The document summarizes the major muscles of the head, neck, back, shoulder, arm, and forearm. It describes the origin, insertion, nerve supply, and action of each muscle. For example, it states that the sternocleidomastoid muscle originates from the sternum and clavicle, inserts into the mastoid process, and acts to rotate and tilt the head. The document provides an anatomical reference for students and lists over 30 muscles in the upper body regions.

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Chapter 12 Muscular system
Muscles of Head and neck
1. Scalene muscles
The scalene muscles are a group of three pairs of muscles in the
lateral neck:
scalenus anterior, scalenus medius, and scalenus posterior
The scalene muscles are related to the thoracic outlet syndrome
i. Scalene anterior:
Origin: transverse processes of C3 – C6
Insertion: scalene tubercle of 1st rib
Nerve supply: anterior rami of C6 – C8
Action: raises the first rib and bends neck to one side
ii. Scalene Medius
Origin: transverse processes of C1 – C6
Insertion: upper surface of 1st and 2nd ribs
Nerve supply: anterior rami of C3 – C8
Action: raises the first rib and bends neck to one side
iii. Scalene Posterior
Origin: transverse processes of C5 – C7
Insertion: upper surface of 2nd rib
Nerve supply: anterior rami of C7 – C8

2. Action: raises the second rib and bends neck to one side
2. Sternocleidomastoid/ Sternomastoid
It is given the name sternocleidomastoid because it originates
from the sternum (sterno) and clavicle (cleido), and inserts into
the mastoid process of the temporal bone of the skull. It is also
called the sternomastoid muscle.
Origin: manubrium sterni + medial portion of the clavicle
Insertion: mastoid process of the temporal bone and superior
nuchal line
Nerve Supply:
motor: accessory nerve
sensory: cervical plexus
Action:
Acting alone it tilts head to its own side and rotates it so the
face is turned towards the opposite side.
Acting together, flexes the neck, raises the sternum and assists
in forced inspiration.
3. Infrahyoid or “strap” muscles
Strap-like muscles occupy each side of the midline of the neck
from the mandible to the manubrium sterni.
Between these 2 points lie the hyoid bone, and below it is the
Adam’s apple or thyroid cartilage; to them certain muscles gain
attachment.
They include:
Sternohyoid m., Sternothyroid m., Thyro-hyoid m. and
Omohyoid muscles.
These four muscles, also known as the "strap" muscles, function
to depress the hyoid bone and larynx during swallowing and
speaking (except for Thyrohyoid).
i. Sternohyoid
Origin: Posterior surface of manubrium sterni, adjoining parts
of clavicle and the posterior sternoclavicular ligament

3. Insertion: Medial part of lower border of hyoid bone
Nerve supply: Ansa cervicalis
Action: Depresses/ stabilizes hyoid bone
ii. Sternothyroid
Origin: Posterior surface of manubrium sterni and adjoining
part of first costal cartilage
Insertion: Oblique line of thyroid cartilage
Nerve supply: Ansa cervicalis
Action: Depresses/ stabilizes thyroid cartilage
iii. Thyrohyoid
Origin: Oblique line of the thyroid cartilage
Insertion: Lower border of the body and the greater cornu of the
hyoid bone
Nerve supply: Cervical spinal nerve 1 via the hypoglossal nerve
Action: Elevates larynx + Depresses/ stabilizes hyoid bone
iv. Omohyoid (superior belly)
Origin: Intermediate tendon
Insertion: Hyoid bone
Nerve supply: Ansa cervicalis
Action: Depresses/ stabilizes hyoid bone
v. Omohyoid (inferior belly)
Origin: Superior border of scapula
Insertion: Intermediate tendon
Nerve supply: Ansa cervicalis
Action: Depresses/ stabilizes hyoid bone
4. The Suprahyoid Muscles
This group of muscles is located superior to the hyoid bone and
connects to this bone and the skull.
This group includes:
mylohyoid, geniohyoid, stylohyoid and digastric muscles.
Mylohyoid and genihyoid muscles form the floor of the mouth.
i. Mylohyoid
Origin: Mylohyoid line (inner surface of the mandible)

4. Insertion: Median raphé (connecting ridge)
Nerve supply: mylohyoid nerve
Action: Raises the oral cavity floor, elevates the hyoid bone,
depresses the mandible
ii. Geniohyoid
Is situated superior to the medial border of the mylohyoid
muscle. It is named for its passage from the chin (genio) to the
hyoid bone.
Origin: mandible (It arises from the inferior mental spine, on
the back of the symphysis menti)
Insertion: hyoid bone (into the anterior surface of the body of
the hyoid bone)
Nerve supply: hypoglossal nerve
Action: elevates the hyoid bone and depresses the mandible
iii. Digastric
It is named digastric as it has two bellies
Origin: medial aspect of the mastoid process of skull (posterior
belly) and the digastric fossa of mandible (anterior belly)

5. Insertion: Hyoid bone
2 Nerves supply: The anterior belly is innervated by the
mandibular division of the trigeminal (CN V3)
The posterior belly by the facial nerve (CN VII)
Action:
Opens the jaw when the masseter and the temporalis are relaxed
and elevates the hyoid bone.
Stylohyoid muscle runs with the posterior belly digastric
iv. Stylohyoid
Origin: styloid process (temporal bone)
Insertion: greater cornu of hyoid bone
Nerve supply: facial nerve (CN VII)
Action:
Elevate the hyoid during swallowing
Muscles of mastication
Four important muscles on each side are devoted to the tasks of
biting and chewing
Temporalis m., Masseter m., Medial pterygoid m. and Lateral
pterygoid m.
i. Temporalis
Origin: temporal lines on the parietal bone of the skull.
Insertion: coronoid process of the mandible.
Nerve supply: mandibular nerve of the trigeminal nerve
Action: elevation and retraction of mandible

6. ii. Masseter
Origin: zygomatic arch and maxilla
Insertion: coronoid process and ramus of mandible
Nerve supply: mandibular nerve of the trigeminal nerve V3.
Action: elevation (closing of the mouth) and retraction of the
mandible
iii. Medial pterygoid / internal pterygoid
Origin:
Deep head: medial side of lateral pterygoid plate behind the
upper teeth
Superficial head: palatine bone and maxillary tuberosity
Insertion: medial angle & ramus of the mandible
Nerve supply: mandibular nerve of the trigeminal nerve V3.
Action:
Elevates the mandible, closes the jaw
Helps lateral pterygoids in moving the jaw from side to side
iv. Lateral pterygoid / external pterygoid
Origin: (also 2 heads)
Great wing of sphenoid and lateral side of lateral pterygoid
plate
Insertion:
Condyle of mandible
Nerve supply: mandibular nerve of the trigeminal nerve V3
Action: depresses the mandible

7. Facial muscles
Includes: Frontalis, Orbicularis oculi, Platysma and Orbicularis
oris
i. Frontalis
It has NO bony attachments.
Origin:
Its medial fibers are continuous with those of the Procerus
muscle;
Its immediate fibers blend with the Corrugator and Orbicularis
oculi muscles, thus attached to the skin of the eyebrows;
And its lateral fibers are also blended with the latter muscle
over the zygomatic process of the frontal bone.
From these attachments the fibers are directed upward, and join
the
galea aponeurotica below the coronal suture.
Nerve supply: facial nerve
Action:
In the eyebrows, its primary function is to lift them- wrinkles
eyebrow
ii. Platysma
Origin:
Skin over lower neck and upper lateral chest
Insertion
Inferior border of mandible and skin over lower face and angle
of mouth
Action:
Depresses and wrinkles skin of lower face and mouth. Aids
forced depression of mandible
Nerve supply: Cervical branch of facial nerve (VII)

8. iii. Orbicularis oculi
Origin: frontal bone; medial palpebral ligament; lacrimal bone
Insertion: lateral palpebral raphe
Nerve supply: zygomatic branch of Facial nerve VII
Action: closes eyelids
iv. Orbicularis oris
Origin: Maxilla and mandible
Insertion: Skin around the lips
Nerve supply: buccal branch of the Facial nerve cranial nerve
VII
Action: It closes the lips
v. Buccinator
Origin: from the alveolar processes of the maxillary bone and
mandible, Pterygomandibular raphe
Insertion: in the fibers of the orbicularis oris
Nerve supply: facial nerve (cranial nerve VII)
Action:
The buccinators compresses the cheeks against the teeth and is
used in acts such as blowing.
It is an assistant muscle of mastication (chewing).
vi. Zygomaticus major &minor
· Zygomaticus Minor
Origin: zygomatic bone and continues with orbicularis oculi on
the lateral face
Insertion: into the outer part of the upper lip
Action: It draws the upper lip backward, upward, and outward
(used in making sad facial expressions)
Nerve supply: it is innervated by the facial nerve (CN VII)
· Zygomaticus Major

9. Origin: zygomatic arch (cheekbone)
Insertion: to the corners of the mouth
Nerve supply: it is innervated by the facial nerve (CN VII)
Action: It raises the corners of the mouth when a person smiles.
Muscles of upper limb
The upper limb comprises many muscles which are organized
into anatomical compartments. These muscles act on the various
joints of the hand, arm, and shoulder, maintaining tone,
providing stability and allowing precise fluid movement.
Axioappendicular groups of muscles arise from the axial
skeleton to act upon the pectoral girdle. Scapulohumeral
muscles originate from the scapula and insert into the proximal
humerus. Included in this category are the rotator cuff muscles
which provide stability to the glenohumeral joint. In the arm,
the muscles of the anterior compartment are involved in flexion
of the forearm, and the posterior comprises of the forearm
extensors. Similarly, the anterior compartment of the forearm
contains the flexors of the hand and posterior has extensors. The
hand is divided into the thenar, the hypothenar, the adductor
compartment, as well as the short muscles of the hand.
Anterior Axioappendicular Muscles (Thoracoappendicular
Muscles)
Pectoralis major
· Function: flexion, adduction, medial rotation of the humerus.
· Origin: clavicular head: medial clavicle anteriorly,
sternocostal head: anterior sternum and costal cartilages of ribs
1 to 6 as well as external oblique aponeurosis
· Insertion: lateral edge of intertrabecular groove of humerus
· Innervation: medial pectoral nerve (C8, T1) lateral pectoral
nerve (C5, C6, C7) of brachial plexus

10. Pectoralis minor
· Function: Depression of shoulder, protraction of scapula
· Origin: Third, fourth, fifth ribs close to their respective costal
cartilages
· Insertion: Coracoid process
· Innervation: Medial pectoral nerve (C8, T1)
Subclavius
· Function: Depression and stabilization of clavicle
· Origin: First rib medially
· Insertion: Middle of clavicle, inferiorly
· Innervation: Nerve to subclavius (C5, C6)
Serratus anterior
· Function: Protraction of scapula, rotation of scapula
· Origin: Lateral first to the eighth rib
· Insertion: anterior scapula, medially
· Innervation: long thoracic nerve (C5, C6, C7)
Posterior Axioappendicular Muscles
Superficial layer
Latissimus dorsi
· Function: Adduction, medial rotation, extension of humerus
· Origin: Spinous processes of seventh to 12th thoracic
vertebrae, iliac crest, thoracolumbar fascia, and inferior third
and fourth rib
· Insertion: Intertubercular groove of humerus
· Innervation: Thoracodorsal nerve (C5,C6,C7)
Trapezius
· Function: Elevation, depression, and retraction of the scapula,
rotation of glenoid cavity
· Origin: Superior nuchal line, nuchal ligament, occipital
protuberance, spinous processes of C7- T12
· Insertion: Spine of scapula, acromion, and lateral clavicle

11. · Innervation: CN XI
Deep Layer
Levator scapulae
· Function: Adduction, medial rotation, extension of humerus
· Origin: Transverse processes of C1 through C4 vertebrae
· Insertion: Scapula at its medial border
· Innervation: Thoracodorsal nerve (C5, C6, C7)
Rhomboid major
· Function: Retraction of scapula and depression of glenoid
cavity
· Origin: Spinous processes of T2 through T5 vertebrae
· Insertion: Inferior aspect of medial scapula
· Innervation: Dorsal scapular nerve (C4, C5)
Rhomboid minor
· Function: Retraction of scapula and depression of glenoid
cavity
· Origin: Nuchal ligament as well as spines of C7 and T1
vertebrae
· Insertion: Superior aspect of medial scapula
· Innervation: Dorsal scapular nerve (C4, C5)
Scapulohumeral (Intrinsic Shoulder Muscles)
Deltoid
· Function: Anterior part: flexion and medial rotation of arm,
middle part: abduction of arm, posterior part: extension and
lateral rotation of arm
· Origin: Lateral clavicle, acromion and scapular spine
· Insertion: Deltoid tuberosity
· Innervation: Axillary nerve (C5, C6)
Teres major
· Function: Adduction and medial rotation of arm
· Origin: Posterior surface of scapula at its inferior angle
· Insertion: Intertubercular groove on its medial aspect

12. · Innervation: Lower scapular nerve (C5, C6)
Supraspinatus
· Function: Initiation of arm abduction
· Origin: Posterior scapula, superior to the scapular spine
· Insertion: Superior aspect of the greater tubercle
· Innervation: Suprascapular nerve (C5, C6)
· Part of rotator cuff muscles
Infraspinatus
· Function: Lateral rotation of arm
· Origin: Posterior scapula, inferior to the scapular spine
· Insertion: Greater tubercle of humerus, between supraspinatus
and teres minor insertion
· Innervation: Suprascapular nerve (C5, C6)
· Part of rotator cuff muscles
Teres minor
· Function: Lateral rotation of arm
· Origin: Posterior surface of scapula at its inferior angle
· Insertion: Inferior aspect of the greater tubercle
· Innervation: Axillary nerve (C5, C6)
· Part of rotator cuff muscles
Subscapularis
· Function: Adduction and medial rotation of the arm
· Origin: Anterior aspect of scapula
· Insertion: Lesser tubercle of humerus
· Innervation: Subscapular nerves (C5, C6, C7)
· Part of rotator cuff muscles
*Rotator cuff muscles: supraspinatus, infraspinatus, teres minor,
subscapularis

13. Muscles of Anterior Compartment of Arm (Flexors of Arm)
Biceps brachii
· Function: Major flexion of forearm, supination of forearm,
resists dislocation of shoulder
· Origin: Short head originates from the coracoid process. The
long head is from the supraglenoid tubercle of scapula
· Insertion: Radial tuberosity and forearm fascia (as bicipital
aponeurosis)
· Innervation: Musculocutaneous nerve (C5, C6)
Brachialis
· Function: Flexion of forearm
· Origin: Distal anterior humerus
· Insertion: Coronoid process and ulnar tuberosity
· Innervation: musculocutaneous nerve (C5, C6, C7 small
contribution)
Coracobrachialis
· Function: Flexion and adduction of arm
· Origin: Coracoid process
· Insertion: Middle of the humerus, on its medial aspect
· Innervation: Musculocutaneous nerve (C5, C6, C7)
Muscles of Posterior Compartment of Arm (Extensors of Arm)
Triceps brachii
· Function: Major extensor of forearm, resists dislocation of
shoulder
· Origin: Lateral head: above the radial groove, medial
head: below the radial groove, long head: infraglenoid tubercle
of scapula
· Insertion: Olecranon process of ulna and forearm fascia
· Innervation: Radial nerve (C6,C7,C8)
Anconeus
· Function: Extension of forearm, stabilization of elbow joint
· Origin: Lateral epicondyle of humerus
· Insertion: Olecranon process and posterior ulna
· Innervation: Radial nerve (C7, C8, T1)

14. Muscles of Anterior Compartment of Forearm (Flexors of
Forearm)
Superficial layer
Pronator teres
· Function: Pronation of radio-ulnar joint
· Origin: Coronoid process and medial epicondyle of humerus
· Insertion: Lateral surface of the radius
· Innervation: Median nerve (C6, C7)
Flexor carpi radialis
· Function: Flexion and adduction at the wrist
· Origin: Medial epicondyle of humerus
· Insertion: Base of second metacarpal
· Innervation: Median nerve (C6, C7)
Palmaris longus
· Function: Flexion at the wrist, tensing of the palmaris
aponeurosis
· Origin: Medial epicondyle of humerus
· Insertion: Flexor retinaculum
· Innervation: Median nerve (C7, C8)
Flexor carpi ulnaris
· Function: Flexion and adduction at the wrist
· Origin: Medial epicondyle of humerus and olecranon
· Insertion: Pisiform, hook of hamate and fifth metacarpal
· Innervation: Median nerve (C7, C8)
Intermediate Layer
Flexor digitorum superficialis
· Function: Flexion of the proximal interphalangeal joint of the
second, third, fourth, and fifth finger. Also has a weaker flexion
action on the metacarpophalangeal joints of the same fingers
· Origin: Medial epicondyle, coronoid process, and anterior
radius
· Insertion: Second, third, fourth, and fifth middle phalanges
· Innervation: Median nerve (C7, C8, T1)

15. Deep Layer
Flexor digitorum profundus
· Function: Flexion of the distal interphalangeal joint of
the second, third, fourth, and fifth finger
· Origin: Medial and anterior surface of proximal ulna and
interosseous membrane
· Insertion: Second, third, fourth, and fifth distal phalanges
· Innervation: Ulnar nerve (C8, T1) for the medial part, anterior
interosseous nerve (C8,T1) for the lateral
Flexor pollicis longus
· Function: Flexion of the interphalangeal joint of the thumb
· Origin: Anterior aspect of radius as well as interosseous
membrane
· Insertion: Base of distal phalanx of thumb
· Innervation: Anterior interosseous nerve (C7, C8)
Pronator quadratus
· Function: Pronator of forearm
· Origin: Anterior aspect of distal ulna
· Insertion: Anterior aspect of distal radius
· Innervation: Anterior interosseous nerve (C7, C8)
Brachioradialis
· Function: Weak flexor of the forearm
· Origin: Proximal supracondylar ridge on humerus
· Insertion: Lateral surface of distal end of radius
· Innervation: Radial nerve (C5, C6, C7)
Muscles of Posterior Compartment of Forearm
Superficial

16. Extensor carpi radialis longus
· Function: Extension and abduction of the wrist
· Origin: Proximal supracondylar ridge on humerus
· Insertion: Dorsal base of second metacarpal
· Innervation: Radial nerve (C6, C7)
Extensor carpi radialis brevis
· Function: Extension and abduction of the wrist
· Origin: Lateral epicondyle of humerus
· Insertion: Dorsal base of third metacarpal
· Innervation: Deep branch of the radial nerve (C7, C8)
Extensor digitorum
· Function: Extension of the proximal interphalangeal joint of
the second, third, fourth, and fifth finger. Also has a weaker
extension action on the metacarpophalangeal joints of the same
fingers
· Origin: Lateral epicondyle of humerus
· Insertion: Extensor expansions on dorsal aspect of second,
third, fourth, and fifth middle and distal phalanges
· Innervation: Posterior interosseous nerve (C7, C8)
Extensor digiti minimi
· Function: Extension of the little finger at metacarpophalangeal
joint and interphalangeal joint
· Origin: Lateral epicondyle of humerus
· Insertion: Extensor expansion on dorsal aspect of fifth phalanx
· Innervation: Posterior interosseous nerve (C7, C8)
Extensor carpi ulnaris
· Function: Extension and adduction of the wrist
· Origin: Lateral epicondyle of humerus and posterior ulna
· Insertion: Fifth metacarpal base
· Innervation: Posterior interosseous nerve (C7, C8)
·
Deep Layer
Extensor indicis
· Function: Extension of the index finger
· Origin: Dorsal surface of distal ulna and interosseous

17. membrane
· Insertion: Extensor expansion of second finger
· Innervation: Posterior interosseous nerve (C7, C8)
Supinator
· Function: Supination of the forearm
· Origin: Lateral epicondyle and supinator crest of ulna
· Insertion: Lateral surface of radius
· Innervation: Deep branch of radial nerve (C7, C8)
Abductor pollicus longus
· Function: Abduction of the thumb by acting on the
carpometacarpal joint and the metacarpophalangeal joint
· Origin: Dorsal aspects of proximal radius, ulna, and
interosseous membrane
· Insertion: Base of first metacarpal
· Innervation: Posterior interosseous nerve (C7, C8)
Extensor pollicus longus
· Function: Extension of the thumb by acting on the
carpometacarpal joint, the metacarpophalangeal joint, and the
interphalangeal joint.
· Origin: Dorsal aspects of middle ulna and interosseous
membrane
· Insertion: Distal phalanx of 1st finger
· Innervation: Posterior interosseous nerve (C7, C8)
Extensor pollicus brevis
· Function: Extension of the thumb by acting on the
carpometacarpal joint and the metacarpophalangeal joint
· Origin: Dorsal aspects of middle radius and interosseous
membrane
· Insertion: Distal phalanx of 1st finger
· innervation: Posterior interosseous nerve (C7, C8)
Intrinsic Muscles of Hand
Thenar muscles
Opponens pollicus

18. · Function: Opposition of the thumb
· Origin: Flexor retinaculum and tubercle of trapezium
· Insertion: Lateral aspect of first metacarpal
· Innervation: Recurrent branch of median nerve (C8, T1)
Abductor pollicus brevis
· Function: Abduction of the thumb at the metacarpophalangeal
joint
· Origin: Flexor retinaculum and tubercle of scaphoid
· Insertion: Lateral aspect of proximal phalanx of first finger
· Innervation: Recurrent branch of median nerve (C8, T1)
Flexor pollicus brevis
· Function: Flexion of the thumb at the metacarpophalangeal
joint
· Origin: Flexor retinaculum and tubercle of trapezium
· Insertion: Lateral aspect of proximal phalanx of first finger
· Innervation: Recurrent branch of median nerve (C8, T1)
Adductor Compartment
Adductor pollicus
· Function: Adduction of the thumb
· Origin: Second, third metacarpal, and capitate
· Insertion: Proximal phalanx and extensor expansion of 1st
finger
· Innervation: Deep branch of ulnar nerve (C8, T1)
Hypothenar Muscles
Abductor digiti minimi
· Function: Abduction of the little finger at the
metacarpophalangeal joint
· Origin: Pisiform
· Insertion: Medial aspect of proximal phalanx of fifth finger
· Innervation: Deep branch of ulnar nerve (C8, T1)
Flexor digiti minimi brevis
· Function: Flexion of the little finger at the
metacarpophalangeal joint
· Origin: Flexor retinaculum and hook of hamate

19. · Insertion: Medial aspect of proximal phalanx of fifth finger
· Innervation: Deep branch of ulnar nerve (C8, T1)
Opponens digiti minimi
· Function: Opposition of the little finger
· Origin: Flexor retinaculum and hook of hamate
· Insertion: Medial aspect of fifth metacarpal
· Innervation: Deep branch of ulnar nerve (C8, T1)
Short Muscles
Lumbricals
· Function: Flexion of the metacarpophalangeal joints with
extension of the interphalangeal joints
· Origin: Arise from tendons of flexor digitorum profundus.
First 2 are unipennate, and the third and fourth are bipennate
· Insertion: Extensor expansions of second, third, fourth, and
fifth finger
· Innervation: Median nerve (C8, T1) for the lateral 2
lumbricals, deep branch of ulnar nerve (C8, T1) for the medial 2
lumbricals
Dorsal interossei
· Function: Abduction of the second, third, and fourth finger
away from the axial line
· Origin: Adjacent metacarpals
· Insertion: Extensor expansions and proximal phalanges of
the second, third, and fourth fingers
· Innervation: Deep branch of ulnar nerve (C8, T1)
Palmar interossei
· Function: Adduction of the second, third, and fourth finger
towards the axial line
· Origin: Palmar surfaces of second, fourth, and fifth
metacarpals
· Insertion: Extensor expansions and proximal phalanges of the
second, fourth, and fifth fingers
· Innervation: Deep branch of ulnar nerve (C8, T1)
Muscles of lower limb

20. Muscles of the thigh
The musculature of the thigh can be split into three sections;
anterior, medial and posterior. Each compartment has a distinct
innervation and function.
The muscles in the anterior compartment of the thigh are
innervated by the femoral nerve (L2-L4), and as a general rule,
act to extend the leg at the knee joint.
There are three major muscles in the anterior thigh
the pectineus, sartorius and quadriceps femoris. In addition to
these, the end of the iliopsoas muscle passes into the anterior
compartment.
The iliopsoas mucels:
The iliopsoas is actually two muscles, the psoas major and
the iliacus. They originate in different areas, but come together
to form a tendon, hence why they are commonly referred to as
one muscle.
Unlike many of the anterior thigh muscles, the iliopsoas does
not extend the leg at the knee joint.
· Attachments: The psoas major originates from the lumbar
vertebrae, and the iliacus originates from the iliac fossa of the
pelvis. They insert together onto the lesser trochanter of the
femur.
· Actions: The iliopsoas flexes the lower limb at the hip joint
and assists in lateral rotationat the hip joint.
· Innervation: The psoas major is innervated by anterior rami of
L1-3, while the iliacus is innervated by the femoral nerve

21. Muscles of leg
Anterior compartments
There are four muscles in the anterior compartment of the leg;
tibialis anterior, extensor digitorum longus, extensor hallucis
longus and fibularis tertius.
Collectively, they act to dorsiflex and invert the foot at the
ankle joint. The extensor digitorum longus and extensor
hallucis longus also extend the toes. The muscles in this
compartment are innervated by the deep fibular nerve (L4-L5),
and blood is supplied via the anterior tibial artery.
The tibialis
The tibialis anterior muscle is located alongside the lateral
surface of the tibia.
It is the strongest dorsiflexor of the foot.
To test the power of the tibialis anterior, the patient can be
asked to stand on their heels.
· Attachments: Originates from the lateral surface of the tibia,
attaches to the medial cuneiform and the base of metatarsal I.
· Actions: Dorsiflexion and inversion of the foot.
· Innervation: Deep fibular nerve.
The extensor digitorum longus
The extensor digitorum longus lies lateral and deep to the
tibialis anterior. The tendons of the EDL can be palpated on the
dorsal surface of the foot.
· Attachments: Originates from the lateral condyle of the tibia
and the medial surface of the fibula. The fibres converge into a
tendon, which travels to the dorsal surface of the foot. The

22. tendon splits into four, each inserting onto a toe.
· Actions: Extension of the lateral four toes, and dorsiflexion of
the foot.
· Innervation: Deep fibular nerve.
The extensor hallucis longus
The extensor hallucis longus is located deep to the EDL and TA.
· Attachments: Originates from the medial surface of the fibular
shaft. The tendon crosses anterior to the ankle joint and
attaches to the base of the distal phalanx of the great toe.
· Action: Extension of the great toe and dorsiflexion of the foot.
· Innervation: Deep fibular nerve.
The fibularis tertius muscles
The fibularis tertius muscles arises from the most inferior part
of the EDL. It is not present in all individuals, and is considered
by some texts as a part of the extensor digitorum longus.
· Attachments: Originates with the extensor digitorum longus
from the medial surface of the fibula. The tendon descends with
the EDL, until they reach the dorsal surface of the foot. The
fibularis tertius tendon then diverges and attaches to metatarsal
V.
· Actions: Eversion and dorsiflexion of the foot.
· Innervation: Deep fibular nerve.
Posterior compartments
The posterior compartment of the leg contains seven muscles,
organised into two layers – superficial and deep. The two layers
are separated by a band of fascia.
The posterior leg is the largest of the three compartments.
Collectively, the muscles in this area plantarflex and invert the
foot. They are innervated by the tibial nerve, a terminal branch

23. of the sciatic nerve.
The gastrocnemius
The gastrocnemius is the most superficial of all the muscles in
the posterior leg. It has two heads – medial and lateral, which
converge to form a single muscle belly.
· Attachments: The lateral head originates from the lateral
femoral condyle, and medial from the medial condyle. The
fibres converge, and form a single muscle belly. In the lower
part of the leg, the muscle belly combines with the soleus to
from the calcaneal tendon, with inserts onto the calcaneus (the
heel bone).
· Actions: It plantarflexes at the ankle joint, and because it
crosses the knee, it is a flexor there.
· Innervation: Tibial nerve.
The plantaris
The plantaris is a small muscle with a long tendon, which
can be mistaken for a nerve as it descends down the leg. It is
absent in 10% of people.
· Attachments: Originates from the lateral supracondylar line of
the femur. The muscle descends medially, condensing into a
tendon that runs down the leg, between the gastrocnemius and
soleus. The tendon blends with the calcaneal tendon.
· Actions: It plantarflexes at the ankle joint, and because it
crosses the knee, it is a flexor there. It is not a vital muscle for
these movements.
· Innervation: Tibial nerve.
The soleus

24. The soleus is located deep to the gastrocnemius. It is large and
flat, named soleus due to its resemblance of a sole – a flat fish.
· Attachments: Originates from the soleal line of the tibia and
proximal fibular area. The muscle narrows in the lower part of
the leg, and joins the calcaneal tendon.
· Actions: Plantarflexes the foot at the ankle joint.
· Innervation: Tibial Nerve.
Deep compartment of the posterior leg
There are four muscles in the deep compartment of the posterior
leg. One muscle, the popliteus, acts only on the knee joint. The
remaining three muscles (tibialis posterior, flexor hallucis
longus and flexor digitorum longus) act on the ankle and foot.
Muscles of pelvis
The pelvic floor or pelvic diaphragm is composed of muscle
fibres of: levator ani, coccygeus, and associated connective
tissue which span the area underneath the pelvis
The pelvic diaphragm forms a muscular partition that separates
the pelvic cavity above from the perineal region (including
perineum) below.

25. 1. Levator ani muscle, LA
The Levator ani is a broad, thin muscle, situated on the side of
the pelvis.
It is attached to the inner surface of the side of the lesser pelvis,
and unites with its fellow of the opposite side to form the
greater part of the floor of the pelvic cavity.
It supports the viscera in pelvic cavity, and surrounds the
various structures which pass through it.
In combination with the coccygeus muscle, they form the pelvic
diaphragm.
Parts of levator ani
The levator ani is divided into three parts: Puborectalis muscle,
Pubococcygeus muscle, and Iliococcygeus muscle.
i. Puborectalis muscle
The fibres which form a sling? for the rectum are named the
Puborectalis or Sphincter recti.
They arise from: the lower part of the symphysis pubis and from
the superior fascia of the urogenital diaphragm.
They meet with the corresponding fibers of the opposite side
around the lower part of the rectum, and form for it a strong
sling.
Relaxation reduces the angle between rectum and anus, allowing
defecation in conjunction with relaxation of the internal and
external sphincters.
ii. The Pubococcygeus muscle or PC muscle
It stretches from the pubic bone to the coccyx (tail bone)
forming the floor of the pelvic cavity and supporting the pelvic
organs.

26. It arises from the back of the pubis and from the anterior part of
the obturator fascia, and is directed backward almost
horizontally along the side of the anal canal toward the coccyx
and sacrum, to which it finds attachment.
Between the termination of the vertebral column and the anus,
the two Pubococcygei muscles come together and form a thick,
fibromuscular layer lying on the raphé: a ridge between two
similar parts of a body organ, (anococcygeal raphé).
The greater part of this muscle is inserted into the coccyx and
into the last one or two pieces of the sacrum.
iii. The Iliococcygeus
Arises from the ischial spine and from the posterior part of the
tendinous arch of the pelvic fascia,
Inserts to the coccyx and anococcygeal raphé; it is usually thin,
and may fail entirely, or be largely replaced by fibrous tissue.
An accessory slip at its posterior part is sometimes named the
Iliosacralis.
Innervation of LA
The levator ani muscles are mostly innervated by the
pudendal nerve, perineal nerve and inferior rectal nerve.In
addition, sacral spinal nerves (S3, S4) innervate the muscles
directly as well (in ~70% of people).
Sometimes (in ~40% of people) the inferior rectal nerve
innervates the levator ani muscles independently of the
pudendal nerve.
Function
· The pubococcygeus, the main part of the levator ani, runs
backward from the body of the pubis toward the coccyx and may
be damaged during parturition.Some fibres are inserted into the
prostate, urethra, and vagina. . A strong PC muscle has also
been linked to a reduction in urinary incontinence and proper
positioning of the baby's head during childbirth.
· The right and left puborectalis unite behind the anorectal
junction to form a muscular sling. Some regard them as a part of

27. the sphincter ani externus. It controls urine flow. Thus it aids in
urinary control and childbirth
Pelvic diaphragm Openings
There are 2 openings/gaps/hiatus in the pelvic diaphragm to
allow the structure to pass from the pelvis to perineum.
· Urogential hiatus: an anteriorly situated gap, which allows the
passage of urethra (and also vagina in females)
· Rectal hiatus: a centrally positioned gap, which allows
passage of the anal canal
Between the urogenital hiatus and the anal canal lies a fibrous
node known as the perineal body which joins the pelvic floor to
the perineum
Levator Ani Syndrome
Levator Ani Syndrome (also known as levator syndrome and
proctodynia) is episodic rectal pain, caused by spasm of the
levator ani muscle.
The etiology is unknown.
Symptoms include a dull ache high in the rectum and a feeling
of constant rectal pressure or burning. The pain may also be felt
in the low pelvis or perineum.
The discomfort may be relieved by walking or pelvic tightening
exercises similar to Kegel exercises.
Other treatments include massage of the muscle, warm baths,
muscle relaxant medications, and biofeedback.
Electrical stimulation of the levator ani muscle has been used to
try to break the spastic cycle. Injection of botulinum toxin A
has also been used.
2. Coccygeus muscle
The Coccygeus is a muscle of the pelvic wall (i.e. peripheral to
the pelvic floor), situated behind the levator ani and in front of
the sacrospinous ligament.

28. It is a triangular plane of muscular and tendinous fibers, arise
by its apex from the spine of the ischium and sacrospinous
ligament and inserted by its base into the margin of the coccyx
and into the side of the lowest piece of the sacrum.
It assists the Levator ani and Piriformis in closing in the back
part of the outlet of the pelvis.
Function
It is important in providing support for pelvic viscera (organs),
e.g. the bladder, intestines, the uterus (in females) and in
maintenance of continence as part of the urinary and anal
sphincters.
Clinical significance
In women, the levator ani muscles or their supplying nerves can
be damaged in pregnancy or childbirth. This occurs more
commonly after a difficult obstructed vaginal delivery
There is some evidence that these muscles may also be damaged
during a hysterectomy.
Treatment: Pelvic floor exercises, also known as Kegel
exercises, may improve the tone and function of the pelvic floor
muscles, which is of particular benefit for women (and less
commonly men) who experience urinary incontinence.
Pelvic organ prolapse occurs in women when pelvic organs (e.g.
the vagina, bladder, rectum, or uterus) protrude into or outside
of the vagina.
The causes of pelvic organ prolapse include inappropriate
(asymmetrical, excessive, insufficient) muscle tone and
asymmetries caused by trauma to the pelvis.
Age, childbirth, family history, and hormonal status all
contribute to the development of pelvic organ prolapse.
Disorders of the posterior pelvic floor include rectal prolapse,
rectocele, perineal hernia.
Kegel exercise: also known as pelvic floor exercise, consists of
repeatedly contracting and relaxing the muscles that form part
of the pelvic floor. The exercise can be performed multiple
times each day, for several minutes at a time, for one to three
months, to begin to have an effect.

29. Kegel exercises can make the pelvic floor muscles stronger.
These are the muscles that hold up the bladder and help keep it
from leaking. Exercises are usually done to reduce urinary
stress incontinence (especially after childbirth) .
Muscles of Respiration
The muscles of respiration are those muscles that contribute to
inspiration and expiration, by helping in the expansion and
contraction of the thoracic cavity.
Basically, all muscles that attach to the rib cage have the
possibility of generating a breathing action.
Muscles that inflate the thoracic cavity are inspiratory muscles
and induce inhalation, while those that deflate the thoracic
cavity are expiratory and induce exhalation.
The diaphragm and the intercostal muscles drive respiration
during quiet breathing.
Primary Muscles
The primary inspiratory muscles are the: external intercostals
and the diaphragm
Accessory Muscles
Accessory muscles of respiration' are typically only used under
conditions of high metabolic demand (e.g. exercise) or
respiratory dysfunction (e.g. an asthma attack).

30. The accessory inspiratory muscles are the sternocleidomastoid,
the scalenus anterior, medius, and posterior, the pectoralis
major and minor, the inferior fibres of serratus anterior and
latissimus dorsi, the serratus posterior superior may help in
inspiration also the iliocostalis cervicis.
The accessory expiratory muscles are the: abdominal muscles;
rectus abdominis, external oblique, internal oblique and
transversus abdominis. And in the thoracolumbar region are the:
internal intercostals, intercostalis innermost and subcostals, the
lowest fibers of iliocostalis and longissimus, the serratus
posterior inferior and quadratus lumborum.
The Thoracic diaphragm
The thoracic diaphragm is a dome-shaped musculotendinous
wall between the thoracic and abdominal cavities. The convex
dome bulges into the thoracic cavity during expiration.
The diaphragm is the principal muscle of respiration and forms
the floor of the thoracic cavity and the roof of the abdominal
cavity.
During respiration, it descends as it contracts and ascends as it
relaxes.
Anatomy of the thoracic diaphragm
The diaphragm is composed of two portions: a peripheral
muscular part, and a central aponeurotic part, the central
tendon.
1. The Muscular Part of the Diaphragm
The muscular part is divided in the: sternal, costal, and lumbar
parts. Fibers forming this muscular part unite radially to the
central tendon.
i. The Sternal Part
This portion consists of two small muscular slips that are
attached to the posterior aspect of the xiphoid process. These

31. slips converge radially to the central tendon.
On each side of these muscular slips, there is a small
anterolateral gap known as the sternocostal hiatus.
ii. The Costal Part
This portion consists of wide muscular slips that arise from the
internal surfaces of the inferior six ribs and their costal
cartilages on each side. These slips interlink with slips of the
transversus abdominis muscles.
The costal part forms the left and right hemidiaphragms or
domes that move during respiration.
iii. The Lumbar Part
This portion arises from the lumbar vertebrae by two
musculotendinous crura (L. legs), which are attached on each
side of the aorta to the anterolateral surfaces of the superior two
(left) or three (right) lumbar vertebrae and their intervertebral
discs.
The crura of the diaphragm blend with the anterior longitudinal
ligament of the vertebral column.
The right crus is broader and longer than the left crus.
The two crura are united opposite the disc between T12 and L1
vertebrae by a tendinous band or narrow arch called the median
arcuate ligament
It passes over the anterior surface of the aorta and provides
attachment for some fibers of the right crus.
Lateral to the median arcuate ligament on each side; medial
arcuate ligaments are found, which are thickenings of the
anterior layer of the thoracolumbar fascia over the superior
parts of the psoas major muscles.
Each ligament forms a fibrous arch that runs from the crus of
the diaphragm, anterior to the psoas major muscle, and attaches
to the transverse process of L1 vertebra.

32. Further lateral to the medial arcuate liagments on both sides, the
lateral arcuate ligaments are thickenings of the anterior layer of
the thoracolumbar fascia over the superior parts of the
quadratus lumborum muscles.
Each ligament forms a fibrous arch that runs from the transverse
process of L1 to the 12th rib.
2. The Central Part of the Diaphragm
The muscular fibers of the diaphragm converge radially to a
strong, sheet-like aponeurosis called the central tendon, which
is fused with the inferior surface of the fibrous pericardium.
The central tendon has no bony attachments and is incompletely
divided into three leaves. This gives it a C-shape.
The right lateral leaf is the largest; the anterior (middle) leaf is
intermediate in size and the left one is the smallest.
The lateral leaves curve posteriorly as they blend with the
corresponding halves of the diaphragm.
The anterior leaf lies just inferior to the heart.
The Diaphragmatic Apertures
There are several apertures in the diaphragm that permits
structures to pass between the thorax and abdomen. The major
orifices are the venal caval foramen, the oesophageal hiatus,
and the aortic hiatus.

33. 1. The Vena Caval Foramen
The foramen for the inferior vena cava is at the posterior
junction of the right and anterior leaves of the central tendon.
It is located at the level of T8 vertebra, 2 to 3 cm to the right of
the medial plane. It is the most superior of the three large
apertures of the diaphragm.
The inferior vena cava is adherent to the margin of the vena
caval foramen; consequently, when the diaphragm contracts
during inspiration, it widens the foramen and stretches and
dilates the inferior vena cava.
These changes facilitate the blood flow through the inferior
vena cava.
2. The Oesophageal Hiatus
The oesophagus passes obliquely through this oval aperture in
the muscular part of the diaphragm, posterior and to the left of
the vena caval foramen.
The hiatus is usually in the right crus of the diaphragm, 2 to 3
cm left of the medial plane and approximately at the level of
T10 vertebra.
The fleshy fibres of the right crus form the oesophageal
sphincter, which constricts the distal end of the oesophagus
during inspiration, helping to prevent reflux of gastric contents
into the oesophagus.
3. The Aortic Hiatus
The aorta does not pierce the diaphragm because this aperture is
posterior to it.
It passes posterior to the median arcuate ligament, which arches
between the crura, anterior to T12 vertebra and to the left of the
median plane.
The aorta is unaffected by the contraction of the diaphragm
because it does not pass through it.
The aortic hiatus also transmits the thoracic duct and the azygos
vein.

34. Innervation of the Diaphragm
The entire motor supply to the diaphragm is from the phrenic
nerves, which arise from the anterior rami of segments C3-5 of
the spinal cord.
The phrenic nerves also supply sensory fibers to most of the
diaphragm.
Peripheral parts of the diaphragm receive their sensory supply
from the inferior six or seven intercostal nerves and subcostal
nerve.
Arterial Supply of the Diaphragm
Superior surface:
Superior phrenic arteries (arise from the thoracic aorta), and the
musculophrenic and pericardiophrenic arteries (branches of the
internal thoracic artery).
Inferior surface:
Inferior phrenic arteries (branches of the abdominal aorta).
Venous Drainage of the Diaphragm
Superior surface: pericardiophrenic and musculophrenic veins,
which drain into the internal thoracic vein.
Inferior surface: Inferior phrenic veins.
The right inferior phrenic vein usually opens into the inferior
vena cava, whereas the left inferior phrenic vein usually joins
the left suprarenal vein.
Actions of the Diaphragm
· The diaphragm is the chief muscle of inspiration.
· When it contracts its right and left domes move inferiorly so
that its convexity is flattened. The descent of the domes
increases the vertical diameter of the thoracic cavity.
· As the diaphragm descends, the intra-thoracic pressure is
decreased and the intra-abdominal pressure is increased.
· Diaphragmatic movements are also important in blood
circulation because of the changes in pressure in the thoracic
and abdominal cavities accompanying the contraction of the

35. diaphragm. Blood from the inferior vena cava is forced
superiorly into the heart.
· The diaphragm is also an important muscle for abdominal
straining. It assists the anterior abdominal muscles in raising
intra-abdominal pressure during micturition (urination),
defecation (bowel movements), and parturition (childbirth).
Intercostal Muscles
The intercostals (external and internal), these are muscles
uniting adjacent ribs and so completing the thoracic wall.
They are arranged in two layers: the outer layer; the external
Intercostals and the inner & innermost layer: Internal &
Innermost Intercostals.
The external intercostals are thick behind, thin and aponeurotic
in front. The internal intercostals are aponeurotic behind and
thicker in front
The externals run from up to down while the internals run at
right angles to the externals; thus from down to up.
Features of intercostal muscles
· The intercostal maintain a constant distance between the ribs,
and with the scalene muscle lift the first and second ribs
upward, they move all the ribs upward and forward in
inspiration.
· They also help to bend the trunk forward and sideways and
postural muscles.
· The external intercostals raise the ribs and assist the
diaphragm.
1. External intercostal muscles aid in quiet and forced
inhalation.
Origin: They originate from the lower border of ribs 1-11
Insertion: have their insertion on to the upper border of ribs 2-

36. 12 below
Their fibers are directed obliquely downward and laterally from
the back of the thorax, and downward, forward, to the medially
of the front
Action: The external intercostals are responsible for the
elevation of the ribs, and expanding the transverse dimensions
of the thoracic cavity.
2. Internal intercostal muscles aid in forced expiration (quiet
expiration is a passive process).
Origin: Each muscle arises from the ridge on the inner surface
of a rib, as well as from the corresponding costal cartilage of
ribs 2-12.
Insertion: have their insertions on the inferior border of ribs 1-
11, inserted into the inferior border of the rib above.
2. Internal intercostal muscles aid in forced expiration (quiet
expiration is a passive process).
Their fibers are also directed obliquely, but pass in a direction
opposite to those of the external intercostal muscles.
Action: The internal intercostals are responsible for the
depression and retraction of the ribs decreasing the transverse
dimensions of the thoracic cavity.
3. Innermost intercostal muscle group: it is the deep layer to the
internal intercostal muscles which are separated from them by a
neurovascular bundle.
This in turn is composed of:
Intermost internal muscles
Transversus thoracis muscle
Subcostalis muscle
i. Intermost internal muscles
The innermost intercostal muscles are the deepest muscle of the
three intercostal muscles.

37. Origin: they arise from the inner margin of the costal groove of
the rib above. The fibers run in a downwards, backwards and
lateral
Insertion: they are inserted into the superior border of the rib
below.
Action: fix intercostal spaces during respiration. They are the
weakest intercostal muscles
Although its origin and insertion is similar to the external
intercostal, its direction of fibers is similar and parallel to the
internal intercostal
Some authors describe the muscle as continuous over several
ribs and intercostal space opposed to the external and internal
intercostals which fill one space only each
As their name indicates, they are internal to the internal and
external intercostal muscles. Variably, the muscles become
continuous posteriorly with the subcostal muscles and anteriorly
with the tranversus thoracis muscles.
ii. Transversus Thoracis
This a thin muscle
Origin: arise from the back of the lower ⅓ end of the sternum
and lower costosternal juctions
From there its muscular fibres radiate like rays of the sun,
Insertion: to be inserted on the costal cartilage 2nd -7th
Action: which they pull down and depresses the cartilages, thus
help in expiration
iii. The Subcostales (singular: subcostalis)
Each originates from the inner surface of one rib (of the lower
six ribs) and is inserted into the inner surface of the second or
third rib below, near its angle.
The action of this muscle is unknown, but it is part of the
innermost intercostal muscle group along with the transversus
thoracis muscle which is known to be a synergist in aiding the

38. internal intercostal muscles with forced exhalation (depresses
the lower ribs).

41. 23