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The anatomy of the nasal cavity and paranasal sinuses. The skeletal and smooth muscle tissues. The development of the pharyngeal gut.

6 Dec

The anatomy of the nasal cavity and paranasal sinuses. The skeletal and smooth muscle tissues. The development of the pharyngeal gut.

The anatomy of the nasal cavity and paranasal sinuses.

Nasal Cavity:

*For step by step amazing pictures of the nasal cavity: http://home.comcast.net/~WNOR/lesson9.htm


  • ant = nasal bone (ant nasal aperture = piriform aperture)
  • sup =

    • (ant) nasal part of frontal bone
    • (middle) body of sphenoid,
    • (post) body of sphenoid,
    • the roof of the nasal cavity also has the cribriform plate of ethmoid bone, conveying fibers of CN I
  • med = septum nasi – made by perpendicular plate of ethmoid sup/post, vomer inf/post, and septal cartilage ant
  • inf = hard palate, made of palatine process of maxilla (ant), and horizontal plate of palatine bone (post)
  • post border = outlet = choanae, that lead to nasopharynx
    • lat = med pterygoid plate
    • med = vomer
    • sup = body of sphenoid
    • inf = horizontal plate of palatine bone

There are two parts to the nasal cavity, the nasal vestibule, and the nasal cavity itself

The line that divides the vestibule from the rest of the nasal cavity is limen nasi, which is the alse the line between the cutaneous and mucosal part of the nasal cavity

On the sagittal section of the head, you can find limen nasi, by looking for where the nose hairs stop – and you will be transitioning into the mucosal part.

Medial Wall
The nasal cavity itself is further subdivided into two regions:
upper 1/3 = olfactory part, for smelling
lower 2/3 = respiratory part, for breathing

The medial wall of the nasal cavity is pretty lacking in any features, just mention what makes up the septum.
CLINCIAL NOTE – the nasal septum can be deviated (bent) to one side or the other, if bent so far that it touches the lateral wall, can require surgery, because will affect breathing.

Lateral Wall
The lateral wall is much more complicated, having three projections coming from it, the nasal concha.

There are 3 nasal concha – sup, mid, inf.
Function of the nasal concha: is to spin the air within the nasal cavity, in order to:

  • to help warm the air,
  • as well as aid in filtering it
  • adding moisture to the air.

Above the superior nasal concha, is the sphenoethmoid recess – the sphenoid sinus opens into this space

between each concha, are the nasal meati.
Superior nasal meatus – B/w the superior and middle concha
2 things open here :

  1. the posterior ethmoid air cells (one of the paranasal sinuses)
  2. sphenopalatine foramen – thru it, go the sphenopalatine a, and post/ sup nasal n

Middle nasal meatus = B/w middle and inf concha
This area is a bit more complicated.
There is a bony projection (bulge) into this area, made by middle ethmoid air cells – called the ethmoidal bulla.
Below the ethmoidal bulla is the uncinate process, a horn shaped bony projection.
Leading into the uncinate process is the ethmoidal infundibulum, that contains the fronto nasal duct. This duct leads from the frontal sinus, and allows it to empty into the middle nasal meatus.

B/w the ethmoidal bulla and the uncinate process is a half moon shaped space = semi lunar hiatus.
3 Things open here:

  1. Into the hiatus, the frontal sinus opens ( via the fronto nasal duct),
  2. maxillary sinus opens into the post part of the hiatus,
  3. ant/ mid ethmoid air cells also open here.

So all together that is 4 things that open in the middle nasal concha.

Inf nasal meatus =  below the inf nasal concha,
2 things open here:

  1. Nasolacrimal duct opens here in to the ant part of the meatus, draining excess tears into the inf nasal meatus – this is  why your nose runs when you cry a lot.
  2. Incisive canal – we mentioned this before in the oral cavity, is the connection b/w nasal and oral cavity, has nasopalatine n/a here.

Blood Supply of Nasal Cavity:

  • post lat nasal and post septal br (sphenopalatine a)
  • ant post/ethmoid a (ophthalmic a)
  • Gr palatine a (desc palatine a)
  • Septal br of sup labial a (facial a)
  • Lat nasal br (facial a)

Huge venous plexus drains the nsals mucosa —> flow into sphenopalatine, facial, and ophthalmic v, plays a major role in warming air before it goes to lungs

Innervation of Nasal Cavity:
Respiratory region: SS

  • Post/inf part of nasal cavity = nasopalatine n (V2) to septum, post lat nasal branches (gr palatine n) to lat wall
  • ant /sup part = ant/post ethmoidal n (nasociliary n of V1)

Olfactory region = CN I

* For innervation of mucosal glands of Nasal Cavity, please see topic #3

4 Paranasal sinuses:


  • decrease the weight of the facial skeleton
  • vocal resonance – why your voice changes when you have a cold/sinus infection, and your sinuses fill
  • moisten and warm air

1. Frontal Sinus – located w/ the frontal bone, behind the root of nose, innervated by supraorbital n of V1

2. Maxillary sinuses –  largest paranasal sinuses
roof = floor of orbit
floor = alveolar process of maxilla
apex = zygomatic bone
base – inf/lat wall of nasal cavity

CLINICAL NOTE – maxillary sinus drains by an opening maxillary ostium in to middle nasal meatus, but this opening is located high on the walls, so sinus does not fully drain – can get infected easier = sinusitis

Blood supply = sup alveolar a (Maxillary a)
Innervation = br of ant/mid/post superior alveolar n (V2)

3. Ethmoidal sinuses (air cells)
located lat to most superior part of nasal cavity. If you pinch the bridge of your nose, the ethmoid sinuses would be located post to your fingers.

Innervation = by ant/post ethmoid n (nasocilary n of C1)

4. Sphenoid sinus
located in sphenoid bone, part of roof of nasal cavity
Clincial NOTE – b/c of this sinus, the roof of nasal cavity is weak. If broken in a fight, can cause to the leakage of sinus contents or even CSF out of the nose
Innervation = by post ethmoidal a and post ethmoid n

Histology: The skeletal and smooth muscle tissues.

Smooth Muscle

all musc tissue consist of elongated cells = fibers
cytoplasm of musc cells = sarcoplasm
contains a # of myofibrils, made of actin & myosin
surrounding cell membrane = sarcolemma

Smooth muscle

found in numerous organs = uterus, SI, LI, stomach, a/v, trachealis
contain contractile actin and myosin filaments
not arranged in regular cross striated pattern
appear smooth and non striated
involuntary motion
small, spindle, fusiform in shape – single central nucleus
actin/filaments attach dense bodies (adheron aggregates) to sarcolemme plaques


  • exhibits spontaneous, wave – like activity
  • ureters, uterine tubes, digestive organs: produces peristalsis
  • a/v = regulate luminal diameters

connected w/ gap junctions – rapid ionic communications
regulated by SNS/PNS
influence the rate and force of contractility


  1. Sarcoplasmic reticulum release Ca2+
  2. Ca/calmodulin complex forms
  3. which activates MLCK (Myosin light chain kinase)
  4. this PO4’s myosin –> myosin attaches to actin = contraction

Skeletal muscles

long multinucleated cells w/ peripheral nuclei
very regular formation of myosin & actin in cytoplasm
contractile filaments form distinct cross striation patterns = dark A bands, light I bands

3 CT layers:
Skeletal musc surrounded by dense irregular CT = epimysium
less dense, irregular CT = perimysium – comes inside and divides interior of muscle into fascicles (bundles)
endomysium = CT fibers that go around individual fibers
w/in cell = 4-5 myofibrils
groups of 8-9 myocytes = fascicles

has neuromuscular spindles – CT capsule, contain musc fiber called intrafusal fibers, & n. endings, surrounding fluid filled space

Other features:

  • No cell junctions
  • well developed ER & T tubules
  • voluntary innervation
  • all or non contraction
  • NO mitosis
  • grows in response to demand
  • limited regeneration
  • made by myoblasts of para-axial mesoderm

Thick (A) = Myosin – tail region of globular head
Thin (I) = Actin – twisted chains
1. when myosin head attached to actin – no ATP present
2. ATP binds to head –> ATP becomes ADP + P, head moves away from actin
3. fibers slide past each other
4. length of sarcomere decreases
5. I & H band disappear

Embryology:The development of the pharyngeal gut.

The primitive gut forms during the 4th week of the development as a result of cephalocaudal and lateral folding of the embryo. This endoderm lined cavity is incorporated into the embryo, while the yolk sac and the allantois remain temporarily by outside the embryo.

  • The endoderm of the primitive gut gives rise to the epithelium and glands of the digestive tract.
  • The muscular and fibrous elements of the digestive tract are derived from the splanchnic mesoderm.
  • The epithelium at the cranial and caudal extremities of the digestive tract is derived from the ectoderm of the stomodeum and the proctodeum (anal pit).

Formation of the gut tube

Formation of the primitive gut

Formation of the ventral abdominal wall

Formation of the ventral abdominal wall

1. Foregut
2. Hindgut
3. Midgut
4. Central nervous system
5. Tracheobronchial diverticulum
6. Heart
7. Liver bud
8. Buccopharyngeal membrane
9. Vitelline duct
10. Allantois
11. Cloacal membrane

1. Yolk sac
2. Surface ectoderm
3. Amniotic cavity
4. Neural groove
5. Splanchnic mesoderm
6. Somatic mesoderm

1. Yolk sac
2. Surface ectoderm
3. Amniotic cavity
4. Neural tube
5. Splanchnic mesoderm
6. Somatic mesoderm

1. Gut endoderm
2. Intraembryonic coelomic cavity
3. Amniotic cavity
4. Dorsal mesentery
5. Splanchnic mesoderm
6. Somatic mesoderm
7. Neural tube

The primitive gut is divided into four parts: a) the pharyngeal gut which extends from the buccopharyngeal (oropharyngeal) membrane to the respiratory (tracheobronchial) diverticulum;

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