Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca+ in regulating muscle contraction

Muscle 80% of lean mass Responsible for: - locomotion - heart beat - peristalsis

Types of Muscle Tissue Smooth Muscle –Involuntary –Visceral organs –Non-striated

Types of Muscle Tissue Smooth Muscle –Involuntary –Visceral organs –Non-striated Cardiac Muscle –Involuntary –Striated –Only in heart

Types of Muscle Tissue Smooth Muscle –Involuntary –Visceral organs –Non-striated Cardiac Muscle –Involuntary –Striated –Only in heart Skeletal Muscle –Voluntary –Striated –Locomotion

Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca+ in regulating muscle contraction

(fascicle) Skeletal Muscle Anatomy Each muscle has several fascicles

(fascicle) Skeletal Muscle Anatomy Each muscle has several fascicles Each fascicle has several muscle fibers

Skeletal Muscle Anatomy Each muscle has several fascicles Each fascicle has several muscle fibers Muscle fibers contain myofibrils (fascicle)

Skeletal Muscle Anatomy Each muscle has several fascicles Each fascicle has several muscle fibers Muscle fibers contain myofibrils Myofibrils composed of sarcomeres (fascicle)

Connective Tissue Sheaths Muscles contain layers of connective tissue

Important Cellular Structures Sarcoplasmic Reticulum Transverse “T” Tubules Sarcomere

Skeletal Muscle Cell Anatomy Sarcoplasmic Reticulum: Hollow tubules Surround myofibrils Stores Ca + Control Ca + release

Skeletal Muscle Cell Anatomy Transverse “T” Tubules: Inward protrusion of Sarcolemma Carry AP from motor neuron into muscle cell Diffusion of the “contract” signal

Sarcomere Structure: Myofilaments Composed of 2 filament types Position defines bands Thin filaments attach at “Z” lines Thick filaments attach at “M” lines

Microscopic View of a Sacromere I BandA Band H Zone Z LineM Line Sarcomere

Remember this from lab? Striations caused by Actin/Myosin overlap

Myofilament Anatomy Myosin: Heads act as “cross-bridges” to pull on Actin Head has 2 binding sites

Myofilament Anatomy Actin: Contains active sites for Myosin attachment Tropomyosin blocks binding site in resting muscle

Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca+ in regulating muscle contraction

Sliding Filament Theory of Contraction Relaxed Muscle: Slight overlap of Actin and Myosin

Sliding Filament Theory of Contraction Relaxed Muscle: Slight overlap of Actin and Myosin Muscle Contraction: Actin slides past Myosin Sarcomere shortens

Relaxed Contracted

Myosin Actin crossbridges How Does Contraction Occur?

Sliding Filament Theory Step 1 – Cross Bridge Formation: Resting state of muscle (a “cocked gun”) Myosin head bound to ADP + P i Myosin weakly attached to Actin binding site

Sliding Filament Theory Step 2 - The Power Stroke: Myosin head bends, pulls Actin towards center of sarcomere ~ 10 nm ADP + P i released Tight binding of Actin and Myosin (“rigor state”)

Sliding Filament Theory Step 3 - Cross Bridge Detachment: New ATP binds to Myosin head Myosin head detaches from Actin

Sliding Filament Theory Step 4 - Cocking the Myosin Head: ATP hydrolyzed to ATP + P i Head returns to “cocked” high-energy form Cycle repeats numerous times

Physiology of Sliding Filament Theory Contractions involve cycles of Myosin-Actin attachment & detachment Series of working strokes

Physiology of Sliding Filament Theory Contractions involve cycles of Myosin-Actin attachment & detachment Series of working strokes “Centipede walking” of Myosin heads on Actin

Myosin Actin crossbridges How is contraction regulated?

Outline I. Types of Muscle II. Anatomy of Skeletal Muscle III. Sliding Filament Theory IV. Role of Ca + in regulating muscle contraction

No contraction without Ca + Contraction depends on calcium Muscle in resting state (step 1) without Ca +

No contraction without Ca + Contraction depends on calcium Muscle in resting state (step 1) without Ca + Ca + allows steps 2-4 to occur

No contraction without Ca + Contraction depends on calcium Muscle in resting state (step 1) without Ca + Ca + allows steps 2-4 to occur Ca + shifts tropomyosin out of the way

Tropomyosin: muscular “safety switch”

Rigor Mortis Ca + diffusion Tropomyosin shift Rigor State

Rigor Mortis Ca + diffusion Tropomyosin shift Lack of ATP Myosin head stuck Rigor State Need ATP

Rigor Mortis Ca + diffusion Tropomyosin shift Lack of ATP Myosin head stuck Rigor State Need ATP

How do Packing Plants Prevent Rigor?

Nervous Control of Contraction Sarcoplasmic Reticulum Sequesters Ca + in muscle fibers Membrane densely packed with Ca + pumps

Nervous Control of Contraction Neuromuscular Junction Synapse between motor neuron and muscle fiber Motor neuron stimulates AP in membrane of muscle fiber

Nervous Control of Contraction Transverse “T” tubule Invagination of muscle fiber’s membrane Enables AP to spread deep within muscle fiber

Summary The sarcomere is the functional unit of muscle tissue Sarcomere contains Actin and Myosin Muscle contraction occurs via nervous stimulation and the association/ dissociation of Actin and Myosin filaments Sarcoplasmic reticulum stores Ca+ which allows shift of tropomyosin