Axial Musculature

Axial skeleton includes:

• bones of the skull

• sternum

• ribs

• vertebrae

• sacrum and coccyx

• and other associated bones of this part of human skeleton

Axial musculature

• muscles that position the head and vertebral column

• muscles that move the rib cage

Axial muscles subdivided into:

• appendicular musculature

• Axial musculature (muscles that stabilize or move appendicular skeleton)

Axial muscles can be placed into 4 groups based on location or function:

• muscles of head and neck

• muscles of vertebral column

• muscles of rib cage and lateral walls of the abdominal and pelvic cavities (thoracic and abdominal wall muscles)

• muscles of the pelvic floor

Muscles of head and neck

• muscles of facial expression — move skin of face

• extra-ocular muscles — move the eyeball

• muscles of mastication — chewing muscles

• muscles of the tongue

• muscles of pharynx — throat wall

• anterior muscles of the neck

What cranial nerve innervates these expressive muscles?

Facial nerve (CN VII)

Superior oblique

draws eye laterally and inferiorly

Inferior oblique

draws eye laterally and superiorly

Facial expression focus on these: occipitofrontalis, orbicular oculi, orbicularis oris, zygomaticus major/minor, platysma

Important neck muscles to know is

sternocleidomastoid

Buccinator muscle

located in the cheeks (the walls of the mouth). It helps to circulate food around the mouth as we chew.

It can help generate suction as we drink through a straw. It keeps the cheeks tight so that we do not bite down on the inside wall of the mouth when we chew. This muscle distends out when you see someone playing the trumpet. The name ‘buccinator’ translates as trumpeter.

Muscles that physically move the eyeball around are known as the …

extraocular muscle

Mastication

chewing

Main chewing muscles:

• masseter

• temporalis

• pterygiods

for the most part, these muscles are working to elevate the mandible so that the biting surfaces of the teeth are brought closer together to crush food

muscles of tongue will have a …

“-glossus” in their names

they help w mechanical breakdown of food along w swallowing

muscles in the throat wall usually have …

“-pharyngeus” in their names

they work to move food from mouth into the esophagus

Muscles operating on the skull and spinal column:

These muscles are found in pairs: (one on the left and one on the right)

Bilateral contraction: muscle is contracting on both sides of the body at same time

unilateral contraction: muscle is actively contracting on one side of the body

ipsilateral: body moves toward the SAME side on which contraction takes place

Contralateral: body moves toward the OPPOSITE side on which contraction takes place

Bilateral and unilateral actions of the sternocleidomastoid muscle in the neck…

Uni - ipsilateral lat flexion; contralateral lat rotation

Bi - flexion/extension of neck (depends on position/context); forced breathing

Name main suprahyoid muscles: DMS

• Digastric: elevates the hyoid bone and helps depress the mandible during swallowing and chewing.

• Mylohyoid: forms the floor of the mouth and elevates the hyoid and tongue during swallowing.

• Stylohyoid: elevates and retracts the hyoid bone, elongating the floor of the mouth during swallowing.

Their main functions (they elevate and fixate the hyoid bone and larynx in the neck)

Name main infrahyoid muscles: SOTS

• Sternohyoid: depresses the hyoid bone after it has been elevated during swallowing.

• Omohyoid: depresses, retracts, and stabilizes the hyoid bone.

• Sternothyroid: depresses the thyroid cartilage (larynx) during swallowing.

• Thyrohyoid: depresses the hyoid bone and elevates the larynx.

Erector spinae muscles of the back

powerful group of muscles consisting of 3 vertical columns of muscle running up and down the length of the back.

From lateral to medial: iliocostalis ; longissimus ; spinalis

Iliocostalis column

has segments that are attaching to portions of the ribcage

Bilateral and unilateral actions of erector spinae group:

• bilateral movements: extension of vertebral column (straightening the back); in practice, these muscles are actually working to reduce the movement of the spinal column

• Unilateral movements: lateral flexion and rotation to the same side

The splenius muscle are found

along the back of the neck

Scalene muscles exist in 3 segments:

anterior, middle, posterior

What do Scalene muscles help with

depending on the context and what movement the body is creating, they can assist with forced inspiration. Or, they can help w stabilizing the cervical spine or laterally flexing it.

Remember: the roots of the brachial plexus emerge b/w the anterior and middle scalene muscles

Intercostal muscles are

thin layers of muscle found in b/w adjacent ribs. Main ex of this group are the external intercostals and internal intercostals. The externals assist w forced inspiration. internals assist with forced expiration

Names and functions of muscles of abdominal wall

External oblique, internal oblique, the rectus abdominis, and the transversus abdomens are the main abdominal wall muscles

Common functions are to flex the torso, or to create compression of the torso — this is basically sucking in ur gut to tighten the abdominal wall

movements of diaphragm during phases of breathing

Inspiration (Inhale/breathing in) = diaphragm contracts & descends to allow for lung expansion
Expiration (Exhale/breathing out) = diaphragm relaxes & ascends to allow for lung contraction

Weakness of pelvic floor muscles can lead to …

urinary incontinence (urinary leakage)