Complete Diagrams PNS 18 and 19

Complete PNS 23 Worksheet 3 #1 only

Complete PNS 24 Practice Quiz

ACTIVITIES

Introduction

Vision

THE SPECIAL SENSES

Structures designed to respond to stimuli

Variable complexity

RECEPTORS

Transducers

Receptor potential

Generator potential

GENERAL PROPERTIES OF RECEPTORS

Stimulus causing receptor potentials

Generator potential in afferent neuron

Nerve impulse

GENERAL PROPERTIES OF RECEPTORS

SENSATION AND PERCEPTION

Stimulatory input

Conscious level = perception

Awareness = sensation

Information conveyed by receptors

Modality

Location

Intensity

Duration

GENERAL PROPERTIES OF RECEPTORS

ADAPTATION

Reduction in rate of impulse transmission when stimulus is prolonged

Stimulus Modality

Chemoreceptors

Thermoreceptors

Nociceptors

Mechanoreceptors

Photoreceptors

CLASSIFICATION OF RECEPTORS

Origin of stimuli

Exteroceptors

Interoceptors

Proprioceptors

CLASSIFICATION OF RECEPTORS

Vision

Hearing

Olfaction

Gustation

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

VISION INTRODUCTION

The eye is a photoreceptor organ

Refraction

Conversion (transduction) of light into AP’s

Information is interpreted in cerebral cortex

VISION INTRODUCTION

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 apparatus

Lacrimal gland and ducts that connect to nasal cavity

Lacrimal secretion (tears)

Dilute saline solution

Mucus, antibodies, and lysozyme

Blinking spreads the tears toward medial commissure

Drain into the nasolacrimal duct

ACCESSORY STRUCTURES

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

ACCESSORY STRUCTURES

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)

THE EYEBALL

Three layers

1) Fibrous tunic

Sclera

Cornea

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

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

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

Photoreceptors

Rods

More numerous at peripheral region

Dim light

Indistinct, fuzzy, non-color peripheral vision

About 100 million per eye

THE EYEBALL

Photoreceptors

Cones

Red, blue and green

Highest density in macula lutea

Concentrated in fovea centralis

Operate in bright light

High-acuity color vision

THE EYEBALL

Figure 15.7

Macula

lutea

Central artery and vein emerging from the optic disc

Optic disc

Retina

Lens

Biconvex, transparent, flexible

Attached to ciliary body by suspensory ligaments

Allows precise focusing of light on the retina

Forms a partition

Creates an anterior and posterior cavity

THE EYEBALL

Figure 15.14 (1 of 3)

Focal

plane

Focal point is on retina.

Emmetropic eye (normal)

Figure 15.8

Sclera

Bulbar

conjunctiva

Scleral venous sinus

Posterior chamber

Anterior chamber

Anterior

segment

(contains

aqueous

humor)

Corneal- scleral junction

Cornea

Cornea

Corneal epithelium

Corneal endothelium

Aqueous humor

Iris

Lens

Lens epithelium

Lens

Posterior

segment

(contains vitreous

humor)

Ciliary zonule

(suspensory

ligament)

Ciliary

processes

Ciliary

muscle

Ciliary body

1 Aqueous humor is formed by filtration from the capillaries in the ciliary processes. 2 Aqueous humor flows from the posterior chamber through the pupil into the anterior chamber. Some also flows through the vitreous humor (not shown). 3 Aqueous humor is reabsorbed into the venous blood by the scleral venous sinus.

1

2

3

Visual acuity

Ratio of distances

20/20

20/40

Less visual acuity

20/15

More visual acuity

THE PHYSIOLOGY OF VISION

5 processes produce a visual image

1. Refraction

2. Accommodation

3. Pupil constriction

4. Convergence

5. Photoreception

THE PHYSIOLOGY OF VISION

The bending of light rays

REFRACTION

Figure 15.14 (1 of 3)

Focal

plane

Focal point is on retina.

Emmetropic eye (normal)

Focal length is fixed in the eye

Light passing through a convex lens (as in the eye) is

bent so that the rays converge at a focal point

The image formed at the focal point is upside -down

and reversed right to left

REFRACTION

Figure 15.13a

Lens

Inverted

image

Ciliary zonule

Ciliary muscle

Nearly parallel rays from distant object

(a) Lens is flattened for distant vision. Sympathetic

input relaxes the ciliary muscle, tightening the ciliary

zonule, and flattening the lens.

Sympathetic activation

Refracting media

Light is refracted by

Cornea

Aqueous humor

Lens

Vitreous humor

Change in lens curvature

Allows for fine focusing of an image

REFRACTION

Eye is adapted for distance vision

Ciliary muscle is relaxed = lens is flat

As light moves closer greater curvature required

Ciliary muscle contracts = lens is curved

ACCOMMODATION

Figure 15.13a

Lens

Inverted

image

Ciliary zonule

Ciliary muscle

Nearly parallel rays from distant object

(a) Lens is flattened for distant vision. Sympathetic

input relaxes the ciliary muscle, tightening the ciliary

zonule, and flattening the lens.

Sympathetic activation

Figure 15.13b

Divergent rays from close object

(b) Lens bulges for close vision. Parasympathetic

input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge.

Inverted image

Parasympathetic activation

Near vision

Accommodation

Ciliary muscles contract

Eye strain

Near point

Maximum bulge

Aging

ACCOMMODATION

Close vision requires

Accommodation

Pupil constriction Prevents most divergent light rays from entering the eye

Convergence Medial rotation of the eyeballs toward the object being

viewed (binocular vision)

CLOSE VISION

Contraction of the circular muscles

Contraction of the radial muscles

CONSTRICTION OF THE PUPIL

Sensory transduction

Light energy is converted into nerve impulses

Takes place in retina

Photoreceptors

PHOTORECEPTION

Rods and cones

Outer segment of each contains visual pigments

Molecules that change shape as they absorb light

PHOTORECEPTION

Figure 15.15a

Process of

bipolar cell

Outer fiber

Apical microvillus

Discs containing

visual pigments

Melanin

granules

Discs being

phagocytized

Pigment cell nucleus

Inner fibers

Rod cell body

Cone cell body

Synaptic terminals

Rod cell body

Nuclei

Mitochondria

Connecting

cilia

Basal lamina (border

with choroid)

The outer segments

of rods and cones

are embedded in the

pigmented layer of

the retina.

Pig

me

nte

d la

ye

r

Ou

te

r se

gm

en

t

In

ne

r

se

gm

en

t

Figure 15.15b

Rod discs

Visual

pigment

consists of

• Retinal • Opsin

(b) Rhodopsin, the visual pigment in rods, is embedded in

the membrane that forms discs in the outer segment.

Figure 15.16

11-cis-retinal

Bleaching of

the pigment:

Light absorption

by rhodopsin

triggers a rapid

series of steps

in which retinal

changes shape

(11-cis to all-trans)

and eventually

releases from

opsin.

1

Rhodopsin

Opsin and

Regeneration

of the pigment:

Enzymes slowly

convert all-trans

retinal to its

11-cis form in the

pigmented

epithelium;

requires ATP.

Dark Light

All-trans-retinal

Oxidation

2H+

2H+

Reduction

Vitamin A

2

11-cis-retinal

All-trans-retinal

Figure 15.18 (1 of 2)

Na+

Ca2+

Ca2+

Photoreceptor

cell (rod)

Bipolar

cell

Ganglion

cell

In the dark

In the dark, cGMP opens sodium

channels and depolarizes

photoreceptors

Inhibitory neurotransmitter is

released (glutamic acid)

Bipolar cells are

constantly inhibited

in the dark

Figure 15.18 (2 of 2)

1 cGMP-gated channels

are closed, so Na+ influx

stops; the photoreceptor

hyperpolarizes.

Voltage-gated Ca2+

channels close in synaptic

terminals.

2

No neurotransmitter

is released.

3

Lack of IPSPs in bipolar

cell results in depolarization.

4

Depolarization opens

voltage-gated Ca2+ channels;

neurotransmitter is released.

5

EPSPs occur in ganglion

cell.

6

Action potentials

propagate along the

optic nerve.

7

Photoreceptor

cell (rod)

Bipolar

cell

Ganglion

cell

Light

Ca2+

In the light

In the presence of light

bipolar cells are not

inhibited

Breakdown of

rhodopsin causes closing

of sodium channels

Excitation of cones

Method of excitation is similar to that of rods

There are three types of cones

Named for the colors of light absorbed: blue, green & red

Light absorbed depends upon opsins present

PHOTORECEPTION

Adaptation to light

Rhodopsin is completely bleached in daylight

No contribution to daylight vision

PHOTORECEPTION

Light adaptation Occurs when moving from darkness into bright light

Large amounts of pigments are broken down instantaneously

Produces glare

Pupils constrict

Dramatic changes in retinal sensitivity

Rod function ceases

Cones and neurons rapidly adapt

Visual acuity improves over 5–10 minutes

PHOTORECEPTION

Dark adaptation

Occurs when moving from bright light into darkness

The reverse of light adaptation

Cones stop functioning in low-intensity light

Pupils dilate

Rhodopsin accumulates in the dark

Retinal sensitivity increases within 20–30 minutes

PHOTORECEPTION

Duplicity theory

Why do we have 2 kinds of photoreceptors?

Neural circuits for night are not suited for day

Rods:Bipolar cell

600:1

Spatial summation of large field = poor detail

Cones:Bipolar cell

1:1

Best for detail in small receptive fields

PHOTORECEPTION

Axons from medial portion of each retina cross at

optic chiasma

Continue as optic tracts

Optic radiation fibers connect to the primary visual

cortex in the occipital lobes

Visual input from both eyes is interpreted by brain

Distance

Depth perception

VISUAL PATHWAY TO THE BRAIN

Figure 15.19a

Pretectal nucleus

Fixation point

Optic radiation

Optic tract

Optic chiasma

Uncrossed (ipsilateral) fiber Crossed (contralateral) fiber

Optic nerve

Lateral geniculate

nucleus of

thalamus

Superior colliculus Occipital lobe (primary visual cortex)

The visual fields of the two eyes overlap considerably.

Note that fibers from the lateral portion of each retinal field do not cross at the optic chiasma.

Suprachiasmatic

nucleus

Myopia

(nearsightedness)

Close objects seen

clearly

Image is focused in

front of the retina

Correction = concave

lens

ABNORMALITIES OF VISION

Hyperopia

(farsightedness)

Distant objects seen

clearly

Image is focused

behind the retina

Correction = convex

lens

ABNORMALITIES OF VISION

Astigmatism

Detached retina

Conjunctivitis

Glaucoma

Cataract

Diplopia

Night blindness

Color blindness

Macular Degeneration

ABNORMALITIES OF VISION

ABNORMALITIES OF VISION

Astigmatism

Detached retina

ABNORMALITIES OF VISION

Conjunctivitis

ABNORMALITIES OF VISION

Glaucoma

ABNORMALITIES OF VISION

Cataract

ABNORMALITIES OF VISION

Diplopia

ABNORMALITIES OF VISION

Nightblindness

ABNORMALITIES OF VISION

Colorblindness

ABNORMALITIES OF VISION

Macular degeneration

ABNORMALITIES OF VISION

QUESTIONS?

Activity

Special Senses 20, #11-25