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The
Cranial Nerves

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اول بحث في مجال طب الاسنان Cranial_nerves

Cranial Nerve:		Major Functions:
I Olfactory		smell
II Optic		vision
III Oculomotor		eyelid and eyeball movement
IV Trochlear		innervates superior oblique turns eye downward and laterally
V Trigeminal		chewing face & mouth touch & pain
VI Abducens		turns eye laterally
VII Facial		controls most facial expressions secretion of tears & saliva taste
VIII Vestibulocochlear (auditory)		hearing equillibrium sensation
IX Glossopharyngeal		taste senses carotid blood pressure
X Vagus		senses aortic blood pressure slows heart rate stimulates digestive organs taste
XI Spinal Accessory		controls trapezius & sternocleidomastoid controls swallowing movements
XII Hypoglossal		controls tongue movements

The cranial nerves are composed of twelve pairs of nerves that
emanate from the nervous tissue of the brain. In order reach their
targets they must ultimately exit/enter the cranium through openings in
the skull. Hence, their name is derived from their association with the
cranium. The function of the cranial nerves is for the most part similar
to the spinal nerves, the nerves that are associated with the spinal
cord. The motor components of the cranial nerves are derived from cells
that are located in the brain. These cells send their axons (bundles of
axons outside the brain = a nerve) out of the cranium where they will
ultimately control muscle (e.g., eye movements) , glandular tissue
(e.g., salivary glands) or specialized muscle (e.g., heart or stomach).
The sensory components of cranial nerves originate from collections of
cells that are located outside the brain. These collections of nerve
cells bodies are called sensory ganglia. They are essentially the same
functionally and anatomically as the dorsal root ganglia which are
associated with the spinal cord. In general, sensory ganglia of the
cranial nerves send out a branch that divides into two branches: a
branch that enters the brain and one that is connected to a sensory
organ. Examples of sensory organs are pressure or pain sensors in the
skin and more specialized ones such as taste receptors of the tongue.
Electrical impulses are transmitted from the sensory organ through the
ganglia and into the brain via the sensory branch that enter the brain.
There are two exceptions to this rule that should be noted when the
special senses of smell and vision are discussed. In summary, the motor
components of cranial nerves transmit nerve impulses from the brain to
target tissue outside of the brain. Sensory components transmit nerve
impulses from sensory organs to the brain.

CN I.
Olfactory Nerve

The olfactory nerve is actually a
collection of sensory nerve rootlets that extend down from the olfactory
bulb and pass through the many openings of the cribriform plate in the
ethmoid bone. These specialized sensory receptive parts of the olfactory
nerve are then located in the olfactory mucosa of the upper parts of
the nasal cavity. During breathing air molecules attach to the olfactory
mucosa and stimulate the olfactory receptors of cranial nerve I and
electrical activity is transduced into the olfactory bulb. Olfactory
bulb cells then transmit electrical activity to other parts of the
central nervous system via the olfactory tract.

[size=16]CN
II. Optic Nerve

The optic nerve originates from
the bipolar cells of the retina which are connected to the specialized
receptors in the retina (rod and cone cells). Light strikes the rod and
cone cells and electrical impulses are transduced and transmitted to the
bipolar cells. The bipolar cells in turn transmit electrical activity
to the central nervous system through the optic nerve. The optic nerve
exits the back of the eye in the orbit and enters the optic canal and
exits into the cranium. It enters the central nervous system at the
optic chiasm (crossing) where the nerve fibers become the optic tract
just prior to entering the brain.

CN III.
Oculomotor Nerve

The oculomotor nerve originates
from motor neurons in the oculomotor (somatomotor) and Edinger-Westphal
(visceral motor) nuclei in the brainstem. Nerve cell bodies in this
region give rise to axons that exit the ventral surface of the brainstem
as the oculomotor nerve. The nerve passes through the two layers of the
dura mater including the lateral wall of the cavernous sinus and then
enters the superior orbital fissure to access the orbit. The somatomotor
component of the nerve divides into a superior and inferior division.
The superior division supplies the levator palpebrae superioris and
superior rectus muscles. The inferior division supplies the medial
rectus, inferior rectus and inferior oblique muscles. The visceromotor
or parasympathetic component of the oculomotor nerve travels with
inferior division. In the orbit the inferior division sends branches
that enter the ciliary ganglion where they form functional contacts
(synapses) with the ganglion cells. The ganglion cells send nerve fibers
into the back of the eye where they travel to ultimately innervate the
ciliary muscle and the constrictor pupillae muscle.

CN
IV. Trochlear Nerve

The trochlear nerve is purely a
motor nerve and is the only cranial nerve to exit the brain dorsally.
The trochlear nerve supplies one muscle: the superior oblique. The cell
bodies that originate the fourth cranial nerve are located in ventral
part of the brainstem in the trochlear nucleus. The trochlear nucleus
gives rise to nerves that cross (decussate) to the other side of the
brainstem just prior to exiting the brainstem. Thus, each superior
oblique muscle is supplied by nerve fibers from the trochlear nucleus of
the opposite side. The trochlear nerve fibers curve forward and enter
the dura mater at the angle between the free and attached border of the
tentorium cerebelli. The nerve travels in the lateral wall of the
cavernous sinus and then enters the orbit via the superior orbital
fissure. The nerve travels medially and diagonally across the levator
palpebrae superioris and superior rectus muscle to innervate the
superior oblique muscle.

[size=16]CN V.
Trigeminal Nerve

The trigeminal nerve as the name
indicates is composed of three large branches. They are the ophthalmic (V[size=12]₁,
sensory), maxillary (V₂,
sensory) and mandibular (V₃, motor
and sensory) branches. The large sensory root and smaller motor root
leave the brainstem at the midlateral surface of pons. The sensory root
terminates in the largest of the cranial nerve nuclei which extends from
the pons all the way down into the second cervical level of the spinal
cord. The sensory root joins the trigeminal or semilunar ganglion
between the layers of the dura mater in a depression on the floor of the
middle crania fossa. This depression is the location of the so called
Meckle's cave. The motor root originates from cells located in the
masticator motor nucleus of trigeminal nerve located in the midpons of
the brainstem. The motor root passes through the trigeminal ganglion and
combines with the corresponding sensory root to become the mandibular
nerve. It is distributed to the muscles of mastication, the mylohyoid
muscle and the anterior belly of the digastric. The mandibular nerve
also innervates the tensor veli palatini and tensor tympani muscles. The
three sensory branches of the trigeminal nerve emanate from the ganglia
to form the three branches of the trigeminal nerve. The ophthalmic and
maxillary branches travel in the wall of the cavernous sinus just prior
to leaving the cranium. The ophthalmic branch travels through the
superior orbital fissure and passes through the orbit to reach the skin
of the forehead and top of the head. The maxillary nerve enters the
cranium through the foramen rotundum via the pterygopalatine fossa. Its
sensory branches reach the pterygopalatine fossa via the inferior
orbital fissure (face, cheek and upper teeth) and pterygopalatine canal
(soft and hard palate, nasal cavity and pharynx). There are also
meningeal sensory branches that enter the trigeminal ganglion within the
cranium. The sensory part of the mandibular nerve is composed of
branches that carry general sensory information from the mucous
membranes of the mouth and cheek, anterior two-thirds of the tongue,
lower teeth, skin of the lower jaw, side of the head and scalp and
meninges of the anterior and middle
cranial fossae.

Phylum Chordata

Phylum Chordata
includes the vertebrates. Although not as common as the invertebrates,
teeth and bones from different classes of vertebrate animals can be
found at Canal sites.
Chondrichthyes, or “cartilage
fish,” include the sharks, skates, and rays. Teeth and vertebrae from
these animals are the most common types of vertebrate fossil found. They
may be found on the surface of a rock outcrop or in various spoil
piles.
The most commonly found shark teeth belong to the extinct
shark Squalicorax. These broad and serrated teeth are easy to identify
to the genus level, but it is more difficult to distinguish between the
species. Teeth of the goblin shark, Scapanorhynchus, are the largest
shark teeth found at the Canal, with some specimens reaching over two
inches in length. The teeth of this shark have caused workers much
confusion because teeth from different parts of the mouth have different
and distinct shapes. At one time there were three different names given
to the teeth of this single shark species.
Osteichthyes,
or “bony fish,” are represented by the dagger-like teeth of the
Cretaceous predator Enchodus. Single, isolated teeth and small sections
of the jaw with teeth still attached are relatively common finds. Teeth
from other bony fish include Anomoeodus and Stephanodus. Vertebral
columns of bony as well as cartilaginous fish are also found on the
spoil piles.
Reptile remains are rare and thus the
most treasured finds from the Delaware Cretaceous. Teeth of the
sea-going reptile Mosasaurus and fragments from the upper and lover
shells of turtles are the usual finds. Most collectors have to hunt for
years before they find a single mosasaur tooth. اول بحث في مجال طب الاسنان ChondrichthyesPH1

اول بحث في مجال طب الاسنان ChondrichthyesPH1

8. Batoid vertebra - specimen from the
Marshalltown Formation, also occurs in the Mount Laurel Formation and
the Merchantville Formation
9. Shark vertebra - specimen from the
Merchantville Formation, also occurs in the Mount Laurel Formation and
the Marshalltown Formation

Cretaceous Chondrichthyes photograph
from Plate 8, DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

اول بحث في مجال طب الاسنان ChondrichthyesPH2

اول بحث في مجال طب الاسنان ChondrichthyesPH2

1, 2, 3. Scapanorhynchus texanus - specimens
from the Marshalltown Formation, also occur in the Merchantville
Formation
4. Squalicorax kaupi - specimen from the Marshalltown
Formation, also occurs in the Mount Laurel Formation and the
Merchantville Formation
5,6. Squalicorax pristodontus - specimens
from the Marshalltown Formation
7, 8. Odontaspis sp. - specimens from
the Marshalltown Formation, also occur in the Mount Laurel Formation
and the Merchantville Formation
9. Ischyrhiza mira - specimen from
the Merchantville Formation, also occurs in the Mount Laurel Formation
and the Marshalltown Formation

Cretaceous Chondrichthyes
photograph from Plate 9, DGS Special Publication No. 18, by E. M.
Lauginiger, 1988.
اول بحث في مجال طب الاسنان ChordataIL19

- Shark's tooth

Cretaceous Chordata
illustration from Page 15, DGS Special Publication No. 9, 1992.
اول بحث في مجال طب الاسنان ChordataIL

- Squalicorax kaupi - occurs in the Mount Laurel
Formation, the Marshalltown Formation, and the Merchantville Formation
-
Shark vertebrae - occurs in the Mount Laurel Formation, the
Marshalltown Formation, and the Merchantville Formation
-
Scapanorhynchus texanus - occurs in the Marshalltown Formation and the
Merchantville Formation
- Odontaspis sp. - occurs in the Mount Laurel
Formation, the Marshalltown Formation, and the Merchantville Formation
-
Ray vertebrae - occurs in the Mount Laurel Formation, the Marshalltown
Formation, and the Merchantville Formation
- Ischyrhiza mira - occurs
in the Mount Laurel Formation, the Marshalltown Formation, and the
Merchantville Formation
- Enchodus ferox - occurs in the Mount Laurel
Formation, the Marshalltown Formation, and the Merchantville Formation
-
Anomoeodus phaseolus - occurs in the Mount Laurel Formation, the
Marshalltown Formation, and the Merchantville Formation
- Bony fish
vertebrae - occurs in the Mount Laurel Formation, the Marshalltown
Formation, and the Merchantville Formation
- Mosasaurus sp. - occurs
in the Mount Laurel Formation, the Marshalltown Formation, and the
Merchantville Formation
- Turtle shell fragment - occurs in the
Marshalltown Formation and the Merchantville Formation

Cretaceous
Chordata illustrations from Figure 14, DGS Special Publication No. 18,
by E. M. Lauginiger, 1988.
اول بحث في مجال طب الاسنان ReptiliaPH

اول بحث في مجال طب الاسنان OsteichthyesPH

1. Turtle shell fragment from the plaston -
specimen from the Merchantville Formation, also occurs in the
Marshalltown Formation
2. Trionyx sp. - middle scute from the
carapace of a soft shelled turtle - specimen from the Merchantville
Formation
3. Mosasaur teeth - isolated teeth from a sea-going reptile
- specimen from the Mount Laurel Formation, also occurs in the
Marshalltown Formation and the Merchantville Formation

Cretaceous
Reptilia photograph from Plate 8, DGS Special Publication No. 18, by E.
M. Lauginiger, 1988.
4. Anomoeodus phaseolus - complete lower jaw
section of a bony fish - specimen from the Marshalltown Formation, also
occurs in the Mount Laurel Formation and the Merchantville Formation
5.
Enchodus ferox - side view of an isolated tooth - specimen from the
Mount Laurel Formation, also occurs in the Marshalltown Formation and
the Merchantville Formation
6,7. Teleost fish vertebra - specimens
from the Mount Laurel Formation

Cretaceous Osteichthyes
photograph from Plate 8, DGS Special Publication No. 18, by E. M.
Lauginiger, 1988.

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