chapter 10&11
DESCRIPTION
MuscleTRANSCRIPT
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Muscular
Tissue
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• Like nervous tissue, muscles are excitable or "irritable”– they have the ability to respond to a stimulus
• Unlike nerves, however, muscles are also:
– Contractible (they can shorten
in length)
– Extensible (they can extend or
stretch)
– Elastic (they can return to their
original shape)
Functions of Muscular Tissue
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Location Function Appearance Control
Skeletal
skeleton
movement,
heat,
posture
striated, multi-
nucleated
(eccentric), fibers
parallel
voluntary
Cardiac
heartpump blood
continuously
striated, one
central nucleus
involunta
ry
Visceral
(smooth
muscle)
G.I. tract,
uterus, eye,
blood
vessels
Peristalsis,
blood
pressure,
pupil size,
erects hairs
no striations,
one central
nucleus
involunta
ry
Three Types of Muscular Tissue
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• Muscle makes up a large percentage of the body’s weight
• Their main functions are to:
– Create motion – muscles work with nerves, bones, and
joints to produce body movements
– Stabilize body positions and maintain posture
– Store substances within the body using sphincters
– Move substances by peristaltic contractions
– Generate heat through thermogenesis
Functions of Muscular Tissue
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(b) Cardiac muscle (c) Visceral smooth muscle
(a) Skeletal muscle
Three Types of Muscular Tissue
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Location Function Appearance Control
Skeletal
skeleton
movement,
heat,
posture
striated, multi-
nucleated
(eccentric), fibers
parallel
voluntar
y
Cardiac
heartpump blood
continuously
striated, one
central nucleus
involunta
ry
Visceral
(smooth
muscle)
G.I. tract,
uterus, eye,
blood
vessels
Peristalsis,
blood
pressure,
pupil size,
erects hairs
no striations,
one central
nucleus
involunta
ry
Skeletal Muscle
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Skeletal Muscle
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Skeletal muscle fibers are very long “cells” -
next to neurons (which can be over a meter
long),
perhaps the longest in the body
The Sartorious muscle contains
single fibers that are at least
30 cm long
A single skeletal muscle fiber
Skeletal Muscle
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Sarcolemma
Motor neuron
The terminal processes of a
motor neuron in close proximity
to the sarcolemma of a skeletal
muscle fiber
Skeletal Muscle
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• In groups of muscles the
epimysium continues to
become thicker, forming
fascia which covers many
muscles
• This graphic shows the
fascia lata enveloping the
entire group of quadriceps
and hamstring muscles in
the thing
Organization of Muscle Tissue
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Organization of Muscle Tissue
Organization of a single muscle
belly
Epimysium
Perimysium
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Organization of a fasciculus
Organization of Muscle Tissue
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Organization of a muscle fiber
Organization of Muscle Tissue
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A muscle, a fasciculus, and a fiber all visualized
Organization of Muscle Tissue
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• An aponeurosis is
essentially a thick
fascia that connects two
muscle bellies. This
epicranial aponeurosis
connects the muscle
bellies of the occipitalis
and the frontalis to form
“one” muscle: The
occipitofrontalis
Epicranial aponeurosis
Frontal belly of the occipitofrontalis m.
Organization of Muscle Tissue
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Veins, arteries, and nerves are located in the
deep fascia between muscles of the thigh.
Organization of Muscle Tissue
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You should learn the names of the internal
structures of the muscle fiber
Sarcolemma
Sarcoplasm
T-tubules
Triad (with
terminal cisterns
Sarcoplasmic reticulum
Sarcomere
Myofibril
The Skeletal Muscle Fiber
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The Skeletal Muscle Fiber
Increasing the level of magnification, the
myofibrils are seen to be composed
of filaments
Thick filaments
Thin filaments
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A scanning electron micrograph of a
sarcomere
• The basic functional unit of skeletal muscle fibers
is the sarcomere: An arrangement of thick and thin
filaments sandwiched between two Z discs
The Skeletal Muscle Fiber
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The “Z line” is really a Z disc when considered in
3 dimensions. A sarcomere extends from Z disc
to Z disc.
• Muscle contraction occurs in the sarcomeres
The Skeletal Muscle Fiber
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• Myofibrils are built from three groups of proteins
– Contractile proteins generate force during contraction
– Regulatory proteins help switch the contraction process
on and off
– Structural proteins keep the thick and thin filaments in
proper alignment and link the myofibrils to the
sarcolemma and extracellular matrix
Muscle Proteins
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• The thin filaments are comprised mostly of the structural protein actin, and the thick filaments are comprised mostly of the structural protein myosin
• However, in both types of filaments, there are also other structural and regulatory proteins
Muscle Proteins
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• In the thin filaments actin proteins are strung
together like a bead of pearls
• In the thick filaments myosin proteins look
like golf clubs bound together
Muscle Proteins
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In this first graphic, the myosin binding sites on
the actin proteins are readily visible.
The regulatory proteins troponin and
tropomyosin have been added to the bottom
graphic: The myosin binding sites have been
covered
Muscle Proteins
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In this graphic the troponin-tropomyosin
complex has slid down into the “gutters” of the
actin molecule unblocking the myosin binding
site
The troponin-tropomyosin complex can slide
back and forth depending on the presence of
Ca2+
Myosin binding site exposed
Muscle Proteins
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• Ca2+ binds to troponin which changes the shape of the
troponin-tropomyosin complex and uncovers the myosin
binding sites on actin
Muscle Proteins
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• Besides contractile and regulatory proteins,
muscle contains about a dozen structural
proteins which contribute to the alignment,
stability, elasticity, and extensibility of
myofibrils
• Titan is the third most plentiful protein in
muscle, after actin and myosin - it extends
from the Z disc and accounts for much of the
elasticity of myofibrils
• Dystrophin is discussed later as it relates to
the disease of muscular dystrophy
Muscle Proteins
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• With exposure of the myosin binding sites on actin (the thin
filaments)—in the presence of Ca2+ and ATP—the thick and
thin filaments “slide” on one another and the sarcomere is
shortened
The Sliding-Filament Mechanism
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• The “sliding” of actin on myosin (thick filaments on thin
filaments) can be broken down into a 4 step process
The Sliding-Filament Mechanism
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• Step 1: ATP hydrolysis
• Step 2: Attachment
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• Step 3: Power Stroke
• Step 4: Detachment
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The Sliding-Filament Mechanism
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The brain
The motor neuron
Acetylcholine (ACh)
Acetylcholinesterase
enzyme
Ach receptors on the
motor endplate
Na+-K+ channels on the
sarcolemma
Na+ flow
K+ flow
Regenerate AP
The T-tubules
The SR
Ca2+ release
Troponin/
Tropomyosin
ATP
Myosin binding
Filaments slide
Muscles contract
Role Players in E-C
coupling
Excitation-Contraction Coupling
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Excitation-Contraction Coupling
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Excitation-Contraction Coupling• EC coupling involves putting it all together
– The thought process going on in the brain
– The AP arriving at the neuromuscular junction
– The regeneration of an AP on the muscle membrane
– Release of Ca2+ from the sarcoplasmic reticulum
– Sliding of thick on thin filaments in sarcomeres
– Generation of muscle tension (work)
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• Excitation-Contraction coupling (EC coupling)
involves events at the junction between a motor
neuron and a skeletal muscle fiber
Neuromuscular Junction
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• An enlarged view of the neuromuscular
junction– The presynaptic membrane is on the neuron while the postsynaptic
membrane is the motor end plate on the muscle cell. The two membranes
are separated by a space, or “cleft”
Neuromuscular Junction
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• Conscious thought (to move a muscle) results in activation of a motor neuron, and release of the neurotransmitter acetylcholine (AcCh) at the NM junction
• The enzyme
acetylcholinesterase
breaks down AcCh
after a short period
of time
Neuromuscular Junction
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• The plasma membrane on the “far side” of the NMJ belongs
to the muscle cell and is called the motor end plate
• The motor end plate is rich in chemical (ligand) - gated
sodium channels that respond to AcCh. Another way to say
this: The receptors for AcCh are on the ligand-gated sodium
channels on the motor end plate
Neuromuscular Junction
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• The chemical events at the NMJ transmit the electrical
events of a neuronal action potential into the electrical
events of a muscle action potential
Neuromuscular Junction
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Excitation-Contraction Coupling
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Limited contact between actin and myosin
Compressed thick
filaments
Length-Tension Relationship• Sarcomere shortening produces tension within a
muscle
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Sources of Muscle Energy• Stored ATP
– 3 seconds
• Energy transferred from stored creatine phosphate
– 12 seconds
• Aerobic ATP production
• Anaerobic glucose use
– 30-40 seconds
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Sources of Muscle Energy
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Sources of Muscle Energy
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Sources of Muscle Energy
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• In a state of homeostasis, muscle use of O2 and
nutrients is balanced by the production of manageable
levels of waste products like
– CO2
– Heat - 70-80% of the energy used by muscles is lost as
heat - muscle activity is important for maintaining body
temperature
– Lactic acid (anaerobic)
Skeletal Muscle Metabolism
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• Oxygen Debt, or "Excess Post-Exercise Oxygen Consumption" (EPOC) is the amount of O2 repayment required after exercise in skeletal muscle to: – Replenish ATP stores– Replenish creatine phosphate and
myoglobin stores– Convert lactic acid back into pyruvate
so it can be used in the Krebs cycle to replenish ATP
Skeletal Muscle Metabolism
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Skeletal Muscle Metabolism
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Cardiac and Smooth Muscle Metabolism• In response to a single AP, cardiac muscle
contracts 10-15 times longer than skeletal muscle,
and must continue to do so, without rest, for the
life of the individual
• To meet this constant demand, cardiac muscle
generally uses the rich supply of O2 delivered by
the extensive coronary circulation to generate ATP
through aerobic respiration
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Cardiac and Smooth Muscle Metabolism
• Like cardiac muscle, smooth muscle (in your deep
organs) is autorhythmic and is not under
voluntary control (your heart beats and your
stomach digests without you thinking about it).
• Unlike cardiac (and skeletal muscle) however,
smooth muscle has a low capacity for generating
ATP and does so only through anaerobic
respiration (glycolysis)
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• Motor Unit is composed of a motor neuron plus all of the
muscle cells it innervates
• High precision
– Fewer muscle fibers per neuron
– Laryngeal and extraocular muscles (2-20)
• Low precision
– Many muscle fibers per neuron
– Thigh muscles (2,000-3,000)
The Motor Unit
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Florescent dye is used to show the terminal
processes of a single neuron which terminate on a
few muscle fibers
The Motor Unit
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• All-or-none principle of muscle contraction
– When an individual muscle fiber is stimulated to
depolarization, and an action potential is
propagated along its sarcolemma, it must contract
to it’s full force—it can’t partially contract
– Also, when a single motor unit is recruited to
contract, all the muscle fibers in that motor unit
must all contract at the same time
The Motor Unit
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• A twitch is recorded when a stimulus that results in
contraction (force) of a single muscle fiber is
measured over a very brief millisecond time frame
Tension in a Muscle
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• Applying increased numbers of action potentials to a muscle
fiber (or a fascicle, a muscle, or a muscle group) results in
fusion of contractions (tetanus) and the performance of
useful work
Tension in a Muscle
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• Two motor units, one in green, the other in purple,
demonstrate the concept of progressive activation of a
muscle known as recruitment
– Recruitment allows a muscle to accomplish increasing
gradations of contractile strength
Tension in a Muscle
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Muscle Contraction• Isotonic contractions results in movement
– Concentric isotonic is a type of muscle contraction in which
the muscle shorten while generating force
– Eccentric isotonic is a contraction in which muscle tension is
less than the resistance (the muscle lengthens)
• Isometric contractions results in no movement
– Muscle force and resistance are equal
– Supporting objects in a fixed position and posture
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Muscle Contraction
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• Skeletal muscle fibers are not all alike in appearance or
function. By appearance:
– Red muscle fibers (the dark meat in chicken legs) have a
high myoglobin content, more mitochondria, more energy
stores, and a greater blood supply
– White muscle fibers (the white meat in chicken breasts)
have less myoglobin, mitochondria, and blood supply
Skeletal Muscle Fiber Types
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• Slow oxidative fibers (SO) are small, appear dark red, are
the least powerful type. They are very fatigue resistant
– Used for endurance like running a marathon
• Fast oxidative-glycolytic fibers (FOG) are intermediate in
size, appear dark red, and are moderately resistant to
fatigue. Used for walking
• Fast glycolytic fibers (FG) are large, white, and powerful
– Suited to intense anaerobic activity of short duration
Skeletal Muscle Fiber Types
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Skeletal Muscle Fiber Types
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Smooth Muscle
• Cells are not striated• Fibers smaller than those in skeletal
muscle• Spindle-shaped; single, central
nucleus• More actin than myosin• No sarcomeres
– Not arranged as symmetrically as in skeletal muscle, thus NO striations.
• Dense bodies instead of Z disks – Have non contractile
intermediate filaments
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Smooth Muscle• Grouped into sheets in walls of hollow organs
• Longitudinal layer – muscle fibers run parallel to organ’s long axis
• Circular layer – muscle fibers run around circumference of the organ
• Both layers participate in peristalsis
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Smooth Muscle
• Visceral or unitary smooth muscle– Only a few muscle fibers innervated in each group– Impulse spreads through gap junctions
• Multiunit: – Cells or groups of cells act as independent units– Arrector pili of skin and iris of eye
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Cardiac Muscle• Found only in heart where it forms a thick layer called
the myocardium• Striated fibers that branch• Each cell usually has one centrally-located nucleus• Fibers joined by intercalated disks
– IDs are composites of desmosomes and gap junctions– Allow excitation in one fiber to spread quickly to adjoining fibers
• Under control of the ANS (involuntary) and endocrine system (hormones)
• Some cells are autorhythmic– Fibers spontaneously contract (aka Pacemaker cells)
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Cardiac Muscle Tissue
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Disorders of Muscle Tissue
• Muscular dystrophy – a group of inherited muscle destroying disease– Affected muscles enlarge with fat and
connective tissue – Muscles degenerate
• Types of muscular dystrophy– Duchenne muscular dystrophy – Myotonic dystrophy
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Disorders of Muscle Tissue
• Myofascial pain syndrome – pain is caused by tightened bands of muscle fibers
• Fibromyalgia – a mysterious chronic-pain syndrome– Affects mostly women– Symptoms – fatigue, sleep abnormalities,
severe musculoskeletal pain, and headache
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Developmental Aspects: Regeneration
• Cardiac and skeletal muscle become amitotic, but can lengthen and thicken
• Myoblast-like satellite cells show very limited regenerative ability
• Cardiac cells lack satellite cells• Smooth muscle has good regenerative ability• Women’s skeletal muscle makes up 36% of their
body mass• Men’s skeletal muscle makes up 42% of their body
mass
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Developmental Aspects: Male and Female
• These differences are due primarily to the male sex hormone testosterone
• With more muscle mass, men are generally stronger than women
• Body strength per unit muscle mass, however, is the same in both sexes
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Developmental Aspects: Age Related
• With age, connective tissue increases and muscle fibers decrease
• Muscles become stringier and more sinewy• By age 80, 50% of muscle mass is lost
(sarcopenia)• Decreased density of capillaries in muscle• Reduced stamina• Increased recovery time• Regular exercise reverses sarcopenia
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• Exercise-induced muscle damage– After intense exercise electron micrographs
reveal considerable muscle damage including torn sarcolemmas and disrupted Z-discs
– Blood levels of proteins normally confined only to muscle (including myoglobin and the enzyme creatine kinase) increase as they are released from damaged muscle
Imbalances of Homeostasis
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• Spasm
– A sudden involuntary contraction of a single muscle within
a large group of muscles – usually painless
• Cramp
– Involuntary and often painful muscle contractions
– Caused by inadequate blood flow to muscles (such as in
dehydration), overuse and injury, and abnormal blood
electrolyte levels
Imbalances of Homeostasis
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• Disease States and Disorders– Fibrosis (myofibrosis)
• Replacement of muscle fibers by excessive amounts of connective tissues (fibrous scar tissue)
– Myosclerosis• Hardening of the muscle caused by calcification
– Both myosclerosis and muscle fibrosis occur as a result of trauma and various metabolic disorders
Imbalances of Homeostasis
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• Aging– In part due to decreased levels of physical
activity, with aging humans undergo a slow, progressive loss of skeletal muscle mass that is replaced largely by fibrous connective tissue and adipose tissue
– Muscle strength at 85 is about half that at age 25
– Compared to the other two fiber types, the relative number of slow oxidative fibers appears to increase
Imbalances of Homeostasis
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Naming Muscles
• Location
– tibialis anterior
Tibialis anterior
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• Size
– gluteus maximus
• Number of
Attachments
o biceps; triceps
Naming Muscles
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• Location/Direction of
Fibers
– transversus abdominus
Naming Muscles
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• Attachments
(origin &
insertion)
o sternocleidomas
toid
Naming Muscles
Styloid process
Hyoid bone
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• Muscle action
– levator scapulae
– adductor magnus
– tensor tympani
Naming Muscles
Levator scapulae
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• Combination of above– Fibularis longus
Naming Muscles