This document provides an overview of the anatomy and physiology of the musculoskeletal system. It describes the bones that make up the skull, vertebral column, pelvis, and extremities. It discusses the types of joints in the body including fibrous, cartilaginous, and synovial joints. It also covers the microscopic structure of skeletal muscle fibers and their attachments, blood supply, and function. The document is an introductory overview of the key components and structures of the musculoskeletal system.

1. Anatomy and Physiology
of Musculoskeletal
daninurriyadi

4. Periferal nervous
system
Afferent
Efferent
somatomotoric autonomic
Parasympathic Sympathic
Central Nervous System
RECEPTOR
Somatic Visceral
EFFECTOR
Skeletal
muscle
Smooth muscle
Cardiac muscle
Gland
ascendense descendense

5. The Skeleton

6. The Skull
• The skull, the body’s most complex bony
structure, is formed by the cranium and facial
bones
• Cranium – protects the brain and is the site of
attachment for head and neck muscles
• Facial bones
– Supply the framework of the face, the sense organs, and
the teeth
– Provide openings for the passage of air and food
– Anchor the facial muscles of expression

7. Skull: Anterior View

8. Parietal Bones and Major Associated
Sutures
• Form most of the superior and lateral aspects of the skull
Figure 7.3a

9. Occipital Bone and Its Major
Markings
• Forms most of
skull’s posterior
wall and base
• Major markings
include the
posterior cranial
fossa, foramen
magnum,
occipital
condyles, and the
hypoglossal canal
Figure 7.2b

10. Vertebral Column
• Formed from 26 irregular bones (vertebrae)
connected in such a way that a flexible
curved structure results
– Cervical vertebrae – 7 bones of the neck
– Thoracic vertebrae – 12 bones of the torso
– Lumbar vertebrae – 5 bones of the lower back
– Sacrum – bone inferior to the lumbar vertebrae
that articulates with the hip bones

11. Vertebral Column

12. Vertebral Column: Ligaments
• Anterior and posterior longitudinal
ligaments – continuous bands down the
front and back of the spine from the neck to
the sacrum
• Short ligaments connect adjoining
vertebrae together

13. Vertebral Column: Ligaments

14. Vertebral Column: Intervertebral
Discs
• Cushionlike pad composed of two parts
– Nucleus pulposus – inner gelatinous nucleus that
gives the disc its elasticity and compressibility
– Annulus fibrosus – surrounds the nucleus pulposus
with a collar composed of collagen and fibrocartilage

15. Vertebral Column: Intervertebral
Discs

16. Sacrum
• Sacrum
– Consists of five fused vertebrae (S1-S5), which
shape the posterior wall of the pelvis
– It articulates with L5 superiorly, and with the
auricular surfaces of the hip bones
– Major markings include the sacral promontory,
transverse lines, alae, dorsal sacral foramina,
sacral canal, and sacral hiatus

17. Coccyx
• Coccyx (Tailbone)
– The coccyx is made up of four (in some cases
three to five) fused vertebrae that articulate
superiorly with the sacrum

18. Sacrum and Coccyx: Anterior View

19. Sacrum and Coccyx: Posterior View

20. Bony Thorax (Thoracic Cage)
• The thoracic cage is composed of the thoracic vertebrae
dorsally, the ribs laterally, and the sternum and costal
cartilages anteriorly
• Functions
– Forms a protective cage around the heart, lungs, and great
blood vessels
– Supports the shoulder girdles and upper limbs
– Provides attachment for many neck, back, chest, and shoulder
muscles
– Uses intercostal muscles to lift and depress the thorax during
breathing

21. Bony Thorax (Thoracic Cage)

22. Pectoral Girdles (Shoulder Girdles)

23. The Upper Limb
• The upper limb consists of the arm
(brachium), forearm (antebrachium), and
hand (manus)
• Thirty-seven bones form the skeletal
framework of each upper limb

24. Arm
• The humerus is the sole bone of the arm
• It articulates with the scapula at the
shoulder, and the radius and ulna at the
elbow

25. Arm
• Major markings
– Proximal humerus includes the head, anatomical and
surgical necks, greater and lesser tubercles, and the
intertubercular groove
– Distal humerus includes the capitulum, trochlea,
medial and lateral epicondyles, and the coronoid and
olecranon fossae
– Medial portion includes the radial groove and the
deltoid process

26. Humerus of the Arm

27. Forearm
• The bones of the forearm are the radius and ulna
• They articulate proximally with the humerus and distally
with the wrist bones
• They also articulate with each other proximally and
distally at small radioulnar joints
• Interosseous membrane connects the two bones along
their entire length

28. Bones of the Forearm

29. Hand
• Skeleton of
the hand
contains wrist
bones
(carpals),
bones of the
palm
(metacarpals),
and bones of
the fingers
(phalanges)

30. Pelvic Girdle (Hip)

31. The Lower Limb
• The three segments of the lower limb are
the thigh, leg, and foot
• They carry the weight of the erect body, and
are subjected to exceptional forces when
one jumps or runs

32. Femur

33. Tibia and Fibula
Figure 7.29

34. Foot
• The skeleton of the
foot includes the
tarsus, metatarsus,
and the phalanges
(toes)
• The foot supports
body weight and
acts as a lever to
propel the body
forward in walking
and running

35. Tarsus

36. Arches of the Foot
• The foot has three arches maintained by
interlocking foot bones and strong ligaments
• Arches allow the foot to hold up weight
• The arches are:
– Lateral longitudinal – cuboid is keystone of this arch
– Medial longitudinal – talus is keystone of this arch
– Transverse – runs obliquely from one side of the foot
to the other

37. Arches of the Foot

38. Joints

39. Fibrous Structural Joints: Sutures

40. Fibrous Structural Joints:
Syndesmoses
• Bones are connected by a fibrous tissue
ligament
• Movement varies from immovable to
slightly variable
• Examples include the connection between
the tibia and fibula, and the radius and ulna

41. Fibrous Structural Joints:
Syndesmoses

42. Fibrous Structural Joints:
Gomphoses
• The peg-in-socket fibrous joint between a
tooth and its alveolar socket
• The fibrous connection is the periodontal
ligament

43. Cartilaginous Joints
• Articulating bones are united by cartilage
• Lack a joint cavity
• Two types – synchondroses and symphyses

44. Cartilaginous Joints:
Synchondroses
• A bar or plate of hyaline cartilage unites the bones
• All synchondroses are synarthrotic
• Examples include:
– Epiphyseal plates of children
– Joint between the costal cartilage of the first rib and the
sternum

45. Cartilaginous Joints:
Synchondroses

46. Cartilaginous Joints: Symphyses
• Hyaline cartilage covers the articulating surface of the
bone and is fused to an intervening pad of fibrocartilage
• Amphiarthrotic joints designed for strength and
flexibility
• Examples include intervertebral joints and the pubic
symphysis of the pelvis

47. Cartilaginous Joints: Symphyses

48. Synovial Joints
• Those joints in which the articulating bones
are separated by a fluid-containing joint
cavity
• All are freely movable diarthroses
• Examples – all limb joints, and most joints
of the body

49. Synovial Joints: General Structure
• Synovial joints all have the following
– Articular cartilage
– Joint (synovial) cavity
– Articular capsule
– Synovial fluid
– Reinforcing ligaments

50. Synovial Joints: General Structure

51. Synovial Joints: Friction-Reducing
Structures
• Bursae – flattened, fibrous sacs lined with synovial
membranes and containing synovial fluid
• Common where ligaments, muscles, skin, tendons, or
bones rub together
• Tendon sheath – elongated bursa that wraps completely
around a tendon

52. Synovial Joints: Friction-
Reducing Structures

53. Types of Synovial Joints
• Plane joints
– Articular
surfaces are
essentially flat
– Allow only
slipping or
gliding
movements
– Only examples
of nonaxial
joints

54. Types of Synovial Joints
• Hinge joints
– Cylindrical projections of one bone fits into a trough-
shaped surface on another
– Motion is along a single plane
– Uniaxial joints permit flexion and extension only
– Examples: elbow and interphalangeal joints

55. Types of Synovial Joints
Figure 8.7b

56. Pivot Joints
• Rounded end of one bone protrudes into a “sleeve,” or
ring, composed of bone (and possibly ligaments) of
another
• Only uniaxial movement allowed
• Examples: joint between the axis and the dens, and the
proximal radioulnar joint

57. Pivot Joints

58. Condyloid, or Ellipsoidal, Joints
• Oval articular surface of one bone fits into a
complementary depression in another
• Both articular surfaces are oval
• Biaxial joints permit all angular motions
• Examples: radiocarpal (wrist) joints, and
metacarpophalangeal (knuckle) joints

59. Condyloid, or Ellipsoidal, Joints

60. Saddle Joints
• Similar to condyloid joints but allow
greater movement
• Each articular surface has both a concave
and a convex surface
• Example: carpometacarpal joint of the
thumb

61. Saddle Joints

62. Ball-and-Socket Joints
• A spherical or hemispherical head of one
bone articulates with a cuplike socket of
another
• Multiaxial joints permit the most freely
moving synovial joints
• Examples: shoulder and hip joints

63. Ball-and-Socket Joints

64. Synovial Joints: Knee
• Largest and most complex joint of the body
• Allows flexion, extension, and some rotation
• Three joints in one surrounded by a single joint
cavity
– Femoropatellar
– Lateral and medial tibiofemoral joints

65. • Tendon of the
quadriceps femoris
muscle
• Lateral and medial
patellar retinacula
• Fibular and tibial
collateral ligaments
• Patellar ligament
Synovial Joints: Knee Ligaments and
Tendons – Anterior View

66. • Anterior cruciate ligament
• Posterior cruciate ligament
• Medial meniscus (semilunar cartilage)
• Lateral meniscus
Synovial Joints: Knee –
Other Supporting Structures

67. Synovial Joints: Knee –
Other Supporting Structures

68. • Adductor magnus
tendon
• Articular capsule
• Oblique popliteal
ligament
• Arcuate popliteal
ligament
• Semimembranosus
tendon
Synovial Joints: Knee –
Posterior Superficial View

69. Synovial Joints: Shoulder
(Glenohumeral)
• Ball-and-socket joint in which stability is
sacrificed to obtain greater freedom of
movement
• Head of humerus articulates with the
glenoid fossa of the scapula

70. Synovial Joints: Shoulder
Stability
• Weak stability is maintained by:
– Thin, loose joint capsule
– Four ligaments – coracohumeral, and three
glenohumeral
– Tendon of the long head of biceps, which travels
through the intertubercular groove and secures the
humerus to the glenoid cavity
– Rotator cuff (four tendons) that encircles the shoulder
joint and blends with the articular capsule

71. Synovial Joints: Shoulder
Stability

72. Synovial Joints: Shoulder
Stability

73. Synovial Joints: Hip (Coxal)
Joint
• Ball-and-socket joint
• Head of the femur articulates with the
acetabulum
• Good range of motion, but limited by the
deep socket and strong ligaments

74. • Acetabular labrum
• Iliofemoral
ligament
• Pubofemoral
ligament
• Ischiofemoral
ligament
• Ligamentum teres
Synovial Joints: Hip Stability

75. Synovial Joints: Hip Stability

76. Synovial Joints: Elbow
• Hinge joint that allows flexion and
extension only
• Radius and ulna articulate with the humerus

77. • Annular ligament
• Ulnar collateral ligament
• Radial collateral ligament
Synovial Joints: Elbow Stability

78. Synovial Joints: Elbow Stability

79. Sprains
• The ligaments reinforcing a joint are
stretched or torn
• Partially torn ligaments slowly repair
themselves
• Completely torn ligaments require prompt
surgical repair

80. Cartilage Injuries
• The snap and pop of overstressed cartilage
• Common aerobics injury
• Repaired with arthroscopic surgery

81. Dislocations
• Occur when bones are forced out of alignment
• Usually accompanied by sprains, inflammation, and joint
immobilization
• Caused by serious falls and are common sports injuries
• Subluxation – partial dislocation of a joint

82. Muscles and Muscle Tissue

83. Functional Characteristics of
Muscle Tissue
• Excitability, or irritability – the ability to
receive and respond to stimuli
• Contractility – the ability to shorten forcibly
• Extensibility – the ability to be stretched or
extended
• Elasticity – the ability to recoil and resume
the original resting length

84. Muscle Function
• Skeletal muscles are responsible for all
locomotion
• Cardiac muscle is responsible for coursing the
blood through the body
• Smooth muscle helps maintain blood pressure, and
squeezes or propels substances (i.e., food, feces)
through organs
• Muscles also maintain posture, stabilize joints, and
generate heat

85. Skeletal Muscle
• Each muscle is a discrete organ composed of
muscle tissue, blood vessels, nerve fibers, and
connective tissue
• The three connective tissue sheaths are:
– Endomysium – fine sheath of connective tissue
composed of reticular fibers surrounding each muscle
fiber
– Perimysium – fibrous connective tissue that surrounds
groups of muscle fibers called fascicles
– Epimysium – an overcoat of dense regular connective
tissue that surrounds the entire muscle

86. Major Skeletal Muscles: Anterior
View
• The 40
superficial
muscles here
are divided
into 10
regional areas
of the body

87. Plantar Muscles: Fourth Layer

88. Skeletal Muscle

89. Skeletal Muscle: Nerve and
Blood Supply
• Each muscle is served by one nerve, an
artery, and one or more veins
• Each skeletal muscle fiber is supplied with
a nerve ending that controls contraction
• Contracting fibers require continuous
delivery of oxygen and nutrients via arteries
• Wastes must be removed via veins

90. Skeletal Muscle: Attachments
• Most skeletal muscles span joints and are
attached to bone in at least two places
• When muscles contract the movable bone, the
muscle’s insertion moves toward the immovable
bone, the muscle’s origin
• Muscles attach:
– Directly – epimysium of the muscle is fused to the
periosteum of a bone
– Indirectly – connective tissue wrappings extend
beyond the muscle as a tendon or aponeurosis

91. Microscopic Anatomy of a
Skeletal Muscle Fiber
• Each fiber is a long, cylindrical cell with multiple nuclei
just beneath the sarcolemma
• Fibers are 10 to 100 µm in diameter, and up to hundreds
of centimeters long
• Each cell is a syncytium produced by fusion of
embryonic cells

92. Microscopic Anatomy of a
Skeletal Muscle Fiber
• Sarcoplasm has numerous glycosomes and a
unique oxygen-binding protein called myoglobin
• Fibers contain the usual organelles, myofibrils,
sarcoplasmic reticulum, and T tubules

93. Myofibrils
• Myofibrils are densely packed, rodlike contractile
elements
• They make up most of the muscle volume
• The arrangement of myofibrils within a fiber is such that
a perfectly aligned repeating series of dark A bands and
light I bands is evident

94. Myofibrils

95. Sarcomeres
• The smallest contractile unit of a muscle
• The region of a myofibril between two successive
Z discs
• Composed of myofilaments made up of
contractile proteins
– Myofilaments are of two types – thick and thin

96. Sarcomeres

97. Myofilaments: Banding Pattern
• Thick filaments – extend the entire length
of an A band
• Thin filaments – extend across the I band
and partway into the A band
• Z-disc – coin-shaped sheet of proteins
(connectins) that anchors the thin filaments
and connects myofibrils to one another

98. Myofilaments: Banding Pattern
• Thin filaments do not overlap thick
filaments in the lighter H zone
• M lines appear darker due to the presence
of the protein desmin

99. Myofilaments: Banding Pattern

100. Ultrastructure of Myofilaments:
Thick Filaments
• Thick filaments are composed of the protein
myosin
• Each myosin molecule has a rodlike tail and two
globular heads
– Tails – two interwoven, heavy polypeptide chains
– Heads – two smaller, light polypeptide chains called
cross bridges

101. Ultrastructure of Myofilaments:
Thick Filaments

102. Ultrastructure of Myofilaments:
Thin Filaments
• Thin filaments are chiefly composed of the protein actin
• Each actin molecule is a helical polymer of globular
subunits called G actin
• The subunits contain the active sites to which myosin
heads attach during contraction
• Tropomyosin and troponin are regulatory subunits bound
to actin

103. Ultrastructure of Myofilaments:
Thin Filaments

104. Arrangement of the Filaments in
a Sarcomere
• Longitudinal section within one sarcomere

105. Sarcoplasmic Reticulum (SR)
• SR is an elaborate, smooth endoplasmic reticulum that
mostly runs longitudinally and surrounds each myofibril
• Paired terminal cisternae form perpendicular cross channels
• Functions in the regulation of intracellular calcium levels
• Elongated tubes called T tubules penetrate into the cell’s
interior at each A band–I band junction
• T tubules associate with the paired terminal cisternae to form
triads

106. Sarcoplasmic Reticulum (SR)

107. T Tubules
• T tubules are continuous with the
sarcolemma
• They conduct impulses to the deepest
regions of the muscle
• These impulses signal for the release of Ca2+
from adjacent terminal cisternae

108. Triad Relationships
• T tubules and SR provide tightly linked signals for
muscle contraction
• A double zipper of integral membrane proteins protrudes
into the intermembrane space
• T tubule proteins act as voltage sensors
• SR foot proteins are receptors that regulate Ca2+
release
from the SR cisternae

109. Sliding Filament Model of
Contraction
• Thin filaments slide past the thick ones so that the actin
and myosin filaments overlap to a greater degree
• In the relaxed state, thin and thick filaments overlap only
slightly
• Upon stimulation, myosin heads bind to actin and sliding
begins

110. Sliding Filament Model of
Contraction
• Each myosin head binds and detaches several times
during contraction, acting like a ratchet to generate
tension and propel the thin filaments to the center of the
sarcomere
• As this event occurs throughout the sarcomeres, the
muscle shortens

111. Skeletal Muscle Contraction
• In order to contract, a skeletal muscle must:
– Be stimulated by a nerve ending
– Propagate an electrical current, or action potential,
along its sarcolemma
– Have a rise in intracellular Ca2+
levels, the final trigger
for contraction
• Linking the electrical signal to the contraction is
excitation-contraction coupling

112. Nerve Stimulus of Skeletal
Muscle
• Skeletal muscles are stimulated by motor
neurons of the somatic nervous system
• Axons of these neurons travel in nerves to
muscle cells
• Axons of motor neurons branch profusely
as they enter muscles
• Each axonal branch forms a neuromuscular
junction with a single muscle fiber

113. Neuromuscular Junction
• The neuromuscular junction is formed from:
– Axonal endings, which have small membranous sacs
(synaptic vesicles) that contain the neurotransmitter
acetylcholine (ACh)
– The motor end plate of a muscle, which is a specific
part of the sarcolemma that contains ACh receptors
and helps form the neuromuscular junction
• Though exceedingly close, axonal ends and
muscle fibers are always separated by a space
called the synaptic cleft

114. Neuromuscular Junction

115. Neuromuscular Junction
• When a nerve impulse reaches the end of an
axon at the neuromuscular junction:
– Voltage-regulated calcium channels open and
allow Ca2+
to enter the axon
– Ca2+
inside the axon terminal causes axonal
vesicles to fuse with the axonal membrane

116. Neuromuscular Junction
– This fusion releases ACh into the synaptic cleft via
exocytosis
– ACh diffuses across the synaptic cleft to ACh
receptors on the sarcolemma
– Binding of ACh to its receptors initiates an action
potential in the muscle

117. Destruction of Acetylcholine
• ACh bound to ACh receptors is quickly destroyed
by the enzyme acetylcholinesterase
• This destruction prevents continued muscle fiber
contraction in the absence of additional stimuli

118. Action Potential
• A transient depolarization event that
includes polarity reversal of a sarcolemma
(or nerve cell membrane) and the
propagation of an action potential along the
membrane

119. Role of Acetylcholine (Ach)
• ACh binds its receptors at the motor end
plate
• Binding opens chemically (ligand) gated
channels
• Na+
and K+
diffuse out and the interior of the
sarcolemma becomes less negative
• This event is called depolarization

120. Depolarization
• Initially, this is a local electrical event
called end plate potential
• Later, it ignites an action potential that
spreads in all directions across the
sarcolemma

121. • The outside
(extracellular) face
is positive, while
the inside face is
negative
• This difference in
charge is the
resting membrane
potential
Action Potential: Electrical
Conditions of a Polarized Sarcolemma

122. • The predominant
extracellular ion is
Na+
• The predominant
intracellular ion is K+
• The sarcolemma is
relatively
impermeable to both
ions
Action Potential: Electrical
Conditions of a Polarized
Sarcolemma

123. • An axonal terminal of a
motor neuron releases
ACh and causes a patch
of the sarcolemma to
become permeable to
Na+
(sodium channels
open)
Action Potential: Depolarization and
Generation of the Action Potential

124. • Na+
enters the cell,
and the resting
potential is
decreased
(depolarization
occurs)
• If the stimulus is
strong enough, an
action potential is
initiated
Action Potential: Depolarization and
Generation of the Action Potential

125. • Polarity reversal of
the initial patch of
sarcolemma changes
the permeability of
the adjacent patch
• Voltage-regulated Na+
channels now open in
the adjacent patch
causing it to
depolarize
Action Potential: Propagation of the
Action Potential

126. • Thus, the action
potential travels
rapidly along the
sarcolemma
• Once initiated, the
action potential is
unstoppable, and
ultimately results in
the contraction of a
muscle
Action Potential: Propagation of the
Action Potential

127. Action Potential: Repolarization• Immediately after the
depolarization wave
passes, the sarcolemma
permeability changes
• Na+
channels close and
K+
channels open
• K+
diffuses from the
cell, restoring the
electrical polarity of the
sarcolemma

128. Action Potential: Repolarization
• Repolarization occurs
in the same direction as
depolarization, and
must occur before the
muscle can be
stimulated again
(refractory period)
• The ionic concentration
of the resting state is
restored by the
Na+
-K+
pump

129. Excitation-Contraction Coupling
• Once generated, the action potential:
– Is propagated along the sarcolemma
– Travels down the T tubules
– Triggers Ca2+
release from terminal cisternae
• Ca2+
binds to troponin and causes:
– The blocking action of tropomyosin to cease
– Actin active binding sites to be exposed

130. Excitation-Contraction Coupling
• Myosin cross bridges alternately attach and detach
• Thin filaments move toward the center of the sarcomere
• Hydrolysis of ATP powers this cycling process
• Ca2+
is removed into the SR, tropomyosin blockage is
restored, and the muscle fiber relaxes

131. Excitation-Contraction Coupling

132. • At low intracellular Ca2+
concentration:
– Tropomyosin blocks the
binding sites on actin
– Myosin cross bridges
cannot attach to binding
sites on actin
– The relaxed state of the
muscle is enforced
Role of Ionic Calcium (Ca2+
) in the
Contraction Mechanism

133. • At higher intracellular
Ca2+
concentrations:
– Additional calcium binds
to troponin (inactive
troponin binds two Ca2+
)
– Calcium-activated
troponin binds an
additional two Ca2+
at a
separate regulatory site
Role of Ionic Calcium (Ca2+
) in the
Contraction Mechanism

134. • Calcium-activated
troponin undergoes a
conformational change
• This change moves
tropomyosin away from
actin’s binding sites
Role of Ionic Calcium (Ca2+
) in the
Contraction Mechanism

135. • Myosin head can
now bind and cycle
• This permits
contraction (sliding
of the thin
filaments by the
myosin cross
bridges) to begin
Role of Ionic Calcium (Ca2+
) in the
Contraction Mechanism

136. Sequential Events of Contraction
• Cross bridge formation – myosin cross bridge attaches to
actin filament
• Working (power) stroke – myosin head pivots and pulls
actin filament toward M line
• Cross bridge detachment – ATP attaches to myosin head
and the cross bridge detaches
• “Cocking” of the myosin head – energy from hydrolysis
of ATP cocks the myosin head into the high-energy state

137. Myosin cross bridge attaches to
the actin myofilament
1
2
3
4 Working stroke—the myosin head pivots and
bends as it pulls on the actin filament, sliding it
toward the M line
As new ATP attaches to the myosin
head, the cross bridge detaches
As ATP is split into ADP and Pi,
cocking of the myosin head occurs
Myosin head
(high-energy
configuration)
Thick
filament
Myosin head
(low-energy
configuration)
ADP and Pi (inorganic
phosphate) released
Sequential Events of Contraction
Thin filament

138. Contraction of Skeletal Muscle
Fibers
• Contraction – refers to the activation of myosin’s
cross bridges (force-generating sites)
• Shortening occurs when the tension generated by
the cross bridge exceeds forces opposing
shortening
• Contraction ends when cross bridges become
inactive, the tension generated declines, and
relaxation is induced

139. Contraction of Skeletal Muscle
(Organ Level)
• Contraction of muscle fibers (cells) and
muscles (organs) is similar
• The two types of muscle contractions are:
– Isometric contraction – increasing muscle
tension (muscle does not shorten during
contraction)
– Isotonic contraction – decreasing muscle length
(muscle shortens during contraction)

140. Motor Unit: The Nerve-Muscle
Functional Unit
• A motor unit is a motor neuron and all the
muscle fibers it supplies
• The number of muscle fibers per motor unit
can vary from four to several hundred
• Muscles that control fine movements
(fingers, eyes) have small motor units

141. Motor Unit: The Nerve-Muscle
Functional Unit

142. Motor Unit: The Nerve-Muscle
Functional Unit
• Large weight-bearing muscles (thighs, hips)
have large motor units
• Muscle fibers from a motor unit are spread
throughout the muscle; therefore, contraction
of a single motor unit causes weak
contraction of the entire muscle

143. Muscle Twitch
• A muscle twitch is the response of a muscle to a
single, brief threshold stimulus
• The three phases of a muscle twitch are:
– Latent period –
first few milli-
seconds after
stimulation
when excitation-
contraction
coupling is
taking place

144. Muscle Twitch
– Period of contraction – cross bridges actively form
and the muscle shortens
– Period of relaxation –
Ca2+
is reabsorbed
into the SR, and
muscle tension
goes to zero

145. Graded Muscle Responses
• Graded muscle responses are:
– Variations in the degree of muscle contraction
– Required for proper control of skeletal
movement
• Responses are graded by:
– Changing the frequency of stimulation
– Changing the strength of the stimulus

146. Muscle Response to Varying
Stimuli
• More rapidly delivered stimuli result in
incomplete tetanus
• If stimuli are given quickly enough,
complete tetanus results

147. Muscle Response: Stimulation
Strength
• Threshold stimulus – the stimulus strength at
which the first observable muscle contraction
occurs
• Beyond threshold, muscle contracts more
vigorously as stimulus strength is increased
• Force of contraction is precisely controlled by
multiple motor unit summation
• This phenomenon, called recruitment, brings more
and more muscle fibers into play

148. Stimulus Intensity and Muscle Tension

149. Treppe: The Staircase Effect
• Staircase – increased contraction in response to
multiple stimuli of the same strength
• Contractions increase because:
– There is increasing availability of Ca2+
in the
sarcoplasm
– Muscle enzyme systems become more efficient
because heat is increased as muscle contracts

150. Treppe: The Staircase Effect

151. Muscle Tone
• Muscle tone:
– Is the constant, slightly contracted state of all
muscles, which does not produce active
movements
– Keeps the muscles firm, healthy, and ready to
respond to stimulus

152. Muscle Tone
• Spinal reflexes account for muscle tone by:
– Activating one motor unit and then another
– Responding to activation of stretch receptors in
muscles and tendons

153. Isotonic Contractions
• In isotonic contractions, the muscle changes
in length (decreasing the angle of the joint)
and moves the load
• The two types of isotonic contractions are
concentric and eccentric
– Concentric contractions – the muscle shortens
and does work
– Eccentric contractions – the muscle contracts as
it lengthens

154. Isotonic Contractions

155. Isometric Contractions
• Tension increases to the muscle’s capacity,
but the muscle neither shortens nor
lengthens
• Occurs if the load is greater than the tension
the muscle is able to develop

156. Isometric Contractions

157. Muscle Metabolism: Energy for
Contraction
• ATP is the only source used directly for
contractile activity
• As soon as available stores of ATP are
hydrolyzed (4-6 seconds), they are regenerated
by:
– The interaction of ADP with creatine phosphate (CP)
– Anaerobic glycolysis
– Aerobic respiration

158. Muscle Metabolism: Energy for
Contraction

159. Muscle Metabolism: Anaerobic
Glycolysis
• When muscle contractile activity reaches
70% of maximum:
– Bulging muscles compress blood vessels
– Oxygen delivery is impaired
– Pyruvic acid is converted into lactic acid

160. Muscle Metabolism: Anaerobic
Glycolysis
• The lactic acid:
– Diffuses into the bloodstream
– Is picked up and used as fuel by the liver,
kidneys, and heart
– Is converted back into pyruvic acid by the liver

161. Muscle Fatigue
• Muscle fatigue – the muscle is in a state of
physiological inability to contract
• Muscle fatigue occurs when:
– ATP production fails to keep pace with ATP use
– There is a relative deficit of ATP, causing
contractures
– Lactic acid accumulates in the muscle
– Ionic imbalances are present

162. Muscle Fatigue
• Intense exercise produces rapid muscle
fatigue (with rapid recovery)
• Na+
-K+
pumps cannot restore ionic balances
quickly enough
• Low-intensity exercise produces slow-
developing fatigue
• SR is damaged and Ca2+
regulation is
disrupted

163. Oxygen Debt
• Vigorous exercise causes dramatic changes in
muscle chemistry
• For a muscle to return to a resting state:
– Oxygen reserves must be replenished
– Lactic acid must be converted to pyruvic acid
– Glycogen stores must be replaced
– ATP and CP reserves must be resynthesized
• Oxygen debt – the extra amount of O2 needed for
the above restorative processes

164. Heat Production During Muscle
Activity
• Only 40% of the energy released in muscle
activity is useful as work
• The remaining 60% is given off as heat
• Dangerous heat levels are prevented by
radiation of heat from the skin and sweating

165. Force of Muscle Contraction
• The force of contraction is affected by:
– The number of muscle fibers contracting – the
more motor fibers in a muscle, the stronger the
contraction
– The relative size of the muscle – the bulkier the
muscle, the greater its strength
– Degree of muscle stretch – muscles contract
strongest when muscle fibers are 80-120% of
their normal resting length

166. Force of Muscle Contraction

167. Control of Body Movement

168. Periferal nervous
system
Afferent
Efferent
somatomotoric autonomic
Parasympathic Sympathic
Central Nervous System
RECEPTOR
Somatic Visceral
EFFECTOR
Skeletal
muscle
Smooth muscle
Cardiac muscle
Gland
ascendense descendense

169. • Neural Reflexes: types & pathways
• Autonomic Reflexes pathways and functions
• Skeletal Muscle reflexes, myotactic units and
movement
• Combining reflexive and voluntary behavior into
locomotion
• Movement in visceral muscles

170. • Stimulus
• Sensory receptor
• Sensory (afferent) neuron
• CNS integration
• Efferent (motor) neuron
• Effector (target tissue)
• Response (movement)
• Feedback to CNS
Neural Reflexes: Overview

171. Neural Reflexes: Overview

172. • Effector Division
– Somatic
– Autonomic
• Integration site
– Spinal
– Brain
• Neurons in pathway
– Monosynaptic
– Polysynaptic
Neural Reflexes: Classification
of Pathways

173. Neural Reflexes: Classification
of Pathways

174. • Regulate internal organs
• Integrate in spinal cord or lower brain
• Coordinate with hormones & pacemakers
Autonomic Reflexes: “visceral
reflexes”

175. Autonomic Reflexes: “visceral
reflexes”

176. • Muscle spindle
– In muscles
– Sense stretch
• Golgi tendon organ
– Near tendon
– Sense force
• Joint receptors
– Sense pressure
– Position
Skeletal Muscle Reflex Sensory
Receptors: Proprioceptors

177. Skeletal Muscle Reflex Sensory
Receptors: Proprioceptors

178. • Muscle tone
• Stretch reflex
Muscle Spindles: Mechanism

180. • Alpha neurons
• Gamma neurons
Muscle Spindle Innervation:
Alpha-gamma Coactivation

181. • Myotactic unit: all
pathways controlling
a joint
• Example: elbow
joint – all nerves,
receptors, muscles
A Myotactic Unit and Stretch
Reflex Illustrated

182. • Force pulls collagen
fibers which squeeze
sensors
• Overload causes
inhibition of
contraction
Golgi Tendon Reflex: Response
to Excessive Force

183. • Tendon strike stretches quads-
reflexive contraction
• Reciprocal (hamstring) muscle is inhibited
Knee Jerk Reflex:
Stretch & Reciprocal Inhibition
Reflexes

184. Knee Jerk Reflex:
Stretch & Reciprocal Inhibition Reflexes

185. • Pain stimulus
• Nociceptors
• Spinal integration
• Flex appendage away
• Signal to brain (feel pain)
Flexion Reflex: Pull away from
Painful Stimuli

186. Flexion Reflex: Pull away from
Painful Stimuli

187. • Opposite leg
• Extensors
stimulated
• Flexors inhibited
• Body supported
Cross Extensor Reflex: To Keep
Balance

188. • Reflexive Movement
– Spinal integration
– Input to brain
• Postural reflexes
– Cerebellum
integration
– Maintains balance
– Input to cortex
Movement: Coordination of
Several Muscle Groups

189. • Cortex at top of several CNS integration sites
• Can be initiated with no external stimuli
• Parts can become involuntary: muscle memory
Voluntary Movement:
“Conscious”

190. Voluntary Movement:
“Conscious”

191. • Cortex initiation
• Central pattern
generators
– In spine
– Maintain motion
• Combines
movements
– Reflexive
– Voluntary
Rhythmic Movements

192. • Anticipates body movement
– Reflexive adjustment to balance change
– Prepares body for threat: blink, duck, "tuck & roll"
• Combines with feedback
Feed Forward: Postural Reflex

193. • Reflex pathways: spinal, cranial
– Sensor, afferent, integration, efferent, effector
– Classified by effector, integration site or synapses
Summary

194. • Proprioceptor types, functions, role in reflexes &
balance
• Motor reflex pathways: stretch, Golgi tendon,
flexion, reciprocal inhibition & crossed extensor
• Myotatic unit structure and coordination
• Movement coordination: reflexive, voluntary,
rhythmic
• Feed forward and feedback coordination
• Visceral movement of body organs
Summary