Chapter 6 The Muscular System
Be Able To
• Identify the major muscles of the human body and state their action.
Gross Anatomy of Skeletal Muscles
Head and Neck Muscles
• Facial muscles permit facial expressions.
• Chewing muscles or muscles of
mastication physically broken down food.
Facial Muscles
• Frontalis covers the frontal bone
running from the cranial aponeurosis to the skin of eyebrows for wrinkling of the forehead.
• Orbicularis Oculi fibers run in circles around the eyes for blinking, squinting, and winking.
• Orbicularis Oris is the circular muscle of the lips that allows closing of the
mouth.
• Buccinator runs horizontally across the cheek and inserts into the orbicularis oris for flattening of the cheek, e.g. whistling.
• Zygomaticus extends from corner of the mouth to the cheekbone and allows
smiling.
Locate the facial muscles on this diagram
Cranial aponeurosis
A B
C
D
E
Gross Anatomy of Skeletal Muscles
Head and Neck Muscles
Muscles of Mastication
• Masseter covers the lower jaw from the zygomatic process of the temporal bone to the mandible for closing the jaw.
• Temporalis overlies the temporal bone and is a synergist for closing the jaw.
Neck Muscles
• Platysma is a single sheetlike muscle covering the anterolateral neck originating in the chest and inserting into the area around the mouth producing downward sag of the mouth.
• Sternocleidomastoid are paired muscles on each side of neck arising from the
clavicle and sternum and inserting into the mastoid process of the temporal bone both acting to flex the neck or rotation.
Locate the neck muscles and muscles of mastication on this
diagram.
A B
C D
Gross Anatomy of Skeletal Muscles
Head and Neck Muscles
A
B C D E
F
G
H
I
J
Gross Anatomy of Skeletal Muscles
Trunk Muscles
Anterior Muscles
• Pectoralis major or pecks cover the upper chest and originate from the shoulder girdle and the first 6 ribs
and inserts into the proximal end of the humerus and
acts to adduct and flex the arm.
• Intercostal muscles are
the deep muscles of the ribs that depress the rib cage to move air out of the lungs.
Some move the vertebral column, ribs, head, and arms; abdominal muscles form the girdle of the abdominal wall.
A B
Gross Anatomy of Skeletal Muscles
Trunk Muscles
Muscles of the Abdominal Girdle
• Rectus Abdominis are paired superficial
muscles that run from the pubis to the rib cage to flex the vertebral column and compress the abdominal contents for defecation and
childbirth.
• External obliques are paired superficial
muscles that run posteriorly and medially from the last 8 ribs to insert at the ilium to flex the vertebral column and to rotate and bend laterally.
• Internal Obliques are paired deep muscles that run at right angles to the external obliques and originate from the iliac crest and insert into the last 3 ribs.
• Transverse Abdominis is the deepest muscles of the abdominal wall and run horizontally
across the abdomen by originating from the lower ribs and inserting into the pubis for compression of abdominal contents.
Fibers of each muscle or pair run in different
directions.
D A
B C
Gross Anatomy of Skeletal Muscles
Posterior Muscles
• Trapezius muscle originate from the occipital bone and cervical & thoracic vertebrae and insert into the scapular spine and clavicle where they extend the head and aid in scapular movement.
• The paired latissumus dorsi are large flat muscles covering the lower back that originate on the lower spine and ilium and insert at the proximal humerus and are important for moving the arm downward.
• Erector spinae group are deep muscles of the back that are the prime movers of back extension.
• The longissimus, iliocostalis, and
spinalis span the length of the vertebral column and provide resistance for
bending at waist.
• Deltoid muscles are triangular shaped muscles of the shoulder that originate at the scapular spine & clavicle and insert at the deltoid tuberosity of the humerus
where it abducts the arm.
A B
C
Gross Anatomy of Skeletal Muscles
Muscles of the Upper Limbs
Muscles of the Humerus
• Biceps brachii originates by two heads from the shoulder girdle and insert into the radial tuberosity to act as prime movers for flexion of the forearm.
• Brachialis lies deep to the biceps muscle where its origin at the distal humerus and insertion at the coronoid process of the ulna acts in forearm flexion.
• The brachioradialis originates at the distal end of the humerus and inserts a the styloid
process of the radius and acts as a synergist of forearm flexion.
• The triceps brachii has three heads that
originate at the scapula, posterior and medial head of the humerus and inserts at the
olecranon fossa for forearm extension.
A
B
Gross Anatomy of Skeletal Muscles
Muscles of the Lower Limbs
• Cause movement at the hip, knee, and foot joints.
• Longest & strongest specialized for walking and balance.
• Muscles of thigh are massive to act against gravity.
• Thigh muscles cross the knee and cause flexion and extension.
• Various muscles with origins on the leg cause assorted
movements and the ankle and toe joints.
Gross Anatomy of Skeletal Muscles
Muscles at hip joint
• Gluteus maximus is the largest and most superficial muscle of the buttock; origin in sacrum and iliac bones and insertion on gluteal tuberosity of femur; action hip extensor and extremely important for climbing and jumping.
• Gluteus medius is a thick muscle covered largely by gluteus maximus; origin on ilium and insertion on greater trochanter of
femur; action hip abductor and important for steadying pelvis during walking.
• Iliopsoas is a fused muscle composed of the lilacus and psoas major; origins on iliac bone and lower vertebrae and
insertion on lesser trochanter of femur;
action prime mover for hip flexion and keeps body upright when standing.
The adductor group have origins on pelvis and insertion on proximal femur and adduct or
press thighs together.
A B
C
D
Gross Anatomy of Skeletal Muscles
Muscles at knee joint
• Hamstrings are the 3 fleshy muscles of the posterior thigh that cross both the hip and knee joints.
• The hamstrings are prime movers of thigh extension and knee flexion.
• Name comes from old butchers’ practice of using the tendons of this group to hang hams for
smoking.
• Hamstrings are composed of the biceps femoris, semimebranosus, and semitendinosus.
• Biceps femoris has 2 heads and is the most lateral of the group.
• Semitendinosus is largely a tendon and lies medial to biceps femoris.
• Semimembranosus is deep to the semitendinosus.
B A C
Gross Anatomy of Skeletal Muscles
Muscles at knee joint
• Sartorius is a thin straplike muscle that is the most superficial of the thigh; origin anterior iliac crest insertion medial side of tibia; action weal thigh flexor.
• Quadriceps group consists of four muscles.
• As a whole act to extend the knee powerfully.
• Rectus femoris is the most superficial and runs straight down the leg from the pelvis.
• Vastus lateralis forms lateral thigh and is used for intramuscular injections in infants.
• Vastus medialis forms inferomedial thigh.
• Vastus intermedius lies between lateralis and medialis.
All quads insert into the tibial tuberosity via the patellar
ligament.
A B C
D
Gross Anatomy of Skeletal Muscles
Muscles at ankle and foot
• Tibialis anterior is a superficial muscle of the anterior leg; origin upper tibia
insertion tarsal bones; action dorsifexes and inverts the foot.
• Extensor digitorum longus is lateral to the tibialis anterior; origin lateral tibial condyle and proximal fibula insertion phalanges of toes 2-5; action prime
mover of toe extension and dorsiflexion of foot.
• Fibularis muscles are composed of the peroneus tertius, brevis, and longus;
origin fibula insertion metatarsals; action flexes and everts foot.
A
B C
D E
Gross Anatomy of Skeletal Muscles
Muscles at ankle and foot
• Gastrocnemius is a superficial posterior lower leg pair; origin one each side of distal femur insertion through calcaneal
tendon; action prime mover for plantar flexion of foot.
• Soleus is deep to the
gastrocnemius on posterior calf;
origin superior tibia and fibula insertion calcaneal tendon;
action strong plantar flexor of foot.
Developmental Aspects of the Muscular System
• Muscular dystrophy is an inheritable disease that enlarges specific muscle groups due to fat and connective tissue deposits and degeneration of muscle fibers.
• Duchenne muscular dystrophy inflicts primarily male children between 2-6
years of age.
• The disease spreads from the
extremities upward and by age 12 most are wheel chair bound until their death.
• Observing a baby’s muscle control indirectly tests their nervous system.
• Myasthenia gravis is a rare muscular adult disease that involves a shortage of Ach receptors ultimately leading to
death.
