lab 8 Flashcards
(15 cards)
during the fatigue experiment in lab, you would expect signal to increase while the dynamometer readings decrease. Explain both changes, Be sure to include what is measured by each in your explanation
dynamometer measures power/force of muscles while electromyogram measures electrical activity. Fatigue is the inability of muscles to maintain force so force should decrease (dynamometer) but the electrical activity will increase since muscle is tiring out
two students are testing their grip strength with a dynamometer. Both have roughly equal percentage of fat tissue in their arms, but student 1’s forearm diameter is 20% larger than student 2s. which student do you predict to have the highest grip strength?
student will probably have higher strength bc that shows an increased diameter in muscle fiber which is usually associate with regular exercise.
name the units of muscle from largest to smallest (starting from whole muscle) which of these are muscle cells
muscle –> muscle fibre bundle(fascicle) –> muscle giber –> sarcolemma –> myofibril –> sarcomere(specialized PM of skeletal muscle cell)–> myofilament
olympic gymnastics gold medalist simone biles is performing a grip strength test to make sure she is prepared for the next olympics. Would you expect her grip strength to be higher in her dominant or non-dominant arm?
her grip strength would be higher in her dominant arm. your dominant arm tends to be larger than non-dominant in circumference. The neural connection on dominant side is stronger, and this allows you to recruit muscle fibers more readily and supports a slightly increase in strength
one day as you are jogging, you notice your legs getting tired. You remember from your favorite science class that lack of O2 is one cause of fatigue. how does lack of O2 cause muscle fatigue?
muscles will begin converting glucose into lactic acid instead of energy, an anaerobic exercise takes over and power output drops =fatigue
in the muscle lab, you conducted both electromyography and dynamometry. what did each measure? also, give the units
electromyogram (EMG)- electrical activity of muscles (mv/ (time in seconds) mv/s
dynamogram- measures force of muscle (power) (kg/s)
force (kg) vs time (sec)
you are measuring time to muscle fiber in lab, you hook up electrodes to produce the EMG and you grip/squeeze a ______ (fill in) to measure force. over time, as fatigue occurs, what do you expect to happen to the EMG? to force? explain
grip/squeeze a hand dynamometer
fatigue is the inability of muscles to maintain force of contraction after prolonged activity
would result in an increase in amplitude in EMG and decrease in frequencies = signals will decrease overall
briefly explain the roles of troponin and tropomyosin in skeletal muscle contraction
tropomyosin is held in place by troponin which changes conformation in presence of calcium. in a relaxed muscle tropomyosin blocks attachment site for the myosin cross bridge, preventing contraction
what is a motor unit
motoneurons and all the muscle fibers that the motoneuron innervates. skeletal muscle is stimulated to contract when the brain and spinal cord activate motor units
what is motor unit recruitment
the sequential activation of motor units to perform a designated task
what cells are producing the electrical signal by the EMG? what is happening to those cells to cause the signal?
electrical signals are generated when an excitable cell (like a nerve or muscle cell) experiences a change in its resting membrane potential caused by a movement of ions across the cell membrane. An EMG proves an extracellular view of the changes in muscle cell membrane potentials that are linked with the propagation of APs
summary of muscle contraction
- Action potential in a motor neuron triggers the release of Ca2+ ions from the sarcoplasmic reticulum
- Calcium ions bind to troponin (on actin) and cause tropomyosin to move, exposing binding sites for the myosin heads
- The actin filaments and myosin heads form a cross-bridge that is broken by ATP
- ATP hydrolysis causes the myosin heads to swivel and change orientation
- Swiveled myosin heads bind to the actin filament before returning to their original conformation (releasing ADP + Pi)
- The repositioning of the myosin heads move the actin filaments towards the centre of the sarcomere
- The sliding of actin along myosin therefore shortens the sarcomere, causing muscle contraction
true or false
when there is an action potential in a motoneuron, there is a AP in all of these fibers of the motoneuron
true
a complex EMG signal is a net result of
propagation of motor nerve impulses, transmission of motor nerve impulses to motor unit, propagation of muscle impulses
What muscle fibers are recruited for contraction, what order are they recruited in? are they recruited in the same order each time?
the higher the recruitment the stronger the contraction , recruited in order of smallest to largest (slow –> twitch)
type 1 first, type 2a, type 2b
