special senses -ANAT

what are the 6 special senses?

taste, olfaction, hearing, vision, and equilibrium

what is the tongue ?

it is a large muscle of the mouth, helps manipulate food while eating

whats taste and taste buds

taste: is a chemical sense conveyed by taste buds

taste bud: are the receptors for taste 

• contain gustatory cells which act as taste receptors and relay info to the brain 

• contain taste pore which are pores for chemical to activate gustatory cells 

what is papillae and what are the 4 types 

1. filiform papillae 

2. fungiform papillae 

3. circumvallate papillae 

4. foliate papillae

Papillae are elevations on dorsal surface of tongue 

explain the 4 types of papillae

filiform papillae

• anterior 2/3 of tongue

• no taste buds

• detect temp and manipulate food

fungiform papillae

• located on tip and sides of tongue

• contain only a few taste buds each

circumvallate papillae

• arranged in an inverted V-shape on the back of the tongue

• majority of taste buds

foliate papillae

• extend as ridges on posterior lateral side

• house taste buds that are used during childhood and infancy

what are the basic taste sensations ?

• salty

• sweet

• sour

• bitter

• umami: savory taste

• all sense combine to give different taste sensations

3 pathway of taste 

• taste buds activate CN VII, IX and X 

1. CNs synapse in brainstem 

2. neurons from brainstem project to thalamus 

3. neurons from thalamus project to insula 

whats olfaction?

• it is a chemical sense conveyed by olfactory receptors

• consist of olfactory neurons CN I that detect chemicals in air dissolved in mucus

2 pathway of smell

• olfactory cells synapse in olfactory bulb

1. CN I axons travel through cribiform plate and synapse on neurons in olfactory bulb

2. Neurons from oflactory bulb project to form olfactory tract which projects to temporal lobe

* olfaction is not relayed through the thalamus *

explain eyebrows, eyelashes, eyelids, palpebral fissure, medial/later palpebral commissures, and lacrimal caruncle 

eyebrows: keep sweat out of eyes 

eyelashes: protect surface of eye 

eyelids (palpebrae): moveable protective covering, distribute tears (lacrimal fluid) during blinking 

palpebral fissure: separates eyelids 

medial and lateral palpebral commissures: unite eyelids, the two “corners” of the eye 

The lacrimal caruncle is the pink region in the medial commissure 

whats conjunctive and what are the 2 layers of it?

conjunctive: lubricate the eye, contain blood vessels to nourish cells of eyeball

ocular conjunctiva:

• continuous lining of the external anterior surface of the eye, and doesn’t cover cornea

palpebral conjunctiva:

• lining of internal surface of eyelids

whats the lacrimal apparatus ?

lacrimal apparatus: produces, collects and drains lacrimal fliud (tears) from eye

• lacrimal gland produces tears

• tears secreted onto eyeball are washed medially toward lacrimal caruncle

• tears flow from lacrimal sac into nasolacrimal duct and then released through nostrils or evaporation

what are the 3 tunics of the eye 

fibrous tunic

• provides protection and attachment site for muscles 

vascular tunic 

• vascularized to provide nourishment to cells 

neural tunic 

• provides sensory function for vision 

what 2 structures are in the fibrous tunic ?

• its the outermost layer of the eye 

1. sclera: “white of the eye”, posterior portion 

2. cornea: anterior continuation of the sclera, transparent protective covering, bends light for focusing 

what are the 3 structures in the vascular tunic ?

• middle layer of the eye

1. Choroid:

• most extensive and posterior region

• vascularized to supply nutrients to retina

• pigmented to absorb light

2. ciliary body: thick anterior projection of the choroid

• focuses the lends

• makes aqueous humor

• suspensory ligaments: extend from ciliary body to lens

• lens: avascular structure of the eye for fine focusing of light

3. iris

• colored portion of the eye

• pupil: black hole in center of iris

• contains muscles that adjusts the size of the pupil in bright/dim light

  • pupillary constrictor: constricts pupil

  • pupillary dilator: dilates pupil

whats the neural tunic and what are some important components of it ?

• innermost layer containing the retina 

• retina: light sensitive, innermost layer containing photoreceptors, there are 2 layers

  • Pigmented layer and neural layer

  • Pigmented layer: cells absorb light energy that passes through the retina and provide photoreceptors

  • Neural layer: organized layer of cells

• ora serrata:

  • jagged margin at the end of the neural layer of the retina

  • other side has continuation of pigmented layer that continues to cover ciliary body and posterior side of iris

what are the 3 layers of the neural tunic?

1. photoreceptor layer: comprised of photoreceptors

• rods and cones

2. bipolar cells: synapse with photoreceptors and ganglion cells

3. ganglion cells: axons of these cells leave the retina and form the optic CN II

explain the 2 photoreceptors ?

1. rods are used in dim light

• more than 100 million per eye

• sees black, white and gray

2. cones are used in bright light

• less than 10 million in each eye 

• concentrated in posterior eye 

• provides sharp vision and color vision 

what are the 2 specialized areas in the neural tunic ?

1. macula lutea

• a region lateral to the optic disk

• contains the fovea centralis

• fovea centralis: a spot with the highest density of cones (provides the sharpest vision)

2. optic disc

• region of retina where axons exit to form optic CN II

• no photoreceptors are present (blind spot)

what are the two cavities in the eye separated by the lens and what humor is there?

Anterior cavity: space between the lends and the cornea

• Anterior chamber of anterior cavity is between the iris and cornea

• posterior chamber of anterior cavity is between lens of iris

• contains aqueous humor which provides nutrients to lens and cornea

Posterior cavity: space between the lends and the retina

• contains vitreous humor which maintains the shape of the eyeball

whats the 3 pathways of vision?

1. optic CN II 

• axons partially cross at optic chasm and travel in bundles as the optic tract 

2. optic tract projects to superior colliculus and the thalamus 

3. axons project from thalamus to the occipital lobe 

what are external anatomy of the ear

auricle (aka pinna)

• the ear

• funnel shaped cartilaginous structure

external acoustic meatus

• the ear canal

• bony tube from pinna to tympanic membrane

tympanic membrane

• the eardrum

• boundary separating the external and middle ear

• vibrates in response to sound

what are the auditory tube and auditory ossicles 

auditory tube is a passageway into the nasopharynx (back of nasal cavity) 

auditory ossicles: three small bones in the middle ear (smallest bones of the body) 

• malleus: first ossicle attached to medial surface of tympanic membrane and the incus 

• incus: middle ossicle 

• stapes: last ossicle attached to incus and oval window 

what are the 2 regions of the temporal bone ?

1. bony labyrinth

• Cavitites within bone

• filled with perilymph fluid

2. membranous labyrinth/cochlear duct

• fluid filled membrane lined tubes and spaces within bony labyrinth

• house receptors for equilibrium and balance

• filled with endolymph fluid

explain cochlea and the components of it

• its a part of the bony labyrinth

• houses receptors for hearing

• connected to two windows

• oval window: carries vibrations into the cochlea

• round window: carriers vibrations out of the cochlea

1. scala vestibuli: superior chamber

2. cochlear duct: middle chamber

3. scala tympani: inferior chamber connected to round window 

what are the membranes in the cochlea that separates the scala (ducts)

vestibular membrane: separates scala vestibuli and cochlear duct

basilar membrane: separates scala tympani and cochlear duct

whats the organ of corti/spiral organ?

• it contains receptors for hearing (hair cells)

• supporting cells sit on the basilar membrane

• hair cells are dispersed within the supporting cells

• stereocilia apical modifications that embed into the overlaying tectorial membrane

• tectorial membrane: gel membrane within cochlear duct

know pathway of sound

medulla oblongata --> pons --> inferior colliculus --> thalamus --> temporal lobe

explain semicircular canals and vestibule

semicircular canals: are part of the bony labyrinth

• 3 canals that are perpendicular to each other

• ampulla: bulbous region at the bottom of each semicircular canal

• detect rotational motion

vestibule: is a part of the bony labyrinth

• contains 2 saclike membranous labyrinth structures

• saccule: detect vertical movement

• utricle: detect horizontal movement

• both detect location of head with respect to gravity