Term
|
Definition
1. extends the length of the muscle (up to .75 meter, or 2.5 feet. long),
2. has multiple nuclei and many mitochondria
3. composed of many myofibrils, each of which extends the length of the
muscle fiber. |
|
|
Term
|
Definition
Composition of a myofibril
a) thick filaments, ~ 1.6 um long
b) thin filaments, ~ 1.0 um lon |
|
|
Term
| Organization of myofibril |
|
Definition
a) A band
(1) Stacked set of thick filaments plus portions of thin
filaments that overlap both ends of thick filaments
b) H Zone
(1) light area in A band where thin filaments don't reach
c) I band
(1) Portion of thin filaments that do not project into A band
d) Z line
(1) Cytoskeleton protein that runs vertically through middle of
I band & connects thin filaments of adjoining sarcomeres
e) Sarcomere
(1) Area between two Z lines
(2) Is the functional unit of skeletal muscle, (i.e. smallest
component that can perform all the functions of that organ),
so sarcomere is smallest contractile unit of muscle
f) M line
(1) Supporting proteins that hold thick filaments together
vertically; extends vertically down the middle of the A
band in the H zone
g) Cross bridges
(1) Extend from thick filaments to thin filaments
(2) Six thin filaments surround every thick filament; the thick
filament projects cross bridges to each of the 6 thin
filaments |
|
|
Term
| 1. Thick filament composed of |
|
Definition
a) myosin molecules lying lengthwise parallel to each other
b) half are oriented in one direction
c) half are oriented in other direction |
|
|
Term
| 2. Myosin molecule structure |
|
Definition
a) Two golf club shaped subunits with tails intertwined and globular
heads (myosin heads also called cross bridges!) projecting out at
one end
b) Each head contains an actin binding site and a myosin ATPase site |
|
|
Term
|
Definition
a) molecules are spherical in shape
b) each has a myosin binding site
c) backbone of thin filament formed by two chains of actin molecules
wrapped around each other, like two chains of pearls |
|
|
Term
|
Definition
a) Threadlike proteins that lie end to end along actin spiral
b) Covers myosin binding sited on actin |
|
|
Term
|
Definition
a) Fastens down each end of the tropomyosin molecules, holding
them in place over myosin binding site |
|
|
Term
| draw the picture of a sacromere |
|
Definition
|
|
Term
|
Definition
|
|
Term
| Transverse Tubules (T Tubules |
|
Definition
Part of surface membrane of muscle fiber that dips into fiber at junction of
A and I band |
|
|
Term
|
Definition
1. Modification of endoplasmic reticulum
2. Surrounds each myofibril with separate segments encircling each A and I
band |
|
|
Term
| Molecular Basis of Contraction: The Sliding Filament Mode |
|
Definition
1. Ach released by terminal button of motor neuron & binds to receptors on
motor end plate
2. Ach binding on motor end plate causes End Plate Potential which causes
an Action Potential to propagate down membrane and down T Tubules
into muscle cell
3. AP in the T Tubule causes sarcoplasmic reticulum to release Ca
++
4. Released Ca
++
bind to troponin on actin filaments, which causes
tropomyosin to move aside and expose myosin binding sites on the actin
molecules
5. Cross bridge cycling: myosin cross bridges bind to actin and stroke
forward (powered by ATP) pulling actin toward center of sarcomere
6. Ca
++
actively taken up by SR when no more AP
7. With Ca
++
no longer bound to troponin, tropomyosin returns to blocking
position over myosin binding site on actin. |
|
|
Term
|
Definition
1. ATP broken into ADP and Pi by ATPase on myosin head; the head holds
onto the ADP and Pi, and is energized and cocked in the “ready” position
2. In presence of Ca
++
, myosin binding site on actin is uncovered, and
myosin head binds to actin
3. On contact of myosin and actin, ADP and Pi released and myosin head
strokes forward
4. Fresh ATP binds to myosin, link with actin broken, and return to step 1.
5. This continues, and myosin heads ratchets actin along (Fig 8-9).
6. When Ca
++
removed, no more heads binding actin, so it slides back into
original place = relaxation |
|
|
Term
| C. Changes in Myofibril during contraction (Fig 12.6) |
|
Definition
1. Sarcomere shortens
2. I band shortens
3. H zone gets smaller
4. A band same width |
|
|
