The Muscles of the Neck and Trunk

The Muscles of the Neck

Regions of the Neck To facilitate the seemingly complicated

area, the neck is divided into two major areas, or triangles, by the sternocleidomastoid muscle. These are:

1. anterior triangle - the area anterior to the SCM and

below the inferior border of the mandible.

2. posterior triangle - the area posterior to the SCM and

is limited posteriorly by the trapezius muscle.

Sternocleidomastoid Muscle

Muscle Action

Sternocleidomastoid muscle Bilateral:Flex the neck

Single:Flex the head and laterally rotate to the opposite side

Trapezius Muscle

Muscle Action

Trapezius muscle Contract to rotate and elevate the scapula Its cervical portion, acting bilaterally, can extend the head and singly, it can rotate the head and face to the opposite side

I. Infrahyoid Muscles

Muscle Action

Omohyoid Depresses the hyoid bone and larynx

Sternohyoid Depresses the hyoid bone and larynx

Sternothyroid Depresses the larynx

Thyrohyoid Depresses the hyoid bone

II. Suprahyoid MusclesMuscle Action

Stylohyoid Elevates hyoid bone

Digastric(Posterior belly)

Raises the hyoid bone

Digastric(anterior belly)

Elevates the hyoid bone

Suprahyoid MusclesMuscle Action

Mylohyoid Elevates the hyoid bone, base of the tongue, and floor of the mouth

Geniohyoid muscle Elevates hyoid bone, protracts hyoid bone

The lateral muscles of the neck

Muscle Action

Platysma Stretches tight the skin of the neck, depresses the mandible

Splenius capitis Bilateral:Extends the headIndividual:Flexes the head laterally

Muscle ActionLevator scapulae Elevates and rotates the

scapula

Scalenius posterior Flexes the neck

Scalenius Medius Flexes the neck

Scalenius anterior Participates in forced inspiration by elevating the ribs and sternum

The Muscles of the Trunk

1. Deep Muscles of the Back

Collectively these muscles control the vertebral column

Muscle Action

Semispinalis thoracis cervicis capitis

Extend the vertebral column and the head; rotate them to the opposite side.

Mulitifudus Extend the vertebral column; rotates it to the opposite side.

Rotatores Extend the vertebral column; rotates it to the opposite side.

Interspinales Extend the vertebral column

Scalenes Flex and rotate the neck; assist in inspiration

Intertransversaril Abduct the vertebral column

Splenius capitis cervicis Acting together they extend the head and the neck; acting singly, they abduct and rotes the head towards the same side

Muscle Action

Erector spinae

Iliocostalis lumborum thoracis cervicis

Extend the vertebral column and bend it to one side

Longisimus thoracis cervicis capitis

Extend the vertebral column and the head; rotate the head to the same side

Spinalis thoracis cervicis Extend the vertebral column

Deep Muscles of the Thorax

Respiratory Muscles

Muscle Action

Diaphragm Pulls central tendon downwards, increasing the size of the thoracic cavity and therefore causing inspiration.

External intercostals Elevates the ribs, aids in inspiration

Internal intercostals Draws ribs together, aiding in expiration

Subcostals Draws ribs together, aiding in expiration

Transversus thoracis Draws the anterior portion of the rib cage downward, aids in expiration

Muscles of the Abdominal Wall

Muscle Action

External oblique abdominis Compresses the abdominopelvic cavity, assists in flexing and rotating the vertebral column.

Internal oblique abdominis Compresses the abdominopelvic cavity, assists in flexing and rotating the vertebral column.

Transversus abdominis Compresses the abdominopelvic cavity

Rectus abdominis Compresses the abdominopelvic cavity, flexes the vertebral column

Quadratus lumborum Pulls the thoracic cage towards the pelvis; abducts the vertebral column downward towards the side to which it is being contracted

Muscles that Form the Floor of the

Abdominopelvic Cavity

Muscle Action

Pelvic diaphragm

Levator ani Supports the pelvic viscera

Coccygeus Supports the pelvic viscera

Muscles that Act on the Scapula

Muscle Action

Trapezius Elevates, depresses, rotates, adducts, and stabilizes the scapula.

Rhomboideus major Adducts, rotates,and stabilizes the scapula, lowering its lateral angle.

Rhomboideus minor Adducts, rotates,and stabilizes the scapula, lowering its lateral angle.

Levator scapulae Elevates the scapula and bends the neck laterally when the scapula is fixed.

Pectoralis minor Draws the scapula anteriorly and downward,lowering its lateral angle.

Serratus anterior Stabilizes, abducts and rotates the scapula upward.

Subclavius Stabilizes the pectoral girdle and depresses it.

Muscles that Act on the Arm

Flexion Extension

Adduction

Abduction

Medial rotation

Lateral rotation

Deltoid Deltoid Pectoralis major

Deltoid Pectoralis major

Deltoid

Pectoralis major

Latissimus dorsi

Teres major

Supraspinatus

Latissimus dorsi

Supraspinatus

Coracobrachialis

Teres major

Coracobrachialis

Subscapularis

Infraspinatus

Infraspinatus

Deltoid Teres minor

Teres major

LET US IDENTIFY THESE MUSCLES!!

Got to study really hard now!