AP 1 exam 2 (Skeletal Muscle Structure)

myofibrils

- bundles of filaments, 100 - 10,000 bundles/cell (include different types of myofilaments)

T- Tubules

-Invaginated extensions of sarcolemma with openings to cell exterior -Lead to depolarization of sarcoplasmic reticulum and release of Ca +2 - Located at A-I band junctions in skeletal muscle, and at Z lines in cardiac muscle

Myosin

-thick filaments (16nm), ~200 myosin - -molecules/filament -Each golfclub/hockeystick shaped myosin protein consists of 4 subunits: -2 heavy chains = tail, 2 light globular subunits = head -ATPase heads form crossbridges that bind to actin

Actin

-thin filaments (6nm). Globular G-actin is polymerized into fibrous F-actin. -strands that form a double helix. -Active sites on actin are myosin receptors.

Major types of fascicle arrangements in skeletal muscle

1. parallel 2. pennate 3. convergent 4. circular (sphincter)

fibers (cells)

10 - 100 microns diameter, up to one foot long

What is an aponeurosis? Name a specific example.

Aponeurosis - broad, flat tendon. Attaches muscle to muscle or muscle to bone eg: fascia latae /iliotibial tract in thigh

List and describe the major connective tissue wrappings that surround and compartmentalize skeletal muscle.

Fascia - broad sheets of connective tissue Tendons - attach muscle to bone (through the periosteum) Aponeurosis - broad, flat tendon. Attaches muscle to muscle or muscle to bone eg: fascia latae /iliotibial tract in thigh

Myofilaments

Myosin Actin Tropomyosin Troponin

What is the difference between a tendon and a ligament?

Tendons - attach muscle to bone (through the periosteum) ligaments which connect bone to bone

Fascia

a.) Superficial (subcutaneous layer of skin) - loose c.t. & adipose - Water & fat storage, insulation, protection, vessel, and nerve pathways b.) Deep - dense c.t. w/no adipose Lines body wall extremities, separates muscle into groups, fascicles, & cells - epimysium: surrounds entire muscle (ex. biceps), continuous with tendons - perimysium: surrounds fascicles (bundles of muscle fibers) - endomysium: surrounds individual muscle fibers (cells), contains capillaries c.) Subserous (visceral) - loose c.t. between deep fascia and serous membrane -Makes up the outer fibrous layer of serous membrane and connects the serous membrane to the body wall -Covers and supports internal organs (viscera)

parallel

a.) straplike - long & narrow (sartorius) b.) fusiform - wide in the middle (biceps brachii)

pennate

a.) uni - fascicles insert on one side of tendon (extensor digitorum longus) b.) bi - fascicles insert on two sides of a tendon, looks like a feather (rectus femoris) c.) multi - fascicles insert on many sides of a tendon (deltoid)

sarcolemma

muscle cell membrane

Troponin

small, globular protein attached to tropomyosin. 3 subunits: 1) TnI (inhibitory) - binds and inhibits active sites on actin 2) TnC (calcium) - binds Ca+2 3) TnT (troponin) - binds to tropomyosin When Ca+2 binds to troponin, the troponin will act as a pull tab and shift the tropomyosin strand exposing the crossbridge binding sites on the actin filament.

sarcoplasmic reticulum

smooth endoplasmic reticulum, contains Ca+2 (blue - covering 1 myofibril)

convergent

triangular shape (pectoralis major)

Tropomyosin

very thin strand that wraps around actin and prevents myosin from binding to actin.