histology Flashcards
what x2 things are contained in the M line?
myomesin - holds thick filaments together
creatine kinase (CK/CPK)
no thin filaments here because it’s only myosin tails, no heads to bind actin
single __ actin come together to form ___ actin
G (globular), F (filamentous)
what anchors the actin filaments at the Z line?
alpha-actinin
function of nebulin:
-helps anchor actin
-runs laterally from the Z line along the actin length
-acts as a template and regulates actin length
function of titin/connectin:
-extends from Z disc to M line
-associates with myosin and maintains its position at the middle of the sarcomere
-an elastic scaffold for myosin
what is a costamere?
connects the sarcomere of the muscle to the cell membrane
desmin function:
surrounds myofibrils at the Z line and interconnects multiple myofibrils to the sarcolemma
KEY PHRASE: connects myofibrils to EACH OTHER
dystrophin function:
-helps link the sarcolemma/matrix to the myofibrils
-“dystroglycan complex”
-“sarcoglycan complex”
function of dystroglycan complex:
connects dystrophin to laminin-2
alpha subunit binds laminin 2 on the membrane
beta subunit binds dystrophin intracellularly
where does desmin connect the myofibrils to the sarcolemma?
at the costamere (wraps around the Z lines of the fibrils)
plectin function
connects desmin filaments to each other
function of alpha-beta crystallin
protects desmin
mutations in sarcoglycan complex lead to:
limb girdle muscular dystrophies
loss of dystrophin causes..
Duchennes muscular dystrophy
mutation of laminin causes…
congenital muscular dystrophy
mutations in desmin, plectin, or crystallins cause…
loss of myofibrils
Duchennes clinical features:
loss of dystrophin
loss of myofibrils
loss of myofibers
increasing adipose tissue to fill in atrophied areas
T tubule arrangement in skeletal muscle:
triads
SR terminal cisternae - T tubule - SR terminal cisternae
at the A-I junction
name of junction between muscle and tendon:
-myotendinous junctions
-dense regular CT
-tendons connect muscle fibers to bone, skin, or other muscles
-continuous with CT (deep fascia) around muscle (epimysium)
development of myofibers
-single nucleate - myoblasts (nucleus at center)
-fuse to form skeletal myotube (numerous nucleus at center)
-myotubes differentiate into myofibers (peripheral nuclei)
fate of myoblasts that don’t fuse into the myotube:
satellite cells
in basal lamina outside of sarcolemma
proliferate and replace injured muscles
what are golgi tendon organs?
encapsulated bundles of type 1 collagen
receive sensory innervation only (no motor!)
-collagen has no mechanism for contraction itself
contraction compresses the collagen
compresses afferent nerve fiber
relays to CNS
components of a muscle spindle:
-capsule
-intrafusal muscle fibers
-stretch receptor
what is a muscle spindle?
sensory AND motor innervation
intrafusal muscle fibers in between extrafusal
surrounded by a capsule
propioception - senses stretch and tension (stretch receptors)