The Muscular System
Anatomy & Physiology I
Chapter 8
Types of Muscle
Smooth
Cardiac
Skeletal
Smooth Muscle
Makes
up walls of hollow body organs
(digestive tract, blood vessel wall), respiratory
passageways, uterus, iris
Involuntary
Cell
movement
structure
◦ Tapered ends
◦ Single, central nucleus
◦ No visible bands (striations)
Stimulated
stretching
by nerve impulses, hormones,
Cardiac Muscle
Makes
up wall of heart
Involuntary movement
Cell structure
◦ Branching interconnections
◦ Single, central nucleus
◦ Striated
◦ Membranes are intercalated disks
Stimulated by electrical impulses, nervous stimuli,
hormones
Skeletal Muscle
Attached
to bones, muscles, or skin
Voluntary movement
Cell structure
◦ Long and cylindrical
◦ Multiple nuclei per cell
◦ Heavily striated
Stimulated
by nervous system
Number of individual skeletal muscles in the
body: 600+
The Muscular System
Skeletal muscle has three primary functions
 Skeletal movement
 Posture maintenance
◦ muscles provided a steady partial contraction
(muscle tone) of muscles of the thigh, abdomin,
back, neck and shoulders

Heat generation
◦ heat is a natural by-product of muscle cell
metabolism
Structure of a Muscle
Muscle
Fiber - one muscle cell
Fascicles - bundles of muscle fibers
Structure of a Muscle:
Connective Tissue Components
Endomysium
– deep layer of connective tissue
surrounding indvidual muscle fibers
Perimysium – connective tissue surrounding
each fascicle
Epimysium (deep fascia) – connective tissue
sheath enclosing an entire muscle
the endomysium, perimysium and epimysium
merge to form tendons
Tendon – the band of connective tissue that
connect muscle to bone
Structure of a Skeletal Muscle Fiber
Muscle
fiber
Nucleus
A band
I band
Z disc
Mitochondria
Openings into
transverse tubules
Sarcoplasmic
reticulum
Triad:
Terminal cisternae
T ransverse tubule
Sarcolemma
Sarcoplasm
Myofibrils
Myofilaments
Structure Of A Skeletal Muscle
(A) Structure
of a muscle showing the tendon that attaches it to a bone.
(B) Muscle
tissue seen under a microscope. Portions of several fascicles are shown with
connective tissue coverings.
ZOOMING IN • What is the innermost layer of connective tissue in a muscle? • What layer of
connective tissue surrounds a fascicle of muscle fibers?
Muscle Cells in Action
Motor
unit is a single neuron and all the
muscle fibers it
Skeletal
muscle contraction requires
stimulation by a neuron
◦Paralysis occurs when the damaged nervous
system can’t get a signal to the muscles
Neuromuscular
junction (NMJ) – the point
of contact between a nerve fiber (axon) and a
muscle fiber.
Neuromuscular Junction (NMJ)

Neurotransmitter – chemical released from
neurons
◦ Acetylcholine (Ach) is the neurotransmitter released at
the NMJ



Synaptic cleft – tiny space between two cells
involved in a synapse
Receptors – specialized structures (on the
muscle cell membranes) that can be excited by
a stimulus
Motor end plate – muscle cell membrane that
contains receptors
Neuromuscular Junction (NMJ)
(A) The
branched end of a motor
neuron makes contact with
the membrane of a muscle
fiber (cell).
(B)
Enlarged view of the NMJ
showing release of
neurotransmitter acetylcholine
(Ach) into the synaptic cleft.
(C) Acetylcholine
attaches to
receptors in the motor end
plate, whose folds increase
surface area.
(D) Electron
microscope
photograph of the
neuromuscular junction.
Properties of Muscle Tissue
Excitability
(ability to respond to stimuli)
◦ Action potential – spreading wave of electrical
current
Contractility
(ability to shorten when stimulated)
◦ Actin – thin protein filament in muscle cells (light)
◦ Myosin – thick protein filament in muscle cells (dark)
 Striations result from the alternating bundles of actin (light)
and myosin (dark) filaments
 Crossbridge – attachment between myosin head and actin
◦ Sarcomere – contracting subunit of skeletal muscle
Sliding Filament Mechanism of Skeletal
Muscle Contraction
(A) Muscle is relaxed and there is no contact between the actin and myosin filaments.
(B) Cross-bridges form and the actin filaments are moved closer together as the
muscle fiber contracts.
(C)The cross-bridges return to their original position and attach to new sites to
prepare for another pull on the actin filaments and further contraction.
ZOOMING IN • Do the actin or myosin filaments change in length as contraction
proceeds?
The Role of Calcium
Calcium
Is
released when nerve fiber stimulates
muscle cell
Attaches
to proteins blocking receptor sites
Allows
cross-bridges to form between actin
and myosin
Returns
to endoplasmic reticulum (ER),
which is called “sarcoplasmic reticulum” in
muscle cells.
Energy Sources
Muscle contraction requires energy (ATP),
oxidized in muscle cells from
Oxygen
Glucose or other usable nutrient
Compounds in muscle cells that store
oxygen, energy, or nutrients
Myoglobin – stores oxygen
Glycogen – stores glucose
Creatine phosphate – stores energy; can be
used to make ATP
Oxygen Consumption
Aerobic
glucose metabolism – cellular
production of ATP in the presence of
adequate oxygen
Anaerobic glucose metabolism – cellular
production of ATP in the presence of low,
inadequate oxygen
◦ Inefficient production of ATP
◦ Lactic acid accumulation
◦ Oxygen debt – rapid breathing after exercise;
replenishes oxygen stores; rid cells of lactic acid
◦ Recovery oxygen consumption – the period
after exercise when extra oxygen is needed
Effects of Exercise
Improved
Increase
balance, joint flexibility
in muscle size (hypertrophy)
Improvements
in muscle tissue
Vasodilation
Strengthened
Improved
efficiency
Weight
heart muscle
breathing and respiratory
control
Stronger
bones
Types of Muscle Contractions
Muscle Tone
(Tonus) – the normal state of balanced
tension or partial contraction while a muscle is in a
passive state; constant state of readiness for action
Isotonic
◦ No change in tension
◦ Muscle length shortens
◦ Movement
Isometric
◦ Great increase in tension
◦ Muscle length unchanged
◦ No movement
Isometric and Isotonic Contractions
Muscle develops
tension but does
not shorten
Muscle shortens,
tension remains
constant
Movement
No movement
(a) Isometric contraction
(b) Isotonic concentric contraction
Muscle lengthens
while maintaining
tension
Movement
(c) Isotonic eccentric contraction
The Mechanics of Muscle Movement
Tendons attach muscles to bones
Origin—attached to more fixed part of
skeleton
Insertion—attached to more moveable
part of skeleton
Muscle Origins and Insertions



Origin
◦ bony attachment at
stationary end of muscle
Belly
◦ thicker, middle region of
muscle between origin and
insertion
Insertion
◦ bony attachment to mobile
end of muscle
Origins
Scapula
Origins
Humerus
Bellies
Extensors:
Triceps brachii
Long head
Flexors:
Biceps brachii
Brachialis
Lateral head
Insertion
Insertion
Radius
Ulna
Muscles Work Together

action – the effects produced by a muscle
◦ to produce or prevent movement

prime mover (agonist) - muscle that produces
most of force during a joint action

synergist - muscle that aids the prime mover
◦ stabilizes the nearby joint
◦ modifies the direction of movement

antagonist - opposes the prime mover
◦ preventing excessive movement and injury
Muscle Actions Across Elbow
Origins
Origins
Scapula
Humerus
Bellies
Extensors:
Triceps brachii
Long head
Flexors:
Biceps brachii
Brachialis
Lateral head
Insertion
Insertion
Radius
Ulna
prime mover
- brachialis
 synergist
- biceps brachii
 antagonist
- triceps brachii

Skeletal Muscle Groups
Characteristics for naming muscles (often
combined)
Location
Size
Shape
Direction
Number
Action
of fibers
of heads (attachment points)
Superficial Muscles (anterior view)
Associated
structure is
labeled in
parentheses.
Superficial Muscles (posterior view)
Associated
structures
are labeled in
parentheses.
Muscles of the Head
Facial
◦
◦
◦
◦
expression (orbicularis) muscles
Orbicularis oculi
Orbicularis oris
Levator palpebrae superioris
Buccinator
Mastication
◦
◦
◦
◦
(chewing) muscles
Temporalis
Masseter
Intrinsic
Extrinsic
Muscles of the Head
Associated
structure is labeled
in parentheses.
ZOOMING IN
• Which of the
muscles in this
illustration is named
for a bone it is near?
Muscles of the Neck
Are
ribbonlike
Extend
up, down, or obliquely
Extend
in several layers in a complex
manner
Most
common is sternocleidomastoid
Muscles of the Upper Extremities
Position
the shoulder
Move the arm
Move the forearm and hand
Muscles That Move the Shoulder and
Arm
Trapezius
Latissimus
dorsi
Pectoralis major
Serratus anterior
Deltoid
Rotator cuff
◦ Supraspinatus
◦ Infraspinatus
◦ Teres minor
◦ Subscapularis
Muscles That Move the Forearm and
Hand
Brachialis
Biceps
brachii
Brachioradialis
Triceps
Flexor
brachii
carpi
Extensor
Flexor
carpi
digitorum
Extensor
digitorum
Muscles That Move The Forearm & Hand
Muscles of the Trunk
Breathing
muscles
Abdominal
muscles
Pelvic
floor muscles
Deep
back muscles
Muscles of Respiration
Diaphragm
Intercostal
muscles
Muscles of Respiration
Associated structures are also shown.
Muscles of the Abdomen and Pelvis
External
oblique
Internal oblique
Transversus abdominis
Rectus abdominis
Levator ani
Muscles of the abdominal wall
Surface tissue is
removed on the right
side to show deeper
muscles.
Associated structures
are labeled in
parentheses.
Muscles of the female perineum (pelvic floor)
Associated structures are labeled in parentheses.
Deep Muscles of the Back
Erector
spinae
Deeper muscles in the lumbar area
Muscles of the Lower Extremities
Among
the longest and strongest in the
body
Specialized for locomotion and balance
Muscles That Move the Thigh and Leg
Gluteus
maximus
Gluteus medius
Iliopsoas
Adductors
Sartorius
Iliotibial (IT) tract
Hamstrings
Muscles of the Thigh
Associated structures are labeled in parentheses.
Muscles That Move the Foot
Gastrocnemius
Achilles
tendon
Soleus
Tibialis
anterior
Peroneus
Flexor
longus
and extensor muscles
Muscles That Move The Foot
Associated structures are labeled in parentheses
Effects of Aging on Muscles
Beginning at about age 40
Gradual
Loss
loss of muscle cells
of power
Tendency
to flex hips and knees
Decrease
in height
Muscular Disorders
Spasms
◦ Colic
◦ Seizure or convulsion
Cramps
Strains
Sprains
Atrophy
Diseases of Muscles
Muscular
dystrophy
Myasthenia
gravis
Myalgia
Myositis
Fibrositis
Fibromyositis
Fibromyalgia
syndrome (FMS)
Disorders of Associated Structures
Bursitis
– inflammation of a bursa
Bunions
- unnatural, bony hump that forms at the base of the
big toe
Tendinitis
- inflammation in or around a tendon
Tenosynovitis
– inflammation of the lubricating sheath
surrounding tendons.
Shin
Splints – pain most likely caused by repeated stress on the
shin bone (tibia) and the tissue that connects the muscle to the
tibia.
Carpal
tunnel syndrome - caused by compression of peripheral
nerves affecting one or both hands. C
haracterized
by a sensation of numbness, tingling, burning and/or
pain in the hand and wrist
End of Presentation