Download 6) Muscular System - Cal State LA

Biology of Human Aging
CHAPTER 6
The Muscular System
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Outline
Review of Structure and Function
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
Age-Related Changes
Skeletal Muscle
Smooth Muscle
Cardiac Muscle
Age-Related Dysfunctions
Parkinson’s Disease
Myasthenia Gravitis
Muscle Cramps
Polymyositis
Polymyalgia
Rheumatica
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
The Muscular System
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Introduction
 More than 600 muscles in our body
 Some so small; the action of obscure of taken for granted (close eyes,
compress chicks, from, smile)
 Aware of larger muscles (joint movement, standing erect [defy gravity],
walking, running)
 Substantial time & effort to develop larger muscles to improve appearance
 Changes in muscular system over time can greatly affect self-image
(confidence)
 Muscles composed of contractile cells that develop tension and shorten
 Some muscles attach to the bone on each side of joint  contraction &
shortening moves the bone
 Some muscles do not attach bones, located in the walls of organs (blood
vessels)  contraction  compresses organ  emptying the organ, material
movement, OR causing heat to maintain normal body temperature
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Review of Structure and Function
 The three types of muscle tissue are:
1.
2.
3.
skeletal muscle
cardiac muscle
smooth muscle
 These types differ in structure, location, function, and
means of activation
 Each type of muscle possess unique structure and
perform specialized functions
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Skeletal Muscle
 Mostly attach to bones; cause movement of the joints
 Voluntary; contraction under conscious control of individual
 sometimes involuntary; reflex acts, painful stimuli, upright
posture
 Contractions under control of signals transmitted by
somatic nervous system
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Microscopic analysis
Skeletal muscle cells (muscle fibers) contain > one nucleus,
alternating light & dark bands  striated or striped appearance
Bands: numerous regularly aligned thread-like myofibrils
oriented length-wise along the muscle fiber
myofibrils separated into a series of repeating segments
named Sarcomeres by thin, dark lines extending across them
Myofibrils are composed of two types of myofilaments
Thick filaments: myosin, Thin: actin, tropomyosin, troponin
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Skeletal Muscle
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Skeletal Muscle Tissue
 Packaged in skeletal muscles that attach to and cover
the bony skeleton
 Has obvious stripes called striations
 Is controlled voluntarily (i.e., by conscious control)
 Contracts rapidly but tires easily
 Is responsible for overall body motility
 under the control of Somatic nervous system
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Mechanism of Skeletal Muscle Contaction
Nerve impulse  surface of muscle  release of acetyl choline
into neuromusclular junction (separates muscle & nerve fiber)
Ach depolarizes muscle membrane  deep into transverse
tubules
Depolarization (Nerve impulse)  release of Ca2+ from ER
Movement of troponin and tropomyosin from their usual site
actin X myosin  cross-bridges b/w thin and thick filaments
ATP hydrolysis  energy for shortening of cross-bridges
thin filament slides in relation to thick
Simultaneous sliding of thousands filaments  muscle
contraction
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Excitation-Contraction Coupling
Figure 9.9
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Skeletal Muscle: Nerve and Blood Supply
Each muscle is a discrete organ composed of muscle tissue,
blood vessels, nerve fibers, and connective tissue
 Each muscle is served by one nerve, an artery, and one
or more veins
 Each skeletal muscle fiber is supplied with a nerve
ending that controls contraction
 Contracting fibers require continuous delivery of oxygen
and nutrients via arteries
 Wastes must be removed via veins
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Cardiac Muscle Tissue
Occurs only in the heart
Is striated like skeletal muscle, but is not voluntary
Contracts at a fairly steady rate set by the heart’s pacemaker
Intercalated discs
Neural controls allow the heart to respond to changes in
bodily needs
Role of chemicals, hormones, and autonomic nervous
system
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Cardiac Muscle
Forms the wall of heart
Like skeletal, striated, but contracts involuntarily (like smooth)
Presence of darkly staining structures called intercalated discs
located at the junction of adjacent cells
Formed by special cell-to-cell junctions in cardiac muscle cells
Contraction: basic mechanisms as skeletal muscle
However, certain cells contact spontaneously and rhythmically
Depolarization spread to adjacent cells
Spontaneous activity may be modified by nerve
impulses carried over autonomic nervous system &
by hormones
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Smooth Muscle Tissue
 Cells lack striation of skeletal muscles
one nucleus, smaller than skeletal muscle
Found in the walls of hollow visceral organs, such as
stomach, urinary bladder, blood vessels, respiratory passages
 Contractions force food and other substances through
internal body channels
 It is not striated and is involuntary (unlike skeletal muscle)
 contractions not controlled consciously, regulated by intrinsic
factors, hormones and signals from the Autonomic nervous
system
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Smooth Muscle
Similar to skeletal muscle, smooth contains thin & thick
filaments (but not striated or sarcomeres)
Cross-bridges do form b/w actin & myosin (need Ca2+)
Contraction involves sliding similar to skeletal
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Smooth Muscle
Composed of spindle-shaped fibers
Found in walls of hollow organs (except the heart)
Peristalsis – alternating contractions and relaxations of
smooth muscles that mix and squeeze substances through
the lumen of hollow organs
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Smooth Muscle
Figure 9.24
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Myofibrils
Myofibrils are densely packed, rodlike contractile elements
They make up most of the muscle volume
The arrangement of myofibrils within a fiber is such that a
perfectly aligned repeating series of dark bands and light
bands is evident
Myofibrils composed of thousands of thinner strands called
myofilaments
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Myofibrils
Figure 9.3 (b)
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Sarcomeres
 The smallest contractile unit of a muscle
 Series of repeating segments
 Composed of myofilaments made up of contractile proteins
 Myofilaments are of two types – thick and thin
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Myofilaments: Banding Pattern
 Thick filaments – extend the entire length of dark band
 Thin filaments – extend across the light band and partway
into the dark band
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Myofilaments: Banding Pattern
Figure 9.3 (c, d)
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Ultrastructure of Myofilaments: Thick Filaments
 Thick filaments are composed of the protein myosin
 Each myosin molecule has a rodlike tail and two globular
heads
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Ultrastructure of Myofilaments: Thin Filaments
 Thin filaments are chiefly composed of the protein actin
 Each actin molecule is a helical polymer of globular subunits
called G actin
 The subunits contain the active sites to which myosin heads
attach during contraction
 Tropomyosin and troponin are regulatory subunits bound to
actin
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Ultrastructure of Myofilaments: Thin Filaments
Figure 9.4 (c)
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Arrangement of the Filaments in a Sarcomere
Longitudinal section within one sarcomere
Figure 9.4 (d)
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Age-related changes
As we age, we notice
1. Gradual reduction in strength and endurance
2. Certain movements are not as well-coordinated as before
3. Reduced functional capability  increased chance of falling
4. Alterations in muscular system may be depressing
5. Age-related muscular changes can be minimized w/ regular
exercise programs
6. Some changes are related to alterations in muscleassociated connective tissues and neurons
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Skeletal muscle:
Reduction in the total mass due to atrophy of muscle fibers
Decrease in number and the diameter of the fibers
Recall: fibers are postmitotic; can not be replaced
Lost fibers are replaces by fat tissue (factors: amount of exercise, nutrition,
heredity)
Lost in strength (more occurring in muscles that are less frequently used)
Benefit of low-intensity (regular, moderate) 6exercise
Function of mitochondria of exercised cells less lactate accumulates
Skeletal muscles: Fast-twitch vs. Slow-twitch
Change in orientation of myofibrils, degeneration w/ aging; replaced by lipofucin
or connective tissue & increase in collagen in skeletal muscle of elderly
Motor unit; reduced nerve stimulation cause of age-related muscle atrophy
Reduction in the amount of neurotransmitters Ach
Three periods of muscle contraction (latent, contraction, and relaxation period)
are lengthened w/ age  skeletal muscles respond more slowly to stimuli
(higher reaction time in older persons)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Age-related changes
Smooth muscle
In the wall of the digestive tracts of older person:
Increased tendency to form saclike pouches called diverticula
(may be due to weakening of the smooth muscle contraction)
Accumulation of large vacuoles containing substances such as
fats, collagenous fibers in the walls of arteries w/ aging
Cardiac muscle
Accumulation of fat among the cardiac muscle fibers
Decrease in elastic connective tissues
Accumulation of lipofuscin granules (brown atrophy of the
heart)
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Age-related Dysfunction
Parkinson’s Disease:
Affects people over 50
Uncontrollable contraction of skeletal muscles  tremor & rigidity
Decrease in normal muscular activity (Walking: no arm swinging,
Emotional situations: no change in facial expression)
Actual cause is in a specific region of CNS
Myasthenia Gravis:
Can occur at any age; prevalent in older persons
Major symptoms: drooping of the upper eyelid, difficulty in speech
& speaking, chronic generalized muscle weakness, fatigue…
 Autoimmune disease; Abs against Ach
 Anti-receptor Abs; role of Ach receptor
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Age-related dysfunctions
Muscle Cramps
 Severe sustained muscle contraction
Last from a few seconds to few hours
Develop during rest or after exercise, not unique to elderly
Most often during sleep, affect calf and feet muscles
 Cause: low O2 (poor circulation), nervous stimulation, low
blood sugar, Ca, Na
Conservative treatment (stretching) of affected muscle
before rest
Polymyositis
Muscle Inflammation  weakness in hips, thighs, neck
Auto-immune disease
Bed rest, immunosuppressive, physical therapy
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Polymyalgia Rheumatica
 Bilateral pain and stiffness of shoulders and thighs
 Can cause immobility, depression, weight loss, fever
 Twice common in women than men
 Incidence increases with age
 Usually resolves w/in five years
 Can cause permanent incapacity
 Responds well to corticosteroids
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings