Chapter 41
Structure and Function of the
Musculoskeletal System
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
Skeletal System





Forms the body
Supports tissues
Permits movement by providing points of
attachment for muscles
Site of blood cell formation
Mineral storage
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
2
Bone


Rigid yet flexible connective tissue
Constituents



Cells
Fibers
Ground substance
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
3
Bone Tissue

Osteoblasts





Derived from mesenchymal cells
Produce type I collagen
Respond to parathyroid hormone
Produce osteocalcin
Synthesize osteoid
• Nonmineralized bone matrix
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
4
Bone Tissue

Osteocyte


Transformed osteoblast surrounded in osteoid as it
hardens from deposited minerals
Osteoclast



The major reabsorptive cell of the bone
Large, multinucleated cells
Contains lysosomes filled with hydrolytic enzymes
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
5
Bone Matrix





35% organic and 65% inorganic
Collagen fibers
Calcium and phosphate minerals
Proteoglycans
Glycoproteins
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
6
Bone Tissue

Compact (cortical) bone


85% of the skeleton
Haversian system
• Haversian canal, lamellae, lucunae, osteocyte, and
canaliculi

Spongy (cancellous) bone

Lack haversian systems
 Trabeculae

Periosteum
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
7
Compact Bone
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
8
Bone


206 bones
Axial skeleton


80 bones
• Skull, vertebral column, thorax
Appendicular skeleton

126 bones
• Upper and lower extremities, the shoulder girdle, the
pelvic girdle
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
9
Skeleton
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
10
Bones

Long bones



Diaphysis
Metaphysis
Epiphysis
• Epiphyseal plate

In a child epiphysis is separated from metaphysis by a
cartilaginous growth plate. After puberty epiphyseal plate
calcifies and epiphysis and metaphysis merge
• Epiphyseal line
 Medullary cavity

Endosteum
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
11
Long Bone
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
12
Bones



Flat bones
Short bones (cuboidal bones)
Irregular bones
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
13
Bone Remodeling



Bone-remodeling units
Repairs microscopic injuries and maintains
bone integrity
Phases



Activation of the remodeling cycle
Reabsorption
Formation of new bone
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
14
Bone Remodeling
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
15
Bone Wound Healing





Hematoma formation
Procallus formation
Callus formation
Callus replacement
Remodeling
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
16
Joints


Site where two or more bones meet
Promote stability and mobility of the skeleton
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
17
Joints

Joint classifications based on movement



Synarthrosis
• Immovable
Amphiarthrosis
• Slightly movable
Diarthrosis
• Freely movable
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
18
Joints


Joint classifications based on structure
Fibrous


Usually synarthroses (immovable)
However, many allow some movement
• Degree of movement depends on the distance between
the bones and the flexibility of the fibrous connective
tissue

Sutures, syndesmoses, and gomphoses
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
19
Joints


Joint classifications based on structure
Cartilaginous
• Symphysis


Bones are united by a pad or disk of fibrocartilage
Example: symphysis pubis, intervetebral disks
• Synchondrosis


Bones are united by hyaline cartilage
Example: joints between the ribs and the sternum
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
20
Joints


Classifications based on structure
Synovial (most movable, most complex) contain:





A fibrous joint capsule (articular capsule)
Synovial membrane that lines inner surface of joint
capsule
Joint cavity (synovial cavity), a space formed by the
capsule
Synovial fluid, which fills the joint cavity and lubricates
joint surface
Articular cartilage, which covers and pads the
articulating bony surfaces
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
21
Joints
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
22
Joints
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
23
Joints
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
24
Joints
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
25
Joints
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
26
Skeletal Muscles






Millions of individual muscle fibers that
contract and relax to facilitate movement
75% water, 20% protein, 5% organic and
inorganic compounds
350 named muscles (most are paired)
2 to 60 cm long
Fusiform muscles
Pennate muscles
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
27
Skeletal Muscles
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
28
Skeletal Muscles

Whole muscle

Fascia
 Epimysium
 Tendon
 Perimysium
 Fascicles
 Endomysium
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
29
Muscle

Skeletal muscle


Voluntary
• Controlled directly by the central nervous system
Striated
• The striated, or striped, pattern of skeletal muscle
• Result from organization of muscle fibers into the contractile
units called sarcomeres

Extrafusal
• Distinguishes skeletal muscle fibers from other contractile
fibers
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
30
Muscle

Motor unit (anterior horn cell, its axon, and its
muscle fiber)





Anterior horn cell of the spinal cord
Axons of motor nerves branch out to innervate a
specific group of muscle fibers; lower motor
neurons
Functional unit of the neuromuscular system
Innervation ratio
Sensory receptors
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
31
Motor Units
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
32
Muscle

Innervation ratio




Motor units per muscle
The greater the innervation ratio of a particular
organ, the greater its endurance
Higher innervation ratios prevent fatigue
Lower innervation ratios allow for precision of
movement
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
33
Muscle

Sensory receptors (send signals to the central
nervous system)




Spindles
• Mechanoreceptors that lie parallel to muscle fibers
• Respond to muscle stretching
Golgi tendon organs: dendrites that terminate and
branch to tendons near the neuromuscular junction
Spindles, Golgi tendon organs, and free nerve
endings report changes in muscle length, tension,
velocity
System of afferent signals responsible for muscle
stretch response and maintaining muscle tone
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
34
Muscle Fibers





Myofibrils
Myoblasts
White muscle (type II fibers)
Red muscle (type I fibers)
Muscle membrane


Sarcolemma and basement membrane
Sarcoplasm
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
35
Muscle Fibers

Sarcotubular system



Transverse tubules
Sarcoplasmic reticulum
Sarcomere



Actin
Myosin
Troponin-tropomyosin complex
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
36
Myofibrils
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
37
Myofibrils
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
38
Muscle Fibers


Creatine and creatine kinase
Phosphate, chloride, calcium, magnesium,
sodium, potassium
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
39
Muscle Contraction

Activation



Coupling
Contraction


Muscle fiber action potential
Cross-bridge theory
Relaxation
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
40
Muscle Contractions and
Movement

Types of contractions



Isometric
Isotonic
• Eccentric
• Concentric
Muscle movement


Agonist
Antagonist
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
41
Test of Bone Function





Gait analysis
Serum calcium and phosphorus
X-rays
Angiography
Bone scanning
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
42
Test of Joint Function




Arthrography
Arthroscopy
MRI
Synovial fluid analysis
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
43
Test of Muscular Function



Serum creatine kinase
Myoglobin
EMG
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
44
Aging and the
Musculoskeletal System

Bones




Bone loss
Stiff, brittle, decreased strength
Bone remodel time is lengthened
Joints


Cartilage becomes more rigid, fragile, stiff
Decreased range of motion
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
45
Aging and the
Musculoskeletal System

Muscles



Sarcopenia
Decrease in muscle strength and bulk
Reduced oxygen intake, basal metabolic rate, and
lean body mass
Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.
46