Nervous - week 4 Flashcards
skeletal muscle properties
- long and cylindrical
- range in length from 1-12 cm
- have striated appearance (banding pattern under the microscope)
- multinucleated
- contain large number of mitochondria
- number within a specific muscle depends on the size of the muscle
sarcolemma
plasma membrane of the muscle cell indentations in the sarcolemma called transverse tubules (T-tubules)
myofibrils
organelles composed of bundles of myofilaments
myofilaments
proteins which appear darker or lighter under the microscope due to thickness
arranged in sarcomeres
sarcomeres
repeating units of contractile proteins that make up the contractile unit of the myofibril
separated from one another by a line of proteins that make a z-shape called z-disc or z-line
thin myofilament
made of 3 associated proteins
1. actin
2. tropomyosin
3. troponin
actin
- globular protein linked to form helical strands
- strung together like beads to form backbone of thin myofilament
- each has a myosin binding site
- associated with 2 regulatory proteins
tropomyosin
- rod-shaped protein of the thin myofilament
- found in grooves made by actin
- partially covers the myosin binding site at rest
troponin
- 3- protein complex attached to both actin and tropomyosin
- hold tropomyosin over myosin binding site on actin at rest
- composed of 3 subunits
troponin A - binds to actin
troponin C - binds to calcium
troponin T - binds to tropomyosin
thick myofilament
made of bundles of 1 protein called myosin
myosin
protein with long tail and 2 heads
- head has actin binding site and ATP binding site
- ATP binding site contains an enzyme that breaks down ATP called ATPase
- myosin head undergies a change in conformation to generate contraction
sliding filament theory
shortening f the sarcomere during a contraction occurs because of an increase in the degree of overlap between the thin and thick myofilament
- increase of overlap due to thin myofilaments sliding over thick myofilaments therefore moving towards M-line
how doe sliding filament theory work
due to cross-bridge of actin in thin myofilament and myosin in thick myofilament
- head of myosin binds to myosin binding site on actin
- when binding, head shape changes propelling thin myofilament toward the M-line
- known as POWER STROKE
thin myofilamint then slide past myosin moving closer to M-line and pullin the Z-lin closer, shortening the sarcomere
the sliding filaments
- contraction is triggered
- myosin head binds to actin and cross bridge is formed
- myosin head changes shape and power stroke occurs
- thin myofilament slides past thick myofilament, oving it towards the M-line
- Z-llines come closer together
therfore shortening sarcomere
ATP hydrolysis
atp binds to atpase binding site on the myosin head
