Flashcards in Chapter 10- Muscles Deck (66)
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Myology
scientific study of muscles
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how much mass do muscles account for
~45%
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functions of muscles
maintain posture and body position
movement
heat production
guard orifices
support visceral organs
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properties of muscle tissue
Excitability
-the ability to receive and respond to electrical or chemical stimuli
Contractility
-the ability to shorten forcibly when stimulated
Extensibility
-ability to be stretched without damaging the tissue
Elasticity
-ability to return to original shape after being stretched
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composition of mucles
-muscles are organs
-consist of many tissue types
-connective tissue
-arteries/veins
-nerves
-lymphatics
-contractile muscle cells
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skeletal muscle characteristics
-attaches to bone, skin, or fascia
-striated with light and dark bands
-voluntary control
-long, thin and multi-nucleated fibers
-arranged into packages that attach to and cover the bony skeleton
-contracts rapidly, but tire easily
-may exert great force
-fiber=1 muscle cells
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muscle structure
-belly: main portion of a muscle (thick part)
-belly is attached to tendons
-tendons are attached to bone
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fascia
-deep fascia
--dense irregular CT around muscle
--holds it in place and separates it form other muscles
-subcutaneous fascia
--loose CT beneath skin, surrounds several muscles
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skeletal muscle organization
-many muscle fibers are bundled together into groups called fascicles
-10-100 muscle cells
-several fascicles make up a muscle (so several hundred fibers(cells))
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skeletal muscle CT
-epimysium
-perimysium
-endomysium
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epimysium
surrounds the whole muscle
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perimysium
surrounds fascicles
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endomysium
separates individual muscle fibers
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tendon formed from what
all connective tissue extended beyond the muscle belly
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aponeuroses
tendons that form thick flattened sheets
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myoblasts
embryonic cells that fuse to form muscle fibers
-causes the length and multinucleation
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myosatellite cells
myoblasts that do not fuse
-assist in repair of damaged cells
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fiber structure
-sarcoplasm: fiber cytoplasm
-sarcolemma: plasma membrane of a fiber
-transverse (T) tubule: extensions of the sarcolemma into the sarcoplasm
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myofibrils
contractile organelles
-extend the length of fiber
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sarcoplasmic reticulum
surrounds the myofibrils
-similar to ER
-contains calcium ions which tell muscle to contract
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sarcomere
functional unit of the myofibril
-made of thick and thin filaments
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thick filaments
myosin
-twisted protein with globular heads
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thin filament
actin
-structural protein
-coiled "beads"
regulatory proteins
-allow/prohibit attachment between actin and myosin
-tropomyosin
-troponin
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sarcomere bands
cause the striated appearance
bands
-A band: entire thick filament range
-I band: only thin filaments
-H band: only thick filaments
- Zone of overlap: both filaments
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Sarcomere lines
divide and flank the sarcomere
-Z line:
--end of sarcomere
--made of actin protein
--anchor thin filaments
-M line:
--middle of the sarcomere
--stabilize thick filaments
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structural proteins
titin: anchors a thick filament to a Z line
-accounts for elasticity and extensibility
nebulin: holds F actin together on thin filaments (runs through center)
actinin: makes up Z line
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sliding filament theory
actin slides over myosin
-zone of overlap enlarges
-h band shrinks
-I band shrinks
- A band remains the same
- Z line moves closer to A band
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Neuromuscular junction is made up of
-motor unit
-neuromuscular junction
-synaptic termical
-motor end plate
-synaptic cleft
-neurotransmitter
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motor unit
neuron and all the muscle cells stimulated by the neuron
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neuromuscular junction
point of contact between the neuron and the muscle
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synaptic cleft
end of axon that contacts motor end plate
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neurotransmitter
chemical released into synaptic cleft
-acetylcholine
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events of muscle contraction
Ach stored in synaptic vesicles
-impulse reaches end of neuron-Ach released
-Ach crosses gap and binds to receptors
-impulse tracels through motor end plate down T-tubules to SR
-Ca2+ ions diffuse out of SR into sarcoplasm
-Ca2+ exposes the active site
-myosin binds to active site
-ATP is used and contraction occurs
-contraction continues as long as Ca2+ concentration is high
-Ach decomposed by acetylcholinesterase
-Ca ions transported back to SR
-actin and myosin links broken
-cross bridges moved back
-active site is blocked again
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acetylcholinesterase
breaks down acetylcholine
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tension produced by muscle
determined by
-frequency of stimulation
-number of motor units stimulated
brain tells muscle how much tension to apply
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all or none law
all fibers in a motor unit full contract if stimulated
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recruitment
steady increase in tension by increasing the number of contracting motor units
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tetanus
muscle never begins to relax, continuous fused contraction
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muscle tone
-motor units contract randomly
-tension, but no movement
-can stabilize joints, hold objects in place, maintain posture
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hypertrophy
-constant, exhaustive stimulation increases the number of organelles/proteins in a fiber
increases:
-mitochondria
-glycolytic enzyme reserves
-myofibrils (more and thicker)
-filaments within myofibrils
Muscle fibers DO NOT reproduce
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atrophy
-lack of constant motor neuron stimulation reduces organelles and proteins
-due to:
age
hormones
lack of use
nerve damage
-reversible if fiber is not dead
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muscle attachments
-origin: attachment site that does not move
-insertion: attachment site that moves
-force= tension
-fascicle arrangement varies based on position of muscle
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parallel muscles
-fascicles parallel to long axis
-unidirectional force
ex= biceps brachii
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convergent muscles
-fan shaped
-multi-directional force
-versatility
-generates least amount of force
-not all parts pulling in same direction at same time
ex. pectoralis major
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pennate muscles
feather shaped
-fascicles oblique to long axis
-tendon passes THROUGH the muscle
-greatest force
ex=deltoid, quadricep
con=distance. cannot pull as far because of angle
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circular muscles
-concentric fascicles around opening
-contraction decreases lumen diameter
ex= orbicularis oculi (eye)
mouth
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articulations and muscle actions: uniaxial
rotation around one axis
movements: rotation (atlantoaxial); pivot joints
Angular: knee, IP joints
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articulations and muscle actions: biaxial
movement occurs along 2 axes
angular motions:
-flexion/extension
-abduction/adduction
-ex: ellipsoidal joint, radiocarpal, metacarpal phelange, carpometacarpal (2-5)
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articulations and muscle actions: multiaxial
-movement on all axes
-angular motion: same as biaxial
-rotation
-circumduction
ex=ball-and-socket
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Actions: agonist
main muscle causing directional force
-this can be any muscle of interest
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actions: antagonist
muscle that contracts to oppose the agonist
ex=bicep brachii vs tricep brachii
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actions: synergist
muscle that assits/modifies movement
ex=brachialis and pronator teres
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actions: fixator
muscle that stabilizes elements associated with agonists
-deltoid stabilizes glenohumeral joint
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levers
lever systems modify movements
-can change:
-magnitude of force
-speed
-direction
-distance of limb movement
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components of lever system
-lever(L): skeletal element
-effort (E): applied force (muscle pulling)
-fulcrum (F): joint
-resistance (R): body part or object moved
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types of levers: first class
teeter totter/see saw
-R opposite of E with central F
ex= neck extension
-E=neck extensors
F=atlanto-occipital joint
-R=skull
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Second class levers
-wheel barrow
-E opposite of R to move R
Ex=plantar flexion
-E=calf
-F=MP joint
-R=weight of body
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Third class levers
-shovel, broom
-E in between F and R
Ex= elbow flexion
-E= biceps brachii
-F=elbow joint
-R=weight distal to joint
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types of skeletal muscle fibers: fast fibers
-fast acting; high energy requirements
-anaerobic
-large diameter
-densely packed myofibrils
-large glycogen reserves
-few mitochondria
-rapid, powerful, brief contractions
LIGHTER, less myoglobin
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types of skeletal muscle fibers: slow fibers
-more myoglbin; slower sustained contraction
-aerobic
-smaller diameter
-longer to contract
-contract for longer time
DARKER b/c myoglobin
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types of skeletal muscle fibers: intermediate fibers
-attributes of both
-similar to fast fibers
-greater resistance to fatigue
-exercise (or lack of) can change one muscle type to another
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smooth muscle characteristics
-attached to hair follicles in skin
-in walls of hollow organs and blood vessels
-nonstriated
-involuntary control
-contractions are slow and sustained
-spindle shaped
-very elastic
do not fuse like muscle cells do
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smooth muscles
characteristics:
-contract slowly
-resistant to fatigue
-stimulated by:
-nervous system
-hormones
-ions
-stretching
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smooth muscle types: single unit
-many gap junctions
-sheets of spindle shaped cells
-contract together
ex: BV's, digestive tract, resp. tract, urinary tract.
-either closed or open, no precision
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smooth muscle types: multi-unit
-no or few gap junctions
-separate fibers; contract independently
-only contract when stimulated by motor nerve
-ex: walls of large BV's, uterus, iris of the eye
-lots of precision, degree of refinement/contraction
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