Final: Musculoskeletal System Slides Flashcards
Overall function of musculoskeletal systems
Convert electrical activity into force that is used for daily activity
Neural pathway/cycle
Stimulus - skin receptors - sensory neuron - interneuron - motor neuron - effector (muscle)
General function of muscles
Excitable cells; receive action potential and act; contractile tissues
Types of muscle (3)
Skeletal (voluntary), smooth (involuntary - found around organs), cardiac (involuntary)
Skeletal muscle organization, large to small
Muscle, fascicles (bundles), muscle fibers/cells, myofibrils, sarcomeres
Myofibrils are ____ proteins
Contractile
Muscle fiber structure
Bundle of cells within each fascicle, unique cylindrical shape; can extend entire length of muscle
Sarcomere function
Functional unit of muscle (contraction); combination of different proteins
What are Z lines?
Network of interconnecting proteins that binds each sarcomere
What are thick filaments composed of?
Myosin (contractile protein)
What do thin filaments contain?
Actin (contractile protein), troponin and tropomyosin (both regulatory proteins)
What is required for force production in sarcomeres?
Interaction (physical contact) between thick and thin filaments
Composition of myosin molecule
Two heads and two tails
What does each myosin head (or cross bridge) contain and what does it do?
Actin binding site, ATP binding site; myosin head is where all activity occurs
Which parts of myosin molecule interact?
Tails (heads don’t interact)
Function and structure of titin
Very large, thick protein; connects thick filaments to Z lines
How is actin arranged in thin filaments?
Actin molecules are globular proteins that polymerize to form intertwined helix
What does a thin filament look like at rest?
The myosin binding site is covered by tropomyosin (arranged like a ribbon; it must be removed to allow binding of myosin)
Troponin structure
3 spherical subunits with 3 binding sites: for actin, tropomyosin, and calcium (need it for muscle contraction)
What happens to sarcomere shape during muscle contraction?
Shortens
Besides the proteins in thick/thin filaments, what causes binding of actin and myosin to occur?
ATP (binding site on myosin) and calcium (binding site on troponin)
Where do muscles get energy?
From ATP, since they’re packed with mitochondria (cell respiration, etc.)
Where does calcium come from in muscles?
Stored in sarcoplasmic reticulum (not available in cytosol, bc we don’t want it to depolarize cell all the time)
What is the sarcoplasmic reticulum?
Modified smooth ER, found around myofibrils, lateral sacs release calcium
What is the modified plasma membrane of muscle cells called?
Sarcolemma
Sarcolemma structure
Extensions (invaginations) that dip deep into cytoplasm: these are T-tubulus
T-tubules (transverse tubules) structure and function
Have special voltage sensitive calcium channels called dihydropuridine receptors (DHPR); increase surface area for electrical activity
Where are ryanodine receptors located?
Lateral sacs of sarcoplasmic reticulum
How does activity at the neuromuscular junction start (eventually causing Ca release)?
Action potential reaches axon terminal - voltage gated calcium channels open - Ca2+ influx from extracellular space- NT vesicles move - NT (ACh) released by exocytosis
What is the electrical activity in muscle cells called?
End plate potential (EPP)
What causes calcium release after ACh released?
ACh binds to its receptors on muscle cell to activate them - Na+ enters cell - depolarizes membrane - EPPs accumulate and cause action potential - action potential travels down sarcolemma and dips into T-tubules - activates DHPR on T-tubules - DHPR activates ryanoside receptors - Ca2+ released from SR
Once released, where does Ca go and what happens?
Binds to troponin on actin - tropomyosin uncovers myosin binding site - Myosin and actin bind
Steps of cross bridge cycle (8 steps)
- ADP and Pi bound to myosin cross bridge
- Myosin binds to actin once it’s exposed
- Pi unbinds from myosin head
- Power stroke (muscle contraction)
- ADP unbinds
- ATP binds to myosin head
- Myosin detaches from actin
- ATP hydrolyzed to ADP and Pi, cycle repeats
Cross bridge cycle: when is it low energy and when is it high energy state?
Low energy: after power stroke to ATP hydrolysis
High energy: after ATP hydrolysis to power stroke
What happens in the power stroke?
Muscle contraction: myosin pulls and “snaps” actin - shortens sarcomere
What stops the cross bridge cycle?
Removing ACh: acetylcholine esterase breaks down acetylcholine
Removing Ca2+: calcium pumped back to SR through active transport pumps
Where does muscle cell get energy from (3)?
Creatine phosphate
Cellular respiration
Glycolysis followed by fermentation
What is creatine phosphate?
Stored form of energy: creatine phosphate + ADP becomes small amount of ATP bound to creatine (in presence of creatine kinase)
What are the two phosphagens and where are they found?
Creatine phosphate: vertebrate animals
Arginine phosphate: invertebrate animals
Advantage/disadvantage of creatine phosphate
Very quick source of energy but only lasts for about a second (then other processes take over)
What causes muscle fatigue?
Local increase of inorganic phosphate
Build up of acid (fermentation)
Depletion of energy: O2 demand > availability
