Warm-Up - Define
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Striated
Voluntary
Involuntary
Origin
Insertion
Primary Action
Flexion
Extension
Rotation
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Abduction
Adduction
Circumduction
Dorsiflexion
Plantar flexion
Inversion
Eversion
Supination
Pronation
Opposition
The Muscular System
2
Three Types of Muscle Tissue
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Skeletal Muscle
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Attached to bone
Most abundant
Moves the Body
Usually under voluntary control
Cardiac Muscle
– Heart Muscle
– Not under voluntary control
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Smooth Muscle
– Found in organs and elsewhere
– Not under voluntary control
Skeletal Muscle
4
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Directly or indirectly attached to bone
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About 700 skeletal muscles
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These will be the ones you have to
know and label.
Functions
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Produces movement of the skeleton
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Maintain posture and body position
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Support soft tissue
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Guard entrances and exits
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Maintain Body Temperature
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Stabilize joints
Facts on the Skeletal Muscles
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Under conscious control
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Cells
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Large
Multi-Nuclei
Vary in Length
Striated
Surrounded and bundled by connective tissue
Because skeletal muscles are long and
slender, they are often called muscle fibers.
Structure of a Skeletal Muscle
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Endomysium –
delicate
connective tissue
around single
muscle fiber
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Perimysium –
coarser fibrous
membrane
around a fascicle
(bundle) of fibers
8
Figure 6.1
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Epimysium – tougher
connective tissue that
covers the entire
skeletal muscle and
blends into the
attachment
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Fascia – on the outside
of the epimysium
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The bundling of the
fibers provides strength
and support to the
muscle as a whole
9
Figure 6.1
Skeletal Muscle Attachments
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Epimysium blends into a connective tissue
attachment
– Tendon – cord-like structure made mostly of tough
collagenic fibers
• Functions to - Anchor muscles, Provide durability and
Conserve space
• Do not tore as they cross bony projections
– Aponeuroses – sheet-like structure
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Sites of muscle attachment
– Bones
– Cartilages
– Connective tissue coverings
10
Warm-Up – 1/9
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Label the lines in the picture below
Smooth Muscle Tissue
12
Smooth Muscle Cells
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Similar in size to cardiac muscle cells
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Single, centrally located nucleus
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Spindle-Shaped Cell
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Found within almost every organ, forming
sheets, bundles or sheaths around other
tissues.
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No striated
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Involuntary
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Can function without direct stimulation
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Connected by gap junctions to each
other
Cardiac Muscle Tissue
15
Cardiac Muscle cells
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Relatively small
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Have a single, centrally placed nucleus
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Found only in the heart
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Striated
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Joined to another muscle cell at an intercalated disc
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Involuntary and not under direct control of the CNS
Warm-Up 1/10
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Define the bold words on 185-186
SKELETAL MUSCLE
ACTIVITY
Stimulation and Contraction
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Special functional properties that enable
muscles to perform their duties
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Irritability – ability to receive and
respond to a stimulus
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Contractility – ability to shorten when an
adequate stimulus is received
The Nerve Stimulus and the
Action Potential
Skeletal muscle cells must be
stimulated by nerve impulses to contract
 One motor neuron can stimulate a few
or hundreds of cell
 Motor unit = one neuron and all the
skeletal muscle cells stimulated
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Axon – long threadlike extension of the
neuron. Also called a nerve fiber
 Axons branches into axon terminal
when it reaches the muscles.
 The axon terminal forms junctions
called neuromuscular junctions with the
sarcolemma of a difference muscle cell
 The gap between the nerve and the
muscle is the synaptic cleft and is filled
with fluid
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Microscope Anatomy of a
Skeletal Muscle Fiber
23
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Many oval nuclei are just beneath the
sarcolemma, or plasma membrane.
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Nuclei are pushed aside by the myofibrils,
which are long ribbon-like organelles that
nearly fill the cytoplasm
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The myofibrils have alternating light (I) and
dark (A) bands along their length
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Both have midline interruption
– The I bands have a Z disc which is a darker
area
– The A bands have H zone which is a lighter
area
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The M line in the center of the H zone
contains tiny protein rods that hold
adjacent thick filaments together.
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The banding revels the working structure
of the myofibrils.
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Sarcomere, chains of tiny contractile units,
make up the myofibrils
– Aligned end-to-end along the length of the
myofibrils
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The banding appearance is produced by
the arrangement of myofilaments within
the sarcomeres
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2 types of threadlike protein
myofilaments
– Thick filaments (myosin filaments) are
made mostly of bundled molecules of the
protein myosin along with ATPase
enzymes, which split ATP to generate the
power for the muscle contractions.
• Extend almost the entire length of the A band
• Midparts are smooth
• Ends are have small projections, or myosin
heads, are called cross bridges when they link
the thick and thin filaments together during
contractions
– The thin filaments are composed of the
contractile protein called actin along with
some regulartoy proteins that play a role in
allowing (or preventing) myosin headbinding to action
• Also called actin filaments
• Anchored to the Z disc
• I band includes parts of two adjacent
sarcomeres and contains only the thin filaments
– Thin filaments overlap the ends of the thick
filaments, they don’t extend into the middle
of a relaxed sarcomere and because of this
is it sometimes called the bare zone.
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When contraction occurs, the light zone
disappears because the overlapping is
complete.
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The sarcoplasmic reticulum (SR) is a
specialized smooth endoplasmic
reticulum
– Surrounds each and every myofibril
– Major role is to store calcium and to
release it on demand when the muscle
fiber is stimulate to contract
Animation
Muscle Contraction
31
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Produce movement by shortening
(contracting)
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Each muscle begins at an origin and
ends at an insertion.
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Each contract to produce a specific
action.
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In general, a muscle’s origin remains
stationary while the insertion moves.
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Recall that muscle can only contract.
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Several muscles that pull in different
directions usually surround each joint.
Steps leading to Muscle
Contraction
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Stimulation of the motor neuron causes it
axon terminals to release acetylchonline
(ACh)– a neurotransmitter
ACh molecules diffuse across the synapse
and attach to receptors in the sarcolemma
Sarcolemma becomes temporarily more
permeable to sodium ions which rush into
the muscle cell and to potassium ions that
diffuse out of the cell
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This change generates an electrical
current called an action potential
– This is unstoppable
– Results in contraction of the muscle cell
ACh is broken down while the action
potential is occurring to prevent
continued contraction
 To return to the resting state:
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– Diffusion of the potassium ion out of the
cell
– Sodium-potassium pump returns to their
initial positions
The Sliding-Filament Model
During muscle contraction, myosin
filaments form cross-bridges with actin
filaments. The cross-bridges then
change shape, pulling the actin
filaments toward the center of the
sarcomere.
 The attachment of the cross-bridges
require calcium ion that are released by
the SR, which is stimulated by the
action potential.
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This decreases the distance between
the Z lines and the fiber shortens
 The cross-bridge then detaches from
the actin and repeats the cycle by
binding to another site on the actin
filament and the fiber shortens.
 This causes the fibers to slide past each
other and the muscles to shorten.
 One ATP molecule = one interaction
between the myosin cross-bridge and
an actin filament
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When the action potential ends, the
calcium ions are immediately
reabsorbed into the SR storage area,
and the muscle relaxs.
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This whole process takes only a few
thousandths of a second.
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Animation
Warm-Up 1/19
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Page 218
– Short Answer Essay Problems 6 and 7
Graded Responses
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Individual muscle fibers follow the all or
none law but not whole muscles
– It will contract to its fullest all the time
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Muscles can react to stimuli with
different degrees of shortening (graded
responses)
– Produced two ways:
1. By changing the frequency of muscle
stimulation
2. By changing the number of muscle cells
being stimulated
Warm-Up 1/20
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Page 219 Questions 1, 5 and 7
Response to Increasingly Rapid
Stimulation
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Muscle twitches occur as a result of
certain nervous system problems
 Normally, nerve impulses are delivered so
rapidly that the muscle do not have time to
relax completely between stimuli
 Fused, or complete, tetenus is when the
muscle is stimulated so rapidly that no
evidence of relaxation is seen and the
contractions are completely smooth and
sustained. Until this is reached the muscle
is exhibiting unfused, or incomplete
tetanus.
Response to Stronger Stimuli
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How forcefully a muscle contracts,
depends largely on how many muscle
fibers are stimulated.
Providing the Energy Needed
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The bonds of ATP molecules are
broken to release the energy needed.
– Very little ATP is stored (4 – 6 seconds
worth)
– Direct phosphorylation of ADP by creatine
phosphate
– Aerobic Respiration
– Muscles use 3 pathways for ATP
regeneration:
– Anaerobic glycolysis and lactic acid
formation
Direct phosphorylation of ADP by
creatine phosphate (CP)
CP is only found in muscle fibers
 CP transfers a high-energy phosphate
group to ADP which regenerates ATP
 CP is also in limited supplies and last
for only about 20 seconds
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Aerobic Respiration
95% of ATP used for muscle activity
comes from this
 Occurs in the mitochondria
 Involves a series of metabolic pathways
that use oxygen
 Glucose is broken down into carbon
dioxide and water and releases energy
 Fairly slow
 Requires oxygen and nutrient fuels
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Anaerobic glycolysis and lactic
acid formation
Doesn’t use oxygen
Glucose is broken down into pyruvic acid
and small amounts of ATP
 If enough oxygen is not present, the
pyruvic acid forms lactic acid
 Produces only about 5% of much ATP as
aerobic respiration
 2.5% faster and provides 30 to 60 seconds
of strenuous muscle activity
 Promotes muscle fatigue and muscle
soreness
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Muscle Fatigue
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Unable to contract even though it is
being stimulated
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Believed to be a result of oxygen debt
Types of Muscle Contraction
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Muscles don’t always shorten when
they contract
– Tension develop in the muscles as the
actin and myosin myofilaments interact and
the myosin cross bridges attempt
Isotonic Contractions
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More familiar to most of us
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Myofilaments are successful in their
movements, the muscle shortens, and
movement occurs.
Isometric Contractions
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Contractions in which the muscles do
not shorten
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The tension in the muscle keeps
increasing
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Trying to slide but the muscle is pitted
against some immovable object
Muscle Tone
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State of continuous partial contractions
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Result of different motor units being
stimulated by the nervous system in a
systematic way
– Even when a muscle is relaxed, some of its
fibers are contracting
– If a muscle is no longer stimulated,
muscles become flaccid and begin to
atrophy
Effects of Exercise
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Inactivity leads to muscle weakness and
wasting
Regular exercise increases muscle size,
strength and endurance
Aerobic, or endurance, exercise result in
more flexible muscles with greater
resistance to fatigue
Resistance, or isometric, exercise pits
muscles against some immovable object.
Increases muscle size and strength due to
enlargement of muscle fibers and amount
of connective tissue increases
Interactions of Skeletal Muscles
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Muscles must be arranged in such a
way that whatever one muscle (or group
of muscles), other can reverse.
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A prime mover has the major
responsibility for causing a particular
movement
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An antagonist oppose or revers a
movement
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Synergists help prime movers by
producing the same movement or by
reducing undesirable movements
– Stabilizes joints
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Fixators are specialized synergists.
– Hold a bone still or stabilize the origin of a
prime mover
Naming Skeletal Muscles
Direction of muscle fibers
 Relative size of the muscle
 Location of the muscle
 Number of origins
 Location of origin and insertion
 Shape of the muscle
 Action of the muscle
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Arrangement of Fascicles
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Fascicle arrangements vary, producing
muscles with different structures and
functional properties
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Determines the muscles range of
motion and power
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Circular
– Concentric rings
– Typically surround external body openings
which they close by contracting
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Convergent
– Converge towards a single insertion
tendon
– Muscle is triangular or fan-shaped
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Parallel
– The length of the fascicles run parallel to the
long axis of the muscle
– Muscles are straplike
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Fusiform
– Modification of the parallel arrangement
– Results in spindle-shaped muscle with an
expanded belly
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Pennate
– Short fascicles attach obliquely to a central
tendon
– Unipennate, bipennate and multipennate