Exam 1: Unit II: CNs Related to Smell, Vision, and Ocular Movement (I,II,III,IV,VI) Flashcards
(119 cards)
1
Q
Where are olfactory neurons found?
A
in olfactory epithelium lining superior part of the nasal cavity and a thin layer of mucus covers this epithelium
2
Q
What are the two neurons involved in the pathway for CN I (olfactory N.)?
A
- Primary sensory neurons called olfactory neurons (bipolar)
- Secondary sensory neurons called Mitral Cells
3
Q
What are olfactory neurons supported by? And what do olfactory “hairs” function as?
A
supported by “supporting cells” and olfactory “hairs” function as receptors
4
Q
The axons (central processes) of olfactory neurons are collected into __________ that convey information to the ________.
A
10-20 olfactory nerves; convey info to olfactory bulb
5
Q
T/F. Olfactory neuron axons are myelinated by Schwann cells.
A
False, they are covered by Schwann cells (every PNS neuron is), but they are UNmyelinated
6
Q
What do olfactory nerves pass through and what do they synapse on? What are formed at the synapse?
A
pass through cribiform plate of ethmoid bone and synapse on dendrites of mitral cells, where synaptic glomeruli are formed
7
Q
Where are the cell bodies for Mitral cells located?
A
in olfactory bulb
8
Q
T/F. Mitral cells relay information anterior via the olfactory tract.
A
False. They relay information posterior via the olfactory tract
9
Q
Where do mitral cells split into medial and lateral olfactory striae (branches)?
A
at the anterior perforated substance
10
Q
What is the path for medial stria fibers of the mitral cell?
A
cross midline via anterior commissure and travel to opposite olfactory bulb to synapse on other mitral cells
11
Q
What is the path for lateral stria fibers of the mitral cell?
A
carry info to primary olfactory cortex; containing the periamygdaloid and prepirifrom area, including uncus (BMA 34)—on medial aspect of temporal lobe
~there is a secondary olfactory cortex
12
Q
What does the secondary olfactory cortex contain?
A
entorhinal area, located in parahippocampal gyrus (BMA 28)
13
Q
When testing smell of a patient what does a clinician need to take into consideration?
A
- make sure no allergies
- cover patients eyes
- use one nostril at a time
- good options: mint, PB
14
Q
What is the word for loss of smell or lack of smell?
A
ansomia
15
Q
What are some other clinical considerations when it comes to the olfactory system?
A
- ansomia
- skull fractures from trauma
- CSF leakage–> halo sign
16
Q
What are the only fibers that are contained in the anterior commisure?
A
the medial stria fibers from the mitral cells, part of the olfactory tract
17
Q
Do we segregate smell?
A
NO. Due to the medial strai fibers from the mitral cells in the olfactory tract crossing over to other olfactory bulb
18
Q
What are two other pathways associated with smell?
A
- Terminal Nerve
2. Vomeronasal Nerve
19
Q
T/F. The vomeronasal Nerve is very well developed in humans.
A
False. It is poorly developed in humans; thought to be important in tracking prey
20
Q
What structure does the Terminal Nerve arise from? What is its function?
A
from nasal septum– has autonomic fxn (“smell fear”)
21
Q
What are the three layers (tunics) of the eye?
A
Outermost = Fibrous tunic Middle = Vascular tunic Innermost = Retina of (Nervous tunic)
22
Q
What does the Fibrous layer of the eye consists of?
A
- sclera (white)
- cornea (clear)
(outermost layer)
23
Q
What does the Vascular layer of the eye consists of?
A
- ciliary body
- iris
- choroid
(middle layer)
24
Q
What are the 10 layers of the retina (nervous tunic) from when light hits and info carried out of eye?
A
(light hits first)
- Pigmented layer
- Rod and Cone receptors
- External limiting membrane
- Outer nuclear layer
- Outer plexiform layer
- Inner Nuclear layer
- Inner plexiform layer
- Ganglion cell layer
- Nerve fiber layer
- Internal limiting membrane
25
The pigmented layer of the retina is adjacent to what structure?
the choroid
26
What are the photosensitive segments of the retina?
the rods and cones receptors
27
What does the outer nuclear layer of the retina contain?
rod and cone cell bodies
28
What occurs in the outer plexiform layer of the retina?
rods and cones synapse with bipolar cells
29
The inner nuclear layer of the retina contains cell bodies of what cells?
bipolar cells
30
What occurs in the inner plexiform layer of the retina?
bipolar cells synpase with ganglion cells
31
What is in the ganglion cell layer of the retina?
ganglion cell bodies
32
What does the nerve fiber layer of the retina contain?
retinal ganglion cell axons--> they are NOT myelinated
33
What is the internal limiting membrane of the retina?
is a glial boundary separating retina from vitreous body
34
What are the photoreceptors?
Rods and Cones
- distal end (called "outer segment"); closest to choroid
- is either cylindrical (cone) or tapered (rod)
35
What are the types of cones found in the retina? What is the function of cones?
Red, Green, Blue
| - fxn = receive color info; require adequate light
36
Where are cones more concentrated in the retina?
toward the center; fovea centralis
37
What is the fovea centralis?
point of retina of clearest vision, where we focus light; CONES only!
38
What is the function of Rods? Where are they located in retina?
sense only light vs. dark (detect shades of grey)
No rods in fovea; periphery of retina = almost all rods
39
Describe some facts on color blindness.
- differ forms
- most sex-linked, recessive trait on X chromosome
- MC in males
- due to lack of certain cones or number of
40
Depolarized photoreceptors relay info to bipolar cells by synapsing in what layer?
the outer plexiform layer
41
Bipolar cells in the retina are found in what layer?
inner nuclear layer
42
In the retina, what is the path of just the cells from when light hits them to where info is carried out of eyeball?
rod/cone photoreceptors --> bipolar cells --> ganglion cells that synapse in 1 of 3 places
43
In the retina, what cells do bipolar cells relay info to? Where does this synapse occur?
to ganglion cells; in inner plexiform layer
44
Where do axons from the ganglion cells (of the retina) located and where do they go/ what is the path to when they reach the optic chiasma?
axons in Nerve Fiber layer; go toward optic disc --> then leave eyeball and carried to optic nerve --> enter skull via optic canal --> unite to form optic chiasma
45
Are the nerve fiber layer axons myelinated?
No
46
Are optic nerve axons myelinated? If so, what cells myelinate them?
YES; myelinated by interfasicular oligodendrocytes
47
Are the axons of ganglion cells PNS or CNS? What about the optic nerve fibers?
ganglion cells = PNS
| optic nerve = CNS
48
In the optic chiasma, fibers from the ______ side of each retina will cross, while fibers from the ______ side of the retina will not cross.
medial (nasal); lateral (peripheral)
49
What is formed after the optic fibers split at the optic chiasma?
optic tracts
50
What structure does the optic tract travel around and what are the 3 places it can synapse?
```
travel around cerebral peduncles
Synapse:
1. Lateral geniculate body (LGB)
2. Superior colliculus
3. Pretectal nucleus in midbrain
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51
Where do the majority of the optic tracts synapse? (which of the possible 3 places it can)
in LGB
52
Where is information relayed to after is synapses in the LGB? Be specific.
to cerebral cortex in occipital lobe (BMA 17)
53
Where will info be relayed to from fibers of the optic tract that synapse in the Superior colliculus?
Tectospinal tract
54
What two muscles are influenced by the tectospinal tract?
SCM and trapezius
55
What do fibers of the optic tract that synapse in the Pretectal nucleus of the midbrain deal with?
the light reflexes
56
How many neurons are in the visual pathway?
4 neurons:
1. rod/cone
2. bipolar cell
3. ganglion cell
4. neuron from LGB to BMA 17 in occipital lobe
57
If there is a lesion to the optic nerve, what occurs?
lose vision in one eye; lack depth perception
58
If there is a lesion to the optic chiasma, where occurs?
tunnel vision; (possible pituitary tumor?)
59
If there is a lesion to the optic tract, what occurs?
lose one side of visual field
60
What structure travels through the optic chiasma and what gland sides near it?
infundibulum stalk travels through it; and pituitary gland sits right by it
61
What are the 4 visual reflexes?
1. Direct and consensual light reflexes
2. Accomodation reflex
3. Corneal reflex
4. convergence
62
Describe what occurs in the direct light reflex and the consensual light reflex. What CNs involved?
Direct -- shine light in L eye and L eye constricts
Consensual (indirect) -- shine light in L eye and R eye will constrict too
CN II (sensory), III
63
What is the accomodaiton reflex and what CNs are involved?
transition of changing focal distance form far to near sight
CN II (sensory), III
64
What is the corneal reflex and what CNs are invovled?
touch cornea and shut eye fast
CN V sensory component
CN VII shuts eye
65
What is the convergence visual reflex and what CNs are involved?
when focus on something coming closer
CN II sensory
CN III medial rectus control
66
What type of fibers does CN III (Oculomotor N) carry?
motor nerve that carries BOTH somatic and parasympathetic fibers
67
What muscles does the Oculomotor Nerve supply with its somatic fibers?
-Levator palpebrae and
Extraocular Muscles:
- Inferior oblique
- superior rectus
- medial recuts
- inferior rectus
68
What does the Oculomotor Nerve supply with its parasympathetic fibers?
(autonomic fibers)
- ciliaris
- pupillary constrictor
69
What is the nucleii of origin for the somatic fibers of CN III? Where is it located?
oculomotor nuclei; located in periaqueductal gray matter (in midbrain)--anterior to cerebral aqueduct, at level of superior colliculi
70
What type of neurons will the cell bodies of the somatic of Oculomotor N. path be?
LMN
71
What part of the cerebral cortex sends axons to the oculomotor nuclei? What other additional places does it receive fibers from?
BMA 8; and superior colliculus and medial longitudinal fasciculus (MLF)
72
Axons of Oculomotor N travel anteriorly through the ___ _____ and exit CNS in the _______ ______. What will the nerve now be covered by?
Red nucleus; interpeduncular fossa (into the cistern); now covered by epineurium
73
After the Oculomotor nerve exits the CNS, it must penetrate the____ _____ and travel along the _____ ____ and exit the the skull.
dura mater; cavernous sinus
74
What does CN III, Oculomotor N. exit the skull through?
superior orbital fissure
75
What the oculomotor N. is in the eye socket, what happens?
it splits into superior and inferior rami (branches)
76
What muscles are supplied by the superior ramus of the oculomotor nerve?
1. pierces inferior aspect of superior rectus and supplies it
2. levator palpebrae superioris
77
How many branches does the inferior ramus of the oculomotor nerve have and what muscles does it supply?
1. medial branch--> medial rectus
2. central branch --> inferior rectus
3. lateral branch --> inferior oblique
78
What kind of neurons does the accessory oculomotor nucleus contain?
preganglionic parasympathetic neurons
79
What is the path for the preganglionic parasympathetic axons ass. with oculomotor nerve and where do they synapse?
arise from accesssory oculomotor nucleus --> travel path of oculomotor nerve --> follow path of inferior ramus for short time --> branch off and synapse in ciliary ganglion on posterior parasympathetic axons
80
Where is the ciliary ganglion located? What does it contain?
posterior to eyeball about 1 cm anterior to superior orbital fissure; contains postganglionic parasympathetic fibers
81
What is the path for the postganglionic parasympathetic axons ass. with the oculomotor nerve?
follow the course of the ciliary arteries, pierce the sclera and travel along the internal surface of the sclera to go supply 2 muscles
82
What do the parasympathetic fibers of the oculomotor nerve supply?
- ciliaris
| - pupillary constrictor
83
Where does the synapse between the preganglionic and postganglionic parasympathetic neurons take place in the oculomotor nerve?
the cilliary body
84
What type of nerve fibers does CN IV carry? What does it supply?
= Trochlear Nerve
- somatic motor nerve
- supplies superior oblique muscle
85
What is the nucleus of origin called for CN IV? Where is it located?
trochlear nucleus, located in periaqueductal grary in midbrain, just caudal to oculomotor nuclei
86
What does the trochlear nucleus give rise to and where is the apparent origin?
gives rise to LMN's that CROSS and exit midbrain just inferior to inferior colliculi
- apparent origin = on posterior side of brainstem
87
Where does the Trochlear N. receive information from?
- BMA 8
- superior colliculus
- medial longitudinal fasciculus (MLF)
(same as CN III)
88
After exiting the CNS, the trochlear nerve curves around the _______ and continues within the lateral wall of the _____ _____, and then exits via____ ___ __.
brainstem (cerebral peduncles); cavernous sinus; superior orbital fissure
89
What are three facts about Trochlear Nerve that makes it unique when compared to the other CNs?
1. crosses
2. apparent origin on posterior brainstem
3. fewest # of fibers = smallest CN
90
What plexus does CN III, IV, and VI have communication with?
cavernous plexus; sympathetic postganglionic fibers from here get "picked up" by CN III, IV, and VI to go and supply smooth muscle in arteriole walls
91
What is the trochlear nerve named for?
the pulley-like mechanism on the superomedial aspect of orbit, that the Superior Oblique passes through
92
What are the actions of the superior oblique muscle?
1. causes eye to look down and out
2. its primary action is depression of the eyeball (looking down)
- --(clinically cannot only do this to test for CN IV--see notes)
93
What type of fibers does CN VI carry? What does it supply?
= Abducens Nerve
- somatic motor nerve
- supplies lateral rectus muscle
94
What is the action of the lateral rectus?
turn eye laterally/out (abduct eye)
95
What is the nucleus of origin for the abducens nerve? Where is it located?
abducens nuclei located in caudal (inf.) part of pons, at floor of rhomboid fossa, near 4th ventricle
96
How do the axons of the abducens nerve travel when leaving the abducens nuclei and where does it exit the CNS?
travel anteriorward and exit CNS at inferior border of pons
97
Where does the abducens nerve receive information form?
1. BMA 8
2. superior colliculus
3. medial longitudinal fasciculus (MLF)
(same as CN III and IV)
98
The abducens nerve penetrates the dura, and travels along what structure? Where does it exit the skull?
cavernous sinus; exits skull via superior orbitial fissure and innervates lateral rectus muscle
99
What travels through the trochela?
the superior oblique (NOT CN IV!!!)
100
What is the apparent origin of the abducens nerve (CN VI)?
the medullopontine sulcus or inferiopontine sulcus
on inf. border of pons
101
What is the term for the eyes not being aligned correclty?
strabismus
102
What are the two kinds of strabismus?
1. Internal (converge)
| 2. External (diverge)
103
In internal (converge) strabismus, what is occurring?
eyes cross; affected eye deviates medially
104
In external (diverge) strabismus, what is occurring?
eyes are directed away from each other; affected eye deviates laterally
- usually lateral rectus effected--> CN VI innervation
105
What is the term for double vision?
diplopia
106
Double vision is ALWAYS ______.
subjective; difficult to demonstrate objectively
107
What is the term for a droopy eyelid? Why does this occur? What may be the cause?
Ptosis: due to weakness of levator palpebrae superioris; cause may be due lesions in Oculomotor N. (CN III)
108
What is the term for dry eye?
miosis
109
What does ptosis and miosis together indicate? What part of NS issue is this?
Horner's sydrome (droopy eyelid + dry eye)
-SNS issue; check T1 and T2
110
What does ophthalmoplegia mean?
is the paralysis or weakness of the eye muscles
111
What are 3 results from External ophthalmoplegia of Oculomotor nerve?
1. External (diverging) strabismus (affected eye deviates down and out)
2. diplopia
3. ptosis
112
What two forms can Oculomotor paralysis be presented as?
1. External ophthalmoplegia
| 2. Internal ophthalmoplegia
113
What would be characteristics of internal ophthalmoplegia? (3)
- inability to constrict pupil
- loss of light reflex
- loss of accommodation reflex
114
What are possible etiologies (causes) of Oculomotor paralysis? (3)
- uncal herniation
- PCA (posterior cerebral artery) aneurysms
- diabetes
115
T/F. Trochlear paralysis is rare.
True
116
What would paralysis of Trochlear N. (CN IV) caseus? (2)
- slight converging (internal) strabismus
| - diplopia when looking down--results in difficulty descending stairs
117
What CN is MC to under go paralysis of the ones innervating the eye?
Abducens paralysis
118
What can occur with paralysis of the abducens nerve?
Internal (converging) strabismus and diplopia
119
What does Internuclear ophthalmoplegia involve damage to? What will you see the eye doing?
```
to MLF (medial longitudinal fasciculus)
- will see nystagmus when abducting involved eye during lateral gaze
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