Cranial Nerves

Question 1

CN I- olfactory

Question 2

CN II- Optic

Question 3

CN III- oculomotor

Question 4

CN IV- trochlear

Question 5

CN V- trigeminal

Question 6

CN VI- abducens

Question 7

CN VII- facial

Question 8

CN VIII- vestibulocochlear

Question 9

CN IX- glossopharyngeal

Question 10

CN X- vagus

Question 11

CN XI- spinal accessory

Question 12

CN XII - hypoglossal nerve

Answer 12

Modality- General somatic efferent
Nucleus- hypoglossal nucleus
Location- medulla
Distribution- motor Innervation to all tongue muscles except palatoglossus(vagus)
Landmarks: joined by C1
- passes between hyoglossus and mylohyoid
Branches- CN XII itself
-branches of C1- meningeal branch, superior root of Ansa cervicalis, nerve to thyrohyoid, nerve to geniohyoid

Course:
1. Arises from hypoglossal nucleus in floor of fourth ventricle
2. Exits brain in pre olivary fissure
3. Two roots pierce dura mater, enter hypoglossal canal, unite and leave cranial cavity
4. Lies deep to IJV,ICA CN IX, X and XII
5. Runs between ICA and ECA within carotid triangle
6. Run deep to styloid process and posterior belly of digastric
7. Through mylohyoid muscle and enters sublingual region to supply muscles of the tongue.

Lesion: by head and neck malignancy, penetrating traumatic injuries or dissection of ICA. hyoglossus nerve palsy; acute pain.
- Patients will present with deviation of tongue towards damaged side on protrusion as well as possible muscle wasting and fasciculations on affected side

Question 13

Discuss the temporal fossa

Answer 13

Boundaries: Bound by temporal lines above and zygomatic arch below
Roof(lateral wall)- temporalis fascia
Floor(medial wall)-pterion
Anterior wall- zygomatic process of frontal bone, zygomatic bone and maxilla

Contents: temporalis muscle which arises from the floor and overlying fascia

Question 14

Sensory stuff

Answer 14

Sensation- perception of a stimulus, which can be from external or internal environment; classified as special and general sensations.

Sensory receptors- structures detect stimuli; convert physical energies of stimulus to biolectric impulses (action potentials) that can be transmitted by sensory neurons; classified as mechano-, thermo-, chemo-, photo-, and nociceptors.

Sensory organs- body organ that houses particular sensory receptors; examples include the skin, eye, tongue etc.

Question 15

Types of sensory modalities

Answer 15

Special sensations: relayed by cranial nerves exclusively
1. Visual- sight
2. Olfactory- smell
3. Gustatory- taste
4. Auditory function- hearing
5. Vestibular functions- equilibrium of the head

General sensations: not limited to head and cranial nerves
1. Pain
2. Temperature - heat and cold
3. Tactile sensation - discriminate touch
4. Pressure
5. Stretch
6. Vibratory
7. Proprioception

Question 16

General outline of ascending (Sensory)relay pathways

Answer 16

1. Sensory receptors- detect stimulus
2. First order neurons- may be in contact with receptor and carries information to CNS
   
   • will terminate at the level of spinal cord or level of brainstem
   • cell body will be outside the CNS and will form sensory ganglion
     -synapse with 2nd order
3. Second order neuron- most likely multipolar
   -must decussate
   
   • reaches thalamus
   • synapse with 3rd order
4. Third order sensory neuron- from thalamus to cerebral cortex
5. Cerebral cortical region of perception