Pathophysiology of Sensory Systems ( Eye & Ear ) Flashcards
Explain the Hearing pathways ( Sensory )
1- CN8 comes in from the basilar membrane in cochlea
2- travels to cochlear nuclei I the Brian stem
3- travels to inferior colliculus in midbrain
4- travels to medial geniculate nucleus in the thalamus
5- Go into sylvan fissure where auditory cortex is in the temporal lobe ( tonotopic map )
Most fibres travel contra laterally , some do ipsilaterally
How do fibres travel in the Hearing Pathway
Most fibres travel contra laterally , some do ipsilaterally
What are the association areas for Hearing
Wernickes area : understanding and processing of language
Close to auditory cortex
What is Conductive Deafness
Difficulty in getting sound waves and relaying them from the outer ear into the cochlea.
What is Sensorineural deafness
Problem converting mechanical vibration into nerve energy. Problem in the cochlea it self or anywhere from the cochlear nerve to the auditory cortex
Common causes of Conductive Deafness
1- Auditory canal : wax
2- Middle ear :
-ruptured tympanic membrane (pressure difference)
- otitis media: infection causing fluid in middle ear
- otosclerosis ; harding of the ossicles
What are the Causes of Sesnsorineural deafness
1- Cochlea :
- result from aging
- acoustic trauma ( sound pollution , damaging high frequency ) - bc loud noises
- Meniere’s disease : inflammation of membranes of the Cochlea
2- Cochlear nerve : Acoustic neuroma ( growth on CN8)
3- Central auditory pathways ( rare ) :
What is Presbycusis
Age related hearing loss : gradual loss of hearing
What are the signs of Meniere’s disease
1- Vertigo
2- Tinitus
3- potential hearing loss
All due to increase of fluid
How to distinguish between sensorineural or conductive deafness
Rinnes test : compares bone and air conduction
- Positive = Air>Bone = normal or sensorineural deafness
- Negative = Bone>Air = Conductive Deafness
Webers test : midline source of bone conduction, running fork at forehead
- should hear it the same in both ears
- might be better in the ear with conductive deafness
Audiometry : playing tones at different frequencies and seeing degree of hearing loss - Can localize where the damage is depending on frequencies
- Can’t hear Low : meniere’s
- Can’t hear High : acoustic trauma
Conductive Deafness would have a positive or Negative Rinnes test and why
Negative
Should be able to hear better via the air conduction than from bone conduction. If that is not the cause then air conduction is being blocked by something
What is the purpose of snellen’s chart , what is normal ?
Tests refracting power and accuracy of the lens.
Normal vision : 6/6 meters away can read the 6th line
What is the purpose of visual field test
To see if there are areas of the retina that are being damaged.
What are the types of refractive defects
1- Presbyopia : Loss of elasticity , receding near point , due to Age
2- Myopia : focussing power too great for eyeball length, needs divergent ( concave ) lenses
3- Hypermetropia: focusing power inadequate for eye length , convergent length
Explain Light Pupillary reflexes
1- Light sources travels down optic nerve into LGB
2- into pretetal nuclei to Edginer Westphal Nuclei in CN3
3- Into Ciliary ganglion and then to Sphincter pupillae
Explain the pathway for Sympathetic pupil dilatation
Exit the T1 , synapses in superior cervical ganglion and then via long ciliary nerve it travels up internal carotid, then affects dilator pupil muscles
Explain the pathway for parasympathetic pupil constriction
1- Signal travels along preganglionic CN3 , then ciliary ganglion to ciliary nerves which stimulates sphincter pupillae
Explain Accommodation Pupillary reflexes
1- Light sources travel down Extraocular spindles+ Optic nerve
2- LGB to convergence centre
3- To Edginer Westphal Nucleus ( CN3 ) to Ciliary Ganglion
4- To sphincter pupillae = constricting
What is Horner’s syndrome
Sympathetic Lesion
Result : ipsilateral defects , pupillary constriction , ptosis , enopthalmous , sweating loss
A dilatation of only 1 pupil to light might mean what
Compression of CN3 resulting in Parasympathetic loss
Bilateral pupillary dilatation to light might mean what
Deep coma / Brian death
Bilateral pupillary constriction to light might mean what
Pontine lesions or the use of opiates
What is Argyll Robertson Pupil ( what causes it )
No light adaptation due to Dorsal Edignger Westphal Nucleus
But Pupil is still constrictiing due to focusing ( accommodation reflex )
What could cause Argyll Robertson Pupil
End stage Neurosyphilis