the muscular system: skeletal muscle tissue and...
TRANSCRIPT
© 2012 Pearson Education, Inc.
9 The Muscular System:
Skeletal Muscle Tissue
and Organization
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Introduction
• Humans rely on muscles for:
• Many of our physiological processes
• Virtually all our dynamic interactions with the
environment
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Introduction
• There are three types of muscle tissue:
• Skeletal muscle • Pulls on skeletal bones
• Voluntary contraction
• Cardiac muscle • Pushes blood through arteries and veins
• Rhythmic contractions
• Smooth muscle • Pushes fluids and solids along the digestive tract
• Involuntary contraction
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Introduction
• Muscle tissues share four basic properties: • Excitability
• The ability to respond to stimuli
• Contractility
• The ability to shorten and exert a pull or tension
• Extensibility
• The ability to continue to contract over a range of
resting lengths
• Elasticity
• The ability to rebound toward its original length
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Functions of Skeletal Muscles
• Skeletal muscles perform the following functions:
• Produce skeletal movement
• Pull on tendons to move the bones
• Maintain posture and body position
• Stabilize the joints to aid in posture
• Support soft tissue
• Support the weight of the visceral organs
• Regulate entering and exiting of material
• Voluntary control over swallowing, defecation, and urination
• Maintain body temperature
• Some of the energy used for contraction is converted to heat
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Anatomy of Skeletal Muscles
• Gross anatomy is the study of:
• Overall organization of muscles
• Connective tissue associated with muscles
• Nerves associated with muscles
• Blood vessels associated with muscles
• Microscopic anatomy is the study of:
• Myofibrils
• Myofilaments
• Sarcomeres
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Anatomy of Skeletal Muscles
• Gross anatomy
• Connective tissue of
muscle
• Epimysium: dense
tissue that surrounds
the entire
muscle
• Perimysium: dense
tissue that divides the
muscle into parallel
compartments of
fascicles
• Endomysium: dense
tissue that surrounds
individual muscle fibers
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Anatomy of Skeletal Muscles
• Connective Tissue of Muscle • Tendons and
Aponeuroses • Epimysium,
perimysium, and endomysium converge to form tendons
• Tendons connect a muscle to a bone
• Aponeuroses connect a muscle to a muscle
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Figure 9.1 Structural Organization of Skeletal Muscle
Epimysium
Muscle fascicle
Endomysium
Perimysium
Nerve
Muscle fibers
Blood vessels
SKELETAL MUSCLE (organ)
MUSCLE FASCICLE (bundle of cells)
Perimysium
Muscle fiber
Endomysium
Epimysium
Blood vessels
and nerves
Endomysium
Perimysium
Tendon
MUSCLE FIBER (cell)
Mitochondria
Sarcolemma
Myofibril
Axon Sarcoplasm
Capillary
Endomysium
Myosatellite
cell
Nucleus
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Anatomy of Skeletal Muscles
• Gross Anatomy • Nerves and blood vessels
• Nerves innervate the muscle
• There is a chemical communication between a nerve and a muscle
• The nerve is “connected” to the muscle via the motor end plate • This is the
neuromuscular junction
• Blood vessels innervate the endomysium to supply oxygen and continuous removal of waste
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Anatomy of Skeletal Muscles • Microanatomy of skeletal muscle fibers
• Sarcolemma
• Membrane that surrounds the muscle cell
• Sarcoplasm
• The cytosol of the muscle cell
• Muscle fiber = a muscle cell
• Can be 30–40 cm in length
• Multinucleated (each muscle cell has hundreds of nuclei)
• Nuclei are located just deep to the sarcolemma
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Anatomy of Skeletal Muscles
• Myofibrils and Myofilaments • The sarcoplasm contains
myofibrils • Myofibrils are responsible
for the contraction of muscles
• Surrounding each myofibril is the sarcoplasmic reticulum
• Myofibrils are made of myofilaments • Actin
• Myosin
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Anatomy of Skeletal Muscles
• Sarcomere
Organization
• Myosin (thick filament)
• Actin (thin filament)
• Both are arranged in
repeating contractile
units called
sarcomeres
• This overlapping
creates the striations
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Anatomy of Skeletal Muscles
• Sarcomere
Organization
• Each sarcomere
consists of:
• Z line (Z disc)
• I band
• A band (overlapping A
bands create striations)
• H zone (band)
• M line
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Anatomy of Skeletal Muscles
• Levels of Organization
• Skeletal muscles consist
of muscle fascicles
• Muscle fascicles consist
of muscle fibers
• Muscle fibers consist of
myofibrils
• Myofibrils consist of
sarcomeres
• Sarcomeres consist of
myofilaments
• Myofilaments are made
of actin and myosin
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Muscle Contraction
• A contracting muscle shortens in length
• Contraction is caused by interactions between
thick and thin filaments within the sarcomere
• Contraction is triggered by the presence of
calcium ions
• Muscle contraction requires the presence of ATP
• When a muscle contracts, actin filaments slide
toward each other
• This sliding action is called the sliding filament
theory
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Muscle Contraction
• The sliding filament
theory
• Upon contraction:
• The H band and I band
get smaller
• The zone of overlap
gets larger
• The Z lines move closer
together
• The width of the A band
remains constant
throughout the
contraction
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Figure 9.10a The Neuromuscular Synapse
A diagrammatic view of a
neuromuscular synapse
Motor
neuron
Axon
Path of action potential
Neuromuscular synapse
Motor end plate
Myofibril
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Figure 9.11 The Events in Muscle Contraction
Ca2
Actin
Myosin
Sarcolemma T tubule
Motor
end
plate
Synaptic
terminal
STEPS IN INITIATING MUSCLE CONTRACTION STEPS IN MUSCLE RELAXATION
Triggered by calcium release Calcium is stored
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Figure 9.12 The Arrangement of Motor Units in a Skeletal Muscle
Motor unit 1
Motor unit 2
Motor unit 3
KEY
SPINAL CORD
Muscle fibers
Axons of motor neurons
Motor nerve
The more motor units contracting,
the more force generated
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Muscle Hypertrophy
• Exercise causes an
increase in:
• the number of
mitochondria
• the concentration of
glycolytic enzymes
• An increase in the
glycogen reserves
• An increase in the
number of myofibrils
• The net effect is an
enlargement of the
muscle
(hypertrophy)
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Motor Units and Muscle Control
• Muscle Atrophy
• Discontinued use of a
muscle
• Disuse causes:
• A decrease in muscle
size
• A decrease in muscle
tone
• Physical therapy helps
to reduce the effects
of atrophy
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Types of Skeletal Muscle Fibers
• Three major types of skeletal muscle
fibers: • Fast fibers (white fibers)
• Associated with eye muscles
• Ex. Sprinting muscles
• Intermediate fibers (pink fibers)
• Slow fibers (red fibers)
• Associated with leg muscles
• Ex. Long distance runners
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Figure 9.13a Types of Skeletal Muscle Fibers
Note the difference in the size of
slow muscle fibers (above) and
fast muscle fibers (below).
LM 170
LM 170
Slow fibers Smaller diameter,
darker color due to
myoglobin; fatigue
resistant
Fast fibers Larger diameter,
paler color;
easily fatigued
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Types of Skeletal Muscle Fibers
• Features of fast fibers:
• Large in diameter
• Large glycogen reserves
• Relatively few mitochondria
• Fatigue easily
• Can contract in 0.01 second or less after
stimulation
• Produce powerful contractions
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Types of Skeletal Muscle Fibers
• Features of slow fibers:
• Half the diameter of fast fibers
• Take three times longer to contract after
stimulation
• Can contract for extended periods of time
• Contain abundant myoglobin (creates the red
color), stores oxygen
• Muscles contract using aerobic metabolism
• Have a more extensive blood supply
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Types of Skeletal Muscle Fibers
• Features of intermediate fibers:
• Contract faster then slow fibers but slower then
fast fibers
• Similar to fast fibers except:
• Have lots of mitochondria
• Have a greater blood supply
• Resist fatigue
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Organization of Skeletal Muscle Fibers
• Muscles can be classified based on shape or
by the arrangement of the fibers
• Parallel muscle fibers
• Convergent muscle fibers
• Pennate muscle fibers
• Unipennate muscle fibers
• Bipennate muscle fibers
• Multipennate muscle fibers
• Circular muscle fibers
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Organization of Skeletal Muscle Fibers
• Parallel muscle fibers
• Muscle fascicles are
parallel to the
longitudinal axis
• Examples: biceps
brachii and rectus
abdominis
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Organization of Skeletal Muscle Fibers
• Convergent muscle
fibers
• Muscle fibers form a
broad area but come
together at a common
point
• Example: pectoralis
major
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Organization of Skeletal Muscle Fibers
• Pennate muscle fibers
• Muscle fibers form an
oblique angle to the
tendon of the muscle
• An example is
unipennate
• All the muscle fibers are
on the same side of the
tendon
• Example: extensor
digitorum
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Organization of Skeletal Muscle Fibers
• An example is
bipennate
• Muscle fibers are on
both sides of the tendon
• Example: rectus
femoris
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Organization of Skeletal Muscle Fibers
• An example is
multipennate
• The tendon branches
within the muscle
• Example: deltoid
muscle
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Organization of Skeletal Muscle Fibers
• Circular muscle fibers
• Muscle fibers form
concentric rings
• Also known as
sphincter muscles
• Examples: orbicularis
oris and orbicularis
oculi
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Muscle Terminology
• Origin, Insertion, and Action
• Origin
• Point of muscle attachment that remains stationary
• Insertion
• Point of muscle attachment that is movable
• Action
• The function of the muscle upon contraction
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Muscle Terminology
• Muscles can be grouped according to their primary actions into four types:
• Prime movers (agonists)
• Responsible for producing a particular movement
• Ex. Biceps brachii – flexes the lower arm
• Antagonists
• Actions oppose the action of the agonist
• Ex. Triceps brachii – extends the lower arm
• Synergists
• Assist the prime mover in performing an action
• Ex. Latissimus dorsi and teres major – contract to move the arm medially over the posterior body
• Fixators
• Agonist and antagonist muscles contracting at the same time to stabilize a joint
• Ex. Flexor and extensor muscles contract at the same time to stabilize an outstretched hand
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Organization of Skeletal Muscle Fibers
• Most muscle names provide clues to their identification or location
• Muscles can be named for:
• Specific body regions or location
• Shape of the muscle
• Orientation of the muscle fibers
• Specific or unusual features
• Its origin and insertion points
• Primary function
• References to occupational or habitual action
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Muscle Terminology
• Examples of muscle names related to:
• Specific body regions or locations
• Tibialis anterior: associated with the anterior tibia
• Shape of the muscle
• Trapezius: trapezoid shape
• Deltoid: triangular shape
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Muscle Terminology
• Examples of muscle names related to:
• Orientation of the muscle fibers
• Rectus femoris: straight muscle of the leg
• External oblique: muscle on outside that is oriented with the fibers at an angle
• Specific or unusual features
• Biceps brachii: two origins
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Muscle Terminology
• Examples of muscle names related to:
• Origin and insertion points
• Sternocleidomastoid: points of attachment are sternum, clavicle, and mastoid process
• Primary functions
• Flexor carpi radialis: a muscle that is near the radius and flexes the wrist
• Adductor longus: a long muscle that adducts the leg
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Muscle Terminology
• Examples of muscle names related to:
• References to occupational or habitual actions
• Buccinator (means “trumpet player”): the buccinator area moves when playing a trumpet
• Sartorius: derived from the Latin term (sartor), which is in reference to “tailors.” Tailors used to cross their legs to form a table when sewing material
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Aging and the Muscular System
• Changes occur in muscles as we age
• Skeletal muscle fibers become smaller in diameter
• There is a decrease in the number of myofibrils
• Contain less glycogen reserves
• Contain less myoglobin
• All of the above results in a decrease in strength and endurance
• Muscles fatigue rapidly
• The ability to recover from muscular injuries decreases