S1B5 - Interior Skull / Intro to Cranial Nerves

Question 1

Describe the location, path and innervation of CN XII.

Answer 1

CN XII - hypoglossal nerve

• motor only
• Exits the skull through the hypoglossal canal
• provides motor innervation to tongue muscles.

Question 2

Describe dural venous sinuses in general.

Answer 2

Dural venous sinuses are endothelium-lined spaces between the two dural layers. Venous blood enters these from cerebral veins, diploic veins (draining cranium), and through emissary veins (passing through skull from external structures). Confluence of sinuses is the dilated region near the internal occipital protuberance where several dural sinuses meet.

Question 3

Describe the dural infoldings of the cranial meninges. What are the names of the main cranial infoldings?

Answer 3

Dural infoldings are formed by the inner membranous layer of dura mater and help to partition and support structures within the cranium.

• Falx cerebri
• Tenrtorium cerebelli
• Falx cerebelli
• Diaphragm sellae

Question 4

Which cranial nerve begins at the telencephalon?

Answer 4

CN I begins from the telencephalon.

Question 5

What are the foramina and grooves of the posterior cranial fossa?

Answer 5

Foramina and grooves of the posterior cranial fossa:

1. foramen magnum
2. jugular foramen
3. internal acoustic meatus
4. hypoglossal canal
5. groove for inferior petrosal sinus
6. groove for sigmoid sinus
7. groove for transverse sinuses

Question 6

What sutures are found in the roof of the cranial cavity?

Answer 6

Sutures of the roof of the cranial cavity.

• The suture between the frontal and parietal bones is the coronal.
• The suture between the paired parietals is the sagittal; and
• the lambdoid suture separates parietals from the occipital.

Question 7

How does anosmia most commonly arise?

Answer 7

Loss of smell (Anosmia) most commonly arises from nasal infection and ethmoidal fractures; unilateral anosmia is rarely noticed, bilateral anosmia can be psychologically debilitating due to the associated loss of taste.

Question 8

Describe the location, path and contents of the hypoglossal canal.

Answer 8

Hypoglossal canal is located anterolaterally within the foramen magnum.

• For CN XII.

Question 9

What are the two main aspects of the cranial cavity?

Answer 9

The space inside the skull occupied by the brain, meninges, and related structures is the cranial cavity, which has two main aspects, the roof and the bowl-shaped floor.

• The roof of the cranial cavity is formed by the calvaria.
• The floor of the cranial cavity has three large depressions, the anterior, middle, and posterior cranial fossae.

Question 10

Describe the location, path and contents of the foramen ovale.

Answer 10

Foramen ovale is large, opens inferiorly into the infratemporal fossa.

• For CN V3 (mandibular nerve), lesser petrosal nerve, and accessory meningeal artery.

Question 11

Describe the location, path and innervation of CN VII.

Answer 11

CN VII - facial nerve

• both sensory and motor
• has parasympathetic functions
• Sensory and motor roots of the facial nerve leave cranial cavity through the internal acoustic meatus, enter the petrous part of temporal bone, where form the genicular ganglion with sensory neurons. After giving off branches within the petrous part of temporal bone, CN VII exits the skull through the stylomastoid foramen.
• Facial nerve provides.
  
  • Motor innervation to the muscles of facial expression and other muscles derived from the 2nd pharyngeal arch.
  • Sensory innervation for taste from the anterior 2/3 of the tongue and general sensory innervation for a small part of the ear.
  • Parasympathetic innervation for the lacrimal gland, some salivary glands and other glands in the nasal cavity and palate.

Question 12

Describe the location and flow of the cavernous sinus.

Answer 12

Cavernous sinus is located bilaterally, lateral to sella turcica. Fibrous extensions between meningeal and periosteal dura layers give it trabeculated form. It connects with structures outside cranial cavity via ophthalmic veins and emissary veins from the pterygoid plexus (possible infection route).

Question 13

Describe the location and flow of the middle meningeal artery.

Answer 13

Middle meningeal artery is the largest of the meningeal arteries and supplies about 80% of the dura. It arises from the maxillary artery (from external carotid) and enters the skull through the foramen spinosum. There are two branches, anterior (lying deep to pterion, can be covered with bone there) and posterior.

Question 14

Describe the trigeminal innervations of the cranial dura.

Answer 14

Trigeminal nerve. All three components have meningeal branches

1. CN V1 supplies the anterior cranial fossa and falx cerebri.
2. CN V1 and CN V2 supply tentorium cerebelli
3. CN V2 and CN V3 supply the middle cranial fossa.

Question 15

Describe the location, path and innervation of CN IX.

Answer 15

CN IX - glossopharyngeal nerve

• both sensory and motor
• has parasympathetic function
• passes through the jugular foramen
• provides:
  
  • Motor innervation to the stylopharyngeus muscle derived from the 3rd pharyngeal arch.
  • Parasympathetic secretomotor to parotid gland.
  • Sensory for taste on posterior 1/3 of the tongue.
  • Sensory innervation from parts of oral cavity and middle ear.
  • Sensory from the chemoreceptors in the carotid body and sinus.

Question 16

Describe the location and flow of the sphenoparietal sinuses.

Answer 16

Sphenoparietal sinuses are small sinuses that receive blood from diploic and meningeal veins and drain into the anterior part of the cavernous sinus.

Question 17

What is the location, path and contents of the foramen magnum?

Answer 17

Foramen magnum is the largest foramen in the skull within the occipital bone.

• For brainstem/spinal cord with meninges, vertebral arteries, and CN XI (spinal accessory nerve).

Question 18

Which dural venous sinus is within the falx cerebelli? What does it drain into?

Answer 18

Within falx cerebelli:

• occipital sinus

Drains into confluence.

Question 19

Describe the location, path and innervation of CN VIII.

Answer 19

CN VIII - vestibulocochlear nerve

• sensory only - hearing and balance
• Passes through the internal acoustic meatus and provides sensory innervation through the vestibular nerve for balance and cochlear nerve for hearing
• Projects to 4 vestibular nuclei and 2 auditory nuclei in the pons

Question 20

Describe the location, path and innervation of CN II.

Answer 20

CN II - optic nerve

• sensory only - vision
• Fibers from retina join to form the optic nerves, which enter the skull through the optic canals. Projects to the Lateral Geniculate Nucleus (Body) of the thalamus.

Question 21

What are the three layers of cranial meninges?

Answer 21

Cranial meninges are similar to spinal meninges with tough outer dura mater, thin middle arachnoid mater lying on the internal surface of the dura mater, and delicate pia mater, which follows contours of nervous tissue and extends into the sulci.

Question 22

Describe the location, path and contents of the carotid canal.

Answer 22

Carotid canal opens into the cranium posteriomedial to the f. ovale.

• For the internal carotid artery and nerve plexus.

Question 23

Describe the spatial relationships of structures surrounding the cavernous sinus.

Answer 23

• Intercavernous sinuses (anterior and posterior) connect the left and right sides.
• Internal carotid artery and CN VI pass within sinus.
• CN III, CN IV, CN V1, and CN V2 lie in lateral wall of sinus (ordered superior to inferior).
• The trigeminal ganglion lies in the medial floor, with the proximal portions of all three divisions of the trigeminal nerve being in the cavernous sinus, V3 quickly leaves.

Question 24

Describe the location, path and innervation of CN V (not branches, that’s another question).

Answer 24

CN V - trigeminal nerve

• both sensory and motor
• Passes over medial aspect of petrous part of temporal bone. Large trigeminal ganglia with sensory neurons are located on anterior surface of petrous part of temporal bone in the trigeminal cave. To keep it simple, all three subdivisions interface with the Trigeminal Nuclei within brainstem.

Question 25

Describe the location, path and contents of the optic canal.

Answer 25

Optic canal goes through the lesser wing of the sphenoid and opens into the orbit

• For CN II and ophthalmic artery.
• Found in base of lesser wings of sphenoid.

Question 26

Are the optic nerves and terminal ganglion cells true nerves?

Answer 26

The optic nerve and the terminal ganglion cells are outgrowths of the brain, not true nerves.

Question 27

Describe the falx cerebelli.

Answer 27

Falx cerebelli is a small, vertical projection from inferior surface of tentorium cerebelli between the two cerebellar hemispheres. It attaches to the internal occipital crest.

Question 28

Which cranial nerves are sensory only, motor only, or mixed?

Answer 28

Mnemonic: Some Say Marry Money, But My Brother Says Big Business Makes More

1. Olfactory nerve - sensory
2. Optic nerve - sensory
3. Oculomotor nerve - motor
4. Trochlear nerve - motor
5. Trigeminal nerve - both
6. Abducent nerve - motor
7. Facial nerve - both
8. Vestibulocochlear nerve - sensory
9. Glossopharyngeal nerve - both
10. Vagus nerve - both
11. Accesory nerve - motor
12. Hypoglossal nerve - motor

Question 29

What is the Optic Chiasm and where is it located?

Answer 29

Immediately postero-medial to the inner opening of the optic canal the medial fibers of the optic tracts cross (decussate) at the Optic Chiasm.

Question 30

What are the bones of the anterior cranial fossa?

Answer 30

Bones of the anterior cranial fossa

• Frontal (anteriorly) forms the roof of the orbit and supports the frontal lobes of the brain.
• Ethmoid (middle) forms a cribriform plate and a median crest, crista galli, for the attachment of the falx cerebri.
• Body and lesser wings of the sphenoid (posteriorly).

Question 31

Describe the location, path, and innervation CN I.

Answer 31

CN I - Olfactory nerve

• Sensory only - sense of smell
• Nerve fibers pass through foramina in cribriform plate and enter olfactory bulb lying above the plate. It projects to the Limbic system (emotions, memory, visceral reflexes via autonomics), so smells can trigger memories and emotions via their shared processing in limbic system.

Question 32

Describe the location and flow of the transverse sinus.

Answer 32

Transverse sinus courses laterally from the confluence of sinuses along attached border of tentorium cerebelli to drain into the sigmoid sinus.

Question 33

Describe the subarachnoid space in the cranial meninges.

Answer 33

Subarachnoid space contains CSF produced by choroid plexuses in brain ventricles and resorbed through arachnoid granulations into the superior sagittal sinus.

Question 34

What are the bones of the middle cranial fossa?

Answer 34

The bones of the middle cranial fossa

• Sphenoid bone forms most of the middle cranial fossa with its bilaterally placed greater wings and the centrally located upper part of body termed sella turcica (meaning “Turkish saddle”).
• Temporal bone. Middle cranial fossa contains parts of the squamous (with grooves for middle meningeal artery) and petrous portions (contains vestibulocochlear apparatus) of the temporal bone

Question 35

What do you need to know about extradural hemorrhages?

Answer 35

Extradural hemorrhage occurs when blood collects between calvaria and periosteal layer of dura. They are typically due to rupture of meningeal artery (almost always middle meningeal artery), which can happen because of a skull (calvaria) fracture. Extradural hemorrhage tends not to cross suture lines because the dura is firmly attached to sutures, thus yielding a lens-shaped hematoma.

Question 36

Describe the location, path and innervation of CN IV.

Answer 36

CN IV - trochlear nerve

• motor only
• Passes through inferior surface of free edge of tentorium cerebelli. Fibers enter orbit through the superior orbital fissure. Innervates the superior oblique muscle of eye. Projects from the trochlear nucleus (in midbrain)

Question 37

What are the features of the anterior cranial fossa?

Answer 37

Features of the anterior cranial fossa

• Foramen cecum (in the frontal on the border with ethmoid) for the passage of nasal emissary veins.
• Cribriform foramina (in the cribriform plate) are for the passage of axons of olfactory nerves.
• Anterior and posterior ethmoidal foramina allow for the passage of ethmoid artery and vein

Question 38

From the optic chiasm, where do the two optic tracts diverge to?

Answer 38

From the optic chiasm the two optic tracts diverge to the Lateral Geniculate Bodies of the thalamus.

Question 39

Describe the location, path and innervation of CN III.

Answer 39

CN III - Oculomotor nerve

• motor only
• Passes through anterior edge of tentorium cerebelli and enters the orbit by passing through the superior orbital fissure. Innervates fibers for most extraocular muscles.

Question 40

Describe the location and flow of the basilar sinus (plexus).

Answer 40

Basilar sinus (plexus) interconnects the two inferior petrosal and cavernous sinuses with internal vertebral plexus.

Question 41

Describe the arterial supply to the cranial dura.

Answer 41

Arterial supply to dura is by meningeal arteries that run within the periosteal layer of the dura mostly supplying the calvaria rather than the dura. They are accompanied by veins.

Question 42

What are the borders of the posterior cranial fossa?

Answer 42

Posterior cranial fossa is the largest, deepest, and most inferior of the three cranial fossae.

• It is limited anteriorly on the midline by the dorsum sellae,
• laterally by the superior border of the petrous part of the temporal bone and
• inferiorly and posteriorly by the occipital bone

Question 43

Describe the location and flow of the occipital sinus.

Answer 43

Occipital sinus is found in falx cerebelli where it attaches to occipital bone; communicates with internal vertebral venous plexus and terminates into confluence of sinuses.

Question 44

Which cranial nerves begin from the pons?

Answer 44

CN V through VIII begin from the pons.

(5-7 like missionary pawns)

Question 45

Describe the diaphragm sellae.

Answer 45

Diaphragm sellae is a small, horizontal sheet of dura that roofs the hypophyseal fossa, which has an opening in the middle for the passage of infundibulum of pituitary gland.

Question 46

What are the bones of the roof of the cranial cavity?

Answer 46

Bones of the roof of the cranial cavity, or calvaria.

• Anteriorly calvaria are formed by the frontal bone,
• in the middle part by the parietal bones, and
• posteriorly by the occipital bone.

Question 47

What are the names of the foramina of the middle cranial cavity?

Answer 47

Foramina of the middle cranial cavity

1. optic canal
2. superior orbital fissure
3. foramen rotundum
4. foramen ovale
5. foramen spinosum
6. carotid canal
7. foramen lacerum

Question 48

Describe the location and flow of the inferior sagittal sinus.

Answer 48

Inferior sagittal sinus is found in the free, inferior border of falx cerebri and ends in straight sinus.

Question 49

Describe the location and flow of the sigmoid sinus.

Answer 49

Sigmoid sinus is the continuation of the transverse sinus as it curves inferiorly to pass through the jugular foramen forming the internal jugular vein.

Question 50

Describe the location and flow of the inferior petrosal sinus.

Answer 50

Inferior petrosal sinus connects posterior part of cavernous sinus to junction of sigmoid sinus and internal jugular vein at jugular foramen.

Question 51

Name the cranial nerves with their associated numbers.

Answer 51

Mnemonic: Oh, Oh, Oh, To Take A Family Vacation. Go Vegas After Hours

1. Olfactory nerve
2. Optic nerve
3. Oculomotor nerve
4. Trochlear nerve
5. Trigeminal nerve
6. Abducent nerve
7. Facial nerve
8. Vestibulocochlear nerve
9. Glossopharyngeal nerve
10. Vagus nerve
11. Accesory nerve
12. Hypoglossal nerve

Question 52

Describe the tentorium cerebelli.

Answer 52

Tentorium cerebelli separates cerebellum from the inferior (occipital) portion of the cerebrum and is raised up “like a tent” by its superior attachment to falx cerebri. It attaches to occipital bone posteriorly, to superior border of petrous part of temporal bone laterally and to the clinoid processes anteriorly. It has a central opening, the tentorial notch, through which the brainstem passes.

Question 53

Describe the location, path and contents of the jugular foramen.

Answer 53

Jugular foramen is at the base of the petrous ridge of the temporal bone.

• For CN IX, CN X, CN XI, sigmoid sinus as it becomes the superior bulb of the internal jugular vein.

Question 54

Describe the cranial meninges at the foramen magnum.

Answer 54

At foramen magnum, all layers except periosteal dural layer are continuous with spinal meninges.

Question 55

Which cranial nerves also have parasympathetic components?

Answer 55

Cranial nerves with parasympathetic components:

• Facial nerve (CN XII)
  
  • Parasympathetic innervation for the lacrimal gland, some salivary glands and other glands in the nasal cavity and palate
• Glossopharyngeal nerve (CN IX)
  
  • Parasympathetic secretomotor to parotid gland
• Vagus nerve (CN X)
  
  • Parasympathetic innervation to smooth muscle and glands in pharynx, larynx, thoracic and some abdominal viscera

Question 56

Which cranial nerves begin from the midbrain?

Answer 56

CN III & IV begin from the midbrain.

Question 57

Describe the location, path and contents of the foramen rotundum.

Answer 57

Foramen rotundum is located posterior to the medical end of the superior orbital fissure and opens externally into the pterygopalatine fossa.

• For CN V2 (maxillary nerve).

Question 58

Describe the location and flow of the superior petrosal sinus.

Answer 58

Superior petrosal sinus runs within tentorium cerebelli where attached to superior border of petrous part of temporal bone. It connects posterior part of cavernous sinus to transverse sinus where becoming sigmoid sinus.

Question 59

What is unusual about the Olfactory Trigone?

Answer 59

At the base of the forebrain the olfactory tract divides into three branches (the Olfactory Trigone). This sensory pathway is unusual for both bypassing the thalamus and lacking a clear topographic representation.

Question 60

Describe the falx ceribri.

Answer 60

Falx cerebri is a large, sickle-shaped dural infolding that passes between two cerebral hemispheres and attaches anteriorly to crista galli and the frontal crest. It ends posteriorly at internal occipital protuberance, continuous with tentorium cerebelli.

Question 61

Where does the optic tract enter the skull?

Answer 61

The optic tract enters the middle cranial fossa through the optic canal.

Question 62

What are the features of the calvaria?

Answer 62

Features of the calvaria (roof of the cranial cavity).

• A midline ridge, frontal crest, on the frontal bone serves for the attachment of the falx cerebri (part of the dura mater).
• Frontal crest terminates at the beginning of the groove for the superior saggital sinus (intradural venous structure).
• Parietal bones have grooves from the middle meningeal artery.
• Granular foveolae are small pits and depressions in the calvaria that host the arachnoid granulations.

Question 63

What are the three large depressions of the floor of the cranial cavity?

Answer 63

The floor of the cranial cavity has three large depressions, the anterior, middle, and posterior cranial fossae.

Question 64

Describe the location, path and innervations of CN X.

Answer 64

CN X - vagus nerve

• both sensory and motor
• has parasympathetic function
• passes through the jugular foramen
• provides:
  
  • Motor innervation to muscles from the 4th and 6th pharyngeal arches including laryngeal muscles and some muscles of tongue, palate, and pharynx.
  • Parasympathetic innervation to smooth muscle and glands in pharynx, larynx, thoracic and some abdominal viscera.
  • Sensory innervation for taste from epiglottis.
  • General sensory innervation from viscera, larynx, parts of ear, and part of dura in the posterior cranial fossa.

Question 65

Descrive the general innervation of the cranial dura.

Answer 65

Innervation of dura. Dura is richly supplied with sensory fibers. The detected pain can refer to cutaneous and mucosal regions also supplied by the nerves innervating the dura.

• mostly innervated by the trigeminal nerve
• Posterior cranial fossa is supplied largely by upper cervical nerves and CN X.

Question 66

Describe the location, path and contents of the superior orbital fissure.

Answer 66

Superior orbital fissure is located between the greater and lesser wings of the sphenoid and opens into the orbit.

• For CN III, CN IV, CN V1 (ophthalmic nerve), CN VI, ophthalmic veins.

Question 67

Describe the locations and features of the olfactory bulb and the olfactory tract.

Answer 67

On the superior surface of the cribriform plate is the Olfactory Bulb which contains a group of cells termed Mitral Cells. The olfactory receptor neurons synapse with the mitral cells. The axons of the mitral cells extend to the brain as the Olfactory Tract. Technically, the olfactory tract and bulb are outgrowths of the brain, not true nerves.

Question 68

Describe the locations and contents of the grooves of the posterior cranial fossa.

Answer 68

Several sinuses converge towards the jugular foramen to form the internal jugular vein. Groove for inferior petrosal sinus is lateral to the clivus; sigmoid sinus is between temporal and occipital bones running towards the jugular foramen, and transverse sinuses extend laterally from the internal occipital protuberance to join the sigmoid sinuses.

Question 69

What do you need to know about subarachnoid hemorrhages?

Answer 69

Subarachnoid hemorrhage is when blood collects in subarachnoid space mixing with the CSF. The most common non-traumatic cause is the rupture of a cerebral aneurysm. First signs often include acute severe headaches, nausea, and vision disturbances.

Question 70

Where are the Olfactory Receptor Neurons located?

Answer 70

The Olfactory Receptor Neurons are clustered into a small, golden-colored, patch of epithelium termed the Olfactory Organ located on the roof of the nasal cavity along the medial side of the superior concha.

Question 71

Describe the location and flow of the small anterior and posterior meningeal arteries.

Answer 71

Small anterior and posterior meningeal arteries supply the respective cranial fossae. They arise from multiple sources.

Question 72

Which cranial nerves supply extraocular muscles that move the eyeball?

Answer 72

CNs III, IV, VI supply extraocular muscles that move the eyeball.

Question 73

Which cranial nerve begins from the diencephalon?

Answer 73

CN II begins from the diencephalon.

(II, 2, DIencephalon)

Question 74

Describe the location, path and innervations of CN XI.

Answer 74

CN XI - accessory nerve

• motor only
• has two roots, cranial accessory nerve and spinal accessory nerve.
• Cranial accessory nerve eventually merges with CN X.
• Spinal accessory nerve arises from the motor neurons in the upper five segments of the spinal cord and enters the cranium through the foramen magnum to then leave it through the jugular foramen
• motor innervation to trapezius and sternocleidomastoid muscles

Question 75

What’s the difference between cranial dura mater and spinal dural mater?

Answer 75

Difference from spinal cord is that cranial dura mater has two layers, an outer periosteal layer, which is continuous with periosteum at openings in the skull and an inner membranous layer, which is a true meninx. Within cranium, the two dural layers are fused except where dural venous sinuses intervene and where dural infolding occurs.

Question 76

Describe the locations, paths and innervations of the branches of CN V.

Answer 76

There are three subdivisions of the trigeminal nerve

1. Ophthalmic nerve (CN V1) (Sensory), which passes through the superior orbital fissure. Sensory innervation from the orbital contents, parts of face, scalp, nasal cavity, sinuses, and dura.
2. Maxillary nerve (CN V2) (Sensory) passes through the foramen rotundum and provides sensory innervation to parts of face, nasal cavities, palate, maxillary teeth, maxillary sinus, and dura.
3. Mandibular nerve (CN V3) (Mixed) passes through the foramen ovale and provides sensory innervation to parts of face, temporomandibular joint, mandibular teeth, tongue (anterior 2/3), mouth, and dura. The nerve also provides motor innervation to muscles of mastication and several other muscles from the first pharyngeal arch.

Mnemonic: Standing Room Only; Superior fissure, Rotundum, Ovale

Question 77

Describe the location, path and contents of the foramen spinosum.

Answer 77

Foramen spinosum is located posterolateral to the f. ovale and opens into the infratemporal fossa.

• For middle meningeal artery (blood supply to the dura mater).

Question 78

What are the bony features of the posterior cranial fossa?

Answer 78

Bony features of the posterior cranial fossa.

• The sphenoid body and the basilar part of the occipital bone form the clivus, a shallow depression behind the dorsum sellae that slopes posteriorly.
• Internal occipital crest runs along the midline from the foramen magnum posteriorly to the internal occipital protuberance and divides the posterior cranial fossa into two bilateral depressions, the deep cerebellar fossae.

Question 79

Describe the path of axons from the olfactory receptor neurons.

Answer 79

The axons from the olfactory receptor neurons coalesce into ~20 fibers, the Filia Olfactoria, which pass through the foramina of the cribriform plate; the filia olfactoria are, technically, the olfactory nerve (CN I).

Question 80

Describe the location and flow of the superior sagittal sinus.

Answer 80

Superior sagittal sinus lies in superior region of the falx cerebri from foramen cecum to end in the confluence of sinuses. It connects with laterally placed venous lacunae into which arachnoid granulations project for return of CSF to venous circulation. Veins from superolateral surfaces of cerebral hemispheres also drain here.

Question 81

What is responsible for the anatomical blind spot of the eye?

Answer 81

The most superficial neuronal cells are the Ganglion Cells; the axons of the ganglion cells line the inner surface of the retina, they coalesce and pass through the retinal layers creating an anatomical blind spot and projecting away from the eye as the Optic Nerve.

Question 82

Describe the location and flow of the accessory meningeal artery.

Answer 82

Accessory meningeal artery is a small branch of maxillary artery that passes through the foramen ovale and supplies semilunar ganglion and surrounding dura.

Question 83

Describe the location, path and innervation of CN VI.

Answer 83

CN VI - abducent nerve

• motor only
• Passes through dura covering clivus, cavernous sinus and superior orbital fissure to innervate the lateral rectus muscle. It projects from abducence nucleus (in pons).

Question 84

Where are photoreceptor neurons located?

Answer 84

Photoreceptor neurons are located within the Retina of the eye, which includes several discrete synaptic layers beyond the photoreceptors, and in each layer there are specialized neurons that integrate signals between adjacent neurons.

Question 85

What are the borders of the middle cranial fossa?

Answer 85

Middle cranial fossa is posterior and inferior to the anterior cranial fossa.

• It is separated from anterior fossa by sphenoidal crests (formed by the lesser wings of the sphenoid), anterior clinoid processes and limbus of sphenoid bone and
• from the posterior cranial fossa by superior border of petrous part of temporal bone.

Question 86

Describe the location and flow of the straight sinus.

Answer 86

Straight sinus lies at junction of falx cerebri with tentorium cerebelli; formed by the merging of inferior sagittal sinus and great cerebral vein; terminates in confluence of sinuses.

Question 87

Which dural venous sinuses are within the falx cerebri? What do they drain into?

Answer 87

Within falx cerebri:

• superior sagittal sinus
• inferior sagittal sinus
• straight sinus

Drain into confluence.

Question 88

What features of the sphenoid bone are in the middle cranial cavity?

Answer 88

Sphenoid bone forms most of the middle cranial fossa with its bilaterally placed greater wings and the centrally located upper part of body termed sella turcica (meaning “Turkish saddle”).

• The limbus of the sphenoid forms the anterior boundary of the chiasmatic sulcus, which is formed as the continuation of the optic canals where the optic nerves cross.
• Sella turcica is surrounded by the anterior and posterior clinoid processes. It is formed by
  
  • Tuberculum sellae is an elevation at the posterior aspect of chiasmatic sulcus.
  • Hypophysial fossa is a depression housing pituitary gland.
  • Dorsum sellae is a bony ridge projecting superior with posterior clinoid processes as lateral edges.

Question 89

Which cranial nerves begin from the medulla?

Answer 89

CN IX - XII begin from the medulla.

XI also from spinal cord.

Question 90

What do you need to know about subdural hemorrhages?

Answer 90

Subdural hemorrhage occurs when blood collects between the meningeal layer of the dura and the arachnoid layer. This type of hemorrhage is usually due to rupture of veins draining in to dural venous sinuses. The spread of blood is not confined by dural attachment to sutures, thus yielding a crescent shape. Density of the hematoma depends on its age (acute=hyperdense; chronic=hypo-).

• Acute subdural hematoma is usually in people with an obvious head blow.
• Chronic subdural hematomas is more common in elderly people with relatively mild trauma.

Question 91

What features of the temporal bone are in the middle cranial cavity?

Answer 91

Temporal bone.

• Middle cranial fossa contains parts of the squamous (with grooves for middle meningeal artery) and petrous portions (contains vestibulocochlear apparatus) of the temporal bone.

Question 92

Describe the location, path and contents of the internal acoustic meatus.

Answer 92

Internal acoustic meatus is located anteriosuperior to the jugular foramen within the petrous portion.

• For CNs VII and VIII, and labyrinthine artery.

Question 93

Describe the location, path and contents of the foramen lacerum.

Answer 93

Foramen lacerum lies posterolateral to the hypophyseal fossa and is partially filled with cartilage during life.