MUSCLE Flashcards
in muscle contraction, what decreases (SFT)
sarcomere length (Z-Z)
H zone
I band
in muscle contraction, what remains constant (SFT)
A band (length of thick filaments)
in muscle contraction, what increases (SFT)
zone of overlap
what is the “super power” of muscle
ability to contract => tension
3 types of muscle and their classifications
skeletal (voluntary, striated)
cardiac (involuntary, striated)
smooth (involuntary, non striated)
what allows voluntary muscle to contract
neural input
what happens if involuntary muscle is denervated
can still contract; neves only regulate, don’t initiate contraction
3 layers of CT in muscle
epimysium (entire muscle)
perimysium (fascicle)
endomysium (muscle fibre/cell)
another name for muscle cell
muscle fibre
name of proteins within sarcoplasm
myofibrils
Sharpey’s fibres
collagen fibres of tendon continuous with collagen fibres of periosteum
T or F: neuromuscular bundles perforate CT layers of muscle
T; pierce CT covering then branch to reach ind’l muscle fibres
how many nuclei in muscle fibre
multinucleate (>100/fibre)
how do muscle fibres develop
fusion of myoblasts (mesodermal cells)
function of myosatellite cells
limited repair of skeletal muscle (normally, damaged -> replaced with fibrous CT)
how long can 1 muscle cell be
> 1m (skeletal muscle fibre)
what cell-cell junctions exist in skeletal muscle
none; fibres arranged in parallel; surrounded by endomysium
where are nuclei in skeletal muscle fibres
squeezed to periphery
what ensures that skeletal fibres contract together
endomysium transfers tension
sarcoplasm
muscle fibre cytoplasm
sarcolemma
muscle fibre cell membrane
transverse tubules
tubular extensions of sarcolemma; perpendicular to surface
sarcoplasmic reticulum
ER of skeletal muscle fibre
terminal cisterna
expanded sarcoplasm reticulum on either side of T tubule
triad in skeletal muscle
t tubule with adjacent terminal cisterna
bundles of myofilaments
myofibrils
2 types of myofilaments
actin (thin), myosin (thick)
what feature => striations
sarcomeres
how long are myofibrils relative to cell
length of whole cell
2 types of actin
G actin (globular subunit) F actin (filamentous; 300-400 G actin)
what covers actin binding sites
tropomyosin
what holds tropomyosin in place
troponin
what runs like a string covering actin
tropomyosin
what causes troponin to change conformation
calcium binding
what happens when troponin binds calcium
tropomyosin shifts; exposing actin binding sites for myosin
structure of troponin
trimer
normally, intracellular calcium is kept ___
low
2 proteins wound together => myosin
myosin tails & myosin heads (cross bridges)
what part of myosin binds actin
myosin heads
how many myosins = 1 thick filament
~500
which direction do myosin heads face
1/2 half one way, 1/2 the other
how many thin filaments surround 1 thick filament
6; arranged helically
can thin filaments be shared between thick filaments’ 6?
yes; between adjacent thick filaments
delineates sarcomere border
z disc
where do thin filaments attach
z disc
m line
where myosin attaches; m= middle
zone of overlap
overlap between thick and thin (only thing that increases with contraction)
h zone
thick filaments only
i zone
thin filaments only
a band
length of myosin
__ + ___ = a band
H zone + zone of overlap
where do neuron and muscle fibre communicate
neuromuscular junction
3 components of NMJ
synaptic terminal
synaptic cleft
motor end plate
where are cell bodies of motor neurons
spinal cord
T or F: axon can contact only 1 muscle fibre
F; axon can branch into collaterals and contact multiple skeletal fibres
what is in synaptic vesicles at NMJ
acetylcholine
how and where is ACh released after AP
exocytosis; synaptic cleft
which receptors on motor end plate
Acetylcholine receptors
what kind of channel is AChR
ligand-gated ion channel; ACh (ligand) binding => open
what ion depolarizes fibre once AChR open; which direction
Na+; influx
similarity between muscle fibres and neurons
both excitable
what happens to ACh after exocytosis
broken down by acetylcholerinesterase (AChE) in synaptic cleft; taken up by synaptic terminal, reused
Na moves _____ its concentration gradient
down
when does ACh release stop
when AP ends
how do muscle fibres control Ca2+ levels
actively; pump into SR (terminal cisterna), ECF
how does AP reach SR
travels down T tubule (membrane extension); contacts terminal cisterna (SR extension)
muscle contraction depends on _____ of intracellular Ca2+ upon AP
increase
with AP, Ca2+ moves ____ its gradient
down; into intracellular (concentrated in SR)
T or F: myosin heads attach once per AP
F; attach, reattach; as long as CA channels open
when do ca2+ channels close
when membrane potential difference returns to rest
muscle relaxation is _____; 3 reasons
passive;
elasticity of tissues
pull of antagonist muscles
gravity
how many NMJ does a muscle fibre have
one
motor unit
SINGLE motor neuron (spinal cord) and the muscle fibres it innervates
what determines force produced by neural control
of motor units recruited
T or F: motor units have varying # of innervated muscle fibres
T
T or F: muscle fibres of motor unit all adjacent
F; intermingled; tension distributed throughout tissue
if less muscle fibres in motor unit
precise control i.e. eye movements
example of muscle with many fibres/motor unit
anti-gravity muscles in back
T or F: sometimes, all muscle fibres relaxed
F; active; resting tension, but not enough to contract
how do antigravity muscles avoid fatigue
rotate motor units active
what does aerobic metabolism: require? produce?
required: O2, organic molecules, mitochondrial enzymes
produced: ATP, CO2
what does anaerobic metabolism: require? produce?
required: glycogen, glycolytic enzymes
produced: ATP, lactic acid
metabolism of slow twitch
aerobic (think: takes time to do things right)
metabolism of fast twitch
anaerobic
colour of slow vs fast twitch
slow = red (myoglobin; needs oxygen) fast = white
which muscle type has larger diameter
fast twitch (doesn’t have to worry about oxygen diffusion)
which muscle type has higher max tension
fast twitch; greater diameter
which muscle type is fatigue resistant
slow; as long as breathing, oxygen supplies ATP (while fast = limited glycogen, glycolytic enzymes)
which muscle type can use more substrates for ATP production
slow (carbs, lipids, proteins); fast can only use glycogen
example locations of slow twitch
fatigue resistant; back, legs (like dark meat on chicken)
what is required for muscle hypertrophy
repeated stimulation to near maximal tension
what 3 results increase ATP generating capacity in muscle hypertrophy
more mitochondria
more glycogen reserves
more glycolytic enzymes
T or F: number of myofibrils and myofilaments increases with muscle hypertrophy
true
why do muscles get bigger
each fibre gets bigger; not increasing #
what happens with muscle atrophy
reduced myofibrils, myofilaments
fibres become smaller, weaker
how are myofibrils removed in muscle atrophy
lysosomal activity
T or F: muscle atrophy is permanent
F; initially reverisble
cardiac muscle: # of nuclei
1/cell
size of cardiac muscle cells
smaller than skeletal
junctions between cardiocytes
intercalated discs
what cells set rate of contraction in cardiac
pacemaker cells
what modules cardiac cells rate
autonomic NS, hormones
3 junctions at intercalated discs in cardiocytes
gap junctions (communication), fascia adherens (in epithelia, zonula adherens; but here, not belt); desmosomes
why do cardiac cells contract autonomously
unstable membrane potential
T or F: cardiocytes can regenerate
F; if damaged (i.e. ischemic attack) replaced by fibrous CT
location of nuclei in cardiocyte
central
metabolism of cardiocytes
aerobic
energy reserves in cardiac muscle
glycogen, lipid droplets
why is smooth muscle nonstriated
myofilaments : irregular arrangement
4 locations of smooth muscle
respiratory, digestive, reproductive, circulatory
what cells set rate of contraction in smooth muscle
pacesetter (unstable membrane potential)
regeneration in smooth muscle?
yes (i.e. hyperplasia in uterus)
what makes smooth muscle contract as whole
gap junction
where are nuclei in SMC
central
which muscle type has smallest cells
smooth muscle
which muscle has more nuclei in cross section: cardiac or smooth?
smooth; cells are smaller
