Assessing Specific Cranial Nerves I and II Flashcards
C.N rarely tested in a clinical practice. Only done in response to a specific complaint rather than a screening test. Easily tested when done.
C.N. I
Most recognizable smells require olfaction, however, some strong irritating agents, like ______, can be recognized by the __________ and do not require an olfactory pathway
Ammonia
Nasal epithelium
T/F The olfactory nerve is considered a peripheral nerve
FALSE.
It is considered a CNS tract that terminates in the olfactory bulb
Second order ______________ (true olfactory nerves) pierce the cribiform plate of the ethmoid bone and terminates in the mucus membrane that lines the nasal cavity.
Ganglion nerve cells
What must happen to the molecules in the nasal cavity before a particular smell is able to reach the nerve endings?
The molecules must dissolve into mucus overlying the cribriform plate and supply chemical stimulation to the nerve endings in that location
Complete loss of smell
Anosmia
T/F Anosmia is a classical sign of a cortical lesion
FALSE
Anosmia is usually not indicative of a cortical lesion
Symptoms usually indicative of a cortical lesion
Perversion, hallucinations or diminution of smell
Anosmia is more indicative with these conditions
- Viral infections
- Allergic rhinitis
- Aging
- Head trauma (fracture of the cribriform plate)
- Rhinorrhea (CSF drainage)
- Backwash meningitis
T/F Neurons that attach to the cribriform plate can be sheared off even in the absence of fracture
True.
Head and neck injuries can cause the shearing off of nerves that transverse the cribriform plate
T/F The sense of smell may return secondary to injury, but often it doesn’t
True
Lesion of the __________ in the anterior temporal lobe may cause hallucinations of smell associated with strong feelings of _____ and are termed ________ or seizures
Uncinate gyrus
Deja vu
Unicinate fits
A decreased sense of smell
Hyposmia
An increased sense of smell
Hyperosmia
A perversion of smell
Parosmia
Abnormally disagreeable smell
Cacosmia
Procedure to check for sense of smell
- One nostril must be occluded
- Instruct the patient to close his or her eyes
- The examiner should ask the patient to identify when he smells the object and what smell he is identifying
- The substances should be non-irritating smells such as peppermint, coffee, lemon, or pine
- When checking the other nostril, a second substance should be utilized
Common causes of bilateral anosmia
- Blocked nasal passage
- Common cold
- Trauma
- Relative loss occurs with aging
Primary neurons of C.N. I
Unmyelinated processes of the ciliated receptors in the upper part of the nasal mucosa are gathered into about 20 branches which pass through the cribriform plate of the ethmoid bone to the olfactory bulb.
Secondary neurons of C.N. I
Myelinated processes of the bipolar cells of the bulb from the olfactory tract and terminate in the primary olfactory cortex
Primary olfactory cortex
Periamygdaloid cortex
Prepiriform cortex
Tertiary neurons of C.N. I
Neurons extend from the primary olfactory cortex to the entorhinal cortex, lateral preoptic area, amygdaloid body, and medial forebrain bundle
Brodmann area for the entorhinal cortex
Area 28
Association fibers to the ____________ and ________ pass directly as 3rd order neurons from the anterior perforated substance and indirectly from the ________ via the fornix and olfactory projection tracts through the ______________ and anterior nuclei of the _____________
Tegmentum Pons Hippocampus Mammillary bodies Thalamus
T/F Reflex connections established with nuclei of the other cranial and spinal nerves may be functionally significant in swallowing and digestion
True
T/F Unlike C.N. I, C.N. II is a true nerve
FALSE.
C.N. I and C.N. II are both not true nerves but instead are fiber tracts of the brain
1st order neurons of C.N. II
Rods and Cones
3rd order neurons of C.N. II
Ganglion cells
Cells that connect 1st order and 3rd order neurons in C.N. II
Bipolar cells
What forms the optic nerve?
Myelinated axons arising from ganglion cells
At the ________, the nerve fibers from the half of each retina decussate. The temporal fibers from each half of the retina are uncrossed.
Optic chiasm
Fibers from the ipsilateral halves of the retina form the optic ________, passing along to the _________ geniculate bodies, ________ colliculi, and ________ region
Tract
Lateral
Superior
Pretectal
Tract that contains the 4th order neurons from the lateral geniculate bodies and passes to the occipital cortex
Geniculocalcarine tract
Fan-like radiating portion that curves around the inferior horn of the lateral ventricle
Meyer’s Loop
Central connections of the optic nerve
- Pretectal region to the Edinger-Westphal nucleus via the posterior commissure
- Superior collicul via the tectobulbar and tectospinal tracts to other cranial and spinal nuclei
- Occipital cortex to other cortical and subcortical areas
Fibers from this region are responsible for the simple and consensual light reflexes
Pretectal region
Tract concerned with visual perception. A continuation of the lateral geniculate body.
Geniculocalcarine tract
Reflex fibers pass from the occipital cortex to other cortical centers and to the superior colliculi and thus through the tectobulbar and tectospinal tracts to:
- Cranial and spinal nuclei for involuntary reflexes
- Pontine nuclei, via the corticopontine tract for postural reflexes
Retinal area for central vision
Macula
Small central pit composed of closely packed cones, where vision is sharpest and color discrimination most acute
Fovea centralis
Cells stimulated by relatively high intensity light and are responsible for sharp vision and color discrimination
Cones
Cells that react to low intensity light and function in twilight and night vision
Rods
T/F Cones are more numerous in the retina than rods
FALSE.
Rods are more numerous
Lesion of the optic nerve or tract, the most common cause is multiple sclerosis
Retrobulbar neuritis
Lesion includes various forms of tetinitis
Optic or bulbar neuritis
Commonly seen symptom of increased intracranial pressure due to brain tumors, abscesses, hemorrhage, hypertension, and other causes
Papilledema (chocked disc)
Associated with decreased visual acuity and a change in the color of the optic disc to light pink, white, or gray
Optic atrophy
Caused by processes that involve the optic nerve and do not produce papilledema
Primary optic atrophy
A sequel of papilledema
Secondary optic atrophy
May be due to tabes dorsalis , multiple sclerosis, or hereditary
Primary (simple) optic atrophy
May be due to neuritis, glaucoma, or increased intracranial pressure
Secondary optic atrophy
Corneal scars, arteriosclerotic changes, and tumors are all possible examples of this
Opacities of the lens
May be caused by tumors at the base of the frontal lobe and is characterized by ipsilateral blindness and anosmia (with atophy of the optic and olfactory nerve) and contralateral papilledema
Foster-Kennedy Syndrome
Cerebromacular degeneration with severe mental deficiency occurring in Jewish families and is associated with blindness, optic atrophy, and a dark cherry red spot in place of the macula lutea
Amaurotic familial idiocy (Tay-Sachs disease)
Pupil that reacts only to accomodation. It has neither a direct or indirect reaction to light. It was once considered pathognomonic of tabes dorsalis (neurosyphilis), but it has now been found to occur as a diabetic complication
Argyll-Robertson pupil
Characterized by a tonic pupillary reaction and the absence of one or more tendon reflexes. The pupil is myotonic which a very slow, almost imperceptible contraction to light and in near vision, a slower dilation upon removal of the stimuli
Holmes-Adie syndrome
Deviation of bilateral eye alignment.
Heterotropia
Outward/lateral deviation of the eye
Exotropia
Inward/medial deviation of the eye
Esotropia
Upward deviation of the eye
Hypertropia
Downward deviation of the eye
Hypotropia
