Flashcards in 13. Muscle conduction to contraction Deck (38)
Muscle contraction - steps
neurotransmitter release --> postsynaptic ligand --> depolarization --> Ca2+ release from saecoplasmatic reticulum --> tropoinin C to tropomyosin system --> displacement of myosin on the actin filament --> myosin binds and hydrolyses ATP
muscle contraction - neurotransmitter release is caused by
action potential depolarization opens presynaptic voltage - gated Ca2+ channels, inducing neurotransmitter release
muscle contraction - post synaptic ligand leads to
muscle cell depolarization in motor end plate
muscle contraction - depolarization process
it starts from ligand binding --> depolarization travels along muscle cell and down the T- tubule
muscle contraction - depolarization result to -->
depolarization of the voltage - sensitive dihydropyridine receptor, mechanically coupled to the ryanodine receptor on the sarcoplasmic reticulum --> conformation change --> Ca2+ release from sarcoplasmic reticulum
muscle contraction - Ca2+ action ( and mechanicals changes )
released Ca2+ binds to troponin C causing a conformation change that moves tropomyosine out of the myosin-binding groove on actin filaments
muscle contraction - myosin action
myosin release bound ADP and inorganic PO4(3-) --> displacement of myosin on the actin filament ( power stoke) --> binding a new ATP causes detachment of myosin head from actin filament --> hydrolysis ---> high energy position ( cocked) for the next cycle
sarcomere anatomy - M line
M line : middle line
sarcomere anatomy - H band
myosin between myosin heads ( in the middle of the sarcomere)
sarcomere anatomy - A band
all mysosin ( in the same sarcomere ) ( thick filaments
sarcomere anatomy - I band
from the end of the myosins of the one sarcomere to the end of the myosins of the next sarcomere
sarcomere anatomy - Z lines
the lines of sarcomere
transverse (T) tubules ?
extensions of plasma membrane part of juctaposed with terminal cisternae ( part of sarcoplasmic reticulum )
Terminal cisternae are
enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules
T tubules and Terinal cisternae - numbers
in skeletal muscle : 1T +2 terminal cisternae ( triad) in cardiac muscle : 1T + 1 terminal cisternae ( diad )
contraction - appearance of bands
- shortening of H band + I band + sarcomere
-A band remains the same length
H band after contraction
A band after contraction
I band after contraction
sarcomere band after contraction
muscle contraction - post synaptic ligand binding leads to muscle cell depolarization in the
motor end plate
muscle depolarization travels muscle cell and down the
muscle cells - T - tubule receptor
muscle cells - sarcoplasmic reticulum receptor
• At the synapse of a neuromuscular junction, which ion influx into the axon triggers the release of neurotransmitter?
Calcium, through voltage-gated channels
• After presynaptic neuron neurotransmitter release, postsynaptic ligand binding leads to the depolarization of which membrane?
The motor end plate of the muscle cell (postsynaptic membrane)
• As an action potential travels along a muscle cell, it goes down into invaginations in the membrane called what?
• A new drug inhibits the ryanodine receptor. What ion will not be released from the sarcoplasmic reticulum as a result?
• During skeletal muscle contraction, what is the result of calcium binding to troponin C?
A conformational change that allows tropomyosin out of the myosin-binding groove on actin filaments
• During skeletal muscle contraction, which bands of the sarcomere shorten in length?
H band and I band between the Z lines (HIZ shrinkage)
• Ryanodine receptors on the ____ surface are coupled with ____ receptors on the cell membrane.
Sarcoplasmic reticulum; dihydropyridine
• In a sarcomere, the M line is the site of ____ (actin/myosin) attachment and the Z line is the site of ____ (actin/myosin) attachment.
• What happens during a power stroke in a myocyte?
Myosin releases ADP and inorganic PO43- and is displaced on the actin filament
• A poison affects the release of certain molecules, such that myosin cannot be displaced on the actin filament. What molecules are these?
ADP and inorganic PO43-
• In a sarcomere, why does the A band remain the same length during contraction?
The A band represents myosin, which is fixed relative to sarcomere contraction between the Z lines
• What happens when ATP binds to a myosin head that is attached to the actin filament?
It triggers its release; subsequent hydrolysis of the ATP to ADP places myosin in a cocked position for the next contraction cycle
• What are T-tubules, and what is their relation to the muscle?
T-tubules are extensions of plasma membrane juxtaposed with terminal cisternae and are part of the sarcoplasmic reticulum