MSK 3 - Overview of skeletal muscle

How do types of skeletal muscle fibers differ? What are the three main types of skeletal muscle fiber?

- Differ in myoglobin content (redness), contraction speed (fast vs slow switch), how ATP is generated (anaerobic vs aerobic), slow or fast of fatigue. 3 main types: - Slow oxidative: don't have much force but do not fatigue (postural muscles) - Fast oxidative glycolytic: an intermediate level of strength and fatigue (endurance muscles) - Fast glycolytic: produce lots of force but fatigue fast (ex. extraocular eye movement)

What are tendons? What are they located, and what are some of the main characteristics of tendons? What is an aponeurosis?

- a flexible but inelastic cord of strong fibrous collagen tissue attaching a muscle to a bone - Highly ordered collagen fibers, poorly vascularized - Have different shapes and sizes. Ex. aponeurosis which is a flat sheet of tendons linked to multiple muscles. example of this is the one in the palm or abdomen.

What are satellite cells, and what are the functions of these cells?

- myoblasts that persist in the mature skeletal muscle - retain the capacity to fuse with other satellite cells or with damaged muscle cells to fix small damage, however they are not enough to compensate for significant damage.

What are the different components of a myofiber? Functions and characteristics of each component?

1) sarcolemma: Outside sheath plasma membrane. 2) Transverse (T) tubules: invaginations of the sarcolemma. Allow for APs to quickyl spread throughout the myofiber 3) Sarcoplasm: Is the cytoplasm and contains myofibrils, mitochondria, myoglobin, glycogen, sarcoplasmic reticulum. Important for storage of calcium. 4) myofibrils: contractile element, extend the entire length of the muscle fiber. Composed of myofilaments including actin and myosin. This is where hypertrophic growth occurs. Made up of sarcomeres. 5) sarcoplasmic reticulum: similar to smooth ER, Fluid-filled system of membranous sacs that encircle each myofibril, Stores Ca2+ in relaxed muscle. Include terminal cisterns which when 2 are combined with the T tubule, make up the triad. when triggered, Ca is released from here into sarcoplasm. 6)

What are the different types of muscular tissue? Main distinguishing characteristics of each, and where are they typically located?

1) skeletal muscle cells: voluntary and striated (everywhere) 2) Cardiac muscle cells: considered striated and involuntary, autorythmic. (heart) 3) smooth muscle, not striated, shorter, involuntary. much more elastic. (organs)

What are the properties of muscular tissue?

1. Electrical excitability - 2. Contractility 3. Extensibility 4. Elasticity

What are the functions of muscular tissue?

1. Producing body movements 2. Stabilizing body positions 3. Storing and moving substances within the body 4. Generating heat

What are the 3 main types of myofilaments of a myofiber? What functions are associated with each type? What are examples and functions of these proteins?

Contractile (actin and myosin)- convert ATP into mechanical motion. Myosin( thick filament) pulls actin (thin filament) towards the M line causing contraction. Each actin moleucle has a myosin binding site. No actual shortening of filaments. regulatory (troponin and tropomyosin) - part of thin filament, tropomyosin blocks myosin binding site on actin. when calcium is present, troponins makes conformation change on tropomyosin opening myosin binding site and allowing for myosin attachment. structural (titan, nebulin, and dystrophin) - titan helps stablize thick filament, nebulin helps stabalize thing filament, dystrophin links thin filament to proteins in sarcolemma which disburse the force of contraction throughout the myofibril. lack of dystrophin leads to muscular dystrophy.

How does exercise affect skeletal muscle tissue?

Exercises can induce changes in skeletal muscle tissue Endurance (aerobic) exercises: Can lead to transformations from FG to FOG fibers Body builders (great strength; short periods): Increase size (hypertrophy) and strength of FG fibers

How do muscles grow?

Hypertrophy- increase in the size existing cells through increased production of myofibrils and organelles. results from forceful repetitive muscular activity Once maturity is reached, cell division is not possible.

What do the terms origin and insertion mean in terms of muscle attachment? What are these terms being phased out?

Origin Attachment of tendon to stationary bone Typically proximal or superior Insertion Attachment of tendon to movable bone Typically distal or inferior - Origin and insertion are often referred to as proximal vs distal - Usually the distal moves towards the proximal

• Understand what the terms prime mover, antagonist, fixator, and synergist mean.

Prime mover - Main muscle responsible for producing a specific movement - Concentric contraction Antagonist - Muscle that opposes the action of another muscle - Eccentric contraction Fixator - Muscle that steadies proximal parts of a limb while movements are occurring in distal parts - Isometric contraction Synergist - Complements action of prime mover - May provide a weaker component of same action - May assist indirectly by serving as a fixator for intermediate joint

What are other types of muscle contraction?

Reflexive contraction Automatic (not voluntarily controlled) Produces movement Tonic contraction Muscles are almost always slightly contracted (muscle tone) Does not produce movement

How are muscle cells/fibers formed?

Through formation of 100+ myoblasts which congregate and form muscle cells and satellite cells

What is the sliding filament mechanism?

contraction is accomplished by thin filaments from the opposite sides of each sarcomere sliding closer together between the thick filaments towards the M line. No actual shortening

What are the different layers of connective tissue associated with muscle? How are these related to tendons?

endomysium surrounds each muscle fiber, has small blood vessels. perimysium surrounds fascicles (Groups of muscle fibers) Epimysium bind all connective tissue together to form muscle belly and tendon at the end of muscle All layers are continuous and emerge from the belly as tendons. Blend with collagen of osseous extracellular matrix.

What is fascia? Where is it located?

is- dense irregular CT which wraps around groups of muscles and structures, separates anterior and posteiror muscles

What are the types of phasic muscle contractions, and how do these differ?

isometric: muscle does not change in length, equal resistance to gravity (postural muscles) Isotonic: muscle changes length. 2 types: Concentric Muscles shorten and produce movement to reduce angle at joint Eccentric: Muscle lengthens