muscle

Examples of muscle in the following topics:

• Muscles and Joints

  • Muscles and joints involve very interesting applications of statics.
  • Muscles can only contract, so they occur in pairs.
  • In the arm, the biceps muscle is a flexor: it closes the limb.
  • The triceps muscle is an extensor that opens the limb.
  • Because muscles can contract but not expand beyond their resting length, joints and muscles often exert forces that act in opposite directions, and thus subtract.

• Electric Potential in Human

  • Resting membrane potential is approximately -95 mV in skeletal muscle cells, -60 mV in smooth muscle cells, -80 to -90 mV in astroglia, and -60 to -70 mV in neurons.
  • When the brain decides on an action, it sends an impulse that cascades to the extremity where a muscle contracts.

• Humans and Electric Hazards

  • Electric shock occurs upon contact of a body part with any source of electricity that causes a sufficient current through the skin, muscles, or hair.
  • The muscles that close the fingers are stronger than those that open them, so the hand involuntarily closes around the wire shocking it.
  • Pathway: If current flows through the heart muscle, it is more likely to be lethal.
  • (a) The victim is "thrown" backward by involuntary muscle contractions that extend the legs and torso.
  • (b) The victim can't let go of the wire that is stimulating all the muscles in the hand.

• Humans: Work, Energy, and Power

  • The many small muscle actions accompanying all quiet activity, from sleeping to head scratching, ultimately become thermal energy, as do less visible muscle actions by the heart, lungs, and digestive tract.
  • Shivering, in fact, is an involuntary response to low body temperature that pits muscles against one another to produce thermal energy in the body (and do no work).
  • Of course, during vigorous exercise, the energy consumption of the skeletal muscles and heart increase markedly.
  • The BMR is a function of age, gender, total body weight, and amount of muscle mass (which burns more calories than body fat).

• Pumps and the Heart

  • A complete cardiac cycle is one round of the heart pumping blood and consists of two parts: systole (contraction of the heart muscle) and diastole (relaxation of the heart muscle).

• Applications: Ultrasound, Sonar, and Medical Imaging

  • ., between bone and muscle, or muscle and fat), part of the wave is reflected and part of it is transmitted.

• Nerve Conduction and Electrocardiograms

  • Second, nerves carry messages from the central nervous system to muscles and other organs.
  • Just as nerve impulses are transmitted by depolarization and repolarization of an adjacent membrane, the depolarization that causes muscle contraction can also stimulate adjacent muscle cells to depolarize (fire) and contract.
  • The voltage between the right arm and the left leg is called the lead II potential and is an indicator of heart-muscle function.

• Nearsightedness, Farsidedness, and Vision Correction

  • The eye's ciliary muscles control the shape of the lens.
  • When you focus on something, you squeeze or relax these muscles.

• Electric Activity in the Heart

  • As can be seen in , there is a thick wall of muscle separating the right side and the left side of the heart called the septum.
  • These cells are specialized cardiomycetes (cardiac muscle cells).
  • This causes the muscle tissue of the ventricles to contract, thus enabling a force to eject blood out of the heart.

• NMR and MRIs

  • MRI shows a marked contrast between the different soft tissues of the body, making it especially useful in imaging the brain, the muscles, the heart, and cancerous tissue—as compared with other medical imaging techniques such as computed tomography (CT) or X-rays.