The Muscular and Skeletal Systems

1
The Muscular and Skeletal Systems

• Starr/McMillans
• Human Biology
• Fourth Edition Chapter 5
• Third Edition Chapter 4

2
Fig. 5.2, p. 89
3
Row, Row, Row Your Boat

• The McCagg sisters have genetically determined
  characteristics (tall bodies, long thigh bones)
  that contribute to their amazing rowing ability.
• But they must also endure rigorous training to
  develop the bone and muscle mass that is
  necessary for their sport.

Fig. 5.1, p. 88
4
Functions of Bone

• Movement
• Protection
• Support
• Mineral storage
• Blood cell formation

5
Basic Bone Functions and Structure

• The bones are moved by muscles thus the whole
  body is movable.
• Bones protect vital organs such as brain and
  lungs.
• The bones support and anchor muscles.

6
Key Concepts

• Bone tissue acts as a depository for calcium,
  phosphorus, and other ions.
• Parts of some bones are sites of blood cell
  production.
• There are four types of bones long (arms), short
  (wrist), flat (skull), and irregular (vertebrae).
• Bone is a connective tissue with living cells
  (osteocytes) and collagen fibers distributed
  throughout a ground substance that is hardened by
  calcium salts.

7
Bone Development

• How Do Bones Develop?
• Osteoblasts secrete material inside the shaft of
  the cartilage model of long bones.
• Calcium is deposited cavities merge to form the
  marrow cavity.
• Eventually osteoblasts become trapped within
  their own secretions and become osteocytes
  (mature bone cells).
• In growing children, the epiphyses (ends of bone)
  are separated from the shaft by an epiphyseal
  plate (cartilage) which continues to grow under
  the influence of growth hormone until late
  adolescence.

8
How the Skeleton Grows and Is Maintained

• How Bone Remodeling Works
• Bone is renewed constantly as minerals are
  deposited (by osteoblasts) and withdrawn (by
  osteoclasts) during the "remodeling" process.
• Bone turnover helps to maintain calcium levels
  for the entire body.
• Parathyroid hormone causes bone cells to release
  enzymes that will dissolve bone tissue and
  release calcium to the interstitial fluid and
  blood calcitonin stimulates the reverse.
• Watch Broken Bone Video

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How the Skeleton Grows and Is Maintained

• Bone Remodeling Over Time
• Before adulthood, bone turnover is especially
  important in increasing the diameter of certain
  bones.
• Osteoporosis (decreased bone density) is
  associated with decreases in osteoblast activity,
  sex hormone production, exercise, and calcium
  uptake.

10
Overview of the Skeleton

• The 206 bones of a human are arranged in two
  major divisions (axial and appendicular).
• Bones are attached to bones by ligaments bones
  are connected to muscles by tendons.

11
Joints

• Synovial joints are the most common and move
  freely they include the ball-and-socket joints
  of the hips and the hingelike joints such as the
  knee.

• They are stabilized by ligaments.
• A capsule of dense connective tissue surrounds
  the bones of the joint.
• The capsule produces synovial fluid that
  lubricates the joint.

12
Arthritis

• In osteoarthritis, the cartilage at the end of
  the bone degenerates.
• In rheumatoid arthritis, the synovial membrane
  becomes inflamed, the cartilage degenerates, and
  bone is deposited into the joint.

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• Cartilaginous joints (such as between the
  vertebrae ) have no gap, but are held together by
  cartilage and can move only a little.

cervical vertebrae (7)
thoracic vertebrae (12)
intervertebral disks
lumbar vertebrae (5)
sacrum (5 fused)
coccyx (4 fused)
Fig. 5.8, p. 95
14
Fibrous joints also have no gap between the bones
and hardly move flat cranial bones are an
example.
Fig. 5.7a, p. 94-95
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Science Comes to Life Replacing Joints
Artificial Knee Joint
patella
femur
tibia
Fig. 5.12, p. 99
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TRICEPS BRACHII
BICEPS BRACHII
PECTORALIS MAJOR
DELTOID
TRAPEZIUS
SERRATUS ANTERIOR
EXTERNAL OBLIQUE
LATISSIMUS DORSI
RECTUS ABDOMINUS
GLUTEUS MAXIMUS
ADDUCTOR LONGUS
BICEPS FEMORIS
SARTORIUS
QUADRICEPS FEMORIS
GASTROCNEMIUS
TABIALIS ANTERIOR
Fig. 5.15, p. 101
17
The Muscular System

• All types of muscle are capable of contracting in
  response to stimulation and returning to the
  original resting position.
• Skeletal muscle responds to nervous system
  signals and interacts with the skeleton to cause
  movement.
• Cardiac (heart) muscle contracts intrinsically.
• Smooth muscle (intestine) responds to stimulation
  by nerves, hormones, and can contract
  intrinsically.

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Skeletal Muscles and Bones Interact

• The human body's skeletal muscles (600 of them)
  are arranged in pairs or groups.
• The origin end of the muscle is designated as
  being attached to the bone that moves relatively
  little whereas, the insertion is attached to the
  bone that moves the most.
• Because most muscle attachments are located close
  to joints, only a small contraction is needed to
  produce considerable movement of some body part
  (leverage advantage). Some work together
  synergistically others operate antagonistically.
• Reciprocal innervation dictates that only one
  muscle of an antagonistic pair (e.g. biceps and
  triceps) can be stimulated at a time.

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Antagonistic Muscles
Triceps contracts
Biceps contracts
Biceps relaxes
Triceps relaxes
20
A Closer Look at Muscles
outer sheath of connective tissue
bundles of muscle cells each surrounded by
connective tissue
one muscle cell
one myofibril
Fig. 5.16a, p. 102
See next slide
21

• Muscles are composed of individual muscle cells
  (fibers), each of which is composed of many
  myofibrils, divided into contractile units called
  sarcomeres
• Z lines mark sarcomere ends

myofibril
Z band
Z band
Z band
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• Myofibrils are composed of thin (actin), and
  thick (myosin) filaments.
• Each actin filament is actually two beaded
  strands of protein twisted together.

• Each myosin filament is a protein with a head
  (projecting outward) and a long tail (which is
  bound together with others).

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Sliding Filament Model of Contraction
Within each sarcomere there are two sets of actin
filaments, which are attached on opposite sides
of the sarcomere myosin filaments lie suspended
between the actin filaments. During contraction,
the myosin filaments physically slide along and
pull the two sets of actin filaments toward each
other at the center of the sarcomere this is
called the sliding-filament mechanism of
contraction.
relaxed
contracted
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sliding-filament model

• Cross-bridges form between the heads of myosin
  molecules and actin filaments.
• When a myosin head is energized, it attaches to
  an adjacent actin filament and tilts in a power
  stroke toward the sarcomere's center.
• Energy from ATP drives the power stroke as the
  heads pull the actin filaments along.

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sliding-filament model

• After the power stroke the myosin heads detach
  and prepare for another attachment (power
  stroke).
• ATP supplies the energy for both attachment and
  detachment.
• A single contraction involves multiple power
  strokes.
• At death, there is no ATP to cause the heads to
  detach, and the body enters rigor mortis. Stiff

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Control of Muscle Contraction

• Skeletal muscles contract in response to signals
  from the nervous system that trigger action
  potentials along the plasma membrane and into the
  interior of the muscle cell.

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Control of Muscle Contraction

• Eventually the signal reaches the sarcoplasmic
  reticulum (internal tubes), which responds by
  releasing stored calcium ions that will bind to
  troponin, which is associated with another
  protein, tropomyosin, both of which are parts of
  the actin filaments.

Sarcoplasmic reticulum
T tubule
Z band
Z band
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• When calcium binds to troponin, the conformation
  of actin changes allowing myosin cross-bridges to
  form.
• When nervous stimulation stops, calcium ions are
  actively taken up by the sarcoplasmic reticulum
  and the changes in filament conformation are
  reversed the muscle relaxes.

29
Junctions Between Nerves and Muscles

• At neuromuscular junctions impulses from the
  branched endings of motor neurons pass to the
  muscle cell membranes by acetylcholine.
• When the neuron is stimulated, calcium channels
  open allow calcium ions to flow inward, causing a
  release of acetylcholine into the synapse.

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Sources of Energy for Contraction

• During periods (few seconds) of intense muscle
  activity, creatine phosphate is the source of
  phosphate to remake ATP.
• During intense and prolonged muscle action,
  anaerobic lactate fermentation produces low
  amounts of ATP and leads to a buildup of lactate.
• When muscle action is moderate, most of the ATP
  is provided by aerobic electron transport
  phosphorylation, which is dependent on oxygen
  supply and number of mitochondria present.

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Properties of Whole Muscles

• Muscle Tension
• The cross-bridges that form during contraction
  exert muscle tensiona mechanical force that can
  perform work.
• An isometrically contracting muscle develops
  tension but does not shorten.
• An isotonically contracting muscle shortens and
  moves a load.

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How Motor Units Function

• A single, brief stimulus to a motor unit causes a
  brief contraction called a muscle twitch.
• A second stimulus that quickly follows the first
  results in temporal summation.
• Repeated stimulation without sufficient interval
  causes a sustained contraction called tetany

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time
latent period
1 twitch
strength of contraction
relaxation phase
contraction phase
stimulus
time
4 twitches
1
2
3
4
stimuli (arrows)
6 twitches
1
2
3
4
5
6
tetanic contraction
tetanus
Fig. 5.22, p. 107
twitch
10
20
30
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How Motor Units Function

• Individual muscle cells contract according to the
  all-or-none principle.
• The number of motor units that are activated
  determines the strength of the contraction Small
  number of units weak contraction large number
  at greater frequency stronger contraction.
• Muscle tone is the continued steady, low-level of
  contraction that stabilizes joints and maintains
  general health.

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"Fast" and "Slow" Muscle

• Humans have two general types of skeletal muscle
  cells
• "Slow" muscle is more red in color due to
  myoglobin and blood capillaries its contractions
  are slower but more sustained.
• "Fast" or "white" muscle cells contain fewer
  mitochondria and less myoglobin but can contract
  rapidly and powerfully for short periods.
• When athletes train, one goal is to increase the
  relative size and contractile strength of fast
  (sprinters) and slow (distance swimmers) muscle
  fibers.