The muscles of the neck are
muscles that cover the area of the neck. These muscles are mainly responsible for
the movement of
the head in all
directions. They consist of 3 main groups of muscles: anterior, lateral and posterior groups,
based on their position in the neck. The musculature of the neck is further
divided into more specific groups based on a number of determinants; including
depth, precise location and function.
The position of a muscle or
group of muscles in the neck generally relates to the function of the
muscles. For example, the muscles in the posterior neck are responsible for
extension of the neck. The muscles of the neck are closely related to a number of
important structures that pass between the thorax
and the head, including major blood vessels, nerves and elements of the respiratory and gastrointestinal systems.
This article will introduce
you to the anatomy of the muscles of the neck.
|
Key facts about the neck muscles |
|
|
Definition and function |
A large group of muscles in
the cervical area, responsible for the movement of the head in all directions |
|
Anterior muscles of the neck |
Superficial muscles: Platysma, sternocleidomastoid |
|
Lateral (vertebral) muscles
of the neck |
Scalene muscles: Anterior scalene,
middle scalene, posterior scalene muscles |
|
Posterior muscles of the
neck |
Superficial layer: Trapezius, splenius capitis, splenius cervicis |
Anterior neck muscles
The anterior neck muscles are
a group of muscles covering the anterior aspect of the neck. They are further
divided into 3 subgroups:
·
The superficial muscles are
the most superficial in the anterior neck, and include the platysma
and sternocleidomastoid.
·
The suprahyoid muscles,
as the name suggests, are found superior to the hyoid bone,
and include the digastric, mylohyoid, geniohyoid and stylohyoid.
·
The infrahyoid muscles are
found inferior to the hyoid bone and consist of the sternohyoid, omohyoid, sternothyroid and thyrohyoid.
Superficial muscles
Platysma
The
platysma is a sheet-like muscle that lies within the subcutaneous tissue of the anterior
neck, superficial to the investing layer of deep cervical fascia.
It originates from the skin and fascia overlying the region of the clavicle and passes superiorly along the neck. The platysma
inserts into several points, including the mandible, the skin of the lower face, lower
lip and the corners of the mouth.
The
platysma is innervated by
the cervical branch of facial
nerve (CN VII), and vascularized by the
submental branch of the facial
artery, and suprascapular
branch of the thyrocervical trunk.
Due
to its direct attachment to the skin of the lower face, the platysma functions mainly as a muscle of facial expression.
For example, it contributes to producing an expression of sadness by pulling
the corners of the mouth inferiorly.
Sternocleidomastoid
muscle
The
sternocleidomastoid is a large, two-headed muscle of the neck. Its clavicular head originates from the
medial third of the clavicle, while its sternal head arises
from the manubrium of sternum. The heads come together and ascend diagonally to
insert onto the mastoid
process of the temporal bone.
The
sternocleidomastoid muscle is innervated by
the accessory nerve (CN XI) and anterior rami of spinal
nerves C2 and C3. Vascular supply to this muscle is
derived from branches of the occipital, posterior auricular, superior thyroid and suprascapular artery.
The
function of the sternocleidomastoid muscle depends on whether the muscle acts
alone or together with its contralateral counterpart.
·
Unilateral
contraction produces lateral flexion of the neck on the same
(ipsilateral) side and lateral rotation of the head to the opposite
(contralateral) side.
·
Bilateral
contraction of the sternocleidomastoid muscles produce flexion
of the neck, drawing the head towards the chest. When the head and neck are
fixed, the sternocleidomastoid can also elevate the sternum and clavicle and
thereby expand the thoracic cavity during forced inspiration.
Suprahyoid muscles
The suprahyoid muscles
are four muscles located superior to the hyoid
bone. They connect the hyoid
bone to the mandible and the base of the skull and form the floor of the oral
cavity. These muscles include
the digastric, mylohyoid, geniohyoid and stylohyoid muscles.
Generally,
the main function of these muscles is positioning of the hyoid bone and
coordination of the movements of the floor of the mouth and the hyoid bone
while swallowing or vocalization.
Digastric
The
digastric muscle is a small muscle situated below the mandible, that extends
from the mastoid process of temporal bone to the chin. The muscle is composed
of a posterior and an anterior belly, connected by an intermediate tendon, which represents their
common insertion point.
·
The posterior belly arises
from the medial surface of mastoid notch, a deep groove found on the mastoid
process of temporal bone.
·
The anterior belly arises
from the digastric fossa of the lower border of mandible.
The
muscle bellies both travel towards the hyoid bone and connect via the
intermediate tendon, a fibrous tissue sling that is anchored to the superior
aspect of the body of hyoid bone.
The
digastric muscle has dual innervation.
The anterior belly is innervated by the nerve to mylohyoid, a branch of the
inferior alveolar nerve, while the posterior belly receives innervation from
the digastric branch of the facial nerve. The blood supply for
the digastric muscle is derived from the submental branch of the facial artery,
and posterior auricular and occipital arteries.
The function of the digastric muscle
depends on its point of action.
·
If the mandible is fixed and the muscle is acting from
below, it causes an elevation of
the hyoid bone and larynx. This results in the closing of the epiglottis, preventing the inhalation of the food bolus during
swallowing.
·
If the hyoid bone is fixed and the muscle acts from
above, it depresses the mandible,
aiding the act of opening the mouth.
Mylohyoid
The
mylohyoid is a sheet-like muscle that forms the majority of the floor of the mouth. The mylohyoid arises
from the mylohyoid line on the inner surface of mandible, and inserts into the
mylohyoid raphe and superior aspect of the body of hyoid bone.
The
mylohyoid is innervated by
the nerve to mylohyoid muscle that arises from the inferior alveolar branch of
the mandibular nerve (CN V3). Its blood supply is
derived from the sublingual, inferior alveolar and submental arteries.
Like
the digastric muscle, the function of
the mylohyoid depends on its point of action.
·
If the mandible is fixed, the mylohyoid elevates the hyoid bone and the floor
of the mouth, which aids the act of deglutition by pressing the tongue against the hard
palate.
·
If the hyoid bone is fixed, the muscle depresses the mandible and assists in
opening the mouth.
Geniohyoid
The
geniohyoid is a short muscle that arises from the inferior mental spine of the
mandible and runs posteroinferiorly to insert into the superior border of the
body of the hyoid bone.
The
geniohyoid muscle is innervated by
the anterior ramus of spinal nerve C1 via the hypoglossal nerve (CN XII) and vascularized by
the sublingual branch of the lingual
artery.
The
main function of the geniohyoid is similar
to other suprahyoid muscles:
·
If the mandible is fixed, the muscle acts to elevate the hyoid bone and move the
larynx and pharynx
anterosuperiorly. The geniohyoid thus aids the act of deglutition and voice
production.
·
If the hyoid bone is fixed, the geniohyoid muscle depresses the mandible and assists in
opening the mouth.
Stylohyoid
The
stylohyoid is a thin muscle that extends between the temporal and hyoid bones. It originates from the
posterior surface of the styloid process of temporal bone and passes
anteroinferiorly and medially to attach on the body of hyoid bone.
The
stylohyoid muscle is innervated by
the stylohyoid branch of the facial nerve (CN VII). Its blood supply is derived from the
facial, occipital and posterior auricular arteries.
The function of the stylohyoid is to
elevate the hyoid bone and retract the tongue, which facilitates deglutition
because it pushes the food bolus towards the soft
palate. The stylohyoid also
keeps the pharynx open during inspiration.
Infrahyoid muscles
The infrahyoid muscles are four muscles
located inferior to the hyoid bone, that connect it to the larynx, sternum and scapula.
These include the sternohyoid, omohyoid, sternothyroid and thyrohyoid muscles.
Generally, the main function of
these muscles is positioning of the hyoid bone and movement of the thyroid
cartilage of the larynx during vocalization, swallowing and mastication.
Sternohyoid
The
sternohyoid muscle is a strap-like muscle found in the muscular triangle of the neck.
It arises from the superior part of the manubrium of sternum and the posterior surface of the medial end of
the clavicle. The sternohyoid then courses superiorly and medially to insert
into the inferior border of the body of hyoid bone.
The sternohyoid is innervated by the anterior rami of the
first three cervical spinal nerves via the ansa cervicalis, that arises from
the cervical plexus. The muscle is vascularized by
the superior thyroid branch
of the external carotid artery.
The function of
the sternohyoid muscle is to depress the hyoid bone and larynx after it has
been elevated by the suprahyoid muscles. This action opens the airways again
and reestablishes breathing after swallowing.
Omohyoid
The omohyoid is a narrow muscle
that connects the scapula to
the hyoid bone. The muscle is composed of two
bellies connected by an intermediate tendon, similar to the digastric muscle.
·
The inferior belly arises from the
superior border of the scapula and runs anterosuperiorly to insert onto the
intermediate tendon at the level of the arch of cricoid cartilage.
·
The superior belly originates from
the intermediate tendon at the level of the internal jugular vein and courses superiorly to insert
at the lower border of the body of hyoid bone.
The nerve supply to
the omohyoid is provided by the ansa cervicalis. Its blood supply stems
from the superior thyroid branch of the external carotid artery, and inferior
thyroid branch of the thyrocervical trunk.
As other infrahyoid muscles, the
omohyoid functions to
depress the hyoid bone and larynx to reopen the laryngeal inlet after
swallowing. In addition, since the intermediate tendon of the omohyoid is
connected to the carotid
sheath, when the muscle contracts, it pulls on the
sheath and decreases the pressure in the internal jugular vein. This action is
convenient as it increases the venous return from the head to the superior vena cava.
Sternothyroid
The
sternothyroid is a strap-like muscle that runs in the muscular triangle of the neck. It arises
from the costal cartilage of the first rib and the posterior surface of the
manubrium of the sternum. The muscle then courses superiorly to insert onto the
oblique line of the thyroid cartilage.
The nerve supply to
the sternothyroid muscle is derived from the ansa cervicalis (C1-C3). Its blood supply stems from the branches
of the lingual and superior thyroid arteries.
Like other infrahyoid muscles, the function of the sternothyroid muscle
is to depress the hyoid bone and larynx, and thereby open the laryngeal inlet
and reestablish breathing after swallowing. In addition, the sternothyroid
muscle can pull the thyroid cartilage away from the hyoid bone and further open
the laryngeal inlet, which can aid forced inspiration.
Thyrohyoid
The
thyrohyoid is a quadrilateral muscle located in the muscular triangle of the neck. It arises
from the oblique line of the lamina of thyroid cartilage, and courses
superiorly to insert onto the lower border of the greater horn and the adjacent
body of hyoid bone.
The thyrohyoid muscle is innervated by the anterior rami of the
first cervical spinal nerve (C1) via the hypoglossal nerve (CN XII). Its blood supply is derived from the
infrahyoid and superior laryngeal branches of the superior thyroid artery, and
the lingual branch of the external carotid artery.
In conjunction with other infrahyoid
muscles, the thyrohyoid functions to
depress the hyoid bone following its elevation during the act of swallowing and
vocalization. However, the thyrohyoid has an additional function when the hyoid
bone is fixed, in which it elevates the larynx. This action is important for
persons that need to sing high notes, such as vocalists.
Anterior
vertebral muscles
The anterior vertebral muscles are
a deep group of muscles located just anterior to the cervical
vertebral column. These include the rectus capitis
anterior, rectus capitis
lateralis, longus capitis and longus colli. These muscles are surrounded
by the prevertebral fascia of the neck, which is why they are commonly referred
to as prevertebral muscles. The principal
function of these muscles is flexion of the head to varying degrees.
Rectus capitis anterior
The rectus capitis is a short
strap muscle that arises from the anterior surface of the lateral mass of atlas
(C1 vertebra) and inserts on the basilar part of the occipital bone, anterior
to the foramen magnum.
The innervation of
this muscle comes from the anterior rami of spinal nerves C1 and C2, while its blood supply is provided by branches
of the vertebral and ascending pharyngeal arteries.
The function of
the rectus capitis anterior is to flex the head at the atlanto-occipital joint,
as well as to stabilize this joint.
Rectus capitis lateralis
The
rectus capitis lateralis is a small muscle that arises from the superior
surface of the transverse process of the atlas (C1) and ascends superiorly to
insert onto the inferior surface of the jugular process of occipital bone.
The muscle is innervated by branches of the anterior
rami of spinal nerves C1 and C2, and vascularized by
the ascending pharyngeal, vertebral and occipital arteries.
The function of
the rectus capitis lateralis is to flex the head laterally at the
atlanto-occipital joint, and to help stabilize this joint during movement.
Longus capitis
The
longus capitis is a long, flat muscle that arises from the anterior tubercles
of transverse processes of vertebrae C3-C6 as four thin muscle strips. These
muscle strips travel superiorly and medially to insert onto the inferior
surface of the basilar part of the occipital bone.
The muscle is innervated by anterior rami of spinal
nerves C1-C3, and vascularized by
the ascending pharyngeal artery, ascending cervical branch of the inferior
thyroid artery and the muscular branches of the vertebral artery.
The longus capitis functions as a weak flexor of the head
when acting bilaterally, while unilateral contraction of the muscle produces
ipsilateral rotation of the head.
Longus colli
The longus colli, also called the
longus cervicis, is a long muscle that spans the entire length of the cervical
spine and the upper vertebrae of the thoracic spine. It is divided into
three parts:
·
The superior part arises from the anterior
tubercles of transverse processes of vertebrae C3-C5 and inserts into the
anterior tubercle of vertebra C1.
·
The intermediate part arises from the
anterior surface of bodies of vertebrae C5-T3 and inserts into the anterior
surface of bodies of vertebrae C2-C4.
·
The inferior part arises from the anterior
surface of bodies of vertebrae T1-T3 and inserts into the anterior tubercles of
transverse processes of vertebrae C5-C6.
The muscle is innervated by the anterior rami of the
spinal nerves C2-C6. Its blood supply stems from branches of the
vertebral, inferior thyroid and ascending pharyngeal arteries.
The main function of the longus colli is to
flex the neck. In addition, the inferior part of the muscle can produce a weak
ipsilateral flexion and contralateral rotation of the neck.
Lateral
neck (vertebral) muscles
The lateral neck muscles, also
called the lateral vertebral muscles, are a group of muscles that pass
obliquely along the lateral sides of the neck. These include the anterior,
middle and posterior scalene
muscles, which extend between the
transverse processes of the cervical vertebrae and the upper two ribs. Due to
their attachments, these muscles mainly produce ipsilateral flexion of the
neck.
Anterior
scalene muscle
The anterior scalene muscle is the most anterior of the scalene muscles.
It arises from the anterior tubercles of the transverse processes of vertebrae
C3-C6, and inserts onto the scalene tubercle and the superior border of the
first rib.
The anterior scalene muscle is innervated by the anterior rami of the
spinal nerves C4-C6, and vascularized by
the ascending cervical branch of inferior thyroid artery.
The function of
the anterior scalene muscle depends on its point of action and whether the
muscle acts alone or together with its contralateral counterpart.
·
When
the ribs are fixed and the muscle is acting from below, bilateral contraction
of the anterior scalene causes flexion of
the neck. In turn, unilateral contraction of the muscle causes lateral flexion
of the neck to the same side.
·
When
the vertebral column is fixed, the muscle produces elevation of the 1st rib, which
combined with the action of the external intercostals expands the
antero-posterior diameter of the thoracic
cage.
This action is important during forced respiration.
Middle
scalene muscle
The middle scalene is the largest of the scalene muscles, that
arises from the transverse processes of axis (C2) and atlas (C1), and the
posterior tubercles of transverse processes of the vertebrae C3-C7. The muscle
then passes posterolaterally to insert onto the superior border of the first
rib.
The middle scalene muscle receives
its nerve supply from the anterior rami of
cervical spinal nerves C3-C8. Its blood supply stems
from the ascending cervical branch of the inferior thyroid artery.
The
main function of the middle scalene muscle
is to produce an ipsilateral flexion of the neck, when acting from below. When
the cervical part of the vertebral column is fixed and the muscle is acting
from above, it stabilizes or raises the 1st rib during forced inspiration.
Posterior
scalene muscle
The posterior scalene is the smallest and most posterior of the scalene muscles
that arises from the posterior tubercles of transverse processes of cervical
vertebrae C4-C6. It then extends posterolaterally and inserts into the external
surface of the second rib.
The nerve supply to
the posterior scalene muscle is derived from the anterior rami of spinal nerves
C6-C8, while its blood supply comes
from the ascending cervical branch of the inferior thyroid artery and the
transverse cervical branch of the thyrocervical trunk.
Similar to the middle scalene, the
main function of the posterior scalene is
ipsilateral flexion of the neck when acting from below, and stabilization or
elevation of the second rib when acting from above.
Posterior
neck muscles
The posterior aspect of the neck
is covered by muscles that connect the skull to the spinal column and pectoral
girdle. These muscles can be divided into three layers;
·
Superficial layer: Trapezius, splenius capitis and splenius cervicis.
·
Deep layer: cervical transversospinalis
muscles (semispinalis capitis, semispinalis cervicis, multifidus cervicis)
·
Deepest layer: suboccipital muscles, interspinales cervicis and
intertransversarii colli muscles
Superficial
layer
Trapezius
The trapezius is a large, flat,
triangular muscle that forms a diamond shape with its contralateral
counterpart. The muscle extends over the posterior aspect of the neck and the
superior part of the thorax. Based on the orientation of its fibers, the trapezius
is divided into three parts; descending, transverse and ascending part, each of
them having distinct attachments.
·
The descending part is composed of the
superior fibers of trapezius, that originate from the medial third of the
superior nuchal line and the external occipital protuberance of the occipital bone. These fibers pass downwards to
insert onto the posterior border of the lateral third of the clavicle.
·
The transverse part is composed of
the middle fibers of trapezius, that originate from the nuchal ligament of the
spinous processes of vertebrae C1-C6, and spinous processes and supraspinous
ligaments of vertebrae C7-T3. These fibers pass horizontally to insert onto the
medial acromial margin and the superior crest of the scapular spine.
·
The ascending part is composed of the
inferior fibers of trapezius, that originate from the supraspinous ligaments and spinous processes of the
vertebrae T4-T12. These fibers pass upwards and laterally to insert onto the
lateral apex of the medial end of the scapular spine.
The trapezius muscle is innervated by the accessory nerve (CN
XI). Its blood supply stems
from branches of the occipital, superficial cervical, transverse cervical and
dorsal scapular arteries.
The main function of the trapezius is to
produce lateral flexion and contralateral rotation of the head when acting
unilaterally, and extension of the head when acting bilaterally. In addition,
the trapezius muscle stabilizes and produces movements of the scapula. Depending
on which part of the trapezius contracts, these movements may be elevation,
depression, retraction and rotation of the scapula.
Splenius muscles
The superficial muscles of the
posterior neck are the splenius muscles; the splenius capitis and splenius
cervicis. These muscles also belong to the superficial layer of the deep (intrinsic) back muscles.
·
The splenius capitis originates from the
spinous processes of vertebrae C7-T3 and the nuchal ligament, and inserts just
below the lateral superior nuchal line of the occipital bone, and the mastoid
process of temporal bone.
·
The splenius cervicis arises from the
spinous processes of vertebrae T3-T6 and inserts onto the transverse processes
of vertebrae C1-C3.
The splenius muscles are innervated by the posterior rami of
middle and lower cervical spinal nerves. The blood supply to
the splenius muscles is by the occipital and transverse cervical arteries.
The function of
the splenius muscles is to extend the head when contracted bilaterally, whereas
unilateral contraction produces lateral flexion and rotation of the head to the
same side.
Deep
layer
The transversospinalis muscles are
a large group of muscles that also belong to the deep layer of the intrinsic
muscles of the back. This group of muscles comprise the semispinalis, multifidus,
and rotatores muscles.
All of these muscles are subdivided further according to the region they span.
The ones that span the posterior
aspect of the neck are the:
·
Semispinalis capitis, that arises from the articular
processes of vertebrae C4-C7 and transverse processes of vertebrae T1-T6. It
then courses upwards to insert between the superior and inferior nuchal lines
of the occipital bone.
·
Semispinalis cervicis, that arises from the transverse
processes of vertebrae T1-T6 and inserts onto the spinous processes of
vertebrae C2-C5.
·
Multifidus cervicis, that arises from the articular
processes of vertebrae C4-C7 and inserts onto the spinous processes of
vertebrae 2-5 levels above the origin.
The semispinalis capitis is innervated by the descending branches
of the greater occipital nerve (C2) and spinal nerve C3, while the semispinalis
cervicis and multifidus cervicis are innervated by the medial branches of
posterior rami of spinal nerves. These muscles receive their blood supply via branches of the
vertebral, deep cervical and occipital arteries.
The function of
the cervical transversospinalis muscles is to extend the head and neck during
bilateral contraction, and to laterally flex and rotate the head to the same
side during unilateral contraction.
Deepest
layer
Suboccipital muscles
The suboccipital muscles are four
small muscles found in the suboccipital region, deep to the semispinalis
muscles. These are:
·
Rectus capitis posterior
major, that
arises from the spinous process of axis and inserts onto the lateral part of
the inferior nuchal line.
·
Rectus capitis posterior
minor, that
arises from the posterior tubercle of atlas and inserts into the medial part of
the inferior nuchal line.
·
Obliquus capitis inferior, that arises from the spinous
process of axis and inserts on the transverse process of atlas.
·
Obliquus capitis superior, that arises from the transverse
process of atlas and inserts on the occipital bone, between the superior and
inferior nuchal lines.
All four of the suboccipital
muscles are innervated by
the suboccipital nerve (C1), and vascularized by
the vertebral artery and the deep descending branches of the occipital artery.
The main function of the suboccipital muscles
is reflected in maintaining posture, but they can also produce movements of the
head. Depending on which muscle of the group contracts, the suboccipital muscle
can produce an extension, lateral flexion and rotation of the head at the
atlanto-axial joint.
Interspinales cervicis
The interspinales cervicis is the cervical part of the interspinales
muscle group. It is composed of six pairs of muscles that span the space
between the tips of the spinous processes of successive vertebrae. Thus, they
arise from the superior aspect of spinous processes of vertebrae C3-T1 and
insert onto the spinous processes of vertebrae C2-C7.
The interspinales cervicis are innervated by the posterior rami of
spinal nerves, and vascularized by
branches of the occipital, vertebral and deep cervical arteries.
The main function of the interspinales cervicis
muscles aid in the extension of the neck.
Intertransversarii colli
The intertransversari colli
represent the cervical
portion of the intertransversarii muscles, which belong to
the deepest layer of the intrinsic back muscles. The intertransversarii colli
are composed of anterior and posterior sets of short slips of muscles that
arise from the superior border of transverse processes of vertebrae C1-T1 and
insert into the inferior border of the transverse processes of the superior
adjacent vertebrae.
The intertransversarii colli are innervated by the anterior and
posterior rami of cervical spinal nerves, and vascularized by
the occipital, deep cervical and vertebral arteries.
Due to their small size, the function of these muscles is to only
assists in lateral flexion of the head and to stabilize the cervical spine
during movement.
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