Special Senses

olfactory organs

olfactory epithelium

• olfactory receptors (starting point where odor is detected)

• supporting cells and stem cells (replacement and support)

olfactory receptors

modified neurons with projections into the mucus of the upper nasal cavity

odor substance binds to the dendrites to depolarize

**odor goes to dendrites, then axon gets action potential

olfactory pathway

• olfactory receptor neurons send signals to the olfactory bulb (cranial nerve 1)

• signals to olfactory cerebral cortex (temporal lobe), hypothalamus so emotional response, and limbic system without a direct relay to the thalamus (no conscious awareness)

• the number of receptors and sensitivity decrease with age

gustation organs

• gustatory receptors over the tongue and portions if pharynx and larynx

• taste buds

• gustatory cells (and microvilli)

• transitional cell

• stem cell

gustatory pathway

• facial cranial nerve, glossopharyngeal nerve, and vagus nerve carry information to the nucleus solitarius of the medulla oblongata

• medial lemniscus tract to thalamus therefore conscious awareness

• 3rd order neuron to gustatory cortex

nucleus solitarius

relay station for visceral infogust

gustatory cortex

further processes information about texture and temperature

external ear

captures vibrations and sound

• auricle

• ear canal

• tympanic membrane (ear drum)

middle ear

magnifies the vibrations

• malleus, incus, stapes (little bones in the ear)

• eustation (auditory) tube

eustation (auditory) tube

communicates with nasopharynx to equalize pressure

inner ear

senses vibrations

• vestibule

• cochlea

vestibule

looks like the head of a snail

works with equilibrium; fluid filled cavity that includes utricle and saccule which detects acceleration and gravity

auditory pathway

• stapes vibrates oval window of vestibule

• vibrations continue down the cochlea and vibrate the organ of corti within the cochlea

• hair cells (mechanoreceptors) are activated when basilar membrane and tectorial membrane vibrate

• cochlear branch of vestibulocohlear nerve carries signal to cochlear nucleus of vestibulocochlear nucleus in medulla and pons

• to the thalamus and cerebral cortex with collaterals to inferior colliculi for auditory reflex

CONTRALATERAL

lateral semicircular canals

detect “no” rotation

anterior semicircular canal

detect “yes” rotation

posterior semicircular canal

detect sidebending

ampulla

bulbous expansion at the base of the ear canal that contains hair cells to sense movement

• hair cells sense movement when they bend

macula

located in the inner ear

home to statoconia crystals over a gel and hair cells that are activated with head orientation and acceleration

vertigo

the inappropriate sense of motion

inner ear problem; crystals are dislodged and can get nystagmus (shaky eyes)

motion sickness

conflicting information from the eyes and inner ear

balance pathway

• info from hair cells travel to the vestibular nucleus in the pons and medulla

output is to the:

• thalamus (therefore conscious)

• superior colliculi (reflexive eye movement)

• vestibulospinal tract

• cerebellum (proprioception)

• red nucleus

vestibulospinal tract

descending tract that gives motor response for head and neck movements

lacrimal gland

responsible for secreting tears

lacrimal sac

located medially on the eye

cornea

avascular so gets its oxygen from tears

anterior chamber with aqueous humor

front part of the eye that covers the pupil and iris

sclera

posterior, dense fibrous CT made of elastic and collagen fibers

forms the outer layer of the eyeball

choroid

vascular layer of the posterior eye between the sclera and the retina

middle layer

retina

just inside the choroid

home to photo receptors

optic disc

where all the axons in the eye converge

lens

focuses the image to the retina

iris

part of the choroid

contains pupillary sphincter muscles that change the size of the pupil when dilating

conjunctiva

thin clear epithelium membrane that covers the eye

pupil

central iris opening

neural retina

contains rods that are light sensitive and cones that are for color vision

ganglion cells

sends action potential to the brain from the optic disc and to the optic nerve

vision pathway

• optic nerves cross at optic chiasm (partial decussation, some information crosses, some remains on the same side)

• can go to the thalamus from the optic chiasm to relay information to the occipital lobe in cerebral cortex

• can go to the superior colliculi in midbrain region which deals with visual reflexes