Special sense organs

neurology, opthalmology and special senses

list all special sense organs

• nose- olfaction

• vomeronasal organ- phermomone detection

• tongue- taste

• eye- vision

• ear- hearing and balance

olfaction

• detected by special cells in muscosa of nasal cavity

• mucose= olfactory epithelium, contain sensory receptors

• neurons (bipolar) pass through epithelial surface to olfactory bulb in cranium after passing through bony cribiform plate (separate cranial cavity from nasal cavity)

• cribiform plate has small pores

• olfactory epithelium held by supporting cells that secrete lipid rich mucus, odorants dissolve in this fliod and reach the sensory receptors

• signal tranduction takes place through neurons

vomeronasal organ

• found on the floor of the nasal cavity

• ducts link nasal and oral cavities caudal to incisor teeth

• are blind ending caudal sacs

• flehmen reaction- pump air in and out (sexual and social behaviour)

• aroma is the combined effect of neural inputs from the sense o smell and taste

gustation

• gustatory receptors found on the tongue mucosa

• sensory neurons carry info to the brain

• receptor cells have one single receptor type so each receptor can only detect one form of taste

• gustatory inputs link directly to centres involving ingestion, food avoidance, insulin release, diuresis when water in pharynx

vision

• eye has transparent media that conducts light to stimulate photoreceptor cells

• vitreous humor is gel like substance filling the eye

• sclera is a tough connective tissue to maintain integrity and strength- continuous with membrane covering the brain.

ear

• outer middle and inner

the eye

Transparent media- Cornea, aqueous humour, lens and vitreous humour direct and converge light on the photoreceptor cells on the retina

Non-Transparent media- Choroid, Uvea, Sclera- Support transparent media

The photosensitive layer - retina made up of rod and cones receptor cells. Cones for daylight vision and rods for night vision.

Light splits chemical compound -Rhodopsin in cones and rods and triggers signal transduction thru optic nerve. The signals are transmitted to the optic cortex of the brain.

outer ear

sound collected from external auditory canal to the tympatic canal and tympatic membrane

middle ear

maleus, incus and stapes conducts sound to oval window. also connected to eustachian tube to the nasopharynx

inner ear

oval window transmits waves to the cochlea which contain sensory receptor cells known as hair cells from where signals are transmitted to the brain via CN VIII

Ear- balance and motion

• inner ear has semicircular canals that detect angular movement while the saccule and utricle (maculae) detect linear acceleration

cochlea

• basilar membrane

• organ of corti

• hair cells

• CN VIII

• fluid movement in the cochlea caused by sound vibration on the oval window cause a standing wave to travel in cochlea canals.

• so hair cells on basilar membrane bends against tectorial membrane

• then signals are generated and sent to the brain

• hair cells bend due to fluid movement and discharge electrical signals to the brain

semi circular canal

• cupula

• hair cell

• CN III

• hair cells of the cupula bend due to fluid movement in the semicircular canals and discharge electrical signals to the brain

saccule and utricle

• detection of linear acceleration

• hair cells

• CN VIII

• hair cells (otoliths) bend due to fluid movement caused by inertia in the saccule and utricle causing them to discharge electrical signals to the brain

• two are in right angles to each other so can only detect linear movement in one plane