Skeletal Muscular Systems

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Skeletal Muscular Systems

• Campbell, 5th ed, Chapter 49
• Nancy G. Morris
• Volunteer State Community College

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Intro to Sensory Reception

• Action potentials that reach the brain via
  sensory neurons are called sensations.
• Interpretation of the sensation by the brain is
  perception.
• Perceptions (colors, smells, sounds, tastes) are
  constructed in the brain do not exist outside
  it.

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An age old question If a tree falls in the
forest and no one is there to hear it, is
there a sound?

• The fall produces pressure waves in the air,
• but if we define sound as perception, then
• there can be no sound unless sensory receptors
  detect the waves an animals brain perceives
  them.

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Sensory reception

• Sensations, their perceptions in the brain,
  begin with sensory reception, the detection of
  the stimulus by sensory cells.
• Sensory receptors specialized neurons or
  epithelial cells existing singly or in groups
• Exteroreceptors detect stimuli from outside the
  body (heat, light, pressure, etc.)
• Interoreceptors detect stimuli within the body
  (blood pressure , body position)

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Skin

• Receptors that detect the sense of touch are
  called mechanoreceptors.
• It also contains thermoreceptors,
• pain receptors,
• chemoreceptors (gustatory, olfactory)

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Figure 49.1Sensory receptors in human skin
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Functions of the Integument

• 1) Largest organ of the body
• 2) Protection
• 3) Waterproofing layer
• 4) Temperature regulation
• 5) Sensory response to stimuli
• 6) Source of vitamin D (ultraviolet rays convert
  cholesterol)
• Horny layer dead, filled with keratin,
  constantly sloughed off
• Continuous division at the basement membrane

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Photoreceptors

• A broad array of photoreceptors has evolved among
  invertebrates
• Vertebrates have single-lens eyes
• The light absorbing pigment rhodopsin operates
  via signal transduction
• The retina assists the cerebral cortex in
  processing visual information

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Figure 49.11Neural Pathways for vision
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Hearing equilibrium

• The mammalian hearing organ is within the inner
  ear
• The inner ear also contains organs of equilibrium
• A lateral line system inner ear detect pressure
  waves in most fishes aquatic amphibians
• Many invertebrates have gravity sensors are
  sound-sensitive

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Ear and hearing
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Movement locomotion

• Movement is the hallmark of animals
• Locomotion is active movement from one place to
  another

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Locomotion

• Animals may swim, crawl, walk, run, hop, or fly
• In all forms, locomotion requires that an animal
  expend energy to overcome two forces that tend to
  keep it stationary friction and gravity.

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Skeletons

• 1) Protection (skull, ribs cage, etc.)
• 2) Support
• 3) Movement (lever systems)
• In vertebrates
• 4) Responsible for blood cell production
• 5) Store minerals

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Three main types of skeletons

• Hydrostatic skeletons
• earthworms
• Exoskeletons
• arthropods
• Endoskeletons
• vertebrates

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Endoskeletons

• Consist of hard supporting elements, such as
  bones, buried within the soft tissues of the
  animal
• Sponges spicules
• Echinoderms hard dermal plates beneath the skin
  and ossicles

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Figure 49.23Peristaltic locomotion in the
earthworm
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Figure 49.25Exoskeleton of an arthropod
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Endoskeletons

• Found only in Chordates
• Composed of cartilage, bone, or combination
• Mammalian skeleton has approximately 200 major
  bones

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Major Divisions of Human Skeleton

• Axial Skeleton
• Cranium, hyoid, vertebral column, sternum and
  ribs
• Appendicular Skeleton
• Pectoral girdle bones of upper appendages
• Clavicle, scapula, humerus, ulna, radius,
  phalanges, metacarpals, carpals
• Pelvic girdle bones of lower appendages
• Pubis, ilium, ischium, femur, patella, tibia,
  fibula, tarsals, metatarsals, phalanges

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Figure 49.24The human skeleton
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"A cast of your skull, sir, until the original
is available, would be an ornament to any
anthropological museum.  It is not my intention
to be fulsome, but I confess that I covet your
skull. "                                          
              The Hound of the Baskervilles, 
Chapter 1,  Sir Arthur Conan Doyle
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Major Joints of Human Skeleton

• Ball-andsocket joint
• Rotation
• Shoulder hip joints
• Hinge joint
• Restrict movement to a single plane
• Knee elbow
• Pivot joint
• Rotation
• Ulna, radius tibia, fibula

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Muscles

• Move skeletal parts by contracting
• Action of the muscle is always to contract.
  (Muscles only pull -- NEVER push.)
• Arranged in antagonistic pairs with each muscle
  working against the other

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Figure 49.25Cooperation of muscles
skeletons in movement
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Structure Function of Vertebrate Skeletal Muscle

• skeletal muscle characterized by smaller and
  smaller parallel units
• bundles of long fibers running the length of the
  muscle
• each fiber is a multinucleated single cell
• each fiber is a bundle of smaller myofibrils
• each myofibril is composed of two myofilaments
  Actin (thin) Myosin (thick)

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Figure 49.26The structure of skeletal muscle
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Skeletal muscle

• striated (repetition of light dark bands)
• each repeating unit is a sarcomere, the
  functional unit of muscle contraction
• borders of sarcomeres, Z lines, are lined up in
  adjacent myofibrils
• thin actin filaments attach to the Z lines
  project toward the center
• thick myosin filaments are centered in the
  sarcomere and stitched together at the M line

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Actin Myosin filaments

• ACTIN
• Thin filaments
• Composed of many globular actin molecules (beads)
  assembled in a long chain (necklace)
• Two protein chains are wound around one another
  to produce a single actin filament
• Contain troponin tropomyosin proteins which in
  the presence of Ca2 uncover binding sites on
  actin

• MYOSIN
• Thick filaments
• Longest known protein chain 1,800 amino acids
• 200 or more parallel protein molecules with free
  globular heads
• Myosin heads
• 1) binding sites for contraction and
• 2) contain enzymes that
• split ATP to power the contraction

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Ultra Structure of the Sarcomere
M line connection between the thick myosin
filaments H zone (from Latin hell meaning
bright or clear) the central zone in the relaxed
sarcomere containing only myosin filaments I band
zone around the Z line that contains only actin
filaments A band marks the extent of the myosin
filaments in the sarcomere Z line the dark
stripe in the center of the I band (bulkhead)
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Skeletal Muscle
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Sliding Filament Theory 1

• Contraction involves the sliding of thin actin
  filaments between thick myosin filaments.
• Innervation by the motor neuron stimulates the
  muscle fiber. The neurotransmitter,
  acetylcholine, acts as the chemical mediator
  diffusing across the membrane.
• Acetylcholine generates electrical depolarization
  (by pumping Ca2 out) in the sarcoplasmic
  reticulum of the entire muscle. Ca2 binds to
  troponin of the thin actin filaments causing
  tropomyosin to uncover the binding sites.

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Figure 49.30Roles of sarcoplasmic reticulum T
tubules in contraction
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Figure 49.29The control of muscle contraction
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Role of calcium in contraction
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Sliding Filament Theory 2

• Myosins globular heads, acting like hooks,
  attach to the uncovered binding sites on actin.
  The result is a temporary cross-bridge. These
  cross-bridges form, break, reform rapidly as
  one filament slides (or is pulled) past another.
• Myosin heads contain enzymes that release the
  energy in ATP (ADP Pi ) to power contraction.
  It is the chemical combination with the next ATP
  that releases the myosin head from the actin
  binding site breaking the temporary cross-bridge.
• Rigor mortis results when the cross-bridges are
  locked in place because no more ATP is
  available to release myosin from its binding
  site.

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Sliding Filament Theory 3

• Because the cross-bridges are forming, breaking,
  reforming, the actin filaments are pulled
  toward the center of the H zone causing
  contraction of the sarcomere.
• The filaments themselves do not change length.
  In response to the stimulus to contract, the
  filaments slide past one another and increase the
  amount by which they overlap, thereby shortening
  (contracting) the sarcomere.

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Figure 49.28Interaction of actin myosin in
muscle contraction
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Figure 49.27The sliding-filament model of
muscle contraction
What zones bands are missing in the contracted
sarcomere?
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Skeletal Muscle
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Motor Units in Vertebrates

• Each muscle fiber (cell) has a single
  neuromuscular junction, or synaptic connection,
  with the motor neuron that controls it.
• Each motor neuron branches controls several
  muscle fibers.
• A motor neuron all the fibers it controls
  constitute a motor unit.

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Figure 48.32Motor units in vertebrate muscle
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A motor unit
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Figure 49.31Temporal summation of muscle cell
contractions
A muscle twitch results from a single stimulus.
More rapidly delivered signals produce a graded
contraction obtained by summation. Tetanus is a
state of smooth sustained contraction obtained
when motor neurons deliver a volley of action
potentials
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Smooth Muscle Tissue Review

• Found throughout the body particularly lining
  vessels hollow organs responsible for
  peristalsis
• Single nucleated cell with tapered ends
• Non-striated because actin myosin filaments are
  not regularly arranged
• Contracts slowly, but greater range than striated

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Cardiac Muscle Tissue Review

• Found only in the heart
• Multinucleated
• Striated, branching cells electrically connected
  by intercalated discs (specialized gap junctions
  that couple cells electrically). An actin
  potential generated in one part of the heart will
  spread to all the cardiac muscle cells, the
  whole heart will contract.
• Generates action potentials without neural input
• Plasma membrane has pacemaker properties