100 milliseconds if tension overcomes resistance of

This preview shows page 7 - 10 out of 15 pages.

100 milliseconds, if tension overcomes resistance of load, muscle shortens o period of relaxation – final phase, 10-100 milliseconds, reentry of Ca into sarcoplasmic reticulum, number of cross bridges declining, tension is 0, if shortened, muscle returns to normal length twitch contractions of some muscles are quick and short, like muscles that control eye movement others contract more slowly, such as calf muscles muscles twitches are not the way muscles normally function o healthy muscle contraction is smooth
Image of page 7

Subscribe to view the full document.

graded muscle responses – variation in strength of contractions based on demands placed on muscles, required for proper control of skeletal movements muscle contraction can be sorted in 2 ways o changing the frequency of stimulation o changing the strength of stimulation Wave Summation: greater muscular force achieved by increasing firing rate of motor neurons if two identical stimuli are delivered to a muscle in rapid succession, the second twitch will be stronger called wave summation – second contraction occurs before muscle has completely relaxed o muscle already partially contracted, more calcium being released, causes more shortening than the first contraction o means the contractions are added together o refractory period always honored, so if second stimulus arrives before repolarization happens, no wave summation occurs if a muscle is stimulated at increasingly faster rate: o relaxation time between twitches becomes increasingly shorter o higher concentration of Ca in cytosol becomes increasingly higher o degree of wave summation becomes increasingly greater, progresses to sustained, quivering contraction called incomplete tetanus o as stimulation frequency continues to increase, muscle tension increases until it reaches maximal tension, all muscle relaxation disappears and contractions fuse into smooth, sustained contraction called complete tetanus complete tetanus happens infrequently prolonged tetanus leads to muscle fatigue and the tension will drop to 0 primary function of wave summation is to produce smooth, continuous muscle contractions by rapidly stimulating a specific number of muscle cells Recruitment: Also called multiple motor unit summation This controls the force of contraction more precisely Increasingly more muscle fibers called into play Stimulus at which first observable contraction occurs is called threshold stimulus o Beyond this, muscle will continue to contract more vigorously Maximal stimulus is strongest stimulus that increases contractile force o All muscle motor units are recruited Recruitment process is dictated by the size principle : o motor units with the smallest muscle fibers are activated first o motor units with larger muscle fibers begin to be excited and contractile strength increases
Image of page 8
o largest motor units controlled by largest, least excitable neurons, only activated when most powerful contraction is needed
Image of page 9

Subscribe to view the full document.

Image of page 10
  • Spring '17
  • muscle tension

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern