Muscle II (WS 16)

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created 3 years ago by sh7606
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1

Muscle Fiber

Myofiber- single muscle cell is a muscle fiber
"Muscle" is a collection of fibers
It is formed from fused myoblasts (precursor cells)
replacement occurs via satellite cells
repair of muscle

2

Myofibrils

The site of contraction components

contractile structures of muscle fibers
thousands in each fiber
made up of filaments (aka myofilaments)
filaments may be thick OR thin (more parts of thin)

3

Types of Myofibrils

1. Actin- primary "thin fibers"
2. Myosin- "thick fibers"
3. Tropomyosin- regulatory on actin
4. Troponin- regulatory on actin
Calcium catcher
5. Titin- elastic anchor for myosin
Z disk to M line
an accessory protein
6. Nebulin- non-elastic
stabilizes actin
lies along the G-actin of thin filaments

*Actin and Myosin are contractile

4

Muscle Fiber Structure

Sarcolemma- cell membrane

Sarcoplasmic reticulum- EPR
T- tubules: extensions of the cell membrane that associate with ends of the sarcoplasmic reticulum
Terminal Cisternae
Myofibrils- contractile proteins
elastic elements
Multinucleate- hundreds per fiber

5

Contractile Proteins

1. Regulatory proteins
2. Accessory proteins

6

Thin Filaments

G actin monomers
Troponin
Tropomyosin
Monomers

7

Sarcomeres

One repeating unit from Z disk to Z disk
Bands- describe the visual pattern
A Band: anisotropic (dark region)
contains myosin only, or myosin and actin overlap
H Zone: a brighter area of the A Band, has no overlapping thick filaments with thin filaments
I Band: Isotropic= light I Band, only thin filaments and no overlap with thick filaments
no myosin, only actin

8

Muscle Contraction

Muscle Tension- Force created by muscle or muscle filaments
Contraction- creation of tension in muscle
Load- weight that opposes contraction
Relaxation- release of tension

9

Muscle Twitch

Rapid contraction or relaxation of muscle fibers

10

Phases of muscle contraction

1. Latent Period
2. Contraction (5-50 msec)
3. Relaxation (5-50 msec)