Osteopathy Journals and Research by Darren Chandler

 

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  1. Muscular anatomy: masseter, temporalis, medial and lateral pterygoid and buccinator muscles

    Masseter

    Superficial layer: zygomatic bone and zygomatic arch --> mandibular ramus.

    Middle layer: zygomatic arch --> mandibular ramus.

    Deep layer: zygomatic arch --> mandibular ramus and coronoid process of the mandible. There is debate as to whether the masseter attaches to the articular disc of the TMJ.

    Temporalis

    Origin (superficial layer): temporal fossa, zygomatic bone, deep temporal fascia.

    Origin (deep layer): superior surface of the zygomatic arch and the muscle that passes beneath the arch.

    Insertion: mandible (coronoid process and ramus). It can attach on to the articular disc of the TMJ.

    Sphenomandibularis

    The sphenomandibularis is the deep belly of the temporalis muscle located on its medial side. It originates from the greater wing of the sphenoid and attaches on to the mandible at the temporal crest, the retromolar triangle and the anterior limit of the mandibular notch (Geers et al 2005). 

    Functions of the masseter and temporalis

    Whilst the masseter and temporalis close the TMJ the temporalis pulls the condyle backwards. This is opposed by the upper head of the lateral pterygoid which pushes the condyle forwards during mouth closing.

    Schmolke (1994) found the attachment of the temporalis fascia to the TMJ joint capusle and of the masseteric fascia to the TMJ articular disc to be much less extensive than the attachment of the lateral pterygoid muscle to the articular disc.

    Therefore this author proposed the function of the temporalis and masseter muscles, because of their extensive complement of muscle spindles, may help to register the position of the articular disc. This would make them a part of the control system regulating the position of the various elements of the TMJ.

    Another interesting finding was noted by Scmidt et al (2009) who found higher EMG activity in the right temporalis and suprahyoid muscles when the tongue was placed against the palate with slight pressure. Relaxation of the temporalis occured with resting the tongue on the floor of the mouth.

    Lateral pterygoid

    Origin (upper head): greater wing of sphenoid; (lower head): lateral pterygoid plate of sphenoid.

    Insertion: neck of the mandible. A part of the upper head may be attached to the TMJ capsule and disc.

    Actions: bilateral contraction results in opening and protrusion of the jaw i.e. the condyle being pulled forwards and slightly down. Only the lower head contracts during mouth opening whilst the upper head relaxes. The upper head pushes the condyle forwards during mouth closing opposing the backwards pull on the condyle from the temporalis.

    Unilateral contraction results in the mandible deviating medially to the opposite side.

    Medial pterygoid

    Origin (deep head): lateral pterygoid plate of the sphenoid; (superficial head): maxilla and palatine bone.

    Insertion: mandible.

    Action: elevates (and with the lateral pterygoid) protrudes the mandible. With the lateral pterygoid unilateral contraction results in the mandible deviating medially to the opposite direction.

    Buccinator

    Origin: alveolar processes of the maxilla, mandible and temperomandibular joint.

    Insertion: Orbicularis oris. It has anatomical connections to the lateral deep slip of the platysma (Hur et al 2015), temporalis (Hur 207), incisivus labii inderioris (Hur et al 2011), zygomaticus major (Shim et al 2008) and parotid duct where it is associated with its function (Kang et al 2006).

    At the aveolar process of the maxilla the buccinator blends with the superificial lamina of the masticatory facsia as it leaves the anterior border of the masseter (Gaughran 1957).

    Fascia of the masticatory space (Gaughran 1957)

    The masticator space is described as a fascial compartment containing:

    • Temporalis.
    • Masseter.
    • Lateral pterygoid.
    • Medial pterygoid.
    • Temporomandibular joint.
    • Ramus of the mandible.
    • Masticatory fat pad (corpus adiposum buccae).
    • Neurovascular structures.

    Inferiorly the fascia of the masticatory space is formed from the superficial lamina of the cervical fascia which attaches to the lower border of the mandible.

    From the mandible attachment arises a deep and superficial sheet of fascia:

    Deep sheet of fascia

    The deep sheet of fascia passes upward on the inside of the medial pterygoid muscle (medial pterygoid fascia). This fascia passes upwards from its attachment to the mandible, over the medial pterygoid, to above the insertion of the pterygoid muscles attaching on the greater wing of the sphenoid (spine of sphenoid, jct of body/greater wing at the pterygoid process) and temporal bone (petrotympanic fissure) (Stecco 2015). It should be noted Stecco et al (2015) described these attachments for both the medial and lateral pterygoid fascia.

    The superficial and deep layer of the fascia fuses:

    • Posteriorly: at the rear edge of the ramus of the mandible.
    • Anteriorly: along the anterior border of the masseter.

    Superficial sheet of fascia

    The superficial sheet of cervical fascia continues superiorly to cover the parotid gland (parotid fascia, Hinganu et al 2018) and masseter muscle (a dense masseteric fascia). The masseteric fascia attaches on to the articular disc of the TMJ (Schmolke 1994) and zygomatic arch (Gaughran 1957).

    From the upper border of the zygomatic arch the fascia continues:

    • Posteriorly and superiorly covering the temporal muscle (temporal fascia or temporal aponeurosis of Batson) attaching to the superior temporal line (Gaughran 1957).
    • Anteriorly and superiorly it continues as the zygomatic fascia (Hinganu et al 2018).

    Anteriorly the superficial fascia attaches on to the anterior border of the ramus of the mandible (possibly becoming continuous with the sheath of the lateral pterygoid muscle) and the buccinator fascia and maxilla.

    The superficial and deep layer of the fascia fuses:

    • Posteriorly: at the rear edge of the ramus of the mandible.
    • Anteriorly: along the anterior border of the masseter muscle.

    At the anterior border of the masseter the fusion of the superificial and deep fascia splits again into a deep and superficial layer of fascia.

    Deep layer of fascia

    The deep layer reflects around the anterior border of the masseter passing towards the anterior border of the mandibular ramus. Here it blends with the insertion of the temporalis muscle and attaches to the mandible. Extending superiorly it attaches to the epimysium of the temporalis muscle.

    Superficial layer of fascia

    Attaches to the maxilla blending with the buccinator fascia and attaches to the deep layer along the mandible

    Interpterygoid, lateral pterygoid and temporalis fascia

    Interpterygoid fascia

    The interpterygoid fascia extends between the pterygoid muscles sometimes reflecting onto the deep surface of the temporalis. It's pierced by the auriculotemporal nerve (Barker and Davies 1972) and merges with the main muscle of the tongue (styloglossus) and with the fascial system of the internal carotid artery (Bordoni 2020). Its attachments are (Barker and Davies 1972):

    • Superiorly: cranial base at the sphenoid and temporal bone (Bordoni 2020 & Komune et al 2019) and the suture between the palatine and sphenoid (Lang 2001). Maxilla (Lang 2001).
    • Posteriorly: extends between the lateral and medial pterygoid muscles.
    • Inferiorly: mandible from above the upper border of medial ptcrygoid insertion extending backwards to the neck of the condyle. Here it blends with the stylomandibular fascia.

    Forms the sphenomandibular ligament (spine of sphenoid --> mandible: lingula of the mandibular foramen). This ligament blends with the lateral pterygoid fascia (Lang 2001) and the discomalleoular ligament and anterior ligament of malleus (refer to 'relations of the TMJ to the middle ear') (Rowicki and Zakrzewska 2006).

    • Anteriorly: the fascia is usually flimsy but it may be reflected to form a septum between the pterygoids and the fascia on the deep surface of the temporalis muscle. This is called temporopterygoid fascia.

    Lateral pterygoid and the deep temporalis fascia are separated at their anterior and medial surfaces but are intimately united more posteriorly.

    Lateral pterygoid fascia

    The lateral pterygoid fascia is a triangular sheet. It extends over the lateral surface of the lateral pterygoid muscle (Lang 2001). Its attachments are:

    • Anteriorly: sphenoid (lateral pterygoid plate) and buccinator fascia (Lang 2001).
    • Superiorly: extends from the TMJ (lateral part of the capsule and disc) --> maxilla --> buccinator fascia --> sphenoid (greater wing)
    • Inferiorly: mandible. Attaches to the medial surface of the mandibular ramus --> coronoid process (below temporalis attachment) --> mandibular notch --> TMJ: lateral part of the joint capsule.

    The lateral pterygoid fascia blends with:

    • Inferior attachment of the interpterygoid fascia at its attachments from the mandible to the TMJ.
    • Sphenomandibular ligament (Lang 2001)
    • Buccinator fascia (Lang 2001)

    Schmolke (1994) found some collagen fibres separate from the lateral pterygoid fascia to attach to the same region as the upper lamina of the articular disc at the petrotympanic fissure. Separate fibres have been observed extending through the petrotympanic fissure into the anterior ligament of the malleus within the tympanic cavity (refer 'relations of the TMJ to the middle ear').

    Deep temporal fascia

    The deep temporal fascia covers the anterior surface of the temporalis. It blends with the epimysium above the level of the mandibular attachment at the coronoid process (Gaughran 1957), lateral ligament of the TMJ and TMJ joint capsule (Schmolke 1994). The fascia covering the temporalis tendons extends further down the mandible to attach on to the oblique line of the mandible and blend with the buccinator fascia.

    The deep temporalis and lateral pterygoid fascia fuse at:

    • Mandible: oblique line of the mandible.
    • Deep temporal fascia extends from the medial edge of the anterior border of the temporalis tendon posteriorly to fuse with the lateral pterygoid fascia.

    Because of this fusion the attachment of the deep temporal fascia to the base of the skull can be considered as being identical with that of the lateral pterygoid fascia. The areas of fusion between the deep temporal and lateral pterygoid fascia are:

    • Between the upper and lower heads of the lateral pterygoid muscle. Within the fascia at this level is the buccal nerve and several anterior deep temporal branches of trigeminal nerve (V3).
    • Superior to the upper and lower heads of the lateral pterygoid, the two fascia usually remain united underneath the temporalis muscle. The buccal nerve emerges superior to the upper head or between the upper and lower heads of the lateral pterygoid muscle. It passes within the fused lateral pterygoid and deep temporalis fascia, to lie against or imbedded within the most medial fibers of the deep part of the temporalis muscle.

    Relations of the TMJ to the middle ear

    Discomalleolar ligament (mandibular-malleolar ligament or the “tiny” Pinto ligament)

    Rowicki and Zakrzewska (2006) found this ligament to be a fibroelastic tissue connecting the TMJ capsule and articular disc to the malleus. It extends from the TMJ and the sphenomandibular ligament* --> through the petrotympanic fissure --> malleus.

    The discomalleolar ligament can attach to the anterior ligament of malleus (Rowicki and Zakrzewska 2006).

    Ligaments of malleus

    There are three ligaments of malleus:

    • Anterior ligament of malleus (Casserio’s ligament): malleus --> anterior wall of the tympanic cavity close to the petrotympanic fissure. Some of the fibers also pass through the fissure to the spine of sphenoid. Within the pterotympanic fissue the anterior ligament of malleus becomes continuous with the sphenomandibular ligament* (Rowicki and Zakrzewska 2006)
    • Lateral ligament of malleus: malleus --> roof of the tympanic cavity.
    • Superior ligament of malleus: malleus --> roof of the tympanic cavity.

    Both the discomalleolar ligament and anterior ligament of malleus pass through the petrotympanic fissure that connects the TMJ through the temporal bone into the tympanic cavity.

    Schmolke (1994) and Rowicki and Zakrzewska (2006) found the TMJ articular disc is tightly fixed to the border of the petrotympanic fissure. Fibres extend through the petrotympanic fissure into the anterior ligament of the malleus within the tympanic cavity.

    The petrotympanic fissure also serves as an attachment for the pterygoid fascia (Stecco et al 2015).

    * Sphenomandibular ligament: spine of sphenoid --> mandible: lingula of the mandibular foramen. It is formed from the interpterygoid fascia. As well as attaching to the discomalleolar and anterior ligament of malleus it also blends with the lateral pterygoid fascia (Lang 2001).

    References

    FASCIAE OF THE MASTICATOR SPACE (1957) GEORGE R. L. GAUGHRAN

    The skull base and related structures: atlas of clinical anatomy (2001). Johannes Lang

    The deep belly of the temporalis muscle: an anatomical, histological and MRI study (2005). C. Geers Æ C. Nyssen-Behets Æ G. Cosnard Æ B. Lengele

    Anatomical considerations on the masseteric fascia and superficial muscular aponeurotic system (2018) DELIA HÎNGANU, CRISTINEL IONEL STAN, CORINA CIUPILAN, MARIUS VALERIU HÎNGANU

    Effects of tongue position on mandibular muscle activity and heart rate function (2009) John E. Schmidt, PhD,a Charles R. Carlson, PhD,b Andrew R. Usery, MD,c and Alexandre S. Quevedo, DDS, PhD,d Rochester, MN, Lexington, KY, and Winston-Salem, NC

    Functional atlas of the human fascial system (2015) Carla stecco

    The relationship between the temporomandibular joint capsule, articular disc and jaw muscles CORDULA SCHMOLKE (1994)

    THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE (1972). B. C. W. BARKER AND P. L. DAVIES

    An anatomical study of the insertion of the zygomaticus major muscle in humans focused on the muscle arrangement at the corner of the mouth. (2008). Shim KS, Hu KS, Kwak HH, Youn KH, Koh KS, Fontaine C, Kim HJ

    A study of the discomalleolar ligament in the adult human (2006) T. Rowicki, J. Zakrzewska.

    Blending of the lateral deep slip of the platysma muscle into the buccinator muscle. (2015) Hur MS, Bae JH, Kim HJ, Lee HB, Lee KS.

    Inferior bundle (fourth band) of the buccinator and the incisivus labii inferioris muscle. (2011). Hur MS, Hu KS, Kwak HH, Lee KS, Kim HJ.

    Anatomical connections between the buccinator and the tendons of the temporalis. (2017). Hur MS

    An anatomical study of the buccinator muscle fibres that extend to the terminal portion of the parotid duct, and their functional roles in salivary secretion. Hyo-Chang Kang, Hyun-Ho Kwak, Kyung-Seok Hu, Kwan-Hyun Youn, Guang-Chun Jin, Christian Fontaine, and Hee-Jin Kim

    The Five Diaphragms in Osteopathic Manipulative Medicine: Myofascial Relationships, Part 1 (2020). Bruno Bordoni

    The Fascial Layers Attached to the Skull Base: A Cadaveric Study (2019). Komune N, Matsuo S, Nakagawa T.

  2. Myofascial attachments to the dura mater in the craniocervical junction

    The dura mater receives myofascial attachments in the craniocervical junction from: 

    • Myodural bridges (Scali et al 2013): bands of fascia crossing the epidural space link the suboccipital muscles and the dura mater. This suboccipital fascia is continuous with the galea aponeurotica (Dacey et all 2018). Myodural bridges reach the dura via the PAO membrane from the Rectus Capitis Posterior Minor (RCPMi) and via the atlantoaxial interspace from the Rectus Capitis Posterior Major (RCPMa), Obliquus Capitis Inferior (OCI) and the Nuchal Ligament (NL). Zheng et al (2019) described the vertebrodural ligaments (refer below) as the final common pathway for the myodural bridge (RCPMa, OCI & NL) in the posterior atlanto-axial interspace.

    The myodural bridges may function in: (i) protect the spinal cord from dural enfolding (ii) transmission of proprioception from the spinal dura (iii) allows the suboccipital muscles to exert a reflexive myostatic response in placing the dura under tension (iv) myodural biofeedback might participate in maintaining the integrity of the subarachnoid space and posterior cerebellomedullary cistern (iv) these muscles exert a pumping effect by deforming the dura providing an important force required to move CSF in the spinal canal (Zheng et al 2014 & Xu et al 2016). Xu et al (2016) found CSF circulation at the craniocervical junction is significantly propelled in a cranial direction by head rotations attributed to the effects of these muscles on the dural sac (as well as changes in heart rate and respiratory rate).

    • Posterior atlanto-occipital membrane (PAO): The PAO membrane extends between the posterior arch of C1 and the occiput. Connective tissue fibres create a PAO membrane-spinal dura complex (Nash et al 2005). 

      The PAO membrane is mainly formed by the rectus capitis posterior minor tendinous fibers, the deep layer of the rectus capitis posterior minor fascia, and arterial and venous perivascular connective tissue sheathes. The rectus capitis posterior minor attaches to the dura indirectly via the PAO (Zheng et al 2019).

    The PAO attachments are:

    Laterally: the membrane extends between the rectus capitis posterior minor tendon (or aponeurosis) --> vertebral artery and vertebral cavernous sinus vascular sheath. Via the vascular sheath this membrane was continuous with the spinal dura.

    Medially: can not be identified but was formed from the rectus capitis posterior minor fascia and the perivascular sheathes of vertebral venous vessels.

    Inferiorly: fuses with the spinal dura and the perivascular sheath of the internal vertebral plexus.

    Superiorly: continues with the deep layer of the rectus capitis posterior minor fascia fusing to the occiput.

    • First (intracranial) denticulate ligament: its attachments extend from (lateral): outer layer of the dura mater of the marginal sinus at the foramen magnum --> pierces the posterior atlantooccipital membrane and dura mater --> (medial): spinomedullary junction (Tubbs et al 2011).
    • Epidural ligaments (of Hoffman): dura mater (dural sac and dural extension of the nerve root sleeve) --> posterior longitudinal ligament, the vertebral canal and the ligamentum flavum (Tardieu et al 2016).
    • Dorsal meningodural ligaments (Shi et al 2014): connective tissue bands running mainly from the ligamentum nuchae but also the laminae to the posterior dural (thecal) sac. Most commonly from C5 up with the strongest attachments being at C1-C2. They only exist in the cervical spine.
    • Vertebrodural ligaments include the verterebrodural ligament (VDL), to be named ligament (TBNL) and the craniale durae matris spinalis (CDMS) (Zheng et al 2014). Even though they are described seprarately all the vertebrodural ligaments are anatomical and functional linked with each other and the myodural bridges. Zheng et al (2019) described the VDL as the final common pathway for the myodural bridge (RCPMa, OCI & NL) in the posterior atlanto-axial interspace:

    i. Vertebrodural ligament: connects C1-2 ligamentum nuchae and posterior wall of the C1 & C2 vertebral canal to the cervical dura mater. The dura mater is distinctly thick at the VDL insertion. 

    VDL subdivided into three parts: Superior portion: C1: posterior arch of the atlas. Middle portion (TBNL’s part): C1-2 interspace. It is continuous with the TBNL. Inferior portion (axial part): C2 lamina. It is continuous with the TBNL which adheres to the lamina. 

    Suboccipital myodural bridge becomes part of the VDL as it passes through the atlantoaxial interspace.

    ii. TBNL: local enhancement of the ligamentum nuchae that forms part of the myodural bridge. It enters the epidural space through the atlanto-axial interspace and terminates at the posterior cervical spinal dura mater.

    Posterior border of ligamentum nuchae* --> atlantoaxial interspace --> C1-2 dura mater.

    *: Ligament nuchae attachments of the TBNL are: main attachment is below C3 SP at the common origins of the splenius capitis, superior posterior serratus and rhomboid minor muscles. Also attaches to the C2 SP.

    As well as its more indirect muscular attachments at C3 it receives direct attachments from the rectus capitis posterior minor, rectus capitis posterior major and obliquus capitis inferior (Yuan et al 2017). 

    Zheng et al (2014) speculated that cervical flexion draws the cervical dura mater posteriorly creating a bulge via the TBNL and VDL passage through the atlantooccipital interspace.

    iii. Ligamentum craniale durae matris spinalis (CDMS): continuous with the deep part of the ligamentum nuchae.

    Edge of the foramen magnum, the posterior border of the O/A joints, nuchal ligament posterior arch of the atlas, and the arch of the axis --> cervical dura.

    Superior attachments of the suboocipital fascia comes from the galea aponeurotica. Dacey et al (2018) found the galea aponeurotica transitions to the suboccipital fascia by dense fibrous attachments. Therefore we have myofascial continuity from Tenon's capsule running posteriorly via the occipitofrontalis to the galea aponeurotica/suboccipital fascia terminating in the upper cervical complex.

    Venous return at the craniocervical junction

    At the craniocervical junction the internal vertebral venous plexus communicates with:

    • Occipital-marginal sinus.
    • Condylar veins: posterior condylar emissary vein and anterior condylar (venous plexus of the hypoglossal canal), lateral condylar vein.
    • Other emissary vein: occipital and mastoid (Ruiz et al 2002).
    • Anterior condylar confluent external to the hypoglossal canal to the posterior cranial fossa and internal jugular vein. 

    Cervical kyphosis causes the internal jugular vein to bend around the transverse process of atlas. This reverses its normal course, as well as potentially compressing the vein which increases the resistance to blood flow.

    Therefore malformations and misalignments of the craniocervical junction may play a role in chronic ischemia and oedema, which may in turn lead to neurodegenerative processes and subsequent diseases (Flanagan 2015). Mandolesi et al (2015) found an anterolisthesis between the first two cervical vertebral bodies is greater than two-fold in patients with MS rather than in those without neurologic disease.

    Haemodynamics of the vertebral venous plexus, marginal sinus and internal jugular vein

    Venous outflow from the cranial cavity is mainly through the internal jugular veins (Urakov et al 2015). However there seems to be reciprocal relationship between the internal jugular venous flow from the head and the marginal sinus-verterbral venous flow.

    The internal jugular vein has a valve just above the termination of the internal jugular vein. It is the only valve between the heart and the brain and prevents the cephalic flow of venous blood. This valve permits an increase in intrathoracic pressure from shooting blood up to the brain and therefore increasing intracranial pressure (Silva et al 2002).

    Because of this valve drainage in the internal jugular vein isn’t as dependent on a pressure gradient. By contrast the dural sinuses, facial veins, and vertebral veins have no valves. This means the direction of venous blood flow is determined by hydrostatic pressure gradients.

    The internal jugular veins are the major cerebral venous outflow pathway that is not reliant on a pressure gradient e.g. when supine. The vertebral venous plexus is the major cerebral venous outflow pathway that is reliant on a pressure gradient e.g. when standing. Both the vertebral and internal jugular vein show twice the outflow when supine than sitting (Ciuti et al 2013).

    When supine, with head elevation, overall there is a a decreased venous pressure toward the head. This becomes zero above the heart or even negative where the veins do not collapse. Accordingly, there is a point or a level, where pressure remains independent of posture, referred to as the hydrostatic indifference point. This point is located a few centimetres below the diaphragm (Peterson et al 2014).

    Even though there is an overall decrease in venous pressure with supine head elevation there is a relative decrease internal jugular venous flow (Urakov et al 2015) and corresponding increase in vertebral vein flow (Tobinick 2017). This is because with head elevation the internal jugular vein bends around the TP of C1, reversing its normal course, as well as potentially compressing the vein (Flanagan 2015).

    When standing the pressure gradient produced means the major cerebral outflow pathway is from the dural sinuses into the vertebral venous plexus (Valdueza et al 2000 & Gisolf et al 2004). 

    However when performing a standing valsalva manoeuvre the internal jugular veins are opened without increasing vertebral venous drainage. This is because the increases intraabdominal pressure redirects venous blood from the body cavities to vertebral venous plexus. By clogging up this drainage route with diverted venous blood from the thoracic and abdominal cavities the body opens up the internal jugular venous pathway (Gisolf et al 2004).

    Fricke et al (2001) found receptors in the dural sinuses and internal jugular bulb that may measure volume changes in the cranial vascular system supporting autonomic reflexes to control intracranial blood flow and volume.

    The jugular bulb is located at the jugular foramen. It is the connection between the sigmoid sinus and internal jugular vein. The myofascial connections of this area are discussed below. Could direct manipulation of myofascial tension andfblood flow through the internal jugular vein produce a therapeutic neurological reflex?

    Venous pressure and CSF production and absorbtion

    Passive production of CSF occurs during upright posture which decreases venous pressure in the vertebral veins and dural sinuses:

    A decrease venous pressure in the superior sagittal sinus means the venous sinus has greater capacity to absorb CSF into it from the subarachnoid space. This increase flow of CSF out of the brain via the dural sinus decreases intracranial CSF volume. To address this reduced CSF volume additional blood gets drawn from the choroid plexus to produce more CSF to make up for that that has been lost. This is called passive production of CSF (Flanagan 2015).

    Superior sagittal sinus venous pressure and flow is affected by posture, respiration, and movement. It is also affected by downstream pressure in the internal jugular and vertebral veins.

    Therefore to maintain constant intracranial pressure there is a balance between the influx of fluid into and out of the cranium:

    DECREASE INTRACRANIAL PRESSURE: increase venous outflow (decreases venous pressure) --> increase CSF absorbtion --> INCREASE INTRACRANIAL PRESSURE: increase arterial inflow --> increase CSF production.

    INCREASE INTRACRANIAL PRESSURE: decrease venous outflow (increases venous pressure) --> decrease CSF absorbtion --> DECREASE INTRACRANIAL PRESSURE: decrease arterial inflow --> decrease CSF production.

    Myofascial anatomy of the internal jugular vein, internal carotid artery, vertebral artery and the jugular foramen

    Rectus capitis lateralis (Cohen et al 2016)

    • Origin and insertion.

    C1 TP --> occiput: jugular process. 

    Kulkarni et al (2001) found these muscles have a high proprioceptive content. These authors disputed their primary role as ipsilateral sidebenders of the head and instead allocated their function to primarily being proprioceptive.

    • Vascular relations

    The rectus capitis lateralis covers the posterior aspect of the opening of the jugular foramen. Its anterior border fuses with the posterior wall of the carotid sheath at the midportion of this muscle.

    The origin of the rectus capitis lateralis on the C1 TP overlays the C1 foramen transversarium, where the vertebral artery exits the TP to enter the dura.

    Extracranial neurovascular compartment of the upper retrostyloid parapharyngeal space

    The extracranial neurovascular compartment of the upper retrostyloid parapharyngeal space is a transitional space between the intracranial aspect of the jugular foramen and the cervical carotid sheath. It is traversed by the structures exiting the jugular foramen.

    The compartment to be bounded by the:

    • Medially: occipital condyle.
    • Laterally: styloid process.
    • Posteriorly: rectus capitis lateralis.
    • Superiorly: jugular foramen.
    • Inferiorly: carotid sheath.

    Condylar triangle

    Condylar triangle:

    • Anterior: rectus capitis lateralis.
    • Posterior: superior oblique.
    • Superior: a line connecting these muscles along the occipital bone superiorly.

    Contains the superior segment of the vertebral artery as it exits the C1 foramen transversarium and bends posteriorly toward the atlantooccipital membrane.

    Fascial relations to the internal jugular vein and internal carotid artery

    The relationship of the rectus capitis lateralis to the carotid sheath has already been described with its anterior border fusing with the posterior wall of the carotid sheath (Cohen et al 2016).

    Komune et al (2019) identified the fascial attachments to the cranial base.

    These authors found at the cranial base a complex fascial network around the internal jugular vein and the internal carotid artery.

    This network is made up from:

    • Prevertebral fascia: fascia of the longus capitis and rectus capitis lateralis.
    • Middle layer of the deep cervical fascia: tensor-vascular styloid fascia.
    • Stylopharyngeal fascia.
    • Deep cervical fascia: carotid sheath. The carotid sheath attaches anteriorly and laterally to the vaginal process (temporal bone) and posteriorly to the fibrocartilaginous tissue around the jugular foramen (temporal bone) and carotid canal (occipital/temporal bone).

    Bordoni (2020) found the fascial network of the internal carotid artery to merge with the:

    • Tensor-vascular styloid fascia: inferior border of the tensor veli palatini --> styloid process and muscles.
    • Fascia of the digastric muscle.
    • Interpterygoid fascia: extends between the pterygoid muscles sometimes reflecting onto the deep surface of the temporalis. It's pierced by the auriculotemporal nerve (Barker and Davies 1972) and merges with the main muscle of the tongue (styloglossus) and with the fascial system of the internal carotid artery (Bordoni 2020). Its attachments are (Barker and Davies 1972):

    i. Superiorly: cranial base at the sphenoid and temporal bone (Bordoni 2020 & Komune et al 2019) and the suture between the palatine and sphenoid (Lang 2001). Maxilla (Lang 2001) 

    ii. Posteriorly: extends between the lateral and medial pterygoid muscles.

    iii. Inferiorly: mandible from above the upper border of medial ptcrygoid insertion extending backwards to the neck of the condyle. Here it blends with the stylomandibular fascia.

    Forms the sphenomandibular ligament (spine of sphenoid --> mandible: lingula of the mandibular foramen).

    iv. Anteriorly: the fascia is usually flimsy but it may be reflected to form a septum between the pterygoids and the fascia on the deep surface of the temporalis muscle. This is called temporopterygoid fascia.

    In addition to the preverterbal fascia vascular relations in forming a fascial network around the internal jugular vein and internal carotid artery there are also relations to the vertebral artery.

    The triangle of the vertebral artery is formed lower down where the prevertebral fascia splits between the longus colli and scalene anterior.

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