Lecture 24: The Skull & Cranial Nerves

Question 1

How many bones are in the skull and how do they unite?

Answer 1

22- immobile joints called sutures

Question 2

What are the 3 major parts of the skull?

Answer 2

Cranium, facial bones, mandible

Question 3

What are the floor and the roof of the cranium?

Answer 3

Base and vault

Question 4

What are the bones of the cranium?

Answer 4

2 Parietal – sides
1 Occipital – back
2 Frontal – suture down the middle but suture is so fused that its really one bone
2 Temporal – important because they contain the apparatus that allows us to 1 Sphenoid – important to give structure inside the cranium
1 Ethomoid – at the base of the frontal bone

Question 5

What are the facial bones?

Answer 5

• Maxilla – covers upper jaw
• Zygomatic bones – lateral to maxilla, form prominent cheek bones
• Inside the orbit and nasal cavity – nasal bones, lacrimal bones, vomer, palatine bones, inferior conchae
• Mandible

Question 6

What are the sutures in the skull?

Answer 6

• Coronal – 2 parietal bones join with frontal bone
• Sagittal – 2 parietal bones join in the midline
• Lambdoidal – D shaped suture, joins two parietal bones with the occipital bone

Question 7

What are the borders of the anterior cranial fossa?

Answer 7

• Anterior is frontal bone
• Posterior is lesser wing of sphenoid (where middle cranial fossa starts)
• Floor is made up of the orbital plates of frontal bone and cribriform plate of ethmoid

Question 8

What are the borders of the middle cranial fossa?

Answer 8

• Anterior is lesser wing of sphenoid
• Posterior part is petrous portion of temporal bone: fat region of temporal bone, bulge, houses cochlear
• Laterally formed by temporal bone, greater wing of sphenoid, parietal bone

Question 9

What are the borders of the posterior cranial fossa?

Answer 9

• Anterior formed by petrous portion of the temporal bone
• Floor formed by basilar, condylar and squamous (flat, smooth part that forms the back of the skull) portions of the occipital bone and the mastoid process of the temporal bone

Question 10

What are the contents of the posterior cranial fossa?

Answer 10

Cerebellum, pons, medulla oblongata

Question 11

What are the characteristics of the sphenoid bone?

Answer 11

Upper wing (lesser) and lower wing (greater) an gap between for passage of things into the orbit. Middle part is turkish saddle - pituitary gland

Question 12

Where do cranial nerves originate?

Answer 12

Exit ventral surface of brainstem, except CNIV which exits rostrally

Question 13

Which cranial nerves exit via the brain/CNS?

Answer 13

1 and 2

Question 14

What side of actions are the cranial nerves associated with and what is the exception?

Answer 14

Associated with ipsilateral side, except for CNIV with is associated with the contralateral side

Question 15

What are the features of CNI?

Answer 15

OLFACTORY

• Sense of smell
• Exits skull at cribiform plate within the ethmoid bone
• Moves through olfactory tract and bulb

Question 16

What are the features of CNII?

Answer 16

OPTIC

• Sensory for vision
• Exits skull through optic canal in sphenoid bone
• One optic nerve does not only control vision in one eye – mixed

Question 17

What are the features of CNIII, CNIV, CNVI?

Answer 17

OCCULOMOTOR, TROCHLEAR, ABDUCENT

• 6 extraocular muscles – coordinate movement of eyes, controlled by 3 nerves
• Act in a coordinated fashion to move eyes
• Occulomotor is most important – innervates 4 muscles
• Enter and exit orbit through superior orbital fissure – gap between two wings of sphenoid

Question 18

What are the features of CNV?

Answer 18

TRIGEMINAL

• Somatic sensory to face (fine touch, pain, temp) & motor to muscles of mastication
• Back of head not controlled by this – controlled by spinal nerve
• Has 3 major branches – V1 – ophthalmic (forehead and eye, exits skull through superior orbital fissure), V2 - maxillary (sensation to upper jaw and cheek and exits through foramen rotundum), V3 – mandibular (sensation to lower jaw, exits skull through foramen ovale)

Question 19

What are the features of CNVII?

Answer 19

FACIAL

• Motor to muscles of facial expression
• Visceral efferent (PS) to lacrimal and sublingual glands
• Visceral sensory – taste to anterior 2/3 of tongue
• Somatic sensory
• Exits skull through internal acoustic meatus
• 5 terminal branches: temporal (forehead, eyebrow raise, close eyelid), zygomatic (cheek movement), buccal (smiling), marginal mandibular (lower jaw muscles), cervical

Question 20

What are the features of CNVIII?

Answer 20

VESTIBULOCOCHLEAR

• Hearing and balance
• Exits skull through internal acoustic meatus next to petrous portion of temporal bone

Question 21

What are the features of CNIX?

Answer 21

GLOSSOPHARYNGEAL

• Sensory for posterior 1/3 of tongue, pharynx, middle ear and carotid body
• Taste to posterior 1/3 of tongue
• Visceral motor – PS to parotid
• Motor – stylopharyngeus
• Exits skull at jugular foramen with other cranial nerves

Question 22

What are the features of CNX?

Answer 22

VAGUS

• Visceral motor – mostly autonomic
• Motor to muscles of soft palate, pharynx, larynx, upper oesophagus and 1 tongue muscle
• Somatic sensory to pharynx and larynx
• Visceral sensory – taste and general baroreceptors
• Exits skull at jugular foramen

Question 23

What are the features of CNXI?

Answer 23

SPINAL ACCESSORY

• Provides motor input of sternomastoid and upper part of trapezius – shrugs shoulders and turns head
• Nerve enters cranium via foramen magnum and then travels with vagus and exits jugular foramen

Question 24

What are the features of CNXII?

Answer 24

HYPOGLOSSAL

• Motor innervation to intrinsic and extrinsic muscle of the tongue (except palatoglossus which is innervated by vagus)
• If nerve is damaged tongue deviates to side of problem
• Exits skull at hypoglossal foramen