Head, Neck, and Trunk Muscles

Objective 10.12

10.12.1 Give the origin, insertion, and action of the major muscles of the head, neck, and trunk.

10.12.2 Identify these muscles on a picture or image.

 

Head, Neck & Trunk 

Masseter

The masseter is a major muscle of mastication (chewing).

An illustration showing the origin and insertion of the masseter muscle.

Muscle Origin Insertion Primary Action(s)
Masseter Zygomatic Bone (zygomatic arch) Mandible Mandibular Elevation (closes mouth)

 

Sternocleidomastoid (SCM) 

The sternocleidomastoid is a lot of people’s favorite muscle because it is fun to say. You will often see it abbreviated as SCM. Sterno- refers to the sternum. Cleido- refers to the clavicle. Mastoid refers to the mastoid process of the temporal bone.

An illustration showing the origin and insertion of the sternocleidomastoid muscle.

Muscle Origin Insertion Primary Action(s)
Sternocleidomastoid Sternum (manubrium) Clavicle Mastoid Process (temporal bone) Ipsilateral Neck Tilt

Contralateral Neck Rotation

 

Trapezius

The trapezius is named for its shape. When looking at both the right and left trapezius muscles together, they form a trapezoid, hence their name. It is common for people to get muscle pain in this muscle, especially if they are stressed. The trapezius has many functions, but we will not explore too many of them here.

An illustration showing the origin and insertion of the trapezius muscle.

Muscle Origin Insertion Primary Action(s)
Trapezius Occipital Bone

Cervical Spine

 Clavicle

Scapula

 Elevate Scapula (shrug shoulders)

 

Breathing Muscles: Diaphragm, Internal & External Intercostals

The diaphragm, internal intercostals, and external intercostals play a role in breathing. You will remember from Unit 1 that the diaphragm separates the thoracic cavity from the abdominal cavity. The diaphragm is active for inhalation and relaxes for exhalation. The intercostals are muscles that run between the ribs. They play a role in either exhalation or inhalation as noted below by either elevating or depressing the ribs. We will study these muscles more in the respiratory system (Unit 17).

An illustration showing the origin and insertion of the diaphragm and intercostal muscles.

Muscle(s) Primary Action(s)
Diaphragm Inhalation (muscle active)
Internal Intercostals Exhalation
External Intercostals Inhalation

 

Abdominals

The abdominal muscles perform a variety of functions, but for this unit, we just want you to be familiar with their names and basic functions.

An illustration showing the origin and insertion of the abdominal muscles.

Muscle(s) Primary Action(s)
Rectus Abdominus Spinal Flexion

Compression of Abdomen
External Oblique
Internal Oblique
Transversus Abdominus

 

Erector Spinae 

The erector spinae are a grouping of three muscles: spinalis, longissimus, iliocostalis. You do not need to know them individually, just collectively. Together, they are spinal extensors. They play a major role in maintaining upright posture.

An illustration showing the origin and insertion of the erector spinae muscle group.

Muscle(s) Primary Action(s)
Erector Spinae Spinal Extension

 

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Integrated Human Anatomy and Physiology Copyright © by Travis Price; Jim Hutchins; Justin Burr; Maddison Johnston; Pamela Silberman; Jeffery Speth; Jordan West; Misty Allen; and Elizabeth Rebarchik is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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