Visual and Auditory Pathways Flashcards
What are the 3 layers of the eye?
- outer layer = cornea
- middle layer = vascular layer
- inner layer = retina
What is the outer layer of the eye made up of?
- cornea (front, transparent)
- sclera (back, opaque/white)
What is the outer layer of the eye important for?
protection, refraction and transmission of light
What does the middle layer of the eye include?
- choroid
- ciliary body
- iris
What does the ciliary body control?
the tension of the suspensory ligaments on the lens
What happens when the ciliary body contracts?
the tension on the lens is reduced and becomes more convex (used for looking at near objects; accommodation)
What is the pupil?
an opening within the iris that allows light to pass through to the lens
What does the ciliary body secrete?
aqueous humour
Where is aqueous humour reabsorbed?
scleral venous sinus or canal of Schlemm
What happens if the absorption and secretion of aqueous humour is inhibited?
pressure can build up in the anterior chamber and press against the lens which in turn presses against the posterior compartment and beyond leading to glaucoma (blindness)
What does the iris do?
control the size of the pupils
What are the muscles of the iris?
- circularly arranged sphincter pupillae muscles
- radially arranged dilator pupillae muscles
What does the choroid do?
supply nutrients to the retina via a layer of rods and cones
What are the 2 sources of nutrition (blood supply) to the retina?
- central artery of the retina that supplies the majority of the retinal arterial supply except the layer of cones and rods
- diffusion from the carotid artery
What can renal detachment due to trauma cause?
blindness
What are the 3 layers of the retina?
- rods and cones
- bipolar cells
- retinal ganglion cells
What do the retinal ganglion cells do?
form the axons of the optic nerve and send signals to the lateral geniculate nucleus in the thalamus and then to the primary visual cortex in the occipital lobe
What are the cranial nerves involved in visual and auditory pathways?
- CNII - optic nevre
- CNIII - oculomotor nerve
- CNIV - trochlear nerve
- CNVI - abducens nerve
- CNVIII - vestibulocochlear nerve
What is the optic nerve formed by?
axons of retinal ganglion cells in the retina
What is the sheath that covers the optic nerve made up of?
arachnoid trabeculae, pillars, and septa compartmentalising the subarachnoid space
What does the optic tract do?
relay in the lateral geniculate nucleus before terminating in the primary visual cortex
What happens at the optic chiasma?
- axons from the nasal hemiretina cross the midline to the opposite side
- axons from the temporal hemiretina do not cross the midline
Where is the left visual field from both eyes represented?
on the right visual cortex (and vice versa)
Where do some axons in the retina end up?
the Edinger-Westphal nucleus in the midbrain
What do axons that end up in the Edinger-Westphal nucleus do?
mediate the afferent part of the pupillary light reflex (parasympathetic fibres in the oculomotor nerve mediate the efferent part)
What is consensual pupillary light reflex?
the change in pupil size in the eye opposite to the eye to which the light is directed e.g. if the light is shone in the right eye, the left pupil also constricts consensually
What is the myelin of the optic nerve formed by?
oligodendrocytes
What does damage to the optic nerve result in?
blindness