Lecture 9 Flashcards
what is the neuromuscular junction (NMJ)?
somatic motor neurons from the anterior horn of the spinal cord that goes to skeletal muscle through a spinal nerve
neuromuscular is efferent or afferent?
efferent (away from brain)
what occurs after nerve ending makes a junction near the midpoint of a skeletal muscle fiber NMJ?
each nerve fiber branches and stimulates 3- hundreds of skeletal muscle fibers
fine muscles have ____ NMJ
larger muscles have _____ NMJ
more
less
at the NMJ, the end of the motor neuron divides into a _______
cluster of synaptic end bulbs
suspended in the ____ of each synaptic end bulb are hundreds of ________
cytosol
synaptic vesicles
- membrane-enclosed sacs
within each synaptic vesicle at the end bulb there are thousands of molecules of neurotransmitter ________
acetylcholine (ACh)
NMJ is a _____ synapse
chemical
what is the cell membrane of a muscle fiber
sarcolemma
what is the region of the sarcolemma opposite the end bulbs ?
motor end plate
the motor end plate contains ________ which are integral membrane proteins that bind specifically to _____
30-40 million ACh receptors
ACh
ACh receptors are ___________ channels and requires ____ ACh to bind to open channel
ligand gated cation channels
2
the space between the synaptic end bulb and motor end plate is the __________
synaptic cleft
at surface of muscle there are usually ______ which greatly increase the surface area where the synaptic transmitter can act
subneural clefts
a nerve impulse reaches NMJ and the action potential spreads over the nerve terminal and activates __________ in the neural membrane. ______ flow in from the synaptic space to the interior of the nerve terminal and cause the synaptic vesicles within the end bulbs to fuse with _______.
The ____ then empty their ACh into the synaptic space by way of _______. ACh diffuses across the ______ and binds to ______ located in the motor end plate. ___ ACh bind to the receptor portion of the channel, whiches causes a confirmation change that opens the channel
voltage gates calcium channel
Calcium ions
neural membrane adjacent to the channels
vesicles
exocytosis
synaptic cleft
ACh gated ion channels
2
the ACh channel open up to a diameter of ____ which allows mainly _____, and ___ and ___ to move easily through the channel while _____ at the mouth of the channel keep _____ from entering
0.65 nm
Na
K and Ca
negative charges
negative charges
the influx of positive charge creates a local positive charge potential change inside the muscle fiber membrane called a ____________
end plate potential
the end plate potential initiates an _______ that spreads through the muscle membrane causing _____________
action potential
muscular contraction
ACh must be removed from the synaptic cleft or else it will continue to acti ate ACh receptors, so maximum amount of excitation is _____
a few milliseconds
what are the two means of ACh removal?
- acetylcholinesterase in synaptic cleft destroys remaining ACh
- a small amount simply diffuses out of the synaptic cleft
what are the three connective tissue layers?
epimysium
perimysium
endomysium
the three connective tissue layers extend from _____ to help protect and strengthen skeletal muscle
deep fasia
epimysium
outermost connective tissue surrounding the entire muscle
perimysium
connective tissue layer that surrounds groups of 10-100 or more muscle fibers, separating them into bundles called fascicles
what are fascicles
bundles of muscle fibers
endomysium
connective tissue layer that penetrates to the interior of each fascicle
separating individual muscle fibers from one another
skeletal muscle is composed of ______ which is composed of individual _____
muscle fascicles
muscle fibers (cells)
each skeletal muscle fiber contains several hundred to several thousand _______
myofibrils
each myofibril is a highly organized bundle of _____
1500 myosin filaments (thick)
3000 actin filaments (thin)
the many myofibrils of muscle fiber are suspended side by side in a fluid intracellular substance called ____
sarcoplasm (muscle fiber cytoplasm)
the sarcoplasm contains _____ and ______
mitochondria
sarcoplasmic reticulum
what is the sarcoplasmic reticulum and what does it do
stores calcium and winds around each myofibril
the sarcolemma of the muscle fiber contains thousands of tiny invaginations called ________
transverse (T) tubules
where/how are T tubules located in the sarcolemma
tunnel in from the surface toward the center of the muscle fiber
- adjacent to end regions of sarcoplasmic reticulum (terminal cisternae)
T tubules are open to the _____ of the fiber and filled with _________.
outside
interstitual fluid
the arrangement of T tubules in skeletal muscle ensures that _______________.
an action potential excites all parts of the muscle fiber simultaneously
in a myofibril, myosin and actin _______ in a repeating pattern, causing alternating light and dark bands
interdigitate (cross eachother)
one repeat of the light and dark fiber pattern is called a _____
sacromere
what is the basic contractile unit of the myofibral
sacromere
what is a springy filamentous protein that holds myosin and actin filaments together so that contractile machinery is in a functional position
titin
I bands
light bands containing only actin filaments.
A bands
dark bands containing myosin filaments and the ends of overlapping actin filaments
H zone
Center of each A band and contains thick but no thin filaments
M line
Supporting proteins that hold the thick filaments together at the center of the H zone
Z disc
Passes through the center of each I Band and is composed of filamentous proteins. Pass crosswise connecting myofibril to myofibril
what makes the anchor for contraction
M line and Z zisc
what are the three types of proteins that participate in muscle contraction?
Contractile
Regulatory
Structural proteins
contractile proteins
actin and myosin
regulatory proteins
tropomyosin
troponin
structural proteins
titin
myomesin
nebulin
dystrophin
actin is made up of _____ and _____ on the surface
troponin (random) and tropomyosin (twirled around)
what is the thick filament?
myosin
myosin head contains an ________ and an _______ that does what?
ATP binding site
ATPase
enzyme that hydrolyzes ATP (makes ADP)
in an actin filament, there are active sites that contain ____ and serve as the ____ for ____ during muscle contraction
ADP
attatchment point
myosin heads
role of tropomyosin
covers active sites
role of troponin
hold tropomyosin in place
Sliding filament Mechanism
- actin potential propagates along the muscle fiber membrane reaching the center of the muscle fiber through T tubules.
- flow of electrical charge causes Calcium release from sarcoplasmic reticulum into sarcoplasm.
- myosin head hydrolyzes ATP to ADP
- calcium binds to troponin complex, confirmational change that lifts tropomyosin off of the myosin binding sites.
- energized myosin head attaches to myosin-binding site on actin and releases the phosphate (crossbridge formation)
- myosin head tilts toward the arm and drag actin filament along with it (power stroke)
- at end of power stroke, crossbridge remains attatcheduntil it bind with another ATP.
- when ATP binds on myosin head, the head detached from actin.
contraction cycle repeats and continues as long as _____ is available
Calciu
active calcium pumps on the membrane of ___ pumps calcium ions away from the ______ back into the ___.
__________ needed for contraction to continue
SR
myofibrils
SR
series of repeated action potentials
For skeletal muscle, optimal myofilament overlap indicates ______________. what is the optimal length of micrometers that developers maximum tension.
how forcefully the muscle will contract
2-2.4 micrometers (myosin and actin overlap fully)
If sarcomeres are stretched too far, actin-myosin overlap decreases and cannot form ________ , so it ______.
cross-bridge
produces less tension
If sarcomeres are not stretched enough (compressed together), strength of the contraction approaches _____since __________ – which means ______
0
filaments crumple
no space for powerstrokes
_____ degrees is where we have the most overlap of actin and myosin
90 degrees
what is the basis of classifications of skeletal muscle?
- content of myoglobin
- red (binds oxygen in muscle fibers) vs. white fibers - metabolic reaction used to generate ATP
- oxidative vs. glycolytic fibers - How quickly the muscle fiber fatigues
- fast vs. slow fibers
slow oxidative fibers (SO)
- smallest diameter muscles
- appear dark red (large amount of myoglobin)
- use oxygen to make ATP aerobically (a lot of mitochondria)
In slow oxidative Fibers, ATPase in the myosin head hydrolyzes ATP _____, therefore the contraction cycle proceeds at a ____ pace.
But contractions are ______, and these fibers are resistant to _______.
Adapted for maintaining _____ and for _____ type activity
slowly
slower
prolonged
fatigue
posture
aerobic endurance
In fast Oxidative Glycolytic (FOG) fibers, the sizing is _____ diameter, appear _____, and involve _____ because myosin heads hydrolyze ATP _____ than SO fibers
intermediate diameter
red (large amount of myoglobin)
fast twitch
3-5x faster
Fast Oxidative Glycolytic (FOG) fibers generate ATP __________ giving them a moderately _____ resistance to fatigue
Intracellular _________ is high so they also can generate ATP by___________.
- Contribute to activates like ___________.
aerobically
high
glycogen
anaerobic glycolysis
walking and sprinting
fast glycolytic fibers have a diameter that is ______. They contain the most ______ and so they generate _______.
____ myoglobin, ____ appearance
generate ATP _____ through ______
the largest
myofibrals
the most powerful contraction
low, white
anaerobically thru glycolysis
Fast Glycolytic Fibers
Due to their large size and ability to hydrolyze ATP rapidly, they contract ______ and _____.
Fatigue?
Contribute to activities such as _______.
strongly and quickly
fatigue quickly
weight-lifting
