Muscle Structures and Molecules Facilitating Muscle Contraction

What is structure H (more than one choice may be selected)

• Actin

• Myosin

• Thin Filment

• Thick Filament

Answer explanation

In this image, the close-up shows us the structure of the myofibril which is made of sarcomeres.

Sarcomeres have both thin and thick protein filaments.

The thin filaments in sarcomeres are made of the protein actin (blue in the image).

What is structure A?

• Muscle

• Fascicle

• Muscle Fiber

• Myofibril

Answer explanation

In any images, the structure attached directly to a bone will be the whole muscle (in this image it does look like the arrow is closer to the tendon).

What is structure G?

• Muscle

• Fascicle

• Muscle Fiber

• Myofibril

Answer explanation

This image is another version of the diagram from the question. Going from largest level of structure to smallest, the order of muscle structures is:

1. Muscle or Whole muscle

2. Fascicle

3. Muscle Fiber (Cell)

4. Myofibril

So the fourth level of structure should show the myofibril.

What is structure F?

• Muscle

• Fascicle

• Muscle Fiber

• Myofibril

Answer explanation

In this image we are looking at the cylinders that make up a fascicle.

Fascicles are made of muscle fibers (cells).

Structure C is a covering for structure E. What is the name of the covering?

• Epimysium

• Perimysium

• Endomysium

• Sarcolemma

Answer explanation

This image shows that the fascicles are wrapped in a perimysium covering.

Structure B is a covering for structure A. What is the name of the covering?

• Epimysium

• Perimysium

• Endomysium

• Sarcolemma

Answer explanation

In this image we can see that the whole muscle (attached to bone) is covered by epimysium.

Structure D is a covering for structure F. What is the name of the covering?

• Epimysium

• Perimysium

• Endomysium

• Sarcolemma

Answer explanation

This image has a bit more of a close view. In this cas. we can see that the muscle fiber (cells) have a covering called the endomysium.

What is structure E?

• Muscle

• Fascicle

• Muscle Fiber

• Myofibril

Answer explanation

The second level of structure in this image is a fascicle. Muscles are essentially bundles of fascicles.

What is structure I?

• Actin

• Myosin

• Thin Filament

• Thick Filament

Answer explanation

Here we are again looking at the internal structure of a sarcomere.

The Thick filaments in the filaments are colored red and are made of the protein myosin.

Structure G is a myofibril. What are myofibrils made of?

• Muscles

• Myofilaments

• Sarcomeres

• Fascicles

Answer explanation

The myofibril in this image is at the bottom.

it is made of repeating sarcomeres.

Sarcomeres are made of alternating myofilaments called actin and protein.