Study Guides

Skull

The skull is divided into the neurocranium or calvaria (contains the brain and its meningeal coverings) and the facial skeleton. The skull is composed of 22 bones (excluding the middle ear ossicles), with 8 forming the cranium and 14 forming the face. The orbits (eye sockets) lie between the calvaria (skull cap) and the facial skeleton and are formed by contributions from 7 different bones.

• Function of skull

  • Encloses, supports, and protects brain and meninges

  • Contains foramina for transmission of nerves and vessels

  • Forms foundation for face

  • Contains specialized cavities and openings for sense organs (e.g., nasal, oral)

• Neurocranium

  • Cranial vault and base of skull

  • Encloses and protects brain

  • Composed of 8 bones

  • Bones united by interlocking sutures

  • Can be divided

    • Calvaria—domelike roof

    • Cranial base

  • Calvaria composed of 4 bones

    • Frontal bone anteriorly

    • Occipital bone posteriorly

    • Two parietal bones laterally

  • Cranial base formed from

    • Ethmoid bone

    • Parts of occipital and temporal bones

• Facial skeleton

  • Composed of 14 bones

  • Encloses orbits, nose, paranasal sinuses, mouth, and pharynx

  • Maxillae and mandible form upper and lower jaw, respectively, and house the teeth

• Three auditory ossicles

  • Malleus, incus, and stapes

  • Found spanning tympanic cavity

  • First bones to be completely ossified during development

Mandible

• Unpaired bone of lower jaw

• Largest and strongest bone in face

• Articulates with temporal bone at temporomandibular joint

• Consists of

  • Body

    • Can be divided into lower base and upper alveolar part

    • Has mental protuberance anteriorly and inferiorly where two sides come together

    • Mental spine: rough projection on inner surface of body in midline

    • Mental foramen below second premolar transmits terminal branch of inferior alveolar nerve to supply skin and mucus membrane of lower lip and chin

    • Mylohyoid line: ridge extending upward and backward on internal surface of alveolar part of mandible for attachment of mylohyoid muscle

    • Submandibular fossa: long depression below mylohyoid line, which accommodates submandibular gland

    • Sublingual fossa: concavities on either side of mental spine for sublingual gland

  • Rami

    • Lateral vertical projections from body

    • Each meets body inferiorly at angle of jaw

    • Two processes at superior end: coronoid process and condylar process

    • Coronoid process—attachment of temporalis muscle

    • Condylar process—part of temporomandibular joint

    • Mandibular notch—concavity between condylar and coronoid processes

    • Mandibular foramen: on inner surface of ramus; entrance to mandibular canal, through which passes the inferior alveolar nerve

    • Lingula—thin projection of bone overlapping mandibular foramen

    • Mylohyoid groove—groove leading anteriorly and inferiorly from mandibular foramen, indicating course of mylohyoid nerve and vessels

Temporomandibular Joint

The mandible articulates with the temporal bone, and in chewing and speaking it is only the mandible or lower jaw that moves; the upper jaw or maxillary bone remains stationary. The teeth are contained in the alveolar portion of the mandible.

• Articulation between condylar process of mandible, articular tubercle of temporal bone, and mandibular fossa

• Modified hinge-type synovial joint

• Contains fibrocartilaginous disc, which divides joint cavity into two compartments

  • Gliding movements (protrusion and retrusion/retraction) occur in upper compartment

  • Hinge movements (depression and elevation) occur in lower compartment

• Stabilized by three ligaments

  • Lateral temporomandibular ligament

    • Lateral thickened parts of articular capsule

    • Prevents posterior dislocation of joint

  • Sphenomandibular ligament

    • Primary passive support

    • Runs from spine of sphenoid bone to lingula of mandible

    • Serves as swinging hinge and check ligament

  • Stylomandibular ligament

    • Thickening in capsule of parotid gland

    • Runs from styloid process to angle of mandible

• Movements

  • Depression—suprahyoid and infrahyoid muscles, gravity

  • Elevation—temporalis, masseter, and medial pterygoid muscles

  • Protrusion—lateral pterygoid, masseter, and medial pterygoid muscles

  • Retraction/retraction—temporalis, masseter muscles

  • Side-to-side grinding—retractors of same side, protractors of opposite side

Cervical Vertebrae (See Section 2.2 , Bones And Ligaments)

Arteries of The Face

• Facial artery

  • Major arterial source for face

  • Arises from external carotid artery, crosses mandible, and traverses face to medial angle of eye

  • Branches to upper and lower lip and nose

• Superficial temporal artery

  • Terminal branch of external carotid

  • Enters temporal fossa and ends in scalp

• Transverse facial artery

  • From superficial temporal

  • Crosses face below zygomatic arch

Veins of The Face

• Supratrochlear vein

  • Descends from forehead to nose

  • Joins supraorbital vein to form angular vein

• Supraorbital vein

  • Begins in forehead and passes medially to join supratrochlear vein

  • Sends branch through supraorbital notch to joint superior ophthalmic vein

• Facial vein

  • Two veins provide main venous drainage of face

  • Follow course of facial artery

  • Drain directly or indirectly into internal jugular vein

  • Communicates with pterygoid venous plexus and cavernous sinus via superior ophthalmic vein

• Superficial temporal vein

  • Drains scalp and forehead

  • Unites with maxillary vein to form retromandibular vein

• Retromandibular vein

  • Descends through parotid gland

  • Sends branch to facial vein

  • Joins posterior auricular vein to form external jugular vein

Lymphatic Drainage of The Face

• Superficial lymphatics travel with veins

• Deep lymphatics travel with arteries

• Lateral face → parotid lymph nodes

• Upper lip and lateral lower lip → submandibular lymph nodes

• Chin and central part of lower lip → submental lymph nodes

• All lymphatic drainage eventually reaches deep cervical lymph nodes

Innervation of The Face

• Cutaneous branches of cervical nerves

  • From cervical plexus

  • Innervate posterior neck, ear, and area over parotid gland

• Trigeminal nerve (CN V)

  • Sensory for the face

  • Motor for muscles of mastication

  • Branches of ophthalmic nerve (CN V ₁ )

    • Nasociliary nerve → external nasal branch to skin on dorsum of nose

    • Nasociliary nerve → infratrochlear nerve to skin and lower eyelid

    • Frontal nerve → supratrochlear nerve to skin in mid forehead

    • Frontal nerve → supraorbital nerve to skin of forehead and upper eyelid

  • Branches of maxillary nerve (CN V ₂ )

    • Infraorbital nerve to skin of cheek, lower lid, lateral nose and mouth, upper lip

    • Zygomaticotemporal nerve to skin over anterior temple

    • Zygomaticofacial nerve to skin over zygomatic arch

  • Branches of mandibular nerve (CN V ₃ )

    • Auriculotemporal nerve—to skin of external ear, posterior temple, anterior to ear

    • Buccal nerve—to skin of cheek

    • Mental nerve—to skin of chin and lower lip

• Facial nerve

  • Sole motor supply to muscles of facial expression

  • Has five main branches

    • Temporal

    • Zygomatic

    • Buccal

    • Mandibular

    • Cervical

  • Names refer to areas they supply

Other Muscles Associated With The Face: Muscles of Mastication

The muscles of mastication include four pairs of muscles (left and right sides) that attach to the mandible, are embryological derivatives of the 1st pharyngeal arch, are all innervated by the mandibular division of the trigeminal nerve (CN V ₃ ), and are important in biting and chewing food.

• All attach to mandible

• Responsible for biting and chewing (movements at temporomandibular joint [TMJ])

• All are innervated by branches of mandibular nerve (CN V ₃ )

• All are supplied by branches of maxillary artery

• Group of four muscles

  • Temporalis

    • Large, fan-shaped

    • Covers most of the side of the head

    • Inserts on coronoid process of mandible

  • Masseter

    • Deep to parotid gland and crossed by parotid duct

    • Inserts on entire lateral surface of ramus of mandible except for condylar process

  • Lateral pterygoid

    • Deep to temporal muscle

    • Runs horizontally backward from infratemporal fossa and lateral pterygoid plate to insert on mandible

    • Covered with dense pterygoid plexus of veins

  • Medial pterygoid

    • Covered by inferior fibers of lateral pterygoid

    • Runs from inner surface of lateral pterygoid plate inferiorly to inner surface of ramus of mandible

Triangles of The Neck

• Sternocleidomastoid (SCM) muscle on each side of neck divides each side into two triangles

  • Anterior

  • Posterior

• Facilitates description of anatomy of the neck

• Posterior triangle

  • Boundaries

    • Posterior—anterior border of trapezius muscle

    • Anterior—posterior border of SCM

    • Inferior—medial third clavicle

    • Roof—superficial layer of deep cervical fascia

    • Floor—muscles

  • Muscles of floor

    • Splenius capitis

    • Levator scapulae

    • Middle scalene

    • Posterior scalene

  • Vessels in triangle

    • External jugular vein

    • Subclavian vein

    • Third part of subclavian artery

    • Transverse cervical artery (from thyrocervical trunk)

    • Suprascapular artery (from thyrocervical trunk)

    • Occipital artery (from external carotid)

  • Nerves in triangle

    • Accessory nerve (CN XI)

    • Ventral rami (roots) of brachial plexus

    • Cutaneous branches of cervical plexus

    • Suprascapular nerve

    • Phrenic nerve

  • Subdivided by inferior belly of omohyoid muscle

    • Occipital triangle

      • Larger triangle superiorly

      • Crossed by accessory nerve

    • Supraclavicular triangle

      • •Smaller inferior triangle

      • •Contains external jugular vein, suprascapular artery, and subclavian artery

• Anterior cervical triangle

  • Boundaries

    • Lateral—anterior border of SCM

    • Anterior—anterior midline of neck

    • Superior—inferior mandible

  • Divided into four smaller triangles for descriptive purposes

  • Submandibular triangle (1)

    • Between inferior mandible and anterior and posterior bellies of digastric muscle

    • Contains submandibular gland

    • Submandibular duct

    • Submandibular lymph nodes

  • Submental triangle (2)

    • Between body of hyoid bone and right and left anterior bellies of digastric muscles

    • Apex is mandibular symphysis

    • Contains submental lymph nodes

  • Carotid triangle (3)

    • Bounded by anterior belly of omohyoid muscle, posterior belly of digastric muscle, and anterior border of SCM

    • Contains carotid sheath, with common carotid artery, internal jugular vein, and vagus nerve

    • Bifurcation of common carotid to internal and external carotid arteries

    • Carotid sinus

    • Carotid body

  • Muscular triangle (4)

    • Bounded by anterior border of SCM, superior belly of omohyoid muscle, midline of neck

    • Contains infrahyoid muscles, thyroid, parathyroid

Fascial Layers of The Neck

• Superficial fascia

  • Between dermis and investing layer of deep fascia

  • Contains

    • Cutaneous nerves and vessels

    • Lymphatics

    • Fat

    • Platysma muscle anteriorly

• Deep fascia

  • Consists of three layers

    • Investing

    • Pretracheal

    • Prevertebral

  • Also includes carotid sheath: condensation of deep fascia around carotid vessels

  • Investing layer of deep fascia

    • Surrounds entire neck, beneath superficial fascia

    • Inferior attachments

      • Manubrium

      • Superior border clavicle

      • Acromion

      • Spine scapula

    • Superior attachments

      • Superior nuchal line

      • Zygomatic arches

      • Angle mandible

      • Mastoid process

• Spinous processes of cervical vertebrae

  • • Splits to enclose SCM and trapezius muscles

    • Encloses parotid and submandibular glands

    • Forms roof of anterior and posterior triangles of neck

  • Pretracheal fascia

    • Only in anterior neck, from hyoid bone to fibrous pericardium

    • Invests infrahyoid muscles

    • Visceral layer invests

      • Trachea

      • Thyroid and parathyroid glands

      • Esophagus

    • Attaches inferiorly to adventitia of great vessels

    • Attaches superiorly

      • Thyroid cartilage

      • Buccopharyngeal fascia of pharynx

    • Blends laterally with carotid sheath

  • Prevertebral fascia

    • Sheath for C1–T3 vertebrae and associated muscles

      • Longus colli and capitis

      • Anterior, middle, and posterior scalenes

      • Deep cervical muscles

    • Described as having two laminae: anterior and posterior

    • Superior attachment of both laminae to base of skull

    • Inferior attachment

      • Anterior lamina to anterior longitudinal ligament and posterior esophagus anteriorly

      • Posterior lamina to fascia over thoracic vertebral column posteriorly

    • Extends laterally as axillary sheath around axillary artery and brachial plexus

Carotid Sheath

• Condensation of fascia around great vessels of the neck

• Extends from base of skull to root of neck

• United medially with prevertebral fascia

• Contains

  • Common carotid artery

  • Internal carotid artery

  • Internal jugular vein

  • Vagus nerve (CN X)

  • Deep cervical lymph nodes

  • Sympathetic fibers

• Communicates inferiorly with mediastinum

Facial Spaces

• Retropharyngeal space

  • Largest and most significant space in neck

  • Potential space between prevertebral layer of deep fascia and buccopharyngeal fascia

  • From base of skull to posterior mediastinum

  • Permits movement of pharynx, larynx, trachea, and esophagus during swallowing

  • Infection originating in pharyngeal area can spread to retropharyngeal space and inferiorly into superior mediastinum

• Pretracheal space

  • Space between investing fascia and pretracheal fascia

  • Limited by attachments of fascia to thyroid cartilages superiorly

  • Can spread into thorax anterior to pericardium

• Space between laminae of prevertebral fascia

  • Critical space

  • Extends from base of skull and through thorax

External Nose

The nose is composed primarily of cartilages except at the “bridge” of the nose where the nasal bone resides. Anteriorly, the air enters or leaves the nose via the nares, which open into the nasal vestibule, whereas posteriorly the nasal cavity communicates with the nasopharynx via paired apertures called the choanae.

• Composed of bone and hyaline cartilage

• Bones

  • Paired nasal bones

  • Frontal processes of maxillary bone

  • Nasal part of frontal bone

• Cartilages

  • Paired lateral cartilages

  • Paired alar cartilages

  • Septal cartilage

• Associated muscles dilate and flatten nares (nostrils)

  • Nasalis

  • Compressor nares

  • Dilator nares

• Innervation via ophthalmic and maxillary divisions of trigeminal nerve (CN V ₁ and CN V ₂ )

• Blood supply

  • Ophthalmic artery

  • Facial artery

• Venous drainage

  • Facial veins → internal jugular veins

  • Ophthalmic veins → cavernous sinus

Nasal Septum

The nasal cavity is separated from the cranial cavity by portions of the frontal, ethmoid, and sphenoid bones and from the oral cavity inferiorly by the hard palate. A nasal septum, usually deviated slightly to one side or the other, divides the nasal cavity into right and left chambers. The anterior third of the nasal septum is cartilaginous and the posterior two-thirds is bony.

• Divides nasal cavity into two chambers

• Composed of

  • Bone

    • Vomer

    • Perpendicular plate of ethmoid bone

  • Septal cartilage

    • Septal cartilage articulated with edges of bony septum

Nasal Cavity

The lateral wall of the nasal cavity is characterized by three shell-like conchae, or turbinates, that protrude into the cavity; along with their covering of nasal respiratory epithelium, they greatly increase the surface area for warming, humidifying, and filtering the air. At the most superior aspect of the nasal cavity resides the olfactory part, with its olfactory epithelium and specialized sensory cells for the detection of smells.

• Each cavity is narrow above and wider below, separated from each other by nasal septum

• Extend from nares to choanae

  • Naris = external opening of nose

  • Choana = opening into pharynx

• Vestibule

  • First part of cavity

  • Lined with skin with hairs

  • Bounded laterally by alar cartilages

  • Limen nasi

    • Crescentic line

    • Marks upper limit of vestibule

• Nasal mucosa

  • Lines nasal cavities except for vestibule

  • Bound to periosteum and perichondrium of surrounding bones and cartilages

  • Extends into all chambers, cavities, and sinuses communicating with nasal cavities

  • Upper one-third is olfactory areas (mucosa)

  • Lower two-thirds is respiratory areas (mucosa)

• Boundaries (walls) of nasal cavity

• Nasal conchae

  • Three horizontal projections from lateral wall

  • Superior, middle, and inferior nasal conchae

  • Divide nasal cavity into four areas

    • Superior meatus

    • Middle meatus

    • Inferior meatus

    • Sphenoethmoidal recess

• Superior meatus

  • Between superior and middle conchae

  • Has openings from posterior ethmoidal sinuses

• Middle meatus

  • Wider and longer than superior

  • Depressed area—atrium—at anterior end

  • Ethmoidal infundibulum at anterior end

    • Leads to frontonasal duct

    • Duct leads to frontal sinus

  • Ethmoidal bulla (swelling)

    • Rounded projection at inferior root of middle meatus

    • Represents bulge of ethmoidal air cells (sinuses)

    • Groove called semilunar hiatus immediately beneath leads to infundibulum

  • Contains openings for frontal, maxillary, and anterior ethmoidal sinuses

    • Frontal sinus opening at anterior end of semilunar hiatus/infundibulum

    • Maxillary sinus opening at posterior end of semilunar hiatus

    • Variable openings for ethmoidal air cells

• Inferior meatus

  • Below inferior concha

  • Receives nasolacrimal duct and opens into anterior end

• Sphenoethmoidal recess

  • Posterior and superior to superior concha

  • Receives opening of sphenoidal sinus

• Innervation

  • Posterior region of nasal cavity

    • Nasal septum: maxillary nerve (CN V ₂ ) → nasopalatine nerve to nasal septum

    • Lateral wall: lateral branches of lateral palatine nerve

  • Anterior and superior regions of nasal cavity: anterior and posterior ethmoidal nerves, branches of nasociliary nerve from ophthalmic nerve (CN V ₁ )

  • Olfactory epithelium innervated by olfactory nerve (CN I)

• Arterial supply

  • Sphenopalatine artery (branch of maxillary artery)

  • Anterior and posterior ethmoidal arteries

  • Greater palatine artery

  • Superior labial and lateral nasal branches of facial artery

• Venous drainage

  • Plexus of veins beneath nasal mucosa drains to

    • Sphenopalatine veins

    • Facial veins

    • Ophthalmic veins

• Lymphatic drainage

  • Posterior nasal cavity to retropharyngeal nodes

  • Anterior nasal cavity to submandibular nodes

Paranasal Sinuses

There are four pairs of paranasal sinuses, which are open chambers within several of the bones surrounding the nose and orbits. They are lined with respiratory epithelium, assist in warming and humidifying the inspired air, and drain their mucus secretions into the nasal cavities. Blowing the nose clears the nasal cavity and sinuses of excess secretions.

• Extensions of nasal cavity into maxillary, ethmoid, frontal, and sphenoid bones

• Lined with respiratory epithelium

• Present at birth and increase in size until adulthood

• Air filled

• Frontal sinuses (2)

  • Between inner and outer tables of frontal bone

  • Can be detected around age 7

• Maxillary sinuses (2)

  • Largest of paranasal sinuses

  • Occupy most of body of maxillary bone

• Ethmoidal sinuses

  • Several in number

  • Not well developed until after age 2

• Sphenoidal sinuses

  • Derive from extensions of ethmoidal sinuses into sphenoid bone around 2 years of age

  • Numbers different on either side

  • Bony septum between two sides

  • Only a thin plate of bone separates them from critical structures in the anterior and middle cranial fossae: optic nerves, pituitary gland, internal carotid arteries, cavernous sinuses.

Muscles of Pharynx

• Wall of pharynx is unique

  • Composed of outer circular and inner longitudinal layers of muscles

  • External circular layer consists of three constrictor muscles: pharyngeal constrictors

  • Inner longitudinal layer consists of three paired muscles

• Pharyngeal constrictors = three muscles

  • Superior, middle, and inferior pharyngeal constrictor muscles form a muscular sleeve

  • Have strong internal facial lining: pharyngobasilar fascia

  • Contract involuntarily in sequence = peristalsis

  • All supplied by pharyngeal plexus of nerves

• Inner longitudinal layer = three muscles

  • Elevate larynx

  • Shorten pharynx

  • Act during swallowing and speaking

  • Stylopharyngeus

  • Palatopharyngeus

  • Salpingopharyngeus

• Gaps between constrictors

  • Areas where structures can enter and leave pharynx

  • Between superior constructor and skull

    • Levator veli palatini

    • Auditory tube

    • Ascending palatine artery

  • Between superior and middle pharyngeal constrictors

    • Stylopharyngeus muscle

    • Glossopharyngeal nerve

    • Stylohyoid ligament

  • Between middle and inferior pharyngeal constrictors

    • Internal laryngeal nerve

    • Superior laryngeal artery and vein

  • Below inferior pharyngeal constrictor

    • Recurrent laryngeal nerve

    • Inferior laryngeal artery

Arterial Supply of Pharynx

• Tonsillar artery (from facial artery) to tonsil

• Branches from

  • Ascending pharyngeal

  • Lingual

  • Ascending and descending palatine

Venous Drainage of Pharynx

• External palatine vein → pharyngeal plexus

• Pharyngeal venous plexus → internal jugular vein

Lymphatic Drainage of Pharynx

• General drainage to deep cervical nodes

• From tonsillar tissue to nodes near angle of mandible and tonsillar (jugulodigastric) node

Innervation of Pharynx

• From pharyngeal plexus (motor and almost all sensory)

• Motor

  • From pharyngeal plexus via vagus nerve from cranial root of accessory nerve (CN XI)

    • To all muscles of pharynx except stylopharyngeus (CN V ₂ )

  • Branches from external and recurrent branches of vagus

    • To inferior pharyngeal constrictor muscle

• Sensory

  • Mainly from glossopharyngeal nerve (CN IX) via plexus

  • Also

    • Maxillary nerve (CN V ₂ ) to anterior and superior nasopharynx

    • Tonsillar nerves from branches of glossopharyngeal and vagus (CN X)

Swallowing (Deglutition)

• Voluntary

  • When food is in the mouth, breathing occurs through the nasopharynx.

  • Food is chewed (masticated) and mixed with saliva to produce a bolus.

  • Bolus of food is compressed against hard palate

  • Palatoglossal folds relax

  • Muscles of tongue and soft palate push bolus into oropharynx

  • Cycle lasts 1 to 2 seconds

• Involuntary

  • Reflexive; mediated via glossopharyngeal nerve

  • Nasopharynx is closed off by tension and elevation of soft palate

    • Prevents reflux of food/fluids into the nose

    • Mediated by tensor veli palatine and levator veli palatine muscles

  • Suprahyoid muscles and longitudinal pharyngeal muscles contract

    • Elevate larynx

    • Close epiglottis

    • Propel bolus

• Involuntary swallowing and passage of food

  • Food is propelled through pharynx by peristalsis (sequential contraction of all three constrictors)

  • On reaching distal end of pharynx, high pressure causes relaxation of terminal part of inferior pharyngeal constrictor muscle (also called the cricopharyngeus muscle), which serves as superior esophageal sphincter

  • Food enters esophagus

  • As bolus passes, pressure drops and sphincter closes

  • Larynx and epiglottis return to normal positions

Laryngeal Skeleton

• Comprises three paired and three nonpaired cartilages

• Epiglottic cartilage (epiglottis)

  • Leaf-shaped elastic cartilage

  • Posterior to root of tongue and hyoid bone, anterior to laryngeal inlet

  • Broad superior end is free

  • Inferior end attached in midline to angle of thyroid laminae by thyroepiglottic ligament

  • Quadrangular membranes run between lateral sides of epiglottic cartilage and arytenoid cartilages on either side.

  • Upper free margin of quadrangular membrane + covering mucosa = aryepiglottic fold

  • During swallowing overlies laryngeal inlet

• Thyroid cartilage

  • Composed of two flat laminae

  • Lower two-thirds of laminae fuse in midline to form laryngeal prominence (Adam’s apple)

  • Upper one-third of laminae diverge to form superior thyroid notch

  • Posterior superior border of each plate projects superiorly as superior horns

  • Posterior inferior border of each plate projects inferiorly as inferior horns

  • Superior horns and superior borders of laminae attach to hyoid bone by thyrohyoid membrane

• Cricoid cartilage

  • Signet ring–shaped, signet (lamina) facing posteriorly

  • Strong, thick, complete circle of cartilage

  • Attached to inferior thyroid by median cricothyroid ligament

  • Attached to 1st tracheal ring by cricotracheal ligament

• Arytenoid cartilages (paired)

  • Pyramid shaped with three sides

  • Articulate with lateral superior parts of cricoid lamina

  • Have three processes

    • Apex at superior end

    • Vocal process projects anteriorly

    • Muscular process projects laterally

  • Apex: corniculate cartilage sits atop; attaches to aryepiglottic fold

  • Vocal process: posterior attachment for vocal ligament

  • Muscular process: attachment for posterior and lateral cricoarytenoid muscles

• Corniculate and cuneiform cartilages

  • Nodules in posterior aryepiglottic folds

  • Cuneiforms do not attach to other cartilages

  • Corniculates attach to apices of arytenoids

Internal Anatomy of The Larynx

• Laryngeal cavity

  • From laryngeal inlet to tracheal cavity

  • Can be divided into three parts

    • Vestibule—above vestibular folds

    • Ventricle—sinus between vestibular folds above and vocal folds below

    • Infraglottic cavity—from below vocal folds to inferior border of cricoid cartilage

• Vocal folds

  • Paired, project into laryngeal cavity on either side

  • Consist of

    • Vocal ligament—medial free edge of lateral cricothyroid ligament (conus elasticus)

    • Vocalis muscle—medial fibers of thyroarytenoid muscle

    • Overlying mucosa

  • Source of sound

  • Produce audible vibrations when free edges of folds closely approximate each other

  • Are sphincter of larynx when folds are tightly approximated

• Rima glottidis

  • Space between vocal folds

  • Varies in size with activity

    • During normal breathing: narrow wedge

    • During forced respiration: wide apart

    • During phonation: slitlike

• Vestibular folds (false vocal cords)

  • Folds of mucous membrane over vestibular ligaments superior to vocal folds

  • Extend between thyroid and arytenoid cartilages

  • Protective in function

• Ventricles of larynx: lateral outpocketings between vocal and vestibular folds on either side

Muscles of The Larynx

• Extrinsic muscles

  • Attached to hyoid bone and thus move thyroid

  • Infrahyoid muscles: lower larynx and hyoid bone

    • Sternohyoid

    • Omohyoid

    • Sternothyroid

    • Thyrohyoid

  • Suprahyoid muscles: fix hyoid or elevate hyoid bone and larynx

    • Stylohyoid

    • Digastric

    • Mylohyoid

  • Stylopharyngeus—elevates hyoid bone and larynx

• Intrinsic muscles

  • Alter length and tension of vocal cords

  • Alter rima glottides

  • Adductors

    • Lateral cricoarytenoid muscles

    • Transverse arytenoids

  • Abductors: posterior cricoarytenoid muscles

  • Sphincters

    • Transverse arytenoid muscles

    • Oblique arytenoid muscles

    • Aryepiglottic muscles

  • Tensors: cricothyroid muscles

  • Relaxers

    • Thyroarytenoid muscles

    • Vocalis muscles

  • All except cricothyroid supplied by recurrent laryngeal nerve

Joints of the Larynx and Movements at the Joints

• Cricothyroid joints

  • Thyroid cartilage glides and rotates here

  • Changes length of vocal folds

• Cricoarytenoid joints: movement of arytenoid cartilage on lamina of cricoid

  • Slide toward and away from each other

  • Rotate

  • Tilt forward and back

Arterial Supply To Larynx

• Superior laryngeal artery

  • Through gap in thyrohyoid membrane

  • Supplies internal larynx

  • Accompanied by superior laryngeal nerve

• Inferior laryngeal artery

  • Supplies inferior internal larynx

  • Accompanied by recurrent laryngeal nerve

Venous Drainage of Larynx

• Superior laryngeal vein to internal jugular vein

• Inferior laryngeal vein to inferior thyroid vein or thyroid venous plexus (left brachiocephalic)

Lymphatic Drainage of Larynx

• Above folds: to deep cervical nodes

• Below folds: to paratracheal nodes to deep cervical nodes

Innervation of Larynx

• Sensory

  • Above vocal folds: internal laryngeal nerve (branch of superior laryngeal nerve)

  • Below vocal folds: inferior laryngeal nerve (branch of recurrent laryngeal nerve)

• Motor

  • Recurrent laryngeal nerve to all intrinsic muscles except cricothyroid

  • External laryngeal nerve to cricothyroid

Innervation of Thyroid Gland

• Parasympathetic: external branch of superior laryngeal nerve (branch of vagus nerve)

• Sympathetic

  • From superior, middle, and inferior cervical ganglia

  • Vasomotor, not secretomotor

Arterial Supply of Thyroid Gland

• Superior thyroid artery

  • Branch of external carotid artery

  • Divides into anterior and posterior branches

  • Anterior branch

    • Supplies anterior thyroid

    • Anastomoses with opposite anterior branch

  • Posterior branch

    • Supplies posterior thyroid

    • Anastomoses with inferior thyroid artery

• Inferior thyroid artery

  • Branch of thyrocervical trunk from subclavian artery

  • Supplies inferior pole of thyroid

• Thyroid ima artery

  • Branch of aorta

  • Occurs in 10% of all people

  • Unpaired, on left of midline

  • Supplies isthmus

Venous Drainage of Thyroid Gland

• Three pairs of thyroid veins

• Superior thyroid vein

  • Drains superior region of thyroid

  • Tributary of internal jugular vein

• Middle thyroid veins

  • Drain middle of gland

  • Tributaries of internal jugular vein

    • Inferior thyroid veins

    • Drain inferior region of thyroid

    • Tributaries of brachiocephalic vein

Lymphatic Drainage of Thyroid Gland

• Lymphatic vessels run with arteries.

• Drain to capsular network of lymphatics

• To prelaryngeal, pretracheal, or paratracheal nodes

• To deep cervical nodes

Innervation of Thyroid Gland

Sympathetic from cervical sympathetic ganglia

Eyelids

• Two moveable folds of skin that cover the eye anteriorly

• Protect the eye from injury and excessive light and keep corneas moist

• Eyelids separated by an elliptical opening, the palpebral fissure

• Covered by thin skin externally and palpebral conjunctiva internally

  • Palpebral conjunctiva continuous with bulbar conjunctiva of eyeball

  • Lines of reflection of palpebral conjunctiva onto eyeball are deep recesses: superior and inferior conjunctival fornices

• Strengthened by plates of dense connective tissue: tarsal plates

  • Tarsal glands embedded in plates

  • Produce a lipid secretion

    • Lubricates edge of eyelids to prevent them from sticking together

    • Barrier for lacrimal fluid

      • Medial palpebral ligaments

        • Attach tarsal plates to medial margin of orbit

        • Orbicularis oculi attaches to this ligament

• Lateral palpebral ligaments attach tarsal plates to lateral margin of orbit

• Orbital septum from tarsal plates to margins of orbit, continuous with periosteum of bony orbit

• Skin around the eyes devoid of hair except for eyelashes

  • Are arranged in double or triple rows on the free edges of eyelids

  • Ciliary glands associated with eyelashes: sebaceous glands

• Muscles of the eyelids

  • Orbicularis oculi

  • Levator palpebrae superioris

Lacrimal Apparatus

• Functions

  • Secretes tears

  • Prevents desiccation of cornea and conjunctiva

  • Lubricates eye and eyelid

  • Antibacterial

• Consists of

  • Lacrimal glands

  • Lacrimal ducts

  • Lacrimal canaliculi

  • Nasolacrimal ducts

• Lacrimal gland

  • Lies in fossa for lacrimal gland in superolateral orbit

  • Consists of two parts

    • Larger orbital

    • Smaller palpebral

  • Divided by expansion of tendon of levator palpebrae superioris

  • Twelve lacrimal ducts open from deep surface of gland into superior conjunctival fornix.

  • Secrete lacrimal fluid upon stimulation by parasympathetic secretomotor fibers from CN VII

• Lacrimal canaliculi

  • Drain tears from lacrimal lake at medial angle of eye

  • Drain to lacrimal sac

• Lacrimal sac drains to nasal cavity via nasolacrimal duct

Eyeball

• Surrounded by fascial sheath (Tenon’s capsule)

  • From optic nerve to junction of cornea and sclera

  • Forms socket

  • Pierced by tendons of extraocular muscles

• Three layers

  • Outer fibrous = sclera and cornea

  • Middle vascular = choroid, ciliary body, and iris

  • Inner pigmented and nervous = retina

• Fibrous coat

  • Sclera = opaque part of fibrous coat

    • Covers posterior five-sixths of eyeball

    • Visible through conjunctiva as the white of the eye

    • Pierced posteriorly by optic nerve

  • Cornea

    • Transparent part of fibrous coat

    • Transmits light

• Middle vascular layer

  • Choroid

    • Outer pigmented layer

    • Inner vascular layer

    • Lies between sclera and retina

    • Lines most of sclera

    • Terminates anteriorly as ciliary body

  • Ciliary body

    • Connects choroid with iris

    • Contains smooth muscle that alters shape of lens

    • Folds on internal surface (ciliary processes) produce aqueous humor and attach to suspensory ligament of lens

  • Iris

  • Pigmented diaphragm with central aperture: the pupil

  • Contains smooth muscle that alters size of pupil to regulate amount of light entering eye

  • Radial fibers of dilator pupillae muscle open pupil

  • Circular fibers of sphincter pupillae muscle close pupil

• Inner (retinal) layer

  • Consists of three parts

    • Optic part (1)

      • Receives light

      • Composed of two layers: inner neural layer and outer pigmented layer

      • Inner neural layer contains photosensitive cells: rods for black and white and cones for color

    • Ciliary and iridial parts (2 and 3)

      • Continuation of pigmented layer plus a layer of supportive cells

      • Cover ciliary body and posterior surface of retina

  • Fundus

    • Is posterior part of eye

    • Contains optic disc = depressed area where optic nerve leaves and central artery of retina enters

    • Optic disc contains no photoreceptors = “blind spot”

  • Macula lutea

    • Small oval area of retina

    • Contains concentration of photoreceptive cones for sharpness of vision

    • Depression in center = fovea centralis, area of most acute vision

  • Neural retina ends anteriorly at ora serrata

    • Serrated border posterior to ciliary body

    • Termination of the light-receptive part of retina

  • Vasculature of retina

    • Central artery of retina from ophthalmic artery

    • Retinal veins drain to central vein of retina

    • Rods and cones receive nutrients directly from vessels in choroid

• Chambers of the eye

  • Anterior chamber

    • Between cornea anteriorly and iris/pupil posteriorly

    • Contains aqueous humor

  • Posterior chamber

    • Between iris’s pupil anteriorly and lens and ciliary body posteriorly

    • Contains aqueous humor

  • Vitreous chamber

    • Between lens and ciliary body anteriorly and retina posteriorly

    • Contains vitreous body and vitreous humor

Muscles of The Orbit

• Intrinsic (intraocular) muscles

  • Ciliary muscle

  • Constrictor pupillae of iris

  • Dilator pupillae of iris

• Extrinsic (extraocular) muscles

  • Six muscles

  • Four arise from common tendinous ring surrounding optic canal and part of superior orbital fissure

    • Lateral and medial rectus (2)

      • Lie in same horizontal plane

      • Rotate eyeball laterally and medially, respectively

    • Superior and inferior rectus (2)

      • Lie in same vertical plane

      • Pull eyeball superiorly and inferiorly, respectively

  • Inferior oblique

• Works with superior rectus

• Pulls eyeball superiorly and laterally

  • Superior oblique

    • Works with inferior rectus

    • Pulls eyeball inferiorly and laterally

  • Sheathed by reflection of fascial sheath around eyeball (Tenon’s capsule)

    • Medial and lateral check ligaments

      • Triangular expansions of sheath of medial and lateral rectus muscles

      • Attached to lacrimal and zygomatic bones

      • Limit abduction and adduction

    • Suspensory ligament

      • Union of ligaments with fascia of inferior rectus and inferior oblique muscles

      • Forms sling that supports eyeball

Vasculature of The Orbit

• Arteries

  • Ophthalmic artery (main supply)

    • Enters orbit through optic canal

    • Lateral to optic nerve

  • Infraorbital artery from maxillary

  • Branches of ophthalmic artery

    • Supraorbital

    • Supratrochlear

    • Lacrimal

    • Dorsal nasal

    • Ethmoidal—anterior and posterior

    • Central artery of retina

      • Branch of ophthalmic

      • Runs within dural sheath of optic nerve

      • Emerges at optic disc and branches over retina

    • Posterior ciliary arteries

      • Branches of ophthalmic

      • Six short to choroid

      • Two long to ciliary plexus

    • Anterior ciliary

      • From muscular branches of ophthalmic

      • Anastomoses with posterior ciliary arteries

• Venous drainage

  • Superior ophthalmic vein

    • Formed by union of supraorbital and angular veins of face

    • Receives blood from anterior and posterior ethmoidal, lacrimal, and muscular branches; central vein of retina; and upper two vorticose veins of retina

    • Drains to cavernous sinus

  • Inferior ophthalmic vein

    • Forms in floor of orbit

    • Receives blood from lower extraocular muscles and lower two vorticose veins of retina

    • Drains to cavernous sinus

    • Communicates with pterygoid plexus of veins through inferior orbital fissure

Innervation of The Orbit

• Optic nerve

  • Formed from axons of retinal ganglion cells

  • Exits through optic canal

  • Fibers from medial half of each retina cross at optic chiasm and join uncrossed fibers from lateral half of contralateral retina to form optic tract.

• Oculomotor nerve (CN III)

  • Runs in lateral wall of cavernous sinus

  • Enters orbit through superior orbital fissure

  • Contains parasympathetic fibers to sphincter pupillae and ciliary muscles

  • Supplies

    • Levator palpebrae superioris

    • Superior rectus muscle

    • Medial rectus muscle

    • Inferior rectus muscle

    • Inferior oblique muscle

• Trochlear nerve (CN IV)

  • Runs in lateral wall of cavernous sinus

  • Passes through superior orbital fissure

  • Supplies superior oblique muscle

• Abducens nerve (CN VI)

  • Courses through cavernous sinus

  • Enters orbit via superior orbital fissure

  • Innervates lateral rectus muscle

• Branches of the ophthalmic nerve (CN V ₁ )

  • Lacrimal nerve to lacrimal gland

  • Frontal nerve

    • Divides into supraorbital and supratrochlear

    • Supplies upper eyelid, forehead, and scalp

  • Nasociliary nerve and its branches

    • Infratrochlear to eyelids, conjunctiva, and nose

    • Anterior and posterior ethmoidal nerves to sphenoidal and ethmoidal sinuses and anterior cranial fossa

    • Long ciliary nerves to dilator pupillae muscle

• Short ciliary nerves

  • Branches from ciliary ganglion

  • Carry parasympathetic and sympathetic fibers

  • Innervate ciliary body and iris

External Ear

• Auricle, or pinna

  • Skin-covered elastic cartilage

  • Collects sound and directs it to external auditory meatus

  • Features

    • Deep depression: concha

    • Lobule: earlobe

• External auditory (acoustic) meatus

  • From deepest part of concha to tympanic membrane

  • Through tympanic part of temporal bone

  • Lateral one-third is cartilaginous and lined with normal skin

  • Medial two-thirds are bony and lined with thin skin continuous onto tympanic membrane

  • Ceruminous glands (wax producing) and sebaceous glands are found in superficial fascia of lateral one-third

• Tympanic membrane

  • Forms labyrinthine wall of external ear, lateral wall of middle ear

  • Oval and semitransparent

  • Covered with thin skin externally and mucous membrane internally

  • Has shallow, conelike depression at its center (seen otoscopically) with umbo at center of depression

  • Lateral process (handle) of malleus embedded in tympanic membrane and tip extends to umbo on internal surface

  • Pars tensa

    • Part of membrane below handle of malleus

    • Contains circular and radial fibers

    • Part of membrane above handle of malleus

    • Contains no fibers

  • Moves in response to air vibrations

  • Transmits vibrations to auditory ossicles of middle ear via handle of malleus

Middle Ear

• Contained within petrous part of temporal bone

• Includes tympanic cavity and epitympanic recess

• Is connected anteriorly with nasopharynx by auditory tube (auditory canal)

• Contains

  • Auditory ossicles (bones of middle ear)

    • Malleus (hammer)

    • Incus (anvil)

    • Stapes (stirrups)

  • Stapedius and tensor tympani muscles

  • Chorda tympani nerve

  • Tympanic plexus (nerves)

• Walls of tympanic cavity

  • Roof

    • Thin bone—tegmen tympani

    • Separates tympanic cavity from middle cranial fossa

  • Floor

    • Bony

    • Separates tympanic cavity from superior bulb of internal jugular vein

  • Labyrinthine wall

    • Separates tympanic cavity from inner ear

    • Features

      • Promontory : round projection overlying basal turn of cochlea

      • Vestibular (oval) window into which footplate of stapes fits—covered by secondary tympanic membrane

      • Fenestra cochlea or cochlea (round) window

  • Anterior wall

• Separates tympanic cavity from carotid canal

• Superiorly has opening of auditory tube and canal for tensor tympani muscle

  • • Mastoid wall

• Superiorly, aditus (opening) to mastoid antrum, connecting to mastoid air cells

• Between mastoid wall and aditus, prominence of canal of facial nerve

• Pyramidal eminence

  • • • Tiny cone-shaped prominence

      • Contains proximal attachment of stapedius muscle

  • Lateral wall

    • Tympanic membrane

    • Lateral wall of epitympanic recess

    • Handle of malleus

• Ossicles

  • Chain of bones across tympanic cavity

  • Extend from tympanic membrane to vestibular (oval) window on labyrinthine wall

    • Handle of malleus attaches to tympanic membrane, and head articulates with incus

    • Incus articulates with head of malleus and end of long limb with stapes

    • Head of stapes articulates with long limb of incus and base (footplate) fits into vestibular (oval) window on labyrinthine wall

    • Increase force but decrease amplitude of vibrations from tympanic membrane

• Auditory tube

  • Formerly called eustachian tube

  • Communication between middle ear and nasopharynx

  • Allows equalization of atmospheric pressure in middle ear

  • Actively opened by coordinated contractions of levator and tensor veli palatini muscles

• Muscles

  • Function to dampen movement of auditory ossicle

  • Tensor tympani

  • Stapedius

• Nerves

  • Chorda tympani

    • Branch of facial nerve (CN VII)

    • Emerges from facial canal through canaliculus in mastoid wall of middle cavity

    • Carries taste fibers to anterior two-thirds of tongue

    • Crosses medial surface of neck of malleus

    • Exits anteriorly via canaliculus to petrotympanic fissure

  • Tympanic plexus

    • On promontory of labyrinthine wall

    • Contributions from tympanic branch of glossopharyngeal nerve (CN IX)

    • Twigs from internal carotid plexus

    • Twig from facial nerve

    • Supplies

      • Mucous membrane of tympanic cavity

      • Mastoid antrum

      • Mastoid air cells

      • Auditory tube

Inner Ear

• Concerned with reception of sound and maintenance of balance

• Buried within petrous portion of temporal bone

• Membranous labyrinth suspended within bony labyrinth

• Bony labyrinth

  • Occupies lateral region of petrous ridge of temporal bone

  • Space filled with perilymph

  • Surrounded by bony capsule harder than petrous bone

  • Cochlea

    • Concerned with hearing

    • Contains membranous cochlear duct

    • Consists of

      • Spiral canal

      • Bony core, the modiolus

    • Canal spirals around modiolus

    • Basal turn forms promontory of labyrinthine wall of tympanic cavity

  • At basal turn, bony labyrinth communicates with subarachnoid space above jugular foramen via cochlear aqueduct

  • Vestibule

    • Small oval chamber

    • Contains membranous utricle and saccule

    • Vestibular (oval) window is on lateral wall

    • Continuous with

      • Cochlea anteriorly

      • Semicircular canals posteriorly

    • Communicates with posterior cranial fossa via aqueduct of vestibule

      • Extends to posterior surface of petrous ridge of temporal bone

      • Contains membranous endolymphatic duct

  • Semicircular canals

    • Anterior, posterior, and lateral

    • Set at right angles to each other in three planes

    • Lie posterosuperior to vestibule

    • Each opens into vestibule

    • Swelling at one end of each canal: ampulla

    • Contain membranous semicircular ducts

• Membranous labyrinth

  • Collection of ducts and sacs

  • Suspended within bony labyrinth

  • Filled with endolymph

  • Vestibular labyrinth

    • Utricle

      • Has specialized area of sensory epithelium: macula

      • Hair cells in macula innervated by vestibular division of vestibulocochlear nerve (CN VIII)

      • Hairs respond to tilting of head and linear acceleration and deceleration

    • Saccule

      • Communicates with utricle

      • Continuous with cochlear duct

      • Contains macula, identical in structure and function to that of utricle

    • Semicircular ducts

      • Within semicircular canals

      • Each has ampulla at one end

      • Ampullary crest in each ampulla senses movement of endolymph in plane of duct

      • Hair cells in crest innervated by vestibular division of vestibulocochlear nerve (CN VIII)

      • Detect rotational (tilting) movements of head

  • Cochlear labyrinth

  • Spiral ligament suspends cochlear duct from external wall of spiral canal

  • Cochlear duct

    • Triangular in shape

    • Filled with endolymph

    • Spans spiral canal, dividing it into two channels, each filled with perilymph

    • Two channels: scala tympani and scala vestibule, meet at apex of cochlea (helicotrema)

    • Third, middle channel = cochlear duct

    • Roof of duct = vestibular membrane

    • Floor of duct = basilar membrane

      • Spiral organ of Corti

  • Found on basilar membrane

  • Covered by gelatinous tectorial membrane

  • Contains hair cells—tips embedded in tectorial membrane

  • Hair cells innervated by cochlear division of vestibulocochlear nerve (CN VIII)

• Propagation of sound

  • Initiated by sound waves

    • Transmitted as vibrations by ossicles

    • Stapes vibrates in vestibular (oval) window

    • Creates waves of pressure in perilymph of vestibule

    • Waves ascend in spiral canal in scala vestibule

    • Transfer to scala tympani at helicotrema

    • Pass down scala tympani to cochlea (round) window

    • Dissipated via secondary tympanic membrane in cochlea (round) window to air of middle ear cavity

  • Reception of sound

    • Deformation of cochlear duct by pressure waves in perilymph

    • Stimulates hair cells of spiral organ embedded in tectorial membrane

    • Base of spiral organ receives high-frequency sounds and apex receives low-frequency sounds.

• Internal auditory (acoustic) meatus

  • 1-cm-long tiny canal in petrous ridge of temporal bone

  • Opening in posteromedial aspect of ridge in posterior cranial fossa

  • Transmits facial nerve (CN VII) and vestibulocochlear nerve (CN VIII)

Weber Test

• A tuning fork is struck and placed on the patient’s forehead.

• The patient is asked to report in which ear the sound is heard louder.

• This test cannot confirm normal hearing, because hearing defects affecting both ears will equally produce an apparently normal test result.

• A Rinne test should be done at the same time.

Rinne Test

• The Rinne test compares the perception of sounds as transmitted by air or by sound conduction through the mastoid.

• This is achieved by placing a vibrating tuning fork (512 Hz) initially on the mastoid and then next to the ear and asking which sound is loudest.

• A patient with normal hearing with a positive Rinne test on both sides would hear the sound equally in both ears or may not even hear it at all if the room is noisy enough to mask the subtle sound of the tuning fork.

• A patient with a unilateral (one-sided) conductive hearing loss would hear the tuning fork loudest in the affected ear (conduction through bone is more effective that the normal route through the outer and middle ear).

Brainstem

• Parts of brain hidden by cerebral hemispheres and cerebellum

• Contains third and fourth ventricles and cerebral aqueduct

• Composed of

  • Midbrain

  • Pons

  • Medulla oblongata

• Contains masses of gray matter, many of which are sensory and motor nuclei of cranial nerves

Arterial Supply To The Brain

• Internal carotid artery

  • Arises in neck

  • Enters cranial cavity via carotid canals

  • Terminates as

    • Anterior cerebral artery—connected to opposite artery by anterior communicating artery

    • Middle cerebral artery

  • Joined to posterior cerebral artery near termination by posterior communicating artery

• Vertebral arteries

  • Ascend through transverse foramina of C1–C6 cervical vertebrae

  • Perforate dura

  • Enter posterior cranial fossa via foramen magnum

  • Unite at posterior pons to form basilar artery

  • Ascends on clivus

  • Divides into two posterior cerebral arteries

    • Unite with internal carotid artery via posterior communicating arteries

• Circle of Willis

  • Cerebral arterial circle

  • Composed of

    • Anterior communicating artery

    • Anterior cerebral arteries

    • Internal carotid arteries

    • Posterior communicating arteries

    • Posterior cerebral arteries

• Areas supplied by anterior cerebral artery

• Medial and superior brain

• Frontal pole

• Areas supplied by middle cerebral artery

  • Lateral brain

  • Temporal pole

• Posterior cerebral artery

  • Inferior brain

  • Occipital pole

Meninges

• Surround and protect the brain

• Support for arteries, veins, and venous sinuses

• Enclose subarachnoid space

• Enclose cerebrospinal fluid (CSF)

• Similar in name, structure, and arrangement to those around spinal cord

• Dura mater

  • Thick fibrous layer

  • Consists of two layers (unlike the dura mater around spinal cord)

  • Outer periosteal layer = periosteum on inner surface of calvaria

  • Inner meningeal layer

    • Tightly bound to periosteal layer

    • Continuous with dura mater of spinal cord

• Arachnoid mater

  • Thin, nonvascular membrane

  • Loosely attached to dura mater

  • Separated from pia mater by subarachnoid space

• Pia mater

  • Adherent to brain and spinal cord

  • Highly vascular connective tissue

• Subarachnoid space

  • Real space between arachnoid mater and pia mater

  • Contains CSF from ventricular system—cushions brain

• Subarachnoid cisterns

  • Areas where pia mater and arachnoid mater are widely separated

  • Collect large pools of CSF

  • Occur mainly at base of brain

Venous Drainage of The Brain

• Cerebral veins

  • Superior and lateral surfaces of brain to superior sagittal sinus

  • On posterior and inferior aspects of brain drain into straight, transverse, and superior petrosal sinuses

  • Thin-walled and valveless

• Superior cerebellar veins to straight, transverse, and superior petrosal sinuses

• From dural venous sinuses to internal jugular vein

Dural Infoldings

• Created by internal meningeal layer of dura mater

• Form septa that separate regions of brain from other regions

• Falx cerebri

  • Largest of infoldings

  • Lies in longitudinal fissure

• Tentorium cerebelli

  • Second largest infolding

  • Crescent-shaped fold separating cerebral hemispheres from cerebellum

  • Attaches

    • Anteriorly to clinoid processes of sphenoid bone

    • Laterally to petrous part of temporal bone

    • Posteriorly and laterally to internal occipital and parietal bones

      • Falx cerebri, which suspends tentorium

  • Tentorial notch

    • Gap in anterior border

    • Allows for passage of brainstem

• Diaphragma sellae

  • Circular sheet of dura mater

  • Suspended between anterior and posterior clinoid processes

  • Contains gap for passage of pituitary stalk and accompanying veins

Dural Venous Sinuses

• Endothelium-lined channels between periosteal and meningeal layers of dura mater

• Thick-walled and valveless

• Formed where dura mater attaches

• Confluence of sinuses: where superior sagittal, straight, occipital, and transverse sinuses meet at internal occipital protuberance

• Superior sagittal sinus

  • From crista galli to confluence of sinuses

  • Communicates via slitlike openings with lateral venous lacunae

• Inferior sagittal sinus: from crista galli to straight sinus

• Straight sinus: formed by union of inferior sagittal sinus and great cerebral vein (of Galen)

• Transverse sinus

  • Drains confluence of sinuses

  • Runs along posterolateral attachment of tentorium cerebelli

  • Becomes sigmoid sinus

• Sigmoid sinus

  • Traverses jugular foramen

  • Becomes internal jugular vein

• Occipital sinus: at attached border of falx cerebelli

• Cavernous sinus

  • On either side of sella turcica

  • Composed of a network of thin, valveless veins

  • Sinuses communicate with each other via intercavernous sinuses

  • Receives blood from

    • Superior and inferior ophthalmic veins

    • Superficial middle cerebral vein

    • Sphenoparietal sinus

  • Contains

    • Internal carotid artery

    • Oculomotor nerve (CN III)

    • Trochlear nerve (CN IV)

    • V ₁ division of trigeminal nerve (CN V)

    • Abducens nerve (CN VI)

    • Sympathetic plexus around artery

• Superior petrosal sinus: from posterior ends of cavernous sinuses to transverse sinuses

• Inferior petrosal sinus: from posterior ends of cavernous sinuses to internal jugular vein

• Emissary veins connect dural sinuses with veins outside cranium

Cerebrospinal Fluid

• Maintains balance of extracellular fluid in the brain

• Similar in content to blood

  • Less protein

  • Different ion concentrations

• Formed by choroid plexuses in four ventricles of brain

• Are plexuses of capillaries that project into lateral, third, and fourth ventricles

• Circulates through ventricular system

  • From lateral ventricles to interventricular foramina to third ventricle

  • From third ventricle through cerebral aqueduct to fourth ventricle

  • From fourth ventricle through paired lateral apertures and a single midline aperture in roof into subarachnoid space

• Absorbed through arachnoid granulations into venous blood in dural venous sinuses

  • Arachnoid granulations are tufts of arachnoid villi protruding into dural venous sinuses

  • Subarachnoid space with CSF extends into core of tufts

  • Approximately 400 mL/day of CSF → venous circulation

Vasculature of Dura Mater

• Primarily provides blood to calvaria

• Middle meningeal artery

• Branch of axillary artery

• Enters through foramen spinosum

• Anterior and posterior branches

• Meningeal branches of

  • Ophthalmic arteries

  • Occipital arteries

  • Vertebral arteries

• Venous drainage: meningeal veins

  • Accompany meningeal arteries

  • Occur in pairs

  • Frequently torn in skull fractures

  • Middle meningeal veins drain to pterygoid venous plexus

Sensory Innervation of The Dura Mater

• Dura mater of cranial fossae innervated by meningeal branches of cranial and cervical nerves

• Anterior cranial fossa

  • Anterior meningeal branches of ethmoidal nerves from ophthalmic nerves (CN V ₁ )

  • Meningeal branches of maxillary nerves (CN V ₂ )

  • Meningeal branches of mandibular nerves (CN V ₃ )

• Middle cranial fossa

  • Meningeal branches of maxillary nerves (CN V ₂ )

  • Meningeal branches of mandibular nerves (CN V ₃ )

• Posterior cranial fossa

  • Tentorial branch from ophthalmic nerve (CN V ₁ )

  • Meningeal branches directly from C2 and C3 spinal nerves or carried by CN X (vagus) or CN XII (hypoglossal)

Cervical Plexus

• Formed from anterior rami of C1–C4 spinal nerves

• Consists of a series of loops and branches from the loops

• Lies deep to SCM muscle and anteromedial to levator scapulae and middle scalene muscles

• Cutaneous branches of cervical plexus

  • Emerge from posterior border of SCM

  • Nerves from loop formed between anterior rami of C2 and C3

    • Lesser occipital (C2) to skin of neck and scalp posterior to auricle

    • Great auricular (C2 and C3) to skin over parotid gland, mastoid process, auricle, and between angle of mandible and mastoid process

    • Transverse cervical nerve (C2 and C3) to skin over anterior cervical triangle

  • Supraclavicular nerves

    • Arise from C3–C4 loop

    • Emerge from under SCM

    • Supply skin over clavicle, superior thoracic wall, and shoulder

• Motor branches

  • Considered deep branches

  • Innervate prevertebral muscles

    • Sternocleidomastoid (C2 and C3)

    • Trapezius (C3 and C4)

    • Levator scapulae (C3 and C4)

  • Motor fibers from C1 travel with hypoglossal nerve

    • Some C1 fibers leave hypoglossal nerve and innervate

      • Thyrohyoid muscle

      • Geniohyoid muscle

  • Rest leave hypoglossal as its descending branch

  • Motor fibers from C1 and C2 directly innervate thyrohyoid (an infrahyoid strap muscle)

  • Motor fibers from C2 and C3 form descending cervical nerve

  • Ansa cervicalis

    • Loop formed by descending branch from hypoglossal nerve (superior root) (C1) and descending cervical nerve (inferior root) (C2, C3)

    • Branches from ansa innervate remaining infrahyoid strap muscles

      • Omohyoid

      • Sternohyoid

      • Sternothyroid

  • Motor fibers from C3, C4, and C5 contribute to roots of phrenic nerve

• Phrenic nerve

  • Formed by branches of anterior rami of C3, C4, and C5 spinal nerves

  • Contains a mix of fibers

    • Sole motor supply to respiratory diaphragm

    • Sensory fibers from central part of respiratory diaphragm (sensory fibers from periphery provided by intercostal nerves)

    • Sympathetic nerve fibers from cervical sympathetic ganglia to smooth muscle of blood vessel walls

Venous Drainage of The Brain

• Dural venous sinuses

  • Drain venous blood from superficial and deep veins of the brain

  • Sinuses drain to internal jugular vein via jugular foramen

• Veins on superior and lateral surfaces of brain drain to superior sagittal sinus

• Basal veins run laterally and dorsally around cerebral peduncle to end in great vein of Galen, which drains to straight sinus

• Veins on posterior and inferior surfaces of brain, superior cerebellar veins, and transverse sinuses drain to several sinuses

  • Straight

  • Transverse

  • Superior petrosal

Arterial Supply To The Face, Scalp, And Neck