Human Anatomy Special Senses

Special Senses Olfaction -- smell Gustation -- taste The Ear Equilibrium Hearing 4. Vision

1. Olfaction (Smell) As few as 4 molecules can activate neurons

1. Olfaction (Smell)

2. Gustation (Taste) Differential distribution of taste buds

2. Gustation (Taste) Start w/ 10,000 taste buds and by 50 yo half are lost Explains why kids don’t like spicy food

Gustation (Taste) VII – ant. 2/3 IX – post. 1/3

3. The Ear Is divided into 3 anatomical regions External ear External auditory meatus to tympanic membrane

3. The Ear Ceruminous glands secrete cerumen – ear wax

3. The Ear Middle Ear Medial to tympanic membrane Contains 3 auditory ossicles Eustachian tube connects middle ear to pharynx

Middle Ear

Auditory Ossicles Base of stapes fills the oval window 20X amplification Malleus Incus Stapes Air movement

The Ear Inner Ear Consists of hollow bony structures filled w/ fluid -- endolymph Contains the organs of: Equilibrium – semicircular canals Hearing -- cochlea

The Inner Ear

The Inner Ear

Semicircular Canals Three Detect motion in three planes: Yes No Tilting head from side to side

Semicircular Canals Hollow bony tubes Filled with endolymph Inside lined with hair cells – specialized neurons Axons, in part, form VIII Otoliths float across hair cells when head is in motion.

Hair Cells

Hair Cells

Otoliths Activate hair cells

Cochlea Spiral shaped Hollow bony, filled with endolymph Lined by hair cells Organ of Corti consists of: Hair cells Tectorial membrane – stimulates hair cells

Cochlea

Cochlea

Organ of Corti

Organ of Corti VIII

Hair Cells

4. The Eye Organ of vision Slightly smaller than a ping pong ball Divided into two cavities Anterior chamber Posterior chamber 2 chambers separated by the lens Consists of 3 layers

Chambers of the Eye L E N S

4. The Eye Outer wall consists of 3 layers From outer to inner: Fibrous tunic Sclera and cornea Sclera is CT 6 extrinsic eye muscles attach Cornea is clear

1. Fibrous Layer sclera (white of the eye) cornea

2. Vascular Layer Middle layer Highly vascular Regulates amount of light into eye – iris Secretes and absorbs aqueous humor –canal of Schlemm

2. Vascular Layer

Iris Iris – pigmented area of middle layer Its margin defines the pupil. pupil iris

Pupillary Muscles parasympathetic Iris sympathetic

Canal of Schlemm

Canal of Schlemm Drains aqueous humor from anterior chamber Can get blocked Aqueous humor continues to be produced Pressure builds up in anterior chamber Causes pressure in posterior chamber Retinal blood vessels are compressed and blood flow decreases Retinal cells die – glaucoma Result is blindness which is irreversible

Glaucoma pressure

3. Retina Innermost layer – nervous layer Consists of several layers of cells including modified neurons that react to light Rods – light-sensitive, allow us to see in low light (125 million/retina) Cones – detect colors (6 million/retina)

3. Retina Axons form Optic n. (II)

Optic Nerve (II) Axons from ganglion cells

Optic Disc Part of retina where ganglion cell axons leave retina

Optic Disc No rods and cones in optic disc– blind spot

Fovea Centralis Center of retina, site of sharpest vision, has highest concentration of rods and cones

Fovea Centralis