Week 41- Vision and Cranial Nerves Flashcards
1
Q
What causes the rotation of the eyeball?
A
Extraocular muscles
2
Q
Where are the nuclei located that innervate the eye muscles?
A
Within the brainstem
3
Q
What are the three nerves that innervate the ocular muscles?
A
Oculomotor nerve III
Trochlear nerve IV
Abducens nerve VI
3,4,6
4
Q
What nuclei/nerve innervates the lateral rectus muscles?
A
Abducens nerve (cranial nerve 6, VI)
5
Q
What nuclei/nerve innervates the superior oblique muscles?
A
Trochlear nerve (cranial nerve 4, IV)
6
Q
What nerve innervates all other extraocular muscles?
A
Oculomotor nerve (cranial nerve 3, III)
7
Q
What is convergence in the eyes?
A
Bringing optical axes together to allow for binocular vision of close objects
8
Q
What muscle allows the eyes to converge in convergence?
A
Medial rectus muscle –> innervated by the oculomotor nerve
9
Q
What does convergence mean practically?
A
When we focus on a point –> the convergence of the eyes allows the point to fall on identical portions of the retina of each eye (fovea)
10
Q
What are the two main muscles that control the pupil diameter?
A
Dilator (M. dilator pupillae)
Sphincter (M. sphincter pupillae)
11
Q
What direction is the dilator fibres for pupil control?
A
Radial direction
12
Q
What direction is the sphincter fibres in for pupil control?
A
Circular
13
Q
What is the pupil affects of contraction of the dilator muscles vs sphincter muscles?
A
Dilators –> causes pupil dilation (midriasis)
Sphincters –> decrease in pupil diameter (myosis)
14
Q
What is the difference in innervation of the dilators vs sphincter muscles for pupils?
A
Dilators –> sympathetically innervated
Sphincters –> parasympathetically dilated
15
Q
What is the pupillary reflex?
A
Activated by bright light –> the pupil reduces its diameter –> reduces light entering the eye
16
Q
What is the mechanism steps behind the pupil reflex?
A
Light is shined through one eye e.g right
Action potentials from right eye reach both right and left pretectal nuclei
The pretectal nuclei stimulate both sides of the Eddinger-Westphal nucleus even if light was only perceived in only the right eye
Right and left sides of the Eddinger-Westphal nucleus generate action potentials through the right and left oculomotor nerves –> causing pupil constriction
17
Q
What are cataracts?
A
Opacity of a normally clear lens –> stops the entry of light into the eye and to the retina
18
Q
What is refraction?
A
The changing of light direction when interfacing between two medias with different refraction indices
19
Q
How does the lens function in the eye?
A
Functions as a prism to refract light and direct it onto the retina
20
Q
What is focal length?
A
The distance which it takes the light rays to be brought to focus by the lens
21
Q
What is larger in short focal lengths?
A
The optical refractive power is larger
22
Q
How is optical refractive power (optical power) measured?
A
Dioptres –> 1 diaopters is the optical power of a lens that converges parallel rays at a focal length of 1m
23
Q
What structure in the eye provides the most optic power?
A
The anterior surface of the cornea
24
Q
What is the total refractive power of the eye?
A
59 diopters
25
What is accommodation?
The movement of the lens shape (more or less convex) to change the focal power to get a clear focus of light on the retina --> brain adjusts accommodation in concert with convergence
26
What is the default shape of the lens without externally directed tension?
Spherical shape
27
What causes the lens to flatten?
Tension from the suspensory ligaments
28
What causes the lens to increase its curvature?
Both meridional and circular fibres of the ciliary muscles --> reduces tension by ligaments
29
What kind of innervation is ciliary muscles controlled by?
Parasympathetic
30
What is the term for a less elastic lens which makes accommodation difficult/impossible?
Presbyopia
31
How many layers are in the retina?
4 layers:
Pigmented Epithelium
Photosensitive cells (rods and cones)
Two layers of neurons (bipolar cells and ganglion cells)
32
What neuron layer forms the optic nerve?
Axons of the ganglion cells
33
What is the purpose of the outer Pigmented epithelium layer?
Prevents the reflection of light
34
What is the Fovea?
It lies in the macule area --> small depression in the retina of the eye where visual acuity is highest.
The centre of the field of vision is focused in this region
35
What is most concentrated at the fovea?
retinal cones are particularly concentrated
36
What are the main structural differences between the fovea and the retinal periphery?
High ratio of rods to cones
Higher ratio of photoreceptors to ganglion cells
More sensitive to low light
37
Why is central vision the most accurate (high acuity vision)?
Fovea has less internal cellular layers --> means less light dissipation before hitting photoreceptors
Cones are much smaller and tightly packed with a 1:1 convergence on bipolar cells
38
What are the two types of photoreceptors?
Rods and cones
39
What is the role of photoreceptors?
Electromagnetic radiation (light) into neural signals
40
What is the general structure of rods?
Long, cylindrical outer segment with many disks
41
What is the general structure of cones?
Shorter, tapering outer segment with fewer disks
42
Which photoreceptor is more sensitive to light?
Rods are 1000 times more sensitive
43
Why is peripheral vision better at night?
Central vision is the work of the macule --> high density of cones --> cones not sensitive to low intensity light
Peripheral vision has more rods --> which are much more sensitive to low intensity light
44
What is the mechanism of phototransduction in rods?
Light energy interacts with photopigment
Produces change in membrane potential
Causes a change in second messenger (similar to G-protein-coupled neurotransmitter receptor) but instead of increasing second messenger it decreases second messenger
45
What is the ion channel response to phototransduction?
Decrease Na+ conductance --> photoreceptor hyperpolarizes
46
What state is a photoreceptor in during the dark vs light?
Depolarised in dark
| Hyperpolarised in light
47
What is the molecule that absorbs photons of visible light?
Rhodopsin
48
What is the role of the retina?
Conversion of light stimulus at the inputs (rods and cones) to neuronal discharge of ganglion cells at output
49
What is the basis for colour vision?
There is different opsins (molecules that absorb visible light and act like G-protein coupled receptors)
50
What are the three different opsins needed for colour vision?
Red (long wavelength)
Green (medium wavelength)
Blue (short wavelength)
51
What is the term for normal colour vision?
Trichromats
52
What is the term for lacking one type of cone/colour in vision?
Dichromats
53
What chromosome is Rhodopsin on?
Chromosome 3
54
What chromosome is the blue cone on?
Chromosome 7
55
What chromosome is red and green cones on?
X chromosome --> why males are affected more often
56
Where do most of the ganglion cell axons from the retina project to?
The lateral geniculate nucleus (LGN) in the thalamus
57
From the thalamus where do neurons project?
Via optic radiations --> to the occipital cortex
58
In humans where do the axons of the LGN neurons synapse with the cortical neurons in the primary visual cortex?
Area 17 --> in the occipital lobe --> mainly around the medial surface around the calcarine fissure
59
What happens to axons at the optic chiasm?
Axons from nasal side of the retina --> decussate (cross over)
Axons from the temporal side of the retina --> don’t cross over
60
What is the affect of axons crossing over/ nor crossing over at the optic chiasm?
Nasal side --> cross over --> project on contralateral side of the brain (opposite side)
Temporal side --> don’t cross over --> project on ipsilateral side of brain (same side)
61
What is the effects of decussation on vision?
Each half of the binocular vision is detected by the opposite side of the brain
62
What does bitemporal hemianopsia appear like and what can cause it?
Person only sees straight ahead without peripheral vision --> caused by an issue in signals from the nasal sides of the retina --> can be caused by pituitary adenoma
63
What are some factors in dark adaption?
Dilation of pupils
Regeneration of unbleached rhodopsin
Adjustment of functional circuitry
64
How are photoreceptors adapted going from dark to bright light?
Initially bright light is glary to dark adapted eye
| Adaption increases dynamic range of cones by about 1000 times
65
What does the adaption mechanisms of the photoreceptors rely on?
cGMP gated Na+ channels in photoreceptor are also Ca2+ permeable
Ca2+ inhibits the enzyme guanylyl cyclase
Intracellular Ca2+ is pumped out by a membrane exchange pump (4Na+ in --> Ca2+ + K+ out)
66
Slow adaption of photoreceptors in bright light mechanism:
1. cGMP levels in outer segment initially fall to very low level
2. All cGMP gated Na+ channels close – causing maximal hyperpolarization (to -70 mV). Photoreceptor is now saturated.
3. Ca++ influx stops
4. Intracellular Ca++ level slowly falls
5. Guanylyl cyclase activity increases
6. cGMP levels rise
7. More cGMP dependent Na+ channels open
8. Photoreceptor depolarizes – no longer saturated
67
What is the term for an eye with no refractive defects?
Emmetropia
68
What are the two common refractive abnormalities?
Myopia
| Hyperopia
69
What is the problem with myopia?
The lens refracts the light too powerfully and it focuses too early and misses the retina
70
What is the problem with Hyperopia?
The lens refracts too little and the light focuses on a point behind or past the retina
71
What kind of lens is required to correct myopia?
A diverging lens
72
What kind of lens is needed to correct Hyperopia?
Converging lens
73
What is the normal optical power across the meridians of the eye?
The same across
74
What is astigmatism?
A refractive abnormality where there is a difference in optical power in different meridians of the eyes lens (normally) --> can cause distorted or blurred vision
75
What is the various axis's that may be affected by astigmatism?
Vertical, horizontal or anywhere in between
76
What produces intraocular fluid?
Within the cilia of the ciliary bodies
77
What is a normal value for intraocular pressure?
12-20mmHg
78
What is glaucoma?
Elevated intraocular pressure (up to 70mmHg) --> causes optic nerve issues --> may lead to blindness
79
How is intraocular pressure measured?
Through non-contact tonometer
80
What are the cranial nerves pneumonic?
Oh oh oh to touch and feel virgin girls vaginas ah heaven
81
What are all the cranial nerves?
```
O --> olfactory nerve
O --> optic nerve
O --> oculomotor
T -> trochlear
T --> trigeminal
A --> abducens
F --> facial
V --> vestibular
G --> glossopharyngeal
V --> Vagus
A --> accessory
H --> Hypoglossal
```
82
What is the function of the olfactory nerve?
It relays sensory data to the brain, and it is responsible for the sense of smell.
83
What is the function of the optic nerve?
The job of the optic nerve is to transfer sensory visual information from the retina to the vision centres of the brain via electrical impulses.
84
What is the function of the oculomotor nerve?
Innervation to the pupil and lens (autonomic, parasympathetic) Innervation to the upper eyelid (somatic) Innervation of the eye muscles that allow for visual tracking and gaze fixation (somatic)
85
What is the function of the trochlear nerve?
The trochlear nerve is a motor nerve, and it controls the superior oblique muscle of the eye. The superior oblique muscle controls the downward movement of the eyeball and, in part, keeps the eyeball from rolling upward into the orbit (eye socket).
86
What is the function of the trigeminal nerve?
Its main function is transmitting sensory information to the skin, sinuses, and mucous membranes in the face. It also stimulates movement in the jaw muscles.
87
What is the function of the abducens nerve?
that controls the movement of the lateral rectus muscle, responsible for outward gaze. It is a somatic efferent nerve.
88
What is the function of the facial nerve?
controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue.
89
What is the function of the vestibular nerve?
responsible for both hearing and balance and brings information from the inner ear to the brain
90
What is the function of the glossopharyngeal nerve?
It receives general somatic sensory fibres (ventral trigeminothalamic tract) from the tonsils, the pharynx, the middle ear and the posterior 1/3 of the tongue. It receives special visceral sensory fibres (taste) from the posterior 1/3 of the tongue.
91
What is the function of the Vagus nerve?
helps to regulate many critical aspects of human physiology, including the heart rate, blood pressure, sweating, digestion, and even speaking.
92
What is the function of the accessory nerve?
supplies the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle tilts and rotates the head, while the trapezius muscle, connecting to the scapula, acts to shrug the shoulder.
93
What is the function of the hypoglossal nerve?
motor control of the extrinsic muscles of the tongue: genioglossus, hyoglossus, styloglossus, and the intrinsic muscles of the tongue.
94
What is eyesight?
An ability of a person to see clearly without any corrective lenses (visual acuity)
95
What is visual field?
The area that can be seen by the eye when it is directed forward --> including peripheral vision
96
How is eyesight tested clinically?
An eye chart
97
How is visual field tested clinically?
Examiner directly across from patient
Hands, fingers, or instrument used to move around patients field of view --> essentially comparing field of view to your own
98
What are the terms for refractive error in the eyes?
Myopia --> light focused in front of retina
Hyperopia --> light focuses behind the retina
99
What is the normal anatomy of the pituitary gland?
Pea sized --> sits behind bridge of the nose --> has 3 lobes:
Anterior
Posterior
Intermediate --> less important
100
What is the functions of the pituitary gland?
Regulate function of endocrine glands
| Master gland --> controls --> thyroid, adrenal, ovaries, testes
101
What are some hormones of the Anterior lobe of the pituitary gland?
```
Adrenocorticotropic hormone (ACTH)
Follicle stimulating hormone (FSH)
Growth hormone (GH)
Luteinizing hormone (LH)
Prolactin
Thyroid stimulating hormone (TSH)
```
102
What are some hormones of the posterior lobe of the pituitary gland?
Anti-diuretic hormone (ADH)
| Oxytocin
103
Why can pituitary tumours cause visual field disturbances?
Pushes on the optic chiasm --> disturb optic nerve signals
104
What are the two main categories of headache?
Primary --> not a symptom for another disease --> headache from headache (benign)
Secondary --> symptom of another disease --> needs to be ruled out
105
When is a primary headache diagnosed?
When a secondary headache is ruled out
106
Common causes of primary headaches?
```
Alcohol
Changes in sleep
Poor posture
Skipped meals
Stress
```
107
What is believed to be the cause of migraine?
The pain nucleus of the trigeminal nerve becomes spontaneously active; pain is felt in the head or upper neck and blood flow in the face and scalp increases reflexly. Noradrenaline is released from the adrenal gland and causes the platelets to release serotonin. Serotonin in the circulation is thought to reflect levels of this neurotransmitter in the brain.
The brainstem nuclei of one side have a reciprocal effect on those of the other side; their effects may alternate, causing cortical changes on one side and headache on the other, or causing the headache itself to change from side to side.
--> essentially caused by brain interactions with the cranial blood vessels
108
Who are Torres straight islanders?
are the Indigenous peoples of the Torres Strait Islands, which are part of the state of Queensland, Australia. Ethnically distinct from the Aboriginal people of the rest of Australia, they are often grouped with them as Indigenous Australians
109
Which cranial nerve controls pupil diameter?
Cranial nerve 3 --> oculomotor
110
What is mydriasis?
It is the opening of the pupil in response to low light
111
What is Miosis?
The constriction of the pupil in bright light
112
What kind of innervation constricts the pupils?
Parasympathetic --> circular muscle constriction
113
What kind of innervation dilates the pupils?
Sympathetic --> radial muscles contract
114
What movement would be impaired if CN4 was compressed?
Superior oblique movement
115
How would a patient present with CN4 compression?
Diplopia
Head tilt away from lesion
Double vision when going down stairs
116
What would infection of CN6 impair?
Lateral rectus muscle --> eye abduction
117
Which way does the eye deviate in CN6 issues?
Will adduct --> move towards the nasal side
118
What pattern of visual loss is expected in Homonymous hemianopia?
Half of vision gone in both eyes --> can be nasal or temporal side
119
What is the consensual reflex in pupils?
Light in one eye --> other eye constricts
120
What is the direct pupil reflex?
Light in a eye --> and that eye constricts
121
What pattern of visual loss is expected in macula degeneration?
Blurry vision in centre of eye
122
What pattern of visual loss is expected in bitemporal hemianopia?
Both temporal sides on each eye lost --> peripheral vision loss
123
What pattern of visual loss is expected in right optic nerve ischaemia?
Vision loss on the right side
124
Where would the lesion be with one upper quarter vision loss on the right ride?
R upper quadrant loss is from issue with upper L optic radiations
125
What happens to the image as it passes the LGN?
Flips Horizontal to vertical
126
Where does the upper quadrant visual info get processed?
Temporal
127
Where does the lower quadrant visual info get processed?
Parietal
128
What cranial nerve closes the eyelid by relaxing the muscle??
Facial nerve
129
Where is the cranial nerve 3 nucleus?
Brainstem --> midbrain
130
small visual field loss on nasal side of left eye --> what side of the retina has a deficit?
Temporal side of retina
131
Flashing lights --> like I had cobwebs over the eye --> what does this point to diagnostically?
Retinal detachment
132
What is bells palsy?
temporary weakness or paralysis of the muscles in the face. It can occur when the nerve that controls your facial muscles becomes inflamed, swollen, or compressed.
133
Why is important if the forehead affected by a facial droop?
Upper vs Lower motor neuron issue
If they can move forehead --> upper issue --> increases stroke risk
If they cant --> lower motor neuron issue --> more likely bells palsy
134
What cranial nerve is important for bells palsy and facial movement?
Cranial nerve 7 --> facial nerve
135
What causes bell's palsy?
It's believed to be the result of swelling and inflammation of the nerve that controls the muscles on one side of your face. Or it might be a reaction that occurs after a viral infection.
136
What is the nerve controlling the sensory part of the corneal reflex?
Cranial nerve 5 --> V1
137
What is the nerve controlling the motor part of the corneal reflex?
Cranial nerve 7
138
Where do you poke someone for the corneal reflex?
Gently poke cotton in the lower middle eye
