Articulatory IV - Tongue and CN XII

which muscle is referred to as the ‘muscular hydrostat”?

the tongue

how can the hydrostat be described?

• a “fluid”-filled, incompressible epithelial bag

• the muscles serve as the “fluid”

what makes the tongue a constant volume system?

any reduction in volume in one part is associated with an equivalent increase in volume within another part of the tongue

what is the oral tongue?

the anterior 2/3 of tongue that is within the oral cavity

what is the tongue dorsum?

the superior surface of the tongue?

what is the pharyngeal tongue?

posterior 1/3, within oropharynx

what is the oropharynx?

oral cavity to pharynx

what is the pharyngeal tongue also known as?

the tongue base

how is the oral tongue described?

thick, rough epithelial covering

what are papillae?

microscopic projections on the tongue

what are the 4 types of papillae on the oral tongue?

• fungiform

• filiform

• foliate (simple)

• vallate

what is the longitudinal sulcus?

the midline depression on the oral tongue

what are the fungiform papillae?

mushroom shaped papillae

where are the fungiform papillae?

• scattered over tongue dorsum and sides of tongue

• predominant on tip of tongue

which papillae contain the taste buds?

fungiform papillae, foliate, and vallate

what innervates the fungiform papillae?

chorda tympani of CN VII

what is the most numerous papillae?

the filiform papillae

what are the filiform papillae?

very small, sharp pointed projections on tongue dorsum

what are te filiform papillae used for?

used to grip food

how are the filiform papillae arranged?

in parallel rows

which papillae is variable in humans?

the foliate papillae

which papillae are known as the “simple” papillae

the foliate papillae

what are the features oof foliate papillae?

• mucosal folds present on the lateral aspects of the tongue, anterior to the palatoglossal arch

• covered by epithelium containing taste receptors

which papillae are the largest?

vallate papillae

how are the vallate papillae arranged?

7-12 arranged in posteriorly pointing arrowhead

how are the vallate papillae shaped?

cylinder-shape surrounded by a ‘moat’ with taste buds on the cylinder and in the wall of the moat

what are the vallate papillae innervated by?

CN IX (glossopharyngeal)

how is the pharyngeal tongue described?

smooth, thin, nodular covering due to presence of lingual tonsils in underlying submucosa

what is the terminal sulcus?

groove just posterior to circumvallate papillae

what is the foramen cecum?

small pit within the terminal sulcus, marks the embryological origin of the thyroid gland

what is the valleculae?

part of pharyngeal tongue formed by median and lateral glossoepiglottic folds at junction with epiglottis

what is the ventral and inferolateral tongue made up of?

thin, smooth mucous membrane

what are the features of the ventral and inferolateral tongue?

• lingual frenulum

• lingual veins

• sublingual papilla

• sublingual folds

• sublingual salivary glands

what does lingual mean?

relating to, near, or facing the tongue

what is the lingual frenulum?

fold of mucosa that attaches underside of tongue to floor of mouth

where are the lingual veins?

seen through thin mucosa on either side of lingual frenulum

what are the sublingual papilla?

opening of duct of submandibular salivary gland

how do we taste?

the tongue transmits information about 5 basic taste sensations

what are the 5 taste sensations?

salty, sweet, sour, bitter, umami

what is the old theory of taste?

• once thought that the taste sensations could be mapped onto the dorsum of the tongue

• i.e. the tip was for sweet and salty

what is the current hypothesis for taste?

each papilla contains receptors for each taste sensation

how is taste supplied to the tongue?

• anterior 2/3 of tongue is supplied by chorda tympani of VII, posterior 1/3 of tongue is supplied by CN IX

• taste from soft palate and lingual surface of epiglottis is also supplied by CN IX

• taste from laryngeal surface of epiglottis and larynx is supplied by CN X

where are the primary neurons for taste?

the gustatory nucleus of the NTS

what is the NTS?

nucleus tractus solitarius

where are the secondary neurons for taste?

the thalamus

where are the tertiary neurons for taste?

the gustatory cortex in the insula

what is the pathway for taste in the brain?

NTS (gustatory nucleus) → thalamus → insula (gustatory cortex)

what does complex taste also involve?

the participation of smell and CN I

how do the tongue muscles work?

all muscles are bilateral, with the 2 sides partially separated by the median septum

what is the median septum?

a fibrous partition that runs from tongue tip to hyoid bone (doesn’t reach surface of tongue)

what do the intrinsic tongue muscles do?

shape the tongue

what do extrinsic tongue muscles do?

position and shape the tongue

what are the intrinsic tongue muscles?

• superior longitudinal

• inferior longitudinal

• transverse

• vertical

what is the superior longitudinal?

intrinsic tongue muscle that forms broad band beneath the dorsal epithelium

where does the superior longitudinal muscle originate and insert?

o: fibrous tissue near the epiglottis & hyoid, and the median septum

i: lateral regions of tongue and apex

what is the action of the superior longitudinal muscle?

shortens tongue;,acts on tongue tip – elevating, retracting, turning tip unilaterally

what innervates all intrinsic tongue muscles?

CN XII

what is the transverse muscle?

instrinsic tongue muscle arranged at right-angle to the longitudinal fibres

where does the transverse muscle originate and insert?

o: the median septum

i: fibrous tissues at lateral margins

what is the action of the transverse muscle?

narrows and elongates tongue

what is the vertical muscle?

intrinsic toingue muscle perpendicular to transverse and longitudinal

where does the vertical muscle originate and insert?

o: inferior and lateral margins of tongue

i: dorsal membranous cover

what is the action of the vertical muscle?

flattens and widens tongue

what are the extrinsic muscles of the tongue?

• genioglossus

• hyoglossus

• styloglossus

• palatoglossus

what do all of the extrinsic tongue msucles end with?

‘glossus’

what is genioglossus?

large extrinsic tongue muscle making up bulk of tongue

what is the origin and insertion of genioglossus?

o: mental spine (genial tubercle) of mandible

i: mucous membrane of tongue dorsum from base to tip, inferior fibres insert on hyoid bone

what is the action of the genioglossus?

protrudes tongue, and depresses central portion

what is the hyoglossus?

extrinsic tongue muscle, quadrilateral sheet on side of tongue, lateral to genioglossus

where does the hyoglossus originate and insert?

o: greater cornu and body of hyoid bone

i: mucous membrane on lateral margins of tongue

what is the action of the hyoglossus?

pulls down sides of tongue

what is the styloglossus?

slender extrinsic tongue muscle, runs inferiorly/anteriorly, passing below superior constrictor of pharynx

where does the styloglossus originate and insert?

o: styloid process of temporal bone, stylomandibular ligament

i: posterolateral portion of tongue, interdigitates with hyoglossus

what is the action of the styloglossus?

lifts sides of tongue, pulls tongue backward

what is the palatoglossus?

extrinsic tongue muscle that forms anterior faucial pillars, marks junction between oral cavity and pharynx

what is the origin and insertion of the palatoglossus?

o: inferior surface of palatal aponeurosis (palatine bone)

i: posterolateral portion of tongue

what is the action of the palatoglossus?

elevates and retracts tongue base; depresses soft palate (narrows the oropharyngeal isthmus)

what is the only (extrinsic) tongue muscle not innervated by CN XII?

the palatoglossus

what innervates the palatoglossus?

pharyngeal branch of CN X via pharyngeal plexus

what is CN XII?

hypoglossal nerve with one fibre type

what is the fibre tyep of the hypoglossal nerve?

somatic motor

what is somatic motor?

voluntary movement

why aren’t CN XII fibres branchial?

they don’t develop from a branchial arch

what is the only tongue muscle with contralateral innervation?

the genioglossus

where is the hypoglossal nerve in the brainstem?

cell bodies of LMNs are contained in the hypoglossal nucleus in medulla

how does the hypoglossal nerve leave the skull?

via the hypoglossal foramen in the posterior cranial fossa (near foramen magnum)

where does the hypoglossal nerve go outside the skull?

divides to supply hyoglossus, styloglossus, genioglossus (and geniohyoid), and the intrinsic tongue muscle

how do we test the integrity of CN XII and why?

with the action of genioglossus, because it is contralateral

what will happen if the innervation of genioglossus is impaired?

tongue will deviate laterally on protrusion

what does clinical exam of CN XII test?

• symmetry of tongue at rest (inside oral cavity)

• symmetry on protrusion; also range of motion and strength on protrusion

• range of motion on lateralization (corner of mouth, inside cheek); alternating motion and strength

• range of motion on elevation (to palate); range of motion around lips

• range of motion on retraction (pull back along palate)

• accuracy and speed of diadochokinesis (puh, tuh, kuh)

what does the oral tongue arise from?

mounds of tissue at the fusion line between the mandibular processes of the 1st arch

what are the tuberculum impar and lateral lingual swellings?

mounds of tissue that oral tongue arise from in development

what does the palatopharyngeal tongue arise from?

arises from a swelling, hypobranchial eminence, at the midline between the 3rd and 4th arches

where do the muscles of the tongue arise from?

occipital somites

what are the occipital somites?

blocks of tissue in the occipital region

how is thge epiglottis formed?

• anterior half of the hypobranchial eminence migrates forward (tongue

base)

• transverse depression appears between anterior and posterior halves of hypobranchial eminence

• depression becomes deeper with backward migration of the posterior half = glossoepiglottic

fossa; then divided into the valleculae by the median glossoepiglottic fold