The Senses
! Special senses
o Smell
o Taste
o Sight
o Hearing
o Equilibrium
The Eye and Vision
! 70 percent of all sensory receptors are in the eyes
! Each eye has over 1 million nerve fibers
! Protection for the eye
o Most of the eye is enclosed in a bony orbit
o A cushion of fat surrounds most of the eye
Accessory Structures of the Eye
! Eyelids and eyelashes
! Conjunctiva
! Lacrimal apparatus
! Extrinsic eye muscles
Accessory Structures of the Eye
! Eyelids
o Meet at the medial and lateral commissure (canthus)
! Eyelashes
o Tarsal glands produce an oily secretion that lubricates the eye
o Ciliary glands are located between the eyelashes
Accessory Structures of the Eye
! Conjunctiva
o Membrane that lines the eyelids
o Connects to the outer surface of the eye
o Secretes mucus to lubricate the eye and keep it moist
Accessory Structures of the Eye
! Lacrimal apparatus = lacrimal gland and ducts
o Lacrimal gland—produces lacrimal fluid; situated on lateral aspect of each eye
o Lacrimal canaliculi—drain lacrimal fluid from eyes medially
o Lacrimal sac—provides passage of lacrimal fluid towards nasal cavity
o Nasolacrimal duct—empties lacrimal fluid into the nasal cavity
© 2015 Pearson Education, Inc.
, Accessory Structures of the Eye
! Function of the lacrimal apparatus
o Protects, moistens, and lubricates the eye
o Empties into the nasal cavity
! Lacrimal secretions (tears) contain:
! Dilute salt solution
! Mucus
! Antibodies
! Lysozyme (enzyme that destroys bacteria)
Accessory Structures of the Eye
! Extrinsic eye muscles
o Six muscles attach to the outer surface of the eye
o Produce eye movements
Structure of the Eye
! Layers forming the wall of the eyeball
o Fibrous layer: outside layer
o Vascular layer: middle layer
o Sensory layer: inside layer
! Humors are fluids that fill the interior of the eyeball
Structure of the Eye: The Fibrous Layer
! Sclera
o White connective tissue layer
o Seen anteriorly as the “white of the eye”
! Cornea
o Transparent, central anterior portion
o Allows for light to pass through
o Repairs itself easily
o The only human tissue that can be transplanted without fear of rejection
Structure of the Eye: Vascular Layer
! Choroid is a blood-rich nutritive layer in the posterior of the eye
o Pigment prevents light from scattering
! Modified anteriorly into two structures:
1. Ciliary body—smooth muscle attached to lens by ciliary zonule (suspensory
ligament)
2. Iris—regulates amount of light entering eye
! Pigmented layer that gives eye color
! Pupil—rounded opening in the iris
© 2015 Pearson Education, Inc.
! Special senses
o Smell
o Taste
o Sight
o Hearing
o Equilibrium
The Eye and Vision
! 70 percent of all sensory receptors are in the eyes
! Each eye has over 1 million nerve fibers
! Protection for the eye
o Most of the eye is enclosed in a bony orbit
o A cushion of fat surrounds most of the eye
Accessory Structures of the Eye
! Eyelids and eyelashes
! Conjunctiva
! Lacrimal apparatus
! Extrinsic eye muscles
Accessory Structures of the Eye
! Eyelids
o Meet at the medial and lateral commissure (canthus)
! Eyelashes
o Tarsal glands produce an oily secretion that lubricates the eye
o Ciliary glands are located between the eyelashes
Accessory Structures of the Eye
! Conjunctiva
o Membrane that lines the eyelids
o Connects to the outer surface of the eye
o Secretes mucus to lubricate the eye and keep it moist
Accessory Structures of the Eye
! Lacrimal apparatus = lacrimal gland and ducts
o Lacrimal gland—produces lacrimal fluid; situated on lateral aspect of each eye
o Lacrimal canaliculi—drain lacrimal fluid from eyes medially
o Lacrimal sac—provides passage of lacrimal fluid towards nasal cavity
o Nasolacrimal duct—empties lacrimal fluid into the nasal cavity
© 2015 Pearson Education, Inc.
, Accessory Structures of the Eye
! Function of the lacrimal apparatus
o Protects, moistens, and lubricates the eye
o Empties into the nasal cavity
! Lacrimal secretions (tears) contain:
! Dilute salt solution
! Mucus
! Antibodies
! Lysozyme (enzyme that destroys bacteria)
Accessory Structures of the Eye
! Extrinsic eye muscles
o Six muscles attach to the outer surface of the eye
o Produce eye movements
Structure of the Eye
! Layers forming the wall of the eyeball
o Fibrous layer: outside layer
o Vascular layer: middle layer
o Sensory layer: inside layer
! Humors are fluids that fill the interior of the eyeball
Structure of the Eye: The Fibrous Layer
! Sclera
o White connective tissue layer
o Seen anteriorly as the “white of the eye”
! Cornea
o Transparent, central anterior portion
o Allows for light to pass through
o Repairs itself easily
o The only human tissue that can be transplanted without fear of rejection
Structure of the Eye: Vascular Layer
! Choroid is a blood-rich nutritive layer in the posterior of the eye
o Pigment prevents light from scattering
! Modified anteriorly into two structures:
1. Ciliary body—smooth muscle attached to lens by ciliary zonule (suspensory
ligament)
2. Iris—regulates amount of light entering eye
! Pigmented layer that gives eye color
! Pupil—rounded opening in the iris
© 2015 Pearson Education, Inc.
