Muscle Flashcards
individual muscle cell is called
myocyte
muscle fiber
muscle cytoplasm=
sarcoplasm
muscle plasma membrane/plasmalemma=
sarcolemma
3 types of Mm
skeletal
smooth
cardiac
all three types of muscle are derived from the
mesoderm
skeletal muscle is responsible for the
movement of skeleton
skeletal muscle is under
voluntary motor control
–% of the body mass is skeletal mm
40%
skeletal mm cells nuclei are
multinucleate
multinucleate cells form
syncytial
syncytial forms due to
fusion of myoblasts into a multinucleate myotube during development
myotubes synthesize
contractile proteins which assemble sarcomeres
skeletal muscle nuclei migrate to the
periphery of the cell
skeletal muscle nuclei lose the ability to
proliferate
individual muscle fibers are surrounded by connective tissue called
endomysium
several fibers bound together into
fascicles
fascicles surrounded by connective tissue
perimysium
many fascicles together form
muscle
entire muscle surrounded by
epimysium
epimysium is continuous with
tendinous attachment
blood vessels and Nn tend to follow connective tissue epi and perimysial for
support
two types of skeletal muscle fibers
fast twitch
slow twitch
Early in development of myotubes, “fast” Mm fibers are innervated by “—” Nn & “slow” Mm fibers by “—” Nn
fast
slow
Also differences in development of contractile proteins
“fast” myosin & “slow” myosin
slow myosin are — fibers with a large amount of —
small
myoglobin
type 1 uses — — — for oxidative metabolism
1’ aerobic respiration
type 1 have a large number of mitochondria, used for
ATP
type 1 muscle fibers are resistant to
fatigue
type 1 muscle fibers generate — muscle tension
moderate
where are type 1 slow fibers common?
in peripheral limbs
color of type 1 slow twitch fibers
dark red, almost black bc they’re rich in myoglobin
type 2 fibers are — fibers with — myoglobin and — mitochondria
large
less
fewer
how do type 2 fibers use — — — for energy production
1’ anaerobic glycolysis
type 1 fibers have abundant
glycogen
type 2 have extensive sarcoplasmic reticulum for rapid
ca release
type 2 fibers fatigue
readily
type 2 fast twitch fibers generate — muscle tension for short bursts of activity
high
intermediate filaments (2)
type 2a
type 2b
type 2a
oxidative and fatigue resistant
type 2b
glycolytic and fatigue sensitive
most muscles are
mixed
during peak periods of exertion, both type 1 and 2 fibers metabolism glycogen via
anaerobic glycolysis to produce ATP
intermediate metabolites (lactic acid) predicate as crystals in muscle, leading to
tearing of muscle fibers and pain after heavy exertion
if oxygen debt is severe, it can lead to (3)
ischemia
muscle cramps
cell death
extreme exertion may lead to (2) due to the release of myoglobin and clogging of glomeruli
acute rhabdomyolysis and subsequent myoglobinuric nephrosis
acute rhabdomyolysis
breakdown of actin and myosin
myoglobinuric nephrosis
kidney failure
during normal exercise, muscle fibers develop
microtears
hypertrophy
with exercise, muscle cells increase in size
why do muscle fibers increase in size? (3)
increase in number of mitochondria
increase in volume of contractile proteins
splitting/branching of individual muscle fibers
production of new muscle fibers is relatively
rare
atrophy
with disuse, muscle cells decrease in size
why do muscle cells decrease in size? (2)
immobilization (splint, cast)
denervation (never damage least to muscle atrophy)
sarcopenia
with increased age, progressive loss of skeletal muscle fibers `
lost muscle fibers are not replaced, therefore
increase in number and decrease in size of muscle mass
skeletal muscle ability to regenerate following injury
limited ability
primary source of regeneration
satellite cells
satellite cells
small myogenic cells adjacent to sarcolemma
after injury, cells proliferate and differentiate into
myoblasts
– types of proprioceptors located within mm
2
intrafusal fibers
modified skeletal muscle fibers associated with modified nerve endings
neuromuscular spindles
muscle spindles
located within belly of mm
neuromuscular spindles are sensitive to changes in
length
neurotendinous spindles
Golgi tendon organs
located within tendon
neurotendinous spindles are sensitive to changes in
tension
both prevent overstretching and tearing of mm; used in (2)
postural reflexes
coordination
individual muscle fibers are composed of
myofibrils
myofibrils are composed of numerous
myofilaments or contractile proteins in parallel bundles
two types of myofilaments
actin
myosin
actin
thin filament
6-8 nm in diameter
myosin
thick filament
15 nm in diameter
actin and myosin ratio is skeletal muscle
2:1
striated muscle
parallel arrangement of contractile proteins which give a striated appearance in longitudinal section
actin and myosin overlap in the - band but not the - band
A band
I band
(striations)
skeletal muscles are stopped in C-S due to
hexogonal array of microfilaments
myofibrils are arranged in
sarcomeres
sarcomeres
the functional units of muscle cells
z discs act as anchoring points for
actin myofilaments
during muscle contraction, sarcomeres shorten, but — remain the same length -
myofilaments
due to thick and thin filaments sliding over one another via energy from ATP,
shortening of sarcomere, via repeated binding and unbinding of actin and myosin filaments
neuromuscular junction (NMJ)
the site where skeletal muscle is innervated by motor neurons
motor end plate
dilated terminal portion of axon surrounded by myelin
the motor end plate rests on
sarcolemma
terminal button is similar to the motor end plate, except
unmyelinated
synaptic cleft
the space between the motor end plate of neurons and sarcolemma of muscle
which chemical neurotransmitter is the neuromuscular junction typically bridged by?
acetylcholine
what does the depolarization of the muscle fiber travel down?
transverse tubule system (t tubules)
t tubules
extensive network of tubules continuous with the sarcolemma
t tubules indirectly links the extracellular space with (2)
ER
intracellular environment
ends of t tubules are bounded by enlarged
terminal cistern of either side
triad
2 terminal cisternal and one t tubule
sarcoplasmic reticulum and terminal cisternal act as – reservoirs when muscle is relaxed
ca
– is necessary for muscle contraction
ca
influx of sodium ions into the cytoplasm from t tubules trigger depolarization of
sarcolemma
depolarization of sarcolemma releases – from the ER and terminal cisternae into the cytoplasm during contraction
ca
what do ca ions activate?
sliding filament mechanism during contraction
how does ca activate the sliding filament mechanism?
ca causes conformational change in troponin which interacts with tropomyosin molecules (bound to actin), exposing myosin binding site on actin filament. myosin binding causes conformational change in myosin head and sliding of myosin past actin. myosin heads repeatedly bind and unbind to actin in the presence of ca and pi causing contraction
all or none response
muscle fiber either contracts or it doesn’t
total number of muscle fibers contracting at any given time determines the
strength of overall contraction
graded response
strength of overall contraction
motor unit
a group of muscle fibers supplied by a single motor neuron
stimulation of a motor neuron results in contraction of — muscle fibers within the motor unit
all
– of motor units varies
size
recruitment increases the number of
motor units firing within a muscle
muscular dystrophy
degenerative wasting disease
muscle weakness due to genetic defect in muscle protein
cell dead
what form of muscular dystrophy affects protein?
dystrophin
myasthenia graves
autoimmune disease caused by production of antibodies to act receptors resulting in muscle weakness
treatment of myasthenia graves
achase inhibitors
inherent contractility
rhythmic, wave like contractions independent of neurological stimulation
smooth muscle organization
endothelial peri epi
smooth muscle fibers are bound together into highly irregular, branching fascicles specialized for
prolonged contractions with low force
smooth muscle nucleus
single, long, central
are skeletal or smooth muscle fibers larger?
skeletal
actin and myosin ratio in smooth muscle
15:1
randomly arranged
arrangement of smooth muscle
random
myofilaments are not arranged in sarcomeres
no striations
dense bodies
equivalent functionally to z discs
provide attachment sites for actin
smooth muscle lacks
troponin complex that controls myosin binding
instead of troponin, smooth muscle uses
calmodulin
calmodulin
binds ca and activates myosin cross binding
smooth muscle lacks t tubule system and terminal cisternal of ER. instead, cell membrane has
caveolae
caveolae
pockets/ divets in the membrane
what does smooth muscle rely on for contraction?
extracellular ca
what is smooth muscle influenced by? (3)
autonomic nervous system
hormones
local metabolites
smooth muscle autonomics
most has dual sympathetic and parasympathetic innervation
is smooth muscle voluntary?
no, involuntary
response of smooth muscle depends on
receptor tupe (alpha or beta)
sympathetic stimulation in the gut leads to
inhibitory and parasympathetic stimulation, then stimulation to Smooth muscle
smooth muscle as a single unit
tonic smooth muscle
fibers contract as a unit
ex. visceral smooth muscle of the gut, most common
smooth muscle as a multi unit
phasic smooth muscle
individual muscle fibers contract independently
ex. ciliary body of iris, erector pili muscle
smooth muscle retains the ability to divide and repair itself following
injury
smooth muscle cells can develop from (3)
endothelial cells
pericytes of blood vessels
fibroblasts
glandular epithelial cells can also differentiate into
myoepithelial cells
pericardium
sac like, fibrous connective tissue surrounding the heart
layers of the heart (2)
fibrous connective tissue layer
inner serous layer (continuous with epicardium)
inner serous layer contains
mesothelial cells
pericardium contains
pericardial fluid for lubrication
heart layers
epicardium
myocardium
endocardium
epicardium
outermost layer, simple squamous mesothelium on the external surface of the heart
epicardium is supported by
underlying fibroblastic connective tissue and adipose tissue
blood vessels and nerves are located within
subepicardial layer
the heart is surrounded by a protective layer of
adipose tissue
myocardium
cardiac muscle itself, thicker in ventricles than atria
what is particularly present in the myocardium?
endo, peri, epimysium
the myocardium is composed of
fibroblasts and collagen
cardiac muscle intermediate between skeletal and smooth muscle both
structurally and functionally
cardiac muscle myocyte nucleus
one centrally located, occasionally two
cardiac muscle fibers are —, but —-
striated
involuntary
arrangement of contractile p[roteins into sarcomeres similar to skeletal muscle, but cardiac myocytes contain intracellular —, not —
diad
diad
composed of one t tubule and one cisternal of ER located at the z disc
endocardium
lines atria and ventricles, covers heart valves
cell type of endothelium
simple squamous
endocardium is supported by
sub endothelial fibroblastic connective tissue, interspersed with reticular fibers and smooth muscle
endocardium is thicker in
atria than ventricles (greater turbulence in atria)
where are purkinje fibers located?
within subepi and endocardial layers
cardiac valves contain layer of fibrous connective tissue called — — covered by endothelium
lamina fibrosa
valves are surrounded by tough, fibrous rings at the
base of the aorta and pulmonary artery (~AV valves) and extending into IVS
occasionally ossify to form body rings at the base of AV values called
os cordis
individual cardiac myocytes exhibit
inherent automaticity
ends of fibers abut at
intercalated discs
intercalated discs
unique to cardiac muscle, specialized connections between cells
intercalated discs enhance speeds of
contractile stimulus between cells and allow synchronous contractions
intercalated discs also provide increased — — for attachment of myofibrils between adjacent cells
surface area
what junctions make up intercalated discs? (3)
desmosomes
fascia adherents
gap junctions
desmosomes
macula adherents
bind individual myocytes together laterally and on the ends
fascia adherents
adherent junctions
like zonula adherents but join ends of muscle fibers
gap junctions
located laterally, provide iconic communication between cells, synchronize contractions, and allow muscle to behave as a syncytium
condition system of the heart consists of (4)
SA node
AV node
bundle of His
purkinje fibers
all consist of highly modified cardiac myocytes that coordinate conduction, joined by extensive
gap junctions
calls larger than surrounded cardiac muscle cells conduct impulses ~-x faster
4x
paler staining than surrounding muscle due to
higher glycogen content
SA node
pacemaker
SA node is located at junction of the
superior vena cava and RA
SA node generates impulses that induce
contraction of atria
as impulses travel across atria, this stimulates the
AV node
AV node is located between
RA and V
the AV node delays atria, giving time to
contract
travels down inter ventricular septum (IVS) via
bundle of His
branches into
Land R AV bundles within IVS
fibers further subdivide in ventricular myocardium and ramify into — — within subendo and subepicardium of ventricular free wall, gradually merge with myocardium, initiate ventricular contraction
purkinje fibers
inherent rhythm of SA node modulated by autonomic nervous system
sympathetic stimulation from:
parasympathetic stimulation from:
sympathetic stimulation from dympethic ganglia increase heart rate
parasympathetic stimulation from vagus nerve decrease heart rate
