(8) Muscle Physiology: Sarcomeres and Crossbridges

Muscles generate

Movement, force, and heat

Skeletal muscle is controlled

Voluntarily

Striated means

Having stripes

Cardiac muscle is controlled

Involuntarily

Cardiac muscle is modulated by the

Nervous system

Smooth muscle is found in

Hollow organs and tubes

Smooth muscle is controlled

Involuntarily controlled by the autonomic nervous system

Origin

The end of the muscle that is attached closest to the torso or to a more stationary bone

Insertion

Other end attached farther from the torso or to a more mobile bone

Action

What happens when a muscle contracts

Flexion

Brings the connected bones closer together

Extension

Moves the connected bones farther apart

Antagonist Pair

At most joints, a flexor muscle and extensor muscle are positioned to provide opposing motion (bicep, tricep)

Each skeletal muscle is an ________

Organ

Muscle fasicles

Muscle cells bound together by connective tissues into bundles

Muscle fibers (myofibers)

Individual muscle cells

Muscle fibers span the entire length of the _________

Muscle

Multinucleate

Have multiple nuclei

Sarcomeres

A specific arrangement of proteins that contract muscle

T-tubules

Infoldings of the cell membrane, continuous with ECF

Sarcoplasmic Reticulum

Modified ER that extends thorughout the fiber, surrounding all the myofibrils

Terminal Cisternae

Expansions of the SR next to T tubules

Triad

T-tubule and the cisternae on either side

Sarcolemma

Cell membrane of a muscle cell

Myosin

Thick filaments

Actin

Thin filaments

Z- disk

The boundary between adjacent sarcomeres, attachment point for thin filaments

M-line

The attachment point for thick filaments in the middle of a sarcomere

I- band

Region occupied by only the thin filaments

A-band

Region occupied by the overlap of both filaments

H-zone

Region occupied by only think filaments

What is myosin made of?

Heavy chain with two light chains intertwined and ending with myosin heads

What is actin made of?

Two chains of globular proteins (G actins) twisted together

Nebulin

Provides structure to align actin in thin filaments

Titin

Stabilizes the myosin through an elastic connection to the z disk

Excitation-Contraction Coupling

The process of action potential in motor neurons being translated into Ca2+ signals in muscle fibers

Contraction-Relaxation Cycle

The process of developing movement and force in response to a Ca2+ signal

Muscle contract because actin and mysosin _________ and _________

Bind and slide

Crossbridges

Myosin heads binding to actin molecules

Tropomyosin

A thread like protein wrapped around like a chain.

What does Tropomyosin prevent?

Crossbridges in a relaxed muscle

Troponin binding sites

Tropomyosin, actin, calcium

Step 1 of Opening Crossbridge

Ca2+ must be present in the sarcoplasm (ICF)

Step 2 Opening Crossbridge

Binds to troponin

Step 3 Opening Crossbridge

Troponin pulls tropomyosin, uncovering myosin binding sites

Step 4 Opening Crossbridge

Myosin heads can bind to actin

Step 5 Opening Crossbridge

Movement of the myosin heads pull the actin filament, shortening sarcomere

Myosin is an _________, it converts ________ to ADP by dephosphorylating it

ATPase, ATP

What is the energy released by Myosin used for?

Change the position of the myosin head

Rigor state

Myosin heads tightly bound to G actin molecules

When ATP binds to the myosin head, myosin ________

Detaches from actin

Both ADP and Pi stay bound to what as energy is released?

Myosin

Power Stroke

Pi is released and myosin head swivels, pulling actin toward the M-line

What happens to myosin when ATP is hydrolyzed?

Myosin head rotates to the "cocked" position and binds with new actin