SPECIAL SENSES

Special Senses

• Vision

• Hearing and balance

Visual System: Accessory Structures

• Eyebrows: shade; inhibit sweat• Eyelids (palpebrae) with

conjunctiva. • Conjunctiva: thin transparent

mucous membrane• Eyelashes: double/triple row of

hairs.

Lacrimal Apparatus

• Lacrimal gland: produces tears to moisten, lubricate, wash. Tears pass through ducts and then over eye.

• Lacrimal canaliculi: collect excess tears through openings called puncta.

• Nasolacrimal duct: opens into nasal cavity

Extrinsic Eye Muscles

Anatomy of the Eye

• Three coats or tunics:• Fibrous: sclera (whites) and cornea (transparent)• Vascular: choroid (w/in sclera), ciliary body (attaches lens), iris• Nervous: retina

Retina

• Rods – sensory cells used in low illumination

• Cones – sensory cells that detect color – 3 types of pigment – blue, red, green

• Most images focused on fovea centralis (most concentrated area of cones)

• Rods and cones synapse with bipolar cells – which then synapse with ganglion cells – which form the optic nerves

Focusing

The Ear

• External ear: hearing. Terminates at eardrum (tympanic membrane). Includes auricle (pinna) & external auditory meatus

• Middle ear: hearing. Air-filled space containing auditory ossicles • Inner ear: hearing and balance. Interconnecting fluid-filled tunnels

and chambers within the temporal bone

Inner Ear

Auditory Function

• Sound waves funnel down auricle and external acoustic meatus to vibrate tympanic membrane (ear drum)

• Tympanic membrane vibrations passed along auditory ossicles (ear bones) to inner ear

• These vibrations cause lymph to vibrate which moves the stereocilia of inner hair cells

• Bending of stereocilia causes mechanical opening of ion channels – depolarization

• Depolarization leads to action potentials in vestibulocochlear nerve

A

C

B

D

E

F

Practice Questions

The receptors for sound reception and equilibrium are located in the

A. in the outer, middle and inner cavities. 

B. inner ear cavity. 

C. middle ear cavity. 

D. in the middle and inner ear cavities. 

E. outer ear cavity.

When a person cries, he or she tends to keep on wiping their dripping nose. The nose drips because

A. special secretory glands are located in the nose start to produce secretions into the nose. 

B. lacrimal gland secretions wash the eyeball and drain into the lacrimal duct which empty into the nasal cavity. 

C. the nasal mucosa is sensitized to produce mucous into the nose. 

D. the eyeball produces tears that drain into the nasolacrimal duct and then into the nose. 

E. when a person cries olfactory mucosa are sensitized to increase secretions into the nose.

When focusing on a distant object the lens is    

A. more concave. 

B. more flattened. 

C. more convex. 

D. not changed.

The auditory tube allows pressure equalization between the middle ear and the external environment. 

 True False

The semicircular canals respond to rotational movements. 

 True False

The size of the pupil is dependent on the contraction of the muscles of the iris.

 True False

The rods of the retina operate in bright light and provide high acuity vision.

 True False

Impulses from the olfactory epithelium are sent to the brain via cranial II. 

 True False

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The cornea is part of the vascular tunic. 

 True False