sense organs

Primary Sentient Sense Organs

Lecturer – professor Boronikhina Tatiana Vladimirovna

Analyzer – the organ complex to realize sensitivity

Peripheral part Middle part Central part

Visual analyzer

Sense organ classification

Primary sentient organs receptor cells are neurons

Include: the eye the organ of smell

Secondary sentient organs receptor cells are epithelial Include:

the organ of hearing the organ of equilibrium the organ of taste

Eyeball is a peripheral part of the visual analyzer

The eyeball tunics

Sclera Choroid (vascular tunic) Retina

posterior wall of the eyeball

Tunic modifications on the eyeball anterior aspect

Sclera

dense regular connective tissue

Functions: mechanical protection shape maintenance the oculomotor muscle attachment

Cornea is sclera modification

epithelium Bowman’s membrane stroma Descemet’s membrane endothelium

Functions:

light passage light refraction

Corneal epithelium

afferent innervation

Cornea is transparent

Corneal stroma demonstrates regular fiber arrangement possesses unique glycosaminoglycan composition lacks blood vessels and lymphatics

Cornea is avascular and supplied by diffusion

corneal center - from the aqueous humor of the anterior chamber corneal periphery - from the limbus

Limbus is the corneal-scleral junction

houses trabecular meshwork canal of Schlemm

drains aqueous humor from the anterior chamber into the eye venous system

Choroid (vascular tunic)

loose connective tissue pigment cells blood vessels

Functions:

nutrition

light absorption

Iris and ciliary body are the choroid modifications

Iris

is discoid structure with a central aperture – the pupil

separates the anterior and posterior chambers one from another

Iris histology

pigmented LCT blood vessels pupillary muscles posterior pigment epithelium

Iris functions

prevents light from entering the eye, except via the pupil regulates the amount of light entering the eye

Ciliary body

consists of the corpus and processes

suspensory ligaments arise from the ciliary processes and insert into the lens capsule

Ciliary body histology

pigmented LCT blood vessels ciliary muscles ciliary pigmented epithelium

ciliary process epithelium produces aqueous humor

Aqueous humor

nourishes the lens, cornea, and the other inner eye structures

Ciliary muscles are muscles of accommodation

Accommodation is the focus on a close object

Lens

is a biconvex transparent flexible structure

is held in place by the suspensory ligaments

Lens is an epithelial structure

lens capsule subcapsular epithelium lens fibers

Functions: passes and refracts light rays passively takes part in accommodation

Vitreous body

consists of water (99%)collagenhyaluronic acid

Functions: passes and refracts light rays maintains the eyeball shape

Retina is responsible for photoreception

Pigmented retina pigmented epithelium Neural retina

neurons glial cells blood vessels

neurons are arranged in layers

Retinal neuron types

Photoreceptors (rods and cones)modified bipolar sensory neurons

Associative neurons: bipolar ganglion horizontal amacrine

Rods

contain in the outer segments stacks of flat membranous disks rhodopsin

are sensitive to light of low intensity responsible for black-white vision

Cones

contain in the outer segments plasma membrane invaginations iodopsin

are sensitive to bright light responsible for colour vision

Scanning electron micrograph of photoreceptors

Each retina contains120-130 million of rods6-7 million of cones

Retinal associative neurons

Bipolar cells Ganglion cells form the retinal link of the optical tract

Horizontal cells Amacrine cells form lateral bonds in the retinal layers

ganglion cell axons form the optic nerve

Human retina is of inverted type

photoreceptor outer segments face the eye back

light passes the all retinal layers before reaching the photoreceptors

Optic disk

lacks the rods and cones lacks visual activity (blind spot)

blood vessels enter the retina

Fovea centralis and yellow spot

contains only cones is responsible for the greatest visual activity

Retinal glial cells – Muller cells

form the retinal limiting membranes

OLM

ILM

Retinal blood vessels

branch out between the limiting membranes

photoreceptor dendrites are supplied by diffusionOLM

ILM

Pigmented retina

is a single layer of pigmented epithelial cells cell microvilli invest the photoreceptor tips

Pigmented epithelium functions

light absorption light adaptation phagocytosis of the shed photoreceptor tips substance transport from the choroid

dark

light