Muscles Flashcards
what are the three fates of myoblasts?
- skeletal muscle cells
- cardiac muscle cells
- smooth muscle cells
what is a myoblast?
a stem cell that produces different lines of muscle tissue. They lack myofilaments but contain many free ribosomes used to synthesize the myofilaments that give muscle cells their characteristic contractile properties
Skeletal Muscle Cells characterisitcs
striated
-voluntary (somatic nervous system)
-have satellite cells between plasma membrane and external lamina
long/cylindrical
-multinucleated (right underneath the plasma membrane.. on the outer edge)
what is the function of satellite cells in skeletal muscle? where can they be found
function is to produce more skeletal muscle (limited regeneration of skeletal muscle). Located in between the plasma membrane and external lamina of skeletal muscle cells
cardiac muscle
- arise from mesenchyme
- striated
- mono or bi-nucleated
- branched
- autorhythmic (but monitored by PS and SS of ANS)
- very limited regeneration
- have intercalated disks
- nucleus is CENTRALLY located
smooth muscle cells
- no striations (sarcomeres)
- small, spindle shaped,
- single nucleus.. centrally located (decreased cytoplasm)
- usually arranged in sheets around tubular organs
- capable of moderate regneration
organization of skeletal muscle (myfibril..fiber etc)
myofilament: actin/myosin arranged into a sarcomere
myofibril: repeat units of sarcomere
myofiber: the muscle cell: groups of myofibrils
Individual muscle cells are wrapped in endomysium
Fasicle: groups of myofibers
fascicle is wrapped in perimysium
gross muscle: groups of fascicles; wrapped in epimysium
what is epimysium
dense irregular CT covering the gross muscle
what is perimysium
collagenous CT that wraps fascicles within the gross muscle
what is endomysium? where is it found?
wraps individual muscle cells (myofibers).
A loose, highly vascularized, CT matrix
contains type I and III collagen
-the individual muscle cell is wrapped in an external lamina, innervated by a single axon, and wrapped in epimysium
how long is an individual skeletal muscle cell?
spans the entire length of the muscle
what is a sarcomere? define it’s contents/bands
repeat subunits that make up the myofibril
runs from Z-line to Z-line
the functional unit of contraction in cardiac and skeletal muscle
-has one A-band (dArk)
and two halves of I-band (LIght) that are shared with the neighboring sarcomeres
what aligns adjacent myofibrils? where are they located? what do they connect?
desmin and vimentin intermediate filaments
-link adjacent myofibrils together at the Z-line and bind them to the plasma membrane
why does skeletal and cardiac muscle appear striated?
due to the alignment of sarcomeres
what is the z-line?
where the actin filaments are anchored
what anchors actin filaments?
alpha-actinin
what is bound to actin?
regulatory proteins: troponin and tropomyosin
what are troponin and tropomyosin bound to?
actin filaments
where are myosin filaments bound?
m-line
what anchors myosin filaments?
myomesin
what is a myosin molecule made up of?
two-helical chains and two-globular heads containing an ATP-binding site, an actin binding site, and an ATPase
what protein runs between the z-line and m-line? what is it’s function?
titin; centers the myosin filaments and helps in relaxation of the sarcomere after contraction stops
a-band
dark band. it runs the length of myosin. dark because portion of it is actin + myosin (where they bind)
-includes the h-band and m-line
h-band
runs between actin ends (just myosin).. so its lighter. its in the middle of the sarcomere
m-line
runs down the middle of the h-band. includes myomesin (anchors myosin filaments)
alpha actinin vs. myomesin
alpha actinin anchors actin at z-line
myomesin anchors myosin at m-line
explain the regulation of skeletal muscle contraction
tropomyosin combine with troponin (calcium dependent protein) to prevent actin/myosin interaction because they associate with actin and block the myosin heads
- in the presence of calcium (ie: AP) calcium binds to troponin and changes troponins shape so that it releases tropomyosin. this reveals the myosin binding site on the actin molecule (tropomyosin pulled off of it)
- now myosin can bind to actin
what is the “power stroke”
after the myosin binding sites on actin are revealed (tropomyosin pulled off) the myosin heads bind to actin and rotate to move the actin relative to the myosin
why is ATP necessary for muscle contraction?
to break the interaction between actin and myosin (no ATP= rigor mortis)
what happens to the sarcomere (zline/mline/iband) during contraction
zline moves towards the mline and the iband and sarcomere shorten ** a band doesnt change size (because its always going to be the length of the myosin) but h-band does (because now you are contracting on the myosin, so it pulls smaller)
what is present between the myofibrils of skeletal muscle?
mitochondria (to provide ATP)
glycogen (glucose storage.. anaerobic metabolism)
sER called “sarcoplasmic reticulum” that sequesters calcium
what is the sarcoplasmic reticulum
smooth ER that stores calcium using the calcium binding protein “calsequestrin”
T-tubules: what are they? what are their functions? where are they located
found at the junction of A/I band (2 per sarcomere)
they are a continuation of plasma membrane that conduct electrical activity into the depths of the muscle cell.
contracted via dilations of the SR
what is a “triad” ? what type of muscle is it found in?
sarcoplasmic reticulum + 2 t-tubules in skeletal muscle
how do the t-tubules and SR work together to control muscle contraction?
AP (electrical activity) passes through t-tubules, activate the voltage sensitive receptor in the t-tubule to open calcium channels in the SR.
the calcium diffuses to bind to troponin an initiate contraction
what are the voltage sensitive receptors in t-tubules called?
dihydrophyridine
what are the calcium channels/receptors in the SR called?
ryanodine channels/receptors
what happens to the calcium ions after a contraction?
they get pumped back into the sarcoplasmic reticulum
what anchors actin at the end of a MYOFIBRIL? at a SARCOMERE?
myofibril: dystrophin
sarcomere: alpha actinin
how are myofibrils connected to tendons/gross muscles? ie: whats the organization/cascade?
actin at the end of a myofibril binds to DYSTROPHIN (spectrin like actin binding protein) .
DYSTROGYLCAN: links dystrophin to LAMININ (of EL)
RETICULAR FIBERS: link laminin (EL) to collagenous CT of tendon
CT: continuos with PERIOSTEUM
SHARPEY FIBERS: connect tendon to bone
muscular dystrophy
absence/defects of dystrohpin causes progressive weakening in skeletal muscle
lipofuscin granules
found in cardiac muscles
a lysosomal lipid
what are the differences/similarities between cardiac cells and skeletal muscle cells?
both are striated ( have the same mechanism of contraction)
-Cardiac: mitochondria are HUGE and can run the entire length of the sarcomere
ONLY ONE T-TUBULE (dyad)
-intercalated disks
what are intercalated disks? what type of muscle are they found in? what is their function/location?
in cardiac muscle
join the ends of cardiac muscle cells
has three components:
1. dense plaque (fascia adherens) that actin binds into
2. desmosomes (macula adherens) that binds adjacent cells together via IM desmin and vimentin (similar to skeletal muscle)
3. gap junctions for electrical continuity
what are purkinje fibers?
travel in the ventricular wall to conduct electrical signals to regulate heart contractions
what are caveloe? in what tissue are they found?
found in smooth muscle. thought to replace the sarcoplasmic reticulum/t-tubules that are characteristic of skeletal and cardiac muscle. (regulate the contraction of smooth muscle via calcium release)
smooth muscle
NO myofibrils NO striations NO troponin YES actin/myosin one centrally located nucleus that is flat/spikey
how are actin/myosin arranged in smooth muscle?
- actin filaments are interconnected with intermediate filaments and anchored at cytoplasmic densities containing alpha actinin (similar to skeletal muscle)
- myosin is arranged into bundles (smaller than skeletal muscle), NO TROPONIN to regulate! instead the myosin heads regulate contraction
how is contraction regulated in smooth muscle cells?
NO TROPONIN
-a signal arrives at the muscle cell and causes calcium concentration to increase (from calveoli) . The calcium binds to CALMODULIN which activates MYOSIN LIGHT CHAIN KINASE which phosphorylates the myosin light chain and causes the actin binding site to be uncovered so that actin can bind.
SLOW but highly efficient (only takes 1/5 the ATP)
what type of muscle can regenerate?
smooth muscle (it can make collagen also!)
what are the three types of cells that can release collagen?
fibroblasts, chondrocytes, smooth muscle
what provides the mechanical linkage between cells in smooth muscle tissue
gap junction (not desmosomes or fascia adherens)
what is common to all forms of muscle?
contain actin and myosin
have an external lamina
**all have different tissue coverings! and anchored by different things
-all use the intermediate filaments desmin and vimentin to bind cell
