The Skeleto-Muscular System

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Chapter 6

• The Skeleto-Muscular System

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Movement

• Movement is a defining characteristic of animal
  life
• Humans move by applying tension to the bones and
  joints of the skeletal system
• tension is applied by the muscular system
• The skeletal and muscular systems work as a unit

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The Skeleto-Muscular System

• The skeleto-muscular system works together to
  perform several key functions
• provide movement and locomotion
• manipulate the environment
• protect organs in the thoracic and abdominopelvic
  cavities
• help maintain homeostasis by generating internal
  heat
• maintain upright posture and bipedalism
• the skeleton produces blood cells
  (hematopoiesis), and stores and releases minerals
  such as calcium and phosphorus (used in muscular
  contraction)

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Movement

• Movement is possible because of the unique
  arrangement of muscle and bone
• All human skeletal muscles have a similar
  function and structure
• they contract, or get shorter, to produce
  movement
• muscles can relax to their original (resting)
  length or even elongate beyond that point

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Bone and Muscle

• Both bone and muscle are living tissue
• separately neither is able to produce movement
• Muscular tissue contracts (gets shorter)
• when the muscle shortens, it pulls on the bone
• Bones are held together by joints, most of which
  permit movement between the bones
• pulling on one bone causes movement at the
  accompanying joint

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Bone Formation

• Bones are a form of connective tissue produced by
  immature bone cells called osteoblasts
• Ossification (bone formation) can be endochondral
  or intramembranous
• most bones are endochondral (formed within
  cartilage)

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Bone Formation
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Bone Formation

• Bones grow longer and thicker
• growth occurs at the outer surface of the bone
• cells within the membrane that covers the bone,
  the periosteum, differentiate into osteoblasts
  and begin to add matrix to the exterior
• accumulating matrix entraps these osteoblasts,
  which mature into osteocytes, creating new bone
  tissue around the exterior of the bone

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Bone Formation

• Intramembranous ossification forms the flat bones
  of the skull, clavicle, and mandible
• bone is laid down within embryonic connective
  tissue
• bones form deep in the dermis of the skin and
  thus are often called dermal bones

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Bone Tissue

• Bony tissue comes in two forms
• compact (dense)
• compact bone material usually occurs at the edges
  of the bone and is composed of many individual
  osteons
• the central canal of the osteon houses the blood
  and nerve supply for the bone tissue
• spongy
• spongy bone is less organized than compact bone
  and lacks osteons
• instead, spongy bone has trabeculae, or struts,
  that form in response to stress

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Bone Tissue
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Bone

• In a typical bone, dense compact bone surrounds
  the organ and spongy bone comprises the inner
  support
• The ends of the bones, or epiphyses, include the
  epiphyseal plate, an area of cartilage where long
  bones continue to grow during childhood and
  adolescence
• when bones cease growing, this cartilage is
  replaced by bone, leaving the epiphyseal line
• Wherever two bones meet, you will find a layer of
  hyaline cartilage
• this articulating cartilage prevents bone from
  grinding against bone at a joint

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Bone Marrow

• The central canal of the long bone houses the
  marrow
• blood cells form in red marrow
• energy is stored in yellow marrow

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Bone Remodeling

• Bones are dynamic structures, constantly being
  remodeled and perfected to suit the needs of the
  body, and continuously making subtle changes in
  shape and density
• Bones cease growing in length at maturity, but
  continue to change shape throughout life
• the calcium within each bone is being removed and
  new calcium is added in response to blood calcium
  levels and the amount of stress placed on the
  bones
• the bones are a storehouse for calcium needed in
  physiological processes such as nerve impulse
  transmission and muscle contraction
• when the blood calcium level drops, osteoclasts
  go to work to release stored calcium to the blood
• when the blood calcium level rises, the
  osteoblasts create new matrix, removing excess
  calcium from the blood

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Osteoclasts

• Osteoclasts are large cells that adhere to the
  surface of bony tissue and release acids and
  enzymes
• The end result of the activity of these cells is
  the breakdown of the bony matrix and the addition
  of calcium and other minerals to the bloodstream
• Osteoblasts build the mineral structure back up,
  pulling calcium and minerals from the bloodstream
  
• the osteoblasts first secrete an organic matrix
  called osteoid
• they then cause an increase in local calcium
  concentration around the osteoid, converting the
  osteoid to bone
• this process takes upwards of three months to
  complete

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Bone Repair

• For bone to heal, the ends of the fracture must
  be aligned and immobilized
• closed reduction - when alignment is possible
  without disturbing the skin
• open reduction - the skin must be cut, and often
  metal screws, plates, or pins are used to fix the
  bones in place
• more likely to be needed in compound fractures
• Complete immobilization may not be ideal for
  healing bone
• limited movement, stress, or partial
  weight-bearing activities can actually help the
  bones grow, because those stresses on the bone
  matrix stimulate bone deposition

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The Skeleton

• The human skeleton is composed of 206 bones

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The Skeleton

• The skeleton is divided into
• the axial skeleton (the central axis of the body)
  
• the appendicular skeleton (the appendages arms,
  legs, hands, and feet and girdles holding them
  to the central axis)
• The axial skeleton is comprised of
• 8 cranial bones
• 14 facial bones
• the hyoid bone
• ribs
• vertebrae
• ribs and vertebrae give us our upright posture
  and protect the organs in our thoracic cavity

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Cranial Bones

• Cranial bones surround and protect the brain
• the parietal and temporal bones are paired
• parietal bones protect the upper sides of the
  head
• temporal bones protect the middle sides of the
  head and support the ears
• the frontal bone, occipital bone, ethmoid, and
  sphenoid are single bones
• the frontal bone at the forehead protects the
  frontal lobe of the brain
• the entire back of the skull is a single bone
  (occipital bone)
• two cranial bones comprise the floor of the
  cranial cavity.
• the ethmoid forms the floor of the front portion
  of the cranial cavity
• the sphenoid provides the base for the cranium,
  supporting the brain
• All 8 cranial bones are held together by fixed
  joints called sutures

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Facial Bones

• Anatomically, the 14 facial bones protect the
  entrances to the respiratory and digestive
  systems, and the sensory organs.
• Two facial bones are single, and 12 occur in
  pairs.
• The paired maxillae and palatine bones make up
  the front (maxillae) and roof of the mouth (the
  palatine bones)
• The small, thin, paired nasal bones form the
  bridge of the nose
• The small lacrimal bones (paired) are located on
  either side of the nose
• a small passage in these bones allows the tears
  to collect and pass through the skull into the
  nasal cavity
• The paired zygomatic (cheek) bones bulge outward
  and help protect the eyes
• Inferior nasal conchae bones (paired) form the
  swirling surface of the nasal cavity, helping to
  warm and moisten the air we inhale
• The vomer is the bony separation between nasal
  passages 
• The mandible, the only bone of the skull attached
  by a movable joint, articulates with the
  mandibular fossae of the temporal bone at the
  temporomandibular joint (TMJ)
• The single hyoid bone, which lies below the
  tongue, is the only bone of the skeleton that is
  not directly attached to any other bony structure
• it is instead suspended by the throat muscles

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Cranial and Facial Bones
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Cranial and Facial Bones
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Vertebrae

• These bones allow upright posture and protect
  vital organs of the thoracic cavity
• There are 24 vertebrae, one sacrum, and three to
  five coccyx bones in the adult vertebral column
• The sacrum is actually five fused vertebrae that
  form a solid base for the pelvic girdle
• The tailbone, or coccyx, is our post-anal tail

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Vertebrae

• Vertebrae
• A typical vertebra is composed of three parts
• the vertebral body
• the vertebral arch
• the vertebral articular processes
• serve as points of attachment between adjacent
  vertebra and sites for muscle attachment
• The vertebral column is divided into the cervical
  region (vertebrae C1C7), the thoracic region
  (T1T12), and the lumbar region (L1L5)
• moving down the column, the bodies of the
  vertebrae grow larger, because they must support
  more weight
• between each vertebra is a pad of fibrocartilage
  called the intervertebral disc
• the disc serves as a shock absorber, preventing
  vertebrae from rubbing against one another and
  crushing under the body's weight
• allow limited motion between vertebrae

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The Vertebral Column
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Ribs and Sternum

• We have seven pairs of true ribs and five pairs
  of false ribs
• true ribs attach directly to the sternum or make
  a direct connection with the costal (rib)
  cartilage, which in turn is directly associated
  with the sternum
• false ribs either attach to the costal cartilage
  (ribs 8, 9, and 10), which then joins the
  sternum, or their lateral ends are free
  (sometimes called floating ribs 11 and 12)
• The sternum, or breastbone, protects the anterior
  of the chest
• The sternum has three parts
• the manubrium
• articulates with the appendicular skeleton
• the body
• the xyphoid process
• a small tab of cartilage at the end of the body

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The Thoracic Cage
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The Appendicular Skeleton

• The appendicular skeleton includes all the bones
  that are attached, or appended, to the axial
  skeleton
• the pectoral girdle (shoulder bones)
• the upper appendages (arms and hands)
• the pelvic girdle
• the lower appendages (legs and feet)

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The Pectoral Girdle

• The pectoral girdle
• human bodies have two pectoral girdles, each
  consisting of a clavicle and scapula
• the scapulae (the plural form of scapula) connect
  to the strong back muscles and articulate only
  with the clavicles
• gives each shoulder joint greater range of motion
• The upper appendages
• the humerus is the longest and strongest bone in
  the upper appendicular skeleton
• the ulna is on the medial side of the forearm
• the radius is on the thumb side of the forearm
• the elbow is the joint formed by the distal end
  of the humerus and the proximal ends of the
  radius and ulna
• a large projection of the ulna called the
  olecranon forms the point of the elbow
• the wrist bones (carpals) are in two rows of four
  short bones
• the metacarpals make up the structure of the hand
• the phalanges (finger bones) are considered long
  bones
• each finger has three bones the proximal,
  middle, and distal phalanx
• the thumb (pollex) has only two phalanges

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The Pectoral Girdle and Upper Appendages
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The Pelvic Girdle

• The pelvic girdle
• composed of the hip bones and lower vertebrae
• denser, stronger, and less flexible than the
  appendicular girdle
• The hip bone emerges from three bones that fuse
  in early puberty
• the ilium
• the ischium
• the pubic bone
• the femur articulates at the junction of these
  three bones
• The acetabulum is the curved recess that serves
  as a socket for the head of the femur
• The pelvis is technically made of two large coxal
  bones (hip bones) which make up the pelvic
  girdle, plus the sacrum and the coccyx

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The Pelvic Girdle and Right Lower Limb
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Joints

• Joints link the skeletal system together they
  exist wherever two bones meet
• Joints are classified by function or structure
• Functionally, joints are
• immovable or synarthrotic
• semimovable or amphiarthrotic
• freely movable or diarthrotic (synovial)
• Structurally, a joint is considered a bony
  fusion, or a fibrous, cartilaginous, or synovial
  joint

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Joints
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Muscular Tissue

• Muscular tissue is contractile tissue
• There are three types of muscular tissue
• skeletal muscle a contractile tissue composed
  of protein filaments arranged to move the
  skeletal system
• cardiac muscle
• smooth muscle
• In general, each skeletal muscle has an
• origin - an end that remains stationary when the
  organ shortens
• and an insertion - an end that moves during
  contraction
• Knowing the origin and insertion of any skeletal
  muscle offers clues about its function

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Muscular Tissue
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Skeletal Muscle

• Skeletal muscle is composed of numerous elongated
  structures, running from origin to insertion, one
  nested inside another
• Individual skeletal muscle cells are long,
  slender, and exceedingly fragile
• These long, fragile cells must shorten, creating
  tension
• Without connective tissue support, the soft
  tissue of the muscle cell would not be able to
  withstand the tension needed to provide movement,
  and the cell would rip itself apart rather than
  shorten the organ
•  

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The Skeleto-Muscular System
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The Skeleto-Muscular System
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The Skeleto-Muscular System
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The Skeleto-Muscular System
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The Skeleto-Muscular System
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The Skeleto-Muscular System
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Skeletal Muscle

• Skeletal muscle is grouped into individually
  protected cells, held together in fascicles, and
  then grouped to form the entire organ
• This nested fibers arrangement extends to the
  microscopic organization of skeletal muscle
  tissue
• Inside these myofibrils, we find one final level
  of nested, elongated structures, microfilaments
  composed of the proteins actin and myosin
• These two microscopic proteins interact in a way
  that causes the entire muscle tissue to shorten
  and therefore produce movement
• These proteins are held in regular arrangements
  in contractile units, or sarcomeres, which are
  stacked end to end in the myofibrils

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The Anatomy of a Muscle
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Muscle Contraction

• Contraction starts with a nerve impluse
• the motor neuron ends very close to a group of
  muscle cells, separated only by a small
  fluid-filled space called the synapse, or
  synaptic cleft.
• Nerves send a contraction impulse across the
  synapse via chemical messengers, called
  neurotransmitters
• the most common of these messengers is
  acetylcholine (Ach)
• The contraction cycle continues as filaments
  slide past one another
• the sliding filament model explains our best
  understanding of how muscle cells shorten. In
  this process, calcium initiates contraction, and
  proteins slide past one another
• with millions of sarcomeres lined up in each
  muscle cell, and many muscle cells innervated by
  one motor neuron, these tiny chemical reactions
  shorten the entire muscle

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Muscle Contraction
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Muscle Cells

• There are three types of muscle cells
• fast twitch (or fast glycolytic),
• anaerobic, fatigue quickly
• provide a short burst of extreme energy and
  contraction power
• thicker, contain fewer mitochondria, usually
  contain larger glycogen reserves, and have a less
  developed blood supply
• responsible for hypertrophy
• because short bursts of power come from these
  fibers, exercises that continuously require
  bursts of power will enlarge them
• weight training puts demands on fast twitch
  fibers, resulting in the hypertrophy (muscle
  enlargement) we associate with body-building
• intermediate (or fast oxidative-glycolytic)
• slow twitch (or slow oxidative)
• appear red, have a large blood supply, have many
  mitochondria within their sarcolemma, and store
  an oxygen-carrying protein called myoglobin
• these cells are sometimes called nonfatiguing or
  aerobic cells
• distance running and other aerobic sports
  stimulate these cells
• efficiency and strength come not from increasing
  mass but from using oxygen more efficiently.
• Although training can alter the functioning of
  both red (slow twitch) and white (fast twitch)
  fibers, it does not change their proportions
• the percentage of fast and slow twitch fibers is
  genetically determined