Exam 2: Muscle Flashcards
Myocyte
muscle cell = myofiber = muscle fiber
Myofilaments
filaments in muscle cells
Sarcoplasm
cytoplasm of muscle cells
What are muscle cells specialized for?
forceful contraction
What is muscle derived from? (embryonic tissue)
mesoderm
3 types of muscle
smooth
skeletal
cardiac
Which type of muscle is not striated?
smooth
Smooth muscle characteristics
central nuclei
long/tapered ends (for contraction)
innervated by ANS (involuntary contraction)
What kind of tissue is smooth muscle surrounded by?
Reticular fibers in loose connective tissue w/ myelinated axons (to transmit contractions)
Fusiform / Dense Bodies
attachment points for actin in smooth muscle
coil/contract cells
What structures allow the contraction mechanism of muscle?
actin & myosin
What shape does smooth muscle cell nuclei take during contraction?
elongated –> spiral/coil
Caveolae
invaginations of plasma membrane in smooth muscle
involved in Ca2+ entry/exit during contraction
Smooth muscle contraction
Ca2+ binds to calmodulin
Activates MLCK –> phosphorylates myosin –> cleave ATP = contraction
not rapid | sustained, tonic contraction of organs
Two types of smooth muscle contraction
unitary/visceral
multiunit
Unitary/visceral contraction
smooth muscle contraction
peristaltic waves trigger other cells via gap junctions
Multiunit contraction
fine control (ex. iris)
sheets of cells contract at same time because all innervated individually (not gap junctions)
Skeletal muscle characteristics
striated
multi-nuclei at periphery
reticular fibers important for contraction
Cardiac muscle characteristics
striated
1 nuclei per cell at center | rectangular nuclei
branches | intercalated disks
HIGHLY vascular
Myofibrils
columns of sarcomeres
Explain the mechanical disadvantage of contraction in skeletal muscle
power traded for leverage & speed
Desmin
intermediate filament of skeletal muscle
keeps sarcomeres in register & maintain structural integrity of myofibrils
alpha-actinin
anchors actin filaments at Z-line in skeletal muscle & dense bodies of smooth
Titin
protein that anchors and keeps sarcomere from over-extending (elastic!)
Desminopathies
mutated desmin breaks up sarcomeres which leads to separation
cardiomyopathy is one result of desminopathy
I band
actin filaments not yet overlapping with myosin
transected by Z line
T tubule
invaginations of muscle cell which increases contraction/Ca2+ sequestering
Triad in skeletal muscle
T tubule + SR on both sides
allows for more efficient contraction
Contraction of Skeletal Muscle
Ca2+ binds to troponin (conform change) | moves tropomyosin so myosin can bind to actin |
myosin flexes & actin moves along it as long as ATP / Ca2+ bound
Smooth muscle contraction controlled by activation of…
myosin
Striated muscle contraction controlled by access to…
actin
Type I skeletal muscle fiber
Slow, oxidative
Long, sustained contraction
Type IIa skeletal muscle fiber type
oxidative phosphorylation for relatively fast contraction
Type IIb skeletal muscle fiber type
Rapid contraction, susceptible to fatigue
Epimysium
DICCT sheath around whole muscle
Perimysium
loose CT around fascicles
Endomysium
connective tissue of reticular fibers around each myocyte
highly vascular
Intercalated Disks
cardiac muscle only
junctions that transmit force of contraction between cells
Parts of Intercalated disks
transverse portion
lateral portion
Transverse portion of intercalated disk
transmits force of contraction from one cardiac cell to another
Lateral portion of intercalated disk
communicating junctions from one cell to another (gap junctions) to transmit trigger for contraction
What structures are within intercalated disk?
Fascia adherens
Macula adherens (desmosomes)
Gap Junctions
Fascia adherens
anchors actin filaments in intercalated disk
Diad
structure in cardiac muscle
made of T tubule, SR on one side
Z line around it
How does smooth muscle grow in response to physiological demand?
Hypertrophy AND hyperplasia
Hypertrophy
individual cells get larger
Hyperplasia
division of cells / increase in reproduction rate
How does smooth muscle repair after injury?
cell replacement by connective tissue/scar tissue (DICCT)
some new myocytes from pericytes
How does skeletal muscle grow in response to physiological demand?
Hypertrophy only
How does skeletal mucsle repair after injury?
substantial cell replacement
new myofibers from satellite cells
How does cardiac muscle grow in response to physiological demand?
Hypertrophy only
I band
light band made of actin filaments
in skeletal muscle
A band
dark band containing myosin filaments
in skeletal muscle
Z disk/line
within I band where actin filaments attach
in skeletal muscle
H band
light zone at center of A band, gap between actin filaments
in skeletal muscle
M line
fine threads connecting central part of myosin filaments
in skeletal muscle
