. Surrounds muscle groups and divides muscle groups (allows individual and independent movement)

2. Arrangement:1. Endomysium: fascia which surrounds each muscle

fiber

2. Perimysium: fascia which surrounds a bundle of muscle fibers (fascicle)

3. Epimysium: connective tissue which wraps the entire muscle

Muscle Attachments

1. Direct (Fleshy) attachments- perimysium is fused to peristeum of bone

2. Indirect attachment- the muscle fascia extends beyond the muscle and attaches as a rope-like tendon or aponeurosis.

- Muscles are anchored to one another

Arrangement of Fascicles:

1. Parallel- run with the longitudinal axis of the muscle

1. Strap like- belly is uniform

2. Fusiform- belly is enlarged

Arrangement of Fascicles2. Pennate-

arranged obliquely to the boneA. Unipennate- one sideB. Bipennate- both sides

3. Convergentbroad at origin, narrows to a single tendon.

4. Circular- (sphincter)control diameter of an opening eye squinting, lip puckering

Muscle Cell Structure

• 1. Sarcolema- plasma membrane surface– Sarcoplasm: cytoplasm and glycogen

• 20 or more nuclei– Proteins: myoglobin- binds oxygen (red

protein)– Usual organelles: (mitochondria)– Sarcoplasmic Reticulum: run parallel with

myofibrils, densly packed

• Myofibrils: protiens– A. Myosin: thick filaments

• 2 globular heads– B. Actin: thin filaments

• Active sights where globular heads of myosin attach– C. Tropomyosin: rod shaped spirals around actin,

stiffens– D. Troponin: 3 polypeptides

• T-Tubules- extensions of sarcolema that extend up into the sarcoplasm. – Conducts nerve impulses deep into muscle cells– Transports and regulates glucose, oxygen, calcium

Arrangement of Myofibrils

• Sarcomere: functional unit of muscle

Sliding Filament Theory1. Nerve impulse stimulates muscles. T-tubules release

Calcium ion. Contraction is triggered.2. Cross-bridge attachment-

globular heads of myosin attach to active sites on actin.

3. Power stroke- as myosin binds and pivots:high energy to low energyactin slides over to the center of the sarcomere

4. Cross bridge detachment: requires ATP5. Cocking of Myosin Heads: (rearmed)* Rigomortis: peaks at 12 hours

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter42/animations.html#

All or None Phenomenon

• When stimulated a muscle fiber contracts to its fullest capacity

Neuromuscular Junction:

• Area where axonal end of a neruon fomrs a synaptic cleft with a muscle fiber.

• Acetylcholine- neurotransmitter diffueses across the synaptic cleft and binds to receptors on the sarcolema, then destroyed by cholinesterase.

• 1 impusle causes 1 contraction

• Muscle Tone-– Partial contraction of a muscle fiber due to use

• Awake- highest• Asleep- lower• unconscious- absent

– Twitch: single muscle contraction (1/10 of a contraction)

- Tetanus- prolonged muscle contraction required to do work.

- Myogram- record of a muscle contraction

Muscle contraction

• Isotonic contraction: muscle shortens, movement occurs.

• Isometric contraction: muscle tenses but does not shorten

Muscle fiber types

1. Type I (red, slow twitch) postural muscles long distance

- Large amounts of myoglobin- Many mitochondria- Many blood capillaries- Very good at generating ATP- Split ATP slowly – very resistant to fatigue

2. Type II A- intermediate, fast twitch fast oxidative- very large amounts of myoglobin- many mitochondria- very large supply of blood capillaries- split ATP very rapidly- very quick contraction velocity- less resistant to fatigue

(sprinters, arms)

3. Type II B- white fast twitch, fast glycolytic- low myoglobin content- few mitochondria- few capillaries- large amounts of glycogen- geared for anaerobic respiration- split ATP rapidly- very little resistance to fatigue

• Oxygen Debtthe additional oxygen needed after exercise to return to homeostasis

hyperventilation: to get rid of oxygen debt