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Anatomy Unit 3 Part 2


Chap 11 Muscl Es Unit
  
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Universal Characteristics of Muscle (5)
 

- responsiveness
- conductivity
- contractability
- extensibility
- elasticity
Responsiveness
 

- (excitability)
- capable of response to chemical signals, stretch or other signals, and responding with electrical changes across the plasma membrane
Conductivity
 
local electrical charge triggers a wave of excitation that travels along the muscle fiber
Contractility
 
shortens when stimulated
Extensibility
 
capable of being stretched
elasticity
 

returns to its original resting length after being stretched
Myofibers (muscle fibers)
 

- voluntary striated muscle attached to bones
- as long as 30 cm
Muscle fiber drawing
 
page 406
Triad
 
T tubule and 2 terminal cisternae
Active Site
 
region of a protein that binds to a ligand
Sarcolemma
 

plasme membrane
tunnel like T-tibules that penetrate the cell
carry electric current to cell interior
Sarcoplasm
 

cytoplasm
contains myofibrils, glycogen, myoglobin, mitochondria
Sarcoplasmic Reticulum
 

smooth endoplasmic reticulum
network around each myofibril
Myofibrils
 
bundles of parallel protein microfilaments called myofilaments
Myofilaments
 
3 types: thick, thin, elastic
Terminal Cisternae
 
dilated end sacs that store calcium
Thick filaments
 

made up of ab. 500 myosin molecules
2 intertwined polypeptides (golf clubs)
arranged in a bundle with heads directed outward in a spiral array around the bundled tails
Bare Zone
 
central area with no heads
Thin Filaments
 

2 intertwined strands of fibrous actin (string of golf balls)
have active site for tropomyosin and troponin
G Actin (globular)
 
a subunit of fibrous actin with an active site (individual golf ball)
Tropomyosin
 
a "bar" that blocks the active sites for G actin
Troponin
 

"pad-lock"
calcium binding molecule stuck to each tropomyosin molecule
Elastic Filaments
 

keeps thick and thin filaments aligned with each other
resists overstretching
helps the cell recoil to its resting length
Titin
 

huge springy protein
runs through core of each thick filament
connects thick filament to Z disc
Contractile Protein
 

does the work
ex: myosin and actin
Regulatory Protein
 

ex: troponin and tropomyosin
act like a switch that starts and stops shortening of muscle cell
Accessory Protein
 

ex: dystrophin
links actin of outermost myofilament to peripheral protein
Striations
 
myosin and actin organized in a precise way to produce dark and light bands due to overlapping
A Band
 

dark band of striation
think and thin filaments overlap
I Band
 

light band of striation
thin and elastic filaments overlap
Sarcomere
 
the segment of the myofibril from one Z disc to another
Motor Unit
 
motor neuron and the muscle fibers it innervates
Small Motor Unit
 

fine degree of control
ex: writing tiny letters
Large Motor Unit
 

more strength than control
powerful contractions supplied by large motor units
ex: kicking a door
Synapse
 
point where a nerve fiber meets its target cell
Neuromuscular Junction
 
when target cell is a muscle fiber
Neuromuscular Junction Drawing
 
p. 411
Synaptic knob
 

swollen end of a nerve fiber
contains synaptic vessicles with acetylcholine
ACh released through exocytosis
synaptic cleft
 
tiny gap between synaptic knob and muscle sarcolemma
Schwann Cell
 

envelops and isolates all of the NMJ from surrounding tissue fluid
prevents leakage
Basal Lamina
 

thin layer of collagen and glycoprotein separates schwann cell and entire muscle from surrounding tissues
contains acetylcholinesterase
Polarized
 
having a charge
Resting Membrane Potential
 

due to Na outside of cell and K and other anions inside of cell
-90 mV maintained by the sodium potassium pump
Depolarization
 

moving away from -90 mV
ion gates open allowing Na to rush into cell makind ICF briefly positive
Repolarization
 

going back towards -90 mV
K rushes out of cell making ICF negaitve again
Action Potential
 
quick up and down voltage shift
4 Actions involved in muscle contraction and relaxation
 

1) excitation
2) excitation
3) contraction
4) relaxation
1st step of contraction
 

arrival of nerve signal
nerve signal stimulates voltage gated calcium channels that result in exocytosis of synaptic vesicles containing ACh
2nd step
 
ACh is released
3rd step
 
ACh binds to a receptor on muscle cell
4th step
 

ligand gate opens and causes an end-plate potential
End Plate Potential
 

when Na and K channels open
voltage blips from -90 to 75 quickly
5th step
 

opening of voltage-regulated ion gates
action potentials are created
6th step
 
action potentials spreads down into T tubules
7th step
 
terminal cisternae release calcium
8th step
 
calcium binds to troponin
9th step
 
tropomyosin shifts and active sites on actin are exposed
10th step
 

myosin ATPase in myosin head hydrolyzes an ATP molecule, activating the head and cocking it in an extended position
(causes myosin to bend and come in contact with actin at active site)
11th step
 

myosin-actin cross bridge is formed
(binds to active site on actin)
12th step
 
power stroke (sliding of thin filament over thick filament)
13th step
 

with the binding of more ATP, myosin head releases the thin filament and extends to attach to a new active site further down the thin filament
(binding of new ATP, breaking of cross-bridge)
14th step
 
nerve stimulation ceases and acetylcholinesterase removes ACh from receptors so stimulation of the muscle cell ceases
15th step
 
ACh breaks down acteylcholinesterase
16th step
 

reabsorption of calcium ions by sarcoplasmic reticulum
* calsequestrin
Caslsequestrin
 
isolates calcium
17th step
 

loss of calcium ions from troponin
this moves over the active sites which stops the production or maintence of tension
18th step
 
return of tropomyosin to position blocking active sites of actin
Muscle TOne
 

partial contraction
(makes it not flabby)
Length Tension Relationship
 
amount of tension generated depends on length of muscle before it was stimulated
Threshold
 
minimum voltage necessary to produce action potential
Twitch
 
a single brief stimulus at that voltage produces a quick cycle of contraction and relaxation
Latent Period
 
2 msec delay between the onset of stimulus and onset of twitch response
6 Reasons a twitch will vary in strength
 

1) stimulus frequency
2) concentration of Ca in sarcoplasm
3) how stretched a muscle was before it ws stimulated
4) temperature of muscles
5) lower pH
6) hydration of muscles
Recruitment
 

the process of bringing more motor units into play
MMU
 

multiple motor unit (recruitment)
ex: jug of milk, big box
Treppe
 

each twitch develops more tension than the one before
staircase
Temporal Summation
 
results from 2 stimuli arriving close together
Wave Summation
 
results from one wave of contraction added to another
Incomplete Tetanus
 
each stimulus arrives before the previous twitch is over
Complete Tetanus
 
no time to relax between stimuli so twitches fuse into smooth prolonged contractions
Isometric Muscle Contraction
 

develops tension without changing length
ex: the muscle tension right before you pick up something heavy
Isotonic Muscle Contraction
 

"keep same tone"
concentric and eccentric
Concentric
 

tension development while shortening
ex: curls, lifting the book
Eccentric
 

tension development while lengthening
ex: curls, letting it back down
How a muscle meets immediate demand for energy
 

- short, intense exercise
- 2 enzyme systems control these phosphate transfers
- phosphagen system
Immediate demand for energy in short, intense exercise
 

Oxygen need is briefly supplied by myoglobin (stored)
muscles get ATP by borrowing phosphate groups from other molecules and transfering them to ADP
Myokinase
 
transfers phosphate group from one adp to another
Creatine Phosphate (CP)
 
phosphate-storage molecule
Creatine Kinase
 

obtains phosphate group from CP
fast-acting system that helps maintain the ATP level while other ATP-generating mechanisms are being activated
Phosphagen System
 

ATP and CP collectively
provides nearly all energy used for short bursts of intense activity
Muscle meets Short Term demand for Energy
 

as phosphagen system is exhausted, muscles shift to anaerobic fermentation
- muscles get glucose from blood and stored glycogen
- glycogen lactic acid system
- produces enough atp for 30-40 sec. of activity
Glycogen Lactic Acid System
 
converts glucose to 2 ATP and lactic acid (toxic) in the absense of oxygen
Muscle meets Long Term demand for Energy
 

after a few seconds, respiratory and cardio systems catch up and deliver oxygen to the muscles fast enough for aerobic respiration to meet ATP demands
- aerobic respiration produces 36 ATP per glucose
Fatigue
 
progressive weakness and loss of contractility from prolonged use
Causes of Fatigue
 

- ATP synthesis declines as glycogen is consumed (run out of glucose)
- ATP shortage
- lactic acid lowers pH of sarcoplase making enzymes not work
- extra K lowers membrane potential and excitability
- motor nerve fibers use up ACh
- brain fatigues by unknown process
Oxygen Debt
 
the difference between the resting rate of oxygen consumption and the elevated rate following exercise
EPOC
 

excess post-exercise oxygen consumption- when heavy breathing continues after strenous exercise
- 11 extra liters of oxygen is needed after strenous exercise
4 purposes of extra oxygen
 

1) replease oxygen reserves of myoglobin depleted in the first minute of exercise
2) replenish the phosphagen system
3) oxidizing lactic acid
4) keep the metabolic rate elevated
Slow Oxidative muscle fibers
 

slow-twitch, red, or type I
abundant mitochondria, myoglobin and capillaries (blood)
adapted for aerobic respiration and fatigue resistance
Fast Glycolytic muscle fibers
 

fast-twitch, white, or type II fibers
well adapted for quick responses, bur not fatigue resistance
rich in enzymes... causing fatigue
(fast borrowing)
poor in mitochondria, myoglobin, and blood capillaries- pale apperance
Factors that affect muscle strength
 

1) muscle size
2) fascicle arrangement
3) size of motor units
4) multiple motor unit summation- recruitment
5) temporal summation
6) length-tension relationship
7) fatigue
Resistance Exercise
 

weightlifiting
stimulates cell enlargement due to synthesis of more myofilaments
myofibrils gorw thicker
Endurance Training
 

aerobic exercises
produces an increase in mitochondria, glycogen, and density of capillaries
Skeletal vs. Smooth vs. Cardiac muscles
 
table 11.5 page 431
Smooth Muscles response to stretch
 

stretch opens calcium gate
stress-relaxation response necessary for hollow organs that gradually fill
must contract forcefully when greatly stretched
ex: bladder, esophagus

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