2. The somatosensory and somatomotor innervation of the head and neck. The cells of the connective tissue. The development of the neurocranium.

2. The somatosensory and somatomotor innervation of the head and neck. The cells of the connective tissue. The development of the neurocranium.

  Flash cards:

Trigeminal n. SS of Face and some SM

CN VII Facial N - SM for face

Cervical Plexus - SS/SM of Neck

 

Anatomy: The somatosensory and somatomotor innervation of the head and neck.

 This topic covers basically CN V (SS /SMof face), CN VII (SM of face), Cervical plexus (SS/SM of neck), and parts of CN IX, X, XI (flash cards of these on next topic, #2)

SS of Head & Neck

CN V = Trigeminal n

Remember = Feel the face w/ FIVE = 5th cranial nerve

• major sensory n for face, and is motor n for muscles of mastication, and some other m.

has 3 major divisions:

Ophthalmic n: V1

• exits skull via supraorbital fissure, w/ CN III, IV, VI, and ophthalmic v
• innervates structures that develop from the frontonasal prominences
• Nasociliary n
  • gives Ant ethmoid n –> gives ext nasal br = skin @ tip of nose
  • Post ethmoid n
  • Infratrochlear n = skin @ root of nose
• Frontal n
  • Supratrochlear n – skin @ medial forehead, exit via supratrochlear foramen
  • Supraorbital n – skin @ lat forehead, exit via supraorbital foramen
• Lacrimal n – lacrimal gland, lat upper eyelid

Maxillary n: V2

• exits skull via foramen rotundum, into pterygopalatine fossa
• innervates structures that develop from maxillary prominences
• below level of eyes & above upper lip
• Infraorbital n
  • thru infraorbital foramen, via inferior orbital fissure
  • lat side of nose, lower eyelid, upper lip
  • branches of it –> mucosa of maxillary sinus, upper inscisors, canines, and premolar teeth,  upper gingiva, hard palate
  • Ant, Mid, Post, Sup alveolar n forms maxillary dental plexus
• Zygomaticotemporal n
  • from foramen of same name
  • skin over ant temporal region
• Zygomaticofacial n
  • foramen of same name
  • skin over zygomatic region
  • carries post-ggl fibers from pterygopalatine ggl, via Gr palatine, Lsr palatine, & Nasopalatine n, to Lacrimal n

Mandibular n: V3

• exits skull via foramen ovale
• aff/eff branch of jaw jerk reflex
• innervates structures that develop from mandibular prominences
• level of lower lip and below
• Inf alveolar n
  • goes thru mandibular canal and emerges from mental foramen as mental n
  • supply lower teeth, chin, lower lip
• Auriculotemporal n
  • crosses root of zygomatic process –> temporal region deep to sup temporal a, encircles around middle meningeal a
  • supply ext acoustic meatus, tympanic mem, auricle
• Buccal n
  • only sensory br of motor div. of V3
  • deep to ramus of mandible –> runs ant and thru buccinator
  • supplies mucus membrane lining cheek, post part of buccal surface of gum
• Lingual n
  • SS to ant 2/3 of tongue
• SM = MOTOR branches –> m. of mastication, ant digastric, mylohyoid m, tensor veli palatini, tensor tympani

CN VII Facial n = SM of face

• has motor and sensory roots,
• SM = all muscles of facial expression, including platysma, auricularis m, post digastric m, stylohyoid m, stapedius m
• supplies structures developing from 2nd pharyngeal arch
• VS = taste to ant 2/3 of tongue – via Chorda Tympani (discussed in next topic)
• SS = w/ auricular branches from IX, X –> fibers to external ear, tympanic mem
• Pathway: IAM –> petrous part of temporal bone (through auditory canal) —> exit skull via stylomastoid foramen
• Once exits, gives off Post auricular n = m of auricle, occipitalis m, EAM, w/ branches from CN IX, X
• runs ant and through parotid gland, where it gives its 5 terminal branches
• NOTE DOES NOT INNERVATE PAROTID GLAND, merely runs through it

Terminal branches:

• Temporal – m of forehead, orbicularis oculi
• Zygomatic – m. over zygomatic bone, orbital and infraorbital m
• Buccal – Buccinator m, m of upper lip
• Mandibular (marginal)- m. of chin, lower lip
• Cervical – platysma, *w/transverse cervical n. of Cervical plexus

Cervical Plexus:

• from primary ventral rami of C1-C4, emerge next to ant scalene m
• ant branches = SM, post branches = SS to anterolat neck, sup part thorax

SS of Neck = cutaneous branches of Cervical plexus – see note card at start of this post

1. Lesser Occipital (C2,3) –  scalp behind ear
2. Greater Auricular (C2,3) – scalp around auricle, and parotid region
3. Transverse Cervical (C2,3) – skin of ant cervical triangle
4. Supraclavicular  n (C3,4) – ant, mid, post br to skin of clavicle and shoulder
5. NOTE = NOT A BRANCH OF CERVICAL PLEXUS, but does SS of head/neck – Greater Occipital n (dorsal rami of Cervical spinal n) – post part of scalp

SM of Neck =  2 major motor branches of cervical plexus, + many side motor branches

• Branches not from Cervical Plexus
  • ventral rami of cervical nodes – SM to rohomoids, serratus ant, prevertebral m
• Ansa Cervicalis
  • union of sup root (C1-2) + inf root (C2-3)
  • superior and w/in carotid sheath in ant cervical triangle
  • supplies infrahyoid m, except thyrohyoid (C1 via CNXII)
• Phrenic n – not technically part of neck, but part of plexus
  • arises C4, but rec branches from C3-4
  • has SM, SS, SNS n fibers
  • SM to lat diaphragm, SS to central tendon
  • desc on ant surface of ant scalene m under SCM
  • passes b/w subclavian a/v  –> thorax, joins pericardiophrenic br of int thoracic a
  • SS = mediastinal pleura
• SM br off plexus= longus capitis, longus cervicis, Levator scapulae, scalene m
• Acc phrenic n –  occasional br of plexus, from C5 and joins phrenic n below 1st rib

 SS/SM innervation from other CN:

• CN IX =
  •  SS to post 1/3 of tongue, palatine tonsil & soft palate, tympanic cavity, mastoid antrum, auditory tubes, ext ear
  • SM to stylopharyngeus m,
• CN IX, X, XI = give fibers to the common pharyngeal plexus
  • SM = m. of pharynx, larynx, palate except tensor veli palatini (V3)
• CN XI
  • SM = SCM, trapezius
  • as mentioned above, is part of pharyngeal plexus
  • spinal roots from ant horn of upper cervical segments, emerge from dorsal/ventral roots of spinal n – combine to form 1 trunk –> enter skull via foramen magnum
  • also exits via jugular foramen
• CN X
  • Superior Laryngeal n
    • Int laryngeal n – SS to larynx above vocal fold, lower pharynx, epiglottis
    • Ext laryngeal n – SM to cricothyroid, inf pharyngeal constrictor m.
  • Recurrent laryngeal n
    • hooks around subclavian a on R, and arch of aorta on L (lat to lig arteriosum)
    • asc in groove b/w trachea & esophagus
    • SS = larynx below vocal cord
  • SS from all mucus membranes = lower pharynx, larynx, and down to all thoracic/abdominal organs

 

•  

Histology:The cells of the connective tissue.

 There are two types of Connective Tissue cells:

1. Resident cells – have their own motility within tissue. ex/ histocyte, mast cell, adipocytes, smooth m cells, plasma cells, fibroblasts
2. Transient cells – move in and out of tissue, ex/ WBC – lymphocytes, granulocytes, monocytes

Cells of CT:

• fibroblasts –
  • elongated cell w/ cytoplasmic extensions
  •  ovoid nucleus, sparse chromatin, 1 or 2 nuclei
  • = synthesize  collagen, reticular, elastic fibers, and carbs of ECM
• fibrocyte –
  • more mature, smaller splindle shaped cells 
  •  no cytoplasmic extentions, smaller nucleus than fibroblast
  • = less active, but same function as fibrocyte
• plasma cell –
  • smaller, accentric nucleus, with condensed chromatin,
  • oval shape, cytoplasm mostly clear
  •  = secrete immunoglobulins & develop from B cells
• adipose cell –
  • narrow rim of cytoplasm, flat accentric nucleus
  • large and mostly empty cytoplasm
  • =  store fat
• lymphocyte – 
  • spherical shaped ells, dense chromatin in central nucleus,
  • no nucleoli
  • = mediate immune response, produce antibodies, defend body against infections, secrete proteins
• macrophages –
  • round, irregular cell outlines, small nucleus rich in chromatin,
  • cytoplasm filled w/ injested particles,
  • have feet like extensions called “pseudopodia”,
  • eosinophillic due to increased # of lysozymes
  • = phagocytes that injet bacteria, dead cells, cell debris, are Antigen presenting cells = APCs, also aid in immune response
  • * Look for fuzzy reddish ovoid structure with many spots in cytoplasm – can be found near a/v, but unlikely you would be asked to identify one
• eosinophil –
  • large WBC w/ bilobed nucleus *like headphones*,
  • large eosinophillic granules in cytoplasm – red color
  • = inc in # after parasitic infections or allergic reactions, phagocytose Antigen-antibody complexes after infection
• neutrophil –
  •  large WNC with many lobed nucleus, no granules in cytoplams,
  • cytoplasm more or less unstained
  • = engulf and destroy bacteria @ infection sites
• mast cell –
  • ovoid or circular, small central nucleus,
  • basophillic cytoplasm filled w/ fine closely packed, dense staining granules of histamine and heparin
  • = synthesize and release heparin and histamine.
    • Heparin = weak anticoagulant,
    • Histamine = used in inflammatory response, dilates a/v, increase a/v permiability to fluid, induces signs of allergic reaction
• monocytes –
  • largest  WBC, bean shaped nucleus
  • become macrophages
  • part of MPC = Mononuclear Phagocytotic System
  • = clean up tissue, antigen presentation = APCs

Embryology:The development of the neurocranium.

• 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

Neurocranium = forms protective case around brain
Two parts:
1. Membranous part = flat bones, like Parietal, Frontal, Squamous part of temporal and occipital
2. Cartilaginous part = bones @ base of skull, like ethmoid, sphenoid, petrous part of temporal and occipital

Membranous Neurocranium

• from para-axial mesoderm and neural crest cells
• undergo membranous ossification
  • is the aggregation of mesenchyme cells in the area where bone is to be formed.
  • The tissue in this area becomes more vascularized, 
  •  mesenchyme cells begin to differentiate into osteoblasts,
  • osteoblasts secrete the collagen and ground substance (proteoglycans) of bone matrix (collectively called osteoid).
  • The osteoblasts maintain contact with one another via cell processes.
  •  The osteoid becomes calcified with time, and the processes of the cells (called osteocytes when they are surrounded with matrix) become enclosed in canaliculi.
  • Some of the mesenchymal cells surrounding the developing bone spicules proliferate and differentiate into osteoprogenitor cells.
  •  Osteoprogenitor cells in contact with the bone spicule become osteoblasts, and secrete matrix, resulting in appositional growth of the spicule.
  • Intramembranous ossification begins at about the eighth week in the human embryo.
• bone spicules  grow from primary ossification centers –>periphery
• bones grow by adding new membranous layers on the outside, and at the same time, resorption of inner layers by osteoclasts inside

On Newborn skull,  the flat bones of skull are not united. In fact, you don’t want them to be, as the movement of these bones against each other allow the head to be shaped in certain ways to make birth easier.

At this point, the flat bones are separated by CT sutures:

• sagittal suture – from neural crest cells, b/w two  parietal bones
• coronal suture – from paraaxial mesoderm, b/w frontal and parietal bones

Where more than 2 bones meet = fontanelle

• ant fontanelle – where 2 frontal/2 parietal meet, will close w/in 2 years (like mastoid fontanelle) to become bregma
• post fontanelle – where 2 pariteal/occipital meet, will close w/in 6 months (like sphenoid fontanelle) to become lambda
• some sutures remain open until adulthood

Chondrocranium & Cartilaginous Neurocranium

• formed by many cartilages
• prechordal chondrocranium
  • lie in front of rostral (front/ant) end of notochord (future spinal cord) — hence, prechordal
  • post border = sella turcica
  • neural crest origin
• chordal chondrocranium
  • lie behind  sella turcica
  • develop from occipital somites = para-axial mesoderm origin
  • is the area that will surround the future spinal code — hence, chordal.