- Histology of the cornea.

Histological structure :- is Composed of 5 Layers:-

1- Epithelium:-

• Active mitosis → regeneration within 6- 24 hrs.
• Continue with conjunctiva.

2-Bowman's membrane:-

• Acellular Clear membrane lie under the epithelium.
• Ends abruptly at the limbus. (i.e. end in folded manner)
• Is considered as modified lamella of stroma.
• If destroyed cannot regenerate.

3-Stroma:-

• Represent 90% of corneal thickness .
• Formed of collagen fibrils (Type 1) which has special arrangement which run parallel to each other and parallel to the surface of the cornea making the cornea transparent, unlike sclera in which arrangement is not done in specific way so appear opaque.
• Collagen fibrils lie in mucoid matrix Scattered keratocytes lie between lamellae and are stellate in shape.

4-Descemet's membrane:-

• An elastic membrane which lie ( ) Endothelium and stroma.
• It is resistant to pathology and regenerate easily. 
• This layer is continuous with material of the pectinate ligament or trabecular meshwork of the iris.

5-Endothelium:-
Single layer of flat hexagonal cells with No mitosis.

- Pumps water out → prevent corneal edema → prevent corneal opacification.

(By light microscope)

So Cornea formed of :-

• Epithelium resting on B.M
• Endothelium resting on D.M
• stroma in between

- The Meninges of the Brain.

The Meninges of the Brain

1-The Dura mater.

2-The Arachnoid mater .

3The Pia mater.

1-The Dura mater:


-The dura mater is as two layers:

the endosteal layer and the meningeal layer.

These are closely united except along certain lines,

where they separate to form venous sinuses & folds

which act as septae forming cranial cavity compartments.

- Dural folds :

• Falx cerebri
• Tentorium cerebelli
• Falx cerebelli
  

2-The Arachnoid mater :

-The arachnoid mater is a delicate, impermeable membrane

covering the brain and lying between the pia mater

internally and the dura mater externally.

- It is separated from the dura by a potential space, the subdural space,

- It is separated from the pia by the subarachnoid space,

which is filled with cerebrospinal fluid.


2-The pia mater :

-The pia mater is a vascular membrane that

closely invests the brain,covering the gyri and

descending into the deepest sulci.

See you,

Dr Ibrahim

- The Cranial cavity in brief .

The Cranial cavity in brief

- The cranial cavity, or intracranial space,

is the space formed inside the skull

- The skull or cranium is a bony structure

serves as the general framework for the head....

- Brain : occupies the cranial cavity,

which is lined by the meninges


The meninges are the system of membranes that

envelop the central nervous system and which

contains fluid to cushion blows.

- Cranial cavity is composed by the frontal,

parietal, sphenoid, temporal and occipital bones,

and in part the ethmoid, all covered by

endosteal layer of dura mater.


- The cranial cavity is divided into

three cranial fossae :

1-Anterior cranial fossa which accommodates

the anterior lobe of brain.

2- Middle cranial fossa, much wider than the

anterior cranial fossa contain the 2 temporal lobes of brain.

3- Posterior cranial fossa is much shallower and

wider than the middle cranial fossa and it

accommodates the occipital lobes of the brain.

see you,

Dr Ibrahim

- layers of the scalp.

Scalp is composed of five layers arranged  from outward inward in the manner

" S C A L P "

- Skin:

The skin of the scalp is thick and hair bearing and contains numerous sebaceous glands.


-Connective tissue (superficial fascia):

The superficial fascia is a fibro fatty layer that connects skin to the underlying aponeurosis of the occipitofrontalis muscle and provides a passageway for nerves and blood vessels.

- Aponeurosis (galia aponeurotica):- Sheet like tendon of occipitofrontalis muscle .

-Loose areolar tissue (subglial) .

-Pericranium (periosteum):- Dense fibrous tissue.

Enjoy it, see you,

Dr Ibrahim.

- Excitability and Membrane Electropotential .

Excitability and Membrane Electropotential

Excitability of cells and tissues is a basic function of life.

Also known as irritability, it is the ability of cells to respond to

stimuli, excitability is necessary for the functioning of nerves,

muscles, and hormones, among other things.

The basis for the excitability of cells is their ion distribution, and

the distribution of ions and molecules is determined by transport

mechanisms associated with their plasma membrane structure.

This structure permits and regulates various forms of ionic

and molecular transport.

*The stimuli are classified into two types:-

1-electrical. (galvanic ,faradric)

2-chemical.( ions , chemical transmitters,gases,……etc)


* Excitable cells are those that can be stimulated to create a

tiny electric current e.g,

• Muscle cells .
• Nerve cells (neurons) .
• Glandular cells.
  

*There are 3 types of muscles :

each muscle has a structural & functional unit

which is muscle fiber ( cell):-

1- skeletal muscle ….. skeletal muscle fiber.

2- cardiac muscle…… cardiac muscle fiber.

3- smooth muscle …..smooth muscle fiber.