Cranial nerves Flashcards
Where are the receptors for CN I? where do their axons go?
Nasal mucosa; Axons travel through skull to the olfactory bulb; Information travels to medial temporal lobe of the cerebrum
loss of sense of smell
anosmia
- result from CN I damage
How do we lose function in CN I?
- Head injury – injure axons as they pass through the skull
- Smoking
- Excessive nasal secretions
- Chemicals
- These neurons can regenerate, and the sense of smell may return
What is the pathway that produce sight?
- Retina
- Optic Nerve - PNS
- Optic chiasm - Diencephalon
- Optic tract - CNS
- Lateral geniculate body/ nucleus – thalamus
- Primary Visual cortex
- Retinal field: middle of the eye and medial.
2. Retinal field: middle of the eye and lateral
- Nasal retinal fields
2. Temporal retinal field
R optic nerve carries info from? L optic nerve carries info from?
R eye; L eye
What fibers cross the midline in the optic chiasm?
Information from the nasal retinal field
The LGN and visual cortex receives information from the [ipsilateral/ contralateral] visual field.
Contralateral
R optic tract carries info from? L optic tract carries info from?
Vision from the L side of the world; Vision from the R side of the world
What visual field deficits will there be if there is injury to optic chiasm?
Bitemporal hemianopsia (nasal reticular fibers)
What is a common cause of bitemporal hemianopsia?
pituitary tumor
What visual field deficit will occur if there is injury anywhere past the optic chiasm?
homonymous hemianopsia - loss of cotralateral visual field from both sides
- Damage to optic radiations – may be just upper or lower contralateral quarter
What visual field deficit will you see if there is damage to the visual cortex?
homonymous hemianopsia with macular sparing
Where does CN III originate?
Midbrain
Where does CN IV originate?
Midbrain
- axons leave dorsal surface of brainstem
Where does CN VI originate?
Pons-medulla border
-cell bodies in pontine tegmentum
What are the somatic motor cell bodies of CN III parasympathetic cell bodies?
Oculomotor nucleus;
edinger-westphal nucleus in ciliary ganglia (constricts pupil, accommodation reflex)
What is CN VI’s function?
Abducens nerve - motor
- innervates lateral rectus muscle; abducts eye
What is the pupillary reflex stimulus and response? what is its afferent and efferent nerve?
Stimulus: Light that we shine into an eye
Response: pupil on that side constricts
Afferent nerve: Optic nerve
Efferent: Occulomotor
What is the consensual reflex stimulus and response? what is its afferent and efferent nerve?
Stimulus: shine light into an eye
Response: Constriction of the opposite pupil
Afferent nerve: Optic nerve
Efferent: Occulomotor nerve
What is the pathway for the pupillary and consensual reflex?
Retina –> Pretectal nucleus in midbrain –> parasympathetic nucleus of the oculomotor nerve –> Ciliary ganglion –> Pupillary sphincter
What S and S will be present in an oculomotor nerve lesion?
- Ptosis – drooping of upper eyelid
- Ipsilateral eye looks down and out (Difficulty moving eye medially)
- Double vision
- Loss of reflexes
- Pupillary dilation
What S and S will be present in an trochlear nerve lesion?
- Ipsilateral eye unable to look down and in.
- The involved eye looks up, so the patient will tuck their chin so both eyes look up
- The involved eye is rotated, so the patient will tend to tilt the head to the opposite side
What S and S will be present in an abducens nerve lesion?
- Ipsilateral eye looks inward
- Unable to abduct eye past midline
- Double vision
What is the corneal reflex stimulus and response? what is its afferent and efferent nerve?
Stimulus: touch the eye
Response: blink (constriction of orbicularis occuli)
Afferent nerve: ophthalmic division of trigeminal nerve
Efferent: facial nerve
What S and S will you see when there is damage to the facial nerve or nucleus of the facial nerve?
- damaging LMNs
- will see deficits on whole ipsilateral face (Bell’s Palsy affects axons of facial nerve)
What S and S will you see when there is damage to the UMNs of the facial nerve?
- corticobulbar tract damage
- deficits on lower contralateral face; The forehead will be spared
Deficit in mechanism conveying vibrations from air to the cochlea
Conduction deafness
- any time we have problems moving vibrations from the outside in; mechanical
Deficit in cochlea; transduction (changing the form of energy) of sound waves to action potentials
sensorineural deafness
- deficit in nerves
What is the main parasympathetic nerve?
Vagus
- cell bodies in medulla
- nucleus for head, neck, throacic organs, and superior abdominal organs
What is the vagus nerve motor for?
larynx and pharynx
- speech and swallowing
What are S and S of CN X lesion?
- Difficulty speaking
- Hoarseness
- Difficulty with swallowing
- Poor digestion – loss of parasympathetic innervation to GI tract
Where are the cell bodies of CN XI?
medulla - nucleaus extends to upper C spine
- motor to traps and SCM
What are the 3 main functions of cranial nerves?
- Motor innervation to muscles of face, eyes, tongue, jaw and two neck muscles.
- Somatosensory information from skin and muscles of face and TMJ, and special sensory information (olfactory, visual, auditory, vestibular, taste, and visceral sensations)
- Parasympathetic regulation of heart rate, blood pressure, digestion, breathing, and some eye muscles.
Where are deficits when lesions occur to cranial nerves in periphery due to trauma and inflammation? Lesion to cranial nuclei in CNS (stroke)? Lesion to upper motor neurons that control cranial nerves (stroke)?
- periphery = ipsilateral
- nuclei = ipsilateral (can help localize lesion in the brain)
- UMN = usually do not see significant weakness due to bilateral innervation of CN nuclei
What extra ocular muscles are controlled by CN III?
- Medial rectus (moves eye medially)
- Superior rectus (moves eye up)
- Inferior rectus (eye looks down)
- Inferior oblique
- Levator palpaebrae
- Pupillary sphincter
- Ciliary muscle
What extra ocular muscles are controlled by CN VI?
Lateral rectus (moves eye laterally, or abducts eye)
What extra ocular muscles are controlled by CN IV?
Superior oblique
- If eye adducted, pupil down and in
- If eye abducted, rotates eye
Reflex when we look at near objects (Pupils constrict; Eyes converge = Medial rectus m; Lens becomes more convex);
Requires visual cortex and frontal eye field in the frontal lobe
Accommodation
Space-occupying lesions in the cerebrum can compress the _______, interfering with the functioning of the oculomotor nerve.
midbrain
CN that provides sensory innervation to the face, mucous membranes of head, and meninges
V - trigeminal
- ophthalmic, maxillary, and mandibular (only division with motor)
What are the nuclei of the trigeminal nerve and where are the located?
- Mesencephalic trigeminal nucleus – midbrain (Unconscious proprioception)
- Chief sensory nucleus – mid pons
- Spinal trigeminal nucleus - Caudal pons to upper cervical cord
What are reflexes controlled by the trigeminal nerve?
- Corneal reflex - ophthalmic division
2. Masseter (Jaw jerk) reflex - mandibular division
Where does the facial nerve exit? where are its cell bodies? what is its motor control? sensory control?
- Pontomedullary border
- Cell bodies in pons
- Motor = Muscles of facial expression and Glands of head and neck
- Sensory = Taste on anterior 2/3rd of tongue
Where does the vestibulocochlear nerve exit?where are its cell bodies? what are its functions?
- Pontomedullary border
- Cell bodies in pons
- Two Divisions:
Vestibular – posture and equilibrium
Auditory - hearing
sensory nerve
What can occur with damage to the vestibular nerve?
- Vertigo – sensation of movement
- Nystagmus – involuntary back and forth movements of eyes
- Disequilibrium – loss of sense of balance
Where is the glossopharyngeal nerve? what is its motor control? sensory control?
- medulla
- Motor = Muscles of throat, Parotid gland
- Sensory = Posterior tongue, Skin of external ear, Mucosa of mouth – afferent limb of gag reflex
What deficits will you see with LMN damage of CN XI? UMN damage?
LMN damage – ipsilateral paralysis
UMN damage – hypertonia and mild to moderate paresis with large lesions
Where is the hypoglossal nerve? what is its motor control?
- Medulla
- Motor to intrinsic and extrinsic muscles of ipsilateral tongue
What deficits will you see with LMN damage of CN XII? UMN?
LMN injury – atrophy on involved side, tongue deviates towards involved side
UMN injury – mostly bilateral, may have some contralateral weakness
What cranial nerves are important in speaking?
- damage to these causes dysarthria Larynx and soft palate – X Jaws – V Lips – VII Tongue – XII
What cranial nerves are important in swallowing?
Mouth and jaw muscles – V, VII, IX, X, XII
Pharynx, Larynx – IX, X
Esophagus and GI tract – X
What CN deficits can signal injury to other regions of the NS?
- Pupilary reflex – increased intracranial pressure
2. Bitemporal hemianopsia – pituitary tumor
