Exam 3-Muscle Contraction Lecture

How can the sarcomere shorten if neither the thin or thick myofilaments can get any shorter?

-myosin heads pull the actin inward

smallest to largest order of the following contract

1=sarcomere shortens

2=myofibril shortens

3=muscle fiber shortens

4=whole muscle shortens

molecular motor and an example

-proteins powered by the ATP that produce motion; use chemical energy to cycle through different shapes

ex. responsible for pulling chromosomes apart during mitosis

-molecular motor in muscle is myosin; uses chemical energy in ATP to pivot its heads and pull on actin

describe in detail what would happen next through myosin finally releasing from actin

the newly bound ATP is converted to ADP and inorganic phosphate

two things myosin uses ATP for

-cocked the heads, bind, release from actin myofilament, run the sarcoplasmic reticulum

neurotransmitter used at the neuromuscular junction?

-acetylcholin (ACh)

what is neuromuscular junction (NMJ)

-tiny gap that separates the end of the motor neuron from the sarcolemma

effect a change in electrical charge have on the sarcoplasmic reticulum?

-ACh changes the electrical charge across the sarcolemma; change in charge spreads over the entire sarcolemma and into the T-tubules that reach deep into the muscle

-very quickly the electrical signal reaches the sarcoplasmic reticulum; changes the permeability of the sarcoplasmic reticulum to calcium (Ca2+)

1=sarcolemma, 2=T-tubules, 3=sarcoplasmic reticulum

what things must occur in order to get a long lasting contraction?

-enough ATP

-binding sites on actin must remain open (keeping Ca2+ levels elevated in the sarcoplasm); depends on a high frequency of nervous stimulation

how long does acetylcholine (ACh) persist and why?

-only lasts a split second; degraded by an enzyme

what organelle removes calcium from the sarcoplasm? fast or slow? what type of transport does it use?

-Ca2+ is quickly removed from the sarcoplasm and restored in the sarcoplasmic reticulum; can very quickly reabsorb the Ca2+ via active transport

-w/o Ca2+, binding sites on actin for myosin heads get covered up

Rigor mortis

-stiffness of deceased person's body

-starts about 3 hours after death, usually lasts 15-25 hours

-the supply of ATP begins to drop, Ca2+ levels in the sarcoplasm rise, high Ca2+ causes a prolonged contraction, when ATP is completely gone, myosin heads are stuck to actin

events of muscle contraction in order

T-tubules conduct electrical energy to the sarcoplasmic reticulum, ca2+ levels rise dramatically in the cytoplasm, myosin binds to actin, myosin pivots its head and pulls on actin, myosin binds to a new ATP and release from actin