Muscle and Neuron Physiology Flashcards
What are the three types of muscle tissue?
skeletal muscle, smooth muscle, cardiac muscle
What is the difference between striated and smooth muscle?
striated: most muscles have a mix of large diameter and small diameter muscle fibers… alternating light and dark bands which give it that striated look.
smooth: not involved in voluntary contractions. not attached to skeleton. keep in mind that cardiac muscle IS striated though but is INVOLUNTARY.
What is a muscle fiber?
a muscle fiber is a muscle cell.
skeletal muscle fibers develop from embryonic myoblasts.
Name the three connective tissues that bind together and cover skeletal muscle?
epimysium: sheath that surrounds each skeletal muscle.
perimysium: subdivides each whole muscle into numerous, visible bundles of muscle fibers.
endomysium: delicate layer of CT that separates the individual muscle fibers within each fascicle.
Where are the epimysium, perimysium and endomysium located?
epimysium located is the outermost layer surrounding the entire muscle
perimysium is the next layer within, and surrounds the muscle fascicles themselves
endomysium is the innermost layer surrounding bunnies of individual muscle fibers that compose a fascicle
What is actin, myosin and troponin/tropomyosin? Which of these is the thin filament, which is the thick?
The sarcomere consists of actin (thin) myofilaments and myosin (thick) myofilaments. It is the relationship of troponin and tropomyosin that dictates when the skeletal muscle will contract.
How do actin and myosin interact to cause a muscle contraction?
A cross bridge forms when the myosin binds to the actin, actin strands are pulled toward the H-zone, the H-zone disappears.
Hence the events occurring in muscular contraction are H-zone disappears, I-band reduces in width, The width of A band is unaffected and M-line and Z-lines come closer. Sarcomere shortens.
What is a sarcomere? Describe the parts of a sarcomere: A line, Z line, I band etc…
A sarcomere is a boundary line. It is the smallest portion of a muscle that can contract. Sarcomeres join end to end to form the myofibrils.
I band: lighter regions (includes a darker A band region), each of two I bands include a Z disk and extend to end of myosin myofilaments. I bands contain only actin (why they are light colored).
A band: darker-staining band in center of each sarcomere. A band contains both actin and myosin overlapping, except in the center of the A band. In the center of A band is the H Zone.
H zone: contains only myosin. Middle of each H zone has a dark line called the M line.
M line: M line consists of delicate filaments that hold myosin in place.
Titin: gives muscle ability to stretch, and to recoil.
Why is calcium important in muscle contraction?
Well, once Ca++ diffuses out of the sarcoplasmic reticulum (channels opened by actions potentials triggering voltage gated Ca++ channels to open) and into the sarcoplasm surrounding the myofibrils, Ca++ can will now bind to the troponin molecules of the actin myofilaments. Binding Ca++ to troponin causes the tropomyosin to move, which exposes active sites on the actin. Myosin heads then bind to the exposed active sites on actin to form cross-bridges. Muscles contract when cross-bridges move.
What will occur if calcium does not bind to troponin/tropomyosin.
First of all, a muscle cannot contract until the tropomyosin moves to uncover the active sites. Tropomyosin is a long fibrous protein that lies in the groove along the actin strand. It covers the active sites on the actin. The active sites can be thought of as receptor sites for the myosin head.
Troponin prevents tropomyosin from uncovering the actin active sites in a relaxed muscle. Troponin also binds Ca++
(pg 279 textbook)
Ca++ which is stored in the sarcoplasmic reticulum, is key for contraction. (pg 288) Once Ca++ rapidly diffuses out of the sarcoplasmic reticulum due to action potentials carried into the muscle fiber via the T tubules causing voltage gated Ca++ channels in the terminal cistern to open…
***Ca++ binds to troponin molecules of the actin. Binding Ca++ to troponin causes the tropomyosin to move, which exposes the active sites on the actin. The myosin heads then bind to the exposed active sites on actin to form cross bridges. Muscles contract when cross-bridges move.
The heads of the myosin myofilaments bend (power stroke), causing actin to slide past the myosin. As long as Ca++ is present, the cycle repeats.
Why is ATP important in muscle contraction?
ATP is important in muscle contraction because one ATP molecule is required for each cross-bridge cycle. The myosin head stores energy from ATP breakdown that happened during the previous cycle. Myosin head will remain in resting position until the muscle fiber is stimulated by a motor neuron (Ca++ has to bind to the troponin and expose active sites too, then myosin heads bind to them).
Binding of ATP causes the myosin head to detach from the actin. Breakdown of the ATP by the myosin head supplies energy for the recovery stroke.
To summarize…
ATP molecules on myosin heads are broken down to ADP and P, which releases energy needed to move the myosin heads.
ATP is also required to detach the myosin heads from the active sites for the recovery stroke.
ATP is also needed for the active transport of Ca++ into the sarcoplasmic reticulum from the sarcoplasm. (pg 292)
So, you need ATP in place (in advance) for the power stroke and you need one “on the fly” for the recovery stroke.
What would happen if ATP was not available for muscle contraction?
Need ATP for power stroke. ATP is already attached but hydrolyzed to get into that “position.” (chicken or egg question)… The energy released during ATP hydrolysis changes the angle of the myosin head into a “cocked” position. The myosin head is then in a position for further movement, possessing potential energy, but ADP and Pi are still attached. If actin binding sites are covered and unavailable, the myosin will remain in the high energy configuration with ATP hydrolyzed, but still attached.
Where is ATP produced?
ATP is produced from the mitochondria in a basically “reverse photosynthesis” kind of fashion, converting sugar into glucose and combusting with oxygen to make new, energy-rich ATP molecules.
https://www.youtube.com/watch?v=QImCld9YubE
What are the parts of a neuromuscular junction?
Remember, each muscle fiber (cell) is in contact with a motor neuron branch from the brain or spinal cord. A neuromuscular junction consists of: (pg 280)
1) axon terminals (presynaptic, cleft, motor-end plate aka post-synaptic membrane
2) area of the muscle fiber sarcolemma they innervate
What is a neurotransmitter?
Signal molecules that control the effectors. In an axon, the axon endings have many synaptic vesicles which store the signal molecules produced by the neuron aka neurotransmitter.
ex. acetylcholine, epinephrine, norepinephrine
What is a twitch…tetanus?
(pg 294) muscle twitches are all-or-none events when the stimulus frequency is very low, allowing for adequate rest. Muscle fibers stimulated at greater frequencies first display:
wave summation, then
(muscle fibers stimulated more frequently)
incomplete tetanus, then
(merging of more and more muscle twitches)
complete tetanus
(muscle fiber stays completely contracted with no relaxation)
What would happen if the cell does not produce acetylcholinesterase?
this enzyme (-ase denotes it’s an enzyme) keeps acetylcholine from accumulating within the synaptic cleft, otherwise the buildup of this neurotransmitter would constantly stimulate the motor-end plate and produce continuous contraction in the muscle fiber. This enzyme ensures that one presynaptic action potential yields only one action potential at the motor plate.
What is stored in the synaptic vesicles?
Pg 392/393
Neurotransmitter is stored in synaptic vesicles, which can be found in the endings of axons. Example of neurotransmitter would be acetylcholine.
Why is oxygen important in muscle contraction?
It is important for aerobic metabolism, in which O2 is absorbed in mitochondria along with pyruvate to form ATP. ATP is essential for muscle contraction, not to mention life in general.
What role does myoglobin and creatine phosphate have in muscle tissue?
myoglobin is important for oxygen storage, and is found in muscle. Important because oxygen is needed in the synthesis of ATP and aerobic respiration.
pg. 302 under creatine kinase
creatine phosphate’s role in muscle tissue is used when muscle fibers accumulate extra ATP during rest. This extra ATP is utilized in muscle fibers to transfer a phosphate from the ATP to a small protein synthesized by muscle fibers called creatine. The transfer of the phosphate creates the molecule creatine phosphate, this molecule acting like a “bank” for “high-energy” phosphate.
What is a motor neuron?
A motor neuron is a specialized nerve cell responsible for stimulating muscle contraction. Most origination brain/spinal cord and extend to muscle fibers through nerves. Whole muscles are generally supposed by several motor neurons. pg. 275
What causes rigor mortis?
mentioned on pg 290
shortly after a person dies, Ca++ diffuses out of the sarcoplasmic reticulum and the body becomes very still and rigid.
To understand correctly remember, before cross-bridges cycle when a person is alive, Ca++ binds to troponin and tryopomyosin (the chain blocking the active sites) moves out of the way so that the myosin heads can attach to the active sites on the actin. It takes one ATP for the heads to attach, cock their heads, and slide the actin past the myosin (power stroke). It takes ANOTHER ATP for the recovery stroke.
Knowing that, when someone dies, Ca++ floods out of the sarcoplasmic reticulum into muscles. Because of this influx of Ca++, tropomyosin moves out of the way and because your body still has some short-term ATP, so the ATP binds to the myosin, myosin cocks into position, and contracts the muscle. Will continue to contract until ATP stores are depleted. When no more ATP is available, the contracted muscle will stay that way because it does not have another ATP in order to relax.
To sum up, you need:
Ca++
ATP
What is oxygen debt?
If anaerobic respiration continues for a long time, lactic acid builds up in the muscles. Presence of lactic acid in the muscles causes pain and stiffness. Lactic acid can be broken down when an appropriate quantity of O2 reaches the cell. The quantity of O2 required to breakdown lactic acid into carbon dioxide and water is referred to as the OXYGEN DEBT. This additional quantity of O2 supplied to the muscles, comes from the increased rate of breathing that accompanies physical activity.
What causes muscle fatigue?
pg 302
fatigue is a temporary state of reduced work capacity. Without fatigue, muscles would be worked to the point of severe damage. multiple things cause fatigue:
- acidosis and ATP depletion due to increased ATP consumption or decreased ATP production.
- oxidative stress
- local inflammatory reactions