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The Muscular System
Part Two
1. Body movements are often
the result of the activity of
two or more muscles acting
together or against each
other.
2. Muscles are arranged in
such a way that whatever
one muscle (or group of
muscles) can do, other
muscles can reverse.
3. The prime mover is the muscle that
has the major responsibility for
causing a particular movement.
Muscles that oppose or reverse this
movement are called antagonists.
When a prime mover is active, its
antagonist is stretched and relaxed.
4. Synergists help prime
movers by producing the
same movement or reducing
undesirable movements.
Often, synergists stabilize
joints during muscle activity.
5. Fixators are specialized
synergists that hold a bone
still or stabilize the origin of
a prime mover so that all the
tension can be used to move
the insertion bone.
Naming Skeletal Muscles
A.
B.
C.
D.
E.
F.
G.
Rectus: straight
Oblique: slanted
Maximus: largest
Longus: long
Biceps: two origins
Triceps: three origins
Quadriceps: four origins
Naming Skeletal Muscles
H.
I.
J.
K.
Deltoid: triangular
Flexor: causes flexion
Extensor: causes extension
Adductor: causes adduction
7. The two groups of head
muscles are facial muscles
and chewing muscles.
8. Facial muscles are unique
because they are inserted
into soft tissues such as
other muscles or skin.
Sternocleidomastoid Muscle
Shape: two-head muscle found on each
side of the neck
Origins: the sternum and the clavicle
Insertion: mastoid process of the
temporal bone
Action: together, they contract to flex
the neck (bowing the head)
3 Types of Muscles That Make Up
the Trunk
A. Those that move the vertebral
column
B. Anterior thorax muscles, which move
the ribs, head, and arms
C. Abdominal wall muscles
Pectoralis Major
 Shape: large, fan-shaped muscle
covering the upper chest
 Origins: shoulder girdle and first 6
ribs
 Insertion: proximal end of the
humerus
 Action: adduction and flexion of the
arm
Muscles of the Abdominal Girdle
 The muscles of the abdominal girdle
are naturally strong because they
resemble the structure of plywood.
The fibers of each muscle pair run in
a different direction, making the
girdle exceptionally strong for its
thickness
13. The main function of the rectus
abdominus is to flex the vertebral
column. Like the rectus
abdominus, the external obliques
flex the vertebral column, but they
also rotate the trunk and bend it
laterally.
Muscles of the back
Muscle
Shape
Origin
Insertion Action
Trapezius
Diamond
or kiteshaped
Occipital
bone
Scapular
spine and
clavicle
Extend the
head and
move the
scapula
Latissimus
Dorsi
Large, flat, Lower
covering
spine and
lower back ilium
Proximal
end of
humerus
Brings the
arm down
powerfully
Deltoid
Triangular
shaped
and fleshy
Proximal
humerus
Abduction
of arm
Spine of
scapula
and
clavicle
15. All anterior arm muscles
cause elbow flexion.
Anterior Arm Muscles
Muscle
Shape
Origin
Insertion Action
Biceps
Brachii
Forms a
bulge
during
elbow
flexion
Two
heads
from the
shoulder
girdle
The radial
tuberosity
Flexion
and supination of
the
forearm
Triceps
Brachii
Fleshing
from the
posterior
humerus
Shoulder
girdle
and
proximal
humerus
Olecranon
process of
the ulna
Prime
mover of
elbow
extension
Muscles of the Buttocks
Muscle
Location Origin
Insertion Action
Gluteus
Maximus
Superficial
forms the
flesh of
the
buttock
Gluteal
tuberosity
of the
femur
Extends
the hip
Gluteus
Medius
Long,
Ilium
covered by
the
gluteus
maximus
femur
Abducts
the hip
and
steadies
the pelvis
Sacrum
and iliac
bones
The Hamstring Group
Name
Origin
Insertion
Biceps femoris Ischial
Both sides of
the proximal
tibia
Ischial
Semimembranosus tuberosity
Both sides of
the proximal
tibia
Both sides of
the proximal
tibia
tuberosity
Semitendinosus
Ischial
tuberosity
The Sartorius Muscle
Location: most superficial muscle of the
thigh, running obliquely across the
quadriceps
Origin: anterior iliac crest
Insertion: medial side of the tibia
Action: weak thigh flexor and synergist
of crossing the legs
20. The quadriceps group
consists of two groups of
muscles, the rectus femoris
and three vastus muscles.
Rectus Femoris
Location: long fleshy muscle of the
upper thigh
Origin: pelvis
Insertion: tibial tuberosity via the
patellar ligament
Action: extends the knee and flexes the
hip
Vastus Muscle Group
Location: long fleshy muscles of the
upper thigh
Origin: femur
Insertion: tibial tuberosity via the
patellar ligament
Action: extends the knee powerfully
5 Muscles That Move the Foot
Muscle
Location Origin
Insertion Action
Tibialis
Anterior
Superficial
on the
anterior
leg
Upper
tibia
Tarsal
bones
Dorsiflexion and
inversion
Extensor
Digitorum
Longus
Lateral to
the tibialis
anterior
Lateral
tibial
condyle
and
proximal
radius
Phalanges
of toes 2-5
Toe
extension
and foot
dorsiflexion
5 Muscles That Move the Foot
Muscle
Location Origin
Insertion Action
Fibularis
Muscles
Lateral
Fibula
part of the
lower leg
Metatarsals
Plantar
flexion and
eversion of
the foot
Gastrocnemius
Twobellied
muscle on
calf
Distal
femur
Calcaneus
Plantar
flexion of
the foot
Soleus
Deep to
the
gastrocnemius
Tibia
Calcaneus
Plantar
flexion of
the foot
22. The first movements of the
fetus, called the quickening,
are often felt by the mother in
the sixteenth week of
pregnancy.
Duchenne Muscular Dystrophy
Symptoms: males between ages 2 and
6 become clumsy and fall frequently
Causes: diseased muscle fibers lack a
protein that helps maintain
sarcolemma
Results: most victims use wheelchairs
by age 12 and generally die before
adulthood
Myasthenia Gravis
Symptoms: drooping of upper eyelids,
difficulty swallowing and talking,
generalized muscle weakness and
fatigue
Causes: shortage of acetylcholine
receptors at the neuromuscular junction
Results:muscles become progressively
weaker; death results from inability of
respiratory muscles to function