14 - Visual Pathways and Reflexes Flashcards
Where does the optic nerve travel from?
Optic nerve goes from the eye to the optic chiasm
What is the function of the lateral geniculate nucleus?
Receives axons from the retina and relays axons in the optic radiation to the primary visual cortex
What reflex does the E-W nucleus control?
Pupillary light reflex
Which one crosses over - the nasal hemiretina axons or the temporal hemiretina fibres?
Nasal hemiretina
What does a partial optic nerve lesion cause?
Ipsilateral scotoma - patch of blindness
What does a complete optic nerve lesion cause?
Blindness in that eye
What does a optic chiasm lesion cause?
Bitemporal hemianopia - loss of peripheral vision
What does an optic tract lesion cause?
Homonymous hemianopia - loss of one complete visual field
What does damage to the anterior part of meyer’s loop cause?
Homonymous upper quadrantanopia
What does an optic radiation lesion cause?
Homonymous hemianopia
What does a visual cortex lesion cause?
Homonymous hemianopia (macular sparing)
Describe the pupillary light reflex
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
What is the sensory input and motor output for the pupillary eye reflex?
Sensory = CN II Optic Motor = CN III Oculomotor
What blocks the pupillary light reflex?
Atropine
What are the three things that occur in the accommodation reflex?
Pupillary constriction
Thickening of the lens
Convergence
What is the function of the thickening of the lens in the accommodation reflex and what is the output of this
Focus on near objects by reducing tension on the suspensory ligaments by tightening ciliary muscles
Output - parasympathetic part of CN III
What nerve mediates convergence in the accommodation reflex
CN III - Oculomotor
What controls the thickening of the lens and what happens when this is damaged?
Frontal eye fields in the premotor cortex
Damage - inability to direct gaze from one object to another
What controls convergence and what happens when this is damaged?
Visual cortex
Double vision - diplopia
What is the vestibulo-ocular reflex? (Doll’s eye reflex)
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
What is the afferent and efferent nerves of the vestibulo-ocular reflex?
Afferent - Vestibulo-cochlear nerve VIIII recieves signals from the semi-circular canals
Efferent - Abducens CN VI and oculomotor CN III
What is the pathological form of the vestibulo-ocular reflex?
Nystagmus - initial slow rotation followed by a fast flick back
What is the caloric stimulation test? What are the directions of the nystagmus when warm and cold water is put in the ear?
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
