MUSCLES

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MUSCLES

• Skeletal
• Smooth
• Cardiac

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MEMBRANE POTENTIAL

• Electrical potential
• all cells
• sodium and potassium
• Sodium 12X higher outside
• Potassium 40X higher inside

Na
K
K Na
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MEMBRANE POTENTIAL

• Difference in charge across membranes
• 1. Na/K pump
• 3 Na pumped extracellular 2 K pumped
  intracellular
• accounts for about _____ of the energy
  requirements of the nervous system
• 2 proteins inside
• _______________charged
• 3. K diffuses out ___________ X faster than Na
  diffuses in
• Resting potential
• -70 millivolts (mV)

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MEMBRANE POTENTIAL

• Ion Channels
• Two basic types
• 1. Leakage (nongated) channels
• passive channels
• always ____________
• 2. Gated or Active Channels

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GATED CHANNELS

• 1. Voltage gated (regulated) ion channel
• Trigger is change in the membrane potential
• Na, K and Ca voltage regulated gates
• 2. Chemically gated ion channel
• Opens and closes in response to specific chemical
  stimuli
• Chemicals- hormones, neurotransmitters, ions such
  as H and Ca
• Most important are for Na K

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GATED CHANNELS

• 3. Mechanically gated ion channel
• Open or close in response to touch, vibration or
  pressure
• Examples - Meissner and Pacinian corpuscles
• 4. Light gated ion channel
• Open and close in response to light
• Found in rods and cones of the eye

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ACTION POTENTIAL

• Event 1
• Na permeability ____________ 5000 X
• 20,000 Na ions diffuse thru Na voltage gates
• Area of membrane reverses its charge
• Muscle or nerve becomes ________________

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ACTION POTENTIAL

• Event 2
• Instantaneously following the Na leakage, gates
  for _________ close
• Voltage gates for ________ open
• Permeability increases _______ X
• Repolarization

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ACTION POTENTIAL

• Role of Ca
• __________ for Na channels
• Ions that move across the membranes
• 1/100,000 to 1/500,000 of the ions
• Importance? _____________________
• Ionic flow
• Enough Na ions are bled off ________________ area
  that Na gates open and AP begins

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ACTION POTENTIAL

• Spike potential
• Action potential
• Na leak followed by K leak
• Lasts 0.4 ________
• Negative afterpotential
• Excess K leaks out
• Na/K pump

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ACTION POTENTIAL

• Threshold
• Potential that must be reached to trigger an
  action potential
• All-or-none law
• AP same velocity, same intensity, same time span
• Refractory period
• _______________
• Time from Na channels open until K channels close
• _______________
• Time from K channels closed until Resting
  Potential is reached

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MUSCLE

• about 40 of body is skeletal muscle
• another 5-10 is smooth and cardiac muscle
• classify according to location
• a. skeletal- attached to bone
• - 700 different muscles
• b. smooth- internal structures
• c. cardiac- heart

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MUSCLE

• classify according to activity
• a. ______________ - skeletal
• b. ______________- smooth and cardiac
• skeletal may also be voluntary

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CONNECTIVE TISSUE COVERINGS

• Epimysium
• Entire muscle
• Perimysium
• Surrounds fascicles
• Endomysium
• Surrounds individual muscle cells

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ATTACHMENTS

• proximal attachment
• epimysium fuses with ______________ or
  perichondrium
• indirect attachment
• aponeuroses- ___________
• tendons- ______________
• certain tendons such as those of wrist and ankle
  are enclosed by tubes of connective tissue called
  ____________________

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ATTACHMENTS

• ______________- to less moveable end of the
  bone, generally proximal
• _______________- to more moveable end of a bone,
  usually distal

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HISTOLOGY - MUSCLE CELL

• sarcoplasm cytoplasm
• may contain an abundance of glycogen and
  myoglobin
• sarcolemma plasma membrane
• multiple nuclei
• mitochondria
• sarcoplasmic reticulum- smooth ER
• T-tubules -- tunnel-like infoldings
• myofibrils
• 100s lying in parallel are found in a muscle cell

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HISTOLOGY - Myofibrils

• A band, anisotropic band
• M line
• H Zone
• I band, isotropic band
• Z line- Zwischenscheibe means disc
• Sarcomere
• functional contractile unit of the muscle fiber

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THIN MYOFILAMENTS

• actin
• single units - G or globular actin, each has an
  active site
• linear stands- F or fibrous actin
• tropomyosin
• thread-like along surface of actin
• each covers 7 active sites of actin
• troponin
• complex of 3 globular proteins
• One (I) has affinity for actin
• One (T) has affinity for tropomyosin
• One (C) has affinity for calcium

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THICK MYOFILAMENTS

• each myofilament contains about 500 myosins
• myosin
• made up of two identical subunits
• 2 bulbous heads- called cross bridges
• connection between head and tail functions as a
  hinge
• central area which contains no cross bridges is
  called bare zone
• each thick filament has a core of titin which
  will recoil after stretching

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CONTRACTIONSLIDING FILAMENT THEORY

• 1. Exposure of active sites
• calcium ions bind to _____________
• causes troponin to change shape and pull
  ________________ off of active sites of
  _________
• 2. Attachment of crossbridges
• when active sites are exposed, the myosin
  cross-bridges ___________ to them

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CONTRACTION

• 3. Pivoting Power Stroke
• _____________ in myosin head is released causing
  the myosin head to tilt
• tilting of the head pulls the actin
• ADP and P are released from the head
• 4. Detachment of cross-bridges
• once cross bridge is tilted, shape change exposes
  a site in head where _________ can bind
• binding of ATP causes head to ____________ from
  the actin

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CONTRACTION

• 5. Reactivation of myosin
• ATP cleaved once head detaches from actin, ATP
  cleaves to form ADP and P and releases energy
• myosin head contains an enzyme called myosin
  _______________ which releases energy from ATP
• crossbridge to tilt back to its original
  perpendicular position
• energizes the crossbridge
• 6. Rebinds with new active site
• or
• 6. Relaxes

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SINGLE CONTRACTION

• each contraction shortens muscle by about ____
• - each head can carry out about 5 strokes per
  second and each cycle of the head consumes one
  molecule of ATP
• skeletal muscle can shorten up to ______

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NEUROMUSCULAR JUNCTION

• usually one junction located near middle of
  muscle fiber
• ________ receptors located on motor end plate of
  muscle
• Muscle potential
• muscle resting potential -90 mV
• duration 1-5 msec, 5 times longer than in large
  myelinated nerve fibers
• velocity 3-5 meters per sec, 1/18th velocity of
  large myelinated nerve fibers that excites the
  muscle

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RELAXATION

• acetyl cholinesterase (AChE)
• enzyme released into synaptic cleft
• breaks down ACh into _________ and __________
• Calcium pump in the ____________________ removes
  Ca from around the myofilaments
• Ca binds to a protein called calsequestrin in the
  sarcoplasmic reticulum
• troponin changes shape pulling the ____________
  back onto the active sites of _________

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RELAXATION

• Muscle returns to its resting length because of
  two forces
• 1. Elastic components recoil
• 2. Contraction of antagonist muscle helps
  lengthen the relaxed muscle

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TRANSVERSE TUBULES

• impulse flows down to the interior
• T tubules rest on __________________
• impulse stimulates SR to release _______ around
  the myofibrils
• as long as impulses continue, Ca will be released
• continually active Ca pump continually
  concentrates Ca ___________ X higher in the
  interior of the SR

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PATHOLOGIES

• Rigor mortis - no ___________
• muscle begins to stiffen 3 - 4 hours after death
• peaks at about 12 hours and diminishes over the
  next 48-60 hours
• Curare
• from resin of a South American tree
• binds to ___________ receptors only on the motor
  end plate of _____________ muscle
• Myasthenia gravis
• abnormal production of antibodies that destroy
  ACh receptors

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SOURCES OF ENERGYANAEROBIC

• 1. ATP
• ATP --gt _______ ________ Energy
• 2 seconds
• 2. Creatine phosphate
• ADP CP --gt _______ _____________
• 15 seconds
• uses enzyme __________________
• damaged muscle from skeletal or heart muscle can
  leak ___________________ into the blood

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SOURCES OF ENERGYANAEROBIC

• 3. Glycogen --gt glucose --gt ______________
• produces only ______ ATPs per glucose
• produces ATP 2.5 faster than aerobic
• 30 - 40 seconds
• causes ________ to drop
• decreases enzyme activity, muscle contraction
  cannot continue
• _____ of lactic acid diffuses into blood
• heart, kidney and liver cells can use lactic acid
  to produce ATP

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SOURCES OF ENERGYAEROBIC

• 1. ATP
• ATP --gt ADP P Energy
• 2. Creatine phosphate
• ADP CP --gt ATP creatine

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SOURCES OF ENERGYAEROBIC

• 3. Glucose --gt __________ and _____________
• mitochondria
• oxygen
• generates _______ ATPs per glucose
• resting cell -- _______ of its energy
• in activities that last more than ______ minutes,
  provides 90 of ATP

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OXYGEN DEBT OR RECOVERY PERIOD

• heavy breathing is triggered by drop in ______
• repay oxygen debt
• lactic acid --gt _____________ acid
• mostly in the ___________
• reestablish ______________ reserves in skeletal
  muscle
• reestablish creatine phosphate reserves
• reestablish ATP reserves
• replace oxygen removed from ________________ and
  hemoglobin

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Muscle Supplements - Creatine

• Creatine accounts for 180 million of the 800
  million spent on all sports supplements spent in
  1998
• Oral supplements with high doses of creatine
  resulted in 20 increase in skeletal muscle
  creatine
• Possible positive results
• creatine may enhance anaerobic ATP production
  during maximal exercise
• creatine phosphate production may be enhanced
• muscle size may increase

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Muscle Supplements - Creatine

• Potential adverse effects
• Muscle cramping
• increased water retention increases the pressure
  on muscle
• Gastrointestinal effects
• diarrhea and gastrointestinal pain
• Renal dysfunction
• short-term (5 days) creatine supplementation does
  not appear to impair kidney function
• Dehydration
• water retention can increase the risk of
  dehydration

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Muscle Supplements 4-androstenedione and
steroids

• Androstenedione is a prohormone
• converted in the liver and testes to testosterone
• not known if the elevated testosterone levels
  translate into greater muscle mass
• Anabolic steroid are synthetic forms of
  testosterone

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MUSCLE FATIGUE

• poorly understood
• ATP production fails to keep pace with ATP
  utilization
• anaerobic
• pH drop (______________ acid buildup)
• exhaustion of ATP and CP reserves
• aerobic
• deplete glycogen, lipid and protein reserves
• diminished supplies of oxygen
• buildup of carbon dioxide and lactic acid
• physical damage to _____________________

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OXYGEN SUPPLY

• muscle contains oxygen binding protein called
  ________________________
• globular protein is related to hemoglobin
• myoglobin rich cells can contract for longer
  periods
• ________ fibers
• myoglobin poor cells often contract faster
• _________ fibers

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HEAT PRODUCTION

• efficiency of muscle contraction
• at rest ______ of energy is captured, _______
  is released as heat
• active skeletal muscle releases 85 of energy as
  heat
• contributes to maintenance of _______________
• if body becomes too cold
• shivering mechanism- heat can rise 4-5 times
  above normal

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TYPES OF CONTRACTIONS

• 1. Isometric
• muscle attempts to move a load greater than the
  force the muscle can develop
• constant _______________
• ______________ increases greatly
• energy released as ____________ instead of work
• no work being done since object does not move
• causes muscle to hypertrophy to a greater extent
• does little for __________________ system

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TYPES OF CONTRACTIONS

• 2. Isotonic
• constant ______________
• muscle length changes, work is being done
• increases vascularity to skeletal and cardiac
  muscle
• two types
• a. Concentric - muscle tension exceeds
  resistance - muscle _____________
• B. Eccentric - muscle tension does not exceed
  resistance - muscle _____________

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MUSCLE FIBERS - BASIS

• efficiency of myosin-ATPase
• fast or slow
• amount of myoglobin
• red or white
• predominant pathway for ATP
• aerobic or anaerobic

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FAST FIBERS, TYPE II-A (IIx) FIBERS

• most of the skeletal muscle fibers are fast
  fibers
• probably about 1/2 of fibers are these
• characteristics
• fast acting myosin ATPase
• fatigues fast
• small amount of ________________ -- white
• anaerobic pathway for ATP (glycolysis --gt lactic
  acid)
• large in diameter - about ______ times slow
  twitch fibers
• large ______________ reserves
• few mitochondria
• suitable for _____________________ contractions
• example muscles that control fingers and eyes

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SLOW FIBERS, TYPE I (I) FIBERS

• characteristics
• slow acting myosin ATPase
• fatigue resistant
• large amount of myoglobin -- red
• aerobic pathway for ATP
• half the diameter and takes _______ times longer
  to contract after stimulation
• many _________________
• relies more on breakdown of stored _____________
  rather than glycogen
• more extensive capillary system
• example postural muscles of spine

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INTERMEDIATE FIBERSTYPE II-B (IIa)FIBERS

• resemble fast fibers
• characteristics
• fast acting myosin ATPase
• fatigues slower than fast because have more
  extensive capillary system
• small amount of myoglobin -- white
• anaerobic pathway for ATP
• intermediate amounts of mitochondria

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TRAINING

• long distance running
• IIX (fast/anaerobic)) --gt I (slow, aerobic)
• weight lifting
• IIX --gt IIA
• stop weight lifting
• IIA --gt IIX
• building muscle - can increase size (not number)
  of cells by 25
• muscle tears and attracts satellite cells which
  fuse to muscle and add their nuclei
• builds more muscle protein
• Training for anaerobic events
• IIX --gt IIA
• stop for a week before an event, IIA --gt IIX

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TWITCH CONTRACTION

• simplest muscle contraction
• a single stimulus-contraction-relaxation sequence
• 7.5 msec to 100 msec
• isolated twitch is a __________ phenomenon
• periods - 100 msec twitch
• a. _________________ period
• period between application of stimulus and
  beginning of contraction
• about 10 msec
• b. ______________ period - about 40 msec
• c. ______________ period - about 50 msec

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TWITCH CONTRACTION
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TREPPE CONTRACTION

• muscle relaxed for a long time
• muscle contracts more ____________ in response to
  same strength of a stimulus after it has
  contracted several times
• rationale
• Ca concentration increases
• temperature increases

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WAVE SUMMATION

• same stimulus
• second stimulus arrives _______________
  relaxation phase completed, a second more
  powerful contraction occurs
• rationale
• increased Ca release
• energy is put into contraction and not tightening
  of tendons and muscles

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TETANIZATION

• increase frequency and/or magnitude of stimulus
• frequency is finally reached at which successive
  contractions ____________ together
• incomplete tetany
• complete tetany
• ___________ does not have time to be reabsorbed
  into the sarcoplasmic reticulum
• ___________ muscle action
• not same as tetanus produced by Clostridium
  tetani

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TETANIZATION
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TONUS CONTRACTION

• sustained ________________ contraction
• tightens muscle but not enough to produce
  movement
• _______________ muscle cells do not function
  continually
• essential for maintaining posture

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MOTOR UNIT

• all muscles fibers innervated by a single
  ____________________
• average size 150 muscle fibers
• laryngeal muscle- 2-3 fibers
• gastrocnemius- 1900 fibers
• motor unit summation
• activate _____________ motor units first
• asynchronous motor unit summation
• motor units activated on a _____________ basis
• less than maximum tension

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MUSCLE ACTIONS

• agonist or prime mover
• antagonist
• synergist
• fixator

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SMOOTH VS SKELETAL MUSCLE

• nucleus
• skeletal is multinuclear
• smooth - single
• size
• skeletal muscle is 20X larger in diameter and
  1000X longer
• sarcoplasmic reticulum
• skeletal - well developed SR
• smooth - poorly developed

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SMOOTH MUSCLE CELLS
Longitudinal Section
Cross Section
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SMOOTH VS SKELETAL MUSCLE

• T system
• skeletal - well developed
• smooth - no T system but caveolae- shallow
  grooves that may function as a T system
• ratio of thick to thin myofilaments
• skeletal - 1 thick 2 thin
• smooth - 1 thick 15 thin myofilaments
• Z bands, sarcomeres, striations
• none in smooth, found in skeletal
• smooth - has dense bodies that are equivalent of
  Z lines - attach to actin

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SMOOTH VS SKELETAL MUSCLE

• Protein that combines with calcium
• skeletal uses troponin
• smooth uses calmodulin
• associated with myosin
• activates an enzyme called myosin light-chain
  kinase which activates myosin ATPase which
  hydrolyzes the ATP and causes the power stroke
• Nervous system control
• skeletal - somatic motor nervous system
• smooth - autonomic nervous system
• each branch has 20,000 varicosities along its
  length that release neurotransmitters
• there is no motor end plate
• Ca source
• skeletal - sarcoplasmic reticulum
• smooth- extracellular fluid

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SMOOTH VS SKELETAL MUSCLE

• control mechanism
• skeletal - neural, single neuromuscular junction
• smooth - neural, spontaneous, hormonal, oxygen
  and carbon dioxide levels, irritation, stretching
• contraction
• skeletal - rapid onset, tetanization, fatigues
  rapid
• takes 50 - 100 msec
• smooth - slow onset, may tetanize, resistant to
  fatigue
• takes 1 - 2 seconds

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SMOOTH MUSCLE - CONTRACTED
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SMOOTH VS SKELETAL MUSCLE

• Energy source
• skeletal - aerobic or anaerobic with intense
  activity
• smooth - aerobic - takes only 1 of energy as
  skeletal
• Division
• skeletal - fission
• smooth - hyperplasia

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SMOOTH VS SKELETAL MUSCLE

• Change in length
• skeletal - 40
• 20 shorter to 20 longer
• smooth - 150
• 2X longer to 1/2 as long

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SMOOTH MUSCLE TYPES

• 1. multiunit
• composed of discrete smooth muscle fibers
• each operate ________________
• individual fibers separated by glycoprotein
• control is exerted almost entirely by
  __________________
• ex. iris of eye, arrector pili muscle, large
  blood vessels

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SMOOTH MUSCLE TYPES

• 2. unitary or visceral
• most common
• arranged in bundles or sheets and cell membrane
  contact each other via __________ junctions
• usually 2 sheets
• a. longitudinal
• b. circular
• contraction spreads as ______________ waves
• not all muscle cells are innervated by neurons