Histology

1. Primary Sentient Sense Organs
Lecturer – professor Boronikhina Tatiana Vladimirovna

2. Analyzer – the organ complex to realize sensitivity
 Peripheral part
 Middle part
 Central part
Visual analyzer ⇒

3. 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

4. Eyeball is a peripheral part of the visual analyzer

5. The eyeball tunics
 Sclera
 Choroid (vascular tunic)
 Retina
⇐ posterior wall of the eyeball

6. Tunic modifications on the eyeball anterior aspect

7. Sclera
 dense regular connective tissue
Functions:
 mechanical protection
 shape maintenance
 the oculomotor muscle
attachment

8. Cornea is sclera modification
 epithelium
 Bowman’s membrane
 stroma
 Descemet’s membrane
 endothelium
Functions:
 light passage
 light refraction

9. Corneal epithelium
afferent innervation ⇒

10. Cornea is transparent
Corneal stroma
 demonstrates regular fiber arrangement
 possesses unique glycosaminoglycan composition
 lacks blood vessels and lymphatics

11. Cornea is avascular and supplied by diffusion
 corneal center - from the aqueous humor of the anterior chamber
 corneal periphery - from the limbus

12. Limbus is the corneal-scleral junction
houses
 trabecular meshwork
 canal of Schlemm
drains aqueous humor
from the anterior chamber
into the eye venous system

13. Choroid (vascular tunic)
 loose connective tissue
 pigment cells
 blood vessels
Functions:
 nutrition
 light absorption

14. Iris and ciliary body are the choroid modifications

15. Iris
 is discoid structure with a central
aperture – the pupil
 separates the anterior and posterior
chambers one from another

16. Iris histology
 pigmented LCT
 blood vessels
 pupillary muscles
 posterior pigment epithelium

17. Iris functions
 prevents light from entering the eye, except via the pupil
 regulates the amount of light entering the eye

18. Ciliary body
 consists of the corpus and processes
 suspensory ligaments arise from
the ciliary processes and insert into the lens capsule

19. Ciliary body histology
 pigmented LCT
 blood vessels
 ciliary muscles
 ciliary pigmented epithelium
⇐ ciliary process epithelium produces
aqueous humor

20. Aqueous humor
 nourishes the lens, cornea, and
the other inner eye structures

21. Ciliary muscles are muscles of accommodation
 Accommodation is
the focus on a close object

22. Lens
 is a biconvex transparent
flexible structure
 is held in place by the suspensory ligaments
⇑

23. Lens is an epithelial structure
 lens capsule
 subcapsular epithelium
 lens fibers
Functions:
 passes and refracts light rays
 passively takes part in accommodation

24. Vitreous body
 consists of
water (99%)
collagen
hyaluronic acid
Functions:
 passes and refracts light rays
 maintains the eyeball shape

25. Retina is responsible for photoreception
 Pigmented retina
pigmented epithelium
 Neural retina

neurons

glial cells

blood vessels
neurons are arranged in layers ⇒

26. Retinal neuron types
 Photoreceptors (rods and cones)
modified bipolar sensory neurons ⇒
 Associative neurons:
 bipolar
 ganglion
 horizontal
 amacrine

27. Rods
contain in the outer segments
 stacks of flat membranous disks
 rhodopsin
are
 sensitive to light of low intensity
 responsible for black-white vision

28. Cones
contain in the outer segments
 plasma membrane invaginations
 iodopsin
are
 sensitive to bright light
 responsible for colour vision

29. Scanning electron micrograph of photoreceptors
 Each retina contains
120-130 million of rods
6-7 million of cones

30. 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 ⇒

31. Human retina is of inverted type
 photoreceptor outer segments face the eye back
 light passes the all retinal layers
before reaching the photoreceptors

32. Optic disk
 lacks the rods and cones
 lacks visual activity (blind spot)
⇑
blood vessels enter the retina

33. Fovea centralis and yellow spot
 contains only cones
 is responsible for the greatest visual activity
⇔

34. Retinal glial cells – Muller cells
 form the retinal limiting membranes
OLM ⇒
ILM ⇒

35. Retinal blood vessels
 branch out between the limiting membranes
photoreceptor dendrites
are supplied by diffusionOLM ⇒
ILM ⇒
⇐

36. Pigmented retina
 is a single layer of pigmented epithelial cells
 cell microvilli invest the photoreceptor tips

37. Pigmented epithelium functions
 light absorption
 light adaptation
 phagocytosis of the shed photoreceptor tips
 substance transport from the choroid
⇐ dark
light ⇒