Biology 350: Biology 350: Biology & Space ExplorationBiology & Space Exploration
Biology 350: Biology 350: Biology & Space ExplorationBiology & Space Exploration
Col Ronald D. Reed, PhDProfessor & Head of Biology
U.S. Air Force Academy 1999
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1. Define key terms/concepts
2. Describe muscle structure & function; explain how normal hypertrophy occurs
3. Describe muscle fiber types and how contraction & relaxation occur (isometric vs. isotonic; concentric vs. eccentric)
4. Explain atrophy with disuse or disease on Earth; compare to selective atrophy of spaceflight (muscle types & groups); discuss possible mechanisms
5. Describe the adaptation to different loading conditions on Earth & in microgravity
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Ob
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6. Describe bone & connective tissue structures
7. Discuss mechanisms linking physical activity/ stress to the maintenance & reformation of bone
8. Explain bone loss in microgravity, including its long-term impacts; relate to hormonal or other changes
9. Explain the role of intervertebral discs in weightbearing and spinal movements; correlate to mechanisms of spinal lengthening and back pain in space
10. Discuss countermeasures and evaluate their effectiveness vs. musculoskeletal changes in space
Some mission patcheswhen effects were
studied
Skeletal Muscle FunctionsSkeletal Muscle Functions
Exert force to change joint angle Concentric - muscle shortening Eccentric - muscle lengthening
Exert force to maintain joint angle - isometric (static tension)
Produce body heat
Review of AnatomyReview of Anatomy
Whole Muscle Muscle fiber (cell) Myofibril Sarcomere Myofilaments
Myosin Actin Cross-bridging & “ratcheting”
Z membrane(end of sarcomere)
Cross-bridgeBinding Site(need Ca2+)
Thick Filament (myosin)
Thin Filament (actin)
Muscle contractionMuscle contraction
Coupled reaction:
Chem. energy physical motion
ATP hydrolysis force
[Ca2+] in cell allows reaction
Slow- & fast-twitch muscle specializations
Twitch Rate Slow FastGlycogen Content Low HighGlycolytic Capacity Low HighFatigue Resistance High LowRespiration Type Aerobic AnaerobicCapillary Supply High Low
Slow- & Fast-Twitch MusclesSlow- & Fast-Twitch Muscles
Slow-twitch found more in muscles (like postural muscles)that must sustain contractions for long times without fatigue.Depend relatively more on fats for energy.
Atrophied Fiber
Control Fiber
Force (% of Peak Force)
Pow
er
(un
x f
t/s)
Studies of Rat Hindlimb Muscle, Nerves, Biomechanics, etc.
Studies of Rat Hindlimb Muscle, Nerves, Biomechanics, etc.
Focus on antigravity (postural) muscles
Why hindlimb? In g rats use forelimbs to move in cages; hindlimbs float except for grasping. Also, have Earth model.
Results:
Significant atrophy, protein & mass
Shift in major muscle fiber type (ST FT)
capacity to break down certain nutrients & some shift from fat to glycogen use in ST
Studies of Rat Hindlimb Muscle, Nerves, Biomechanics, etc.
Studies of Rat Hindlimb Muscle, Nerves, Biomechanics, etc.
More Results: Muscle atrophy in g not returned
to normal in 14 days back on Earth susceptibility to damage
on return to Earth Interstitial edema & lesions in
sarcomeres developed postflight -- damage
May impair movements linked to antigravity muscle function and/or postural control
Some Human Results in Spaceflight
Some Human Results in Spaceflight
On one 27-day mission: 10% leg muscle volume
20% strength
Negative nitrogen balance (muscle & body) Highest day #1 ( food intake)
lean body mass, especially calves, & strength
Negative phosphate balance
Some fatiguability (plus, see on landing)
Some evidence reach new steady state with time
Motion & Coordination Issues
Motion & Coordination Issues
Rearrange biomechanical nature of moving Changes relation of body mass & effort
Elimination of static work & dynamic work activity of postural-tonic musculature Few eccentric muscle contractions
No “gravity assist” when lowering objects No “gravity fighting” posturally
175-day Russian missions show atrophy leads to increase EMG signal per torque
Formation of new coordination patterns and alteration of the motor activity as a whole
Summary of Some Causes for Muscle Changes in gSummary of Some Causes for Muscle Changes in g
Removal of mechanical loads & less work for many muscle groups
Deconditioning of postural muscles Elimination of foot support Restructuring of normal motor patterns Fluid shifts, microcirculatory changes,
or altered tissue nutrition?
Bones !Bones !
Dynamic, living tissue
Mechanical support
Calcium hemostasis
Strength due to matrix of calcium, phosphorous, and collagen
Cells in BoneCells in Bone
Osteoblasts - bone-forming
Osteoctyes - embedded osteoblasts
Osteoclasts - Breakdown bone & release Ca2+
Formation or Resorption?Formation or Resorption?
Depends on stress (“?” Effect) & hormones
In space, overall: Bone demineralization strength & density Metabolic changes & Ca2+ mobilization Elevated Ca2+ excretion (I.e., negative
calcium balance)
Bone
Osteo______?Blood
Calcium
Osteo______?
Net Calcium BloodFactor -blasts -clasts Absorption Calcium
Physical Activates Inhibits N/A No DirectStress Effect
Calcitonin ? InhibitsPTH ? Activates
Intestine&
Kidney
Net CalciumAbsorption
Bone
Osteo______?Blood
Calcium
Osteo______?
Net Calcium BloodFactor -blasts -clasts Absorption Calcium
Physical Activates Inhibits N/A No DirectStress Effect
Calcitonin ? Inhibits Decreases DownPTH (PH) ? Activates Increases Up
Intestine&
Kidney
Net CalciumAbsorption
Mechanism of g DemineralizationMechanism of g Demineralization
Not well known Removal of gravitational load on the
skeleton Changes in blood flow and
metabolism in bones Changes in hormonal and immune
status
Bone, Calcium, & Space Flight (Morey-Holton, et al.)
Bone, Calcium, & Space Flight (Morey-Holton, et al.)
Used young rats in rapid growth stage Housing affects the response
Animals housed individually showed more in-flight changes & slower readaptation to Earth than animals in group cages
Not all regions of bones or all bones affected Long bones formation on the periosteal
surface, but not endosteal surface No changes in the ribs, vertebra ,or maxilla
(jaw), so response is not same everywhere
Pathophysiology of Mineral Loss in Space Flight (Arnaud, et al.)
Pathophysiology of Mineral Loss in Space Flight (Arnaud, et al.)
In g calcium is lost from bones, blood calcium , & calcium is excreted in the urine.
This study examined changes in the balance of calcium entering and leaving the body. Saw: loss of calcium Parathyroid hormone was consistent with
response to the calcium levels
The Musculoskeletal System in Space
NASA video AAV-1543
The Musculoskeletal System in Space
NASA video AAV-1543
Notes from video: Adaptations to MicrogravityNotes from video: Adaptations to Microgravity
Muscle atrophy Reduce muscle tone and strength Increased muscle fatigue Reprogramming muscle synergism Reduced motor control Motor endplate degeneration Increased contraction velocity Bone demineralization and redistribution Connective tissue degeneration Back pain
Z membrane
Cross-bridgeBinding Site
Thick Filament (myosin)
Thin Filament (actin)
Muscular System SpecificsMuscular System Specifics
Does adapt, but have weakness -- possible muscle tears
See muscle atrophy, especially slow-twitch Decreased tone, strength, & size (regional) Decreased protein synthesis Negative nitrogen balance Increased plasma amino acids Increased plasma creatinine & 3-
methylhistidine
Physiological mechanisms that may explain muscle related adaptations associated with microgravity
Loss of static & dynamic loads along longitudinal axis of body
Cephalic fluid shifts
Adaptations associated with the skeletal system during microgravityAdaptations associated with the skeletal system during microgravity
External forces are decreased Bone synthesis is reduced Bone architecture and composition
are modified to accommodate the new lower load conditions
Altered calcium metabolism Reduced bone strength
Bone mineral densityBone mineral density
Normal changes in overall whole body bone density
Increased 4.2% in skull ! Bone loss is functional (structural &
mineral changes; impacts overall quality) Calcium loss at rapid rate at first, then
continues (plateau?) Data suggest bone loss occurs at rates of
0.5 - 2.0% / month
2 Mechanical factors affecting bone loss2 Mechanical factors affecting bone loss
Changes are regional and function specific
Loading bearing Muscle pull - Greatest site of
mineral loss is at muscle insertion sites
Possible physiologic mechanism underlying skeletal deconditioningPossible physiologic mechanism underlying skeletal deconditioning
Principal stimuli to skeleton are altered Biomechanical stress Fluid pressure Bone redistribution from feet to
head during space flight Cell mechanism unknown
Spaceflight(- biomechanical stress/fluid shifts)
+ serum Calcium levels
- Parathyroid hormone
+ Serum Phosphorous
- 1,25 dihydroxyvitamin D
- Intestinal calcium absorption
- Calcium balance
Calcium/Endocrine SkeletonFocal/Regional
Resorption > formation
Diet
Adrenal Activity
Calcitonin
- Bone Mass
+ Urinary CalciumExcretion
Spinal ChangesSpinal Changes
Increased height 68% experience back pain Possible Factors
Spine unloading Intervertebral disc swelling Spinal lengthening Outer disc annulus and facet joint distension Spinal ligament stretching Paraspinal muscle stretching Nerve root dysfunction
Countermeasure for overall musculoskeletal deconditioningCountermeasure for overall musculoskeletal deconditioning
Current countermeasures Treadmill Rowing Bicycle
Current measures time consuming (how much?) & ineffective (why?)
Recovery on Earth also incomplete
Potential countermeasures for musculoskeletal deconditioningPotential countermeasures for musculoskeletal deconditioning
Exercise: Resistive Aerobic
Human centrifuge Exercise against LBNP (possibly
with counter-pressure suit) Pharmacologic agents -- e.g.??
Benefits of research to EarthBenefits of research to Earth
Disease - osteoporosis, muscular dystrophy
Fracture healing Rehabilitation
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