Neuro - Session 7 - Special senses

Created by mlom100 

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Smell

CN1&2
noxious stimuli = pain receptors

Describe the olfactory receptor cells

olfactory cilia are chemoreceptors, odours dissolve in mucus and bind to receptors

unusual that second order neuron is CN

first order afferent goes through the cribiform plate

Describe the olfactory pathways

CN1
first order neurons - through cribiform plate and synapse with the second order neurons in the olfactory bulb

second order neurons - travel along olfactory tract (CN1) to the primary olfactory area

third order neurons -thalamus and on to primary olfactory cortex

what is anosmia, hyposmia & hypersmia

unilat = inability to perceive odours
caused by colds, trauma, nasal polyps, allergy

Hyposmia - reduction in ability to perceive smells - caused by cold hay fever and sinusitis

Hyper - psycholgical background (AKA olfactory hyperesthesia)

specific anosmia - loss of selective odurant receptor - poss genetic basis

what is Olfactory Agnosia?

Can physically smell but not name odour, caused by Central Lesions

what is parosmia, phantosmia, cacosmia

distortion of smell
olfactory hallucinations
nasty/bad olfactory auras

what are the four primary modalities of taste?

sweet, salt, sour, bitter, savoury

name the four types of papilla, what is their function, which does not have taste buds

fungiform
foliate
circumvallate

Filiform - have no taste buds

mircovilli act as chemoreceptors

name the nerve that are involved with taste

CNVII - Facial nerve - anterior 2/3 of tongue
CNIX - Glossopharyngeal - posterior 2/3 of tongue
CNX - Epiglottis and Pharynx

what is the taste pathway - Gustatory

first order neuron - receptor to brainstem via CN VII, IX, X
second order neuron - cross at level of the medulla ascend via central Tegmental tract to the thalamus
third order neuron - thalmus to the primary Gustatory cortex

what does Aguseia, hypogeusia, Dysgeusia and Cacoguesia mean?

Aguseia - bi lat taste loss
hypogeusia - decreased taste - age related
Dysgeusia - distortions in taste
Cacoguesia - bad tastes - linked with tumours or epilepsy

Describe the basic structure of the Ear

external ear - Pinna, ear canal sep by tympanic membrane

Middle Ear - Eustacian tube - links pharnx to the middle earossicular chain - pressure transmission and attenuation

inner ear - vestibular system and cochlea

controlled by CN 8

what is the purpose of the middle ear?

movement of the ossicular chain transmits sound waves to the inner ear through vibration. There are muscle that act to reduced the movement of the tympanic membrance and dampen vibration of the staples

what is the labyrinth of the ear comprised of?

bony: cavities in temperal bone filled wit PERILYMPH made of;
semicircular canals
vestibule
cochlea
membranous: inside the bony part and filled with ENDOLYMPH

what is the role of the cochlea in hearing?

The cochlea is auditory portion of inner ear.
It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis
A core component of the cochlea is the Organ of Corti, contains sensory receptors

How do the hair cell help with hearing?

vibration is transmitted through the perilymph cause movement of the membrane boundaries of the organ of corti

this bend the cilia on the hair cell which activates the sensory fibres for CNVIII

the outer hair cells can change length to act as a cochlea amplifier

Describe the auditory pathway

First order: spiral ganglion to the cochlear branch of the CNVIII to the medulla to snapse with the second order neurons in the cochlear nuclei or the superior olive

second order: ipslat to the inferior colliculi or medial genticule nucleus

third to the auditory cortex

name the three types of auditory disturbances

How do you test for the difference

conductive
sensorineural
central

tuning folk test 256HZ - weber/rinne
voice test
audiometry

rinne test

comparison of air vs bone conduction , place tuning folk on the mastoid and then vibrate the folk by the person ear, bone should be shorter than ear this is a positve rinne test

in a conductive hearing loss bone will be better than air

in a sensory neurone loss there should be equal difference between the conduction and air loss thus no real difference should be noted

webers test

unilateral conductive hearing loss would be in ear with the hearing loss.

unilateral sensorineural loss would be heard better in the ear with out loss

what is conductive hearing loss? what are the causes

prevention of transmission of sound to the inner ears

causes include: wax, otitis media, tumour, otosclerosis

what is sensorineural hearing loss? what are the causes?

cause by damage to the cochlea of the CVVIII

common cause: old age, noise exposure, trauma, immune disorders, tumour (acoustic neuroma), medications (NSAIDS)

what are the causes of central hearing loss? causes

due to multiple areas involved

causes by brainstem lesions - damage to the inferior colliculi

define: auditory agnosia

able to hear the sounds but unable to interpret them

define pure word deafness

unable to distinguish between of verbal sounds

define cortical deafness

combination of auditory agnosia, pure word deafness, cortical deafness

how is balance controlled?

vestibular system comprises of the;
3 semicircular canals (each canal contains a ampulla which contrains a crista
utricle and saccule (otolith organs) - each contain a macula

macula - sense static head position
cristae sense kininetic/dynamic movement

describe the static Labyrinth

contains the macula which is in the uricle and the saccule

muculae contain hair cell embedded in the gel matrix (Ca crystals called otoconia)

each long hair cell has a long body and shorter cilia

when gravity acts on the sterocilia this cause movement towards the body and then depolarisation

Describe the dynamic

semicircular canals, ampulla contains a cristae

contain kinocilium hairs

head movement cause perilymph to move in the same direction an the endolymph to move in the opposite direction

displacement of the capula excites the nerve endings

describe the vestibular pathways

first order: afferent for the cristea and the macula travel vis CNVIII to the vestiular neclei of the brainstem

second order - give rise to vestibulo spinal tracts and project to hte medial longitudinal fasciculus to the thalamus

third order - from the thalamus project to the cortex

what is the vestibulo-ocular reflex?

vestibular rotation for the eye to maintain focus of an object

if head rotate to far than the ear flick back to find a new object to focus on

further rotation will cause a flicking back of the eye in alternating fast and slow movements -Nystagmus

Name some disorders of balance

explain their formation

vertigo - spinning sensation
caused by a misplacement of the ca crystals in the ear or central brain lesion

vestibular Nystagmus - uncontrollable oscillation of the eyes - fast phase is AWAY from side of the lesion

peripheral lesion = delayed
central = delayed or intermediate

How do you assess the vestibular nerve?

vestibular assessment
clinical tests - head thrust test - get pt to focus on your nose and move their head 30o
they should be a delay when pt is rotated to the side of the lesion

caloric tests - vestibulo-ocular reflex that involves irrigating cold or warm water or air into the external auditory canal.

COWS: Cold Opposite, Warm Same.

opposite side of the cold water filled ear

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