Title: Unit III Muscular System Structure and Physiology
1Unit IIIMuscular System Structure and Physiology
2Muscle functions
- Producing body motions
- Walking, running, nodding, grasping, etc.
- Stabilizing body positions
- Sustained contractions of neck hold head up
- Storing moving substances within body
- GI tract, cardiac muscle
- Generating heat (_______________)
- Exercise, shivering
34 Properties of muscle tissue
- _________________ respond to stimuli by
producing electrical signals (AP) - ___________ ability of muscle tissue to
contract forcefully when stimulated by AP - _____________ stretch w/out being damaged
- ____________ return to original length shape
after contraction or extension
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5Structure of skeletal muscle, fig 10.1
- Each _______________________________
- composed of 100-1000s cells
- muscle ______ muscle _____ myofibers
- Endomysium CT surrounds each fiber
- B.V. nerves penetrate into muscle
- Perimysium CT surrounds the fascicle
- _______ 10s-100s of cells (fibers) bundled
together - Epimysium CT surrounds many fascicles to bundle
a whole muscle together as an organ
6Structure of skeletal muscle (2)
- All 3 layers of CT (endo, peri, epimysium)
- protect and strengthen
- extend from deep fascia - dense irregular CT bind
muscles w/ similar function - ________ fibrous membrane covering
- Supporting separating muscles
7Submicroscopic skeletal muscle
- _____________ muscle fibers plasma mem.
- Skeletal muscle fibers can have gt100 nuclei just
beneath the sarcolemma - ____________ invaginations in sarcolemma
- tunnel into center of fiber, filled w/ ECF
- assists in exciting entire muscle fiber during AP
- _____________-cytoplasm within muscle fiber
- contains ___________________ ? ATP
- stuffed w/ myofibrils
8- Myofibrils threadlike structures
- contractile elements, extend entire length of
muscle - Arranged in ___________- basic functional units
- Striated appearance
- Myofilaments - composed of contractile proteins
- DO NOT extend whole length of fiber
- 2 types
- _______________________
- _______________________
9- _____________- red, oxygen binding protein
- only in muscle fibers
- Contributes oxygen for ATP synthesis
- Mitochondria- many in skeletal muscle
- Myoglobin sarcoplasm have ingredients for ATP
production - O2
- Glucose
- _____________________ (SR)- fluid-filled system
of membranous sacs, similar to sER - in relaxed muscle stores Ca 2
- release of Ca 2 causes muscle contraction
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11- ____________- appearance due to light I bands and
dark A bands - ____________- small mesodermal cells
- Embryonic skeletal muscle fibers arise from
fusion of 100 or more - 100s of nuclei
- Satellite cells- myoblasts persisting in mature
skeletal muscle - capacity to fuse w/ one another or w/ damaged
muscle fibers - Regenerate functional muscle fibers
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14Motor neuron its muscle fibers
- Figure 10.11- neuromuscular junction (NMJ)
- __________________- motor neuron all the muscle
fibers it stimulates - __________________- region of sarcolemma that
includes Ach receptors - Near synaptic end bulbs
- ___________________ (NMJ)- a synapse between axon
terminals of a motor neuron sarcolemma of a
muscle fiber
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16Graded potential
- ________________ from membrane potential that
makes the membrane more or less polarized (Na
Ca 2 in, K out) - occur in dendrites cell body of the motor
neuron - if graded potential reaches the axon
- voltage-gated ion channels open?AP
17All-or-none principle
- When ______________ voltage is reached voltage
gated channels will open and an action potential
occurs - Different neurons may have different thresholds
BUT the point is - ________________________________
- Push over first domino, the rest fall
18- __________________- molecules within axon
terminals - Released into synaptic cleft in response to
- Nerve impulse
- Change in membrane potential
- ___________________- NT released at NMJ
- 1000s of molecules in each synaptic vesicle
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20- Acetylcholine receptor (AChR)- at each motor end
plate 30-40 million - Transmembrane protein binds ACh
- Binding opens ligand-gated ion channels
- Acetylcholinesterase (AChE)- enzyme breaks down
ACh, attached to ECM in synaptic cleft - ACh binding lasts only briefly
- Breaks down excess not bound to receptor
21- Nerve elicits a muscle action potential
- Release of ACh- diffuses across synaptic cleft.
- Activation of AChR binding opens gated ion
channels allowing flow of small cations (most
importantly Na) - Production of muscle AP inflow of Na ?inside
fiber charged, changing membrane potential,
trigger AP - Termination of ACh activity effect of ACh
binding lasts briefly (ACh rapidly broken down by
AChE) - NMJ usually located at midpoint of muscle fibers
propagate toward both ends
22Excitation - depolarization
- Increased Ca 2 concentration in cytosol
initiates muscle contraction - Ca 2 ? due to depolarization of muscle cell
membrane sarcolemma - AP from neuron ? ACh receptors opening Na
channels on the sarcolemma which depolarizes the
muscle- muscle AP travels along T tubules
causing SR to release Ca 2
23Skeletal contraction proteins
- Myofibrils built from 3 types protein
- ________________ proteins- generate force
- Actin and myosin
- ________________ proteins- switch on and off
- Troponin and tropomyosin
- Both are part of the thin filament
- ________________ proteins- proper alignment,
elasticity, extensibility, link myofibrils to
sarcolemma and ECM - ?12 titan, myomesin, dystrophin
24Sliding filament theory fig 10.7,8
- Muscle contraction
- ______ heads attach walk along _____
- Walking towards both ends of sarcomere
- Thin filaments ? M line
- Thick filaments ? Z disc
- Length of thick and thin NOT changing
- Sarcomere shortening ? whole muscle fiber
shortens ? shorten entire muscle
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26- _______- motor protein (push and pull)
- found in all 3 types muscle
- 300 molecules/thick filament
- ______________- convert chemical energy in ATP to
mechanical energy of motion force production - Shaped like 2 golf clubs twisted together
- ______- molecules join to form filament in form
of helix - On each actin molecule is a myosin binding site
for myosin head to attach
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28The contraction cycle, fig 10.8
- Ca 2 released from SR
- Binds troponin-tropomyosin complex move it
- In relaxed muscle, myosin binding sites are
blocked by - ______________- Are held in place by
_______________ - Contraction cycle can begin
- ATP hydrolysis
- Myosin attaches actin, form crossbridges
- Power stroke
- Detachment of myosin from actin
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30Contraction of skeletal muscle
- Treadmill analogy
- Myosin moving draws Z discs together
- neighboring sarcomeres pulled together
- Skeletal muscle shortens, pulls CT tendons
- Tension passes thru tendon, move bone
- Fig. 10.11 to summarize contraction
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33Calciums role
- ? Ca2 in cytosol starts contraction
- (decrease stops contraction)
- Muscle fiber relaxed Ca2 low, BUT huge amt of
Ca2 stored in SR. - AP propogates along sarcolemma ?T tubules,
________________________ in SR membrane open - Ca2 flows out into cytosol, combines with
troponin to change its shape - Myosin binding sites are now free
34Sources of energy
- Figure 10.12
- ______________ powering contraction cycle,
pumping Ca2 to SR for relaxation ( other
metabolic rxns) - Relaxed state- modest amount used
- Contracting- using at rapid pace
- Amt present only enough for a few seconds of
contraction - If strenous activity more ATP made
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363 ways to produce ATP
- _____________________________
- Unique to muscle fibers
- While relaxed, muscle making more ATP than needed
- Excess ? creatine phosphate an energy rich
molecule - Enzyme creatine kinase (CK) catalyzes transfer
of one phosphate of ATP to creatine ?creatine
phosphate ADP - When contraction begins, ADP levels ? so CK
transfers phosphate group from creatine phosphate
back to ADP creating ATP (enough energy to last
15 sec) - _______________________________
- _______________________________
37Cellular respiration muscle
- Anaerobic- ATP-producing rxns, without O2
- Muscle activity but no creatine phosphate ?
glucose is catabolized to generate ATP - Glucose blood ? muscle fibers, glycogen
breakdown within muscle - Glycolysis 1 glucose ?(10 rxns) 2 pyruvate
yields 2 ATP - Pyruvic acid enters mitochondria enters series
of O2 requiring rxns to produce large amt of ATP - If no O2, pyruvic acid ? lactic acid in cytosol
- Liver cells take lactic acid ? glucose
38- Aerobic cellular respiration- series of O2
requiring rxns in the mitochondria produce ATP - muscle activity longer than ½ minute
- Pyruvic acid? ATP, CO2, H2O, and heat
- Slower than glycolysis BUT yields more
- 1 glucose ? 36-38 ATP molecules.
- F.a. molecule ? over 100 ATP molecules
- Oxygen comes from
- Diffuses into muscle from blood
- Released from myoglobin within muscle fibers
39Motor unit recruitment
- Process of ____________________________
- Typically different motor units in a whole muscle
are NOT stimulated to contract in unison - Alternation delays muscle fatigue
- Contraction of whole muscle can be sustained for
long pds - One factor responsible for producing smooth
movements rather than series of jerks - Recruitment causes small changes in muscle tension
40Comparing isotonic isometric
- ___________ contraction- iso same, tonic
tension - Contraction where tension remains same
- Occurs when constant load is moved thru the range
of motions possible at a joint - Lifting a book off a table
- _______________ contraction- iso same, metric
measure - Contraction in which tension of the muscle
increases but there is only minimal shortening so
that no visible movement is produced - Holding a book in an outstretched hand
41Simple twitch figure 10.15
- __________________- brief contraction of all
muscle fibers in motor unit due to a single AP in
motor neuron - Myogram
- Skeletal muscle twitch 20-200msec
- _____________ period- brief delay between
application of stimulus beginning of
contraction (_at_2msec) - Ca2 being released from SR filaments exert
tension, elastic components stretch, shortening
begins
42- _______________ period 10-100msec
- _______________ period 10-100msec
- Active transport of Ca2 back into SR
- Duration of all periods depends on type of muscle
fiber (see table 10.1) - Fast twitch (as in eye) 10 msec for each
contraction and relaxation - Slow twitch (as in legs) 100 msec for each
contraction and relaxation
43Repolarization happens
- During the relaxation period Ca2 is actively
transported back to the SR - Refractory period period of lost excitability
- Characteristic of all muscle and nerve cells
- Duration varies with muscle involved
- Skeletal ? 5msec
- Cardiac ? 300msec
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45- ___________ minimum stimulus the least amount
of voltage required for contraction - _________________ the voltage at which maximal
force is generated (increasing voltage will not
increase force of contraction) - All motor units are stimulated
- All muscle fibers are contracting
- Graded response (graded potential) small
deviation in the membrane potential that makes
the membrane more polarized or less polarized
46Terms assoc. w/ frequency
- _______________________________-
- Maximal voltage applied to muscle in which all
fibers in unit are stimulated - series of shocks at max voltage causes separate
twitches - each twitch will stronger than the previous
- Stimuli all at same intensity, cause muscle to
contract more efficiently each time - May be warm-up effect, due to ? intracellular
Ca2 needed for contraction
47- Wave summation- (summation of contraction) ?
strength of muscle contraction that results when
muscle APs occur one after another in rapid
succession - ? frequency ? strength of contraction
- Tetany- fused tetanus -hyperexcitability of
neurons muscle fibers - Sustained or fused contraction
- Continuous tonic muscular contractions
individual twitches not discerned - May be due to hypoparathyroidism
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49Muscle fatigue
- Inability to mantain force of contraction after
prolonged activity - usually results from ? w/in muscle fiber
- May feel tired, desire to cease activity
- Central fatigue (CNS)
- Mechanism unknown, possibly protective
- Suspect contributing factors
- Inadequate release of Ca2 from SR
- Depletion of creatine phosphate (ATP levels not
much change) - Insufficent oxygen, depletion of glycogen,build
up of lactic acid and ADP, failure of AP to
release Ach
50Recovery oxygen uptake
- Formerly called ___________________ the added
oxygen that is taken into body after exercise - Recovery few minutes to several hours depending
upon intensity of exercise - Depletions during exercise
- Convert lactic acid ? glycogen in liver
- Resynthesize creatine phosphate ATP
- Replace oxygen removed from myoglobin
- Post exercise oxygen needs remain high
- ? body temp ? chemical rxns
- Heart muscles still working hard ? ? ATP use
- Tissue repair processes
51Definitions
- Tonus Muscle tone - state of partial contraction
- characteristic of normal muscle
- maintained at least in part by a continuous motor
impulses originating from reflex, and serves to
maintain body posture - AKA muscle tone
- ______________- wasting away or decrease in size
of a part due to a failure, abnormality of
nutrition, or lack of use - _______________- excessive enlargement or
overgrowth of tissue without cell division
52Cardiac muscle
- Figure 20.9, table 10.2
- Only in heart
- forms most of the heart wall
- Striated
- Action is involuntary
- alternating contraction relaxation cannot be
consciously influenced. - beats due to pacemaker- ________________
53Cardiac muscle (2)
- Requires constant O2, many mitochondria
- Hormones and neurotransmitters adjust heart rate
by speeding or slowing the pacemaker - _______________- thickening of sarcolemma
connecting ends of fibers together - Gap junctions to communicate from cell to cell
54Smooth muscle, fig 10.18, 19
- In walls of hollow internal structures
- b.v., airways, and most organs of abdominopelvic
cavity, also in skin and attached to hair
follicles. - Looks ____________________________
- Action is usually ___________, some also has
autorhythmicity-built in or intrinsic rhythm. - Regulated by neurons of autonomic NS and by
endocrine hormones - Compared to other types of muscle cells
- Contraction usually slower, lasts longer
- Can stretch and shorten to greater extent
55Muscle disorders myopathies
- Myopathy- signifies disease or disorder of
skeletal muscle tissue. - Neuromuscular diesase problems at all 3 sites
- Somatic motor neuron, NMJ muscle fibers
- Myasthenia gravis autoimmune disease, chronic,
progressive damage to NMJ - AB bind and block AchR at motor end plates
- 75 of patients have hyperplasia or tumors of
thymus - Thymic abnormality may be the cause
- 1st affects eye? swallowing, chewing,
talking?limbs - Death may result from paralysis of respirtory
muscles - Anticholinesterase drugs (inhibits AchE)
56- Muscular dystrophy- group of inherited muscle
destroying diseases - Degeneration of skeletal muscle fibers
- DMD Duchenne muscular dystrophy
- Mutation on X chromosome ? strikes males almost
exclusively - Difficultly running, jumping, hopping
- Unable to walk _at_12, resp or cardiac failure
usually ? death between 20-30 yrs - Gene defect protein dystrophin
- Little or no dystrophin, sarcolemma tears during
contraction - Gene therapy- inject myoblasts w/functional gene
57- _______________- painful, nonarticular rheumatic
disorder - Usually ages 25-50, 15X more in females
- Affects fibrous CT components of muscle, tendons
and ligaments - Pain at tender points from gentle pressure
- Fatigue, poor sleep, headaches, depression
- ______- sudden involuntary contraction of single
muscle of large muscle group - __________- painful spasmodic contraction
58- ______- spasmodic twitching made involuntarily by
muscles that are usually under voluntary control - Eyelid, facial muscles
- _____________- rhythmic, involuntary, purposeless
contraction that produces quivering or shaking - _____________-involuntary brief twitch of an
entire motor unit that is visible under skin - _________________- spontaneous contraction of
since muscle fiber that is not visible but can be
recorded - May signal destruction of motor neurons