LAB QUIZ 2 Flashcards
When does a muscle fiber twitch occur?
when the threshold stimulus (Ach) occurs at the motor end plate of a skeletal muscle
What does a muscle fiber twitch cause?
causes an AP to be conducted in all directions along the sarcolemma (all or none response).
What does a muscle fiber twitch result in?
a single contraction of each sarcomere to the greatest extent possible
T or F
The force of a whole muscle contraction is a graded response
True
T or F
All muscle fibers (motor units) are stimulated to contract at the same time
False - contractions of whole muscles vary in strength, so not all muscle fibers are stimulated to contract at the same time
What things determine strength of a whole muscle contraction?
of motor units recruited
Tension (force) produced by each muscle cell
Extent of fatigue
What factors contribute to tension?
treppe (thermal kinetic energy)
frequency of stimulation
initial fiber length
thickness of fiber
Explain twitch summation
If a muscle fiber is re-stimulated before it has completely relaxed, the second twitch is added to the first twitch, resulting in summation
Explain muscular fatigue
muscle no longer responds to stimulus possibly due to chemical changes within the cell
Explain neuromuscular fatigue
fatigue at the neuromuscular junction due to motor neurons being unable to make Ach fast enough to sustain a series of APs
Explain central fatigue
CNS no longer sends signals. Motor neurons don’t generate APs even if the muscles could still respond to stimulation. Often physiological (i.e. pain)
Explain what causes the “lub dub” during the cardiac cycle
AV valve closes = Lub
Semilunar valve closes = Dub
What is systolic pressure
the maximum pressure exerted by the heart when the L ventricle contracts
What is diastolic pressure
the lowest pressure experienced by the arteries when the L ventricle relaxes
What influences blood pressure?
blood volume (hydrostatic pressure due mostly to plasma volume) and cardiac output (HRxSV)
