Musculoskeletal System and Locomotion

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Musculoskeletal System and Locomotion Powered By Docstoc
					Sensory and Motor
Mechanisms

Chapter 49
AP Biology
Moving has its
challenges…
            Muscles and Movement




   Requires muscles and some kind of skeletal
    structure
       Levers and fulcrums…
       Skeleton types
 Hydrostatic
   Found   in
    earthworms, other
    soft-bodied
    creatures
   Fluid in body
    cavity under
    pressure
      Skeleton types
 Exoskeleton
  Insects,
   crustaceans
  Chitinous
  Can be
   calcareous
      Skeleton types

 Endoskeleton
   Calcareous,
    proteinaceous
   Protects internal
    organs
          Bones
 Ossified structures that
  provide structure and
  protection for internal
  organs
   Axial skeleton
   Appendicular skeleton

 Provide anchorage
  points for muscles
   Act   as levers
       Ligaments and Tendons
 Ligaments:  strong,
  elastic connective
  tissue band that
  connects bones to
  bones
 Tendons: dense cord
  of connective tissue
  that connects muscles
  to bones
        Joints
 Articulation   of two
  bones
 Do not always permit
  movement
   Fixed joints in
    cranium, sacrum
 Moveable joints
   Capsule with synovial
    fluid
   Cartilage for
    cushioning between
    bones
Hip and Knee Joints:
compare their motion
The elbow
 Component                       Function
Humerus,       Act as levers to bring about movement and
radius, ulna   maintain posture/position
Biceps muscle Anchored to scapula, attached to radius so
              that contraction flexes the lower arm
Triceps muscle Anchored to scapula, attached to ulna so
               contraction extends the lower arm
Ligaments      Hold bones in correct positions at the joint
Capsule        Contains joint without restricting movement

Synovial       Secretes synovial fluid, which lubricates and
membrane       nourishes the joint, removes detritus
Cartilage      Rubbery material that cushions and reduces
               friction
       Role of Nerves
 Nerves  stimulate
  muscles to contract
 Neuromuscular
  junction is where
  motor nerves meet
  muscle fibres
 Nervous system
  coordinates
  movement
         Muscles: Skeletal
 Cause    movement by
  contraction
 Occur in antagonistic
  pairs
    Significance?

 Functions:
    Maintain position/posture
    Cause movement at
     joints
    Aid in circulation of blood
         Muscle Structure
 Made   up of bundles
  of multinucleate
  muscle fibers
 Fibers made up of
  myofibrils
 Myofibrils made up
  of actin, myosin
  proteins
Muscle Fibers
           Sarcomere




   The sarcomere is a repeating unit of muscle fibers
    found between 2 Z lines.
        Muscle Contraction
 Sliding filament theory:
 actin and myosin
 filaments slide over
 one another in
 response to nervous
 stimulation by
 elongating and
 thickening
   Thick filaments:
    myosin
   Thin filaments: actin
Step 1: An action
potential arrives at
the neuromuscular
junction. ACh
diffuses across the
synaptic cleft and
binds to ACh
receptors on the
muscle cell
membrane.
Step 2: The AP
propagates along the
membrane and down
the T tubules.
Step 3: The AP
triggers the release
of Ca+2 ions from the
sarcoplasmic
reticulum
(specialized ER in
muscle cells)
Step 4: Ca+2 ions
bind to troponin,
which changes
shape so it doesn’t
block actin’s active
sites.
Step 5: Contraction of
the fibers as myosin
cross bridges attach and
detach to actin filaments,
pulling them toward the
sarcomere’s center.
Filament sliding powered
by ATP.
Step 6: Ca+2 is
removed by
active transport
into the
sarcoplasmic
reticulum after
the AP ends.
Step 7:
Tropomyosin
once again
blocks actin,
contraction ends
and muscle fiber
relaxes.
         Electron micrographs of
         muscle fiber contraction




•The sarcomere (between the z-lines) gets shorter upon
contraction but the thick filaments (dark lines) do not
change
•This demonstrates the sliding filament action of the
muscle fibers.