Lecture 8 Muscle Physiology Flashcards
How long are muscle cells?
As long as the whole muscle
What kind of nucleation does skeletal muscle have?
multinucleated
How do muscle cells become a multinucleated syncitium?
By fusing myoblasts together into muscle fibers
T/F CT around and within skeletal muscle is continuous with the CT of bones.
True
What are the CT layers from the endomysium of muscle to the periosteum of bone?
Endo-peri-epi-deep fascia-tendon-periosteum
Mnemonic: Every Person Eats Donuts for The Paste
What are the series-elastic components of the musculoskeletal system?
All of the interconnected tissues in muscles that are attached to the bone membrane from endomysium to the periosteum
What is the specialized plasma membrane of muscle cells?
Sarcolemma
The sarcolemma is _______ at rest.
Polarized
What can depolarize the sarcolemma?
Acetylcholine released by motor neurons
What are the tubular infoldings of the sarcolemma?
T-tubules (transverse tubules)
What do T-tubules do?
Penetrate into the cell and carry the electrochemical current into the cell
What is sarcoplasm made of?
Highly organized myofibrils (actin and myosin), glycogen, and myoglobin
What does glycogen do in the sarcoplasm? What does myoglobin do in the sarcoplasm?
Stores energy. Stores oxygen
What is the specialized endoplasmic reticulum of muscle cells?
Sarcoplasmic reticulum
What storage sacs is the sarcoplasmic reticulum connected to? What do these sacs store?
Termincal cisternae. They store calcium ions
What protein complex anchors myofibrils inside muscle cells?
Dystrophin
How does dystrophin attach myofibrils to the endomysium?
Dystrophin attaches the myofibrils next to the sarcolemma to integral membrane proteins that extend into the endomysium
What is the difference between the sarcolemma, sarcoplasm, and sarcoplasmic reticulum?
Sarcolemma is the outer plasma membrane of muscle cells.
Sarcoplasm is the cytosol (flesh)
Sarcoplasmic reticulum is the series of interconnected tubules connected to the terminal cisternae
Are the T-tubules of the sarcolemma and the interconnected tubules of the sarcoplasmic reticulum the same thing?
No. The T-tubules are larger invaginations of the sarcolemma. The t-tubules are surrounded on either side by the terminal cisternae. The terminal cisternae are interconnected by the tubules of the sarcoplasmic reticulum
What is the triad formed surrounding the myofibrils?
The T-tubule surrounded on either side by the calcium storing terminal cisternae
T/F The sarcolemma is surrounded by the endomysium.
True. Endomysium surrounds individual muscle cells made of myofibrils
What is the difference between a myofiber and a myofibril?
The myofiber is the muscle cell which is composed of myofibrils making up its cytoplasm (sarcoplasm)
What are the three bands of a sarcomere?
A band, H band, and I band
Which of the three sarcomere bands does not change in size?
A band is the length of the thick myosin filaments
Which sarcomere band changes in size and is a region of pure myosin? Pure actin?
H band is pure myosin. I band is pure actin
What starts a wave of depolarization in the muscle cell?
The binding of ACh to the AChR (acetylchone receptor)
How far does the wave of depolarization spread over the sarcolemma?
The sarcolemma down to the T-tubules
Where are calcium channels found that open to release calcium on the sarcomeres?
On the sarcoplasmic reticulum buried deep among the myofibrils
What must calcium bind to for the release of tropomyosin off of the active sites on actin?
Troponin
What do the AHM I Z regions of the sarcomere stand for?
A anisotropic (dark appearance of myosin) H helle (german for bright) region of myosin w/o actin M middle I Isotropic (light appearance of actin) Z Zwischen (german for between) anchor site of titin
T/F Thin filaments are globular subunits. Myosin is composed of two entwined polypeptides each shaped like a golf club
True
The heads of myosin can also be called which enzyme?
ATPase
Are actin and myosin filaments elastic?
No, They stay the same size
If actin and myosin are not elastic how are they considered contractile?
Because they contract the cell (myofiber) by moving over each other in a series of sarcomeres
Which muscle filament is elastic?
Titin
Where are the cell bodies of somatic motor neurons?
Brainstem and spinal cord
What is the range of branching in the axons of motor neurons?
From 3-6 to over 200 branches
T/F Each axon branch of a somatic motor neuron contacts one muscle fiber (cell)
True
What is a motor unit?
A motor neuron and all the muscle fibers it innervates
What kind of control are small motor units good for? Large motor units?
Fine control (eye muscles). Strength (can have as many as 1000 muscle fibers per nerve fiber)
Much of the intracellular protein is _______ (anionic or cationic
anionic
What four actions are involved in Muscle contraction and relaxation?
- Excitation
- Excitation-Contraction Coupling
- Contraction
- Relaxation
What is excitation-contraction coupling?
action potentials on the sarcolemma activate myofilaments
How is the resting membrane potential disrupted?
When ligand-gated Na+ channels on the motor end plate bind to ACh and open to let Na+ into the cell which depolarizes the membrane
During the powerstroke in which direction does the myosin head pull the thin actin filament relative to the z line?
Towards the Z line
With out ATP where is the myosin head relative to the active site of the actin?
The myosin head is bound to the active site of actin
T/F ATP is required for the myosin head to release actin.
True
During Rigor Mortis, where does the Ca++ come from to activate the actin-myosin cross bridges?
The SR releases Ca++ as it deteriorates
What molecule is needed for the myosin to bind with the actin? What molecule is needed for the myosin to release the actin?
Ca++. ATP
How does Botox work?
It blocks the ACh release from motor neurons. Muscles cannot contract to cause wrinkles in those areas
What are paralytic neuromuscular toxins?
Muscle relaxants such as Botox, Curare, TTX
What are spasmodic neuromuscular toxins?
Muscle stimulants that cause uncontrollable muscle contraction and spasms
What is the role of glycine in muscle contraction?
It prevents overstimulation of muscles
Which autoimmune disease mimics the effects of curare?
Myasthenia Gravis
How does myasthenia gravis inhibit the generation of an end-plate potential?
Antibodies bind and inhibit ACh receptors from sensing ACh
How is myasthenia gravis treated?
With acetylcholinesterase inhibitors, thymus removal or immunosuppressive agents
What is the only source of energy for muscle contraction?
ATP
Which enzyme system regenerates ATP from ADP and Pi?
Phosphagen enzyme system.
What are the two main phosphogen enzymes?
Myokinase and Creatine Kinase
Where does myokinase get its Pi in ATP formation?
From ADP producing ATP and AMP
Where does creatine kinase get its Pi for ATP formation?
Creatine phosphate
Where does the immediate source of ATP come from? How long does the immediate source provide ATP?
Aerobic metabolism using O2 released from myoglobin in muscles. Also, from Phosphagen system. Lasts about 10 seconds
Where does the short-term energy source of ATP come from? How long does it last?
Anerobic metabolism thru the glycogen-lactic acid system? Lasts for about 30-40 seconds
Where does the long term energy source of ATP come from? When does it begin?
Respiratory and cardiovascular systems catch up to the O2 demand for aerobic respiration. Begins after 40 seconds of sustained exercise and supplies more than 90% of ATP at this stage
Which muscle fiber type has lots of myoglobin and syntesizes ATP aerobically?
Red Slow Twitch (Type 1)
Which muscle fiber type uses anaerobic metabolism to produce ATP? Which one uses both anaerobic and aerobic metabolism?
White Fast Twitch (Type IIb). Pink Intermediate (Type IIa)
Which muscle type has striated muscle cells linked to each other by intercalated discs?
Cardiac muscle
What junctions line the intercalated discs?
Gap junctions and desmosomes
What do gap junctions facilitate in cardiac muscle?
The facilitate the synchronization of muscle contractions
Where does the Ca++ come from in cardiac muscle? What facilitates the Ca++ absorption?
From the extracellular fluid. Large T-tubules
Which striated muscle type forms triads of the SR with the T-tubules? Which one forms diads?
Triads are formed in skeletal muscle where the T-tubule is sandwiched between two terminal ciseternae of the SR. Diads are formed in cardiac muscle - the T-tubule is paired with the SR only on one side
What kind of respiration does cardiac muscle use almost exclusively?
Aerobic. Cardiac muscle is an obligate aerobe
How are damaged cardiac cells repaired?
By fibrosis not mitosis.
Which muscle cells are fusiform and have only one nucleus?
Smooth muscles
What kind of nucleation does cardiac muscle have in humans? (mono or multi-nucleated)
Mononucleated just like smooth muscle. Skeletal muscle is multinucleated
Where do the thin filaments attach to in smooth muscles?
Dense bodies scattered throughout the sarcoplasm, which are attached to dense plaques on the sarcolemma
T/F Both cardiac and smooth muscles can be described as a functional syncitium
True. They both are mononucleated but have gap junctions that allows depolarization to spread from cell to cell
Where does smooth muscle get its Ca++ for contractions?
From a poorly developed SR and extracellular fluid
What does the poorly developed SR have instead of T-tubules?
Caveolae which are shallow invaginations of the SR
What doe stretching do to smooth muscles?
Opens mechanically-gated calcium channels causing contraction
What happens when smooth muscle is stretched gently?
It briefly contracts and then relaxes
How can smooth muscle be made to contract forcefully?
By being stretched greatly. The contraction force matches the degree of stretching.
T/F Smooth muscles responds to hormones, low pH, and high CO2
True
What regulatory protein must calcium bind to in the cytoplasm of smooth muscle in order to activate the MLCK?
Calmodulin
What is MLCK?
Myosin light chain kinase. It uses ATP to phosphorylate the myosin head
What do the actin thin filaments pull on to shorten Smooth muscle?
the interconnected dense bodies which may be seen as the Z discs in skeletal muscles
How many ATP are needed for the power stroke in smooth muscle?
Two ATP. One used by the MLCK to activate the myosin head and a second to ratchet the myosin head causing contraction
