sense organs
TRANSCRIPT
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