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Muscular System

Terms in this set (30)

-Each fiber is a long, cylindrical cell with multiple oval nuclei just beneath the sarcolemma
- Each cell is a syncytium produced by fusion of hundreds of embryonic cells
( *syncytium is when skeletal muscle fuse together; big cells with many nuclei)
Sarcolemma=cell membrane of muscle fiber
Sarcoplasm=cytoplasm of muscle fiber that contains nuclei and mitochondria

Sarcoplasm: *cytoplasm of cell
1.) Glycosomes
(stores sugar): are granules of stored glycogen

- *takes oxygen from hemoglobin and stores m it
- muscle molecules that bind oxygen and store it ( similar to hemoglobin)
- *a unique oxygen-binding protein
-Red pigment that stores oxygen

3.) The usual organelles plus three highly modified structures: myofibrils, sarcoplasmic reticulum, and T tubules.

: (fills the space)
-are with the cytoplasm lying parallel to each other
- rod-like contractile elements
-Make up most of the muscle volume
- hundreds to thousands of myofibrils in a single muscle fiber
- *It's arrangement within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident = striations
- the arrangement gives the striations
Light=I band (striations) Dark = A band (striations)

: *structual unit of cardiac muscle
-section of myfibril
-smallest contractile unit of skeletal and cardiac muscle
*Functional unit of skeletal muscle
-located between two successive Z discs
( Z discs - coin-shaped sheet of proteins that anchors the thin filaments
- Z line to the next Z line is a Sarcomere
composed of 3 myofilaments:
1.) Thick filament
- extend the entire length of an A band
-myosin and actin drive a contraction
-myosin is composed of protein

2.) Thin filament
(actin) troponin and trypomysin
-Extends across the I band and partially into the A band
- *Made of actin, troponin, and tropomyosin
- actin is composed of protein

Sarcoplasmic reticulum
(stores calcium)
-is the same as SER
- *Stores Calcium in high concentraion
-Functions in the regulation of intracellular calcium ions levels
-inner lining of perimysium

T tubule
- opens to outside of muscle fiber
-contains extracellular fluid
-continuous with the sarcolemma
-conduct impulses to the deepest regions of the muscle
-These impulses open voltage sensor proteins, which release Ca2+ from adjacent SR terminal cisternae
-The relationship between the paired SR terminal cisternae and the T tubule is called triad.
2. Depolarization
a. The inside of the membranes becomes less negative
1. Change from -70mV to -65mV or more
b. If threshold (-55mV) is reached, an action potential is ignited.
i. AP = Constant electrical signal that can be propagated over long distances without decay.
ii. 3The AP spreads in both directions from the neuromuscular junction by opening voltage-gated channels.
iii. Once initiated, the action potential is unstoppable, and ultimately results in the contraction of a muscle.
iv. All or nothing phenomenon
3. Repolarization
a. The membrane returns to its resting membrane potential (-70mV)
b. After depolarization, the sarcolemma permeability changes by:
i. Closing the Na+ channels
ii. Opening of K+ channels
1. K+ diffuses from the cell, restoring the electrical polarity of the sarcolemma
c. Repolarization occurs in the same direction as depolarization
4. Hyperpolarization
a. K+ voltage channel close slower than sodium channels causing the mm potential to go beyond -70mV.
5. Refractory period
a. Before the muscle can be stimulated again, repolarization must occur.
b. Absolute refractory period
i. Allows Na+ channel to reset
ii. Another AP cannot be generated
c. Relative refractory period
i. A second action potential can be generated
ii. The ionic concentration of the resting state is restored by the Na-K pump
6. Repolarization only restores the electrical membrane potential (-70mV)
a. However, the ionic concentration of the resting state is restored by the Na+ - K+ pump
i. 3 Na+ out
ii. 2 K+ in