Anatomy and Physiology 2e · The Muscular System

Axial Muscles of the Head, Neck, and Back

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On this page 9 sections

In 30 seconds
Why this matters
The college version
Eli explains
Worked example
Key takeaway
Check yourself
Study tools
Sources & references

In 30 seconds

attach to the axial skeleton — the skull, vertebral column, and rib cage — and position the head, neck, and trunk. This topic surveys the axial muscles of the head, neck, and back, which fall into functional families: muscles of facial expression (move the skin of the face; facial nerve, CN VII), muscles of mastication (move the mandible; trigeminal nerve, CN V), muscles of the tongue, extrinsic eye muscles, muscles of the anterior neck (including the hyoid muscles of swallowing), and intrinsic muscles of the back that extend, laterally flex, and rotate the spine and head.

A key organizing idea: facial expression muscles insert into skin, not bone, which is why they can wrinkle a forehead or lift a smile; the intrinsic back muscles insert on bone and act like guy-wires holding the spine upright.

Why this matters

These muscles run your most visible and most vital behaviors. Facial expression muscles are the machinery of emotion — and their failure is a cardinal sign in conditions like Bell's palsy (facial weakness on one side). Mastication and tongue muscles are essential for eating and speaking; the hyoid muscles position the larynx during swallowing, directly relevant to aspiration risk. Neck muscles hold up a head that weighs several kilograms and are frequent sites of strain. The intrinsic back muscles keep you upright against gravity all day, and dysfunction here is central to low back pain — one of the most common reasons people seek healthcare.

The college version

Core Concepts

Muscles of facial expression

These thin muscles originate on skull or fascia and insert into the skin of the face; all are innervated by the facial nerve (CN VII). Key players:

— the scalp muscle with two bellies: frontalis (raises eyebrows, wrinkles forehead) and occipitalis (back of skull), joined by the flat galea aponeurotica.
Orbicularis oculi — the ring around the eye; closes the eyelid (blinking).
Orbicularis oris — the ring around the mouth; closes and purses the lips.
— the deep cheek muscle that presses the cheek against the teeth during chewing.
Zygomaticus major and minor — cheekbone to mouth corner; pull it up and back — the smile muscles.
Platysma — a broad neck sheet that pulls the lower lip down and tenses the neck skin.

Muscles of mastication

These move the mandible during chewing; all are innervated by the mandibular division of the trigeminal nerve (CN V3):

— the thick muscle at the cheek angle; the main elevator of the mandible (clenching).
Temporalis — the fan-shaped muscle over the side of the skull; elevates and retracts the jaw.
Medial pterygoid — elevates and protrudes the mandible, working with the masseter.
Lateral pterygoid — opens the mandible, protrudes it, and moves it side to side; alternating pterygoids produce chewing's grinding motion.

Muscles of the tongue

The tongue has intrinsic muscles (within it, shaping it) and extrinsic muscles (anchored outside, moving it) — (protrudes), styloglossus (retracts/elevates), hyoglossus (depresses) — all innervated by the hypoglossal nerve (CN XII), the nerve of tongue movement.

Extrinsic eye muscles

Six small muscles rotate the eyeball: four recti and two obliques — the recti move it side to side and up and down; the obliques rotate it. Innervation is a classic exam question: lateral rectus = CN VI (abducens), superior oblique = CN IV (trochlear), the other four = CN III (oculomotor).

Muscles of the anterior neck

Hyoid muscles attach to the hyoid bone, the small U-shaped bone anchoring the tongue and larynx. Suprahyoid muscles (digastric, stylohyoid, mylohyoid, geniohyoid) lie above and elevate it, positioning the larynx during swallowing; infrahyoid muscles (sternohyoid, omohyoid, sternothyroid, thyrohyoid) lie below and depress it. Their coordination is essential for safe swallowing and speech.
— the strap from sternum and clavicle to the mastoid process; one side tilts the head and rotates the face to the opposite side; both sides flex the neck. It also assists inspiration.
Scalenes — three muscles from the cervical vertebrae to the first two ribs; they laterally flex the neck and elevate the ribs during deep inspiration.

Intrinsic muscles of the back

These deep muscles run along the vertebral column and act on the spine and head:

Splenius capitis and cervicis — the most superficial intrinsic neck/back muscles; extend the head and neck and rotate them to the same side.
— the great vertical column on either side of the spine, with three parallel columns: iliocostalis (lateral), longissimus (middle), and spinalis (medial). Together they extend the spine (standing up from a bent-over position); one side alone laterally flexes it.
— deeper muscles running obliquely between vertebral processes: semispinalis, multifidus, rotatores. They extend and rotate the spine; the multifidus stabilizes individual segments.

How It Works / Step-by-Step Process

Tracing a smile: (1) motor cortex signals down CN VII; (2) branches reach the zygomaticus muscles; (3) the zygomaticus major pulls the mouth corner up and back as the orbicularis oculi tightens, crinkling the eyes; (4) the skin moves because these muscles insert into it, not bone.

Common Confusions

Do Not Confuse	With	Difference
Muscles of facial expression	Muscles of mastication	Expression muscles move skin (CN VII); mastication muscles move the mandible (CN V3)
Buccinator	Masseter	Buccinator compresses the cheek; masseter elevates the jaw
Suprahyoid muscles	Infrahyoid muscles	Suprahyoid elevate the hyoid/larynx; infrahyoid depress them
Erector spinae	Transversospinales	Erector spinae extend; transversospinales rotate and stabilize
Splenius rotation	Sternocleidomastoid rotation	Splenius rotates to the same side; sternocleidomastoid to the opposite side
Lateral rectus nerve	Superior oblique nerve	Lateral rectus = CN VI; superior oblique = CN IV; the rest = CN III

Eli explains

The same idea, in plain words

Explain it like I’m 10

Some of your muscles are attached to your skin instead of your bones — that's how you can smile, frown, and raise your eyebrows. Other muscles, like the strong ones in your cheeks and back, are attached to bones and do the heavy lifting: chewing, holding your head up, and keeping your spine straight. Neck muscles also help you swallow safely so food doesn't go down the wrong pipe.

Worked example

A swallowing checkpoint. You take a sip of water. The suprahyoid muscles (mylohyoid, geniohyoid, digastric, stylohyoid) contract, lifting the hyoid bone and larynx upward and forward, helping close the airway and guiding the bolus into the esophagus. The infrahyoid muscles then gently lower the hyoid and larynx back to rest, while the tongue — pushed by the genioglossus and shaped by its intrinsic muscles — moves the water backward. If the cranial nerves controlling these muscles are impaired (as can happen after a stroke), coordination fails and aspiration risk rises — a direct clinical reason this muscle group matters.

Key takeaways

Facial expression muscles insert into skin and are all innervated by CN VII (facial nerve); damage → facial weakness (e.g., Bell's palsy).
Mastication muscles move the mandible via CN V3: masseter and temporalis elevate; lateral pterygoid opens, protrudes, grinds.
Extrinsic tongue muscles: CN XII (hypoglossal).
Eye muscle mnemonic: CN VI = lateral rectus, CN IV = superior oblique, CN III = the rest.
Hyoid muscles: suprahyoid elevate, infrahyoid depress the hyoid/larynx (swallowing). Sternocleidomastoid: one side tilts/rotates; both sides flex the neck.
Erector spinae (iliocostalis, longissimus, spinalis) extend and laterally flex the spine.
Transversospinales (semispinalis, multifidus, rotatores) rotate and stabilize spinal segments.

Check yourself

6 review questions from the chapter. Try each one, then open the answer.

Which cranial nerve innervates all muscles of facial expression, and why do these muscles insert into skin?
Show answer
The facial nerve (CN VII). They insert into facial skin, so contraction creates expressions.
Name the four muscles of mastication and the nerve that drives them.
Show answer
Masseter, temporalis, medial pterygoid, and lateral pterygoid — all innervated by the mandibular division of the trigeminal nerve (CN V3).
What is the difference between suprahyoid and infrahyoid muscles, and what do they do together?
Show answer
Suprahyoid muscles lie above the hyoid and elevate it (and the larynx); infrahyoid muscles lie below and depress it. Together they position the larynx for safe swallowing.
Which back muscle group is the main extensor of the vertebral column, and what are its three columns?
Show answer
The erector spinae group — its three columns are iliocostalis, longissimus, and spinalis.
Which nerves innervate the lateral rectus and the superior oblique eye muscles?
Show answer
Lateral rectus: abducens (CN VI). Superior oblique: trochlear (CN IV).
Contracting the right sternocleidomastoid alone produces what movement of the head?
Show answer
It tilts the head to the right and rotates the face to the left (opposite side).

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Study tools & related lessonsKey vocabulary · Related

Key vocabulary

axial muscles: Muscles attached to the axial skeleton (skull, vertebral column, rib cage)
epicranius: Scalp muscle with frontalis and occipitalis bellies joined by the galea aponeurotica
buccinator: Deep cheek muscle that presses the cheek against the teeth
masseter: Powerful muscle that elevates the mandible
pterygoid muscles: Medial and lateral deep jaw muscles
genioglossus: Extrinsic tongue muscle from the chin
suprahyoid / infrahyoid: Hyoid muscles above / below the hyoid bone
sternocleidomastoid: Neck strap from sternum + clavicle to mastoid process
erector spinae: Three-column back group (iliocostalis, longissimus, spinalis)
transversospinales: Deep back muscles (semispinalis, multifidus, rotatores)

Sources & references

openstax.org — Anatomy And Physiology 2e

This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.

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