Special Senses

4 Special senses

1. Sight

2. Hearing

3. Taste

4. Smell

Protects eye

cushion of fat

4 Accessory structures of eye

1. Extrinsic eye muscle

2. Eyelids

3. Conjuctiva

4.Lacrimal apparatus

Eyelid

Protects eye anteriorly

Papebral fissure

Space between eyelids when eye is open

Tarsal glands

Located along edges of eyelids, Responsible for excreting oily substance that assists lubricating eye

Conjunctiva

1. Lines the eyelids and covers outer surface of eyelids and eye itself

2. Binds with corneal epithelium

3. Secretes mucus, keeping eye moist

Lacrimal apparatus

1. Lacrimal gland

2. Number of ducts draining lacrimal secretions into nasal cavity

Lacrimal glands

1. Located superior laterally to each eye

2. Act to continually release dilute salt solution onto anterior surface of eye

Lacrimal secretions

1. Muscus

2. Antibodies

3. Lysozyme

2 Functions of tears

1. Protect eye

2. Moisten eye

Extrinsic eye muscle

1. 6 total

2. Produce gross eye movements

3. Allow to actively follow moving object

4. Attach to outer portion of eye

3 Layers of the eye

1. Fibrous

2. Vascular

3. Sensory

Internal eye structure

1. Spherical

2. Made of 3 layers

3. Fluid filled center

Fibrous layer of eye

1. Outmost layer

2. Consists of sclera and transparent cornea

Sclera

1. Made of thick, white connective tissue

2. Can be seen anteriorly

Cornea

1. Located in center of sclera

2. Clear area where light enters eye

3. Supplied with nerve endings

4. Vulnerable to damage

5. Ability to repair itself

6. Can be transplanted without rejection

Vascular layer of the eye

1. Middle layer of ear

2. 3 distinguishable regions

3 Regions of vascular layer of ear

1. Choroid

2. Ciliary body

3. Iris

Choroid

1. Most posterior region of vascular layer

2. blood rich nutrient covering

3. Contains dark pigment to prevent light scattering in eye

Ciliary body

Region where lens attaches via ciliary zone

ciliary zone

suspensory ligament

Iris

1. Pigmented area

2. Contains pupil

Pupil

1. Rounded opening in iris

2. Smooth muscle fibers act to open or close

Sensory layer of eye

1. Inner layer of the eye

2. Primarily made of retina

Retina

2 layered structure, Extends anteriorly to ciliary body of eye

Pigmented layer of retina

Reacts similar to choroid, Removes dead cells and photoreceptors, Stores vitamin A

Inner layer of retina

1. Transparent

2. Contains rods and cones or photoreceptor cells

Optic disc

1. AKA blind spot

2. Only place where photoreceptors are not scattered in retina

3. Where the optic nerve exits

Rods

1. Most dense on periphery of retina

2. Number decreases towards center of retina

3. Allow for seeing gray tones in dim light and peripheral vision

Cones

1. Allow for seeing details and color in bright light

2. 3 types in sensory layer

3. Each type sensitive to specific wavelength of visible light

Fovea centralis

1. Lateral to blind spot

2. Tiny area of high cone concentration

3. High visual acuity

Lens

1. Focuses light on the retina

2. Held upright by ciliary zonule

3. Attached to ciliary body

4. divided into 2 chambers providing structure and intraocular pressure

2 Chambers of lens

1. Aqueous

2. Vitreous

Aqueous chamber

1. Anterior

2. contains clear watery fluid called aqueous humor

Vitreous chamber

1. Posterior

2. contains gel-like substance called vitreous humor

Internal eye muscles

1. Controlled b y autonomic nervous system

2. Control pupil size

3. Control lens configuration

External eye muscles

1. Eye movement

2. Controlled by somatic fibers of cranial nerves

Photopupillary reflex

1. Pupil constricts to prevent light from damaging photoreceptor cells

2.Pupils constrict when objects are close for more acute vision

2 Distinct functions of ear

1. Hearing

2. Balance

3 Main parts of ear

1. External ear (hearing)

2. Middle ear (hearing)

3. Internal ear (hearing and balance)

External ear

1. Comprised of auricle (pinna) and external auditory meatus (auditory canal)

Auditory meatus

1. Short narrow chamber

2. Lined with skin and cerminous glands

cerminous glands

Secrete cerumen (ear wax) which traps foreign bodies and repels insects

Ear drum

functions as end of external ear and beginning of middle ear

Middle ear

1. AKA tympanic cavity

2. Small, air-filled mucosa line cavity within temporal bone

Pharyngotympanic tube

1. AKA auditory tube

2. Runs obliquely downward

3. Links middle ear with throat

4. Typically closed but briefly opens

Ossicles

1. 3 bones in the ear

2. Transmit vibration motion of eardrum to fluids of inner ear

3 bones of middle ear

1. Malleus (hammer)

2. Incus (anvil)

3. Stapes (stirrup)

Sound transfer process

1. Ear drum moves transferring motion to malleus

2. Malleus hits incus

3. Incus transfers to stirrup

4. Stirrup press on oval window and sends motion to fluid located in inner ear

Inner ear

1. Maze of bony chambers (filled with perilymph)

2. AKA Osseous labyrinth

3 Distinct parts of osseous labyrinth

1. Cochlea

2. Vestibule

3. Semicircular canals

Membranous labyrinth

1. Suspended in perilymph

2. system of membrane sac that follow shape of bony labyrinth

3. Contains endolymph

Static equilibrium

1. Allows to keep head erect

2. Made of calcium salts

Maculae

1. Located in membrane sacs of vestibule

2. Receptors influencing static equilibrium

3. Report changes in head position with respect to gravity

Dynamic equilibrium

1. Receptors found in semicircular canals

2. receptors respond to angular or rotator movement of the head

Olfactory system

1. Sense of smell

2. based on chemoreceptors

Olfactory receptor cells

neurons equipped with olfactory hairs (long cilia) protruding from nasal epithelium

Olfactory hairs

1. Surrounded by layer of mucus excreted by nearby glands

2. Hairs are stimulated when chemicals dissolve in mucus

3. Signal is sent to olfactory nerve then transported to olfactory part of brain

2 types of papillae on tongue

1. Circumvallate pappilla

2. Fungiform papilla

Circumvallate pappilla

taste buds on the side

Fungiform papilla

taste buds on top

Gustatory hairs

1. Respond to dissolved chemicals in saliva

2. Protrude through taste pores (once stimulated transmit impulses via cranial nerves