MCAT Biology Ch6: The Musculoskeletal System Flashcards
skeletal system
-skeleton derived from mesoderm
two types of skeleton
exoskeletons and endoskeletons
exoskeletons
- encase whole organism
- protect but organism growth requires shedding
endoskeletons
- vertebrates
- don’t protect surfaces and organs as well as exo but don’t shed
components of skeletal system divded into
axial and appendicular
both covered by other structures (muscle, conn. tissue, and vasculature)
axial
-skull, vertebral column, ribcage
basic central framework
overall shape
appendicular
arms, legs, and pelvic and pectoral girdle attached to axial skeleton for stability
depend on axial for attachment
skeleton created from two major components
cartilage and bone
cartilage
softer and more flexible than bone
consists of chondrin, that’s secreted by chondrocytes
much fetal skeleton made out of this => calcify to bone => adult have only body parts that need little extra flexibility (external ear, nose, walls of larnyx and trachea, and joints) => degradation (old age) => lack of cartilage in joints => bones rub against each other => arthritis
relatively avascular (w/o blood and lymphatic vessels) and no innervated
nonarticular kind can grow and repair throughout life
chondrocytes
secretes chondrin
chondrin
firm (but elastic) matrix that’s secreted by chondrocytes
bone
-composed of conn. tissue derived from embryonic mesoderm
harder than cartilage
lightweight
vascular and innervated
macroscopic bone structure
transplanted cells in hip marrow
compact bone (macroscopic bone structure)
- strength from here
- strong and compact
spongy or cancellous bone (macroscopic bone structure)
-lattice structure
consists of trabeculae
trabeculae
spongy bone consists of this bony spicules (points)
cavities filled w/ bone marrow (red or yellow)
bone marrow
filled cavities of trabculae of spongy bone
red marrow
filled w/ hematopoietic stem cells
responsible for generation of all cells in our blood
yellow marrow
composed primarily of fat and relatively inactive
long bones
bones in appendicular skeleton typically this
characterized by diaphyses and epiphyses
diaphyses
cylindrical shafts that characterize long bones
peripheries composed of compact bone
internal core full of marrow
epiphyses
dilated ends of long bones
peripheries composed of compact bone
internal core have spony bone core inside compact bone for dispersion of force at joints
epiphyseal plate
seperating diaphyses and epiphyses
cartilaginous structure and site of long. growth
seal due to sex hormone effects => growth continues through puberty until 25, although most down between onset of puberty and 18.
periosteum
fibrous sheath
surrounds long bone to protect and serve as muscle attachment
some able to differentiate into bone-forming cells
healthy one necessary for bone growth and repair
microscopic bone structure
bone matrix
bone matrix
strength of compact bone comes from here
organic and inorganic components
minerals like Na, Mg and K also stored in bone
strong bones require uniform dist’n of inorganic material (Haversian, lamellae, etc)
ordered into osteons or Haversian systems
interspersed w/in matrix are lacunae
organic components of bone matrix
collagen, glycoproteins, and other peptides
inorganic components of bone matrix
Ca, phosphate, OH ions => harden =? hydroxypatite crystals
osteons or Haversian systems
bony matrix similarly ordered into structural units
each encircles central Haversian canal
center
Haversian canal
each osteon encircles this
surrounded by lamellae
contain blood vessels, nerve fibers, and lump, keep bone in peak condition
lamellae
concentric circles of bony matrix
surround Haversian canal
rings in tree not touching
lacunae
spaces interspersed w/in matrix
house osteocytes
osteocytes
mature bone cells
housed in lacunae
two ways of bone formation (ossification)
endochondral ossification and membranous ossification
endochondral ossification
most of bones (long)
hardening of cartilage
intramembranous ossification
mesenchymal tissue transformed into, and replaced by bone
mesenchymal tissue
undifferentiated embryonic connective tissue is transformed into, and replaced by bone
bone remodeling
vig. eq. between construction and destruction
endocrine hormones like parathyroid and calcitonin involved in remodeling
two players of bone remodeling
osteoclasts and osteoblasts
both contribute to constant maintenance of bone
osteoclasts
destroy or resorb bone
osteoblasts
build bone
bone reformation
like Ca, Phosphate, obtained from blood
bone resorption (breakdown)
ions released into bloodstream
osteoporosis
inc. osteoclast resorption and slowing bone formation => loss of bone mass => estrogen stimulate osteoblast
joints
made of conn tissue
two major varieties of joints
movable and immovable
movable joints
allow bone to shift relative to another (knees, elbows)
strengthened by ligaments
consist of synovial capsule
ligaments
pieces of fibrous tissue the connect bones to one another
synovial capsule
encloses actual joint cavity (articular cavity)
articular cavity/joint cavity
synovial capsule encloses this
synovial fluid
use since all structure of joints are solid => ease movement
lubricant
articular cartilage
coats articular surfaces of bones => impact restricted to lubricated joint cartilage rather than bones
immovable joints
not want move
ex: skull
3 varieties of muscles
skeletal, smooth, cardiac
skeletal muscle
-innervated by somatic nervous sytem
striated, from alignment of Z-lines and inc. density to other structures
consist of red and white fibers
Ca
somatic
skeletal muscle innervated by this
sarcomere
basic contract unit of a muscle
myofibrils
-sarcomeres put together end by end
sacroplasmic reticulum
myofibril surrounded by this
modified ER, containing a great deal Ca2+, tightly controls so muscle contract when necessary
sacroplasm
outside the sacroplasmic reticulum
modified cytoplasm in cells
myocyte
muscle cell
many myofibrils contained w/in
most cells are multinucleate due to fusion of several embryonic uninucleate cells; nucleus usually found in periphery
muscle
parallel arrangement of myocytes
sacrolemma
cell membrane
can propagate action potential
system of t-tubules connect to this and are perpendicular to myofibrils => ions flow
t tubules
system of this connect to sacrolemma and are perpendicular to myofibrils => ions flow
red fibers
have high myoglobin content
derive energy aerobically
slow twitch
mito-rich
myoglobin
sim. to hemoglobin
consists of single pp chain
binds to o2 more tightly
white fibers
fast twitch
anaerobic
less myoglobin
don’t ETC => mito poor
contract more easily => easier to fatigue
sarcomere structure
made thick and thin filaments
contraction => Hzone, I band, and distance between Z line become smaller, A band remains constant (defined as total length fibers)
thick filaments
organized bundle of myosin
thin filaments
made up of actin along w/ two other proteins, troponin and tropomyosin
myosin
thick filaments organized bundle of this
actin
thin filaments made up of this
troponin and tropomyosin
along w/ actin, make up thin filaments
Z lines (sarcomere)
boundaries of each sarcomere
responsible for striated nature of skeletal and cardiac muscles)
M lines (sarcomere)
runs down sarcomere
I band (sarcomere)
region of thin filaments
H zone
contains thick filaments
A band
thick filaments in entirety, including any overlap w/ thin filaments
sarcomere contraction
series of coordinated steps repeated to induce further shortening
sarcomere contraction: initiation
nervous system send signal via a motor neuron => signal down neuron until reaches nerve terminal (synaptic bouton) => release neurotransmitter (acetylcholine) into synapse => binding neurotransmitter to receptor on muscle => contraction
enough acetylcholine bind to muscle cell => muscle depolarize (action potential generation) => sarcolemma’s permeability will inc.
motor neuron
nervous system send signal via a motor neuron to nerve terminal
nerve terminal (synaptic button)
receives signal from nervous system send signal via a motor neuron
releases neurotransmitter (acetylcholine) into synapse
synapse
releases neurotransmitter (acetylcholine) into synapse from nerve terminal (synaptic button)
binding neurotransmitter to receptor on muscle => contraction
neuromuscular junction
connection between nerve and muscle
sarcomere contraction: shortening of sarcomere
action potential along sarcolemma and T system => muscle fiber => massive release of Ca ions from SR => Ca binds to troponin => tropomyosin shift => expose myosin-binding sites on actin => free globular head myosin move and bind to exposed action => cross bridge allow action pull myosin => thin filaments to center of H zone => shorten sarcomere => ATPase activity in myosin give energy for power stroke => disso. of actin from myosin => myosin resets by binding to another molecule of ATP and free to bind another actin
myosin-binding sites
exposed when Ca binds to troponin => tropomyosin shift
sarcomere contraction: relaxation
when SR receptors not stimulated => Ca fall
product of ATP hydrolysis release from myosin during power stroke => new ATP molecule to bind => disso. of myosin from thin filament => sacromere original width
after death => ATP not produced =>myosin can’t detach from actin => muscle can’t relax = rigor mortis
ATP
used for both contraction and release of muscle fibers
Muscle Response
stimulus coupled to
stimulus intensity
strength of indie response by muscle fiber can’t be adjusted, but muscle control overall force by # of fibers they recruit to respond => all fibers stimulated to contract same time => max response
all or none
innevated by neurons whose basic signal is an action potential => response of muscle cells, completely or not at all
threshold value
stimuli must reach this
tonus
muscles in constant state of low-level contraction
essential for voluntary and involuntary muscles
simple twitch
response of single muscle fiber to brief stimulus at or above the threshold
consists of latent, contraction, and relaxation period
3 period of simple twitch
consists of latent, contraction, and relaxation period
latent period
time between reaching threshold (enough pokes) and onset of contraction (getting punched)
this time => action potential spread along muscle => Ca released from SR => after period, muscle will be unresponsive stimuli
refractory period
after period, muscle will be unresponsive stimuli following Ca released from SR
two types of refractory period
absolute and relative
absolute refractory period
no amount of stimulus (sister poking) will give response since muscle is restoring its resting potential
relative refractory period
muscle can be activated but w/ higher stimulus
summation and tetanus
muscle fiber freq. and prolonged stimulation => not relax => contractions combine => stronger and prolonged => tetanus
frequency summation
contractions combine => stronger and prolonged
tetanus
contraction so freq => no time relax
stronger than simple muscle fiber twitch
prolonged => muscle fatigue
smooth muscle
responsible for involuntary action
controlled by ANS
digestive tract, bladder, uterus, blood vessels walls, and others
actin and myosin, not striated fashion
contract like skeletal, but can longer and more sustained contractions; myogenic activity
single centrally placed nuclei
Ca
autonomic nervous system
smooth muscle controlled by this
myogenic activity
muscles can contract w/o nervous system, will respond, but not require external signals to contract
cardiac muscle
prop of both smooth and skeletal
involuntary
striated
Ca
may myogenic activity
Energy reserves
creatine phosphate and myoglobin
creatine phosphate
energy can be derived from this high-energy compound
time of plenty => store away by transfering phosphate from ATP to creatine; reverse during muscle use (ATP from ADP)
advantageous = immediate ATP making (otherwise from glycolysis or TCA)
myoglobin
generate more energy aerobically => require oxygen
myoglobin in muscle binds o2 tight => when exercise, use if muscles run out of oxygen => exhaust, then ferment remaining pyruvate to regenerate NAD+ and start glycolysis again
lactic acid and fermentation converted back into energy producing intermediates once sufficient O2 available => cori cycle in liver
connective tissue
bind and support other tissues
holds body together
sparsely scattered population of cells in amorphous ground substance may be liquid, jellylike, or solid
two types of connective tissue
loose and dense
loose connective tissue
throughout body
attaches epithelium to underlying tissue
material that holds organs in place
contain proteinaceous fibers of 3 types: collagenous, elastic, and reticular fibers
proteinaceous fibers of 3 types:
collagenous, elastic, and reticular fibers
collagenous fiber
composed of collagen
great tensile strength
elastic fiber
composed of elastin
give conn. tissue w/ resilience
reticular fiber
branched, tightly woven fibers that join conn. tissue to adjoining tissue
two cell types of loose conn. tissue
fibroblasts and macrophages
fibroblast
secrete components of extracellular fibers
macrophage
engulf bacteria and dea cells via phagocytosis
dense conn. tissue
high prop. of collagenous fibers => organized into parallel bundles => great tensile strength
forms tendons and ligaments
tendons
attach muscle to bone
ligaments
holds bones together at joints
muscle-bone interaction
locomotion interactions
muscle (w/ asso. joints) attached two bones => contractiion => one of two bones move
one relax, one contracts
contraction of antagonistic muscle lengthen paired muscle => muscle elongation
origin
end of muscle attached to stationary bone called this
limb muscles => proximal end
proximal end
in limb muscles, this is origin
insertion
end of muscle attached to bone that moves during contraction
limb muscles => distal end
distal end
in limb muscles, this is insertion
synergistic muscle
assist principal muscles during movement
flexor
muscle contract => dec. angle of joint
extensor
muscle contract => straight joint
abductor
moves part of body away from body’s midline
adductor
moves part of body away toward body’s midline
osteoblasts
bone cells involved in secretion of bone matrix
osteoclasts
large, multinucleated cells involved in bone resorption
osteocytes
mature osteoblasts that eventually became surrounded by matrix and primary role in bone maintenance
intramembraneous ossification
where mesenchymal cells directly create bone matrix
