Chapter 8 Muscle Physiology Flashcards
3 Types of muscle tissues
skeletal, smooth, and cardiac
Skeletal muscle is a collection of ____
muscle fibers
Myofibrils
cylindrical intracellular structured that have the ability to contract
muscle fibers contain
myofibrils
each myofibril is made of organized arrangement of thick and thin __________ _______
cytoskeleton microfilaments
A-band
The region of stacked thick filaments (dark space in the middle)
H zone
the middle of the a band where it is lighter due to a lack of thin filaments
M line
Center line of the H zone- contains supportive proteins to hold thick filaments together
I band
region of stacked thin filaments only
z line
flat, cytoskeleton disc in the middle of the I band that connects thin filaments together
Sarcomere
the region between adjacent Z lines- smallest functional unit of muscular contraction
Thick filaments
bundles of myosin proteins
Thin filaments
mostly actin proteins; also tropomyosin and troponin
2 binding sites on the thick filaments (myosin head)
an actin binding site and an ATPace
The heads of the myosin proteins can also be called
the cross bridge heads
T/F Individual actin molecules are monomers
true
Troponin has 3 binding sites which are
- for tropomyosin
- for actin
- for Ca+
In the absent of calcium what happens to the myosin binding sites on the thin filament
tropomyosin will cover the bonding sites so they can’t work together when there isn’t calcium
Titin
elastic protein that helps muscle recoil back to its resting place
Inside there is a very low level of Ca+ which means…
tropomyosin blocks cross-bridge binding sites
When there is an increase in Ca+….
Ca+ will bind to troponin -> tropomyosin rolls away exposing cross-bridge binding sites
Could you identify from a list the sequence of steps describing how actin and myosin interact during skeletal muscle contraction?
1) Binding: Exposure of cross-bridge binding site -> myosin cross bridge bends up at lower neck and binds to site
2) Power stroke: Binding -> upper neck of myosin cross bridge bends back 45°, sliding thick & thin filaments across each other—basis of contraction
3) Detachment: Link between myosin cross bridge and actin breaks -> cross bridge returns to normal position
4) If [Ca2+]i still elevated -> cross-bridge binding sites still exposed -> cycle repeats
Why does the two myosin heads attach to actin at one time?
So filaments don’t slip back after detachment
Thin filaments are pulled in toward the M line causing ….
The H zone becomes shorter and the whole sarcomere becomes shorter
Where does the energy for the power stroke (myosin bending) come from?
ATP
What causes the increase in [Ca2+]i that leads to sarcomere contraction?
An action potential
Transverse (T) tubule
invagination of plasma membrane into a tube that runs down into the muscle fiber at the junction of A and I bands
Voltage gated Na+ channels in the T tubules allows…
action potential to travel down into cell and depolarize
Sarcoplasmic reticulum
network of interconnected membrane-enclosed compartments surrounding each myofibril
What does the SR store?
Calcium
Identify from a list the sequence of steps from neurotransmitter release at the neuromuscular junction to release of Ca2+ from the sarcoplasmic reticulum?
1) Action potential travels down tranverse tubule and activates voltage-gated receptors (dihydropyridine receptors) in the membrane of tubule
2) Activated dihydropyridine receptors activate abutting Ca2+-release channels in membrane of sarcoplasmic reticulum
3) Activated Ca2+-release channels open and Ca2+ flows from SR into cytosol
4) Ca2+ in cytosol later sequestered back into sarcoplasmic reticulum via an ATPase pump (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase [SERCA] pump)
Which events of contraction require ATP (energy) to keep going?
1) Power stroke: Energy from ATP split at myosin ATPase site on cross-bridge
2) Maintenance of Ca2+ gradient: SERCA pump uses energy from ATP to pump Ca2+ back into sarcoplasmic reticulum
3) Maintenance of Na+ and K+ gradients: Na+/K+ pump uses energy from ATP to pump Na+ and K+ across plasma membrane
3 stages of cellular respiration
glycolysis, citric acid cycle, and oxidative phosphorylation
What stage of cellular respiration make the most amount of ATP?
Oxidative Phosphorylation
What stage(s) of cellular respiration use anaerobic exercise
Glycolysis (fast bc of fewer chemical reactions)
What stage(s) of cellular respiration use aerobic exercise
Citric acid cycle and Oxidative Phosphorylation (slow bc of many chemical reactions)
How is anaerobic respiration fueled
with glucose
How is aerobic respiration fueled?
With glucose or fatty acids
Do you use anaerobic or aerobic respiration for high intensity?
Anaerobic
What does glycolysis produce?
Pyruvate
What happens when there’s excess pyruvate that doesn’t enter the citric acid cycle?
It converts pyruvate into lactic acid and that’s where muscle soreness during exercise comes from
Muscle fibers have an alternate pathway for immediate availability of ATP called…
creatine phosphate
How is creatine phosphate involved in ATP synthesis? Under what conditions would this
reaction occur and why?
Muscle fibers have an alternate pathway for immediate availability of ATPàcreatine phosphate
Increased O2 uptake continues after exercise (heavy breathing) partially due to O2 consumption during oxidative phosphorylation to rebuild creatine phosphate reserves
Isometric Contractions
Tension produced without muscle changing in length
Isotonic Contractions
Muscle changes in length
2 types of isotonic contractions
Concentric and eccentric
How does the velocity of muscle shortening change with increased load?
As load increases, maximum velocity of shortening decreases.
Problem: Muscles can only contract a small distance, but our limbs need to move over a much larger distance
Solution: Insert muscle onto bone near joint to make the joint a 3rd-class lever
Most energy used by muscles is converted to _______
Heat
Motor Unit
one motor neuron plus all of the muscle fibers it innervates
Motor unit recruitment
few motor units activated creates weak contraction, while many more units activated creates strong contraction
Twitch Summation
increased rate of action potentials from motor neuron can lead to summation of muscle fiber tension
Twitch summation mostly due to cumulative increase in what?
[Ca2+]I
What happens when there is more Ca2+?
-more exposed cross-bridge binding sites on actin
-more cross-bridge cycling
-more tension
Tension on muscle fibers can also be influenced by…
-length of fiber at onset of contraction
-extent of fatigue
-thickness of fiber
3 types of skeletal muscle fibers
- Slow-oxidative fibers
- Fast-oxidative fibers
- Fast-glycolytic fibers
Whats the difference between slow and fast muscle fibers?
Fast: High myosin ATPace activity
Slow: Low myosin ATPace activity
Difference between oxidative and glycolytic fibers
Oxidative: More capable of producing ATP via oxidative phosphorylation
Glycolytic: More capable of producing ATP via glycolysis
What is muscular hypertrophy, and what causes it?
-An increase in size.
-Regular, short bouts of high-intensity, anaerobic exercise can lead to it.
How do regular, long bouts of aerobic exercise increase oxidative capacity?
Additional mitochondria and capillaries for oxidative fibers -> more efficient use of O2
What are the various nervous system inputs onto motor neurons (or the spinal cord interneurons that directly project to motor neurons)?
Motor Cortex- voluntary movements
Brainstem- postural adjustments for voluntary movements
Afferent input (proprioceptors, nociceptors, tactile mechanoreceptors)- reflexive movements
Local interneurons in spinal cord- rhythmic movements
Muscle Spindle
Proprioceptive afferent fiber ending wrapped around a special intramural muscle fiber
How is a muscle spindle activated?
When muscles lengthen, the spindles are stretched. This stretch activates the muscle spindle which in turn sends an impulse to the spinal cord.
Identify the sequence of steps in the stretch reflex?
Tap on patellar tendon, muscle spindle is the receptor, afferent nerve, spinal cord, efferent nerve, quads flex
Does the withdrawal reflex simply lead to contraction of a muscle, or complementary contraction and relaxation of a set of muscles? In what CNS structure does all of the integration of the withdrawal reflex take place?
It inhibits the antagonist muscle and relaxes it and then contracts the agonist to pull the part away. Integration center is the spinal cord.
How are thick and thin filaments organized differently in smooth muscle fibers?
-Muscle fibers are short and have a tapered shape
-Each smooth muscle fibers only contain one nucleus
-The thick and thin filaments are not stacked instead criss-crossed through cell linked by dense bodies held in place by intermediate cytoskeleton filaments
Are contractions in smooth muscle shorter or longer in duration than those of skeletal muscle cells?
They can contract half their length much longer than skeletal muscle
Although the chemical cascade leading to contraction is different in smooth muscle, what is the ion that triggers it?
They do not have troponin so they are always exposed. The cross-bridge binding is prevented by unphosphorylated myosin-light chain.
Multiunit smooth muscle is neurogenic meaning
it contracts in response to stimulation by autonomic fiber
Single-unit smooth muscle is myogenic meaning
internal electrical oscillations cause contractions, but can be influenced by autonomic input
