Skeletal and cardiac muscle appears
striated
Cardiac and smooth muscle is innervated by
autonomic NS
Smooth muscle lines the
hollow walls of organs
smooth muscle is responsible for
GI motility
constriction of blood vessels
uterine contractions
somatic neurons stimulate
skeletal muscle
Tendons
muscle attached to bones
tendons are composed of
strong connective issue which contains primarily collagen
muscle contracts: the ______ is brought closer to the _____
insertion point is brought closer to the origin
skeletal muscle is composed of muscle &
connective tissue
what is the function of connective tissue in skeletal muscle
Connective Tissue (CT) holds the contractile tissue together in bundles called fasicles to allow flexibility
Muscle fiber is a
single skeletal muscle cell
Skeletal muscle cells are
multinucleated synctia formed by the fusion of individual cells during development
skeletal muscle cells are innervated by
a single nerve ending
all skeletal muscle cells are innervated by ____ motor neurons
all skeletal muscle cells are innervated by __somatic__ motor neurons
Somatic motor neurons release _______ @ NMJ
ACh
the difference in regulation is the ______ of the signal
the difference in regulation is the timing of the signal
Sacrolemma is the
myofiber cell membrane
the sacrolemma differs from the Plasma membrane in that
it has an additional layer of polysaccharide & collagen
sacrolemma’s additional layer helps
fuse with the tendon fibers
myofibrils are units within each
myofiber
myofibrils in the muscle cell is like a specialized
organelle
myofibril is responsible for the
striated appearance of a muscle cell
the contractile force
what proteins are responsible for generation of muscle contraction in the myofibril
actin and myosin
actin
thin filaments
myosin
thick filaments
striated appearance of skeletal muscle is due to
overlapping arrangement of bands of thick and thin filaments in sacromeres
myofibril composition of sacromeres is
myofibril is composed of many sacromeres aligned end-to-end
each sacromere is bound by 2
z lines
thin filaments attach to ____
thin filaments ___ with thick filaments in the middle of the sacromere
z lines
overlap with thick filaments
thick filaments are _____ to z lines
NOT ATTACHED
I bands contain only
thin filaments
A bands
full length of thick
includes overlapping region
H zone
only thick
seen in resting sacromere
Mnemonic
Z line
Z line denotes boundarieZ of Sacromere
Mnemonic
M line
M line in the Middle
Mnemonic
H is
H is thick so thick filaments
Mnemonic
I is
I is thin so thin filaments
Mnemonic
A is
A is thick And thin
Mnemonic to help remember the order
“Zee Intelligent Animal Has Muscle”
Z-I-A-H-M-H-A-I-Z
M is symmetry point
contraction occurs when
thick and thin slide across each other
contraction _____ z lines ____ to each other —> ____ length of muscle cell
contraction draws z lines close to each other —> shortening length of muscle cell
where does the energy for filament sliding come from
ATP hydrolysis
which enzyme uses ATP hydrolysis
myosin uses ATP hydrolysis to generate movement
a myosin monomer is composed of a
head and a tail
myosin head attaches to _____ when attached it is referred to as ______
specific site on actin - myosin binding site
when attached it is referred to as cross bridge
filament sliding
- cross bridge formation
- power stroke
- release of actin
- ATP hydrolysis
power stroke
myosin head moves to lower E. conformation –> pulls actin toward center of sacromere —> release of ADP
each step of filament sliding theory and what is bound to myosin
- myosin binds to actin. Has ADP + Pi
- myosin bound to actin. releases ADP.
- ATP binds to myosin. myosin releases actin
- ATP hydrolysis –> myosin head to cock into high energy conformation
ATP is required for
myosin to release actin
when does myosin hydrolyze ATP
when it is not bound to actin and to move it forward into the high energy conformation
in a myofiber contraction only occurs when cytoplasmic concentration of
calcium increases
thick filaments
contain tropoin-tropomyosin complex
when no Calcium is present
tropoin-tropomyosin complex prevents
tropomyosin
blocks all myosin binding sites
long fibrous proteins
winds along actin polymer
tropoin
calcium binds to tropoin
globular protein
bound to tropomyosin
calcium binds to ______ –> _________ change
calcium binds to tropoin –> conformational change
conformational change results in __________
conformational change causes tropomyosin to move out of the way
in summary binding of calcium to ______ causes _____ change which results in ______ moving and allowing for _________ to attach to _____ resulting in the ______.
in summary binding of calcium to tropoin causes conformational change change which results in tropomyosin moving and allowing for myosin head to attach to actin resulting in the filament_sliding.
NMJ is synapse between axon and ______.
NMJ structure is a ______
myofiber
the structure is a long trough/invagination (infolding)
NOT a single point
What is the purpose of the NMJ being a long trough?
the purpose is to allow neuron to depolarize a large region of the postsynaptic membrane at once
postsynaptic membrane is the _______
motor end plate (myofiber cell membrane)
What neurotransmitter is released at the NMJ?
ACh
chemical synapse
AP arrives @ axon –> triggers opening of Volt. Gated Calcium channels –> increase in calcium in the cell —> release of ACh
post synaptic membrane has ___ receptors which are _______ channels
post synaptic membrane has ACh receptors which are _ligand gated sodium _ channels
since the myofiber is very thick AP on its surface will not depolarize the interior. Thus the solution was to
have deep invaginations of cell membrane –> allow AP to travel to thick of cell
what are the deep invaginations of the myofiber membrane called?
T tubules
Sacroplasmic reticulum
specialized membrane in myofiber
specialized smooth endoplasmic reticulum
Sacroplasmic reticulum contains _____ channels
Sacroplasmic reticulum contains V.G. Calcium channels –> allow Calcium to rush out of the S.R. into the sacroplasm
NS can force increase in contraction by 2 means which are
- motor unit recruitment
2. frequency summation
describe
1. motor unit recruitment
- motor unit recruitment group of myofibrils innervated by single motor neuron’s axon
describe
2. frequency summation
- frequency summation - if insufficient time for the calicum to be sequesterd by the SR then 2nd contraction builds on the first
for f. summation to occur the amount of time must be greater than the ________ but also less than the time for _______
for f. summation to occur the amount of time must be greater than the ___refractory period___ but also less than the time for __calcium to return to low resting potential___
muscles have a lot of what organelle
highly aerobic with lots of mitochondria
myoglobin
Role is an O2 reserve (takes O2 from Hemoglobin and releases it as needed)
similar to 1 subunit of Hemoglobin
globular protein
prolonged contraction leads to
anaerobic respiration –> lactic acid –> blood –> decrease in pH —> picked up by the liver —> pyruvate
anaerobic respiration –> _____ –> blood –> _____ in pH —> picked up by the ____ —> _____
anaerobic respiration –> lactic acid –> blood –> decrease in pH —> picked up by the liver —> pyruvate
Differences between cardiac versus skeletal muscle
- SYNCYTIUM
- Smooth muslce is a STRUCTURAL syncytium (fusion of individual muscle cells forming multinucleated cell)
- Cardiac is a FUNCTIONAL syncytium (cardiac cells are connected by intercalated discs) - Cardiac muscle cells are each connected to several neighbors by intercalated disks
- Cardiac muscle contraction does NOT depend on stimulation by motor neurons
- ACh is inhibitory - AP in cardiac muscle depends on BOTH voltage-gated sodium channels (fast channels) AND on voltage-gated calcium channels (slow channels)
function of intercalated disk
gap junctions
which allow AP propagation throughout the entire heart without allowing nuclei and cytoplasmic contents to be shared (only small ions can pass)
Similarities between cardiac versus skeletal muscle
- both are striated
- thick and thin filaments organized into sacromeres.
- T tubules
- tropoin-tropomyosin regulated contraction in the same way
- length-tension relationship is the same though MORE significant in CARDIAC.
structural syncytium
is a multinucleated cell that results from multiple cell fusions of uninuclear cells
Similarities between smooth and skeletal muscle
- contraction accomplished by actin & mysoin filament sliding
- 4 step contracile cycle
- contraction triggered by increase in calcium
- Do not branch
Differences between smooth and skeletal muscle
- Narrower & shorter
- No T tubules
- only 1 nucleus / cell. connected to neighbors by gap junctions. FUNCTIONAL syncytia
- thick and thin NOT organized into SACROMERES. DISPERSED in cytoplasm
- Tropoin-tropomyosin NOT present. Contraction is regulated by CALMODULIN (binds to Ca) myosin light chain kinase (MLCK)
- Smooth muscle SR poorly developed. cell relies heavily on extracellular calcium
- AP varies based on location on smooth muscle (some have no sodium channels)
- Smooth muscle must sustain longer contractions. AP similar to cardiac
- Smooth muscle has fluctuating resting potential - “slow waves”
- innervated by motor neurons bur are autonomic motor neurons
calmodulin myosin light chain kinase (MLCK):
Calcium binds to _______ –> activates _____ –> ______ myosin –> _____ myosin
Calcium binds to _calmodulin__ –> __activates MLCK__ –> __phosphorylates__ myosin –> __activated__ myosin