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