Muscle Structure - Human & Disease

Muscle Structure


Muscle Structure 

Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement. The major function of muscle is to produce motion,to aid in the maintenance of posture, and to produce heat. In order to provide these functions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.

Muscle Structure Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement. The major function of muscle is to produce motion, to aid in the maintenance of posture, and to produce heat. In order to provide these functions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.
Muscle Structure











What is the structure of muscle?

Each muscle is made up of groups of muscle fibers called fascicles surrounded by a connective tissue layer called perimysium. Multiple units of individual muscle fibers within each fascicle are surrounded by endomysium, a connective tissue sheath.

In the muscular system, muscle tissue is categorized into three distinct types: skeletal, cardiac, and smooth. Each type of muscle tissue in the human body has a unique structure and a specific role. Skeletal muscle moves bones and other structures. Cardiac muscle contracts the heart to pump blood.

A single muscle, is constructed of a bunch of muscle fibers, and these fibers are linked together by a collagenous connective tissue. This connective tissue is networked into three layers:

(a) the endomysium surrounds individual muscle fibers.

(b) the perimysium collects bundles of fibers into fascicles.

(c) the epimysium provides a sheath. around the entire muscle.

Muscle Structure Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement. The major function of muscle is to produce motion, to aid in the maintenance of posture, and to produce heat. In order to provide these functions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.











This continuous fascia connects muscle fibers to tendons and consequently to the periosteum of bone, and the entire unit is known as the MTU (musculotendinous unit).

Muscle fibers:

If skeletal muscle is viewed under a microscope it is seen to consist of thousands of elongated cylindrical cells called muscle fibers or myofibers. These fibers vary in length between 1–400 mm, and can be 10–100 µm in diameter.

Sarcolemma and sarcoplasm:

Each muscle fiber is surrounded by a plasma membrane called the sarcolemma; this membrane allows for both passive and active transport into the cell and thus is an important factor in muscle excitability. The fluid enclosed within thecell by the sarcolemma is termed the sarcoplasm, and this contains fuel sources such as lipids and glycogen, organelles such as the cell nuclei and mitochondria, and the enzymes and contractile proteins required for muscle contraction.

Myofibrils:

Also contained within the sarcoplasm are the myofibrils. These are cylindrical structures, approximately 1–2 µm in diameter that run longitudinally through
the muscle fiber. Each muscle fiber can contain several hundred to several
thousand myofibrils.

Myofilaments:

The myofibrils consist of a bundle of smaller structures called myofilaments.
These structures are approximately 6 nm (thin filaments) or 16 nm (thick filaments) in diameter, and represent the contractile apparatus of the muscle. The thin myofilaments are composed mostly of the protein actin, which is arranged in two strands intertwined into a helical structure. Within the groove of this helix structure sit two strands of the protein tropomyosin, upon which at regular intervals sits the protein troponin. The troponin complex includes three subunits:

(a) troponin I, which binds to actin.

(b) troponin C, which binds to calcium ions.

(c) troponin T, which binds to tropomyosin.

Muscle Structure Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement. The major function of muscle is to produce motion, to aid in the maintenance of posture, and to produce heat. In order to provide these functions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.
The thick filaments are composed mostly of the protein myosin. Myosin has a two-chained helical tail, that at one end terminates in two large globular heads. These heads, during contraction, are referred to as cross-bridges and contain an ATP-binding site that is imperative for muscle contraction to occur.

Triad:

The sarcoplasm also contains a hollow membranous system that is linked to the
sarcolemma and assists in conducting neural commands through the muscle.
This system includes the sarcoplasmic reticulum, the terminal cisternae and
the transverse tubules (T tubules). The sarcoplasmic reticulum runs longitudinally along the fiber and surrounds the myofibril and at specific points it dilates into lateral sacs, or terminal cisternae. Running perpendicularly to the sarcoplasmic reticulum are transverse tubules that open to the outside of the fiber. A single transverse tubule plus two terminal cisternae, one on each side of the tubule, form a triad. The triad is extremely important in aiding the rapid.

Sarcomere:

A myofibril is constructed from a series of sarcomeres added end to end, and it is these sarcomeres that give the muscle its striated appearance under the microscope. The structures of the sarcomere, are identified by how they refract light under the electron microscope. At rest a sarcomere is approximately 2.5 µm in length and is separated from its neighboring sarcomeres by narrow zones of dense material called Z lines or Z bands. The zone containing thick filaments and some interdigitating thin filaments is doubly refractive of light, or anisotropic, and is termed the A or dark band. The areabetween the A bands is singly refractive (isotropic) and is thus called the I or light band. This band contains mainly thin filaments.

Muscle Structure Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement. The major function of muscle is to produce motion, to aid in the maintenance of posture, and to produce heat. In order to provide these functions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.

Muscle Structure Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement. The major function of muscle is to produce motion, to aid in the maintenance of posture, and to produce heat. In order to provide these functions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.













The area in the A band where there is no overlapping of thin filaments is called the H zone, in the center of which lies the M line or M band. The thin filaments are anchored to the Z lines and project in both directions, whilst the thick filaments attach to the M band. During muscle contraction the myosin cross-bridges pull on the actin filaments so that they slide inwards towards the H zone. The sarcomere shortens as the Z lines move towards each other, but the length of the myofilaments does not change. As the thin filaments meet at the center of the sarcomere the H zone narrows or disappears. The shortening of muscle fibers by the sliding of myofilaments is called the sliding-filament theory.

What are the functions of the muscle?

The main functions of the muscular system are:

1- Mobility. The muscular system's main function is to allow movement.

2- Stability. Muscle tendons stretch over joints and contribute to joint stability. 

3- Posture. 

4- Circulation.

5- Respiration. 

6- Digestion.

7- Urination.

8- Childbirth.


How do muscles work?

Muscles move body part by contracting and then relaxing. Muscles can pull bones, but they can't push them back to the original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint.

Shapes Of The Muscles:

Some skeletal muscles are broad in shape and some narrow. In some muscles the fibers are parallel to the long axis of the muscle; in some they converge to a narrow attachment; and in some they are oblique. Each skeletal muscle fiber is a single cylindrical muscle cell.

How do muscles get energy?

Muscle Structure Gross structure Skeletal muscle tissue is highly specialized to generate force and thus movement. The major function of muscle is to produce motion, to aid in the maintenance of posture, and to produce heat. In order to provide these functions muscle tissue can respond to stimuli, can conduct a wave of excitation, can modify its length and can regenerate in growth. These adaptabilities are referred to as the plasticity of muscle.








Muscles use the stored chemical energy of food we eat and convert that to heat and energy of motion (kinetic energy). We need energy to enable growth and repair of tissues, to maintain body temperature and to fuel physical activity. Energy comes from foods rich in carbohydrate, protein and fat.
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