SENSORY, SKIN, ENDOCRINE

Question 1

Eye development

Answer 1

Development of the eye

• Takes place between the 3rd and 10th week of embryonic development.
• The first step is the development of the optic cup and the lens placode.​

Embryonic Development

• Weeks 3 - 4 Eye Fields-Optic Vesicle
• Weeks 5 - 6 Optic Cup, Lens Vesicle, Choroid Fissure, Hyaloid Artery
• Weeks 7 - 8 Cornea, Anterior Chamber, Pupillary Membrane, Lens, Retina
• Weeks 9 - 15 Iris, Ciliary Body
• Weeks 8 - 10 Eyelids

Stages:

• Day-22/ week 4
  
  • Optic grooves
    
    • Paired optic grooves appear on both sides of the forebrain.
  • Optic vesicles
    
    • As neural folds fuse to form prosencephalon, optic grooves evaginate into optic vesicles.
  • • lens pit
  • Lens placode invaginates, giving rise to the lens pit.
  • Simultaneously, optic vesicles begin to invaginate and form the optic cup.
  • The optic cup has a central groove (choroidal fissure), which allows entrance of the blood vessels that supply the eye (hyaloid vessels).

LENS

• Optic vesicles grow to the surface ectoderm and induce the formation of the lens placodes
  
  • A thickening of the ectodermal epithelium
• Lens placode invaginates forming lens pit.
  
  • Pit deepens, edges of the pit gradually approach each other and fuse to form lens vesicle.
• Lens vesicle loses contact with the surface ectoderm and lies in the mouth of the optic cup.
  
  • Cells of the posterior wall begin to elongate anteriorly.

OPTIC CAP

• As the process of lens induction occurs, optic vesicle begins to invaginate and forms:
  
  • The double-walled optic cup
  • The inner and outer layers of cup are separated by a intraretinal space.
    
    • ​this layer dissapears and layer appose eachother
• The invagination also forms the optic stalk=choroid fissure
  
  • Allows the hayaloid artery to reach the inner chamber of the eye
  • (7th week: choroid fissure fuse and the mouth of the optic cup brcomes a round opening: the future pupil)

DEVELOPMENT OF THE OPTIC NERVE

• Closure of the choroid fissure (C);
• cells of the inner layer proliferate and finally close lumen of stalk.
• Axons of ganglionic cells of retina grow into the inner layer.

Cells of the inner layer differentiate

into gliablasts (progenitor glial cells)

DIFFERENTIATION OF THE RETINA

• The two walls of the optic cup give rise to the two layers of the retina:
• Inner layer
  
  • Thick pseudostratified inner wall of the cup develops into the neural retina
    
    • Contains the light-receptive rods and cones

plus associated neural processes

• Outer layer
  
  • Thin outer wall of the cup becomes the cuboidal melanin containing pigmented epithelium
• Intraretinal space
  
  • These two walls are initially separated by a narrow intraretinal space, Disappears by the 7th week.
• Week 5:
  • Pigmented epithelium
  • Intraretinal space
  • Neural retina (thickened pseudostratified columnar epithelium similar to that of the wall of the neural tube)
• Week 9:
  • Pigmented epithelium
  • External limiting membrane
  • Outer neuroblastic layer
  • Inner neuroblastic layer
  • Nerve fiber layer
  • Internal limiting membrane
• Definitive layers
  
  • Pigmented epithelium
  • Rod and cone photoreceptors
  • External limiting membrane
  • Outer nuclear layer
  • Outer plexiform layer
  • Inner nuclear layer
  • Inner plexiform layer
  • Ganglion cell layer
  • Nerve fiber layer
  • Internal limiting membrane
• • There are two major gradients of differentiation in the retina – the vertical and horizontal gradients.
    
    • The first vertical gradient
      
      • proceeds from the inner to the outer layers of the retina:
        
        • ganglionic cells differentiate early,
        • afterwards horizontal and amacrine cells,
        • bipolar neurons, rods and cones
        • differentiate last.
    • The horizontal gradient
      
      • Proceeds from the from the center to the periphery of the retina.

​

A later stage in retinal differentiation is the growth of axons of the ganglionic

cells along the innermost layer of the retina toward the optic stalk.

Development of the anterior and posterior chambers; choroid, ciliary body and iris; cornea and sclera, and the eyelids

• Mesodermally derived mesenchymal cells migrate into the lentiretinal space between the lens vesicle and the inner wall of the expanding optic cup
  
  • secrete a gelatinous matrix called the primary vitreous body
• wall of the lens vesicle differentiate to form long, anteroposteriorly oriented primary lens fibers, which express crystallins (a, b, and ) necessary for the transparency of the lens (Fig. 17-19).
• Elongation of thesecells transforms the lens vesicle into a rounded lens body, obliterating the cavity of the lens vesicle by the 7th week.
• Anterior lens epithelial cells closest to the cornea remain proliferative throughout life.
• Theymigrate peripherally to the lens equator, giving rise

to future secondary fetal and adult cortical lens fibers

(lens bow). Secondary lens fibers start to be formed

from the 6th week.

• During the 7th week, the mesenchyme overlying the lens splits into two layers, that enclose a new cavity – anterior chamber.
• The deep layer of mesenchyme at lens creates by a process of vacuolization the posterior chamber which is separated from the anterior chamber by the pupillary membrane.
• The rim of the optic cup and the overlying choroidal mesenchyme form iris and ciliary body.
• Ciliary muscle develops from the (ecto)mesenchyme; and sphincter and dilator pupillae (pigmented myoepithelium) are derivatives of the outer retinal layer; pigmented epithelium of iris differentiates from the inner retinal layer.

inner layer:

EYE DEVELOPS FROM THREE SOURCES

(1) Neuroectoderm of the forebrain
(2) Surface ectoderm of the head
(3) Head mesenchyme

• Neuroectoderm differentiates into retina
• Surface ectoderm
  
  • thickens to form lens placodes, which are primordia of lenses.
  • Corneal epithelium
• Surrounding mesenchyme gives rise to:
  
  • Vascular coat – choroid; stroma of the ciliary body, and iris
  • Fibrous layer of the eye: sclera, corneal stroma and endothelium

Question 2

Eyball (draw sagittal section)-vascular supply, innervation, chambers, aqueous humor circulation

A. cilioretinalis (cilioretinal a.)

• present in 10-33% of eyes
• branches from the a. ciliaris posterior brevis
  
  • exits the discus n.II separately from a. centralis retinae
  • additional supply to macula lutea from choroidal circulation
• provide a small amount of blood supply to the retina when a. centralis retinae is occluded
• 90% located temporally, 10% nasally
• occlusion of a. cilioretinalis → central visual loss
• occlusion of a. centralis retinae → spare central vision and macula lutea

Answer 2

***Body orbit: Bones and connections

Eyeball

• Contains the optical apparatus of the visual system.
• It occupies most of the anterior portion of the orbit,
• Suspended by extrinsic muscles that control its movements, and a fascial suspensory apparatus.
• Approximately 25 mm in diameter.

General structures/ axseses

• Anterior pole
• Posterior pole
• Equator
  
  • Mucles that insert infornt: recti muscles
  • Behind: oblique muscles
  • Well visible in transverse section , in frontal plane
• Meriadiani
  
  • lines perpendicular to equator
• Lateral/temportal direction
• Medial/ nasal direction
• Axsis bilbi externus and internus
• Optic axse: linea visus
  
  • the 2 optic axsesses converge to form 3D image

Chambers of the eye:

• Anterior chamber
  
  • Area directly posterior to the cornea and anterior to the colored part of the eye (iris).
  • The central opening in the iris is the pupil.
  • Boundaries
    
    • Anterior: posterior surface of the cornea
    • Posterior: anterior surface of the lens, iris, and ciliary body
    • Lateral: trabecular meshwork and the canal of Schlemm
• Posterior chamber
  
  • Posterior to the iris and anterior to the lens​​​
  • Boundaries
    
    • Anterior: posterior surface of the iris
    • Posterior: zonular fibers of the lens and the lens
    • Lateral: ciliary processes
• Viterous chamber
  • The posterior four-fifths of the eyeball, from the lens to the retina
  • Occupied by the postremal (vitreous) chamber
  • Filled with a transparent, gelatinous substance-the vitreous body (vitreous humor).
    
    • This substance, unlike aqueous humor, cannot be replaced.

Aqueous Humour cirulation:

• Aqueous Humour: intra-ocular transparent non-cellular fluid
  
  • General:
    
    • Produced by cillary body
    • 0.2-0.3 ml of transperent, collorless fluid
    • 0.7-1.3% Nacl, traces of urea and glucose (0.1%), no protiens
    • substitutes lymph
      
      • Supplies nutrients to the avascular cornea and lens and maintains the intraocular pressure.
      • If the normal cycle of its production and absorption is disturbed so that the amount of fluid increases, intra-ocular pressure will increase. This condition (glaucoma) can lead to a variety of visual problems.
• Production course
  
  • Produced in the Ciliary body;
  • Secreted into the posterior chamber,
  • Flows into the anterior chamber through the pupil
  • Iridocorneal angle;
  • Absorbed into the scleral venous sinus (the canal of Schlemm),
  • Absorbed into the Canal of Schlemm through spaces of Fontana;
  • Drains through the aqueous venules
  • And then the scleral veins into the episcleral veins.
• intraocular pressure: 14-17 mmHg

increase: intraocular pressure- compression of retina-

glaucoma

Angulus iridocornealis = Iridocorneal angle

• in site of sclerocorneal junction
• trabecular net in the posterior wall = spatia anguli i.c. = Fontana ́s spaces
• no direct connection to Schlemm ́s canal
• reabsorption of humor aquosus
• maintains the intraocular pressure
• no application of parasympatheticolytics in patient with glaucoma !!!
• CB can block the drainage:
  
  • CB: parasympathetic system
  • drugs of parasym. drug will cause retaction of CB which will block the fontanas space
  • bad for glaucoma spaces!!!

Fascial sheath of the eyeball

• (bulbar sheath)
• A layer of fascia that encloses a major part of the eyeball:
  
  • Posteriorly, it is firmly attached to the sclera (the white part of the eyeball) around the point of entrance of the optic nerve into the eyeball;
  • Anteriorly, it is firmly attached to the sclera near the edge of the cornea (the clear part of the eyeball);
  • Additionally, as the muscles approach the eyeball, the investing fascia surrounding each muscle blends with the fascial sheath of the eyeball as the muscles pass through and continue to their point of attachment.

Nervous supply of eye

• n. opticus – special sensory
  
  • pars intraocularis, canalis, itracranialis
  • vagina interna, externa
• n. ophthalmicus (somatosensory, 1st branch of trigeminal nerve)
  
  • nn. ciliares longi –inisde the eye
  • n. lacrimalis, n. frontalis, n. nasociliaris – for surrounding structures
• N III, N IV, N VI: somatomotor
  
  • extrinctic muscle of eye
• Ganglion ciliare –> nn. ciliares breve
  
  • autonomic (visceromotor) smooth muscle
    
    • sympathetic fibres non-interpolated, parasympathetic interpolated)

Blood supply:

• Supplied by the ophthalmic artery,
  
  • First branch of the internal carotid artery, when it has travelled passed the cavernous sinus.
• The ophthalmic artery has numerous branches that supply the muscles that move the eye and surround the eye, the eyelid and the eyeball itself.
• Branches divided into:
  
  • Orbital group (supply the orbit and related structures)
  • Optical group (supply the eye and its muscles)

1- Orbital group

• Lacrimal artery
  
  • Runs with the lacrimal nerve to supply the lacrimal gland.
  • Also supply the eyelids and conjunctiva as the lateral palpebral arteries,
    
    • and pass medially to supply the upper and lower eyelids respectively.
    • Anastomose with the medial palpebral artery
• Supraorbital artery
  
  • Passes over the optic nerve, and runs forwards, along the medial border of levator palpebrae superioris and superior rectus muscles.
  • Passes through the supraorbital foramen in order to supply the:
    
    • upper eyelid
    • frontal sinus
    • levator palpebrae superioris
    • part of the scalp
• Posterior ethmoidal artery
  
  • Enters the nasal cavity by passing through the posterior ethmoidal canal,
  • Supplies the posterior ethmoidal sinuses as well as continuing to enter the skull and supply the meninges.
• Anterior ethmoidal artery
  
  • Branches from the ophthalmic artery within the orbit,
  • Accompanies the nasociliary nerve through the anterior ethmoidal foramen into the middle and anterior air cells as well as the frontal sinus.
  • Before the artery passes into the cranium, it provides a meningeal branch to supply the dura mater.
  • There are also nasal branches that pass into the nasal cavity via a small opening adjacent to the crista galli, and goes on to supply a section of the dorsum of the nose.
• Medial palpebral artery
  
  • Two branches
    
    • Superior and inferior palpebral arteries.
    • They arise opposite the superior oblique muscle.
    • They supply the upper and lower eyelids respectively.

2- Optical group

• Long posterior ciliary arteries
  
  • Run anteriorly on both sides of the eyeball.
  • Run between the sclera and the choroid layers, and they run to supply the ciliary muscle where they divide further.
    
    • These two arteries merge and form the circulus arteriosus major around the iris,
      
      • which run inwards to form a smaller circle of arteries (the circulus arteriosus minor).
  • In all they supply the:
    
    • choroid
    • ciliary body
    • iris
• Short posterior ciliary arteries RODS CONES?
  • 6-12 of these arteries for each eye.
  • Pierce the back of the eye and run between the sclera (which they supply) and choroid, and supply up to the ciliary processes.
  • Smaller branches that supply the optic disc.
    
    • They do this by forming an arterial ring known as the circle of Zinn-Haller.
• Anterior ciliary arteries
  
  • 7 of these arteries per eye
  • Supply the sclera, and rectus muscles.
  • Pierce the sclera, near the cornea, and terminate in the circulus arteriosus major, that surrounds the iris.
  • Medial, inferior and superior rectus are supplied by two branches each, with the lateral rectus receiving the remaining single branch.
• Central retinal artery
  
  • Underneath the optic nerve and lies within the dural sheath of the nerve to reach the eyeball.
  • It pierces the optic nerve itself near the back of the eye, and sends numerous branches over the internal aspect of the retina.
    
    • In diabetic retinopathy, there can be haemorrhages and aneurysms that can form in this artery and its branches.

Venous drainage????????

• The central retinal vein runs through the optic nerve.
  
  • Drains into the or superior ophthalmic vein.
• Superior ophthalmic vein-> cavernous sinus
  
  • Usually the largest and is the principal vein.
  • The veins that drain into it are named as the arteries of the region (medial palpebral, lacrimal, anterior ethmoidal, inferior ophthalmic, central retinal and muscular).
  • Formed when the supraorbital and angular veins unite just behind the trochlea (pulley like structure).
• Inferior ophthalmic vein-> pterygoid plexsus
  • runs over the surface of the inferior rectus muscle,
  • It drains the inferior rectus muscle, inferior oblique muscle, lacrimal sac and lower lid.
• Angular vien-> facial vien -> internal juglar vien

Vortex: no short posterior cillary viens

INSIDE THE EYE NO LYMPH

Question 3

Cornea, sclera and vitreous body, corneal reflex

Corneal Reflex

• Light touching of the cornea or conjunctiva results in blinking of the eyelids.
• Afferent impulses from the cornea or conjunctiva travel through the ophthalmic division of the trigeminal nerve to the sensory nucleus of the trigeminal nerve
• Internuncial neurons connect with the motor nucleus of the facial nerve on both sides through the medial longitudinal fasciculus.
• The facial nerve and its branches supply the orbicularis oculi muscle, which causes closure of the eyelids.

Answer 3

LAYERS OVERVIEW

1- Outer/ Fibrous layer (Corneoscleral coat), tunica fibrosa (externa)

• Encloses the inner two layers except where it is penetrated by the optic nerve.
• Includes:
• Sclera: White portion
• Cornea: Transparent portion

2- Vascular coat, the middle layer, or uvea (tunica vasculosa)

• Includes:
  
  • Choroid and the stroma of the ciliary body
  • Iris.

3- Retina, the inner layer/ tunica interna (nervosa)

• Includes
  
  • Outer pigment epithelium
  • Inner neural retina,
  • Epithelium of the ciliary body and iris.
• The neural retina is continuous with the central nervous system through the optic nerve.

4- Corpus vitreum (vitreous body) + lens

External fibrous layer

• The fibrous layer of the eyeball consists of two components-
  
  • Sclera: covers the posterior and lateral parts of the eyeball, about five-sixths of the surface,
  • Cornea: covers the anterior part

Sclera

• General:
  
  • Dorsal 5/6 of eyebal surface
  • The sclera constitutes the “white” of the eye.
• Function:
  
  • Provides attachment for the extrinsic muscles of the eye.
  • Protective envelope
• Dense connective tissue
  
  • Not transpartent!
• Thickness: 0.4 mm at equator, 1mm dorsally
• 3 layers:
  
  • Episcleral layer
    
    • External layer
    • Loose connective tissue
    • Adjacent to the periorbital fat.
      
      • Internal to the vagina bulbi (metaphore for synovial fluid in joint)
    • Enable movment of eyeball of joint
    • Autoimmune diseases/inflimation: episclaritis
  • Substantia propria
    
    • (sclera proper, also called Tenon’s capsule),
    • Dense network of thick collagen fibers.
  • Suprachoroid lamina (lamina fusca=brown)
    
    • Inner aspect of the sclera,
    • Located adjacent to the choroid
    • Thinner collagen fibers, elastic fibers, fibroblasts, melanocytes, macrophages, and other connective tissue cells.
• 6 structures:
  
  • Vinus venous sclerae: canalis schlemmi
    
    • Oval (on section) circular canal for humour aquous draining
  • Calcar:
    
    • Circular stricture
    • Process of slcera projecing between venous sinus sclerae and cillary body
  • Reticulum trabeculare
    
    • Synonums:
      
      • Lig pectinatum anguli/
      • iridocornealis (fontansa spaces)
    • CT with spaces between anterior cmapber and venous sinus sclerae
    • Space for absorbtion
    • Damage:
  • Sclera sulcus
    
    • Shallow groove
    • At corneoscleral junctio/ limbus corneae
    • insufficently cleaned duting blinking:
      
      • dead space, potential site for spread of infection to cornea
  • Lamina cribosa sclerae: dorsally
    
    • exit of optic nerve fibers
  • Annulus scleralis
    
    • Fibrous ring around exit of the optic n.
    • Visable on eye fundus (base) around discus n. optici (blind spot) ???

Cornea:

• General:
  
  • 1/6 of external fibrous layer, located ventrally
  • Convex structure: relfects light
    
    • Power: 43 diopter
  • Perfectlly transparent
    
    • Fbroblasts and collagen: in perfect arrangment
  • Avascular (in order to be transparent) fed by diffusion from:
    
    • Interoccular fluid: aquous humor
    • Externally: tears, capillaries from sclera and conjunctiva
  • Verticlly 11mm, horizontally 12 mm
    
    • hysiological astigmatism: not perfectly round
      
      • if there is more, need to adjust with
• Function:
  
  • Refracts the light
  • Free nerve ending within epithlium? branchs from V1?, afferent link of pupillary reflex
• Structures:
  
  • Limus corneae/ corneoscleral junction
    
    • wedge shaped margin connecting to sclera
  • Vertex corneae:
    
    • Ventral most point of eyeball
    • Thinnest part of cornea, 555 um thick
      
      • if it is thinner than 400 that cant do lazer surgury for myopia
• Layers: Three cellular layers and two noncellular layers.
• Corneal epithelium:
  
  • ​Stratified squamous, non-keratinized
  • Anteriorlly
  • Basal cell and Surface squamous cells
  • DNA in corneal epithelial cells is protected from UV light damage by nuclear ferritin (iron-containing protein).
  • Injury here heals easily, in deeper layers it leaves a scar- can cause corneal tubidity (impaired vision)
    
    • can be trnspalnted
• Bowman ́s membrane
  
  • Lamina limitans: basment membrane that is thicker than usual (anterior basement membrane)
  • 3-9 um thickness
  • Homogenous layer consisting of meshwork collagen fibrils
  • Acts as a barrier to the spread of infections.
• Corneal stroma: substantia propria
  
  • 90% of the corneal thickness.
  • Collagenous Lamellar regular dense CT
  • Perfectlly arranged parallel bundles collagen fibrils
    
    • Keratocytes: CT cells of cornea, specilized fibrocytes
    • Proteoglycans (sulfated glycosaminoglycans)
      
      • Keratan sulfate (lumican)
      • Chondroitin sulfate
      • Covalently bound to protein (decorin).
• Descement ́s membrane
  
  • (posterior basement membrane)
  • Thick basal lamina of corneal endothelium
  • Extends peripherally beneath the sclera as a trabecular meshwork forming the pectinate ligament.
    
    • Strands from the pectinate ligament penetrate the ciliary muscle and sclera and may help to maintain the normal curvature of the cornea by exerting tension on Descemet’s membrane.
• Corneal “endothelium”, posterior epithlium
  
  • Low cuboidal ion-transporting cells,
  • Regulate the water content in stroma
  • Development:
    
    • Anterior chamber was filled with mesenchyme, the cavity formed inside this tisse. the mesenchymal cells flattened and became endothelium. similar to endothelium of blood vessels.

Vtreous body

• General:
  
  • Jelly like structure behind lens
• Function:
  
  • Pigmented epithlium and retina are not attached firmly attached
  • Viterous body: mainatain the possition of the retina on pigminted epithlium
  • maintains the internal eyeball pressure
  • compress retina to the choroidea
• Structure:
  
  • Membrana:
    
    • Collagen envelope
  • Stroma
    
    • sparse web of collagen fibers and halocytes (produce onyl prenatally)
  • Humor vitreus
    
    • 4 ml, 98% water, hyaloric acid
    • hyaluronic acid, collagen fibres
    • cells – hyalocytes – during development only!
    • no regeneration ! – in trauma flows out and replaced with aqueous humor
• Canalis hyaloideus Cloqueti:
  
  • remnant of fetal hylaloidea a.
• Fossa hyaloidea: impression of the lens

2- Sclera

In children, it has a slightly blue tint because of its thinness;

elderly people, it is yellowish because of the accumulation of lipofuscin in its stromal cells.

• Opaque layer of dense connective tissue
• Can be seen anteriorly through its conjunctival covering as the “white of the eye.”
• It is pierced by numerous vessels and nerves, including the optic nerve posteriorly and provides attachment for the various muscles involved in eyeball movements.

The fascial sheath of the eyeball covers the surface of the sclera externally from the entrance of the

optic nerve to the corneoscleral junction while internally the surface of the sclera is loosely attached

to the choroid of the vascular layer.

Corneal Reflex

• Light touching of the cornea or conjunctiva results in blinking of the eyelids.
• Afferent impulses from the cornea or conjunctiva travel through the ophthalmic division of the trigeminal nerve to the sensory nucleus of the trigeminal nerve
• Internuncial neurons connect with the motor nucleus of the facial nerve on both sides through the medial longitudinal fasciculus.
• The facial nerve and its branches supply the orbicularis oculi muscle, which causes closure of the eyelids.

Question 4

Iris, cilliary body, choroidea, pupillary light reflex

Direct and Consensual Light Reflexes

• If a light is shone into one eye, the pupils of both eyes normally constrict.
  
  • The constriction of the pupil on which the light is shone is called the direct light reflex;
  • The constriction of the opposite pupil, even though no light fell on that eye, is called the consensual light reflex
• The afferent impulses travel through the optic nerve, optic chiasma, and optic tract
  
  • Here, a small number of fibers leave the optic tract and synapse on nerve cells in the pretectal nucleus, which lies close to the superior colliculus.
  • The impulses are passed by axons of the pretectal nerve cells to the parasympathetic nuclei (Edinger-Westphal nuclei) of the third cranial nerve on both sides.
  • Here, the fibers synapse and the parasympathetic nerves travel through the third cranial nerve to the ciliary ganglion in the orbit
  • Finally, postganglionic parasympathetic fibers pass through the short ciliary nerves to the eyeball and the constrictor pupillae muscle of the iris.
• Both pupils constrict in the consensual light reflex because the pretectal nucleus sends fibers to the parasympathetic nuclei on both sides of the midbrain
• The fibers that cross the median plane do so close to the cerebral aqueduct in the posterior commissure.

Pupillary Skin Reflex

• The pupil will dilate if the skin is painfully stimulated by pinching.
• The afferent sensory fibers are believed to have connections with the efferent preganglionic sympathetic neurons in the lateral gray columns of the first and second thoracic segments of the spinal cord.
• The white rami communicantes of these segments pass to the sympathetic trunk, and the preganglionic fibers ascend to the superior cervical sympathetic ganglion.
• The postganglionic fibers pass through the internal carotid plexus and the long ciliary nerves to the dilator pupillae muscle of the iris.

Answer 4

LAYERS OVERVIEW

1- Outer/ Fibrous layer (Corneoscleral coat), tunica fibrosa (externa)

• Encloses the inner two layers except where it is penetrated by the optic nerve.
• Includes:
• Sclera: White portion
• Cornea: Transparent portion

2- Vascular coat, the middle layer, or uvea (tunica vasculosa)

• Includes:
  
  • Choroid and the stroma of the ciliary body
  • Iris.

3- Retina, the inner layer/ tunica interna (nervosa)

• Includes
  
  • Outer pigment epithelium
  • Inner neural retina,
  • Epithelium of the ciliary body and iris.
• The neural retina is continuous with the central nervous system through the optic nerve.

4- Corpus vitreum (vitreous body) + lens

Vascular coat, the middle layer= uvea (tunica vasculosa)

*uveitits: autoimmune disease

Choroidea

• General:
  
  • Posterior part
• Function:
  
  • “Feed” rods and cones and pigment epithlium
  • Dark chamber of camera: relected light is absorbed and dosent irritate other cells
  • Elasticity: retracts cilliary body to neutral possition
• Structure:
• Micro: 4 layers
• Lamina suprachoroidea
  
  • Loose pigmemnted CT
  • Melanocytes
  • Blood vessels and melanin pigment give the choroid an intense dark brown color.
    
    • The pigment absorbs scattered and reflected light to minimize glare within the eye.
• Perichoroid space
• Zona vasculosa/ coroid stroma/ Halleri
  
  • Arteries and viens, melanocytes
  • Posterior cillary breves arteries and branchs
• Lamina Choriocapillaris
  
  • Capillary network
  • Fenestrated capillaries provide nutrients to the cells of retina (rodes and cones, and pigmented epithlium)
• Bruch’s membrane/ basal complex choroidea
  
  • Amorphous refractile layer
  • 1- Basal lamina of capillary endothelium
  • 2- fibrosum externum, elasticum, fibrosum internum: Elastic and reticular fibrils
  • 3- Basal lamina of outer most layer of pigmemted epithlium

Cilliary body

• General:
  
  • Anterior part
  • Thickened portion between the iris and choroid
  • Circular structure, on section, it looks like a triangle
    
    • annular ring
• Main structures:
  
  • Pars plana (annulus cilliaris)= outer part
    
    • surgical approach: pars plana viterctomy
      
      • remove fluid from viterous body
  • Pars plicata: (corona cilliaris) = inner part
    
    • contains:
    • cilliary processes (70-80, higher, fan shapped)
    • Cilliary folds
  • Cilliary zonula: fixation of lens
• Function:
  
  • Contraction: accomidation of lens
  • Production of aqious humor
  • Fixation of lens
• Layers Pars plana
• Supracilliary lamina
  
  • Corrisponds to suprachoroid lamina in sclera
• Smooth cilliary muscle
  
  • Medridional fibers (longitudinal)
    
    • Streching of the choroid, opening of the iridocorneal angle and facilitate drainage of the aqueous humor
  • Radial fibers:
    
    • Flatten the lens – focusing for distant vision
  • Circular fibers:
    
    • Accomodation for near vision
  • Parasympatethic fibers (IN LENS
• Stroma
  
  • Vessels
• Layers: Pars plicata
• Lamina basalis (corrisponds to bruch’s membrane)
• Cilliary epithlium: pars cillaris retinae
  
  • pigmented layer: continuation of pigminted layer of retina
  • Cillary canal: production of aquousus humor
  • Non pigmented layer: corisponds to sensory epithlium of retina
• Coverd by lamina limitans of internal retinae
• Inserion of zona cillaris (sensory apperatus of lens)

Composed of the ciliary ring, epithelium with ciliary processes, and ciliary muscle

CM is covered by the vascular coat which consists of:

Vascularized loose CT

Ciliary epithelium Double layers of low columnar cells:

Outer cells are heavily pigmented,

Inner nonpigmented cells

Fluid transporting epithelium, production of the aqueous humor

Each layer sits on its own basal lamina, apical surfaces attached to each other by junctions

Ciliary processes: fibers that encircle the border of the lens

fibers of the zonule arise from the grooves between the ciliary processes

Posterior part of CB is flat, anterior part is projecting into the ciliary processes (anchoring of the zonular fibers of lens, suspensory ligament of lens).

Iris

• General:
  
  • Thin, flat, annular ring, 21 mm diamter
  • non transparent
  • Continuation of choriod and cillary body, ventrally
  • Contains 2 smooth muscles
  • Divided into 2 regions:
    
    • Outer: cillary margin
    • Inner: pupillary margin
  • Annulus: major and minor
    
    • contain arterial rings
  • Pupil: from 2.5-7 mm opening
  • Anterior surface:
    
    • no epithlium, you can see conju?
    • Zona cilliaris, openings: cryptae
    • Catella: Collarette: remmenant of membra pupilalris attachment
    • Zona cillaris (1.5 mm wide, cryptae pupilaris???
• Function:
  
  • As a diaphragm in pupillary reflex
  • pupillary: interconnects andterior and posterior chamber
  • Regulates the amount of light that impinges on the retina
  • Determines the color of the eye
• Muscles:
  
  • Sphincter pupillae muscle
    
    • parasympatheitc N III- ggl cillary
    • miosis
    • Circular shape muscle, thick bundle in stroma
  • Dilator pupillae muscle
    
    • dialator muscle
    • sympathetic- ggl cervicale superiorius
    • Mydriasis
    • Fan shaped muscle
    • forms thin layer dorsally
• Layers:
  
  • Anterior face
    
    • No epithlium cover!
      
      • Covered by stratum limitans anterius= transormed/modifed stroma
    • Fibroblasts and melanocytes
    • Many visable crypts: absorbtion of aquous humor- small extent into vessels of iris
    • Pupillary ruff: ????
  • Stroma:
    
    • Anterior: small vessels
    • Posterior: bigger vessels: arterial circles
    • Sphincter muscle
  • Posterior epithium: 2 layer
    
    • Dilator muscle: myoepithlial cells
      
      • From neural ecctoderm
    • Anterior: non pigmented cells continuation of cillary body
    • Most posterior layer: Pigminted epithlium
      *

Question 5

Lens - structure and insertion, accommodation

Accommodation Reflex

• When the eyes are directed from a distant to a near object,
  
  • Contraction of the medial recti brings about convergence of the ocular axes;
  • the lens thickens to increase its refractive power by contraction of the ciliary muscle;
  • and the pupils constrict to restrict the light waves to the thickest central part of the lens.
• The afferent impulses travel through the optic nerve, the optic chiasma, the optic tract, the lateral geniculate body, and the optic radiation to the visual cortex.
• The visual cortex is connected to the eye field of the frontal cortex
  
  • From here, cortical fibers descend through the internal capsule to the oculomotor nuclei in the midbrain.
  • The oculomotor nerve travels to the medial recti muscles.
  • Some of the descending cortical fibers synapse with the parasympathetic nuclei (Edinger-Westphal nuclei) of the third cranial nerve on both sides.
  • Here, the fibers synapse, and the parasympathetic nerves travel through the third cranial nerve to the ciliary ganglion in the orbit.
  • Finally, postganglionic parasympathetic fibers pass through the short ciliary nerves to the ciliary muscle and the constrictor pupillae muscle of the iris
    *

Answer 5

General:

• It is a transparent, biconvex elastic disc attached circumferentially to muscles associated with the outer wall of the eyeball.
• Avascular
• Separates the anterior one-fifth of the eyeball from the posterior four-fifths
• 9-10 mm diameter
• Thickness: 3.7-4.4 mm
• 69% water
  
  • ​in diabetes, when level of glucose goes up, the lens gets swollen- can cause cataract

Function:

• Focus
• 12-20 diopter
• (cornea: 43 diopters)
• This lateral attachment provides the lens with the ability to change its refractive ability to maintain visual acuity. The clinical term for opacity of the lens is a cataract.

Structure:

• Fromed by cells, elongated, form fiber like structures
• Fibers terminate at sutures: radii
• Face:
  
  • anterior
  • Posterior
• Pole:
  
  • Anterior
  • Posterior
• Axsis, equator
• Zona ciliaris Zinni: fization apperatus of the lens
  
  • fiber zone
  • septum zone?

Layers:

• Capsula: similar to lamina basalis
  
  • Placment of fibers of zonules
• Epithlium: simple cuboidal, only on aterior face
• Substantia lentis:
  
  • Cortex:
    
    • elecongated hexagonal eosinophillic cells
  • Cells contain filensin, and crystalines

Cataract:

• put artificiall lens lens

Accomidation:

• The process in which the eyes see objects at different distances and maintain clear images of the objects by the convergence and divergence of light.
• The ocular structures involved in accommodation include the ciliary muscle, lens, and pupil.
• Focus at near
  
  • contraction of m. ciliaris
    
    • fibrae zonulares relax
    • lens bulges
  • If you look at close objects: eyes converge
    
    • parallel contraction of m. sphincter pupillae (=miosis)
• Focus at far
  
  • Basic state of eye
  • Cilliary muscle relazes
  • Vessels tone keeps fibrae zonulares tightened
    
    • lens is flatened
  • Contraction of m. dilatator pupillae (= mydriasis)

Accommodation:

• adjustment of the eyes to different distances (near vision versus far vision)
• Primarily mediated by the lens, which changes convexity to adapt the refractory power.
• Changes occur via contraction of ciliary muscles and are mediated by the Edinger-Westphal nuclei bilaterally.

Relaxed ciliary muscle → tense ciliary processes → curvature of lens decreases

Constricted ciliary muscle → relaxed ciliary processes → curvature of lens increases

Question 6

Retina - structure, vascular supply (draw schema of eye fundus)

Answer 6

The retina is the innermost layer of the eye: contain distinct layers

• Outer layer: pigmented epithelial cells
• Internal layer: the retina (nervous tunic)
  
  • Pars ceaca retinae: blind part
    
    • Ciliary part
    • Iris part
  • Ora serrata: (“tooth like”): border
  • Optic part
    
    • From optic nerve papilla to ora serrata
• Inner retinal plexsus

General:

• Development
  
  • Develops from the optic cup;
  • Its outer layer differentiates into the retinal pigment epithelium (RPE)
  • Inner layer thickens and begins a long process of differentiation into neurons, photoreceptors, and neuro- glial cells of the neuronal retina.
  • Two differentiation gradients of retina:
    • a) from the inner to the outer layers,
    • b) from the central to the peripheral parts

Sensory part:

• light sensative neurons: rods and cones (1)
• Transmission neurons: bipolar (2) and ganglionic cells (3)
• Assosiation neurons: horizintal and amacrine cells
• supporting cells (glia): radial cells (muller)

Two notable structures:

• Optic disc, “blind spot”
  
  • Exit of optic nerve
  • and entrance of central retinal artery vien
  • has optic cup
  • Scleral annulus
• Macula, “yellow spot”
  
  • more than 1 layer of retinal ggl cells
  • laterally to optic disc
  • outer layer directed laterally
  • place of most accute vision
  • parts
    
    • umbo: cones and muller cells
    • folveola: neither rods no retinal ggl cells
    • fovea centralis (1.5 mm): no rods
    • :yellow part”: most accute vision 5.5 mm
  • Maccular degeneration: age related
    
    • angiogenesis in this area
    • central scotoma
    • no vision in the central field

Vascular supply- FUNDUS OF THE EYE

diseases you can see

hypertention

diabetes

raised intercranial pressure

Internal layer: the retina (nervous tunic)

• 10-11 layers
  
  • brukes membrane (can be considered apart of choroid or apart of retina)

1- Pigment epithelium

• Simple cuboid on basal lamina (bruch’s membrane of choroid= dark chamber with melanocytes)
• Filled with melanine granules
• Apical processes of cells surround the outer segments of rods and cones
• absorbs light passing through the neural retina
• isolates the retinal cells from blood-borne substances:
  
  • blood-retina barrier
• participates in restoring photo sensitivity of visual pigments
• phagocytoses and disposes of membranous discs from the rods and cones

2- Layer of rods and cones

• outer and inner segments of rods and cones

3- External limiting membrane:

• apical boundary of Müller ́s cells, glial cells

4- Outer layer core (cell bodies+nuclei of rods and cones)

• cell bodies (nuclei) of rods and cones

5- Outer layer plexiform

• contains the processes of rod and cones and horizontal, and bipolar cells that connect to them; synapses of rod and cone axons and bipolar cells

6- Inner layer core/ nucelar layer

• contains the cell bodies (nuclei) of bipolar, amacrine, and Müller ́s cells

7- Inner layer plexiform

• contain the processes of horizontal, amacrine, bipolar, and ganglion cells that connect each other; synapses of bipolar and ganglion c.

8-Layer of ganglion cells

• contains perikarya of ganglion cells (typical neurons)

9-Layer of nerve fibers

• contains axons of ganglion cells
• (optic nerve fibers that lead from the retina to the brain)
• Papilla of optic nerve (also where central artery enters eye)

10-Internal limit membrane

• composed of basal lamina of Müller ́s cells

NEURAL RETINA

• Photoreceptor cells: rods and cones
• Conducting neurons: bipolar neurons and ganglion cells
• Association neurons: horizontal and amacrine neurons 7
• Supporting (glial) cells: Müller’s cells, microglial cells, astrocytes

Photoreceptor cells:

• Primary sensory cells: Sensory process and short axon, but have simillarities to neurons

Visual pigments

• RODS
  
  • Rods are more sensitive to light visual pigment rhodopsin
  • 120 million rods
• CONES:
  
  • Each cone is specialized to respond to one of three colors – red, green or blue- three types of visual pigments - iodopsins
  • 6 - 7 millon cones
  • mostly found in fovea centralis (retina is thinner, allows light rays to get closer to cones so there is minumun light scattering)
• Outer segment
  
  • RODS:
    
    • has cylindrical shape,
    • contains horizontally flattened membrane discs
  • CONES:
    
    • Contrary to rod the interior of cone discs is continuous with the extra-cellular space
  • acctual receptors, sensory processes
• Connecting stalk with cilium
  
  • (BB = basal body, R = striated rootlet)
• Inner segment (metabolic region)
  
  • contains protein synthesis organelles (Golgi complex, ER, free ribosomes, mitochondria)
• “outer limating membrane”
• is formed by a row of zonulae adherentes (ZA) between the apical parts of Müller ́s cells and photoreceptor cells
• Cell body
  
  • contains nuceus
• Axon
• Presynaptic part (synapse with bipolar neuron)

Question 7

Eyelids, conjunctiva, lacrimal apparatus

Answer 7

Eyelids- General:

It receives sensory innervation from the maxillary (V2) branch of the trigeminal nerve (CN V).

• Anterior structures
  
  • Upper eyelids: larger and more mobile
  • Lower eyelids
  • 3-2 mm in thickness
• ​Function:
  
  • Protects the eyeball from excessive light, dryness, and foreign bodies.
  • Keeps corneal surface of eye moist
• Palpebral fissure
  
  • Space between the eyelids when they are open
  • Canthus (medial and lateral)
    
    • place of attachment of upper and lower eyelid
• Lacrimal part:
  
  • Smaller, medial part of eyelid
  • Dosen’t contain eyelashes
• Cilliary part:
  
  • Larger, lateral part of eyelid

*Bony orbit

The layers of the eyelids/palpebrae:

From superficial to deep:

1- Skin

• Thinnest skin in body
• Relativly loose and elastic to accomidate movment
• Cillia/eyelashes
  
  • Rooted at distal end
  • From anterior palbebral margin of eyelid

2- Subcutaneous tissue

• ​Contains 2 types of glands assosiated with the follciles of the eyelashs
• Cilliary gland of Moll
  
  • Modified aporine seat glands
  • Lipid based compund
• Sebaceous glands of Zeis
  
  • Secrete sebum

3- Voluntary muscle

• Orbicularis oculi:
  
  • (Orbital part: surrounds the orbit)
    
    • Closing eyes tightly when contracts
  • Palpebral part: closes the eyelids gently
    • Innervated: facial nerve [VII]
    • Thin
    • Medial palpebral ligament:
      
      • anchores the msucle medially to the anterior lacrimal crest
    • Lateral palpebral ligament

3- Orbital septum

• Extension of periosteum into:
  
  • Upper eyelids
    
    • Attaches to the tendon of levator palpebrae superioris muscle
  • Lower eyelids
    
    • Attaches to inferior tarsus

4- Tarsus

• Support for each eyelid: Dense connective tissue
  
  • Large superior tarsus: Upper eyelid
  • Smaller inferior tarsus: Lower eyelid
  • Attachements
    
    • Medial palpebral ligament
      
      • Connects tarsus to anterior lacrimal crest of the maxilla
    • Lateral palpebral ligament:
      • Connects tarsus orbital tubercle on the zygomatic bone
    • Sponeurosis of levator palbebrae superiors muscle
      
      • Also connects superior tarsal plate
• ​Superior and inferior tarsal muscle
  • Collection of smooth muscle fibers
  • From the inferior surface of the levator to the upper edge of the superior tarsus
  • Innervated
    
    • Postganglionic sympathetic fibers from the superior cervical ganglion​​
• Tarsal glands, Meibomian glands
  
  • Embedded in the tarsal plates
  • Empty onto the free margin of each eyelid.
  • Modified sebaceous glands:
    
    • Secretion: meibum
      
      • Oily substance
      • Increases the viscosity of the tears
      • Decreases the rate of evaporation of tears from the surface of the eyeball.
• Blockage and inflammation of a tarsal gland is a chalazion and is on the inner surface of the eyelid.

*Difference in upper eyelid

• Levator palpebrae superioris muscle
  
  • Raises the eyelid.
  • Origin:
    
    • Posterior part of the roof of the orbit
    • just superior to the optic foramen
  • Insertion:
    • anterior surface of the superior tarsus, with the possibility of a few fibers attaching to the skin of the upper eyelid.
  • Innervated
    
    • Oculomotor nerve [III]
• *Loss of function of either the levator palpebrae superioris muscle or the superior tarsal muscle results in a ptosis or drooping of the upper eyelid.

5- Conjunctiva

• Thin mucous membrane
  
  • Stratified columnar epithelium
  • contains goblet cells, large amount of lymph and conjuctival glands of wolfring
• Function:
  
  • Produces mucin
  • Keeps surface of eyes and eyelids lubricated
  • protection from microbial infection
• Parts:
  
  • Palpebral conjuctiva:
    
    • On dorsal surface of eyelid
    • Marginal region
    • Tarsal region
    • Orbital region
      
      • accesory lacrimal glands: ciaccio glands=glands of wolfring
  • Superior/inferior conjuctival fornix
    
    • Accesory lacrimal glands: Krause glands
  • ​Bulbar conjuctiva:
    
    • converts into corneal epithelium on ventral surface of eyeball
    • It attaches to the eyeball at the junction between the sclera and the cornea.
  • Conjuctival sac
    
    • Upper and lower extensions of this sac are the superior and inferior conjunctival fornices

Clinical anatomy

Stye

• Local inffection of sebaceous glands (Zeis)
• Caused usually by staphy innection (staphylococcal bacteria)
• Tend to occur in periods of immunosuppersion
• Is on the edge of the eyelid.

Chalazion:

• Blockage of tarsal glands (and not from an infection)

Horner’s syndrome

• Caused by a lesion in the sympathetic trunk in the neck
  
  • Results in sympathetic dysfunction.
• It is characterized by three typical features:
  
  • Pupillary constriction
    
    • Due to paralysis of the dilator pupillae muscle;
  • Partial ptosis (drooping of the upper eyelid)
    
    • Due to paralysis of the superior tarsal muscle of the levator palpebrae superioris;
  • Absence of sweating on the ipsilateral side of the face and the neck
    
    • Due to absence of innervation of the sweat glands.

Vessels

• Arterial supply
  
  • Ophthalmic artery;
    
    • Supratrochlear
    • Supra-orbital
    • Lacrimal
    • Dorsal nasal arteries
  • Facial artery
    
    • Angular artery
  • Superficial temporal artery
    
    • Transverse facial artery
    • Branches from the superficial temporal artery itself
• Venous drainage
  
  • External pattern through veins associated with the various arteries
  • Internal pattern moving into the orbit through connections with the ophthalmic veins.
• Lymphatic drainage
  
  • Primarily to the parotid nodes,
  • Some drainage from the medial corner of the eye along lymphatic vessels associated with the angular and facial arteries to the submandibular nodes.

Innervation

Innervation of the eyelids includes both sensory and motor components.

• The sensory nerves
  
  • All branches of the trigeminal nerve [V].
  • Palpebral branches arise from
  • branches of the ophthalmic nerve [V1]
    
    • Supra-orbital
    • Supratrochlear
    • Infratrochlear
    • Lacrimal
  • branch of the maxillary nerve [V2]
    
    • Infra-orbital
• Motor innervation is from:
  
  • Facial nerve [VII],
    
    • Which innervates the palpebral part of the orbicularis oculi;
    • lesion: causes an inability to close the eyelids tightly and the lower eyelid droops away, resulting in a spillage of tears.
  • Oculomotor nerve [III],
    
    • Which innervates the levator palpebrae superioris;
    • Lesion: inability to open the superior eyelid voluntarily, producing a complete ptosis.
  • Sympathetic fibers,
    
    • Which innervate the superior tarsal muscle.
    • Lesion: causes a constant partial ptosis

Lacrimal apparatus

General:

• Group of structures that:
  
  • Generates tears
  • Involved in the movement, and drainage of fluid from the surface of the eyeball.
• Tear fluid:
  
  • Made of water, containing electrolytes and protiens
  • Lubricant of eye
• Components:
  
  • Lacrimal gland and its ducts,
  • Lacrimal canaliculi,
  • Lacrimal sac,
  • Nasolacrimal duct.

1- Lacrimal gland

• Anterior in the superolateral region of the orbit
• Divided into two parts by the levator palpebrae superioris:
  
  • Orbital part
    
    • Larger
    • In the lacrimal fossa, a depression in the frontal bone
  • Palpebral part
    
    • Smaller
    • Inferior to levator palpebrae superioris
    • In the superolateral part of the eyelid.

2- Excretory ducts of lacrimal gland:

• Usually 12 ducts
• Transport fluid from the lacrimal gland to the conjunctival sac
• Fluid is continually being secreted by the lacrimal gland and moved across the surface of the eyeball from lateral to medial as the eyelids blink.

3- Lacrimal caruncle in lacrimal lake

• Medial part of eye, inbetween eyelids
• Contains sebaceous and swaet glands
• “Junk in the morning when you wake up”

4- Lacrimal lake:

• Fluid accumulates her

5- Lacrimal papillae

• Sittuated superior and inferior to lateral caruncle
• Medial part of each eyelid
• Lacrimal punctum
  
  • In the center of each papillae
  • Opening through which fluid enters each canaliculus.

6- Lacrimal canaliculi

• Fluid is drained from the lake via canaliculi
• One canaliculus associated with each eyelid
• Superior and inferior are joinded

7- Lacrimal sac ​

• Dilated portion of the nasolacrimal duct
• Gathers tear fluid
• Lacrimal canaliculi eventually join the lacrimal sac between the anterior and posterior lacrimal crests,

8- Nasolacrimal duct:

• Drains into the inferior meatus of the nose
• Opening of nasolacrimal duct
• Draining of exsees tear fluid

*When the orbicularis oculi muscle contracts during blinking, the small lacrimal part of the muscle may dilate the lacrimal sac and draw tears into it through the canaliculi from the conjunctival sac.

Innervation

• Involves three different components:
• Sensory innervation
  
  • Sensory neurons from the lacrimal gland return to the CNS through the lacrimal branch of the ophthalmic nerve [V1].
• Secretomotor (parasympathetic) innervation
  • Stimulate fluid secretion from the lacrimal gland.
  • These preganglionic parasympathetic neurons leave the CNS in the facial nerve [VII],
  • Enter the greater petrosal nerve (a branch of the facial nerve [VII]),
  • Continue with this nerve until it becomes the nerve of the pterygoid canal
  • The nerve of the pterygoid canal eventually joins the pterygopalatine ganglion where the preganglionic parasympathetic neurons synapse on postganglionic parasympathetic neurons.
  • The postganglionic neurons join the maxillary nerve [V2] and continue with it until the zygomatic nerve branches from it, and travel with the zygomatic nerve until it gives off the zygomaticotemporal nerve,
  • which eventually distributes postganglionic parasympathetic fibers in a small branch that joins the lacrimal nerve.
  • The lacrimal nerve passes to the lacrimal gland.
• Sympathetic innervation
• Follows a similar path as parasympathetic innervation.
  
  • Postganglionic sympathetic fibers originating in the superior cervical ganglion travel along the plexus surrounding the internal carotid artery
  • They leave this plexus as the deep petrosal nerve and join the parasympathetic fibers in the nerve of the pterygoid canal.
  • Passing through the pterygopalatine ganglion, the sympathetic fibers from this point onward follow the same path as the parasympathetic fibers to the lacrimal gland.

Vessels

• The arterial supply to the lacrimal gland is by branches from the ophthalmic artery and venous drainage is through the ophthalmic veins.

Question 8

Extraocular muscles

Answer 8

There are two groups of muscles within the orbit:

• Extrinsic muscles of eyeball (extra-ocular muscles)
  
  • Involved in movements of the eyeball or raising upper eyelids;
    
    • Levator palpebrae superioris,
    • Superior rectus,
    • Inferior rectus,
    • Medial rectus,
    • Lateral rectus,
    • Superior oblique,
    • Inferior oblique.
• Intrinsic muscles within the eyeball,
  
  • which control the shape of the lens and size of the pupil.
    
    • Ciliary muscle,
    • Sphincter pupillae,
    • Dilator pupillae.

Extrinsic muscles

• Seven muscles in the extrinsic group of muscles,
  
  • one raises the eyelids,
  • whereas the other six move the eyeball itself

1- Levator palpebrae superioris

• It is the most superior muscle in the orbit,
• O:
  
  • From the roof, just anterior to the optic canal on the inferior surface of the lesser wing of the sphenoid
• I:
  
  • Its primary point of insertion is into the anterior surface of the superior tarsus,
  • A few fibers also attach to the skin of the upper eyelid and the superior conjunctival fornix.
• N:
  
  • Superior branch of the oculomotor nerve [III].
• F:
  
  • Contraction of the levator palpebrae superioris raises the upper eyelid.
• A unique feature of levator palpebrae superioris is that a collection of smooth muscle fibers passes from its inferior surface to the upper edge of the superior tarsus
  
  • =The superior tarsal muscle
  • help maintain eyelid elevation and are innervated by postganglionic sympathetic fibers from the superior cervical ganglion.
• Lesion:
  
  • Loss of oculomotor nerve [III] function results in complete ptosis or drooping of the superior eyelid,
  • whereas loss of sympathetic innervation to the superior tarsal muscle results in partial ptosis.

2,3,4,5- Rectus muscles

• Four rectus muscles occupy medial, lateral, inferior, and superior positions
• Originate as a group from a common tendinous ring at the apex of the orbit and form a cone of muscles as they pass forward to their attachment on the eyeball.

Superior rectus

• O:
  
  • From the superior part of the common tendinous ring above the optic canal
• I:
  • Anterior half of eyeball superiorly
• N:
  
  • superior branch of the oculomotor nerve [III]
• F:
  
  • contraction elevates, adducts, and internally rotates the eyeball

Inferior rectus

• O:
  
  • Inferior part of the common tendinous ring below the optic canal
• I:
  • Anterior half of eyeball inferiorlly
• N:
  
  • Inferior branch of the oculomotor nerve [III]
• F:
  
  • Depresses, adducts, and externally rotates the eyeball

Medial rectus

• O:
  
  • From the medial part of the common tendinous ring medial to and below the optic canal,
• I:
  • Anterior half of eyeball medially
• N:
  
  • Inferior branch of the oculomotor nerve [III]
• F:
  
  • Contraction of each medial rectus adducts the eyeball

Lateral rectus

• O:
  
  • From the lateral part of the common tendinous ring as the common tendinous ring bridges the superior orbital fissure
• I:
  • Anterior half of eyeball laterally
• N:
  
  • Abducent nerve [VI]
• F:
  
  • Abducts the eyeball

6,7 Oblique muscles

• Are in the superior and inferior parts of the orbit,
• Do not originate from the common tendinous ring,
• Are angular in their approaches to the eyeball,
• Attach to the posterior half of the eyeball
  
  • Unlike the rectus

Superior oblique

• O:
  
  • From the body of the sphenoid,
  • superior and medial to the optic canal and medial to the origin of the levator palpebrae superioris
• Course:
  
  • Passes forward along the medial border of the roof of the orbit, until it reaches a fibrocartilaginous pulley (the trochlea), which is attached to the trochlear fovea of the frontal bone.
  • The tendon of superior oblique passes through the trochlea and turns laterally to cross the eyeball in a posterolateral direction.
  • It continues deep to the superior rectus muscle
• I:
  
  • Into the outer posterior quadrant of the eyeball.
• N:
  
  • The trochlear nerve [IV] innervates the superior oblique along its superior surface.
• F:
  
  • Contraction of the superior oblique directs the pupil down and out

Inferior oblique

• Only extrinsic muscle that does not take origin from the posterior part of the orbit.
• O:
  
  • From the medial side of the floor of the orbit,
  • just posterior to the orbital rim,
• Course:
  
  • Attached to the orbital surface of the maxilla just lateral to the nasolacrimal groove
  • crosses the floor of the orbit in a posterolateral direction between the inferior rectus and the floor of the orbit
• I:
  
  • into the outer posterior quadrant just under the lateral rectus.
• N:
  
  • inferior branch of the oculomotor nerve
• F:
  
  • Contraction directs the pupil up and out

Paired movements (both eyes working together)

• simultaneous movement of both eyes in the same direction = version (conjugate movements)

– dextroversion (to the right) + levoversion (to the left)
– supraversion (sursumversion) + infra/deorsumversion (up + down)

– dextro/levoelevation + dextro/levodepression (up/down and to side)

– dextro/levocykloversion (rotation to the right/left)

• simultaneous movement of both eyes in
  
  • opposite directions = vergence (disconjugate movements),
  • convergence = both eyes moving nasally or inward ,
  • divergence = both eyes moving temporally or outward

Clinical:

• The extrinsic muscles are supplied by the abducent nerve [VI], the trochlear nerve [IV], and the oculomotor nerve [III].
• The extrinsic muscles work synergistically to provide appropriate and conjugate eye movement:
  
  • lateral rectus-abducent nerve [VI];
  • superior oblique-trochlear nerve [IV];
  • remainder-oculomotor nerve [III].
• Loss of innervation of the muscles around the eye
  • Orbicularis oculi
    
    • the facial nerve [VII]
    • causes an inability to close the eyelids tightly, allowing the lower eyelid to droop away causing spillage of tears.
    • This loss of tears allows drying of the conjunctiva, which may ulcerate, so allowing secondary infection.
  • Levator palpebrae superioris
    
    • oculomotor nerve [III]
    • damage causes an inability of the superior eyelid to elevate, producing a ptosis.
    • Usually, oculomotor nerve [III] damage is caused by severe head injury.
  • Superior tarsal muscle
    
    • Sympathetic fibers
    • Causes a constant partial ptosis.
    • Any lesion along the sympathetic trunk can induce this.
    • An apical pulmonary malignancy should always be suspected because the ptosis may be part of Horner’s syndrome
    *

Question 9

External acustic meatus and tympanic membrane (draw otoscopic view), paracentesis (miringotomy)

Answer 9

The ear is the organ of hearing and balance.

It has three parts

• External ear
  
  • consisting of the part attached to the lateral aspect of the head and the canal leading inward;
• Middle ear
  
  • a cavity in the petrous part of the temporal bone bounded laterally, and separated from the external canal, by a membrane and connected internally to the pharynx by a narrow tube;
• Internal ear
  
  • consisting of a series of cavities within the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially.
  • Converts the mechanical signals received from the middle ear, which start as sound captured by the external ear, into electrical signals to transfer information to the brain.
  • Also contains receptors that detect motion and position.

External ear

Two parts:

• Auricle (pinna):
  
  • The part projecting from the side of the head
• External acoustic meatus:
  
  • Canal leading inward

Auricle

• On the side of the head
• Assists in capturing sound.
• skin is firmly attached ventrally and sorsally its more loose
• Structure:
  
  • It consists of cartilage covered with skin and arranged in a pattern of various elevations and depressions- elastic cartilage
  • Helix: The large outside rim of the auricle
    
    • It ends inferiorly at the fleshy lobule, the only part of the auricle not supported by cartilage.
      
      • crus, spine, cauda, auricle tubercle
  • Antihelix
    
    • A smaller curved rim, parallel and anterior to the helix
      
      • 2 crurs, form triangular fossa
  • Scapha: between helix and antiheliz
  • Concha of auricle:
    
    • Cavity
      
      • Hollow center of the auricle
      • The external acoustic meatus leaves from the depths of this area.
    • Cymba
  • Tragus
    
    • An elevation anterior to the opening of the external acoustic meatus, in front of the concha
  • Intertragic notch:
  • Antitragus
    
    • Another elevation opposite the tragus, and above the fleshy lobule
  • Lobule: no cartilage
• ​Muscles
  
  • Ligaments: ant, sup, post ligament
  • Intrinsic muscles, rudimentary
    
    • Pass between the cartilaginous parts of the auricle and may change the shape of the auricle
  • Extrinsic muscles
    
    • Auricular mm. (ant, sup, inf)
    • temporoparietialis m
    • Pass from the scalp or skull to the auricle and may also play a role in positioning of the auricle.
  • Both groups of muscles are innervated by the facial nerve [VII].
• Innervation- IMPORANT
  
  • Cervical plexsus
    
    • Lesser occipital n.
      
      • middle helix
    • Great auricular n. (anterior and posterior)
      
      • supply inferior part
  • Auriculotemporal nerve, branch of the mandibular nerve [V3]
    
    • Runs together with artery (superficial temporal a)
  • Vagus nerve [X] (the auricular branch), concea
    
    • goes though bone, mastoid canaliculus
  • MOTOR: facialy nerve
• Blood supply:
  
  • Arteries:
    
    • superficial temporalis a.- anterior auricular branch
    • external carotid artery- posterior auricular brach
  • Viens: external jugular v
  • Lymph: nn mastoid (dorsally), parotid (ventrally)

External acoustic meatus

• Extends from the deepest part of the concha to the tympanic membrane (eardrum)
• Distance of approximately 2.5 cm
• Its walls consist of cartilage and bone.
  
  • Lateral 2/3: cartilaginous extensions from some of the auricular cartilages
    
    • Santorini incisurae: through theis inflamation can spread ventrally and caudally to temporomandibular joint
    • lamnia tragu
  • Medial 1/3: bony tunnel in the temporal bone.
  • Covered with skin, some hair and modified sweat glands producing cerumen (earwax).
• Its diameter varies, being wider laterally and narrow medially.
  
  • Does not follow a straight course: VM, M, VM, 160 angle
• Innervation: The major sensory input
  
  • Mandibular nerve [V3]:
    
    • From branches of the auriculotemporal nerve: (anterior and superior walls),
  • Vagus nerve [X]
    
    • Auricular branch: (posterior and inferior walls).
    • A minor sensory input may also come from a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X].
• Blood supply:
  
  • Similar to auricle: addition of maxillary a.-> deep auricular a.
  • Vien and lymph similar

Tympanic membrane

• Separates the external acoustic meatus from the middle ear
• It consists of a connective tissue core lined with skin on the outside and mucous membrane on the inside.
• located inside tympanic groove
  
  • Around the periphery of the tympanic membrane a fibrocartilaginous ring attaches it to the tympanic part of the temporal bone
• At an angle: Lateral surface faces inferiorly and anteriorly.
• Structure- 3 layers:
  
  • Outer surface: thinned epidermis
    
    • pharyngeal cleft
  • Dense CT: ecto-mesemchyme (mesencgyme of head- 1st and 2 pharyngeal arch)
  • Inner surface: simple cuboid epithelium (endoderm)
    
    • pharyngeal pouch
      
      • Connective tissue core lined with skin on the outside and mucous membrane on the inside.
      • Around the periphery of the tympanic membrane a fibrocartilaginous ring attaches it to the tympanic part of the temporal bone.
      • At its center, a concavity is produced by the attachment on its internal surface of the lower end of the handle of malleus, part of the malleus bone in the middle ear. This point of attachment is the umbo of tympanic membrane.
• Otoscopic view: ​
  
  • Bezolds trias:
  • 1- Umbo of tympanic membrane :
    
    • Center: concavity is produced by the attachment of the lower end of the handle of malleus
  • 2- Stria malleraris
  • 3- Mallear prominence
  • Cone of light/ light reflex: wilde triangle
    
    • Anteroinferior to the umbo
    • is usually visible when examining the tympanic membrane with an otoscope.
  • Anterior and posterior malleolar folds.
    
    • Superior to these folds the tympanic membrane is thin and slack (the pars flaccida),
    • whereas the rest of the membrane is thick and taut (the pars tensa).
• declination: 50 degrees sagittally
• inclination: 45 degrees transverslly
• in lower posterior quadrant: paracentesis, drain fluid from inflamation

Clinical:

• Otitis media (infection of the middle ear) is common, but can usually be treated by antibiotics.
• If the infection persists, the chronic inflammatory change may damage the ossicular chain and other structures within the middle ear to produce deafness.
• From time to time it is necessary to enter the middle ear through the tympanic membrane.
• As the chorda tympani runs in the upper one-third of the tympanic membrane, incisions are always below this level.
• The richer blood supply to the posterior aspect of the tympanic membrane determines the standard surgical approach in the posterior-inferior aspect.

innervation

sensory innervation of the skin on the outer surface of the tympanic membrane is primarily by

the auriculotemporal nerve, a branch of the mandibular nerve [V3] with additional participation

of the auricular branch of the vagus nerve [X], a small contribution by a branch of the facial

nerve [VII] to the auricular branch of the vagus nerve [X], and possibly a contribution from the

glossopharyngeal nerve [IX];

sensory innervation of the mucous membrane on the inner surface of the tympanic membrane

is carried entirely by the glossopharyngeal [IX] nerve.

Question 10

Tympanic cavity, auditory ossicles, auditory tube

Mastoid area

Posterior to the epitympanic recess of the middle ear is the aditus to mastoid antrum, which is the

opening to the mastoid antrum (Fig. 8.112).

The mastoid antrum is a cavity continuous with collections of air-filled spaces (the mastoid cells),

throughout the mastoid part of the temporal bone, including the mastoid process. The mastoid

antrum is separated from the middle cranial fossa above by only the thin tegmen tympani.

The mucous membrane lining the mastoid air cells is continuous with the mucous membrane

throughout the middle ear. Therefore infections in the middle ear can easily spread into the mastoid

area.

Answer 10

Middle ear

• air-filled, mucous membrane-lined space in the temporal bone
• between the tympanic membrane laterally and the lateral wall of the internal ear medially.
• Two parts:
  
  • Tympanic cavity immediately adjacent to the tympanic membrane
  • Epitympanic recess superiorly

Boundries: Tympanic cavity

Tegmental wall (roof)

• Thin layer of bone: separates the middle ear from the middle cranial fossa.
• This layer of bone is the tegmen tympani on the anterior surface of the petrous part of the temporal bone.

Jugular wall (floor)

• Thin layer of bone that separates it from the internal jugular vein.
• Styloid prominence
• Aperture of tympanic canaliculi, Near the medial border
  
  • Small aperture, through which the tympanic branch from the glossopharyngeal nerve [IX] enters the middle ear.

Membranous wall (lateral)

• Consists almost entirely of the tympanic membrane,
  
  • but is does not extend superiorly into the epitympanic recess,
• Upper part of the membranous wall of the middle ear is the bony lateral wall of the epitympanic recess.

Mastoid wall (posterior)

• Aditus (entrance) mastoid
  
  • leads into Antrum
  • Two prominent elevations:
  • Prominence of facial canal
    
    • which is a ridge of bone produced by the facial nerve [VII] in its canal as it passes through the temporal bone;
  • Prominence of lateral semicircular canal
    
    • just above and posterior to the prominence of facial canal is a broader ridge of bone produced by the lateral semicircular canal, which is a structure involved in detecting motion.
  • Antrum
    
    • mastoid cells, air cells
    • has several puches, “cells”, like paranasal sinsuses
• Pyramidal eminance
  
  • hollow cone containing belly of stapedius muscle (attaching to
  • small elevation through which the tendon of the stapedius muscle enters the middle ear;
• Tympanic cord canaliculi eminance
  
  • coverved with mucous fold
  • tympanic apperture
    
    • and the opening through which the chorda tympani nerve, a branch of the facial nerve [VII], enters the middle ear
• tympanic sinus
• Fossa incudis

Anterior wall, caroticus part

• petrotympanic fissure, passes: (not usually drawn)
  
  • tympanic apertura/exit of anterior tympanic canaliculi
  • anterior mallear ligament (passes thought the fissure)
    
    • attached to spine of spenoidal bone
• caroticotympanic canaliculi
• Musculotubarius canal
  
  • semicanal- upper part: for tensor tympani musscle
  • process cochleariformis
  • semicanal- for auditory tube
• Opeining of lesser petrosal nerve canal

Labyrinthine wall (medial)

• Also the lateral wall of the internal ear.
• Promontory:
  
  • a rounded bulge
  • produced by the basal coil of the cochlea
• Groove on promontory: for tympanic plexsus, contributions from:
  
  • Tympanic branch of the glossopharyngeal nerve [IX]
  • branches from the internal carotid plexus
  • Branch of the tympanic plexus (the lesser petrosal nerve) leaves the promontory and the middle ear
    
    • Travels across the anterior surface of the petrous part of the temporal bone,
    • and leaves the middle cranial fossa through the foramen ovale to enter the otic ganglion: supply parotid and buccal glands
• Two openings:
• Oval window:
  
  • Point of attachment for the base of stapes (footplate)
  • Ends the chain of bones that transfer vibrations initiated by the tympanic membrane to the cochlea of the internal ear;
    
    • annular stapedular ligament
• Round window
  
  • Secondary tympanic membrane
  • Vibrations of the footplate of the stapes are transmitted to the round window through the perilymph, which causes it to vibrate in the opposite phase of the oval window.
  • Injury to the round window (e.g., violent nose blowing, barotrauma while diving) causes sensorineural hearing loss.

Arteries:

come from 5 diffrent directions

• inferior: assending pharyngeal A
  
  • posteripr meningeal a (into jugular foramen): assending pharyngeal A
• posterior: from posterior auricular
• anterior: from maxially a, from mandibular part 1st: middle meningeal,
  
  • also A to external accustic meatus and tympanic membran: deep auricular A
  • (bigger branchs of maxillary (middle meningeal, inf alveolar)
• (Petros branch (canaliculsof greater petrosal nerve): middle meningeal,)
• internal carotid atrey branchs-

veins: drain into sinuses from tegmen tympani (superior petrosal sinus

Vessels

The arterial supply to the pharyngotympanic tube is from several sources. Branches arise from the

ascending pharyngeal artery (a branch of the external carotid artery) and from two branches of

the maxillary artery (the middle meningeal artery and the artery of the pterygoid canal).

Venous drainage of the pharyngotympanic tube is to the pterygoid plexus of veins in the

infratemporal fossa.

Innervation

Innervation of the mucous membrane lining the pharyngotympanic tube is primarily from the tympanic

plexus because it is continuous with the mucous membrane lining the tympanic cavity, the internal

surface of the tympanic membrane, and the mastoid antrum and mastoid cells. This plexus receives

its major contribution from the tympanic nerve, a branch of the glossopharyngeal nerve [IX].

Auditory ossicles

• The bones of the middle ear consist of the malleus, incus, and stapes.
• They form an osseous chain across the middle ear from the tympanic membrane to the oval window of the internal ear
• Muscles associated with the auditory ossicles modulate movement during the transmission of vibrations.

Malleus

• largest of the auditory ossicles
• Attached to the tympanic membrane.
• Head of malleus:
  
  • is the rounded upper part of the malleus in the epitympanic recess.
  • Its posterior surface articulates with the incus.
  • Inferior to the head of malleus is the constricted neck of malleus, and below this are the…
• Anterior process:
  
  • attached to the anterior wall of the middle ear by a ligament: anterior mallear ligament
  • into petrotympanic fissure fissues
• Lateral process:
  
  • Attached to the anterior and posterior malleolar folds of the tympanic membrane,
  • froms prominence
• Handle of malleus
  
  • Attached to the tympanic membrane.
  • syndesmoses

Incus

• The second bone
• Body
  
  • Articulates with the head of malleus
  • In the epitympanic recess
• Long limb (thin)
  
  • Extends downward from the body, paralleling the handle of the malleus, and ends by bending medially to articulate with the stapes;
• Short limb
  
  • Extends posteriorly and is attached by a ligament to the upper posterior wall of the middle ear.
• Lenticular process
  
  • ​articular surface for head of stapes

Stapes

• Most medial bone
• Attached to the oval window.
• Head
  
  • Directed laterally and articulates with the long process of the incus;
• Two limbs
  
  • Separate from each other and attach to the oval base
• Base of stapes
  
  • fits into the oval window on the labyrinthine wall of the middle ear.

Muscles associated with the ossicles

Tensor tympani

• Lies in a bony canal above the pharyngotympanic tube.
• O:
  
  • from the cartilaginous part of the pharyngotympanic tube,
  • the greater wing of the sphenoid,
  • and its own bony canal,
• Course:
  
  • and passes through its canal in a posterior direction
  • semicanalis, cochleariformis process (small hook to make right angle), manubrium mallei
• I:
  
  • ending in a rounded tendon that inserts into the upper part of the handle of the malleus.
• Innervation:
  
  • branch from the mandibular nerve [V3].
• Function:
  
  • Contraction of the tensor tympani pulls the handle of the malleus medially.
  • This tenses the tympanic membrane, reducing the force of vibrations in response to loud noises.

Stapedius

• Very small muscle
• O:
  
  • From inside the pyramidal eminence, which is a small projection on the mastoid wall of the middle ear
• I:
  
  • Its tendon emerges from the apex of the pyramidal eminence and passes forward to attach to the posterior surface of the neck of stapes
• Innervated by a branch from the facial nerve [VII].
• Function:
  
  • Contraction of the stapedius muscle, usually in response to loud noises pulls the stapes posteriorly and prevents excessive oscillation.
• ​Annular stapedial ligament
  
  • ​2 small fissures, infrom and behind, which ossify later ​
  • the ossification can cause the ligament to ossify as well, leading to deafness: ostoclerosis

Joints:

• incudomallearis (saddle shape)
• incudostapedia (ball and socket)
• syndesmosis tympanostapedialis
• syndesmosis tympanomallearis

Ligaments:

• ​Annular stapedial ligament
• lig mallei ant, sup, lat
  
  • anterior: throught petrotympanic fissure: on spine of sphenoid bone
• lig uncudis sup, post
• stepedialis membrane
• secondary tympanic memnrane: closes round window

—————-

Pharyngotympanic tube /auditory tube/ eustachii

• Connects the middle ear with the nasopharynx
• Equalizes pressure on both sides of the tympanic membrane.
• Its opening in the middle ear is on the anterior wall, and from here it extends forward, medially, and downward to enter the nasopharynx just posterior to the inferior meatus of the nasal cavity.
• It consists of:
  
  • a bony part (the one-third nearest the middle ear);
    
    • The opening of the bony part is clearly visible on the inferior surface of the skull at the junction of the squamous and petrous parts of the temporal bone immediately posterior to the foramen ovale and foramen spinosum.
  • a cartilaginous part (the remaining two-thirds).
    
    • 2 plates connected with membrane
• tubal tonsil: just at entrance to auditory tube
• in children: shorter, wider, more horizonal

opened during swalloing by tensor tympani and salpingopharyneus

to open and close there need to be a buffer space: ostmans fat pad

Question 11

Bony and membranous labyrinths (draw cross section of bony cochlea and cochlear duct) vestibulocochlear nerve, nystagmus

Bony labyrinth

consists of the vestibule, three semicircular canals, and the cochlea

These bony cavities are lined with periosteum and contain a clear fluid (the perilymph).

Answer 11

Internal ear

• Parts:
  
  • Series of bony cavities (the bony labyrinth)
  • Membranous ducts and sacs (the membranous labyrinth) within these cavities.
• The structures in the internal ear convey information to the brain about balance and hearing:
  
  • cochlear duct is the organ of hearing;
  • the semicircular ducts, utricle, and saccule are the organs of balance.

The nerve responsible for these functions is the vestibulocochlear nerve [VIII], which divides into:

• vestibular (balance)
• cochlear (hearing) parts after entering the internal acoustic meatus

Bony labyrinth

1- Vestibule:

• Contains the oval window in its lateral wall,
• Communicates anteriorly with the cochlea and posterosuperiorly with the semicircular canals.
• Vestibular aqueduct:
• A narrow canal leaves the vestibule, and passes through the temporal bone to open on the posterior surface of the petrous part of the temporal bone.

Semicircular canals

• Projecting in a posterosuperior direction from the vestibule are the anterior, posterior, and lateral
• semicircular canals
• Each of these canals forms two-thirds of a circle connected at both ends to the vestibule and with one end dilated to form the ampulla.
• The canals are oriented so that each canal is at right angles to the other two.

Cochlea

• Auditory part of inner ear
• Projecting in an anterior direction from the vestibule is the cochlea, which is a bony structure that twists on itself two and one-half to two and three-quarter times around a central column of bone (the modiolus).
• This arrangement produces a cone-shaped structure with a base of cochlea that faces posteromedially and an apex that faces anterolaterally (Fig. 8.121).
• This positions the wide base of the modiolus near the internal acoustic meatus, where it is entered by branches of the cochlear part of the vestibulocochlear nerve [VIII].
• Extending laterally throughout the length of the modiolus is a thin lamina of bone (the lamina of modiolus, or spiral lamina). Circling around the modiolus, and held in a central position by its attachment to the lamina of modiolus, is the cochlear duct, which is a component of the membranous labyrinth.

Question 12

Skin - epidermis and dermis, skin types, skin receptors, skin appendages (hair, nails, glands)

Question 13

Mamma - description and structure, blood supply and innervation, lymphatics

Question 14

Thyroid and parathyroid glands - structure, function, topography, blood supply

Question 15

Suprarenal gland - structure and developmental origin of cortex and medulla, function, syntopy (draw scheme), blood supply

Question 16

Hypophysis - development, structure of adeno and neurohypophysis, function, syntopy