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)
What causes blood flow?
the ratio of pulse pressure / peripheral resistance
What is blood volume
the total volume of blood in the body
What is stroke volume
the amount of blood pumped out of each ventricle with each contraction
What is pulse pressure
the pressure gradient necessary for blood flow
How do you calculate pulse pressure?
PP = systolic - diastolic
What is the Mean Arterial Pressure (MAP)?
the main driving force for blood flow through the systemic circuit
How do you calculate MAP?
MAP = diastolic + (1/3) pulse pressure
What intrinsic mechanisms regulate cardiac output and peripheral resistance?
Frank Starling Law of the Heart (strength of contraction proportional to muscle fiber stretch. More venous return = larger contraction/stroke vol)
SA node responds to stretch (increased AP frequency, increase HR)
Local control of vessel diameter (metabolic changes, myogenic stretch)
What extrinsic mechanisms regulate cardiac output and peripheral resistance?
Sympathetic (NE) and Parasympathetic (Ach) influences on heart
NE + Epinephrin to prolong effects of sympathetic response on blood vessels
Endocrine influences on blood vol (ADH, Aldosterone, Natriuretic peptides)
