MSM - Structure of Muscle Tissue Lesson

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Structure of Muscle Tissue

Each skeletal muscle is an organ in the muscular system and consists of skeletal muscle tissue, connective tissue, nerve tissue, and vascular tissue.The structure of a skeletal muscle is detailed.

An individual skeletal muscle may be made up of hundreds, or even thousands, of muscle fibers.

Each individual muscle fiber is wrapped in a connective tissue called endomysium.

Muscle fibers are arranged in bundles called fascicles.

Fascicles are separated and surrounded by a connective tissue called perimysium.

The epimysium is a layer of connective tissue that surrounds the fascicles; it is the outermost layer of the muscle. Fascia is a connective tissue outside the epimysium that surrounds and separates skeletal muscles.

The multiple layers of connective tissue give support and protection to the delicate muscle fibers and allow them to withstand the force of contraction.

They also function as a passageway for blood vessels and nerves. Active skeletal muscle needs an efficient transport system to provide the muscle with oxygen and nutrients needed for contraction and to remove waste products.

Muscles and Bones

The muscular system needs the skeletal system in order to function properly. Muscles move the body by contracting against the skeleton.

The only thing that muscles are able to do is actively contract. Muscles do extend after contraction, but only passively through relaxation.

Generally, muscles are attached to two different bones, spanning the joint that connects the bones together: One bone that does not move during contraction is called the origin, and another bone that does move during contraction is called the insertion. They are connected to the bones by a rope-like extension of their connective tissue called a tendon.

Tendons and muscles work together and exert only a pulling force on joints.

For example, when you contract your biceps brachii muscle, the force from the muscle pulls on the radius bone (its point of insertion), causing the arm to move up. This action decreases the angle at the elbow joint.

This action is called a flexion, and a muscle that causes the angle of a joint to become smaller is called a flexor. To extend or straighten the arm, the biceps brachii relaxes, and the triceps on the opposite side of the elbow joint contracts.

This action is called an extension, and a muscle that causes a joint to straighten out is called an extensor. Muscles use the bones and joints of the body as levers and pivots to reduce the amount of effort needed for large movements of the body.

In order to move parts of the body in opposite directions, muscles must be attached to bones in pairs that work against each other. These groupings are called antagonistic pairs.

Antagonistic pairs are made up of an agonist and an antagonist muscle. Agonist muscles cause a movement to occur through their own contraction.

When you contract your biceps brachii muscle, the force from the muscle pulls on the radius bone (its point of insertion), causing the arm to move up.

These muscles are often referred to as prime movers since they are the muscles that are considered primarily responsible for generating a specific movement. Antagonists oppose the specific movement of the agonist muscle, controlling and slowing its motion, and return a limp to its initial position.

For example, when the elbow is flexed, the biceps brachii and triceps brachii work as antagonistic pairs. The biceps act as the agonist, contracting and causing flexion in the elbow and the triceps will stabilize the flex as the antagonist.

The pair of muscles will switch roles when the arm is extended.

Muscle Form

Skeletal muscles can vary in size, shape, and arrangement of fibers.

The differences in form and anatomical position dictate the function of each skeletal muscle. There are four simple fiber patterns in muscles:

 Pattern  Description
 Parallel  Fibers run parallel to the direction of the muscle. These muscles function similarly to a single muscle fiber. Most skeletal muscles are in this pattern. 
 Convergent  Fan out from a common point of attachment. Allow for a more versatile type of movement.
 Pennate  Have one or more tendons running through the body of the muscle with the fascicles forming an oblique angle to the tendons. Able to generate a greater tension than the parallel arrangement because they possess a greater amount of muscle fibers. 
 Sphincter  Also known as circular muscles. Arranged concentrically around an opening or recess. As the muscle contracts, it gets smaller. 

The skeletal muscles of the body can be further categorized into seven general types:

Examples of muscle types and specific muscles:
1. Circular muscle: Orbicularis oris
2. Convergent: Pectoralis major
3. Unipennate: Extensor digitorum (posterior view)
4. Parallel: Sartorius 
5. Bipennate: Rectus femoris
6. Parallel-fusiform: Biceps brachii 
7. Multipennate: Deltoid

 

 

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