Exam #2: Cranial Nerves I Flashcards
In regards to the functional components of cranial nerves, what is the difference between general & special fibers?
General= functional components present in typical spinal nerves AND cranial nerves
Special= functional components present ONLY in cranial nerves
What does GSA stand for? What functional components are carried by these fibers?
“General Somatic Afferent”
- Touch
- Pressure
- Pain
- General propcioception
- Temperature
*All FROM somatic structures
What does GVA stand for? What functional components are carried by these fibers?
“General Visceral Afferent”
- Pressure
- Pain
*All FROM visceral structures
What does GVE stand for? What functional components are carried by these fibers?
“General Visceral Efferent”
- Motor impulses TO visceral smooth muscle/ cardiac muscle
- PNS**
What does GSE stand for? What functional components are carried by these fibers?
“General Somatic Efferent”
- Motor impulses TO skeletal muscles
What does SVA stand for? What senses are these fibers associated with?
“Special Visceral Afferent”
- Olfaction
- Gustation
What does SSA stand for? What senses are these fibers associated with?
“Special Somatic Afferent”
- Sight
- Hearing
- Equilibrium
What does SVE stand for? What do SVE fibers innervate?
“Special Visceral Efferent”
- Skeletal muscle (derived from the pharyngeal arches)
What cranial nerves contain GSE fibers?
III, IV, VI, XII
What are somatic efferent nerves?
Cranial nerves that carry GSE fibers
What functional component is CN I associated with?
SVA (smell)
What cranial nerves carry SVA-taste-fibers?
VII
IX
X
What are branchiometric muscles?
Striated muscles of the head and neck that developmentally come from branchial arches i.e. pharyngeal arches.
What cranial nerves are referred to as the “branchiomeric nerves?”
V
VII
IX
X
Which cranial nerve is the only cranial nerve to have a true pain nucleus?
Trigeminal (V)
What is the function of CN I? What type of fibers does the Olfactory Nerve have?
Smell i.e. “Olfactory Nerve”
- SVA
What is the olfactory mucosa?
Most superficial layer of the olfactory epithelium
Where are the olfactory nerves located?
- Lateral wall of the nasal cavity
- Nasal septum
What is the function of the basal cells in the olfactory epithelium?
Stem cell precursors of olfactory receptors
What is the function of the sustentacular cells in the olfactory epithelium?
Support
What is the function of Bowman’s glands in the olfactory epithelium?
Secretion of serous fluid
What type of cells are olfactory receptors?
Modified bipolar neurons
What structure do the axons of the olfactory receptors pass through to enter the brain?
Cribriform plate of the ethmoid bone
What is unique about olfactory receptor cells?
1) Only neurons exposed to the exterior environment
2) Nerve cell bodies located in epithelium vs. ganglion
3) Regenerated every 30-60 days
4) Slowest conducting/ unmyelinated axons of the nervous system
What is the first order neuron of the olfactory pathway?
Olfactory receptor
What is the second order neuron of the olfactory pathway?
Olfactory bulb
What do the axons of the olfactory receptors bundle together to form?
Olfactory fila, which collectively= CN I
**It is the olfactory fila that actually pass through the cribriform plate
Where do the axons of the olfactory bulbs run? What structure do these neurons give off collaterals to?
Axons run in the olfactory tracts & give off collaterals to the “Anterior Olfactory Nucleus”
What do the olfactory tracts divide into?
Olfactory stria (medial & lateral)
*****Note that the lateral olfactory stria is the major pathway of the olfactory system
Where do the olfactory stria project? Why is this unusual?
Olfactory stria bypasses the thalamus & project to the:
1) Amygdala 2) Olfactory cortex
Why is it important that the Olfactory Tract projects to the Amygdala?
The amygdala functions in learning, memory, emotions, & drives
- Each scent has an “emotional tag” b/c of this projection.
Where does the primary olfactory cortex project?
1) Hypothalamus= endocrine & autonomic functions
2) Amygdala
3) Cortical areas associated with memory
4) Olfactory association cortex
What is a common cause of damage to the axons of olfactory receptors?
Head trauma, which causes:
1) Direct trauma to the ethmoid bone
2) Shearing forces on the axons of the olfactory receptors as they pass through the cribriform plate in the ethmoid bone
What happens as a result of a lesion to the axons of the olfactory receptors?
Ansomia= total loss of smell
Hyposmia= partial loss of smell
Parosmia= distorted perception of smell
What are the receptors for the visual system?
Rods
Cones
What is the first order neuron for the visual pathway?
Bipolar neurons in the retina that rods & cones synapse on
What are the second order neurons for the visual system?
Ganglion cells residing in the retina
Where do the axons of the ganglion cells converge?
At the back of the eyeball to form the Optic nerve (CN II)
What is unique about the optic nerve?
The optic nerve is considered to be part of the CNS & is myelianted by oligodendrocytes
Clinically, why is it important that the optic nerve is myelinated by oligodendrocytes?
Multiple Sclerosis–optic will be affected
What is the difference between the optic nerve & optic tracts?
- Optic nerve is formed by the axons of ganglion cells from the retina
- Optic nerves decussate at the optic chiasm
- After the optic chiasm, referred to as the optic tracts
Where do the axons of the 2nd order neurons (ganglion cells) of the optic tract terminate?
1) Lateral geniculate nucleus (LGN) of the thalamus*****
2) Superior colliculus
3) Pretectal area
4) Hypothalamus
What is the function of the superior colliculus?
Reflex head & eye movements in response to sensory stimulation
What is the function of the pretectal area?
Pupillary constriction reflex
What are the third order neurons of the visual pathway?
LGN
What do the axons of the LGN give rise to?
Geniculocalcarine tracts that go to the primary visual cortex of the occipital lobe
What artery supplies the visual cortex (calcarine sulcus)?
Mostly the Posterior cerebral artery (PCA)
*****MCA sends anastamosis
If a thrombus occludes the right PCA, how will the lesion manifest?
“Left homonymous hemianopia w/ macular sparing”
- Left half of visual field in each eye
- Macular region spared
Why is there macular sparing in w/ PCA lesion?
Anastamosis from the MCA
What are the functional components of CN XI?
SVE/GSE= Trapezius, SCM, laryngeal muscles
GP= general proprioception to Trapezius & SCM
What fibers of CN XI supply the laryngeal muscles?
Abberant vagal fibers
What nucleus do the abberant vagal fibers arise from? Where?
Nucleus ambiguious in the MEDULLA
What nucleus do the fibers of CN XI arise from? Where?
Spinal accessory nucleus in the SPINAL CORD
Describe the path of the Spinal Accessory Nerve from the spinal cord.
1) C1-C5/6 in cord
2) Enter foramen magnum
3) Join abberant vagal
4) Exit Jugular foramen
5) Innervation:
- Abberant vagal= laryngeal muscles
- Spinal accessory= SCM & Trapezius
Which SCM contracts to turn the head to the right?
Left
What happens when there is a Spinal Accessory nerve lesion?
Scapular winging
How does lesion of the long thoracic nerve compare to lesion of the accessory nerve?
BOTH produce scapular winging, but each is more prominent with different actions:
- LT= pushing against object & anterior elevation of affected arm
- CN XI= ABduction of affected arm
What functional component does CN XII contain?
GSE i.e. general somatic efferents or motor innervation to the intrinsic & extrinsic muscles of the tongue
Where does the hypoglossal nerve originate?
Hypoglossal nucleus, which is located in the groove between the olive & the pyramid
What are the manifestations of a lesion to CN XII at rest?
- Hemiparalysis on ispsilateral side
- Atrophy
- Fasiculations
What are the manifestations of a LMN lesion to CN XII w/ protrusion of the tongue?
Tongue deviation to SIDE OF LESION
What is the manifestation of left optic neuritis or damage to the left optic nerve?
Total blindness in the left eye
What is the manifestation of a lesion in the left angle of the optic chasma?
Ipsilateral Nasal Hemianopia
- No perception of left nasal field
What is the manifestation of a bilateral ICA aneurism?
Binasal Heteronymous Hemianopia
- No perception of left or right nasal fields
What is the manifestation of a pituitary tumor?
Bitemporal Heteronymous Hemianopia
- No perception of left or right temporal fields
What is the manifestation of a lesion to the left optic tract?
Right Homonymous Hemianopia
What is the manifestation of a lesion to the left Meyer’s Loop?
Right Upper Homonymous Quadrantanopia
- Right “Pie in the Sky” loss
What is the manifestation of a lesion to the Inferior Division of the Geniculocalcarine Tract?
Right Lower Homonymous Quadrantanopia
- Right “Pie on the Floor” loss
What is the general pattern for visual pathway lesions?
- Optic Chiasm & Distal= Heteronymous
- Proximal to optic chiasma= Homonymous
What is the manifestation of a lesion to all the left optic radiation fibers in the occipital lobe?
Right Homonymous Hemianopia
