skeletal-muscle pump

Examples of skeletal-muscle pump in the following topics:

• Blood Flow in Skeletal Muscle

  • Skeletal muscles are important in maintaining posture and controlling locomotion through contraction.
  • Blood vessels are closely intertwined with skeletal muscle tissues lying between the fascicles, or bundles of muscle fibers.
  • Skeletal muscles also play a key role in the movement of blood around the body.
  • The skeletal muscles of the legs are particularly important skeletal muscle pumps as they prevent pooling of the blood in the feet and calves due to gravity.
  • It is unclear whether the action of skeletal muscle pumps influences arterial flow or if this is maintained purely by the pumping of the heart.

• Anatomy of the Heart

  • The heart is an organ responsible for pumping blood through the blood vessels using rhythmic contractions of cardiac muscle.
  • The left side of the heart receives oxygenated blood from the pulmonary vein and pumps it into the aorta, while the right side of the heart receives deoxygenated blood from the vena cava and pumps it into the pulmonary vein.
  • The middle layer of the heart, the myocardium, and contains specialized cardiac muscle tissue responsible for contraction.
  • Cardiac muscle tissue is distinct from skeletal or smooth muscle because it pumps involuntarily based on conduction from the AV and SA nodes.
  • Note the difference in the thickness of the muscled walls of the atrium and the left and right ventricle.

• Types of Muscle Tissue

  • There are three kinds of muscle tissue: skeletal, smooth, and cardiac.
  • Skeletal muscles are highly organized with cells lying parallel to each other.
  • Skeletal muscle fibers are the longest muscle fibers and have stripes on their surface.
  • Skeletal muscle is striated, multinucleate, and involuntary.
  • Cardiac muscle is striated, similar to skeletal muscle, but beats involuntarily.

• Characteristics of Muscle Tissue

  • The three types of muscle tissue are skeletal, smooth, and cardiac.
  • Some skeletal muscle can attach directly to other muscles or the skin, as seen in the face where numerous muscles control facial expression.
  • Cardiac muscle tissue is found only in the heart where cardiac contractions pump blood throughout the body and maintain blood pressure.
  • Cardiac and skeletal muscle are both striated in appearance, while smooth muscle is not.
  • Both cardiac and smooth muscle are involuntary while skeletal muscle is voluntary.

• Lymphatic Vessel Structure

  • The activity of smooth muscles allows lymph vessels to slowly pump lymph fluid through the body without a central pump or heart.
  • By contrast, the smooth muscles in blood vessels are involved in vasoconstriction and vasodilation instead of fluid pumping.
  • Lymph fluid can only flow forward through lymphangions due to the closing of valves after fluid is pushed through by fluid accumulation, smooth muscle contraction, or skeletal muscle contraction.
  • Without valves, the lymphatic system would be unable to function without a central pump.
  • They function similarly to lymphatic valves, though are comparatively more dependent on skeletal muscle contractions.

• Myocardial Thickness and Function

  • The structure of cardiac muscle shares some characteristics with skeletal muscle, but has many distinctive features of its own.
  • Cardiomyocytes are shorter than skeletal myocytes and have fewer nuclei.
  • At these T-tubules, the sarcolemma is studded with a large number of calcium channels which allow calcium ion exchange at a rate much faster than that of the neuromuscular junction in skeletal muscle.
  • Cardiac muscle, like skeletal muscle, is comprised of sarcomeres, the basic, contractile units of muscle.
  • Cardiac muscle  and skeletal muscle both contain the protein myoglobin, which stores oxygen.

• Arrangement of Fascicles

  • Skeletal muscles are grouped into fascicles, which are bunches of muscle fibers surrounded by a perimysium.
  • Skeletal muscle tissue is composed of numerous muscle fibers which are separated from adjacent muscles and other tissues by a layer of dense, elastic connective tissue termed the fascia.
  • Beneath the fascia in skeletal muscle is another layer of connective tissue termed the epimysium which is closely associated with the fascia.
  • Whilst both cardiac and smooth muscles are also wrapped in connective tissue, they are not differentiated in the same way as skeletal muscles.
  • Skeletal muscle is surrounded by a thick outer layer of connective tissue termed the fascia.

• How Skeletal Muscles Are Named

  • The anatomical arrangement of skeletal muscle fascicles can be described as parallel, convergent, pennate, or sphincter.
  • Skeletal muscle can be categorised into four groups based on its anatomical arrangement.
  • Most skeletal muscles in the body are parallel muscles; although they can be seen in a variety of shapes such as flat bands, spindle shaped, and some can have large protrusions in their middle known as the belly of the muscle.
  • In Pennate muscles, the tendon runs through the length of the muscle.
  • Skeletal circular muscles are different from smooth muscle equivalents due to their structure and because they are under voluntary control

• Layers of the Heart Walls

  • It is composed of cardiac muscle cells, or cardiomyocytes.
  • Cardiomyocytes are specialized muscle cells that contract like other muscle cells, but differ in shape.
  • Compared to skeletal muscle cells, cardiac muscle cells are shorter and have fewer nuclei.
  • Cardiac muscle tissue is also striated (forming protein bands) and contains tubules and gap junctions, unlike skeletal muscle tissue.
  • The inner layer of the heart wall is the endocardium, composed of endothelial cells that provide a smooth, elastic, non-adherent surface for blood collection and pumping.

• Interactions of Skeletal Muscles

  • Skeletal muscles interact to produce movements by way of anatomical positioning and the coordinated summation of innervation signals.
  • Skeletal muscle contractions can be grouped based on the length and frequency of contraction.
  • If an additional action potential were to stimulate a muscle contraction before a previous muscle twitch had completely relaxed then it would sum onto this previous twitch increasing the total amount of tension produced in the muscle.
  • For skeletal muscles, the force exerted by the muscle can be controlled by varying the frequency at which action potentials are sent to muscle fibers.
  • Explain the summation interactions of skeletal muscles and how they affect movement