Exam 3-Muscle Mechanics Lecture

two factors that determine the tension at the muscle fiber level

-frequency in nervous stimulation

-muscle fiber length

why is tension low when sarcomere is compressed and stretched

-reduce the effective overlap of actin and myosin, limiting cross-bridge formation and reducing muscle's ability to generate force

if muscle fiber is stimulated by the nervous system just once, what is the name for the type of contraction produced in muscle

-muscle twitch

as the muscle fiber becomes stimulates by a higher frequency of action potentials, what happens to muscle fiber tension

-the greater the frequency of stimulation, the greater the tension produced

what is meant by complete tetanus and what is the frequency needed to produce complete tetanus

-occurs at very high frequencies, no visible relaxation between stimuli and muscle reaches a maximum tension

in a muscle fiber "twitch," why is there a short lag time before tension rises above zero

-caused by the time it takes for electrical signal to trigger the release of calcium and biochemical and mechanical events that allow for cross-bridge and tension

what causes the drop in tension after the peak and why

-removal of calcium ions and deactivation of the cross-bridge cycle leading to muscle relaxation

two factors that determine tension at the whole muscle level

-amount of tension produced within each muscle fiber

-the number (%) of muscle fibers that get activated within the whole muscle

what is a motor unit? how are they used to adjust the amount of tension that our muscles generate

-refers to a single motor neuron and all the muscle fibers it controls

-lifting objects from as little as a pencil (just a few, small motor units) to as big as a car (activate all motor units)

what is the trade-off between large and small motor units and where in the body are there very small motor units

-there is an important trade-off between the amount of tension generated and the degree of fine motor control

explain how motor units are used to increase stamina

-by cycling through different motor units

True or false: the interaction between thick and thin myofilaments is responsible for elongating the muscle as well as contracting the muscle

-false, the interaction between thick and thin can only shorten a muscle; it cannot return a muscle to its original length

3 factors that help contracted muscles return to its original length

-gravity

-elastic recoil

-antagonistic muscles

structures within the body that are responsible for "elastic recoil"

-elastic fibers, large arteries, bladder, heart muscle, joints, lungs

anatagonistic muscle

-muscles usually work in antagonistic pairs (a muscle that flexes is paired with one that extends) ex. quads extend lower leg, hammies flex it

direct source of energy for muscle contractions

-ATP ---> ADP+P

phosphagen system

-ADP and creatine phosphate together make up the "phosphagen system"

-powers nearly all activities requiring brief but intense effort

ex. short sprints, weight-lifting

how much ATP is present in muscle versus how much ATP does the muscle use over a 24 hour period

-amount of ATP used by muscle is huge, but there's little of it in muscle, only enough to support about 2 seconds of intense contractions

-solution: use other compounds to regenerate ATP as needed

how many seconds worth of intense contractions can supply of ATP itself support? the phosphagen system?

-ATP = 2 seconds

-phosphagen system = 15 seconds

what other compounds can be used to regenerate ATP

-ADP: ADP+ADP ---> ATP+AMP

-creatine phosphate: creatine phosphate+ADP ---> creatinine+ATP

advantages/disadvantages of aerobic respiration and anaerobic fermentation

-aerobic respiration = generates lots of ATP, supports 40+ min of intense work; requires O2

-anaerobic fermentation = works w/o oxygen, supports 2 min of intense work; generates lactic acid, get relatively little ATP

if someone goes jogging without warming up...

-what fuels are used at the start

-why cant the heart deliver oxygen fast enough to the muscles

-when the phosphagen system is depleted, what pathway is used to generate ATP

-roughly 40 seconds, what change occurs

-use O2 stored on myoglobin (aerobic respiration)

-phosphagen system is used; relies on anaerobic fermentation which generates ATP from glucose/glycogen but lactic acid builds up

-at about 40 seconds, the heart catches up and can deliver O2 fast enough, so muscles switch over to aerobic respiration; can rely on this until water glucose/glycogen are depleted

two major reasons a person continues to breathe heavily at the end of exercise

-repayment of oxygen debt; replenish its O2 reserves, replace the O2 that was bound to myoglobin and hemoglobin; extra O2 is needed to oxidize all the lactic acid that was generated, most of it enters blood stream and is converted by the liver back into glucose

-2 major types of muscle fibers and how do they differ:

speed, size, vascularization, number of mitochondria, amount of myoglobin

-slow fibers (red; pay as you go) = contract slowly, small, richly vascularized, lots of mitochondria (generate ATP by using oxygen to break down fuel), lots of myoglobin (so muscle fiber can store its own oxygen)

-fast fibers (white; twitch now pay later) = contract rapidly, large, poorly vascularized, fewer mitochondria, less myoglobin

which type of muscle fiber would have the greatest stamina and why

-slow fiber = adapted for aerobic respiration; high stamina, slow to fatigue ex. soleus

-fast fiber = largely on anaerobic fermentation, quick spurts of power but easily fatigue ex. rectus femoris, triceps brachii

most muscles in the human body are actually "pink" what does this mean

-mixture of slow-twitch fibers and fast-twitch fibers

what effect does aerobic training have on muscle fibers

-increased numbers of mitochondria and capillaries, notable in fast fibers

muscular dystrophies? specific cause of duchenne's muscular dystrophy

-degrade and weaken muscles

-missing an important protein called dystrophin, w/o this, tears develop in sarcolemma and muscle fibers die

-common type, 3-7 yr old boys, wheelchair by age 12, early death

trichinosis

-infection with a parasitic roundworm (nematode)

-results from eating undercooked, infected pork

-larvae mature in our intestinal tract where they mate and produce eggs, new generate migrates to skeletal muscle where they form cysts in the peri- and endomysium

similarities and differences among myasthenia gravis, botulism, and tetanus

-myasthenia gravis = autoimmune disease in which the body's own immune system attacks ACh receptors on the sarcolemma, causes paralysis; treatment would be immunosuppressants, boost ACh levels

-botulism = ingesting a bacterial toxi, caused by eating food that was improperly canned and not cooked thoroughly, toxin prevents the release of ACh, resulting in paralysis ---> risks: respiratory paralysis/suffocation

-tetanus (lockjaw) = infection with clostridium bacteria, released a toxin that leads to powerful, abnormal muscle contractions; 40-60% mortality rate *if elderly, often via suffocation