A05 Assessment of Vision and Hearing Flashcards
Where does the visual system start and end?
- It starts at the rods and cones of the retina.
- It ends at the gyri on either side of the calcarine sulcus of the occipital lobe.
What is meant when the visual pathway is said to be retinotopically arranged?
The regions of the retina are represented in discrete regions throughout the tract.
List the layers of the eye from superficial to deep.
1 - Sclera.
2 - Uveal tract.
3 - Retina.
Describe the structure of the sclera.
- It is a continuation of the dura mater surrounding the optic nerve.
- At its most anterior pole it is transparent, forming the cornea.
Describe the structure of the uveal tract.
- It is mostly choroid, which is the vascular layer of the eye.
- Anteriorly, it becomes the ciliary body (which contains the muscles which moves the lens), and the stroma of the iris.
Describe the structure of the retina.
- It is an outgrowth of the CNS.
- The outermost part of the retina which is in contact with the choroid is the retinal pigment epithelium.
- The innermost layer of the retina is the neural retina.
What is the lens?
The transparent, biconvex elastic disc behind the uveal tract that separates the anterior 1/5 of the eye from the posterior 4/5.
What maintains the position and shape of the eye?
Intraocular pressure that is generated by production of aqueous and vitreous humour.
What is a cataract?
Opacity of the lens.
Where are aqueous and vitreous humour stored?
- Aqueous humour is contained within the anterior and posterior chambers.
- Vitreous humour is contained within the postremal / vitreous chamber.
Where are the anterior and posterior chambers?
- The anterior chamber is between the cornea and the uveal tract.
- The posterior chamber is between the uveal tract and the lens.
Which layer of the eye accounts for most refraction of light?
Why is this?
- The cornea.
- Because the refractive index of the aqueous humour, vitreous humour and lens are all very similar.
What is the function of the lens?
It adjusts the focus of the eye for near and far objects by action of the ciliary muscles.
What is the advantage of the refraction that arises from the cornea?
It enables peripheral vision.
Define accommodation.
Changing the focus from viewing one object to another.
What is the effect of contraction of the ciliary muscles?
They cause the anterior surface of the lens to bulge, causing the eye to accommodate to near subjects.
What is the pupil?
The densely pigmented aperture in the middle of the iris.
List the main components of the ear.
List the main contents of each component.
1 - Outer ear, consisting of:
- Auricle (visible part of the ear).
- External auditory canal.
2 - Tympanic membrane (eardrum).
3 - Middle ear (tympanic cavity), consisting of:
- Auditory ossicle bones.
- Eustachian tube.
4 - Inner ear, consisting of:
- Cochlea.
- Vestibule.
- Semicircular canals.
What is the eustachian tube?
What is its function?
- The canal that connects the middle ear to the nasopharynx.
- It controls the pressure within the middle ear, making it equal with the pressure outside the body.
What is the barrier between the external and middle ear?
The tympanic membrane.
Through which passage does sound travel before vibrating the tympanic membrane?
The external acoustic meatus.
Which group of bones vibrate as a result of vibration of the tympanic membrane?
Which bones are included in this group of bones?
- The auditory ossicles.
- The malleus, incus and stapes.
Which structure vibrates as a result of vibration of the auditory ossicles?
A membrane which vibrates the perilymph.
What is perilymph?
Where is it located?
- Extracellular fluid.
- It is found within the scala tympani and scala vestibuli of the cochlea.
What results from the action of the waves in the perilymph?
The spiral organ of Corti transmits action potentials via the cochlear part of CNVIII.
List the components of CNVIII.
1 - The vestibular nerve.
2 - The cochlear nerve.
What is the function of the vestibular nerve?
To transmit information regarding the position of the head in space.
What is the function of the cochlear nerve?
To transmit auditory information from the cochlea.
What is the optic disk?
What is the significance of the optic disk?
- The point of exit for ganglion cell axons leaving the eye.
- It is the cause of the blind spot, since no photoreceptors, interneurones or ganglion cells are present here.
Define myopia.
Near-sightedness.
Define hyperopia.
Long-sightedness.
List the muscles that control the size of the pupils.
1 - DIlator pupillae.
2 - Sphincter pupillae.
What is the direct pupillary light reflex?
Constriction of the pupil when it is directly illuminated.
What is the consensual pupillary light reflex?
Constriction of the pupil when the other eye is illuminated.
Define hemianopia.
Blindness in half of the visual field of either or both eyes.
Define homonymous.
Affecting the same part of the field of each eye.
Define heteronymous.
Affecting different parts of the field of each eye.
List 2 arteries that supply the ear.
Which component(s) of the ear does each artery supply?
1 - External carotid artery (middle and outer ear).
2 - Labyrinthine artery (inner ear).
What is the function of the inferior colliculus?
- It is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex.
- It is a point of integration and enables spatial localisation.
