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Chapter 9
Muscular System
Three Types of Muscle Tissues
Skeletal Muscle
• usually attached
to bones, skin, deep
fascia
• voluntary
• striated
Cardiac Muscle
• wall of heart
• involuntary
• striated
Smooth Muscle
• walls of most viscera,
blood vessels, skin
• involuntary
• not striated
1
Muscle Tissue Characteristics
• Excitability
– Similar to nervous tissue
– Stimulus initiates action potential (impulse)
• Contractility
– Shorten and thicken
– Actively do work when stimulus is received
2
Muscle Tissue Characteristics
• Extensibility
– Ability to be stretched
– Paired muscle groups
• Elasticity
– Ability to return to its original shape after
contracting or extending
3
Muscle Tissue Functions
• Motion
• Maintenance of posture
• Heat production
– 85% of heat generated from muscles
4
Structure of a Skeletal Muscle
Skeletal Muscle
• organ of the
muscular system
- skeletal muscle
tissue
- nervous tissue
- blood
- connective tissues
• fascia
• tendons
• aponeuroses
5
Connective Tissue Coverings
• Superficial Fascia
– Subcutaneous layer
– Immediately deep to the skin
– Stores fat, insulates, protects, provides
pathway for nerves and blood vessels
6
Connective Tissue Coverings
• Deep Fascia
– Lines body walls, extremities, and
holds muscles together
– Splits muscles into functional groups
• Pectoralis major/pectoralis minor
7
Connective Tissue Coverings
• Deep Fascia
– Functions
• Allows free movement of muscles
• Fills space
• Carries nerve and vascular supply
• Sometimes provides origin for muscles
8
Connective Tissue Coverings
• Epimysium
•Wraps the entire
muscle bundle
• Perimysium
•Covers muscle fiber
bundles (fascicles)
• Endomysium
•Covers individual
fibers within the
fascicles
•“-mysiums” may
extend to become
tendon
9
Connective Tissue Coverings
• Epimysium
• Covers entire muscle
• Muscles are bundles
of fascicles
• Perimysium
• Covers individual
fascicles
10
Connective Tissue Coverings
• Fascicle
• Many bundles of
fibers
• Fiber
• Many myofibrils
• Myofibril
• Many myofilaments
11
Connective Tissue Coverings
• Myofilaments
• Smallest part of a
muscle
• DO NOT extend
entire length of
muscle
• Fit into
compartments
called sarcomeres
12
Connective Tissue Coverings
• Sarcomeres
• Contraction of
muscles occurs
here
• Lie end to end
within myofibril
13
Skeletal Muscle Fibers
• Sarcolemma
•Muscle cell
membrane
• Sarcoplasm
•Muscle cell
cytoplasm
• Sarcoplasmic reticulum
•Muscle cell ER
14
Sarcomere Structure
• 2 types of
myofilaments
• myosin• THICK contractile
protein
• actin• THIN contractile
protein
• The ability for actin
and myosin to change
shape allows for the 2
myofilaments to be
pulled (slide) over
each other
15
Sarcomere Structure
• Myofilaments form patterns in the sarcomeres
• “I” band consist of the disc (stationary) and actin filaments
• “A” band consist of myosin overlapping with the ends of the
actin filaments
• “H” zone —is within “A” band and contains only myosin
• Another “I” band
16
Sarcomere Structure
• Structures between
the disc make up
the sarcomere
• Heads or hooks on
the myosin bind
with actin to pull
the myosin filament
over the actin
• Tropomyosin
blocks the binding
site on the actin
when the muscle is
relaxed
17
Myofilaments
Thick Filaments
• composed of myosin
• cross-bridges
Thin Filaments
• composed of actin
• associated with troponin
and tropomyosin
18
Sliding Filament Theory
• The myofibril shortens because the
myofilaments in each sarcomere slide
over each other
19
Neuromuscular Junction
• also known as
myoneural junction
• site where an axon and
muscle fiber meet
• motor neuron
• motor end plate
• synapse
• synaptic cleft
• synaptic vesicles
• neurotransmitters
20
Motor Unit
• single motor neuron
• all muscle fibers controlled by motor neuron
21
Stimulus for Contraction
• acetylcholine (ACh)
• nerve impulse causes
release of ACh from
synaptic vesicles
• ACh binds to ACh
receptors on motor end
plate
• generates a muscle
impulse
• muscle impulse
eventually reaches
sarcoplasmic reticulum
22
Excitation Contraction
Coupling
• muscle impulses cause
sarcoplasmic reticulum
to release calcium ions
into cytosol
• calcium binds to
troponin to change its
shape
• position of
tropomyosin is altered
• binding sites on actin
are exposed
• actin and myosin
molecules bind
23
Sliding Filament Model of Muscle
Contraction
• When
sarcromeres
shorten, thick and
thin filaments slide
past one another
• H zones and I
bands narrow
• Z lines move
closer together
24
Cross-bridge Cycling
• myosin cross-bridge attaches
to actin binding site
• myosin cross-bridge pulls
thin filament
•ADP and phosphate
released from myosin
• new ATP binds to
myosin
• linkage between actin
and myosin cross-bridge
break
•ATP splits
•myosin cross-bridge goes back
to original position
25
Relaxation
• Acetylcholinesterase
•rapidly decomposes Ach remaining in the synapse
• Muscle impulse stops
• Stimulus to sarcolemma and muscle fiber membrane
ceases
• Calcium moves back into sarcoplasmic reticulum
• Myosin and actin binding prevented
•Tropomyosin slides over binding sites
• Muscle fiber relaxes
•Sarcomeres return to original length
26
Major Events of Muscle
Contraction and Relaxation
27
Energy Sources for
Contraction
1) Creatine phosphate
2) Cellular respiration
• creatine phosphate – stores energy that quickly converts
ADP to ATP
28
Oxygen Supply and
Cellular Respiration
• Anaerobic Phase
• glycolysis
• Occurs in cytoplasm
• Produces little ATP
• Aerobic Phase
• Citric acid cycle
• Electron transport chain
• Occurs in mitochondria
• Produces most ATP
• Myoglobin
•Pigment that stores
extra oxygen
29
Oxygen Debt
Oxygen debt – amount of oxygen needed by liver cells to
use the accumulated lactic acid to produce glucose
• Oxygen not available
• Glycolysis continues
• Pyruvic acid converted to
lactic acid
• Liver converts lactic acid
to glucose
30
Muscle Fatigue
• Inability to contract
• Commonly caused from
• decreased blood flow
• ion imbalances across the sarcolemma
• accumulation of lactic acid
• Cramp – sustained, involuntary muscle contraction
31
Heat Production
• By-product of cellular respiration
• Muscle cells are major source of body heat
• Blood transports heat throughout body
32
Muscular Responses
Threshold Stimulus
• minimal strength required to cause contraction
Recording a Muscle
Contraction
• twitch
•Single muscle fiber
response to an impulse
• latent period
•Delay between impulse
and contraction
• period of contraction
33
Muscular Responses
• Period of relaxation
• Refractory period
• Time when neuron
will not respond to
stimulus
• All-or-none response
• Each twitch generates
the same force
34
Length-Tension Relationship
35
Summation
• process by which
individual twitches
combine
• produces sustained
contractions
• can lead to tetanic
contractions
•Lacks partial
relaxation
36
Recruitment of Motor Units
• Recruitment
• Increase in the number of motor units activated
• Whole muscle composed of many motor units
• More precise movements are produced with fewer
muscle fibers within a motor unit
•Eye has fewer than 10 muscle fibers per motor unit
• As intensity of stimulation increases, recruitment of
motor units continues until all motor units are
activated
37
Sustained Contractions
• Smaller motor units (smaller diameter axons)
•Recruited first
• Larger motor units (larger diameter axons)
•Recruited later
• Produce smooth movements
•Spinal cord stimulates contractions in different sets
of motor units at different times
• Muscle tone – continuous state of partial contraction
•Maintains posture
•Completely lost with loss of consciousness
38
Types of Contractions
• Isotonic – muscle contracts
and changes length
• Eccentric – lengthening
contraction
• Concentric – shortening contraction
• Isometric – muscle contracts but
does not change length
39
Fast and Slow Twitch
Muscle Fibers
Slow-twitch fibers (type I)
• Always oxidative
• Resistant to fatigue
• Red fibers
•Contain most myoglobin
• Good blood supply
•Back muscles
Fast-twitch glycolytic fibers
(type IIa)
• white fibers (less myoglobin)
• poorer blood supply
• susceptible to fatigue
•Hand muscles, eye muscles
Fast-twitch fatigueresistant fibers (type
IIb)
• intermediate fibers
• oxidative
• intermediate
amount of
myoglobin
• pink to red in color
•resistant to fatigue
•Limb muscles
40
Abnormal Contractions
• Spasm
• Sudden involuntary contraction of a large
group of muscles
• Tremor
• Involuntary contraction of opposing muscle
groups
• Fasciculation
• Involuntary, brief twitch of a muscle visible
under the skin
• Occurs irregularly and doesn’t move the
affected muscle
41
Abnormal Contractions
• Fibrillation
• Similar to fasciculation except it is not visible
under the skin
• Tic
• Twitch made involuntarily by muscles under
voluntary control
• Eyelids or facial muscles are examples
• Generally tics are of psychological origin
42
Smooth Muscle Fibers
Compared to skeletal muscle fibers
• shorter
• single, centrally located nucleus
• elongated with tapering ends
• myofilaments randomly
organized
• lack striations
• lack transverse tubules
• sarcoplasmic reticula not well
developed
43
Types of Smooth Muscle
Visceral Smooth Muscle
• single-unit smooth
muscle
• sheets of muscle fibers
• fibers held together by
gap junctions
• exhibit rhythmicity
• exhibit peristalsis
• walls of most hollow
organs
Multiunit Smooth Muscle
• less organized
• function as separate
units
• fibers function
separately
• irises of eye
• walls of blood vessels
44
Smooth Muscle Contraction
• Resembles skeletal muscle contraction
• interaction between actin and myosin
• both use calcium and ATP
• both are triggered by membrane impulses
• Different from skeletal muscle contraction
• smooth muscle lacks troponin
• smooth muscle uses calmodulin
• two neurotransmitters affect smooth muscle
• acetlycholine and norepinephrine
• hormones affect smooth muscle
• stretching can trigger smooth muscle contraction
• smooth muscle slower to contract and relax
• smooth muscle more resistant to fatigue
• smooth muscle can change length without changing
tautness
45
Cardiac Muscle
•
•
•
•
•
•
Fibers are quadrangular
Single nucleus
More and larger mitochondria
Contain actin and myosin
Fibers branched and interconnected
2 separate networks (atria and ventricles)
intercalated disc separate each fiber in a network
• impulse stimulates the entire network,
contraction of the entire network
46
Cardiac Muscle
• atria contract—blood to the ventricle
• ventricles contract—blood to the arteries and
through the body
• auto-rhythmicity—nerve impulses only increase
or decrease the rhythmic contractions
• remains contracted 10-15 times longer
• extra refractory period—allows heart to rest and
prevents tetanus
47
Characteristics of Muscle Tissue
48
Skeletal Muscle Actions
• origin – immovable end
• insertion – movable end
• prime mover (agonist) –
primarily responsible for
movement
• synergists – assist prime mover
• antagonist – resist prime
mover’s action and cause
movement in the opposite
direction
49
Body Movement
Four Basic Components of Lever
1. rigid bar – bones
2. fulcrum – point on which bar moves; joint
3. object - moved against resistance; weight
4. force – supplies energy for movement; muscles
50
Levers and Movement
51
Major Skeletal Muscles
52
Major Skeletal Muscles
53
Muscles of Facial Expression
54
Muscles of Mastication
55
Muscles of Facial Expression
and Mastication
56
Muscles That Move the Head
and Vertebral Column
57
Muscles That Move the Head
and Vertebral Column
58
Muscles That Move the
Pectoral Girdle
59
Muscles That Move the
Pectoral Girdle
60
Muscles That Move the Arm
61
Muscles That Move the Arm
62
Muscles That Move the Arm
63
Muscles That Move the
Forearm
64
Muscles That Move the
Forearm
65
Muscles That Move the
Forearm
66
Cross Section of the Forearm
67
Muscles That Move the Hand
68
Muscles That Move the Hand
69
Muscles of the Abdominal Wall
70
Muscles of the Abdominal Wall
71
Muscles of the Pelvic Outlet
72
Muscles of Pelvic Outlet
73
Muscles That Move the Thigh
74
Muscles That Move the Thigh
75
Muscles That Move the Thigh
76
Muscles That Move the Leg
77
Muscles That Move the Leg
78
Muscles That Move the Leg
79
Muscles That Move the Leg
80
Muscles That Move the Foot
81
Muscles That Move the Foot
82
Muscles That Move the Foot
83
Life-Span Changes
• myoglobin, ATP, and creatine phosphate
decline
• by age 80, half of muscle mass has
atrophied
• adipose cells and connective tissues replace
muscle tissue
• exercise helps to maintain muscle mass and
function
84
Clinical Application
Homeostatic Imbalances (Disorders)
• May involve
–
–
–
–
–
–
lack of nutrients,
disease,
injury,
atrophy,
neurological problem
accumulation of toxic products
85
Clinical Application
• Fibrosis
• Formation of fibrous connective tissue where it
normally does not exist
• Mature skeletal and cardiac muscle cannot
undergo mitosis. Damaged fibers are replaced
with fibrous connective tissue
• Most often the result of muscle injury or
degeneration
86
Clinical Application
• Fibromyalgia (algia=painful condition)
• Common non-articular rheumatic disorders
• pain, tenderness
• stiffness of muscles, tendons, and surrounding soft tissue
• Affects the fibrous connective tissue components of
tendons and ligaments
• May be caused or aggravated by physical or mental
stress, trauma, exposure to dampness or cold, poor
sleep
• Relieved by heat, massage, and rest
87
Clinical Application
• Dystrophies (disorders)
– Muscle destroying diseases
– degeneration of individual muscle fibers
which leads to a progressive atrophy of the
skeletal muscle
– Skeletal muscles affected bilaterally
– classified by mode of inheritance, age of
onset, and clinical characteristics
88
Clinical Application
Myasthenia Gravis
• autoimmune disorder
• receptors for ACh on muscle cells are attacked
• weak and easily fatigued muscles result
• difficulty swallowing and chewing
• ventilator needed if respiratory muscles are affected
• treatments include
• drugs that boost ACh
• removing thymus gland
• immunosuppressant drugs
• antibodies
89
Clinical Application
• Duchenne Muscular dystrophy (DMD)
• Most common form
• Genetic
• Gene identified and DNA sequence worked
out (could lead to replacement therapy to
prevent muscle loss
90