Download THE MUSCULAR SYSTEM

THE MUSCULAR SYSTEM
The best way to learn about the human skeleton is by dissection of a human cadaver, but since that isn’t always an
option, you are left with learning from a text. You should be able to identify major superficial muscles on figures and on
yourself, as well as their origin(s), insertion(s), and major actions. Daily repetition of the material will help considerably.
Good luck!
A. HOW SKELETAL MUSCLES PRODUCE MOVEMENT
How do muscles cause movement?
Skeletal muscles produce movement by exerting force on tendons, which in turn pull on bones or other
structures. Most muscles cross at least one joint and are attached to the articulating bones that form that
joint.
Why do the two bones of a joint not move equally?
When a muscle contracts, it draws one articulating bone towards the other, but the two bones do not move
equally in response to the contraction. One bone is held in position because other muscles contract to pull it
in the opposite direction or because its structure makes it less movable.
1. ORIGIN AND INSERTION
Compare the origin of a muscle with its insertion.
The attachment of a muscle to the more stationary bone is called its origin.
The attachment of the muscle to the more movable bone is called its insertion.
The fleshy portion of the muscle between the origin and the insertion is called the belly (gaster).
2. GROUP ACTIONS
Describe how muscles are arranged as functional groups.
Most movements require skeletal muscles acting in groups rather than as individuals and are
arranged into opposing pairs:
flexors vs extensors supinators vs pronators
abductors vs adductors elevators vs depressors
medial vs lateral rotators protractors vs retractors
Define the following:
Agonist -- A muscle that produces a desired action is the prime
mover or agonist (biceps brachii for flexion of the forearm).
Antagonist -- The muscle that opposes the desired motion is the
antagonist; it must be relaxed while the agonist is contracted (triceps brachii for flexion of the
forearm). If the agonist and antagonist contracted with equal force simultaneously, the net
movement produced would be no movement.
Synergist -- Most movements require the action(s) of synergists,
muscles that serve to steady the desired movement, preventing unwanted movements. Ex:-the biceps brachii is the prime mover for flexion at the elbow, while the coracobrachialis and
the brachialis helps the action.
Fixator -- Other muscles act as fixators that stabilize the origin of
the agonist to allow the prime movement to occur more efficiently (muscles of the scapula).
Example: The biceps brachii and the brachialis muscles are synergists to
each other, as are the 3 heads of the triceps brachii. The biceps brachii and the brachialis are antagonistic
to the triceps brachii and vice versa. When one group contracts, the other must relax. Muscles not shown
in this figure are those of the shoulder joint that hold the joint while the elbow is flexed or extended. These
muscles (the rotator cuff) are the fixators
B. REVIEW OF SUPERFICIAL MUSCLES
SELECTED SKELETAL MUSCLES FOR STUDY
MUSCLE
ORIGIN(S)
INSERTION(S)
MAJOR ACTION(S)
mandible at ramus and angle
elevates mandible
zygomatic arch
masseter
*temporalis
temporal and frontal bones
mandible
elevates and retracts mandible
sternocleidomastoid
sternum
mastoid process of temporal
both muscles flex neck
clavicle
latissimus dorsi
spines of T7-L5, scapula,
bone
humerus
crests of sacrum and ilium
one side alone turns head to opposite side
extends, adducts, rotates humerus medially
draws humerus inferior and posterior
inferior 4 ribs
serratus anterior
ribs 1-9
medial border of scapula
rotates and abducts scapula
elevates ribs when scapula fixed
external abdominal oblique
ribs 5-12
linea alba from xiphoid to pubic
symphysis
both sides compress abdomen
one side alone bends vertebral column to that
side (lateral flexion)
rectus abdominis
pubis
cartilage of ribs 5-7
flexes vertebral column
xiphoid process
compresses abdomen
stabilize pelvis during walking
tensor fasciae latae
iliac crest
tibia via the iliotibial band
flexes, abducts, and medially rotates femur
sartorius
anterior superior iliac spine
medial tibial tuberosity
flexes leg; flexes thigh and rotates it laterally,
crossing the leg
gracilis
pubis
medial tibia
adducts and medially rotates femur
flexes leg
vastus lateralis
posterolateral femur
tibial tuberosity
extends leg
vastus medialis
linea aspera of femur
tibial tuberosity
extends leg
rectus femoris
anterior inferior iliac spine
tibial tuberosity
extends leg, extends hip
pectoralis major
clavicle
humerus
flex, adduct, medially rotate humerus
radius
flexes, supinates forearm
sternum
cartilages of ribs 1-6
biceps brachii
by two heads from scapula
flexes arm
tibialis anterior
lateral tibia
1st metatarsal
dorsiflexes and inverts foot
medial cuneiform
trapezius
occiput
clavicle
elevates clavicle
spines of vertebrae C7-T12
scapula
adducts, rotates, and elevates scapula
abducts and extends neck
deltoid
clavicle
humerus
acromion and spine of
laterally rotates humerus, depending upon
scapula
triceps brachii
by one head from scapula
abducts, flexes or extends, and medially or
which fibers are contracting
olecranon process of ulna
extends forearm; extends arm
ilium
ilitotibial tract (fascia lata)
extends, abducts, and rotates femur laterally
sacrum
greater trochanter of femur
by two heads from humerus
gluteus maximus
coccyx
SELECTED SKELETAL MUSCLES FOR STUDY
MUSCLE
ORIGIN(S)
INSERTION(S)
MAJOR ACTION(S)
gluteus medius
ilium
greater trochanter of femur
abducts and rotates femur medially
biceps femoris
by one head from ischial
head of fibula
flexes leg
lateral condyle of tibia
extends thigh
proximal medial tibial shaft
flexes leg
tuberosity
by one head from femur
semitendinosus
ischial tuberosity
extends thigh
semimembranosus
ischial tuberosity
medial condyle of tibia
flexes leg
extends thigh
gastrocnemius
medial and lateral condyles of
femur
calcaneus via the
Achilles’ tendon
plantar flexes foot
flexes leg