Microscopic Anatomy of Skeletal Muscle

What is the sarcolemma?

is a plasma membrane of a muscle fiber

What is the sarcoplasm?

is cytoplasm of a muscle fiber

What are myofibrils?

long protein cords occupying most of sarcoplasm

What does myoglobin do?

a red pigment that provides some oxygen needed for muscle activity

Muscle fibers have multiple flattened or sausage-shaped _____ pressed against the inside of the sarcolemma

mitochondria

Some myoblasts remain as unspecialized satellite cells between the muscle fiber and the endomysium. They play an important role in what?

Regeneration and repair of skeletal muscle tissue

Most other organelles are packed into the spaces between the myofibrils. The smooth endoplasmic reticulum, called the ____  reticulum, forms a network around each myofibril; it periodically has dilated end-sacs called terminal cisternae.

sarcoplasmic

What constitutes a triad?

A T tubule and two terminal cisterns

The sarcoplasmic reticulum is a reservoir of ______ ions. It has gated channels in its membranes that allow a flood of _______ into the cytosol where it activates muscle contraction

calcium, calcium

What are myofilaments?

There are three types thin filaments, thick filaments, and elastic filaments

A ____thick filaments(myosin)_____ molecule is shaped like a golf club, with two chains intertwined to form a shaftlike tail and a double globular head projecting from it at an angle. A thick filament may be likened to a bundle of golf clubs, with their heads directed outward in a helical array around the bundle.

thick filaments (myosin)

The thin filaments, 7 nm in diameter, are composed of two intertwined strands of fibrous actin. Each actin has an active site that can bind to the head of a _____ molecule

myosin

A calcium-binding protein, _____, is bound to every tropomyosin molecule

troponin

Elastic filaments, 1 nm in diameter, are made of a large protein called ____

titin

Elastic filaments run through the core of each thick filament and anchor it to a structure called the _____ at one end and the M line at the other, helping to stabilize the thick filament

Z disc

Why are myosin and actin called contractile proteins?

They directly interact to convert chemical energy into a mechanical force

Why is tropomyosin and troponin called regulatory proteins?

They are called regulatory proteins because they control the interaction between actin and myosin

Tropomyosin and troponin regulatory proteins depend on the availability of what?

the availability of Calcium

Striated muscle has dark ___ (anisotropic) bands alternating with lighter ___ (isotropic) bands, referring to their effect on polarized light

A, I

Each A band consists of thick filaments lying side by side. Part of the A band is especially dark, where each thick filament is surrounded by a hexagonal array of thin filaments. In the middle of the A band is a light region called the __ band, into which thin filaments do not reach

H

The thick filaments are linked to each other through a dark, transverse protein complex called the ___ line in the middle of the ___ band

M,H

Each light I band is bisected by a dark narrow Z disc (Z line), which provides what?

It provides anchorage for thin filaments and elastic filaments 

What makes up a sarcomere; what is a sarcomere?

 They are segments from Z disc to Z disc. It is a functional contractile unit of muscle fiber

A muscle shortens because its individual ________ shorten and pull the Z discs closer together

sarcomeres

The Z discs pull on the ________ to achieve overall shortening of the cell

thin filaments