Visual System Flashcards Preview

MD1 Neuroscience > Visual System > Flashcards

Flashcards in Visual System Deck (223)
1

What forms the supraorbital margin?

Frontal bone (with supraorbital notch for the supraorbital nerve)

2

What forms the infraorbital margin?

  • Zygomatic bone (laterally)
  • Maxilla (medially)

3

What forms the roof of the orbit?

Frontal bone, lesser wing of sphenoid

4

What forms the floor of the orbit?

Maxilla, zygomatic, palatine

5

What forms the lateral wall of the orbit?

Zygomatic, lesser wing of sphenoid

6

What forms the medial wall of the orbit?

Maxilla, lacrimal bone, ethmoid, body of sphenoid

7

Where will blowout fractures to the orbit normally occur?

To the lacrimal bone or ethmoid bone, as they are extremely thin and fragile.

8

What proportion of the eyeball is sclera?

5/6th of the eyeball

9

What does the sclera do?

Maintains the shape of the globe, offering resistance to internal and external forces

10

What two characteristics make the sclera strong?

  1. Made of collagen
  2. Laid down in whirls

11

What does the sclera provide attachment for?

Extraocular eye muscles

12

What are the 3 layers to the eye?

  1. Sclera and cornea
  2. Vascular supply
  3. Neural part

13

What proportion of the eyeball is cornea?

1/6th

14

What is the principal refracting component of the eye?

Cornea

15

What makes the cornea optimum for vision?

Being avascular and transparent

16

Why is the cornea transparent?

Because the collagen fibrils are uniform in diameter, evenly spaced and run in bundles (lamellae) parallel to one another.

17

What does scleral opacity vary depending on?

  • Composition of the stroma
  • Hydration
  • Size and distribution of collagen

18

What will happen to the order of collagen fibrils in the cornea if it is damaged?

The order will not necessarily return and can result in a scar

19

What is the anterior chamber of the eye?

Junction between iris and cornea

20

What happens at the anterior chamber of the eye?

Aqueous humour drains out of eye

21

What are the key structures of the anterior chamber of the eye?

  • Cornea
  • Trabecular meshwork
  • Canal of Schlemm
    • Aqueous humour drains into venous system via canal of Schlemm
  • Ciliary body

22

What happens at the Canal of Schlemm?

Aqueous humour drains into the venous system

23

What forms the middle coat of the eye?

Uvea

24

What forms the middle layer of the eye?

Ciliary body, sclera and conjunctiva

25

What is the function of the ciliary body?

  • Formation of aqueous humour (Ciliary epithelium)
  • Tethers lens (Ciliary processes)
  • Accommodation (Ciliary muscle)

26

What are the important structures within the ciliary body?

  • Ciliary processes (Ciliary epithelium): form aqueous humour and form attachment for lens
  • Ciliary muscle

27

What does the ciliary body produce?

Aqueous humour

28

What does the aqueous humour do?

  • Important for maintaining the health of the lens and cornea.
  • Creates intraocular pressure.

29

What structures does accommodation involve?

  1. Ciliary muscles
  2. Zonules to attach to lens

30

What are zonules?

Ligaments that attach between ciliary processes and lens.

31

Where is the ciliary muscle found?

Within the ciliary body

32

What is the ciliary muscle innervated by?

Parasympathetic NS

33

What kind of muscle is ciliary muscle?

Non-voluntary muscle (smooth muscle)

34

How does the ciliary muscle accommodate?

The circular fibres change the tension on the zonules, deforming the lens

35

What does relaxation of the ciliary muscle result in?

A thin lens that is deformed (distant objects)

36

What does contraction of the ciliary muscle result in?

A relaxed, fat lens (closer objects)

37

What is presbyopia?

  • Amplitude of accommodation varies with age
  • Prebyopia refers to the loss of accommodation with age.
  • Caused by reduction in flexibility of the lens capsule and zonules
  • Treated by the wearing of plus lenses

38

What is the iris?

Aperture of the eye

39

What two muscles comprise the iris?

  • Sphincter pupillae: constricts pupil: innervated by parasympathetic NS
  • Dilator pupillae: dilates pupil: innervated by sympathetic NS

40

What is the choroid?

3 layers of blood vessels underneath the retina that supply nutrients to the retina.

41

Which blood vessels in the choroid are the most important?

Most important is the choriocapillaris, which sits just below the retina.

42

What are the important components of the retina?

  • Optic nerve/optic disc
  • Fovea/foveola
  • Macular
  • Posterior pole
  • Orra serrate

43

What are the 2 specialised regions of the retina?

Fovea and optic nerve

44

What is the fovea?

An avascular area of high visual acuity due to a high density of cones (no rods) where everything is shifted to the side except photoreceptors.

45

What forms the optic nerve?

The axons of ganglion cells as they exit the retina to pass visual information to higher cortical areas.

46

What is the lamina cribrosa?

A band of 3-10 sheets of dense connective tissue that forms a sieve at where the optic nerve exits the eye through which axons must pass. Disease can damage this area and push on axons traversing it.

47

If a patient notices a "curtain come down" over their vision, what is a potential reason?

Arterial occlusion

48

Which artery supplies the inner retina?

Central retinal artery (branch of ophthalmic artery)

49

What are the ciliary arteries?

  • Long posterior ciliary
  • Short posterior ciliary
  • Anterior ciliary

50

Do the anterior ciliary arteries pierce the globe?

No. They supply structures at the front of the eyeball.

51

What do the posterior arteries travel in?

The choroid

52

Which artery supplies the outer retina?

Posterior ciliary artery

53

Which artery supplies the photoreceptors?

Posterior ciliary artery

54

What do the short posterior arteries supply?

Photoreceptors closer to optic nerve and nerve itself

55

What do the long posterior arteries supply?

Photoreceptors all the way around the retina

56

What are the eyelids comprised of?

  • Skin
  • Glands and eyelashes
  • Conjunctiva
  • Muscles:
    • Orbicularis oculi
    • Levator palpebrae superiosis
  • Lacrimal apparatus:
    • Lacrimal gland and ducts
    • Nasolacrimal sac and duct

57

What are the muscles of the orbit?

  • Orbicularis oculi
  • Levator palpebrae superiosis

58

What does levator palpebrae superiosis do?

Elevates the upper lid

59

What type of muscle is levator palpebrae superiosis?

Striated muscle

60

What is levator palpebrae superiosis innervated by?

CNIII (oculomotor)

61

What does orbicularis oculi do?

Depresses upper lid (sphincter muscle)

62

What type of muscle is orbicularis oculi?

Striated muscle

63

What is orbicularis oculi innervated by?

CNVII (facial)

64

Do levator palpebrae superiosis and orbicularis oculi work together?

No. NEVER!

65

What are the 3 basic layers to the eyeball? What is their function?

  1. Outer coat: cornea and sclera
    1. Function: strength
  2. Middle coat: uvea
    1. Function: nutrition
  3. Inner coat: retina
    1. Function: vision

66

What fundamentally limits visual acuity?

  1. Neural factors
  2. Optical factors

67

What is visual acuity?

Ability to resolve fine detail.

68

How is visual acuity tested?

By recognition of letters on a Snellen or LogMAR chart.

69

What result on a visual acuity test is considered legally blind?

6/60

70

What optical factors affect visual acuity?

  • Pupil size
  • Clarity of optical media
    • Cataracts, corneal opacities…
  • Refractive errors → blur
  • Myopia, hypermetropia, astigmatism, presbyopia

71

What is the best visual acuity at phototopic levels?

6/6

72

What type of photoreceptors are present at the fovea?

Cones

73

How far away from the fovea is demonstrable visual acuity loss?

5 minutes of arc away from fovea.

74

What is the best visual acuity at scotopic levels?

6/60

75

Where are rods (and rod pathways) found in the retina?

Between 5-15˚ away from the fovea

76

Where is the best peripheral vision in the retina?

At approx. 8 degrees off centre of the fovea.

77

What is visual acuity in the fovea determined by?

Number of cones

78

What are the 6 neurons of the retina?

Rods, cones, horizontal cells, bipolar cells, amacrine cells and ganglion cells.

79

What are the 2 synaptic layers of the retina?

  • Outer plexiform layer
  • Inner plexiform layer

80

What does light pass through before hitting photoreceptors?

All retinal layers

81

What are the properties of rods?

  • Night vision
  • Scotopic
  • Very sensitive
  • One type only
  • No colour vision
  • 100 million
  • Absent from fovea

82

What are the properties of cones?

  • Day vision
  • Photopic
  • Less sensitive
  • Three types (RGB)
  • Allow colour vision
  • 5 million
  • Densest in fovea

83

What is needed for the finest detail to be resolved?

  • A good optical system
  • Small, closely packed detectors

84

What is the "through" pathway?

Photoreceptors → bipolar cells → ganglion cells → optic nerve

85

What provides lateral interactions and modulations to the through pathway?

  • Horizontal cells
  • Amacrine cells

86

What are the first, second and third order neurons in the through pathway?

  1. Photoreceptor
  2. Bipolar cell
  3. Ganglion cell

87

What are the 10 different types of bipolar cells?

  • 1x rod bipolar cell
  • 9x cone-bipolar cells

88

What are bipolar cells important for?

Spatial vision & colour vision

89

What are OFF bipolar cells?

Bipolar cells that hyperpolarise when light falls on the retina.

90

What are ON bipolar cells?

Bipolar cells that depolarise when light falls on the retina.

91

In which layer are bipolar cells found?

Inner nuclear layer

92

What do horizontal cells receive input from?

Photoreceptors

93

What do horizontal cells provide output onto?

Photoreceptors

94

Which neurotransmitter do horizontal cells use?

Inhibitory neurotransmitter GABA.

95

What effect do horizontal cells have on photoreceptors?

They hyperpolarise.

96

What are amacrine cells?

Axonless cells that laterally inhibit bipolar cells by releasing inhibitory neurotransmitters glycine or GABA.

97

What is in the ganglion cell layer?

Cell bodies of ganglion cells and some displaced amacrine cells.

98

What are ganglion cells?

Ganglion cells are the main output neuron of the retina.

99

What are the different types of ganglion cell?

ON, OFF, M and P

100

What do ganglion cells release?

Glutamate

101

Which cell of the retina is the only neuron to fire APs?

Ganglion cells

102

True or false: vision is just about detection.

False. Vision is not just about detection, but about comparison and contrast.

103

How do ganglion cells respond to light?

By increasing or decreasing their action potential firing rate.

104

What is the receptive field of a ganglion or bipolar cell?

The area of retina that when stimulated with light changes the cell’s membrane potential.

105

What type of receptive field do ganglion cells have?

Concentric-surround

106

What does the level of stimulation of a ganglion cell's receptive field depend on?

Where in the receptive field there is stimulation - the further from the centre, the lower the stimulation.

107

What do photoreceptors contain that responds to light?

Photopigments

108

Which photopigment do rods contain?

Rhodopsin

109

Which photopigment do cones contain?

One of three different cone-opsins

110

What do opsins bind to?

Vitamin A (all-trans Retinal)

111

What happens to photoreceptors when they are stimulated by light?

They hyperpolarise

112

What do photoreceptors use as their neurotransmitter?

Glutamate

113

Do photoreceptors fire action potentials?

No. They respond to light with graded changes in membrane potential.

114

What determines the amount of neurotransmitter released by the photoreceptor?

Graded changes in the resting membrane potential.

115

How do photoreceptors function in the dark?

  • cGMP gates a sodium channel causing continuous influx of sodium ions.
  • Causes depolarization of the cell.

116

How do photoreceptors function in the light?

  1. In the light, cGMP breaks down to GMP
  2. cGMP no longer gates the sodium channels
  3. Flow of Na ions ceases
  4. Cell is hyperpolarized

117

How does phototransduction work?

  1. Light activates rhodopsin
  2. Initiates a cascade of events that ultimately leads to the closure of cGMP gated sodium channels.
  3. Rh → Transducin → PDE → breaks down cGMP
  4. Closure of sodium channels→hyperpolarization

118

What is the hyperpolarising signal form the photoreceptor communicated to?

ON and OFF bipolar cells at the same synapse.

119

What creates black on white sensation?

OFF bipolar cells

120

What creates white on black sensation?

ON bipolar cells

121

What creates the centre-surround?

The central response - determined by the “Through” pathway (Ph-BC-GCs) - and the surround pathways - determined by inputs from horizontal cells. Horizontal cells create the centre-surround

122

What creates the "surround?"

  • Horizontal cells receive input from many photoreceptors and provide output to other photoreceptors
  • Horizontal cells release GABA as their neurotransmitter

123

What is the size of the surround determined by?

The extent of electrical coupling between horizontal cells.

124

What is melanoma associated retinopathy?

  • Rare complication of melanoma.
  • Antibodies are produced directed against ON bipolar cells.
  • Patient treated with oral prednisolone

125

What are the output neurons of the retina?

Ganglion cells

126

What are the 2 different types of ganglion cells? What type of information do they provide?

  • M (midget ganglion cells): motion
  • P (parasol ganglion cells): colour vision, visual acuity

127

What are the 5 targets of ganglion cells?

  1. Lateral geniculate nucleus (thalamus)
    1. Major target of most GCs
    2. Visual pathway
  2. Pretectum (midbrain)
    1. Pupil responses
  3. Suprachiasmatic nucleus (hypothalamus)
    1. Circadian rhythm
  4. Superior colliculus
    1. Eye movements
  5. Other: various nuclei of thalamus a. Photophobia

128

What is the optic chiasm?

Where fibres from right and left optic nerves combine at the base of the brain, anterior to the pituitary.

129

What happens at the optic chiasm?

Nasal visual field fibres decussate.

130

Which hemisphere views the right visual field?

Left

131

Which hemisphere views the left visual field?

Right

132

Where is the pituitary gland located in relation to the optic nerve?

Just below the optic nerve/optic chiasm in the Turkish saddle.

133

Where do most ganglion cells terminate?

Within the thalamus at the LGN.

134

How is the lateral geniculate nucleus (LGN) organised?

  • Segregation of inputs by eye and ganglion cell type
  • Six layers (numbered 1-6)

135

What cell types does the LGN contain and in which layers?

  • Magnocellular layers = layers 1-2
  • Parvocellular layers = layers 3-6

136

Which layers of the LGN is the right eye represented in?

2, 3 and 5

137

Which layers of the LGN is the left eye represented in?

1, 4 and 6

138

How does information get from the LGN to the primary visual cortex?

Via the optic radiations (this is the second order neuron)

139

Where is the primary visual cortex located?

BA17 in the occipital around the calcarine fissure

140

Where is each half of the visual field represented?

On the contralateral visual cortex

141

What is retinotopic organisation?

Neighbouring cells within the retina project to neighbouring cells in the LGN & visual cortex.

142

How will a lesion in the right optic nerve affect vision?

Loss of vision from the left and right visual fields of the right eye.

143

How will a lesion in the optic chiasm affect vision?

Bilateral loss of vision from the temporal visual fields

144

How will a lesion in the right optic tract affect vision?

Bilateral loss of vision in the left visual fields of each eye

145

How will a lesion in the superior part of the right optic radiation affect vision?

Bilateral loss of vision in the left superior visual field

146

How will a lesion of the entire right optic radiation affect vision?

Bilateral loss of vision of the entire left visual field

147

How do migraine auras often manifest?

As visual auras

148

What effect does light exposure have on migraine?

Worsens pain

149

What is migraine pain thought to be due to?

Nerves signalling from the dura (blood vessels in the meninges)

150

Which nerve carries pain from the dura?

Trigeminal nerve

151

What is the pain pathway for migraine?

Dura → trigeminal nerve → brainstem → posterior nucleus of the thalamus

152

Where in the thalamus does the migrain pain pathway terminate?

Posterior nucleus of the thalamus

153

Where do ipGCs project to?

Neurons in the posterior nucleus of the thalamus that are light sensitive.

154

What are ipGCs?

Intrinsically photosensitive GCs.

  • A small population of GCs containing a visual pigment called melanopsin.
  • Melanopsin is similar to visual pigments found in invertebrates.
  • Light activation of melanopsin leads to depolarization of ipGCs.

155

What are the non-vision-related functions of ipGCs?

  • Circadian rhythm
  • Sleep regulation
  • Pupil responses
  • General information about light levels
  • Light Allodynia (photophobia associated with migraine, ocular injury or infection)

156

What happens if light is shone into one eye?

Both pupils will constrict

157

What does the pupil response to light depend on?

The retina being able to detect light and the iris functioning.

158

Which two muscles control the iris?

Dilator pupillae Sphincter pupillae

159

What is the function of ipGCs in pupil responses?

  • Melanopsin GCs project to the optical pretectal nucleus (OPN)
  • Provides the retinal input to the brainstem that controls pupil responses

160

What is the function of ipGCs in circadian rhythm?

ipGCs project to the suprachiasmatic nucleus (SCN) in the hypothalamus, which is important for driving circadian rhythm.

161

What are the inputs to V1?

M and P cells

162

How do the M and P cells arrive at V1?

Segregated into M and P pathways, inputting into different strata of layer IV in V1

163

Which layers of V1 do M cells terminate in in V1?

Layer 4Cα

164

Which layers of V1 do P cells terminate in in V1?

Layer 4Cβ

165

What are the outputs of V1?

  • Layer 3 and IVβ: other cortical areas
  • Layer 5: superior colliculus and pons
  • Layer 6: LGN

166

Which V1 layer projects to the LGN?

Layer 6

167

Which V1 layer projects to the superior colliculus and pons?

Layer 5

168

Which sensory modality are M ganglion cells responsible for?

Motion

169

Which layer of the LGN do M ganglion cells project to?

Magnocellular layers

170

Are M ganglion cells wavelength sensitive?

No

171

Where do M cells from the LGN project to?

IVCα

172

Where do cells in layer IVCα project to?

Layer IVB

173

When is there mixture of M ganglion cells?

After entering IVB in V1

174

How does motion work in V1?

Some cells in layer IVB show orientation selectivity with preference for the direction of motion. Directional selectivity encodes for motion.

175

What percentage of the cortex is involved in vision?

40%

176

What are the two parallel visual streams?

  • Dorsal pathway: Where? - M cells
  • Ventral pathway: What? - P cells

177

What is area MT?

  • An area in the middle temporal lobe (ventral stream) specialised for processing object motion.
  • Receives retinotopic information from cortical areas including V2 and V3.
  • Receives input from cells in layer IVB of V1.
  • Detects objects moving above a certain velocity.

178

What type of selectivity are almost all cells in area MT?

Directionally selective

179

What columns are present in area MT?

Direction-of-motion columns

180

True or false: all neurons in area MT respond to the same type of motion.

False. They respond to different types of motion, e.g. drifting spots of lights.

181

Which type of light will activate all cone photoreceptors?

White

182

When will red and green cones be co-stimulated?

When light is between ~470-590nm.

183

What colour is red always compared with?

Green.

Note: green is always compared with red.

184

What colour is blue always compared with?

Yellow.

Note: yellow is always compared with blue.

185

How is the colour red seen?

P ganglion cells exhibit a colour opponent centre-surround. Some P ganglion cells are excited by red falling on their centre and inhibited by green falling on the surround. The colour perceived is determined by the activity of ganglion cells. If red light falls on the centre of the ganglion cell and no green light on the surround, then the ganglion cell will be maximally excited. If green falls on the surround, the ganglion cell will be maximally inhibited by hyperpolarising horizontal cells.

186

What will happen to the ganglion cell's excitability if red light falls on the centre and the surround?

It will still be maximally stimulated because, whilst the green cones respond to red light, they respond less than red cones.

187

Which part of the visual pathway is affected in blind sight?

The circuit from the LGN to area MT

188

Which area of the visual cortex is the ventral stream?

Area V4

189

Where does area V4 (the ventral stream) receive input from?

The blob and interblob regions of the primary visual cortex via V2

190

What types of selectivity are neurons in V4 (ventral stream)?

Orientation selective and colour selective

191

What area of the temporal lobe is a major output area of area V4?

Area IT (inferior temporal)

192

What do neurons in area IT respond to? What is this important for?

Respond to a wide variety of abstract shapes and colours. Important for visual memory and perception, including perception of faces.

193

What do stimuli that engage neurons for complex recognition rely on?

Addition/summation of stimuli along the pathway.

194

What percentage of the population have colour vision deficiencies?

8% of males, 0.5% of females.

195

What are the 3 different groups of colour vision deficiency?

  • Monochromacy: people have only one type of cone.
  • Dichromacy: sufferers have only two functional cones.
  • Anomalous trichromacy (most common): all three cones function, but one expresses abnormal pigment and doesn’t work the same as normal cones.

196

What are the types of inherited colour vision deficiencies?

  • Protan:
    • Protanope-no red cone
    • Protanomal-abnormal red cone
  • Deutan
    • Deutanope-no green cone
    • Deutanomal-abnormal green cone (most common of all colour vision defects)
  • Tritan
    • Tritanope-no blue cone
    • Tritanomal-abnormal blue cone

197

What do protanopes need in order to be able to see traffic lights properly?

Need colours to be brighter, so that they can see the change in brightness.

198

What is the preliminary means of diagnosing colour blindness?

Pseudoisochromatic plates

199

What are the 2 components involves in the control of gaze?

  • Oculomotor system:
    • Moves the eyes in the orbit (whilst head is still)
    • Involves extraocular muscles and neural pathways that coordinate movement of each eye.
  • Head-movement system:
    • Moves the eye sockets as a whole (whilst head moves).
      • Involves vestibular system as well as oculomotor system

200

What are the 5 different types of eye movements?

  1. Saccadic eye movements: shifts fovea rapidly to a new visual target
  2. Smooth pursuits: keeps the image of a moving target on the fovea
  3. Vergence: moves eyes in opposite directions
  4. Vestibular ocular: holds image still on the retina during brief head movements.
  5. Optokinetic: holds the image stationery during sustained head rotation or translation.

201

What are the 6 extraocular eye muscles?

  • 4 rectus muscles: superior, inferior, medial, lateral
  • 2 obliques: inferior, superior

202

What are the different movements of the eyes?

Elevation, adduction, abduction, depression, intorsion and extorsion.

203

What are the primary actions of the rectus extraocular muscles?

  • Superior Rectus: Elevation
  • Inferior Rectus: Depression
  • Medial rectus: Adduction
  • Lateral rectus: Abduction

204

What are the primary actions of the oblique extraocular muscles?

  • Superior oblique: intorsion
  • Inferior oblique: extorsion

205

Where do the oblique extraocular eye muscles insert?

  • Superior oblique: behind the equator at an oblique angle close to the MR.
  • Inferior oblique: behind the equator close to the MR.

206

Why do multiple muscles elevate and depress the eyes?

Because of the insertion of muscles into the eyeball.

207

When are each of the extraocular eye muscles tested during the eye movement test?

See image.

208

How is the heirarchical control of eye movements organised?

  • Lower motor neurons (cranial nerves)
  • Brainstem eye movement centres (reticular formation)
  • Higher cortical areas (Frontal eye fields)

209

Which nerves innervate the extraocular eye muscles?

  • Oculomotor nerve:
    • innervates SR, IR, MR, IO
  • Abducens nerve (CNVI)
    • innervates LR
  • Trochlear nerve (CNIV):
    • innervates SO

210

How are the movements from one eye coordinated with the other?

  • Medial longitudinal fasciculus (MLF):
    • White matter tract that connects the various cranial nerve nuclei
  • Reticular formation
    • Pontine paramedian reticular formation
    • Mesencephalic paramedian reticular formation

211

What are the two eye movement control centres in the brainstem?

  • Pontine paramedian reticular formation
    • Horizontal gaze centre
    • Coordination of MR and LR of each eye
    • Coordination of CNIII & CNVI
  • Midbrain RF contains
    • Vertical gaze centre
    • Coordination of SO and SR of each eye
    • Coordination of CNIV and CNIII

212

How are horizontal saccades controlled neurally?

  • Pontine Paramedian reticular formation
    • Burst neurons
      • Fire at high frequency just before movement.
      • Several types:
        • Provide excitatory connections with ispilateral abducens.
        • Inhibitory burst neurons suppress the activity of the contralateral abducens
    • Omnipause neurons
      • Fires continuously during the saccade.
      • GABAergic
      • Project to contralateral abducens nucleus

213

What is the circuit for neural control of cascades?

  • Requires simultaneous excitation of burst neurons and inhibition of omnipause neurons
  • Excitatory Burst neurons receive input from Cortex.
  • Inhibitory burst neurons inhibit contralateral abducens nucleus

214

What are eye movements ultimately driven by?

Behaviour

215

Which upper motor neurons are involved in driving the gaze centres?

  • Frontal eye fields, and posterior parietal cortex.
  • FEF controls saccades in the contralateral direction
  • Superior colliculus
  • Basal ganglia

216

What is the vestibulo-ocular reflex?

The ability to maintain focus on stationary object while moving head without loss of visual focus or dizziness.

217

How are the eyes coordinated with the head movements?

  • Vestibular system provides information about the position of the head in space.
  • Coordinates the position of the head and eyes.
  • Semicircular canals & otolith organs (saccule & utricle)
    • Semicircular canals: head position
    • Otolith: linear acceleration

218

What are the components of the vestibular apparatus?

  • Semicircular canals & otolith organs (saccule & utricle)
  • Semicircular canals: head position
  • Otolith: linear acceleration

219

How does transduction of head movements work?

See image.

220

How are head movements transduced into neural signals in the semicircular canals?

See image.

221

What is vestibular information carried by?

CNVIII (vestibulocochlear nerve) to vestibular nuclei in the medulla (#6).

222

Which cranial nerves must be recruited to coordinate head and eye movements?

To coordinate head and eye movements information from the vestibular nuclei must be coordinated with the CNIII, CNVI nuclei.

223

Describe the entire vestibular-ocular reflex involved in turning the head to the left.

  • Turning head left
  • Left horizontal semicircular canal-left vestibular nucleus- contralateral NVI-LR (of Right eye).
  • Another projection from NVI to NIII (via MLF)-medial rectus of LE.
  • To ensure speedy operation there is also a direct projection from left vestibular nucleus to CNIII-MR.
  • Inhibitory input from RIGHT side.