BAI GIANG HE CO XUONG (musculoskeletal system)

Locomotor/Musculoskeletal system
(Hệ vận động- Sinh lý cơ và xương)

In this chapter, students will learn:

•Components of the musculoskeletal system
•Basic of how musculoskeletal system generates motion
•Structure of skeletal muscle: muscle fiber, myofibrils, actin and myosin filaments
• Structures of a sarcomere
•The movements of actin and myosin filaments during muscle contraction
•Molecular mechanism of muscle contraction. The crossbridge cycle. Role of
Ca2+ and ATP in muscle contraction
•Motor unit
•muscle twitch and phases of a muscle twitch
•Isotonic and isometric contraction
•muscle fatigue
•ATP production in muscle cells – Oxygen debt
•Structure of bone tissue, bone cells and their function
•Osteoblast, osteocyte, osteoclast and their function
• long bone elongation and bone remodeling
• Structure of smooth muscle and molecular mechanism of smooth muscle
contraction


Specific terms and keywords
• Muscle
– Muscular system
– Musculature
– Neuromuscular junction
– Muscle force/tension
– Crossbridge

– Sarcomere
– thin and thick filaments
• Skeleton
– Skeletal system
– Musculoskeletal system
– Osteoblast
– Osteoclast
– Bone modeling/remodeling
– Mineralization/calcification


Musculoskeletal system

Cơ nhị đầu (giãn)
Cơ tam đầu (co)

•
•
•
•
•
•

muscles
bones (the skeleton)
cartilage
tendons, ligaments
joints
other connective tissue

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Muscles and skeletal are main components of locomotor system

– striated/skeletal muscle
exoskeletal
– soft-bodied animals
– smooth muscle
– cardiac muscle

endoskeletal,

Hydrostatic skeletal/
hydroskeletal: fluid-filled
cavity surrounded by
muscles


The musculoskeletal system generates motion for
animals

• Muscles are attached to bones
• Bones are connected by joints

• Muscle contraction allows motion of the bone attached at
the joints
• Muscles across joints are arranged in antagonistic
groups allowing motion in different directions

Skeletal muscle – structure and physiology


Structure of a skelelal muscle
xương
gân

Bắp cơ
Mô liên kết

Bó cơ

Sợi cơ
Tơ cơ

Màng sợi cơ
Các sợi cơ
trong bó cơ

•

Các sợi protein

Nhân

Muscle body
– fascicle
• muscle fibers – muscle cell surrounded by sarcolemma: multiple nuclei Cơ tương (chứa
myoglobin), myofibrils, protein filaments
C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

Structure of a muscle cell
Khớp nối thần kinh cơ
Túi synap

Axon của TB thần
kinh vận động

Khe synap

Sợi cơ

Tận cùng vận động
ống T

nhân
Màng bao cơ
Lưới cơ tương

Lưới cơ tương

ống T

Tơ cơ

Ti thể

Sợi dày
(myosin)

Fig. 12.2 C.L. Standfield.2011. Principles of Human Physiology, 4 th edition.

Sợi mỏng
(actin)


Myofibril and sarcomere
Đĩa A
Vạch Z

Đĩa I

Vạch M
Sợi dày

•

Sợi mỏng

•
•
•

Fig. 12.2 C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

Thick and thin
filaments are
orderly arranged (in
a 1:2 ratio) showing

striped appearance
(hence the name
striated muscle)
Z line
M line
Sarcomere (Đơn vị co
cơ): the structure
between two
neighbouring z lines


Structure of a sarcomere
Sarcomere
A band ( dark band)
Z-line

I band
(light band) myosin

H zone
actin

•A band ( dark band): thick
filaments overlapped with
thin filaments at the two
ends
•H zone: center region of A
band where only thick
filaments are present

I band
(light band)

www.arn.org/docs/glicksman/eyw_040901.htm

• I band: structure between A
bands where only thin
filaments are present


Structure of a thick filament

• thick filament myosin:
– A myosin molecule is a dimer
composed of two subunits
wound together making a “golf
stick” shape:
+ Actin-binding site
+ ATPase site

Fig. 12.5 C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Structure of a thin filament
• Thin filament:
–

–
–

–

G actin: monomer containing myosinbinding site
F actin: a strand of G-actin
2 F actins are arranged in double helix
forming actin strands found in thin
filaments
2 regulatory proteins control the
contraction of muslce fiber
• Tropomyosin: long fibrous molecule
extending over actin monomers to
block the myosin-binding site when
muslce is at rest.
• Troponin complex consists of 3
subunites:
– One attaches to the actin strand
– One binds tropomyosin
– One is the site for reversible
binding with Ca2+

Fig. 12.5 C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Sliding -filament model of muscle contraction

Muscle relaxed : H zone is increased in length

Muscle contracted : H zone is decreased in length

Fig. 12.5 C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

Molecular mechanism of muscle contraction: overview

•
•

•

•

Fig. 12.8 C.L. Standfield.2011. Principles of Human Physiology, 4 th edition.

7 steps
T- Tubules (transverse
tubules): membranous tubules
formed by deep invagination of
sarcolemma into the cytoplasm
of the muscle cell
T- tubules transmit action
potential
High Ca2+ concentration in
lumen of the SR (sarcoplasmic
reticulum) when muscle relaxed


Molecular mechanism of muscle contraction, step 1:
acetylcholine release and the generation of action potential in
the motor end plate of neuromuscular junction
• Neuromuscular junction:

- presynaptic motor neuron
(synaptic vesicles containing
Acetylcholine-ACh)
- postsynaptic muscle cell
membrane –motor end plate
(ACh receptors)
- ACh-gated Na+ channels on
motor end plate
- Acetylcholinesterase
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Molecular mechanism of muscle contraction, step 2-3:

action potential propagates down T-tubules triggering
Ca2+ release from sarcoplasmic reticulum

• Voltage-sensitive DHP
receptor in T tubules
• Ryanodine receptors in the
SR membrane associate
with calcium channels
• AP -> DHP receptor-> open
Ca2+ channels-> Ca2+
release from SR to the
cytosol

C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Molecular mechanism of muscle contraction, step 4:

how Ca2+ function in muscle contraction

C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Molecular mechanism of muscle contraction, step 4:

the crossbridge cycle

• Ca 2+

•

C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

ATP


Step 6-7: muscle fiber relaxes after crossbridge cycles

Fig. 12.8 C.L. Standfield.2011. Principles of Human Physiology, 4 th edition.


Rigor mortis (Sự cứng cơ khi chết)

– No more ATP production
– Ca 2+ are still available in the cytosol

Neurotoxins and muscle paralysis

• Spastic paralysis
stiffness of
the muscles and muscular
spasms
(Liệt co cứng ):

+ insecticides,
chemical weapons
inhibit AChE

• Flaccid paralysis
(Liệt mềm nhũn ): a

weakness
or lack of muscle tone
+ Snake venom
+ Curare
+ Botulinum (Clostridium
botulinum)- botulism

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•

Botox


Questions
Regarding muscle contraction process,

What would happen if:
1. Na+ ion channels were blocked and there was no movement of Na+
through membrane of muscle cells ?

2. There was an insufficient amount of ATP available in the muscle cells ?
3. There were an sufficient amount of ATP and an excess amount of
Ca2+ available in the cytosol of muscle fibers ?


Muscle twitch and its phases
• A twitch is the mechanical
response of an individual muscle
cell, a motor unit, or a whole
muscle to a single action potential
– Lag/latent peroid (Giai đoạn tiềm tàng ):
2ms: delay time between the action
potential in the muscle cell and the
start of contraction ( release of Ca 2+ )
– contraction phase (Giai đoạn cơ co): 10100 ms: time between the end of
latent period and the peak of muscular
tension: increasing cytosolic Ca2+
levels, increasing active actin-myosin
crossbridges
– relaxation phase (Giai đoạn cơ giãn):
decreasing cytosolic Ca2+ levels,
decreasing active actin-myosin
crossbridges

C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

• Muscle tension/ muscle force is
measured in unit of mass (gram
(g)


Motor unit (Đơn vị vận động)
• Motor unit :
– A motor neuron
and all the
muscle fibers
innervated by
that neuron are
collectively
defined as a
motor unit

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Isometric and isotonic contraction
• isometric contraction (Co cơ đẳng trường):
- Tension created, but muscle does not
shorten as the load is greater than the
force generated
– Unchanged muscle length
Co cơ đẳng trường

• isotonic contraction (Co cơ đẳng trương):
– Created tension is equal or greater
than the load
– The muscle shortens, muscle length

changes

Co cơ đẳng trương
Fig. 12.13 C.L. Standfield.2011. Principles of Human Physiology,