Muscular Stimulation PT 1

The human body is made of over ____ skeletal muscles

650

Skeletal muscles

• only voluntary muscle in the body

• allows us to actively control our body + interact with the world around us

Each muscle is surrounded by

the epimysium

Epimysium function

• protect muscle from damage

• isolates each muscle from each other allow for each muscle to be used individually

A muscle is made several large bundles called

fascicles

Why are large blood vessels in between fascicles?

to supply the fascicles with nutrient and oxygen, and nerves to stimulate the muscles

The fascicles are surrounded by a layer called

the perimysium

Each fascicle in the muscle is made of bundles of

individual muscle fibers/myofibers

Muscle fibers/myofibers are also known as

muscle cells

Muscle fibers, or myofibers are surrounded by tissue called

the endomysium

What does the endomysium contain?

• extracellular fluid + nutrients to support the muscle fiber

Within each muscle fiber are dozens of smaller protein bundles called

myofibrils

Myofibrils are made of smaller

protein filaments that perform the moving action in muscle

How are muscle cells able to grow into a big muscle?

• by merging with other skeletal muscle cells

(merging results in a single skeletal muscle “cell” having multiple nuclei and other cellular structures)

Myoblasts

undeveloped muscle cells

What happens to myoblasts once muscles have formed?

they turn into satellite cells

What happens when a muscle cell is slightly damaged and needs to be replaced?

• leads to the release of cytokine proteins into surrounding area

• muscle satellite cells are alerted by the cytokine proteins and mature into new muscle cells

Myofibrils are surrounded by

• multiple nuclei

• mitochondria

• sarcoplasmic reticulum

• sarcolemma

• sarcoplasm

Why is there a lot of mitochondria in a muscle?

• mitochondria produce ATP, so they help power the muscles

The sarcoplasmic reticulum stores…

Calcium ions

Sarcolemma

• very porous to allow proteins and ions to flow quickly in and out of the cell when needed

T-Tubules

• indentions in the sarcolemma that connect the sarcollema to the sarcoplasmic reticulum

Sarcoplasm

• filled with lots of proteins and other nutrients needed to fuel cell

What are the repeating protein segments in myofibrils?

sarcomeres

The sarcomere is made of highly organized proteins called

myofilaments (make a strained pattern)

What are the 2 types of myofilaments?

1) Thin filaments

2) Thick filaments

How many proteins are thin filaments composed of?

three

How many proteins are thick filaments composed of?

one

Thin filament proteins (3)

1. Actin

2. Tropomyosin

3. Troponin

Actin

• main core of the thin filament

Tropomyosin

• thin protein

• forms long strands around actin, helping keep its shape

Troponin

• globular protein with 3 binding sites

  • T site

  • I site

  • C site

T site binds to

tropomyosin

I site binds to

actin

C site binds to

calcium ions

What happens when the muscle is at rest?

• troponin is attached to the actin and tropomyosin with the C site opened and not bound

• C site is waiting for calcium ions to bind to it

Thick filament

• made of myosin proteins

A bands contain

both thick and thin filaments

I Bands contain

only thin filaments

M Band (line)

attachment point for thick filaments

Z band (disc)

ends of the sarcomere

Between the thin filaments is a protein called ____

Titin

• helps prevent overstretching of sarcomere

Function of Titin in the sarcomere

1. hold thick filaments in place, keeping A band organized

2. folds and unfurled when muscle contracts and relaxes (helps muscles elasticity)

Myofibrils are anchored in the sarcolemma with proteins called

dystrophin

Dystrophin

• crucial protein in muscle cells

• prevents damage to muscle cells during contraction and relaxation

The heads of myosin in the thick filament are highly attracted to?

the actin in the thin filament

What is the position of troponin during the resting state of a muscle?

• myosin heads are blocked by troponin, preventing the binding with actin