The Muscular System
Learning Objectives
• List the 3 types of muscles and describe the characteristics of each.
• Describe the structure and function of tendons, aponeuroses, and
ligaments.
• Differentiate between prime mover, antagonist, synergist, and
fixator muscles.
• List the locations and actions of the muscles of the head and neck,
abdomen, thoracic limb, pelvic limb, and the muscles of
respiration.
Muscle
• One of the four basic tissues of the body
• Made up of cells that can shorten or contract
•
• Three different types of muscle
skeletal muscle – moves the bones of the skeleton
Voluntary striated muscle
cardiac muscle
smooth muscle –eyes, air passageways in
lungs, stomach, intestines, urinary bladder,
blood vessels, reproductive tract
Striated means stripes (light and dark colored bands)
Skeletal Muscle
Skeletal muscle- multiple nuclei
Smooth muscle cells
Cardiac muscle cells
(intercalated discs)
Questions
• What is muscle?
• What are the three types of muscle and some
characteristics of each?
Muscle Attachments
:
• Are well defined groups of skeletal muscle cells surrounded
by a layer of fibrous (collagen)connective tissue called fascia
• Surrounds, binds together
• Sliding and gliding
• Are attached to bones by tendons (fibrous connective
tissue)
• https://www.youtube.com/watch?v=PdJ5QDkqG2g
• Are attached to bones or other muscles by broad sheets of
fibrous connective tissue called aponeuroses
• Linea Alba-abdominal muscles come together at the linea alba
• Common surgical incision site abdominally (ventral midline)
• https://www.youtube.com/watch?v=dvJzxg1y2rs
Aponeurosis (in human)
Muscle fascia
Muscle Attachment sites
• Origin: the more stable of a muscle's attachment
sites
▫ The bone does not move much when the muscle
contracts
• Insertion: site that undergoes most of the
movement when a muscle contracts
▫ Undergoes most movement when a muscle
contracts
• Belly of a muscle- the bulging central part of a
muscle. (Pretty much between tendon and
tendon)
• Important to know for intramuscular injections
purpose of depositing drug
Questions
• What is the difference between a tendon, fascia
and an aponeurosis?
• What is the origin of a muscle?
• What is the insertion of a muscle?
Muscle Actions
• Muscles contract/ relax…they do not push or
stretch by their own
• Prime mover (agonist): a muscle or muscle
group that directly produces a desired
movement
• Antagonist: a muscle or muscle group that
directly opposes the action of a prime mover
Muscle Actions
• Synergist: a muscle that contracts at the
same time as a prime mover and assists it
in carrying out its action
• Fixator: muscles that stabilize joints to
allow other movements to take place
example
• Bicep Curl movement
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Prime mover is the biceps
Antagonist is triceps
Fixator is deltoid
Synergist is brachialis
Muscle-Naming Conventions
• Action: flexor muscles; extensor muscles
levatator, depressor, rotator, supinator, pronator
• Shape: deltoid means “triangular shaped”
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Quadratus
Rhomboideus
Scalenus
Serratus
Teres
• Location:
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Biceps brachii muscle is located in the brachial region
Pectoral = chest
Epaxial = above pelvic axis
Intercostal=between ribs
Infraspinatus=beneath spine of scapula
Supraspinatus=above spine of scapula
Inferior=below, medius=middle, superior=above
Externus=outer, internus=inner
Orbicularis=surrounding another structure
• Direction of fibers:
▫ rectus means “straight”
▫ Oblique means slanted (outward away from
midline
▫ Transverse means crosswise (to midline)
Muscle-Naming Conventions
• Number of heads or divisions: -cep means
“head”;
▫ biceps brachii muscle has two heads
• Attachment sites:
▫ origin of the sternocephalicus muscle is the
sternum and insertion is the back of the
head
Cutaneous Muscles
• Thin, broad,
superficial muscles
• Found in the fascia
just beneath the skin
• Little or no attachment
to bones
• Serve to twitch the
skin
Cutaneous Muscles
• Cutaneous Trunci
• Platysma
Head and Neck Muscles
Functions
•
•
•
•
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Control facial expressions
Enable mastication
Move structures such as eyes and ears
Support the head
Allow the head and neck to flex, extend, and move
laterally
Head and Neck Muscles
• Masseter muscle - closes the jaw
• Splenius and Trapezius muscles - extend
the head and neck
• Brachiocephalicus muscle - extends the
head and neck; also pulls the front leg
forward
• Sternocephalicus muscle - flexes (LOWER)
the head and neck
Head muscles
• Masseter
O=zygomatic arch
I=mandible
A= elevates mandible to
close mouth
• Temporal
O=temporal fossa
I=coronoid process
(of the mandible)
A=elevate mandible, moves
lower jaw backward
FYI:
Digastric Muscle opens the mouth
Muscles of the Head and Neck
• These muscles move the head and neck
Sternocephalicus
Origin - manubrium (sternum)
Insertion – 2 points of insertion
mastoid
nuchal crest of occipital bone
Action –depresses the head and neck, draws the
head and neck to side
Sternocephalicus
head and neck
• The sternocephalicus,
runs along side the
braciocepalicus (thoracic limb
muscle)
• Forms the jugular groove
Brachiocephalicus is a complex
muscle!
• Dorsal part of Neck :
• Mastoid Process:
Cleidomastoidus – from
clavicle remnant to
mastoid process
Cleidocervicalis – from
clavicle remnant to
dorsal part of neck
Brachiocephalicus
Cleidocervicalis –
from clavicle
remnant to dorsal
part of neck
• From clavicle
remnant to distal
end of humerus:
Cleidobrachialis
Human Clavicle
Brachiocephalicus
Origin
Cleidocervicalis – clavicle remnant
Cleidomastoid –clavicle remnant
Cleidobrachialis-clavicle remnant
Insertion
Cleidocervicalis – dorsal neck
Cleidomastoid – mastoid process (behind external
acoustic meatus)
Cleidobrachialis-humerus
Action – Pulls leg forward, neck and head down, neck
and head side to side.
Brachiocephalicus
Trapezius
• Origin – Dorsal aspect of neck
• Insertion – scapula spine
•
Action – elevates and abducts forelimb
• (Holds shoulder against body)
Trapezius
Rhomboideus
This muscle lies beneath the Trapezius and has
three parts
Origin – Nuchal Crest of Occipital bone
Dorsal neck
T1- T7
Insertion – dorsal border of the scapula
Action - pulls top of shoulder up forwards and
towards the body.
Elevates forelimb
When shoulder is still it can lift the neck.
Rhomboideus
Thoracic Limb Muscles
• Superficial muscles of the shoulder region
▫ Latissimus dorsi muscle - flexes the
shoulder
▫ Pectoral muscles - one superficial and one
deep; adduct the front leg
▫ Deltoid muscle - abducts and flexes the
shoulder joint
Thoracic Limb Muscles
• Brachial muscles
▫ Biceps brachii muscle - flexes the elbow
joint
▫ Triceps brachii muscle - extends the elbow
joint
• Carpal and digital muscles
▫ Extensor carpi radialis muscle - extends the
carpus
▫ Deep digital flexor muscle - flexes the digit
Supraspinatus
• Origin – supraspinatus fossa
Insertion - greater tubericle of humerus
Action - Extends and stabilizes shoulder joint
Supraspinatus
Infraspinatus
• Origin – infraspinous fossa.
Insertion - greater tubericle of the humerus.
Action – flexes the shoulder joint, abducts the
limb at the shoulder
stabilize the shoulder joint.
Infraspinatus
Serratus Ventralis
Origin – 2 points of origin
Neck – transverse process of C3-C7
Chest –Ribs 1 - 7
Insertion – scapula
Action –supports the trunk, depresses the scapula
Serratus Ventralis
Latissimus Dorsi
Origin - On the top of the spines, muscles starting
at the top of the shoulder to the tips of the lumbar
vertebrae as well as from the last two or three ribs.
Spinous process of the lumbar and thoracic
vertebrae (T7 / T8) including ribs
Insertion – tuberosity of the humerus
Action - pulls leg backwards, flexes shoulder joint
Latissimus Dorsi
Deltoid
Origin –
Acromial- Acromion at the bottom end of the spine of
the scapula
Spinal – spine of the scapula
Insertion - humerus
Action – flexes shoulder joint, pulls the foreleg away
from the dog’s body
Deltoid
Biceps Brachii
• Origin – supraglenoid tubercle (distal scapula)
Insertion – proximal medial radius/ ulna
Action - Flexes elbow joint and extends shoulder
joint
Bicep
Tricep
• Origin – caudal border scapula, proximal
humerus
• Insetion – olecranon tubercle
•
Action
• Long head– Flexes the shoulder joint and
extends the elbow joint
Lateral Head – only extends the elbow joint
Tricep
Extensor Muscles of the radius,
ulna, carpus, metacarpus, digits
• Origin-lateral epicondyle of humerus
• Insertion- carpals, metacarpals, digits
• Action- extend carpus, digits
Flexor muscles of radius, ulna,
carpus, metacarpus, digits
• Origin- medial epicondyle of humerus
• Insertion-palmer and medial aspects of the
carpus, metacarpus, digits
• Action- flexes carpus, and/ or digits, abducts
digits
Flexor and Extensor
muscles of the
thoracic limb
Abdominal Muscles
Functions
• Support the abdominal organs
• Help flex the back
• Participate in various functions that
involve straining
▫ Defacation, urination, parturition,
vomiting,regurgitation
• Play a role in respiration
Abdominal Muscles
• Arranged in layers
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▫
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External abdominal oblique muscle
Internal abdominal oblique muscle
Rectus abdominis muscle
Transversus abdominis muscle
• Left and right parts of each muscle come
together on the ventral midline at the linea
alba
External Abdominal Oblique
• O=last rib
• I=Linea Alba
• Action= flexes vertebral
column, compresses abdominal
cavity
Pelvic Limb Muscles
• Gluteal muscles - extensor muscles of the
hip
• “Hamstring" muscle group - extend the hip
joint; main flexors of the stifle joint
▫ Biceps femoris muscle
▫ Semimembranosus muscle
▫ Semitendinosus muscle
Pelvic Limb Muscles
• Quadriceps femoris muscle
▫ - main extensor muscle of the stifle joint
• Gastrocnemius muscle
▫ - extensor muscle of the hock
Superficial Gluteal Muscle
• Origin-sacrum/ coccygeal vertebrae
• Insertion-greater trochanter of femur
• Action-abducts the limb/ extends the hip
Superficial Gluteal Muscle
Gluteus Medius
• Origin-lateral ilium
• Insertion-greater trochanter of femur
• Action-abducts the limb/ extends the hip
Gluteus Medius Muscle (Deep)
Quadriceps Femoris Muscle:
Vastus Lateralis,
Vastus Medius,
Deep Vastus Intermedius,
Rectus Femoris
Quadriceps Femoris
Origin –
Vastus medialis – Proximal femur (inside)
Vastus lateralis – Proximal femur (outside)
Deep vastus intermedius – Proximal femur (inside)
Rectus Femoris – ilium
Insertion - All of the vastus muscles insert into their own areas of
the rectus femoris then they all insert together into the patella and
so also the tibial tuberosity.
Action - extend stifle and flex hip
Quadriceps
Rectus Femoris and Vastus Lateralis
Patella
(remember the patella is
embedded in a tendon that
passes through the trochlea
of the distal end of the femur)
Biceps femoris
• This muscle spans 3 joints: The hip
(coxofemoral joint), stifle, and tarsus
• Origin- ischiatic tuberosity of pelvis
• Insertion-patella, proximal tibia
• Action: extends hip joint, flexes stifle, extends
tarsal joints
Biceps Femoris
(Hamstring)
Semitendinosus
(part of the hamstring group)
• Origin- ischiatic tuberosity
• Insertion- tibia and tuber calcanei
• Action-extends the hip, flexes the stifle
Semitendinosus (Hamstring)
Semimembranosus
(part of the hamstring group)
Origin – ischiatic tuberosity of pelvis
Insertion – femur and tibia
Action - Pulls the limb towards the middle of the body, extends hip
joint
Semimembranous
Sartorius
• O=Crest of ilium
• I=Patella (cranial portion)
Tibia (caudal portion)
• Action= flexes hip,
cranial portion of muscle extends stifle,
caudal portion flexes stifle
Sartorius
Gastrocnemius and Achilles tendon
Origin- medial and lateral
supracondylar tuberosities of femur
(distal end of femur)
Insertion-proximal calcaneal tuber
Action- extends the tarsus, flexes the
stifle
Muscles of respiration
Function
• Increase and decrease the size of the
thoracic cavity
▫ Inspiratory muscles
 Diaphragm
 External intercostal muscles
▫ Expiratory muscles
 Internal intercostal muscles
 Abdominal muscles
Subcutaneous
Intramuscular, SQ, Intradermal
Intramuscular injections
• https://www.youtube.com/watch?v=tQaBenzkUU
Locations of Injection sites
• Cat and Dog
▫ Pelvic limb
 Gluteal Muscles
 Quadriceps Femoris
 Gastrocnemius
 semimembranosus, semitendinosus
Thoracic Limb
Triceps Brachii
Epaxial muscles-why?
IM injection sites
Semitendinosis
Quadriceps
Skeletal Muscle Cells
• Very large
• Multinucleate
• Numerous myofibrils
composed of actin
and myosin
• Network of sarcoplasmic
reticulum
• T tubules
Skeletal Muscle Cells
• A bands: thick
myosin filaments
• I bands: thin
actin filaments
▫ Dark line in the center
of the I band is the Z line
▫ Disk that is the attachment
site for the actin filaments
Skeletal Muscle Cells
• Sarcomere - basic
contracting unit of
skeletal muscle
• Area from one Z
line to the next Z line
• Each myofibril is
made up of many
sarcomeres lined
up end to end.
Neuromuscular Junction
• Nerves and muscles
separated by the
synaptic space
• Synaptic vesicles sacs at the end of a
nerve fiber; contain
acetylcholine
▫ Acetylcholinesterase enzyme in the synaptic
space that removes
acetylcholine
Motor Unit
• One nerve fiber and all the muscle fibers it
innervates
• Muscles that make small, delicate
movements have only a few muscle fibers
per nerve fiber in each motor unit
• Large, powerful muscles may have a
hundred or more muscle fibers per motor
unit
Connective Tissue Layers
• Hold components of the muscle together
• Contain the blood vessels and nerve fibers
that supply the muscle fibers
• Continuous with tendons or aponeuroses
that connect muscle to bones or other
muscles
Connective Tissue Layers
• Endomysium - composed of fine, reticular
fibers; surrounds each muscle fiber
• Fascicles - groups of skeletal muscle fibers
• Perimysium - composed of reticular fibers
and thick collagen fibers; surrounds
fascicles
• Epimysium - fibrous layer composed of
tough collagen fibers; surrounds groups of
muscle fascicles
Initiation of Muscle Contraction &
Relaxation
• Nerve impulse reaches the end bulb of the
motor nerve fiber
• Acetylcholine is released into the synaptic
space
• Acetylcholine molecules bind to receptors
on the surface of the sarcolemma
• Impulse travels along the sarcolemma and
through the T tubules to the interior of the
cell
Initiation of Muscle Contraction &
Relaxation
• Impulse reaches the sarcoplasmic
reticulum
• Calcium ions (Ca++) are released into the
sarcoplasm
• Ca++ diffuses into the myofibrils and starts
the contraction process
Initiation of Muscle Contraction &
Relaxation
• Sarcoplasmic reticulum begins pumping
Ca++ back in again
• Ca++ is pulled out of the myofibrils
• Contraction stops, muscle returns to its
original length
Mechanics of Muscle Contraction
• Relaxed muscle fibers have actin and
myosin filaments that slightly overlap
• When stimulated to contract, crossbridges
on myosin filaments slide back and forth
Mechanics of Muscle Contraction
• Actin filaments on both sides are pulled
toward the center of the myosin filaments.
• This shortens the sarcomere.
• Shortening of all the end-to-end
sarcomeres in a muscle fiber results in a
muscle contraction.
Characteristics of Muscle
Contraction
All-or-nothing principle
• When stimulated, an individual muscle fiber
either contracts completely or not at all.
• Nervous system controls the number of muscle
fibers it stimulates for a particular movement
▫ Small, fine movements require only a few muscle fibers to
contract.
▫ Larger, more powerful movements require contraction of
many muscle fibers.
Muscle Contraction
Three phases:
1. Latent phase - time between nerve stimulus
and beginning of contraction (about 10 ms)
2. Contracting phase - lasts about 40 ms
3. Relaxation phase - lasts about 50 ms
Muscle Contraction
• Maximum contraction efficiency occurs if
nerve impulses arrive about 0.1 second
apart.
• Results in a series of complete muscle fiber
twitches
• Careful timing of the nerve impulses to
motor units of the muscle is needed to
make muscle contract smoothly.
Chemistry of Muscle Contraction
• ATP provides energy to allow the sliding of
the actin and myosin filaments
• Creatine phosphate converts ADP back to
ATP
• Glucose and Oxygen - help produce ATP &
CP
▫ Glucose stored in muscle as glycogen
▫ Oxygen stored as myoglobin
Chemistry of Muscle Contraction
• Anaerobic metabolism - used if oxygen
need exceeds oxygen supply
▫ Results in lactic acid formation
▫ Lactic acid accumulation causes discomfort
Heat Production
• Muscle activity generates heat
• Panting or sweating - mechanisms to
eliminate excess heat
• Shivering - spasmodic muscle contractions
that increase heat production
Cardiac Muscle
• Small cells with single nucleus
• Intercalated disks:
attachments between cardiac
muscle cells
▫ Allow transmission of impulses
from cell to cell for coordinated
contraction of large groups of cells
Physiology of Cardiac Muscle
• Cardiac cells contract without any external
stimulation
• Groups of cardiac muscle cells contract at
the rate of the most rapid cell in the group
• Contractions are rapid and wavelike
Physiology of Cardiac Muscle
Cardiac Conduction System
• Sinoatrial (SA) node
▫ Generates the impulse that starts each
heartbeat
▫ Located in the wall of the right atrium
• Impulse follows a controlled path through
the conduction system of the heart
• Structures in the system transmit, delay,
and redirect
Nerve Supply
• Heart is innervated by nerves from both
the sympathetic and parasympathetic
systems
• Sympathetic fibers stimulate the heart to
beat harder and faster as part of the "fight
or flight response”
• Parasympathetic fibers inhibit cardiac
function, causing the heart to beat more
slowly and with less force
Smooth Muscle Gross Anatomy
Two main forms
• Visceral smooth muscle
▫ Large sheets of cells in the walls of some
hollow organs
• Multiunit smooth muscle
▫ Small, discrete groups of cells
Smooth Muscle Cells
• Small, spindle-shaped;
single nucleus
• Actin and myosin
filaments arranged
as small contractile
units that crisscross
the cell
▫ Attached at both ends to
"dense bodies" that correspond
to the Z lines of skeletal muscle
Visceral Muscle
• Found in the walls of many internal organs
(e.g., stomach, intestines, uterus, urinary
bladder)
• Contracts in large, rhythmic waves
• Contracts without external stimulation
▫ Reacts to stretching by contracting more
strongly
▫ Innervated by nerves from both the
sympathetic and parasympathetic systems
▫ Sympathetic stimulation decreases activity;
parasympathetic stimulation increases
activity
Multi-Unit Smooth Muscle
• Individual smooth muscle cells or small
groups of cells
• Found where small, delicate contractions
are needed (e.g., iris, walls of small blood
vessels)
• Contraction requires autonomic nervous
system impulse
Splenius
Origin - Nuchal ligament and spinous process of C3, C4, C5
Insertion - 5 points
1. Back of the skull (middle and top to mastoid process)
2. C1
3. C3
4. C4
5. C5
Action - move neck up and head forward
One muscle moves neck to one side.