Visual, Gustatory, & Olfactory

MicroanatomyAudrone R. Biknevicius, PhD

Ohio UniversityCollege of Osteopathic Medicine

CPC 2 – Fall quarter 2005

Sclera(with episclera anteriorly)

Cornea

Fibrous LayerUveal Layer

Choroid

Iris

Ciliary Body

Retinal Layer

Retina

Modified from Netter, 1989

Inside/Inner

Outside/Outer

Limbus

Sclera(with episclera anteriorly)

Cornea

Fibrous LayerDura mater

Modified from Netter, 1989

Light

Cornea

Anterior Compartment (Aqueous humor):•Anterior chamber•Pupil•Posterior chamber

Lens

Posterior Compartment (Vitreous humor)

Retina

Gartner & Hiatt, 2001. Figure 22-7

Sclera

Choroid

Retina

Light

Cell Types in the Retina

Support Cells - Müller cells(neuroglial cells)

Retinal Pigment Epithelium

Modified from Gartner & Hiatt, 2001. Figure 22-8

Cell Types in the Retina

Photoreceptors: Rods & Cones

Ganglion cells

Integrating neurons

Neurons:

Horizontal

Bipolar

Amacrine

Modified from Gartner & Hiatt, 2001. Figure 22-8

Vitreous body

Choroid

Modified from Young & Heath, 2000. Figure 21.8

--- Pigment Epithelium

--- Outer Nuclear Layer

--- Inner Nuclear Layer

--- Ganglion Cell Layer

--- Outer Plexiform Layer

--- Inner Plexiform Layer

--- Photoreceptors (rods & cones proper)

--- Optic Nerve Fiber Layer

--- Inner Limiting Membrane

--- Outer Limiting Membrane

Mu

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Cel

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10 Histological LayersO

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I

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Modified from Gartner & Hiatt, 2001. Figure 22-7

--- Pigment Epithelium

--- Outer Nuclear Layer

--- Inner Nuclear Layer

--- Ganglion Cell Layer

--- Outer Plexiform Layer

--- Inner Plexiform Layer

--- Photoreceptors (rods & cones proper)

--- Optic Nerve Fiber Layer--- Inner Limiting Membrane

--- Outer Limiting Membrane

Light

Neu

ral

laye

r

Outer segment

Inner segment

Outer Limiting Membrane

Rod Cone

Light

Retinal Pigment Epithelial Cells

Golgi apparatus & mitochondria

Membranous discs;photopigment

Outer Nuclear Layer

Rods Cones

Rhodopsin IodopsinIodopsinIodopsin

Individual cones have only one type of

iodopsin

All over the retina, more numerous

toward outer edge

All over the retina, but concentrated

in the maculae (fovea)

Low light Bright light

Light

Scotopic vision Peripheral vision

Phototopic visionCentral vision

Eye development

www.img.cas.cz/resrep/ zk/mouse-eye.html

Clinical question: Between which layers of the retina does retinal detachment occur?

www.emedicine.com/ oph/topic411.htm

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Young & Heath, 2000

Information Path

Young & Heath, 2000. Figure 21.8

Action potential!

Light Path

choroid

medlib.med.utah.edu

Visual Acuity

Macula lutea:•Bounded by temporal retinal vascular arcades•Used primarily for central and color vision (phototopic vision)

Fovea centralis:•Depression at center of macula; thinned outer nucleus layer; high density of cones

Foveola:•Only cone receptors•Almost 1 cone : 1 optic tract neuron•Retinal avascular zone

•central vision; maximum visual discrimination•movements of eyes bring light to focus on macula

Netter, 1989

Optic Disc

Optic disc (optic papilla):•Ganglion cell axons exit eye (through lamina cribrosa) to form the optic nerve; lacks photoreceptors (blind spot) •Retinal vessels enter/exit eye

superior

lateral

Netter, 1989

UVEAL (VASCULAR) LAYER

•Choroid•Choroidal vessels (choriocapillaris)supply photoreceptors

•Iris (melanocytes) •Dilator pupillae m.•Sphincter pupillae m.

•Ciliary body•Ciliary m.•Suspensory ligament•Lens

Innervation of intrinsic eye muscles:

Sympathetics: dilator pupillae m.

Parasympathetics (CN III): sphincter pupillae m. ciliary mm.

Arterial Supply to Retina

webvision.med.utah.edu

Central Retinal Artery•Supplies inner 2/3 of retina (including ganglion cells)

Choriocapillaris (capillary lamina of the choroid)•Supplies outer 1/3 of retina (retinal pigment cells & photoreceptors)

Netter, 1989

AVASCULAR TISSUES

•LENS•CORNEA

Metabolites are exchanged via:

•Aqueous humor flow-Produced by ciliary processes in posterior chamber of the anterior compartment-Reabsorbed by canal of Schlemm (venous) at the angle of the anterior chamber

•Oxygen diffuses from corneal surface

Wilson-Pauwels et al., 1988

Visual PathwayPat O’Connor

ChemosensationTaste

Smell

Dysgeusia = Alteration in normal taste sensationAgeusia = Loss of taste sensation

Parosmia = Distortion in the perception of odor Anosmia = Loss of sense of smell

•Flavor = combination of taste + smell

•Chemoreceptor cells regenerate(~2 weeks gustatory; 6-8 weeks olfactory)

•Both senses require that chemical signal molecules be dissolved or suspended in a watery medium

Modified from Netter, 1989

Sweet

Sour

Salty

Bitter

TASTE MODALITIES

Filiform Papilla(“filaments”)

Fungiform Papilla (“mushroom-like”)

Circumvallate Papilla(“around an elevation”)

Von Ebner’s Glands(serous secretion)Modified from Netter, 1989

Lingual Papillae

Vallate(Circumvallate)~50% taste buds

Foliate ~30% taste buds

Fungiform~20% taste buds

Modified from Kandel, et al., 1991

= Taste chemoreceptor(Taste bud)Trough

Basal Cell Taste Receptor Cell

Support Cell

Kandel, et al., 1991

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Primary Sensory Neuron

w3.ouhsc.edu/histology

Von Ebner’s Glands

Ant. 2/3 Post. 1/3 Epiglottis(oral) (pharyngeal) (laryngeal)

Taste Facial n. Glossopharyngeal n. Vagus n.(Chorda tympani) (Sup.laryneal n.)

Touch Trigeminal n. Glossopharyngeal n. Vagus n.(Lingual n.) (Sup.laryneal n.)

Agur (1991) Grant’s Atlas of Anatomy

Anterior 2/3 of tongue(oral tongue)

Posterior 1/3 of tongue(pharyngeal tongue includingvallate papillae)

(also some extrapapillary taste buds scattered in the palate & pharynx)

Kandel, et al., 1991

Project 1st to nucleus of the solitary tract (nucleus solitarius)

CN VII CN IX [CN X]

Nucleus of the Solitary Tract – rostral part (brainstem medulla) (gustatory nucleus)

Nucleusambiguus(CN IX &X)

Dorsal motor nucleus of

CN X

Medullar reticular

formation

Ventropostero- medial nucleus

(thalamus)

Hypothalmus Amygdaloid complex

Parasymp.to viscera

Somatic motor: larynx, pharynx & palate (part)

Reflexes:swallowing,

vomiting

Feeding reflexes, emotions

Gustatory cortex (conscious

perception of taste)

Perception of sensory

stimuli; fear conditioning

(Kinsley Concise Text of Neuroscience)

Lateral Nasal Wall Nasal Septum

Olfactory Epithelium

Netter, 1989

•Size ~ 10 cm2

•Pseudostratified columnar epithelium

Kinsley Concise Text of Neuroscience

Basal cell

Olfactory epithelium:•Olfactory cells•Sustentacular (support) cells•Basal cells

Olfactory Mucosa

Lamina propria:•Bowman’s gland (serous)•Highly vascularized

Heimer The Human Brain and Spinal Cord

Olfactory TractOlfactory Bulb`

Olfactory Nerve (CN I)= Axons of olfactory receptor cells (1st order sensory neurons)- Cells replaced

Heimer The Human Brain and Spinal Cord

•Olfactory receptor cells synapse with mitral cells & tufted cells in the olfactory bulb (glomeruli)

•Numerous interneurons enable complex interactions (recall integrating neurons in retina!)

•Olfactory tract (axons of mitral and tufted cells)

Projections to (without thalamic relay):•Piriform & entorhinal cortex•Amygdala

Basal cell

Trigeminal Nerve & Chemosensation

•Provides most of the sensory innervation of the face: mechanical, proprioception, nociception

•Also sensitive to chemical stimuli in the nose, oral cavity and eye

•Protective mechanism against potentially dangerous chemicals