Lab 4b

define electromyography

a recording of skin-surface voltage that is produced by underlying skeletal muscle contraction

motor unit recruitment

An increase in the number of activated motor units in a skeletal muscle, in order to increase the tension in the muscle

muscle fatigue

Inability of muscle to maintain its strength of contraction or tension; may be related to insufficient oxygen, depletion of glycogen, and/or lactic acid buildup

what are the effects of estrogen and testosterone hormones on skeletal muscle

both hormones aid in keeping the skeletal muscle healthy evidence shows that a loss in sex hormones correlates to age-related decline in bone and skeletal muscle mass Estrogen has also been shown to protect younger women from muscle injury apparently by stabilizing the muscle membrane (28). Whether the glycogen-sparing effects of estrogen (muscle endurance) and the protection of muscle from injury are lost with menopause is largely unexplored. It does appear anecdotally that postmenopausal women are more susceptible to muscle injury. The profound anabolic effect of testosterone on muscle becomes evident at puberty, when boys gain ∼35% more muscle mass than girls. Testosterone stimulates myoblasts and increases the number of satellite cells, which promotes protein synthesis. Once men are in their 20s, testosterone levels begin to decline, and this decline is continuous throughout their lifetime

____________________ is found only in the heart, where it originates and spreads the heartbeats that keep us alive

cardiac muscle

in other cases, muscle fatigue can be attributed to _______________________, in which an accumulation of ______ ions in the transverse tubules of skeletal muscle fibers eventually leads to an inability to produce subsequent _________________

conduction failure K+ action potentials

in a motor unit, whenever the motor neuron is activated, all of its muscle fibers are commanded to _________________________

contract simultaneously

the voltage produced by contraction is weak, but it can be picked up by surface sensors to produce the recording, referred to as an _____________

electromyogram (EMG)

a recording of skin-surface voltage that is produced by underlying skeletal muscle contraction

electromyography

therefore, in real life, ____________ motor units, rather than ____________ muscle fibers, are contracting to accomplish body movements

entire single

skeletal muscle is mainly attached to the various bones of the skeleton; it helps provide a _____________ and _____________ for the body, as well as the ability to move in response to willing an action to occur

framework support

factors in addition to gender that contribute to observed differences in clench strength

one of the main causes seems to be a buildup of lactic acid from the anaerobic respiration of glucose the resulting decrease in blood pH in the vicinity the decreased response of the muscle at low pH in other cases, muscle fatigue can be attributed to conduction failure, in which an accumulation of K+ ions in the transverse tubules of skeletal muscle fibers eventually leads to an inability to produce subsequent action potentials

several factors appear to contribute to muscle fatigue one of the main causes seems to be a buildup of ____________________ from the ____________________________, the resulting decrease in _______________ in the vicinity, and the decreased response of the muscle at _______ pH

lactic acid anaerobic respiration of glucose blood pH low

Small number of activated motor units only generates enough force to pick up a _________________________ object

light weight

the periods of tonus will show up in the BIOPAC data window as very ___________________

low mV readings

however, if that person picks up a 10 lb weight instead, many ___________ motor units will be stimulated, in order to generate enough muscle ___________ to pick up the heavier object

more tension

A single motor neuron plus all of the muscle fibers it controls is called a _________________________

motor unit

An increase in the number of activated motor units in a skeletal muscle, in order to increase the tension in the muscle, is called _______________________________

motor unit recruitment

decrease in muscle mass often stems from disabling circumstances when muscles waste away. The main reason for muscle wasting is a lack of physical activity. This can happen when a disease or injury makes it difficult or impossible for you to move an arm or leg. A symptom of atrophied muscles is an arm that appears smaller, but not shorter, than the other arm.

muscle atrophy

strenuous exercise or work, which requires repeated or sustained maximal muscle contraction, sometimes results in ____________________, a state in which muscle contraction decreases, even when the muscle is still being stimulated

muscle fatigue

each skeletal muscle in our body is composed of thousands of skeletal ____________________ (cells)

muscle fibers

increase in muscle mass (sarcoplasmic and myofibril growth) often associated with lifting weights a term for the growth and increase of the size of muscle cells. The most common type of muscular hypertrophy occurs as a result of physical exercise such as weightlifting, and the term is often associated with weight training.

muscle hypertrophy

when a single muscle fiber is stimulated by its motor neuron to contract, then relaxes completely, and then contacts again, the subsequent contractions all produce the same amount of _____________________

muscle tension

when skeletal muscles are at rest ( not in the process of contracting), they maintain a slight amount of contraction called _________________________

muscle tone or tonus

each motor neuron associated with skeletal muscle fibers innervates (stimulates, controls) a certain ____________________, from fewer than 10 to thousands.

number of fibers

this helps keep the motor units in good health, and in the case of the ______________________, it allows us to maintain good posture for many hours at a time

postural muscles in the back

in resting skeletal muscles, motor units take turns contracting, so that the muscle is always ______________________ on short notice

ready to contract

slow twitch slow oxidative aerobic mitochondria /respiratory enzymes cross country runners/ marathons myoglobin

red skeletal muscle fibers

for example, if a person decides to pick up a 1 lb weight, just a ___________ number of motor units will be activated to contact

small

____________________ is located mostly in the tubular organs of our internal systems; it accomplishes many types o ______________ movement, such as the churning action of the stomach and the transport of urine from the kidney to the bladder

smooth muscle internal

muscle fatigue will be induced by a sustained, maximum fist clench, and will appear on the dynagram as a ____________________________________

steady decline in muscle tension

although there are many motor units in a skeletal muscle, not all of them are _________________ during every muscle contraction

stimulated

skeletal muscle fibers are unique among the three types of muscle tissue in that they contract only in response to ______________ by a _________ neuron

stimulation motor

however, if a muscle fiber is stimulated again, before it has time to relax completely, then the second twitch will generate more tension than the first. This is called _____________________

temporal (wave) summation

a twitch consists of a rapid period of ______________ development and contraction, followed by a ______________ in tension and relaxation of the muscle

tension decrease

when a muscle fiber is stimulated to contract by several stimuli in rapid succession, and there is no opportunity for muscle relaxation between stimuli, the tension increased until it reaches the maximum possible force for that muscle fiber, and then remains at that level until the stimulation stops; this type of sustained contraction is called _________________

tetanus or titanic contraction

______________: slower contraction speed; can sustain contraction for long periods without fatigue; rich capillary supply; more mitochondria; more respiratory enzymes; more myoglobin Said to have high ____________ capacity, so are called slow oxidative fibers Due to myoglobin content (which has a red pigment), these are also called ______ fibers Found in postural muscles

Slow twitch fibers (type I) oxidative red

Explain the source of signals detected by the EMG electrodes.

The electrical activity of muscles and the action potential propagated along the sarcolemma

Define dynamometry

Dynamometry is the measurement of power generated by a muscle group.

________________: faster contraction speed, fatigue fast, fewer capillaries, mitochondria, respiratory enzymes, and less myoglobin Also called white fibers Have more ________________ stores and are called fast glycolytic fibers Found in stronger muscles

Fast twitch fibers (type II) white glycogen

you will use a __________________ hand clench forces pump bulb to generate a recording called a ____________

hand dynamometer dynagram

Recruitment of more motor units has increased the force to the extent that a _________________________ can be lifted

heavier object

as you _____________ the clench force of your fist, more _________________ will be recruited to generate increasing amounts of muscle tension

increase motor units

Temporal (wave) summation is the body's way of _____________________ generated by muscles

increasing the force

skeletal muscle is one of _________ types of muscle tissue in the body

three

you will be able to observe _____________ in the short periods of time between fist clenches.

tonus

the response of a single skeletal muscle fiber to stimulation by its motor neuron is called a ______________

twitch

fast twitch muscle fibers anaerobic fast glyocotytic less mitochondria/ respiratory enzymes weight lifters/ sprinters

white skeletal muscle fibers