Muscles Muscles

Skeletal muscle organization and how it contracts

Vertebrate Skeletal MuscleVertebrate Skeletal Muscle Contract/relax: antagonistic pairs

w/skeleton Muscles: bundle of…. Muscle fibers: single cell w/ many

nuclei consisting of…. Myofibrils: longitudinal bundles

composed of…. Sarcomere: repeating unit of muscle

tissue, composed of…. Z lines~sarcomere border this gives

“striated” appearance in muscle

Sliding-filament modelSliding-filament model

Theory of muscle contraction Sarcomere length reduced Z line length becomes shorter Actin and myosin slide past each other (overlap increases) but

their length stays the same

Actin-myosin interactionActin-myosin interaction

1- Myosin head breaks down ATP to ADP and inorganic phosphate (Pi); termed the “high energy configuration” with ADP and phosphate attaching to the head. (GRABBING ON)

2- Myosin head binds to actin; termed a “cross bridge” 3- Releasing ADP and (Pi), myosin relaxes sliding actin; “low energy

configuration” (PULLS THE ACTINS FROM BOTH SIDES TO BE CLOSER) 4- Binding of new ATP releases myosin head (LET GO) 5- This ATP is broken down (See #1)

Muscle contraction regulation, IMuscle contraction regulation, I

Relaxation: tropomyosin protein blocks myosin binding sites on actin

Contraction: calcium is released from ER of muscle cell due to action potential from neurons. It binds to troponin complex; tropomyosin changes shape, exposing myosin binding sites. MAKES SLIDING FILAMENT POSSIBLE

Muscle contraction regulation, IIMuscle contraction regulation, II

Calcium (Ca+)~ Must be present

Sarcoplasmic reticulum~ a specialized endoplasmic reticulum (ER) in muscle that stores and releases Ca.

Stimulated by action potential in a motor neuron

Ca+ then binds to troponin allowing this to go forward