David Sadava H. Craig Heller Gordon H. Orians William K. Purves David M. Hillis Biologia.blu C

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David Sadava H. Craig Heller Gordon H. Orians
William K. Purves David M. Hillis
Biologia.bluC Il corpo umanoMusculoskeletal
System
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Musculoskeletal System

• How do muscles contract?
• What roles do skeletal systems play in movement?

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Musculoskeletal System - How do muscles contract?

• Muscles and skeletons are the effectors that
  produce movement.
• Three types of vertebrate muscle
• skeletal - voluntary movement, breathing
• cardiac - beating of heart
• smooth - involuntary, movement of internal
  organs.

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Musculoskeletal System - How do muscles contract?

• Skeletal muscle (striated)
• multinucleate cells are called muscle fibers
• form from fusion of embryonic myoblasts
• one muscle consists of many muscle fibers bundled
  together by connective tissue.

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Musculoskeletal System - How do muscles contract?
The structure of skeletal muscle (part 1)
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Musculoskeletal System - How do muscles contract?

• Contractile proteins
• actin - thin filaments
• myosin - thick filaments.
• Each muscle fiber has several myofibrils bundles
  of actin and myosin filament.

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Musculoskeletal System - How do muscles contract?
Each myofibril consists of repeating units
sarcomeres. Sarcomere overlapping actin and
myosin filaments. Bundles of myosin filaments are
held in place by the protein titin, the largest
protein in the body.
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Musculoskeletal System - How do muscles contract?
The structure of skeletal muscle (part 2)
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Musculoskeletal System - How do muscles contract?
The structure of skeletal muscle (part 3)
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Musculoskeletal System - How do muscles contract?

• The sliding filament theory of muscle
  contraction
• depends on structure of actin and myosin
  molecules
• myosin heads can bind specific sites on actin
  molecules to form cross bridges, myosin changes
  conformation causing actin filament to slide 510
  nm.

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Musculoskeletal System - How do muscles contract?
Sliding filaments
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Musculoskeletal System - How do muscles contract?
Actin and myosin filaments overlap to form
myofibrils
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Musculoskeletal System - How do muscles contract?
Action potentials also travel deep within muscle
fiber via T tubules. T tubules (transverse
tubules) descend into the sarcoplasm (muscle
fiber cytoplasm). T tubules run close to the
sarcoplasmic reticulum (ER) a closed compartment
that surrounds every myofibril.
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Musculoskeletal System - How do muscles contract?
T tubules in action
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Musculoskeletal System - How do muscles contract?
Sarcoplasmic reticulum has Ca2 pumps. At rest
there is high concentration of Ca2 in the
sarcoplasmic reticulum. Action potential reaches
receptor proteins and opens the Ca2 channels,
Ca2 flows out of sarcoplasmic reticulum and
triggers interaction of actin and myosin.
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Musculoskeletal System - How do muscles contract?
Actin filaments also include tropomyosin and
troponin. Troponin has three subunits one binds
actin, one binds myosin, and one binds Ca2. At
rest, tropomyosin blocks the binding sites on
actin.
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Musculoskeletal System - How do muscles contract?
When Ca2 is released, it binds to troponin,
which changes conformation. Troponin is bound to
tropomyosintwisting of tropomyosin exposes
binding sites on actin. When Ca2 pumps remove
Ca2 from sarcoplasm, contraction stops.
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Musculoskeletal System - How do muscles contract?
The release of Ca2 from the sarcoplasmic
reticulum triggers muscle contraction
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Musculoskeletal System - How do muscles contract?
Cardiac muscle is also striated cells are
smaller than skeletal and have one
nucleus. Cardiac muscle cells also branch and
interdigitate can withstand high
pressures. Intercalated discs provide mechanical
adhesions between cells.
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Musculoskeletal System - How do muscles contract?
There are three kinds of muscle
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Musculoskeletal System - What roles do skeletal
systems play in movement?
The human skeleton
Human skeleton 206 bones, 2 connective tissue
types (cartilage and bone).
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Musculoskeletal System - What roles do skeletal
systems play in movement?
Cartilage cells produce a tough, rubbery
extracellular matrix of polysaccharides and
protein, mostly collagen. Cartilage is found on
bone surfaces in joints, also ears, nose, larynx.
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Musculoskeletal System - What roles do skeletal
systems play in movement?

• Bone extracellular matrix of calcium phosphate.
• Bone cells
• osteoblasts make new bone matrix, when they
  become enclosed in bone they are called
  osteocytes
• osteoclasts reabsorb bone.
• Bone is constantly being replaced and remodeled.

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Musculoskeletal System - What roles do skeletal
systems play in movement?
Types of joints
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Musculoskeletal System - What roles do skeletal
systems play in movement?
Joints, ligaments, and tendons
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Musculoskeletal System - What roles do skeletal
systems play in movement?
Bones are a system of levers moved by
muscles. Levers have a power arm and a load arm
that work around a fulcrum (or pivot point).
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Musculoskeletal System - What roles do skeletal
systems play in movement?
Bones and joints work like systems of levers