Introduction
Vision
THE SPECIAL SENSES
Structures designed to respond to stimuli
Variable complexity
RECEPTORS
Transducers
Receptor Potential
Generator Potential
RECEPTORS: GENERAL PROPERTIES
Stimulus causing receptor potentials
generator potential in afferent neuron
Nerve impulse
RECEPTORS
SENSATION AND PERCEPTION
Stimulatory Input
Conscious Level = Perception
Awareness = sensation
ADAPTATION
Reduction in rate of impulse transmission when stimulus is prolonged
Modality
Location
Intensity
Duration
INFORMATION CONVEYED BY RECEPTORS
Stimulus Modality
Chemoreceptors
Thermoreceptors
Nociceptors
Mechanoreceptors
Photoreceptors
CLASSIFICATION OF RECEPTORS
Origin of stimuli
Exteroceptors
Interoceptors
Proprioceptors
CLASSIFICATION OF RECEPTORS
Vision
Hearing
Olfaction
Gustation
Vision and hearing involve special sensory structures
SPECIAL SENSES
70% of all sensory receptors are in the eye
Nearly half of the cerebral cortex is involved in
processing visual information
Optic nerve is one of body’s largest nerve tracts
THE EYE AND VISION
The eye is a photoreceptor organ
Refraction
Conversion (transduction) of light into APs
Information is interpreted in cerebral cortex
VISION
Figure 15.1a
Eyelashes
Site where
conjunctiva
merges with
cornea
Lateral
commissure
Medial
commissure
Eyelid
Eyelid
Eyebrow
Palpebral
fissure
(a) Surface anatomy of the right eye
Figure 15.1b
(b) Lateral view; some structures shown in sagittal section
Orbicularis oculi muscle
Eyebrow
Palpebral conjunctiva
Cornea
Eyelashes
Bulbar conjunctiva
Conjunctival sac
Orbicularis oculi muscle
Lacrimal gland and ducts that connect to nasal
cavity
Lacrimal secretion (tears)
Dilute saline solution containing mucus, antibodies,
and lysozyme
Blinking spreads the tears toward the medial
commissure
Drain into the nasolacrimal duct
LACRIMAL APPARATUS
Figure 15.2
Lacrimal gland
Excretory ducts
of lacrimal glands
Lacrimal punctum
Lacrimal canaliculus
Nasolacrimal duct
Inferior meatus
of nasal cavity
Nostril
Lacrimal sac
Six extrinsic eye muscles
EXTRINSIC EYE MUSCLES
Figure 15.3a
Inferior rectus
muscle
Inferior oblique
muscle
Superior oblique
muscle
Superior oblique
tendon
Superior rectus
muscle
Lateral rectus
muscle
(a) Lateral view of the right eye
Figure 15.3c
(c) Summary of muscle actions and innervating cranial nerves
Lateral rectus
Medial rectus
Superior rectus
Inferior rectus
Inferior oblique
Superior oblique
Moves eye laterally
Moves eye medially
Elevates eye and turns it medially
Depresses eye and turns it medially
Elevates eye and turns it laterally
Depresses eye and turns it laterally
VI (abducens)
III (oculomotor)
III (oculomotor)
III (oculomotor)
III (oculomotor)
IV (trochlear)
Muscle Action Controlling
cranial nerve
Wall of eyeball contains three layers (tunics)
Fibrous
Vascular
Sensory (retinal)
STRUCTURE OF THE EYEBALL
Three layers
1) Fibrous tunic
Sclera
Cornea
STRUCTURE OF THE EYEBALL
Figure 15.4a
Sclera
Cornea
Fibrous Tunic
Scleral venous sinus
Corneal Edema
Three layers
2) Vascular tunic (uvea)
Choroid
Ciliary body
Ciliary processes
Ciliary muscle
Iris
STRUCTURE OF THE EYEBALL
Figure 15.4a
Choroid
Sclera
Ciliary body Ciliary zonule
(suspensory
ligament)
Iris Pupil
Lens
Scleral venous
sinus
VascularTunic
Cornea
Three layers
3) Retina
Photoreceptor neurons
Rods and Cones
Bipolar neurons
Ganglion neurons
Optic nerve
Optic disc
STRUCTURE OF THE EYEBALL
Figure 15.4a
Central artery
and vein of
the retina
Optic disc
(blind spot)
Optic nerve
Fovea centralis
Macula lutea Retina Choroid
Sclera
Ciliary body
Ciliary zonule
Cornea
Iris
Pupil
Lens
Scleral venous
sinus
Retina
Figure 15.6b
Pigmented
layer of retina Pathway of light
Pathway of signal output
(b) Cells of the neural layer of the retina
Amacrine cell Horizontal cell
• Rod
Photoreceptors
• Cone
Bipolar
cells Ganglion
cells
Figure 15.6a
(a) Posterior aspect of the eyeball
Neural layer of retina Pigmented
layer of
retina
Central artery
and vein of retina Optic
nerve
Sclera
Choroid
Optic disc
Pathway of light
Blood supply to the retina