Naming Skeletal Muscle
Types of Muscles
• Most often body movements are the result of
the activity of pairs or teams of muscles acting
together or against each other
• Muscles that oppose or reverse a movement
are antagonists
E.g. the biceps is antagonized by the triceps
• The muscle that has the major responsibility
for causing a particular movement is called
the prime mover
Types of Muscle
• The muscles that help prime movers by
producing the same movement or by reducing
undesirable or unnecessary movement are
called synergist (syn= together, erg = work)
• Fixators are specialized synergists. They act to
hold a bone still or to stabilize the origin of a
prime mover so all the tension can be used to
move the insertion bone
e.g. the muscles that anchor the scapula
Naming Skeletal Muscles
• Muscles are named on the basis of several
criteria, each of which focuses on a particular
structural or functional characteristic
Naming Skeletal Muscles
1. Direction of the
muscle fibers: muscles
are named in
reference to some
imaginary line, usually
the midline of the
body or the long axis
of a limb bone
- Rectus: (straight) its
fibers run parallel to
that imaginary line
- Oblique: (slanted) its
fiber run obliquely to
the imaginary line
Oblique Rectus
Naming Skeletal Muscles
2. Relative size of the muscle:
- Maximus: largest
- Minimus: smallest
- Longus: long
e.g. gluteus Maximus
3. Location of the muscle: some muscles are named
for the bone with which they are associated
e.g. temporalis and frontalis
Naming Skeletal Muscles
4. Number of origins: When the
term biceps, triceps or
quadriceps forms part of a
muscle name, one can assume
that the muscle has two, three,
or four origins
5. Location of the muscle’s
origin and insertion: Muscles
are named for their attachment
sites.
e.g. sternocleidomastoid
muscle: has its origin on the
sternum and clavicle and inserts
on the mastoid process of the
temporal bone
Naming Skeletal Muscles
6. Shape of the muscle:
- Deltoid: triangular
7. Action of the muscle:
When muscles are named for
their actions, terms such as
flexor, extensor and adductor
appear in their names
Head Muscles
Facial Muscles
• Frontalis: covers the frontal
bone. This muscle allows
you to raise your eyebrows
• Orbicularis Oculi: fibers
that run in circles around
the eyes. It allows you to
close your eyes, squint,
blink and wink
- Orbicularis: circling
- Oculi: eyelike
Facial Muscles
• Orbicularis Oris: The
circular muscle of the lip, it
is often called the “kissing”
muscle
- Oris: Mouth
• Buccinator (Bu’si-nator):
runs horizontally across the
cheek and inserts into the
orbicularis oris, it flattens
the cheek. It is also listed
as a chewing muscle
Facial Muscles
• Zygomaticus: extends
from the corner of
the mouth to the
cheek bone. It is
often referred to as
the smiling muscle
Chewing Muscles
• Masseter: Covers the angle of
the lower jaw as it runs from
the zygomatic process of the
temporal bone to the mandible.
This muscle closes the jaw by
elevating the mandible
• Temporalis: is a fan-shaped
muscle overlying the temporal
bone. It inserts into the
mandible and acts as a
synergist of the masseter in
closing the jaw
Trunk and Neck Muscles
Anterior Muscle
Sternocleidomastoid
• The paired muscles are two
headed muscles, one found
on each side of the neck.
- One arises from the sternum
and the other arises from the
clavicle
- The heads fuse before
inserting into the mastoid
process of the temporal bone
- When both muscles contract
together, they flex your neck
- If just one muscle contracts,
the head is rotated towards
the opposite side
Pectoralis Major
• A large fan-shaped
muscle covering the
upper part of the chest
• Its origin is from the
shoulder girdle and the
first six ribs and inserts
on the proximal end of
the humerus
• It is the prime mover for
shoulder flexion and
adduction
Intercostal Muscles
• Deep muscles found
between the ribs
• The external intercostals
are important in breathing
because they help to raise
the rib cage for breathing
air in
• The internal intercostals
depress the rib cage,
which helps to move air
out of the lungs when you
exhale
Muscles of the Abdominal Girdle
• Rectus abdominis: the paired
strap-like muscles are the
most superficial muscles of
the abdomen.
• They run from the pubis to
the rib cage
• Their main function is to flex
the vertebral column
• They also compress the
abdominal contents and are
involved in forced breathing
Muscles of the Abdominal Girdle
• External oblique: are paired
superficial muscles that make
up the lateral walls of the
abdomen
• Their fibers run downward and
medially from the last eight ribs
and insert into the ilium
• They flex the vertebral column
but they also rotate the trunk
and bend it laterally
Muscles of the Abdominal Girdle
• Internal oblique: Paired
muscles deep to the external
obliques
• Their fiber run at right angles
to those of the external
obliques
• They raise from the iliac crest
and insert into the last three
ribs
• Their functions are the same as
those of the external obliques
Muscles of the Abdominal Girdle
• Transversus abdominis: The
deepest muscle of the
abdominal wall and has
fibers that run horizontally
across the abdomen
• It raises from the lower ribs
and iliac crest and inserts
into the pubis
• This muscle compresses the
abdominal contents
Which one is which?
Transversus
abdominis
Internal
Oblique
External
Oblique
Trunk and Neck Muscles
Posterior Muscle
Trapezius (Trah-pee-ze-us)
• These muscles are the most
superficial muscles of the
posterior neck and upper trunk
• When seen together, they
form a diamond or kite-shaped
muscle mass
• These muscles are antagonists
of the sternocleidomastoids
• They also can elevate, depress,
adduct and stabilize the
scapula
Latissimus Dorsi
• The large, flat muscle
pair that covers the
lower back
• It originates on the lower
spine and ilium and then
sweeps superiorly to
insert into the proximal
end of the humerus
• It extends and adducts
the shoulder and help
maintain upright posture
Erector Spinae (spi’na)
• It is a prime mover of back
extension.
• Each erector spinae is a
composite muscle consisting
of three muscle columns that
collectively span the entire
length of the vertebral column
• They act as powerful back
extensors and also provide
resistance that helps control
the action of bending over at
the waist
Deltoid
• They are fleshy, triangleshaped muscles that
form the rounded shape
of your shoulders
• The deltoids are the
prime movers of arm
abduction
• It is the antagonist of
latissimus dorsi
Muscles of the upper limb
Upper Limb Muscles
• The upper limb muscles fall into three groups:
1. Muscles that arise from the shoulder girdle and
cross the shoulder joint to insert into the
humerus
E.g. the pectoralis major, latissimus dorsi and
deltoid
2. Muscles that cause movement at the elbow joint
E.g. Biceps, Triceps
3. Muscles of the forearm, which insert on the hand
bones and cause their movement
Biceps Brachii (bra’ke-i)
• It originates by two
heads from the shoulder
girdle and inserts into the
radial tuberosity.
• It is the powerful prime
mover for flexion of the
forearm and acts to
supinate the forearm
Triceps Brachii
• The only muscle
fleshing out the
posterior humerus.
• Its three heads arise
from the shoulder
girdle and proximal
humerus and it inserts
into the olecranon
process of the ulna
Muscles of the lower limb
Iliopsoas (il’e-o-so’us)
• A fused muscle composed
of two muscles
• It runs from the iliac bone
and lower vertebrae deep
inside the pelvis to insert on
the lesser trochanter of the
femur
• It is a prime mover of hip
flexion
• It also acts as a postural
muscle to keep the upper
body from falling backward
when standing up
Adductor Muscles
• The muscle of the adductor
group form the muscle
mass at the medial side of
each thigh
• They adduct the thighs
together
• The adductors have their
origin on the pelvis and
insert on the femur
Gluteus Maximus
• It is a superficial muscle of
the hip that forms most of
the flesh of the buttock
• It is a powerful hip
extensor that acts to bring
the thigh in a straight line
with the pelvis
• It originates from the
sacrum and iliac bones
and runs to insert on the
gluteal tuberosity of the
femur
Gluteus Medius
• It runs from the ilium to the
femur, beneath the gluteus
maximus for most of its
length
• It is a hip abductor and is
important in steadying the
pelvis during walking
• It is an important site for
giving intramuscular
injections
Sartorius
• A thin, strap-like muscle
• It runs obliquely across the
thigh from the anterior iliac
crest to the medial side of
the tibia
• It is a weak thigh flexor
Quadriceps Group
• It consists of four muscles: one
rectus femoris and three vastus
muscles
• The rectus femoris originates
on the pelvis
• The vastus muscles originates
from the femur
• The four muscles insert into the
tibial tuberosity
• The group as a whole acts to
extend the knee powerfully
Hamstring Group
• The muscles forming the
muscle mass of the
posterior thigh are the
hamstrings
• It extends the thigh and
flexes the knee
• The group consists of three
muscles, the biceps
femoris, semimembranosus
and semitendinosus which
originate on the ischial
tuberosity and run down
the thigh to insert on both
sides of the proximal tibia
Tibialis Anterior
• It is a superficial muscle
on the anterior leg. It
arises from the upper
tibia and then parallels
the anterior crest as it
runs to the tarsal bones
where it inserts by a long
tendon
• It acts to dorsiflex and
invert the foot
Peroneus Muscles
• The peroneus muscles of
this group are found on the
lateral part of the leg
• They arise from the fibula
and insert into the
metatarsal bones of the
foot
• The group as a whole
plantar flexes and everts
the foot
Gastrocnemius (gas’trok-ne’meus)
• It is a two bellied muscle that
forms the curved calf of the
posterior leg
• It arises by two heads, one
from each side of the distal
femur, and inserts through
the large Achilles tendon into
the heel of the foot
• It is also known as the toe
dancers muscle