3. The viscerosensory and visceromotor innervation of the head and neck. The fibers of the connective tissue, the extracellular matrix. The development of the viscerocranium.

3. The viscerosensory and visceromotor innervation of the head and neck. The fibers of the connective tissue, the extracellular matrix. The development of the viscerocranium.

Flash Cards:

CN IX, XI - Glossopharyngeal, Accessory n

CN X Vagus n & branches

Autonomic n. and PNS ggl

SNS ganglia in Head & Neck

PNS ggl and SNS/PNS relations to them

Anatomy:The viscerosensory and visceromotor innervation of the head and neck.

This topic consists of mainly CN IX, X, and Autonomic innervation of Head & Neck. Yes, some of these cranial nerves also have SM/SS function, but they are very important inVS/VM function.  Other CN also add innervation of VS/VM in the body.  If you want to know all the branches of CNs, please refer to the cards above.

Viscerosensory of Head & Neck:

Viscerosensory innervation of the head and neck have to do with the special sensation function of the cranial nerves. There is a main sensory function we have to look at: taste

Taste:

CN VII – Facial n

covered mostly in last topic, but know that Chorda Tympani n provides VS innervation to ant 2/3 of tongue

• has motor and sensory roots,
• Pathway: IAM –> petrous part of temporal bone (through auditory canal) —> exit skull via stylomastoid foramen

Pathway of Chorda Tympani = in desc facial canal –> tympanic membrane –> b/w malleus & incus of middle ear –> thru Petrotympanic fissure –> joins lingual n —> submandibular ggl –> 3 places

• VM = submandibular, sublingual, lingual glands (discussed in more detail later)
• VS = ant 2/3 tongue, soft palate
• cxn w/ geniculate ggl & otic ggl

CN IX – Glossopharyngeal n

• exit = Jugular foramen,
• Pathway: from jugular foramen –> follow stylopharyngeus &  passes b/w sup/mid constrictor m. of pharynx –> oropharynx & tongue.
• Location = Find this n. in parapharyngeal space, behind int carotid, CN XII, CNX, on post surface of stylopharyngeus m
• innervates structures from 3rd branchial arch
• receives VS sensation  from parotid gland, carotid body, carotid sinus, pharynx, middle ear
  

Branches of CN IX that provide VS/VM:

• Tympanic n
  • forms tympanic plexus around wall of middle ear (w. SNS fibers from int carotid plexus, br from genu ggl of CN VII)
  • SM = tympanic cavity, mastoid antrum, mastoid air cells, auditory tubes, ext ear
  • VM = provides pre-ggl fibers to otic ggl
• Lingual branches
  • provides VS innervation to post 1/3 of tongue, & vallate papillae for taste sensation, as well as SS to same area

CN X – Vagus n

• exit = jugular foramen,
• Pathway: from foramen –> makes connections w. CN IX, CN XI, SNS sup cervical ggl –> goes thru carotid sheath –> thorax
• innervates structures from 4th & 6th branchial arches
• receives VS  from base of tongue, pharynx, larynx, trachea, bronchi, heart, esophagus, stomach, & intestine
  

Branches of CN X that provide VS/VM in head & neck:

• Mainly VM = will discuss soon

Visceromotor of Head & Neck:

Mainly comes from autonomic innervation. In the head & neck, visceromotor basically means the autonomic innervation of glands, as well as some muscle of the eye.  The four main glands we have to consider are: lacrimal, parotid, submandibular, sublingual, and as well we have to consider the glands of the nasal and oral mucosa & skin. The innervations are primarily run with PNS and SNS ganglia.

If you want to see the information sorted by ganglia, or by PNS v SNS, please refer to flash cards above.

NOTE: SNS fibers only GO THRU ggl (is not part of them, do not synaspe in PNS ggl) – their ggl are the cervical ggl, they are merely hitchhiking with the PNS nerves, and then they run w/ arteries to targets

Cranial Nerves VM innervation:

• CN III = PNS to sphincter pupillae m & ciliary m –> constrict pupil, help lens of eye
• CN VII = PNS to submandibular  & sublingual glands, lacrimal glands, glands of nose & palate
• CN IX = PNS to parotid gland
• CN X = PNS to smooth m of trachea,  bronchi, digestive tract,  & cardiac m of heart

Lacrimal gland

* Pterygopalatine ggl = in pterygopalatine fossa, where held in place by branches of V2, just ant to opening of pterygoid canal , and below V2

PNS pathway:

• Greater petrosal n comes from CN VII @ geniculate ggl, and exits out of petrous part of temporal bone
  • Gtr petrosal n has taste fibers that can go to the palate from ggl
• joins deep petrosal n. which carries SNS fibers @ foramen lacerum
• these two together become n of pterygoid canal –> pterygopalatine fossa
• PNS fibers synapse in pterygopalatine ggl
  
• post ggl fibers from ggl run to lacrimal gland via zygomatic br of V2 & lacrimal n of V1
• also supplies glands of nasal mucosa (via post nasal n) and palate ( Gr palatine n = hard palate, Lsr Palatine n = soft palate)
  

SNS pathway:

• SNS post ggl fibers are from the superior cervical ggl
• these fibers run with deep petrosal n.
  • deep petrosal n is from plexus on int. carotid ggl
    

Submandibular & Sublingual gland & glands of Oral Mucosa

*Submandibular ggl = lies on surface of Hyoglossus m inf to submandibular duct

PNS pathway:

• Chorda Tympani, comes from CN VII just above stylomastoid foramen
• the nerve cross medial to malleus and passes thru petrotympanic fissure
• joins lingual n of V3 in Infratemporal fossa
• PNS fibers synapse in submandibular ggl
• post ggl fibers from ggl run w/ arteries to supply Submandibular gland, Sublingual gland, & glands of Oral mucosa,

SNS pathway:

• SNS post ggl fibers are from superior cervical ggl
• these fibers run thru, BUT DO NOT SYNAPSE  in submandibular ggl,
• then run with PNS post ggl fibers

Parotid Gland

* Otic ggl = located b/w tensor veli palatini & V3, inf to foramen ovale

PNS pathway:

• Tympanic n arises from CN IX and emerges from jugular foramen
• n enters the middle ear via the tympanic canaliculus in petrous part of  temporal bone
• tympanic n forms the tympanic plexus — and lesser petrosal n emerges from this plexus
• lesser petrosal leaves skull via foramen ovale
  
• PNS fibers from it synapse in otic ganglion
• post ggl fibers from ggl RUN W/ auriculotemporal n (from V3) to supply parotid gland
  

SNS pathway:

• SNS post ggl fibers are from superior  cervical ggl via a plexus around middle meningeal a
• post ggl fibers run w/ PNS post ggl fibers on auriculotemporal n
• help supply a/v of parotid gland

Orbital region

*Ciliary ggl = b/w optic n and lateral rectus m.

PNS pathway:

• CN III and its divisions run to ciliary ggl
• post ggl fibers from ciliary ggl pass to ciliary m & sphincter pupillae m
• constrict pupil of eye, help with lens of eye

SNS pathway:

• post ggl fibers from sup cervical ggl  form a plexus around  int carotid a
• and then run with PNS post ggl fibers  to dilater pupillae and tarsal m.
• dilate pupil of eye & a/v of eye

Animation: PNS innervation of Head ===Check it out!!

Histology: The fibers of the connective tissue, the extracellular matrix.

Extracellular Matrix:

Ground Substance:

• transparent, shapeless, colorless extracellular matrix
• high water content
• supports and surrounds CT and its cells and fibers
• loads of Glycosaminoglycans,  glycoproteins, proteoglycans

Matrix glycoproteins:

• most molecule binding cells
• cells bind via integrin receptors: has Arg-Lys-Asp-R group
• regulate function of cells: proliferation, migration, etc
• interconnect cells & collegen fibers
  • ex/ Laminin – bound collagen IV in basal lamina (integrin)
  • hemidesmosomes in epithelial cells
• Ex/ fibronectin, tenasin, osteonectin, etc

Glycoaminoglycans (GAGs):

• polysaccharides, disaccharides, like hexosamine + hexuronic acid
• strong polyanions
  • bind lots of H2O
• Ex/ Hyaluronic acid, heparine, chondrolitine-sulfate, keratin-sulfate, dermatin-sulfate, heparin-sulfate

Proteoglycans (PGs):

• fibrular core proteins w/ 1 GAG side chains
• heparin found intracellularly
• Physiochemical properties = decided by GAG side chains
• Ex/ Syndecan: heparin-sulfacte side chains, membrane-intergrated, receptor function

Fibers of CT:

• Collagen Fibers
  
  • 3 tropocollagen helical units –> collagen fibrils
  • amino acids = Hydroxylated Proline (OH-Pro), Hydroxylated Lysine (OH-Lys), about 40% glycine
    
    • provide mechanical resistance due to OH-aa (Hydroxylate amino acids)
  • amount of glycosylation variable
  • look stratified in microscope
  • broken down by collagenases
  • >20 types, only 3 types  can form fibers themselves w/o aid of others = I,II,III
    • I = skin, bone, ligaments, tendons
    • II = cartilage
    • III = reticular
    • From Avi Sayag Biochem notes: One = Bone, 2 = CarTWOlage, 3 = ReThreecular
  • acidophillic, stain pink with eosin
  • stain well w/ AZAN (blue), H&E (red), Van Geison (spermatic cord)
• Reticular Fibers
  • glycosylated collagen fibers = III
  • made by reticular cells
    
  • low mech resistance
  • filled w/ CARBS
  • forms supporting meshwork of organs
  • stains well w/ Ag impregnation (black), PAS + (magenta, like in sublingual glands), AZAN (blue)
• Elastic fibers
  • made of tropoelastin & fibrillin
    
  • high amount of Gly, Val, Ala, & Pro
  • has hydroxylated-Pro, but not OH-Lys
  • have short amino acid side chains
  • can be extended due to presence of special cross bond –> higher mech resistance
  • broken down by elastases
  • stains well w/ Resorcin-Fuchsin, Orcein (brown)

Embryology: The development of the viscerocranium.

skeletal system develops from paraaxial, lateral plate mesoderm, & neural crest

Paraxial mesoderm forms somites,t hat split into somitomeres, dermatomes, & myotomes

@ 4th week -sclerotomes –> become mesenchyme (embryonic CT)

Mesenchyme can form many things, like osteoblasts = bone forming cells

Neural crest cells in head region can also become mesenschyme

2 types of bone formation:

• (Intra)membranous ossification – mesenchyme of dermis is converted right to bone
• Endochondral ossification – mesenchyme –> hyaline cartilage –> ossified by osteoblasts

Viscerocranium

• Viscerocranium = bones of the face, like nasal, lacrimal, etc
• formed mainly from the first 2 pharyngeal arches
• 1st arch =
  • dorsal portion that becomes maxillary process —> becomes maxilla, zygomatic bone, part of temporal bone
  • ventral portion that becomes mandibular process –> Meckel’s cartilage
• Mesenchyme around Meckel’s cartilage ossifies via membranous ossification *see previous topic for how this works* —> becomes mandible
• Meckel’s cartilage completely disappears except for sphenomandibular ligament
• Dorsal tip of mandibular process = becomes incus, malleus, stapes = bones of inner ear
• The rest of facial bones formed from neural crest cells
• Bones and paranasal sinuses continue to grow through puberty.