HISTOLOGY OF SPECIAL SENSES

SPECIAL SENSORY ORGANS

Olfactory mucosa

Gustatory cells

Retina

Internal ear cochlea

Semicircular

canal.

Olfaction – The Sense of Smell

Olfactory receptors are in the roof of the nasal cavity.

Neurons with long cilia

Chemicals must be dissolved in mucus for detection

Impulses are transmitted via the olfactory nerve

Interpretation of smells is made in the cortex of the Brain

Is the receptor organ for hearing.

Located in the mammalian Cochlea on the Basilar

membrane.

HEARING

Composed of three rows of outer hair cells and one row

of inner hair cells.

Inner hair cells-flask shaped.

Outer hair cells-columnar.

Supporting hair cells-elongated.

Eyeball

Cornea

Five layered structure

Outer corneal epithelium

Bowman’s membrane

Substantia propria

Descemet’s membrane

Inner endothelium

Corneal epithelium Thin Stratified squamous non

keratinized-5 LAYER

Papilla absent

Straight plane avoids refraction

Bowman’s membrane Anterior limiting membrane

Homogenous amorphous with fine collagen

Forms basement membrane for corneal epithelium

Substantia propria

Stroma of cornea

Transparent

Parallel arranged collagen fibers

Ground matrix

glycoaminoglycans+fibroblast

Collagen are arranged in alternate lamellae with regular spacing for light transmission

Descemet’s membrane

Posterior limiting membrane

Thin and homogenous

Layers continues into irido

corneal angle

Endothelium

Single polygonal cells on a basement membrane

RETINA Nervous coat

Extends from optic disc to

ora serrata

Posterior part of retina

shows yellow spot macula

lutea

Optic disc – area where

optic nerve emerges

LAYERS OF RETINA

1. PIGMENT LAYER

2. LAMINA OF RODS AND CONES

3. EXTERNAL LIMITING MEMBRANE

4. OUTER NUCLEAR LAYER

5. OUTER PLEXIFORM LAYER

6. INNER NUCLEAR LAYER

7. INNER PLEXIFORM LAYER

8. GANGLION CELL LAYER

9. LAMINA OF NERVE FIBERS

10. INTERNAL LIMITING MEMBRANE

PIGMENT EPITHELIUM Low cubical cells

Basement membrane known

as Bruch’s membrane

Cells faces towards rods and cones

Appear black due to melanin pigments

One cell contacts > 12 rods and cones

functions Phagocyte, antireflection of light, blood retinal barrier

Rods and Cones

Photoreceptors

Cones are wider and tapers at the end

Rods are narrow and cylindrical

Under EM they exhibit outer and inner segments

Inner segments contains mitochondria for energy

Outer segment shows discoidal membrane

External limiting membrane

Sieve like membrane

Supports rods and cones

Appears pink linear marking

Represents zona adherens of

Muller cells

Outer nuclear layer

Nucleus of rods and cones

Several layers

ONL

OLM

Outer plexiform layer

Synaptic area between rods and

cones with

Bipolar neurons

Horizontal cells

Amacrine cells

Inner nuclear layer

Shows nucleus of bipolar,

horizontal cells, amacrine cells, Muller cells

Inner plexiform layer

Synaptic process of bipolar,

amacrine, Muller with

ganglion cells

Plexiform appearance

Ganglion layer

Cell body and nucleus of large

ganglion cells and amacrine

cells

Nerve fibers

axons of ganglion cells

Internal limiting membrane

Homogenous layer

Formed by end feet of Muller cell and astrocytes

OPTIC NERVE

MENINGES

DURA

ARACHNOID

PIA

NERVE FIBERS

MYELINATED

ARRANGED IN FASCICULI

CENTRAL ARTERY OF RETINA

The Superficial nerve fiber layer.

The Prelaminar region.

The Lamina cribrosa region.

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Olfactory bulb is in forebrain

In bulb nerve axons branch and synapse with mitral cells neurons in clusters of glomeruli

Mitral cells send signals via olfactory tract

Olfactory bulb__

_______Olfactory tract

___Filaments of Olfactory nerve (CN I)

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