chapter 10 your objectives today! - imperial valley …spaces.imperial.edu/thomas.morrell/saladin...

1

10-1

Your objectives today!

• Learn the functions and properties of

muscle

• Master the anatomy of muscles

• Understand the “sliding filament model”

• Learn a few other tidbits

10-2

Chapter 10

Muscular Tissue

• 40-50% of body

weight

Chemical E to

Mechanical E

10-3

Development of Muscle Fibers (cells)

Mature cells develop from fused myoblasts!!!!

• Mature muscle cells can not divide

• Growth is a result of cellular enlargement (hypertrophy)

• Satellite cells can regenerate new cells.

• Fibrosis

10-4

Muscle organization

Muscle = many fascicles

Fascicles = many muscles fibers (cells)

Muscle fibers (cells) = many myofibrils

Myofibrils = many myofilaments

Fig 10.1

10-5

Muscle = many fascicles




Fascicle

Fig 10.1

10-6

Skeletal Muscle -- Connective Tissue

• Superficial fascia: separates muscle from skin

• Deep fascia = connective tissue around muscle

• Connective tissue components of the muscle

include

– epimysium = surrounds the whole muscle

– perimysium = surrounds fascicles of 10-100

muscle cells

– endomysium = separates individual muscle

cells

• All these connective tissue layers extend

beyond muscle to form tendons!!!!!!!!!!!

2

10-7

Connective Tissue Components

Muscle = many fasciles




10-8

10-9

Muscle Fiber (Cell)

• Sarcolemma = muscle cell membrane

• Sarcoplasm = cytoplasm

• Myofibrils

10-10

Myofibrils & Myofilaments

Myofibrils are made up of myofilaments

• Myofilaments are contractile proteins

1. Thin myofilaments = actin

2. Thick myofilaments = myosin

10-11

Other components of Muscle cell

• T-tubules are tubes from surface into the center of the cell (interstitial fluid)

10-12

Sarcoplasmic Reticulum (SR)

• System of tubular sacs

• Stores Ca+ in a relaxed muscle

• Release Ca+ - - contraction

• Let’s return to the Myofibril

Sarcoplasmic

reticulum

3

10-13

Thick & Thin Myofilaments

• The contracting proteins of muscle

Actin Myosin

10-14

Structural Proteins

• The M line (myomesin) connects to titin and

adjacent thick filaments.

• Titin filaments

• Z-discs (Z-lines)

10-15

Myofilaments and the Sarcomere!!!!

• Thick and thin filaments overlap each other

in a pattern that creates striations

• They are arranged in compartments called

sarcomeres!!!!!!!

10-16

10-17

Overlap of Thick & Thin Myofilaments within

a Myofibril

10-18

Myosin myofilaments

• Thick filaments = Myosin

• myosin heads

Actin myofilaments = thin filaments

4

10-19

Actin

• Associated with actin: troponin, & tropomyosin

AKA = T-T Complex

10-20 Figure 9.13a

Motor Unit: a motor neuron AND all the mm

fibers it supplies

10-21

Neuromuscular Junction (NMJ) or Synapse

• NMJ = myoneural junction

10-22

Structures of NMJ Region

• Motor neurons

• End bulbs of motor

neurons release

acetylcholine (ACh)

(neurotransmitter)

11-23

Neuromuscular Junction

(b)

Myelin

Motor nerve fiber

Schwann cell

Basal lamina

Synaptic knob

Synaptic vesicles

(containing ACh)

Sarcolemma

Junctional folds

ACh receptor

Myofilaments

Nucleus

Synaptic cleft Nucleus

Sarcoplasm

Mitochondria

Figure 11.7b

The Big Picture

Figure 12-11a

Myosin head

Myosin thick filament

M line

Axon terminal of

somatic motor neuron

Motor end plate

Sarcoplasmic

reticulum

ACh

DHP

DHP = dihydropyridine L-type calcium channel

RyR

RyR = ryanodine receptor-channel

T-tubule

Muscle fiber

(a) Initiation of muscle action potential

Troponin

Tropomyosin

KEY

Actin

Z disk

Na+

Ca2+

1

2

5

10-25

Muscle contraction:

“Sliding filament model”

• Functional unit of muscle contraction is

the sarcomere

• Two steps to muscle contraction:

1. Chemical

2. Mechanical

10-26

1. Chemical step

• motor nerve stimulates muscle

(acetyocholine)

- this causes an electrical change in the

sarcolema (depolarization)

- electrical impulse moves along

sarcolema

T-tubules

Sarcoplasmic reticulum

10-27

• In response to electrical impulse

sarcoplasmic reticulum releases Ca+

- Released Ca+ causes Actin and Myosin

filaments to slide past each other

• (causes the sarcomere to shorten)

10-28

Figure 38-8

Ca+ Ca+ Ca+

Impulse

10-29

Fig. 38-9 2. Mechanical step

10-30

2. Mechanical step (cross bridges)

- Myosin filaments have little heads

Myosin

Actin

How does this happen?

= binding sites

6

10-31

At rest binding sites on Actin are covered by

Troponin

Tropomyosin

Tropomyosin-

troponin complex

Ca+ released from sarcoplasmic reticulum

- binds to troponin

- causes TT complex to change shape

and move off of the binding site

10-32

•Active sites are exposed

- Myosin heads reach down and bind

“Cross bridges”

- Requires ATP

10-33

Binding

sites

10-34

10-35

Cross bridge

11-36

Muscle Contraction & Relaxation

• four major phases of contraction and relaxation

1. excitation

• firing nerve leads to muscle excitation

2. excitation-contraction coupling

• Wave of depolarization of sarcolemma to

activation of myofilaments

3. contraction

• step in which the muscle fiber develops tension

and may shorten

4. Relaxation

• work is done, muscle fiber relaxes and returns to

its resting length

7

Figure 12-11a

Myosin head

Myosin thick filament

M line

Axon terminal of

somatic motor neuron

Motor end plate

Sarcoplasmic

reticulum

ACh

DHP

DHP = dihydropyridine L-type calcium channel

RyR

RyR = ryanodine receptor-channel

T-tubule

Muscle fiber

(a) Initiation of muscle action potential

Troponin

Tropomyosin

KEY

Actin

Z disk

Na+

Ca2+

1

2

11-38

Excitation-Contraction Coupling

Action potentials propagated

down T tubules

6 Calcium released from

terminal cisternae

7

Ca2+

T tubule

T tubule Terminal

cisterna

of SR

Sarcoplasmic

reticulum

Ca2+

Voltage-gated Ca+ channels on

Transverse Tubules –change shape

and cause Ca+ release channels on

S.R. to release Ca+

11-39

8 Shifting of tropomyosin;

exposure of active sites

on actin

9

Active sites

Myosin

Ca2+

Ca2+ Troponin

Tropomyosin Actin Thin filament

Binding of calcium

to troponin

Process in which APs initiate Ca+ signals that activate a contraction-rleaxation cycle

Excitation-Contraction Coupling Contraction

Tropomyosin

Formation of myosin–actin cross-bridge 11

Hydrolysis of ATP to ADP + Pi;

activation and cocking of myosin head

10

ADP

Pi

Myosin

Cross-bridge:

Actin

Myosin

Troponin

Contraction

Power stroke; sliding of thin

filament over thick filament

12

Binding of new ATP;

breaking of cross-bridge

13

ATP

Pi

ADP

Pi

ADP

10-42

42

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10-43

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Relaxation • Nerve Impulse stops

•No electrical charge (depolorization) over

sarcolemma – t-tubules – sarcoplasmic ret.

•Ca+ moves back into sarcoplasmic reticulum

•Myosin and actin binding prevented

Also Acetylcholinesterase – breaks down Ach

remaining in synapse

• Muscle fiber relaxes

•Rigor Mortis!!!!!!!!!!!!

chapter 10 your objectives today! - imperial valley …spaces.imperial.edu/thomas.morrell/saladin...

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