Physio Lecture 9 Questions (Exam 2)

Front 1

Do all somatic neurons release acetylcholine as their neurotransmitter?

Back 1

yes

Front 2

Where are acetylcholine receptors found on a muscle fiber?

Back 2

In the area called the "motor end plate".

Front 3

Are all motor end plate potentials excitatory?

Back 3

yes

Front 4

How do action potentials spread to the interior of a skeletal muscle cell? .

Back 4

By depolarization of the T-tubules

Front 5

What are the thick and thin filaments?

Back 5

Thick and thin filaments form the sarcomere interior, the thick filaments are made of myosin and the thin filaments are made of three
proteins (actin, tropomyosin, and troponin)

Front 6

What is the physical relationship between thin and thick filaments?

Back 6

The thin filaments (actin et.al.) are physically attached to the Z disks, the thick filaments are tethered in the middle of the sarcomere in between the thin filaments.

Front 7

Where are troponin and tropomyosin found?

Back 7

Tropomyosin is wrapped around the actin helixes, and troponin is attached to the tropomyosin.

Front 8

Does troponin or tropomyosin have a calcium binding site?

Back 8

Yes, troponin has a binding site for calcium.

Front 9

Do actin filaments shorten during contraction?

Back 9

no

Front 10

Do myosin filaments shorten during contraction?

Back 10

no

Front 11

Do sarcomeres shorten during contraction?

Back 11

yes

Front 12

How do sarcomeres shorten during contraction?

Back 12

By myosin filaments binding and "pulling" the actin filaments towards the center of the sarcomere.

Front 13

What is the function of the powerstroke?

Back 13

It physically "pulls" the actin filament incrementally toward the center of the sarcomere.

Front 14

Is there more than one "powerstroke" per contraction?

Back 14

yes, many occur !

Front 15

Where does the energy come from for the power stroke?

Back 15

From the release of the inorganic phosphate, which has been hydrolyzed from and ATP molecule.

Front 16

What ion within the muscle triggers contraction?

Back 16

Calcium (Ca++)

Front 17

Where is Calcium (Ca ++) stored?

Back 17

In the sarcoplasmic reticulum (SR).

Front 18

What stimulates the release of Calcium (Ca++) into the cytosol of the muscle fiber?

Back 18

The depolarization of the sarcolemma spreads into the T-tubule which has voltage-gated DHP receptors in the membrane of the T-tubules. The DHP receptors are
physically linked to gates on the SR and become pulled open, which releases the Ca++
into the sarcoplasma.

Front 19

Once the Calcium (Ca++) is released, where does it go?

Back 19

Into the sarcoplasma (the cytosol
of the muscle fiber.)

Front 20

What is the linkage between action potentials on the sarcolemma surface and sarcomere shortening?

Back 20

It triggers the release of Ca++ which when bound to troponin moves the tropomyosin out of the way so that the myosin binding sites on the actin molecules are
exposed.

Front 21

What prevents actin and myosin binding during muscle relaxation?

Back 21

As Ca++ is resequestered
back into the SR, the tropomyosin starts rolling back over the myosin binding
sites preventing myosin/actin interactions and cross-bridges cannot be formed, so the
muscle returns to its original length (also with the aid of the series elastic components
"tugging" on the ends of the muscle fibers).

Front 22

During contraction are all the myosin crossbridges bound to the actin sites at the same
time?

Back 22

No, absolutely not! As the example I gave in class, if a number of people were
pulling on a rope, the myosin head groups would be like the hands of the people pulling
on the rope.

Front 23

Once a muscle is contracting, what causes it to stop and go back to relaxation length?

Back 23

Removal of the cytosolic Ca++.

Front 24

How is calcium returned to the sarcoplasmic reticulum?

Back 24

By the actions of Ca++ATPase pumps (that are continually working) found in the SR membrane and pumping Ca++
back into the SR.

Front 25

Is ATP used in both contraction and relaxation?

Back 25

yes

Front 26

What are three functions of ATP in the contraction/relaxation cycle?

Back 26

1) Allows myosin head groups to dissociate from the actin binding site.
2) Through hydrolysis and release, provides the energy for the powerstroke.
3) Provides the energy for the Ca++ATPase pumps, to re-sequester Ca++ from the cytosol back into the SR.

Front 27

What happens if a cell runs out of ATP?

Back 27

It will be in a state of rigor mortis - prolonged contraction.

Front 28

Do you think fatigue occurs before a cell runs out of ATP?

Back 28

Yes, definitely

Front 29

Does the length of a muscle affect its ability to develop tension?

Back 29

Yes, the length-tension
relationship is actually a very important variable in the ability of a muscle to develop
tension.

Front 30

At the length that can generate the most tension, what is the relationship of the actin and
myosin?

Back 30

There is a minimal amount of overlap between the actin and myosin filaments

Front 31

Muscle Fiber

Back 31

A single muscle cell which is a relatively long and cylindrical in shape, made up of multiple nuclei that can generate signals for the fiber, consists of multiple myofibrils

Front 32

Sarcolemma

Back 32

Surrounds muscle fiber and goes into muscle to create T-tubules

Front 33

Sarcoplasma

Back 33

Houses SR, myofibrils, mitochondria, and glycogen granules

Front 34

Myofibril

Back 34

A specialized intracellular structure of muscle cells that contains the contractile apparatus, multiple of these combine together to form a single muscle fiber

Front 35

Myofilament

Back 35

The filaments inside of the myofibril that consist of actin and myosin

Front 36

Sarcomere

Back 36

Functional unit of skeletal muscle as well as muscle fiber, the area between two z lines within a myofibril

Front 37

T-Tubule

Back 37

Continuous with sarcolemma, perpendicular infolding of the surface membrane of a muscle fiber, rapidly spread surface electric activity into the central portions of the muscle fiber

Front 38

Somatic Motor Neuron

Back 38

The motor neuron that holds the terminal button and releases the NT acetylcholine that sends the signal for a contraction to occur as the acetylcholine releases and bind on the motor end plate

Front 39

Motor End Plate

Back 39

Specialized portion of a skeletal muscle fiber that lies immediately underneath the terminal button of the motor neuron and possesses receptor sites for binding acetylcholine released from the terminal button, the binding of acetylcholine on these receptor sites opens up the voltage gated K/Na channels to allow for depolarization and an action potential to occur along the sarcolemma

Front 40

Terminal Button

Back 40

A motor neuron’s enlarged knoblike ending that terminates near a skeletal muscle fiber and releases acetylcholine in response to an action potential in the neuron, holds the vesicles containing acetylcholine that get exocytosized

Front 41

DHP (Dihydropyridine) receptor

Back 41

Linked to SR, once the action potential travels down the T-tubules, this receptor gate opens to release Ca from the SR into the sarcoplasma

Front 42

Troponin

Back 42

One of the regulatory proteins found in the thin filaments (actin) of muscle fibers, binds to tropomyosin and calcium when available

Front 43

Tropomyosin

Back 43

One of the regulatory proteins found in the thin filaments (actin) of muscle fibers, attaches to the actin double helix and covers the crossbridge bind sites on the actin

Front 44

SR

Back 44

A fine meshwork of interconnected tubules that surrounds a muscle fiber’s myofibrils, contains expanded lateral sacs, which store calcium that is released into the cytosol in response to a local action potential, when DHP receptor is open the SR releases calcium into the sarcoplasma

Front 45

Myosin

Back 45

Contractile protein that forms the thick filaments in muscle fibers, contains crossbridge heads that bind to actin

Front 46

Actin

Back 46

Contractile protein that forms the backbone of the thin filaments in muscle fibers, form double helixs and has myosin binding sits that tropomyosin covers until calcium is present in which troponin and tropomyosin move out of way

Front 47

Z Disk

Back 47

A flattened disk like cytoskeletal protein that connects the thin filaments of two adjoining sarcomeres, during contraction the z disks get brought closer together by the powerstroke of the sliding filament theory

Front 48

Rigor

Back 48

A state in which no ATP is available so relaxation of muscles cannot occur because the myosin heads cannot detach from the actin

Front 49

Rigor Mortis

Back 49

A state that happens during death, a stiff like state in which all muscles cannot relax

Front 50

Ryanodine Receptor

Front 51

ATP

Back 51

Involved in the sliding filament theory, as myosin needs the detachment of phosphate for the powerstroke to occur, and a new ATP must attach inorder for the myson to detach and find a new actin site