EXAM 2 - Cranial Nerves & Head Structures

Cranial Nerves

The brain's way to communicate with the rest of the

body

all 12 cranial nerves arise from what and exit the cranium via what?

base of the brain and the foramina

all 12 cranial nerves lead mostly to

Lead mostly to sense organs and muscles in the head and neck 1 exception: vagus n - to the whole body

Cranial Nerve Pathways

Many begin in nuclei of the brainstem

⚫ Sensory fibers begin in receptors located mainly in

head and neck and lead mainly to the brainstem

⚫ Most cranial nerves carry fibers between brainstem

and ipsilateral receptors and effectors

Lesion on the L side of the brain stem causes a defect in what side of the body?

left (same side) - Most cranial nerves carry fibers between brainstem and ipsilateral receptors and effectors

Exceptions to cranial nerves carrying fibers between brainstem and ipsilateral receptors and effectors

1. optic nerve - 1/2 (nasal) fibers cross (partial decussation)

2. trochlear nerve - all contralateral

Sensory CN

I, II, VIII

1,2,8

Motor CN

III, IV, VI, XI, XII

3,4,6,11,12

Mixed CN

V, VII, IX, X

5,7,9,10

CN1

olfactory nerve

Sensory Nerve - for SMELL only. Originates in the nasal mucosa as fascicles of the olfactory n. Passes thru foramina in the cribriform plate of the ethmoid bone. Ends at the olfactory bulb.

olfactory tract

the path along which the olfactory receptors send their electrical messages to the brain.

olfactory bulb

a brain structure located above the nasal cavity beneath the frontal lobes

CNII

Optic Nerve

Sensory for VISION only

partial decussation at the optic chiasm

optic chiasm

point at which optic nerve fibers cross in the brain

optic tract

How information from the optic nerve travels to the thalamus.

mixed fibers medially and laterally

CN III

Oculomotor Nerve

motor only

Innervates extraocular muscles (Superior Rectus, Medial Rectus, Inferior Rectus, Inferior Oblique).

Action: move eyeball up, down, and medially

control iris, lens, and upper eyelid

injury to CN III

-drooping eyelid (ptosis), pupil dilation, in ability to move eye in certain directions

CN IV

Trochlear Nerve

motor only

innervates contralateral superior oblique muscle

Motor: abducts, depress, and inferiomedially moves eye (intorsion)

injury to the trochlear nerve

effects are CONTRALATERAL

-paralysis of superior oblique

-impaired ability to turn the affected eyeball inferomedially (leads to extorsion)

- diplopia (double vision)

- Clinically: inability to look down when eye is adducted

CN V

Trigeminal Nerve largest of the CN with a wide sensory distribution to the face and scalp via three branches

"great sensory nerve"

MOST IMPORTANT SENSORY N OF FACE (this is the dentist nerve)

mixed(sensory and motor)

Trigeminal (CN V)

⚫ 3 branches (V1, V2, V3)

Sensory: forehead, face, jaws (V1, V2, V3)

⚫ Supply dermatomes of face (Posterior region of the head via dorsal roots of cervical spinal nerves)

Motor: (V3) for motor outflow to the muscles of

mastication (chewing)

"Oh My Molars"

V1 (Ophthalmic nerve) Fxn

general sensory in forehead region

V2 (Maxillary nerve) Fxn:

general sensory below the eye

V3 (Mandibular nerve) 2 Fxn's

1. Sensory for the lower jaw/mandible and tongue

2. motor innervation of muscles of mastication

Clinical Application - sinus infections

most commonly in the maxillary sinus

-common complaint is a aching of molar teeth because the V2 branches (superior alveolar nerve) innervates the sockets/alveoli of the teeth and mucous membranes of sinuses

- pressure in the sinuses can radiate into the teeth and cause horrible tooth ache in molars because of this overlapping innervation

Trigeminal Nerve-3 Divisions

Cranial Nerve V

1. Ophthalmic

2. Maxillary

3. Mandibular

Clinical Highlight

⚫ Trigeminal Neuralgia (tic douloureux)

Recurring Episodes of intense stabbing pain where CNV innervates (mouth, nose)

Even small stimuli/triggered by:

- light touch

- drink Hot/cold water

- washing face

overactive nerve leads to intense pain to the point of severing the nerve

CN VI

Abducens Nerve

motor only

Innervates the lateral rectus muscle

action: moves the eye laterally

Injury in CN VI

results in an inability to the move the eye laterally, eye appears to move medially

CN VII

Facial Nerve

"Great motor nerve"

- special motor outflow to facial muscles (muscles of facial expressions)

- special sensory to the taste on anterior 2/3 of tongue

5 Main branches of the N

5 main branches of CN VII

branch division occurs deep to the R/L parotid gland

Temporal

Zygomatic

Buccal

Mandibular

Cervical

"those zany biologists memorize cranial nerves"

Injury to the CN VII

lose taste of anterior 2/3 tongue, lose ability to move facial muscle

how to test motor function of CN VII

Ask pt. to wrinkle forehead. Have pt. shut eyes tightly while I try to open them. Raise eyebrows. frown. puff out cheeks. Ask pt. to smile. See if pt. can do these and if there is asymmetry.

Bell's Palsy

paralysis of facial n

- cause: stroke, aneurysm, virus (stress reactivates virus leading to inflammation around facial nerve and paralysis)

Can be pregnancy induced (but cant treat while pregnant)

- drooping of the face on one side

- painful onset

- lost sense of taste (sweet and salty)

- everything is bitter

- problems closing eye, mouth (sipping straw, mouthwash, brushing teeth

- within a year of onset, what has not been repaired is most likely gone

-treatment with painkillers, steroids, antivirals

CN VIII

Vestibulocochlear Nerve

sensory (only) cranial nerve within the labyrinth that consists of two branches, the vestibular nerve (for balance) and the cochlear nerve (for hearing)

injury to CN VIII

nystagmus, deafness, and others

CN IX

Glossopharyngeal Nerve

mixed (sensory and motor)

Sensory: taste for posterior 1/3 of the tongue (bitter)

Motor: control of swallowing, salivation, gag reflex, controls BP and respiration

Injury to CN IX

Loss of bitter taste, impaired swallowing, impaired ability to regulate BP and respiration, impaired gag reflex

CN X

Vagus Nerve

mixed nerve (sensory and motor)

Wondering Nerve

- leaves the head and neck

HUGE Distribution

- cardiac

-respiratory

- GI

- reproductive

- spleen

- urinary

-etc

Injury to 1 and/or both of CN X

1 - impaired swallowing, hoarse voice, and issues with everything it innervates

Damage to both Vagus N's = DEATH

vagal ganglion

CN XI

Accessory Nerve

Motor: muscles move head, neck and shoulder

Goes down to major muscle: TRAPEZIUS and sternocleidomastoid

testing CN XI

shrug shoulders, turn head

testing the muscles allows to test nervous system (CN XI)

Injury to CN XI

impaired muscle movements (movement of head and neck)

head will turn towards one side

Hypoglossal Nerve CN XII

Motor: tongue movement for speech sound articulation, swallowing, and food manipulation

ipsilateral atrophy of CN XII

damage on one side leads to tongue deviation to that injured side

damage to both means can't stick out tongue at all

Scalp

Continuous with the skin of the neck

- Spans: from occipital bone to frontal bone, from temporal to zygomatic arch

5 layers of scalp

Skin

Connective tissue

Aponeurosis

Loose areolar tissue

Pericranium

skin of scalp

thin

highly vascularized

(sebaceous glads)

connective tissue of scalp

thick and dense

dense connective tissue

Aponeurosis of scalp

epicranial aponeurosis

thickening of connective tissue, flattened tendon/fascia sheath

Loose areolar tissue of scalp

loose and allows for free movement of skin on scalp

Pericranium of scalp

Attached to bone itself (periosteum)

Temporomandibular (TMJ) Joint

Modified hinge—synovial

Mandibular elevation

Mandibular depression

Mandibular protrusion/retrusion

Mandibular dislocation

what is the articulation of the TMJ

condyloid process of the mandible articulates with the mandibular fossa of the temporal bone

Elevation TMJ Muscles

this is closing mouth:

temporalis

masseter

med. pterygoid

Depression TMJ muscles

this is opening mouth:

lateral pterygoids

infrahyoid

mylohyoid

GRAVITY is primary mover (sleeping in car and mouth drops open)

protrusion TMJ muscles

masseter

med and lat pterygoids

retrusion TMJ muscles

temporalis-main one

masseter

lateral movements TMJ muscles

temporalis of the same side

pterygoid of the opposite side

Vascular Supply of the face

supra/infra orbital

facial

maxillary

lingual

temporal

occipital

what is special about the vasculature of the nasal cavity

highly vascular nature of the nasal cavity

Venous Drainage and arteries of face

supra/infra orbital

facial

maxillary

lingual

temporal

occipital

Facial veins drainage

-the primary drainage of the face

-joins with the retromandibular v (anterior division) to

empty into the internal jugular v in the neck

Danger Triangle

⚫ Margins:

⚫ Why "Danger"???

bridge of nose to upper lip

highly vascular supply meaning easier to spread infection

Salivary Glands

3 paired:

parotid, sublingual, and submandibular glands

Parotid Gland

Largest

Clinically important: many structures pass through or are associated with it

- ex. Facial nerve branches all pierce it

Location - "sandwiched" between: mandibular rami and the mastoid process of temporal bone

Childhood Disease with parotid gland

mumps

- unilateral or bilateral

Muscles of Facial Expression innervation

All innervated by the facial nerve (CN VII)

muscles of mastication

masseter, temporalis, medial and lateral pterygoids

Origin and insertion of masseter

Origin: zygomatic arch

Insertion: mandible

action: elevate, protract, and retract mandible

innervation: trigeminal, V3

Origin and insertion of temporalis

origin: temporal fossa

insertion: mandible

action: elevate and retract mandible

innervation: All trigeminal, V3

Origin and insertion of medial pterygoid

origin: pterygoid plate

insertion: mandible

action: elevate and protract mandible, and lateral movement of opposite side of mandible

innervation: All trigeminal, V3

Origin and insertion of lateral pterygoid

origin: pterygoid plate

insertion: mandible

action: depress and protract mandible, and lateral movement of opposite side of mandible

innervation: All trigeminal, V3

extrinsic muscles of tongue

Genioglossus

Hyoglossus

Styloglossus

Palatoglossus

action of genioglossus

action: depresses and protrudes tongue

innervation: CN XII (hypoglossal)

action of hyoglossus/hyoglossal

depresses tongue

innervation: CN XII (hypoglossal)

action of styloglossus/styloglossal

retrude and curls the tongue

innervation: CN XII (hypoglossal)

action of palatoglossus/palatoglossal

elevates posterior tongue to palate

innervation: CN X (Vagus)

intrinsic & extrinsic tongue muscles

Extrinsic - originate outside of the tongue and insert on the tongue

intrinsic = Origin and insert within tongue

Extraocular Eye Muscles

superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, inferior oblique

Innervation of EOM

[LR6(SO4)]3

Superior oblique

Depresses eye and turns it laterally

CN IV (trochlear)

Inferior oblique

Elevates eye and turns it laterally

III (oculomotor)

Superior rectus

elevates eye; III oculomotor

inferior rectus

depresses eye; III oculomotor

lateral rectus

moves eye laterally (VI abducens)

medial rectus

moves eye medially (III oculomotor)

Sclera

white of the eye

choroid

middle, vascular layer of the eye, between the retina and the sclera

retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

macula lutea

a yellowish central area of the retina that is rich in cones and that mediates clear detailed vision

fovea centralis

tiny pit or depression in the retina that is the region of clearest vision

optic disc

Region at the back of the eye where the optic nerve meets the retina. It is the blind spot of the eye because it contains only nerve fibers, no rods or cones, and is thus insensitive to light.

ciliary body

ring of tissue behind the peripheral iris that is composed of ciliary muscle and ciliary processes

suspensory ligaments

hold the lens in place

iris

a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

cornea

The clear tissue that covers the front of the eye

pupil

the adjustable opening in the center of the eye through which light enters

lens

the transparent structure behind the pupil that changes shape to help focus images on the retina