Muscular system

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Muscular system
The human muscles, seen from the front, 19th century illustration
Details
Identifiers
Latinsystema musculare
TA98A04.0.00.000
A04.6.02.001
A04.7.02.001
TA21975
FMA72954
Anatomical terminology

The muscular system is an

musculoskeletal system, which is responsible for the movement of the body.[2]

Types

Main article:
Muscle tissue
Three distinct types of muscle (L to R): Smooth (non-striated) muscle in internal organs, cardiac or heart muscle, and skeletal muscle.

There are three distinct types of muscle: skeletal muscle, cardiac or heart muscle, and smooth (non-striated) muscle. Muscles provide strength, balance, posture, movement, and heat for the body to keep warm.[3]

There are approximately 640 muscles in an adult male human body.[4] A kind of elastic tissue makes up each muscle, which consists of thousands, or tens of thousands, of small muscle fibers. Each fiber comprises many tiny strands called fibrils, impulses from nerve cells control the contraction of each muscle fiber.

Skeletal

Main article: Skeletal muscle
See also:
List of muscles of the human body

Skeletal muscle, is a type of

sliding filament model of muscle contraction. Within the sarcomere, actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped myosin heads that project toward the actin filaments,[1][3][5] and provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style; they swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the actin filament. This is called a ratchet type drive system.[5]

This process consumes large amounts of

creatine phosphate, which when necessary can assist with the rapid regeneration of ADP into ATP.[6]

Calcium ions are required for each cycle of the sarcomere. Calcium is released from the sarcoplasmic reticulum into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin-binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the sarcoplasmic reticulum.[5]

There are approximately 639 skeletal muscles in the human body.

  • Skeletal muscles, viewed from the front
    Skeletal muscles, viewed from the front
  • Skeletal muscles, viewed from the back
    Skeletal muscles, viewed from the back

Cardiac

Main article: Cardiac muscle

Heart muscle is striated muscle but is distinct from skeletal muscle because the

sinus node influenced by the autonomic nervous system.[1][3]

Smooth

Main article: Smooth muscle

Smooth muscle contraction is regulated by the autonomic

muscle tissue is also capable of adapting to different levels of stretch and tension, which is important for maintaining proper blood flow and the movement of materials through the digestive system
.

Physiology

Contraction

muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, such as the muscle contractions that result from tetanus. Also, a loss of function at the junction can produce paralysis.[5]

Skeletal muscles are organized into hundreds of motor units, each of which involves a motor neuron, attached by a series of thin finger-like structures called axon terminals. These attach to and control discrete bundles of muscle fibers. A coordinated and fine-tuned response to a specific circumstance will involve controlling the precise number of motor units used. While individual muscle units contract as a unit, the entire muscle can contract on a predetermined basis due to the structure of the motor unit. Motor unit coordination, balance, and control frequently come under the direction of the cerebellum of the brain. This allows for complex muscular coordination with little conscious effort, such as when one drives a car without thinking about the process.[5][7]

Tendon

Main article: Tendon

A tendon is a piece of connective tissue that connects a muscle to a bone.[8] When a muscle intercept, it pulls against the skeleton to create movement. A tendon connects this muscle to a bone, making this function possible.

Aerobic and anaerobic muscle activity

At rest, the body produces the majority of its

mitochondria[9] without producing lactic acid or other fatiguing byproducts. During exercise, the method of ATP production varies depending on the fitness of the individual as well as the duration and intensity of exercise. At lower activity levels, when exercise continues for a long duration (several minutes or longer), energy is produced aerobically by combining oxygen with carbohydrates and fats stored in the body.[6][10]

During activity that is higher in intensity, with possible duration decreasing as intensity increases, ATP production can switch to anaerobic pathways, such as the use of the creatine phosphate and the phosphagen system or anaerobic glycolysis. Aerobic ATP production is biochemically much slower and can only be used for long-duration, low-intensity exercise, but produces no fatiguing waste products that can not be removed immediately from the sarcomere and the body, and it results in a much greater number of ATP molecules per fat or carbohydrate molecule. Aerobic training allows the oxygen delivery system to be more efficient, allowing aerobic metabolism to begin quicker. Anaerobic ATP production produces ATP much faster and allows near-maximal intensity exercise, but also produces significant amounts of lactic acid which render high-intensity exercise unsustainable for more than several minutes. The phosphagen system is also anaerobic. It allows for the highest levels of exercise intensity, but intramuscular stores of phosphocreatine are very limited and can only provide energy for exercises lasting up to ten seconds. Recovery is very quick, with full creatine stores regenerated within five minutes.[6][11]

Clinical significance

See also: Myopathy

Multiple diseases can affect the muscular system.

Muscular Dystrophy

five body outlines, muscle areas outlines
Main areas of muscle weakness in different types of dystrophy

Muscular dystrophy is a group of disorders associated with progressive muscle weakness and loss of muscle mass. These disorders are caused by mutations in a person’s genes.[12] The disease affects between 19.8 and 25.1 per 100,000 person-years globally.[13]

There are more than 30 types of muscular dystrophy. Depending on the type, muscular dystrophy can affect the patient's heart and lungs, and/or their ability to move, walk, and perform daily activities. The most common types include:

  • Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD)
  • Myotonic dystrophy
  • Limb-Girdle (LGMD)
  • Facioscapulohumeral dystrophy (FSHD)
  • Congenital dystrophy (CMD)
  • Distal (DD)
  • Oculopharyngeal dystrophy (OPMD)
  • Emery-Dreifuss (EDMD)

See also

References

  1. ^
    OCLC 548651322
    .
  2. OCLC 920806541.{{cite book}}: CS1 maint: location missing publisher (link
    )
  3. ^
    OCLC 854567882.{{cite book}}: CS1 maint: location missing publisher (link
    )
  4. ^ "THE MUSCULAR SYSTEM" (PDF). www.uc.edu.
  5. ^
    OCLC 434319356.{{cite book}}: CS1 maint: location missing publisher (link
    )
  6. ^
    OCLC 981908072.{{cite book}}: CS1 maint: location missing publisher (link
    )
  7. OCLC 473478856
    .
  8. ^ "Tendon vs. ligament: MedlinePlus Medical Encyclopedia Image". medlineplus.gov.
  9. OCLC 943860
    .
  10. PMID 18500953
    .
  11. PMID 1581850
    .
  12. ^ CDC (2022-11-21). "What is Muscular Dystrophy? | CDC". Centers for Disease Control and Prevention. Retrieved 2023-05-05.
  13. S2CID 2426923
    .

Further reading

External links

The Wikibook Human Physiology has a page on the topic of: The Muscular System
The Wikibook Anatomy and Physiology of Animals has a page on the topic of: Muscles
Library resources about
Muscular system
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