Muscle Flashcards
in multicellular organisms what is movement assumed by
specialized cells = muscle fibers
contract upon appropriate stimulation
name the 3 types of muscle
skeletal striated muscle
cardiac muscle
smooth muscle
is a muscle cell and fiber the same
yesss
describe skeletal muscle generally
elongated multi-nucleated cell
cross striations (appearance of bands)
associated with many capillaries
collagen fibers
satellite cells
quick contraction and forceful
voluntary control
fibrocytes
why is skeletal muscle multinucleated
nuclei divide but cell does not separate and nuclei become embedded
why is skeletal muscle striated
myofibrils - cytoplasm filled with them
why is skeletal muscle associated with many capillaries
need blood to contract
what type of collagen fibers are found in skeletal muscle
type 3
reticular fibers
what is a satellite cell in skeletal muscle
located between sarcolemma (muscle fiber/cell) and BM
stem cell
mononucleated spindle cells
can repair muscle (like when pull muscle)
only in skeletal
limited regeneration via satellite cells
only seen in EM
describe bands of sarcomere
A band = darker
I band = paler
Z line = line in center, middle of I band
describe cardiac muscle generally
one nucleus in center
striated myofibrils
contained between intercalated disks
many capillaries
nuclei surrounded by halo
involuntary contraction
Vigorous and rhythmic
describe myofibrils of cardiac muscle
irregular
heterogenous shapes
what is intercalated disk
point of initiation of cell and other disk = end of cell
why does cardiac muscle need many capillaries
needs more than brain
during myocardial infarction (MI) cardiac tissue dies fast without oxygen - needs lots
describe halo that surrounds nuclei of cardiac muscle
golgi apparatus and glycogen
does not react well with H&E staining
what is hypertrophy and describe
occurs in striated muscle
hyper = above
trophy = nourishment
what does hypertrophy result from
above nourishment of new myofibrils in skeletal muscle
when is hypertrophy abnormal or normal
normal in skeletal
Abnormal in cardiac
why is hypertrophy abnormal in cardiac muscle
Muscle of heart wall will not contract properly
why is hypertrophy normal in skeletal muscle
gym - change in activity
will synthesize myoglobin (proteins) and oxygen binds - since cells need more oxygen
Myofibrils and muscle becomes bigger
describe smooth muscle generally
spindle shaped cells
nucleus centrally located (not always visible due to cross section POS)
will not see myofibrils
corkscrew nucleus
slow contraction
involuntary
does smooth muscle only have actin
NOOOO
some myosin
mainly actin
why will you not see myofibrils in smooth muscle
made of actin filaments
small
describe the spindle shaped cells of smooth muscle
smaller
shorter
thicker
why does smooth muscle have corkscrew nucleus
retracts a bit when fixed with chemicals
why is smooth muscle being involuntary good
body needs contraction all the time
like in vessels and stomach
what is hyperplasia and describe
normal in smooth muscle
hyper = above
plasis = molding
ex = uterine wall during pregnancy
number and size of cells increase
only in smooth muscle since these cells can divide by mitosis
what is epimysium of skeletal muscle
divide muscles into groups of cells
what are skeletal tissues surrounded by
dense ct = bundle or fascicle
what is perimysium of skeletal muscle
thin layer ct
fibrocytes surround bundle
special - connected by gap junctions
what is endomysium of skeletal muscle
BM that surrounds and separates individual cells
very thin
reticular fibers
capillaries
some fibrocytes
what is the role of CT around muscle cells in skeletal muscles
mechanical transducer to the forces generated by contracting muscle cells
associated to tendons and ligaments (produce movement and transduce)
describe breakdown of muscle (fascicle to filaments)
fascicle (bundle of muscle fibers) –> muscle fiber (1-40nmx10-100um) –>1500 myofibrils (1-2um diameter) –>3000 thin filaments (F-actin), 1500 thick filaments (myosin)
what is center of pseudoband H
cross linking proteins
forms M line
H band = only thick filaments
what does myosin have
tail and head
what is sarcomere
smallest repetitive subunit of contractile apparatus
Z line to Z line
what is Z line
alpha actinin
anchors thin filament
what is M line
creatine kinase = cross linking - catalyses
phosphocreatine + ADP –> ATP + creatine
describe thick filament
myosin
4 myosin heavy chains
2 myosin light chains
what happens when use chymotrypsin to split molecules of thick filament into fragments and separate
LMM = light meromysoin
HMM = heavy meromyosin
describe HMM subunits and function
HMMS - 2
HMMS - 1 = 2 activities = binds ATP and has ATPase activity, actin binding site = wants to bind actin and activates ATPase
describe thin filament
actin
globular proteins
polarized molecule
binds in active site
name the important components of broken down thin filament
tropomyosin
troponin
name and describe the 3 troponin subunits
TnI = inhibit actin myosin interaction
TnC = binds calcium
TnT = anchors to tropomyosin
*ONLY with calcium
where is tropomyosin present
in groove
what does troponin do
binds calcium and produces change in conformation of tropomyosin and can bind actin
describe mechanism of action of sarcomere - physically
thin slides over thick - no change in length
pseudoband H becomes smaller and so does I band
describe mechanism of action of sarcomere - chemically
cleaves ATP –> ADP and releases phosphate (activated by calcium) = produces energy for bending of myosin head
since myosin head attached to actin= thin filament displaced and slides over thick = contraction
name and describe proteins involved in mechanism of contraction of sarcomere
titin = spring like, connects myosin to Z line and provides stability
nebulin = surround actin filaments
tropomodulin
describe terminal cisternae
sarcoplasmic reticulum - SER
non granulated
describe connecting tubules
sarcoplasmic reticulum
connect adjacent terminals
mitochondria
describe T tubules
sarcolemma - PM
invagination of PM
follow between 2 terminal cisternae
what is a triad
2 terminal cisternae + t tubule
where is calcium ATPase
on membrane of terminal cisternae
what is calsequestrin
protein
pumps calcium into sarcoplasmic reticulum
dumps molecules without binding
describe when action potential fired in sarcomere
inside T tubule
depolarization of membrane
calcium released into sarcoplasm and will be available for contraction
describe STEPS = 5 when action potential fired in sarcomere
1 - muscle ap propagated
2 - in t tubule = calcium released from lateral sac
3 - calcium binds to troponin = removes blocking action of tropomyosin
4 - cross bridge moves, sliding of actin, head bending = contraction
5 - calcium leaving troponin restores tropomyosin blocking action with calcium resequestration
what are other words for neuromuscular junction
motor end plate
myoneural junction
terminal bouton
how does contraction occur in sarcomeres
Simultaneously in all sarcomeres, in all myofibrils of one muscle cell in all muscle cells in a bundle of muscle
how to ensure synchronous contraction
muscle fibers innervated by myelinated nerves
fast due to myelin
describe myelinated motor nerves
branch out within perimysium and endomysium where each nerve gives rise to several terminal wings called terminal boutons
describe where the myelinated motor nerves penetrate
penetrates at level of epimysium
axons branch in endomysium
synapse between nerve and muscle cell (muscular tissue)
where is ACH receptor present (neuromuscular junction)
post synaptic membrane only
gates - bind acetylcholine
describe synaptic vesicle (neuromuscular junction)
many when have action potential in neuron = stimulates exocytosis
fusion with presynaptic membrane
contain ACH (small molecules released in lumen synaptic cleft)
what happens when ACH binds (neuromuscular junction)
sodium flows in and potassium out
changes polarity of membrane
Origination of ACH on potential - AP spreads to t tubules and sarcolemma
causes depolarization, calcium diffuses towards sarcoplasm = contraction
describe myelin - what its caused bypp
schwann cell - surrounded by BM, synthesis of myelin and wraps around axon
is BM continuous with muscle fiber of (neuromuscular junction)
yup
what is presynaptic membrane (neuromuscular junction)
membrane of axon - terminal bouton
what is synaptic cleft (neuromuscular junction)
space in between pre and post synaptic membranes
what is postsynaptic membrane (neuromuscular junction)
sarcolemma - PM of muscle cell
how would you visualize neuromuscular junction
immunochemistry to visualize proteins = one antibody for axon and one identifies terminal bouton
describe ACH receptor
molecular weight = 270.00
5 subunits = 2 alpha, 2 beta, 1 gamma, 1 delta
under BM
what is myasthenia gravis
produces antibodies against acetylcholine receptor
describe ACH-cholinesterase
present in synaptic celft
ACH after contraction has to be removed = breaks ACH to acetate (recycled) and choline
does cardiac muscle have sarcomeres
yuhhh
name and describe each part of intercalated disk
fascia - zonula adherens (transverse part)
macula adherens (transverse part)
gap junctions (lateral part)
alpha actinin in center
plaque, desmosomes, thin filaments anchors into PM
describe zonula adherens (intercalated disk)
goes all around 2 adjacent PM
bell junction
alpha-actinin/vinculin = actin anchoring of terminal web (into alpha-actinin)
·intercellular space =15 nm cadherins
describe mucula adherens - desmosomes (intercalated disk)
trapped in small spot
bell like
intercellular space = 25nm
intermediate filaments
Transmembrane proteins: desmocollin & desmoglein (provide stability)
plaque: Desmoplakins 1 and 2, plakoglobin & desmocalmin
describe gap junctions (intercalated disk)
coupled connexons (6 connexins)
Channels (1.5 nm diameters) for 2nd messengers like calcium
calcium diffuses through gap junctions = Rhythmic (everything at sametimes)
connexin 48 = predominant in cardiac muscle (if mutated baby will not survive)
describe sarcoplasmic reticulum of cardiac muscle
sometimes has t tubules and terminal cisternae
triad = at level of z line
what does one unit of smooth muscle look like
sarcomere - but not tho
what are smooth muscle cells not similar to
hemidemosomes
describe dense bodies of smooth muscle
anchoring of actin filaments
alpha actinin like proteins - similar to z line but NOT
what is similar to t tubules in smooth muscke
little invaginations represent t tubule = vesicles/caveolae
where is myosin in smooth muscle cells
some myosin filaments all spread and floating in plasma membrane
what do smooth muscle cells have - specifics
dense bodies
PM
BM
reticular fibers
actin and myosin filaments = myosin head binds actin and bends
recall a hemidesmosome and why it is not similar to dense bodies of smooth muscle
tonofilaments (intermediate filaments)
plaque BP-protein anchors to tonofilaments
integrins, laminin and anchoring fibrils (collagen VII) anchor near plaque
no alpha actinin or vinculin like in dense bodies
describe elhers danlos syndrome
mutation of reticular fibers - which confer stability to smooth muscle cells
can cause rupture of digestive system and an aneurysm of arteries
what are myosin heavy chains attached to in smooth muscle
attach to light chain
head attached to tail = myosin cannot bind actin = no contraction
what does calcium initiate
myosin light chain kinase
describe myosin light chain kinase of smooth muscle
ATP –> ADP = generates phosphate = release tail/heavy chains from light chains
now myosin head binds actin = bending of head
why is slow contraction of smooth muscle good
great for intestine - peristalsis
what does relaxation of smooth muscle depend on and explain process
depends on decrease of calcium levels causing subsequent inactivation of myosin light chain kinase = everything returned to normal (calcium removed)
