Order 1240402: Chapter 12 Muscular System

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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

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

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)

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)

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

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

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)

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

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

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

· 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

· 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

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)

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)

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

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 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

· 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

· 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

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 rotation at the hip joint.

· Innervation: The psoas major is innervated by anterior rami of L1-3, while the iliacus is innervated by the femoral nerve

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 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 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

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.

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.

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 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.

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.

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).

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 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.

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.

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.

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 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 2-12 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.

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

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