muscle tissue Flashcards
4 basic tissues
- epithelium
- connective tissue
- muscle tissue
- nervous tissue
muscle cells
- specialized cells capable of contraction to produce movement
- aka myocytes and myofibers
- spindle shaped
- originate from mesoderm (myoblasts)
myotubes
- multinucleated tubes formed from fusion of mesenchymal cells (myoblasts)
- differentiate into myofilaments
satellite cells
cells that do not differentiate and remain as mesenchymal cells
sarcoplasm
cytoplasm of muscle cells, contains glycogen and myoglobin
sarcolemma
plasma membrane of muscle cell
sarcoplasmic reticulum
highly specialized smooth endoplasmic reticulum of a muscle cell
what percentage of body weight does skeletal muscle make up?
50%
what are some of the strongest muscles of the body?
tongue, masseter, and the heart
where are nuclei in myocytes?
peripherally, multiple
what kind of muscles are skeletal muscles? give examples
voluntary, fast contracting
- GI sphincter
- urinary sphincters
- muscle in esophagus
- tongue
skeletal muscle orgainzation
- surrounded by dense irregular CT: epimysium
- made up of smaller bundles: fascicles surrounded by perimysium
- each fascicle made up of muscle cells
- myofibrils contain bundles of myofibrils which contain bundles of myofilaments
perimysium
CT surrounding each fascicle
endomysium
reticular fibers surrounding individual myocytes
myofibers
cylindrical multinucleated cells, peripheral/hypolemmal nuclei
myofibrils
contractile elements, composed of repeating sections of myofilaments: myosin and actin, create light and dark bands
myofilaments
contractile (actin and myosin) and regulatory proteins (tropomyosin)
sarcomere
contractile or functional unit of myocyte
A band
dark and corresponds to are where thick and thin filaments overlap, composed of actin and myosin
I band
pale and composed of only thin filaments
Z line
protein disk that bisect I band, actin filaments anchored to it
type 1 “red muscle”
- slow twitch
- rich in myoglobin
- aerobic metabolism-fatigue resistant (high fat low glycogen, many mitochondria)
type 2 “white muscle”
- fast twitch
- anaerobic metabolism-prone to fatigue (low fat high glycogen, less myoglobin and mitochondria)
motion mediated by muscle cells is based on…
conversion of ATP into mechanical energy by contractile apparatus
myofibrils are composed of..
repeating assemblies of thick and thin filaments
what happens during muscle contraction?
actin filament slide over the myosin filaments resulting in a shortening of the I band
what holds actin and myosin in position?
desmin, tropomyosin, troponin
sliding filament model
each sarcomere shortens–>myofilament length is constant–>I band shortens, almost disappears–>thin filaments slide past thick filaments; summation of all sarcomere shortening produces contraction of the muscle cell
muscle contraction steps
- binding of calcium to troponin
- conformational change in tropomyosin, exposing myosin binding site
- myosin head binds to actin, ATP–>ADP moving myosin head
- thin filaments slide over thick filaments
- shortening of entire muscle fiber
T tubules
- deep invagination of sarcolemma, only in skeletal and cardiac muscle
- allow depolarizaton of the membrane to quickly penetrate interior and release Ca from SR
Sarcoplasmic Reticulum
- equivalent to endoplasmic reticulum, seen in smooth and striated muscle
- stores and releases calcium
terminal cisterna
expanded ends of sacroplasmic reticulum
cardiac muscle
cardiomyocyte= myocardiocyte= cardiac myocyte
- one central nucleus
- cross striated
- intercalcated discs
- lots of mitochondria
- needs lots of oxygen
intercalated discs
- gap junctions, desmosomes
- attach cardiac muscle cells to each other
- provide strength and ability to function as a syncytium
intercalcated discs consist of..
- transverse element: anchor, desmosome, strong attachment
2. longitudinal element: communication, gap junctions, propagate electric impulse
atrial muscle cells
contain membrane bound granules, especially numerous in right atrium
atrial granules
endocrine function, Atrial Natriuretic Peptide (ANP)
two types of cardiomyocytes
- contractile
2. conductile
modified cardiac muscle cells
form the cardiac nodes and fibers involved in impulse conduction
purkinjie fibers
- modified cardiac muscle cells
- 1 or 2 nuclei
- sparse myofibrils
- arranged in groups
smooth muscle cell
- single centrally located nucleus
- no striations: no myofibrils, actin and myosin present but not ordered
- desmosomes and gap junctions
- no t-tubules and sarcoplasmic reticulum is poorly developed
smooth muscle innervation
parasympathetic and sympathetic
-acetylcholine, norepinephrine, epinephrine
smooth muscle cell shape
spindle shaped surrounded by a basal lamina and reticular fibers
single (unitary) smooth muscle
- visceral organs
- cells behave like syncytium contracting in a network
- sparse innervation but communicate via multiple gap junctions
multi-unit smooth muscle
- found in iris of eye
- precise contraction
- individual innervation of each myocyte
- lack gap junctions
peristalsis
wave like contractions, GI tract
vascular dynamics
contraction alters blood flow and important in blood pressure
propulsion
urinary bladder, uterus
tunica muscularis
- innermost circular layer
- outer longitudinal layer
contraction is non-voluntary
contracted state
oblique arrangement of actin/myosin filaments and intermediate filament arrangement allow to shorten up to 80%
myoepithelial cells
- contractile non-muscle cells
- ectodermal orgin
- contain actin/myosin
- similar to smooth muscle
- can be stimulated by hormones (mammary gland)
- basket-like shape
- salivary/mammary/lacrimal glands
satellite cells
-between basal lamina and sarcolemma of muscle
-retain mitotic potential: some repair
-
cardiac muscle regeneration
lack ability
smooth muscle regeneration
limited: some mitotic activity, may be derived from the pericapillary mesenchymal cells
muscle regeneration
in all types repair is completed by scar tissue formation
