Class Notes (810,861)
United States (314,399)
Biology (601)
BIOL 1117 (81)

Muscles: Phases of Contraction, Muscle metabolism, Cardiac muscle

5 Pages
Unlock Document

Northeastern University
BIOL 1117
Christopher Richardson

L20-Muscle Cells 10/24/13 • Isometric and Isotonic Contractions o isometric muscle contraction  This is contraction without a change in length  Contractions do not always lead to a shortening of a muscle; the muscle only develops internal tension  muscle is producing internal tension while external resistance causes it to stay at the same length  can be a prelude to movement after tension is absorbed by elastic component of muscle o isometric muscle contraction  isometric contraction of two antagonistic muscles at a joint maintains joint stability  Two opposite but equal tension forces opposite each other  Each opposing muscle rebuilds up new tension in equal opposition to the other; thus, length of each muscle stays the same  isometric contraction of postural muscles keeps the body erect against force of gravity  In each opposing muscle, cycling cross bridges rebind to same actin molecules with a new force generated repeatedly  Also, carrying an object in front of you is isometric for downward force of load is opposed by equal upward force of muscle tension o isotonic muscle contraction  muscle changes in length with no change in tension  concentric contraction: muscle shortens while maintains tension • This contraction type moves a load as the muscle shortens  eccentric contraction: muscle lengthens as it maintains tension • lengthening of muscle fibers require external forces applied to the muscle • in absence of external lengthening forces, a fiber will only shorten when stimulated • Amuscle fiber can never lengthen under its own power o the chemical changes in the contractile proteins are the same during each type of contraction (both isometric and isotonic) o Whether the muscle shortens, lengthens or does not change in length depends only on the magnitude of the load on the muscle • Isometric and Isotonic Phases of Contraction o at the beginning of contraction: isometric phase  muscle tension rises but muscle does not shorten o when tension overcomes resistance of the load: isotonic phase  tension levels off and muscle begins to shorten and move the load o The heavier the load or greater the R, the longer it takes for the tension to increase to the value of the load o If the load on fiber is increased, eventually a load is reached that the fiber will be unable to move or lift, so the distance of shortening is now zero and the contraction is completely isometric o Most natural movements are produced by muscle contractions that are neither just isometric or just isotonic • Muscle Metabolism o all muscle contraction depends on ATP o ATP supply depends on availability of oxygen and organic energy sources o two main sources ofATP synthesis  anaerobic fermentation • enables cells to produceATP in the absence of oxygen • yields little ATP and toxic lactic acid, a major factor in muscle fatigue  aerobic respiration • produces far moreATP • less toxic end products (CO and water) 2 • requires a continual supply of oxygen o In resting muscle, mostATP is generated by aerobic respiration of fatty acids o During exercise, different mechanisms produceATP depending on duration of exercise • Immediate Energy Needs o short, intense exercise  oxygen need is briefly supplied by myoglobin for a limited amount of aerobic respiration at onset – rapidly depleted  muscles meet most ofATP demand by borrowing phosphate groups (P)ifrom other molecules and transferring them toADP  Until cardiovascular and respiratory systems meet the demand for more oxygen o phosphagen system: two enzyme systems control these phosphate transfers  provides nearly all energy used for short bursts of intense activity • Short-Term Energy Needs o muscles shift to anaerobic fermentation  in the absence of oxygen, glycolysis can generate a net gain of 2 ATP for every glucose molecule consumed  converts glucose to lactic acid  Glucose to pyruvic acid is glycolysis; then pyruv
More Less

Related notes for BIOL 1117

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.