Categories: Anatomy

A Quick Overview of skeletal muscle

Skeletal muscle

Skeletal muscle is an individual of three chief muscle types. It is a type of striated muscle tissue, which is underneath the voluntary control. Most of the skeletal muscles are connected to bones by bundles of the collagen fibers known as the tendons.

Skeletal muscle characteristics

  • This is one of three main  types of muscle
  • It consists of striated muscle tissue
  • This is below the voluntary control of the somatic part of the nervous system.
  • Utmost skeletal muscles are attached directly to bones by packs of collagen fibers which are known as tendons
  • The Muscle fibers of skeletal are cylindrical
  • They have further than one nucleus
  • They moreover have several mitochondria to bump into energy needs.

Have you ever questioned what the number of skeletal muscles you have is in your total body?

  • There are probably above 650 named skeletal muscles in the whole body.

Structure of skeletal muscle

  • A skeletal muscle refers to numerous bundles of cells combined named muscle fibers.
  • The muscles and fibers are enclosed by layers of connective tissue named ac fasciae. Muscle fibers, or cells of muscle, are made from the union of developmental myoblasts in a procedure identified as myogenesis.
  • Muscle fibers have a cylindrical shape and contain more than one nucleus. They also contain many mitochondria to fulfill energy needs.
  • Muscle fibers are made up of myofibrils. The myofibrils are made up of myosin and actin filaments, repetitive in units called sarcomeres, which are the fundamental functional units of all the muscle fiber.
  • The sarcomere is in authority for the absolute striated appearance of the skeletal muscle and it forms the fundamental machinery necessary for the muscle.
  • The stem cells which distinguish into a mature form of muscle fibers are called satellite cells.
  • These cells can be found sandwiched between the basement membrane and the sarcolemma. When these cells stimulated by growth factors, they distinguish and multiply to produce new muscle fiber cells.

The function of skeletal muscle

  • The main functions of the skeletal muscle take place through its intrinsic excitation-contraction coupling process.
  • As the muscle is connected to the bone tendons, the contraction of the muscle leads to the movement of that bone that permits for the presentation of specific movements.
  • The skeletal muscle also is responsible for structural support.
  • It will help in maintaining the posture of the body.
  • The skeletal muscle to work as a storage source for the amino acids that may be used by many different organs of the body for manufacturing the organ-specific proteins.
  • The skeletal muscle as well plays a main role in sustaining thermostatic and work as an energy source through starvation.

Embryology

  • For the duration of embryogenesis, it is that para-axial mesoderm that goes through the stepwise difference to produce the muscle tissue.
  • The para-axial mesoderm on both sides of the neural tube begins to differentiate and go through segmentation to make the somites.
  • Then the somites get stimulated through the myogenic regulatory factors to distinguish into a dermomyotome and sclerotome.
  • These regulatory factors contain the Shh, Wnt and BMP4 proteins.
  • The neural tubes and the surfaces ectoderm are the prime sources of Wnt proteins, the Shh proteins, source from the Notochord, and then the lateral mesoderm plate forms the BMP4 protein.
  • The lateral feature of the dermomyotome goes through epithelial to mesenchymal transition as it continues to travel on the ventral side to make a unique myotome underneath the dermatome.
  • The myotome at that time differentiates to produce the skeletal muscles in the body afterward receiving stimulation after the Sonic Hedgehog (Shh) signaling molecule from the notochord that results in the Myf5 expression and subsequent differentiation.
  • The dorsomedial part of the myotome differentiates into epaxial myotome giving growth to back muscles.
  • The ventrolateral part distinguishes into hypaxial myotome that will give rise to the muscles of the wall of the body.
  • The development of the skeletal muscles in the trunk and the limb hinge on the expression of MyoD and Myf5 and they have effects on the changed myoblasts.
  • These are embryonic myoblasts go through further differentiation to make the primary muscle fibers and ultimately secondary myofibers by the combination of the myoblasts in the fetus.
  • After birth, the satellite cells deed as stem cells and are accountable for the further growth and development of the skeletal muscles.

Blood Supply

  • The chief artery or the primary artery supplying blood toward the skeletal muscle progresses analogous to the longitudinal axis of the muscle fiber.
  • The primary artery contributes off tributaries which are identified as feed arteries that are vertical to that primary artery and continue towards the external connective tissue sheath of the muscle fiber named perimysium.
  • Then the feed artery subdivisions into the primary arterioles which afterward two extra orders of branching provide rise to transverse arterioles, which in turn gives rise to terminal arterioles.
  • The terminal arterioles are the last vascular branches, and then they perfuse to the capillaries that are present inside the endomysium and travel analogous to the longitudinal axis of the muscle fiber.
  • The terminal arteriole end to end with the capillaries that it supplies is identified as a microvascular unit, and it is the smallest unit in the whole skeletal muscle through the blood flow can be controlled.

Lymphatics

  • Lymph capillaries create in skeletal muscle into the microvascular unit inside the endomysium close to the main capillary bed and drain off the tissue fluid.
  • These capillaries combine to make the lymphatic vessels by way of the drain out of the tissue fluid.
  • These lymphatic vessels go from the perimysium and joint with the larger lymphatic vessels.
  • Dissimilar the blood vessels, the walls of the lymph vessels inside the muscle do not have contractile property due to the absence of smooth muscles, so they all depend on the muscle movements and the arteriolar pulsations to drain the lymph out.

Nerves

The neuronal innervation of the skeletal muscle usually includes of the

  1. sensory nerve fibers
  2. motor nerve fibers
  3. Neuromuscular junction.

The nerve fibers are made up of myelinated as well as non-myelinated nerve fibers. The cell bodies of those neurons give rise to large axons which are generally unbranched and then travel to the target muscles for their innervation. Near to the target muscle, the axons divided into the numerous smaller branches to innervate numerous muscle fibers.

The motor nerve terminal consumes abundant mitochondria, endoplasmic reticulum and many membrane-bound vesicles comprising the neurotransmitter- acetylcholine.

Once the action potential touring to the neuromuscular junction, there happens a sequence of processes concluding into the fusion of the membrane of that synaptic vesicles by the presynaptic membrane and succeeding release of the neurotransmitter inside the synaptic cleft.

Muscles

  • Each muscle includes multiple tissues as well as blood vessels, contractile muscle fibers, lymphatics and the sheaths of the connective tissue. The outmost sheath of the connective tissue enclosing each muscle is named as epimysium.
  • For each muscle is composed up of sets of muscle fibers named fascicles which are encircled by a connective tissue layer named as perimysium.
  • Within each fascicle, there are numerous units of the individual muscle fibers enclosed by endomysium, a connective tissue sheath.

Clinical Significance

  • Skeletal muscles permit humans to transport and achieve daily activities.
  • They play a vital role in respiratory mechanics and help in preserving posture and balance.
  • They also look after the vital organs in the body.

Numerous medical conditions happen as a result of abnormalities in the function of skeletal muscles.

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A Quick Overview of Smooth Muscle

Some of these diseases include

  • Myopathies,
  • Paralysis,
  • Myasthenia gravis,
  • Urinary and or bowel incontinence,
  • Ataxia,
  • weakness,
  • Tremors, among others. Disorders of the nerves can cause neuropathy and cause disturbances in the functionality of the skeletal muscles as well.

Muscle Cramps

Muscle cramps result in

  • continuous,
  • involuntary,
  • Painful
  • localized contraction of an entire muscle group, individual single muscle, or select muscle fibers.
  • Generally, the cramp can last from minutes to a few seconds for idiopathic or known causes with healthy subjects or in the presence of diseases. Palpating the muscle area of the cramp will present a knot.

Other appropriate conditions in this include, but are not inadequate to the following:

  • Exercise-induced and heat-related muscle cramping
  • Thoracic outlet syndrome
  • Piriformis syndrome

Palsy/Compression Neuropathy

Numerous muscle palsies happen secondary to the long-term, downstream effects of various nerve conditions and neuropathies that can result in the frankly flaccid condition.  These syndromes include, but are not inadequate to the following:

  • Bell’s palsy
  • Klumpke’s palsy
  • AIN syndrome or PIN syndrome
  • Carpal tunnel syndrome
  • Guyon canal syndrome
  • Supraspinatus and/or infraspinatus atrophy

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