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muscloskeletal system


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5 primary functions of the skeleton?
1) support
2) protection
3) movement
4) storage
5) blood cell production
rigid, strong bone
well suited for bearing weight
the major supporting tissue of the body
function of cartilage?
provides a firm, yet flexible support within certain structures (nose, external ear, rib cartilages, trachea)
What are ligaments?
strong bands of fibrous connective tissue that attach to bones and hold them together
What three things include in support system of the skeleton?
1) rigid, strong bone
2) cartilage
3) ligaments
bone : protenction
bone is hard and protects the organs it surrounds
encloses and protects the brain
surround the spinal cord
rib cage
protects the heart, lungs, and other organs of the thorax
What are the four things importnat in the skletal movement?
1) skeletal muscles
2) joints
3) smooth cartilage
4) ligaments
skeletal muscles
attach to bones by tendons
strong bands of connective tissue
contraction of the skeletal muscle
moves the bones, producing body movements
Where are joints formed?
where two or more bones come together
function of joints?
permit and control the movement between bones
smooth cartilage
covers the ends of bones within some joints, allowing the bones to move freely
function of ligaments?
allow some movement between bones but prevent excessive movements
What are two principle minerals stored into bone?
calcium and phosphorus
Where is fat (adipose tissue) stored?
within bone cavities
many bones contain cavities filled with?
bone marrow
bone marrow gives rise to?
blood cells and platelets
three types of bone cells?
1) osteoblasts
2) osteocytes
3) osteoclasts
What are osteoblasts?
bone-forming cells
primary function of osteoblasts?
to lay down new bone
after forming new bone, osteoblsats become what?
What does an osteoblast produce?
type one collagen & osteocalcin
type I collagen is responsive to?
PTH (parathyroid hormone)
When osteoblasts produce osteocalcin?
when stiumulated by 1,25-dyhydroxyvitamin D
a calcium-binding protein
inhibit Ca-Phosphate precipitation
promotes bone resorption
osteoblasts are active on?
on the outer surface of bones, where they form a SINGLE layer of cells
osteoblasts bring about the formation of new bone by?
by their synthesis of OSTEOID (non-mineralized bone matrix)
What is osteoid?
a protein mixture composed mainly of collagen that is secreted by osteoblasts and becomes mineralized to form bone
What are osteocytes?
are osteoblasts that have become imprisoned within the mineralized bone matrix
function of osteocytes?
help maintain bone by synthesizing new bone matrix molecules
function of osteocytes? #2
not fully known
synthesize certain matrix molecules assisting bone calcification
osteocytes : nutrients
osteocytes obtain nutrients from capillaries in the CANALICULI
help concentrate them in the matrix
help synthesize and replace needed elements of the matrix
obtaining nutrients from calillaries in the canaliculi help what?
help to maintain mineral homeostasis with the help of the PTH and osteoblast cells
definition of osteocyte?
is a transformed osteoblast that is trapped or surrounded in OSTEOID as it hardens from minerals that enter during calcification
What are osteoclasts?
the major resorptive cells of bone
large, multinucleated cells
short life span
osteoclasts develop from?
1)from the hematopoietic stem cells in the bone marrow stroma and adjacent vessels
2) from mononuclear phagocytic cells
function of osteoclasts?
to resorb (remove) bone during of growth and repair
osteoclasts contain what?
lysosomes (digestive vacuoles) filled with hydrolytic enzymes
long bone
thigh bone
humerus of arm
flat bone
parietal bone of skull
short bone
carpals of wrist
wrist bone
irregular bone
sphenoid bone from skull
consists of hundreds to thousands of muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibers
muscle are covered externally by?
the epimysium
discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath
fascicle are surrounded by?
muscle fiber
elongated multinucleate cell; has a banded (striated) appearance
muscle fiber are surrounded by?
motor units are composed of what?
lower motor neurons, which extend to skeletal muscles
another name for motor unit?
the functional unit of the neuromuscular system
motor unit behaves as?
a single entity and contracts as a whole when it receives an electrical impulse
whole muscle may be controlled by?
several motor nerve axones, which innervate many motor units within the muscle
Does the # of motor units per individual muscle vary?
varies greatly
(Ex) Calf - one motor axon will innervate appro. 2000 muscle fibers, out of a total of 1,200,000 muscle fibers
2 types of muscle contraction
1) isometric contraction
2) isotonic contraction
isometric contraction
static or holding contraction
the muscle maintains constant length as tension is increased
example of isometric contraction
when the arm or leg is pushed against an immovable object
the muscle contracts, but the limb does not move
isotonic contraction
the muscle maintains a constant tension as it moves
2 types of isotonic contractions
1) eccentric (lengthening)
2) concentric (shortening)
eccentric isotonic contraction
the muscle lengthens and absorbes energy
concentric isotonic concentration
positive work is accomplished
energy is released to exert force or lift a weight
Do actin and myosin myofillaments change length during contraction of skeletal muscle fibers?
NO! Instead, actin and myosin myofillaments slide past one another in a way that causes the sarcomeres to shoten.
Whar happens during contraction?
1) actin myofillaments at each end of the sarcomere slide past the myosin myofilaments toward the H zone
2) I bands shorten
3) A bands do not chenge
H zone during the contraction?
the H zone narrows or even disappears as the actin myofilaments meet at the center of the sarcomere
the last step of contraction
as the actin myofilaments slide over the myosin myofilaments, the Z disks are brought closer together, and the sarcomere is shortened
contracting muscle
1) sarcomere shortens
2) actin myofilaments move toward H zone
fully contracted muscle
sarcomere is shortened but A band width is unchanged

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