14 - Visual Pathways and Reflexes

Question 1

Where does the optic nerve travel from?

Answer 1

Optic nerve goes from the eye to the optic chiasm

Question 2

What is the function of the lateral geniculate nucleus?

Answer 2

Receives axons from the retina and relays axons in the optic radiation to the primary visual cortex

Question 3

What reflex does the E-W nucleus control?

Answer 3

Pupillary light reflex

Question 4

Which one crosses over - the nasal hemiretina axons or the temporal hemiretina fibres?

Answer 4

Nasal hemiretina

Question 5

What does a partial optic nerve lesion cause?

Answer 5

Ipsilateral scotoma - patch of blindness

Question 6

What does a complete optic nerve lesion cause?

Answer 6

Blindness in that eye

Question 7

What does a optic chiasm lesion cause?

Answer 7

Bitemporal hemianopia - loss of peripheral vision

Question 8

What does an optic tract lesion cause?

Answer 8

Homonymous hemianopia - loss of one complete visual field

Question 9

What does damage to the anterior part of meyer’s loop cause?

Answer 9

Homonymous upper quadrantanopia

Question 10

What does an optic radiation lesion cause?

Answer 10

Homonymous hemianopia

Question 11

What does a visual cortex lesion cause?

Answer 11

Homonymous hemianopia (macular sparing)

Question 12

Describe the pupillary light reflex

Answer 12

Optic nerve is activated and travels to the superior colliculus which travels to the parasympathetic nucleus of CN III (EW nucleus) which then sends impulses to pupillary constrictor muscles to reduce pupil size

Question 13

What is the sensory input and motor output for the pupillary eye reflex?

Answer 13

Sensory = CN II Optic
Motor = CN III Oculomotor

Question 14

What blocks the pupillary light reflex?

Answer 14

Atropine

Question 15

What are the three things that occur in the accommodation reflex?

Answer 15

Pupillary constriction
Thickening of the lens
Convergence

Question 16

What is the function of the thickening of the lens in the accommodation reflex and what is the output of this

Answer 16

Focus on near objects by reducing tension on the suspensory ligaments by tightening ciliary muscles
Output - parasympathetic part of CN III

Question 17

What nerve mediates convergence in the accommodation reflex

Answer 17

CN III - Oculomotor

Question 18

What controls the thickening of the lens and what happens when this is damaged?

Answer 18

Frontal eye fields in the premotor cortex

Damage - inability to direct gaze from one object to another

Question 19

What controls convergence and what happens when this is damaged?

Answer 19

Visual cortex

Double vision - diplopia

Question 20

What is the vestibulo-ocular reflex? (Doll’s eye reflex)

Answer 20

When you turn your head to the side whilst focusing on a distant object
Your eyes rotate in the opposite direction to the head to keep the direction of gaze constant so that the object stays in view

Question 21

What is the afferent and efferent nerves of the vestibulo-ocular reflex?

Answer 21

Afferent - Vestibulo-cochlear nerve VIIII recieves signals from the semi-circular canals
Efferent - Abducens CN VI and oculomotor CN III

Question 22

What is the pathological form of the vestibulo-ocular reflex?

Answer 22

Nystagmus - initial slow rotation followed by a fast flick back

Question 23

What is the caloric stimulation test? What are the directions of the nystagmus when warm and cold water is put in the ear?

Answer 23

Water is irrigated into the external auditory canal
Water is colder than body temperature = Head turns contralateral
Water is water than body temperature = Head turns ipsilateral
COWS = cold - other ear - warm - same ear