Новини освіти і науки:

G+

Тлумачний словник
Авто
Автоматизація
Архітектура
Астрономія
Аудит
Біологія
Будівництво
Бухгалтерія
Винахідництво
Виробництво
Військова справа
Генетика
Географія
Геологія
Господарство
Держава
Дім
Екологія
Економетрика
Економіка
Електроніка
Журналістика та ЗМІ
Зв'язок
Іноземні мови
Інформатика
Історія
Комп'ютери
Креслення
Кулінарія
Культура
Лексикологія
Література
Логіка
Маркетинг
Математика
Машинобудування
Медицина
Менеджмент
Метали і Зварювання
Механіка
Мистецтво
Музика
Населення
Освіта
Охорона безпеки життя
Охорона Праці
Педагогіка
Політика
Право
Програмування
Промисловість
Психологія
Радіо
Регилия
Соціологія
Спорт
Стандартизація
Технології
Торгівля
Туризм
Фізика
Фізіологія
Філософія
Фінанси
Хімія
Юриспунденкция

Neuroglia

In addition to neurons, the nervous system contains several types of supporting cells. These are:

1) Neuroglial cells, found in the parenchyma of the brain and spinal cord.

2) Ependymal cells, lining the ventricular system.

3) Schwann cells, forming sheaths for axons of peripheral nerves. They are also called lemmocytes or peripheral glia.

4) Capsular cells (also called satellite cells or capsular gliocytes) that surround neurons in peripheral ganglia.

5) Various types of supporting cells found in relation to motor and sensory terminals of nerve fibres.

Neuroglial cells may be divided into two major categories: macroglia (or large glial cells) and microglia (or small glial cells)

1. Macroglia (or large glial cells).

a. Astrocytes, which may be subdivided into fibrous and protoplasmic astrocytes. These are small star-shaped cells that give off a number of processes. The processes are often flattened into leaf-like laminae that may partly surround neurons and separate them from other neurons. Astrocytes play a role in maintenance of the blood brain barrier.

b. Oligodendrocytes. These cells have rounded or pear shaped bodies with relatively few processes. These cells provide myelin sheaths to nerve fibres that lie within the brain and spinal cord.

2. Microglia (or small glial cells). These are the smallest neuroglial cells. The cell body is flattened. The processes are short. These cells are frequently seen in relation to capillaries. They become active after damage of nervous tissue by trauma or disease and act as phagocytes.

Questions:

1. What is nervous tissue made up of?

2. Types of neurons.

3. Structural features of neuron.

4. Types of nerve fibres.

5. Structural features of the myelinated nerve fibre.

6. Structural features of the nonmyelinated nerve fibre.

7. Classification of the neuroglia.

____________________________________________________________________________________

THE EYE

The eyeball consists of three layers:

1. sclera;

2. choroid;

3. retina.

Sclera

The sclera is composed of dense fibrous tissue and maintains the shape and size of the eye. The flat bundles of collagen fibres of the sclera lie mainly parallel to the surface, but they intersect in all directions, with fine networks of elastic fibres between the bundles, some ground substance, and a few flattened, branching fibroblasts.

Choroid

Choroid is a spongy, brown membrane that contains extensive venous plexuses.

Retina

The retina is the innermost layer of the eyeball. It in its turn consists of ten layers. In cross section, from external to internal, the layers of the retina are as follows:

1. Pigment epithelium

2. Layer of rods and cones

3. External limiting membrane

4. Outer nuclear layer

5. Outer plexiform layer

6. Inner nuclear layer

7. Inner plexiform layer

8. Ganglion cell layer

9. Optic nerve fibre layer

10. Internal limiting membrane

CORNEA

The cornea is made up of five layers.

1. The outermost layer is of non-keratinized stratified squamous epithelium (corneal epithelium). The cells of the deepest layer of the epithelium are columnar; in the middle layers they are polygonal; and in the superficial layers they are flattened.

2. The corneal epithelium rests on the anterior limiting lamina (also called Bowman’s membrane) which is made up of fine collagen fibrils embedded in matrix.

3. Most of the thickness of the cornea is formed by the substantia propria (or corneal stroma). The substantia propria is made up of collagen fibres embedded in a ground substance containing sulphated glycosaminoglycans.

4. Deep to the substantia propria there is a thin homogeneous layer called the posterior limiting lamina (or Descemet’s membrane). It is true basement membrane.

5. The posterior surface of the cornea is lined by a single layer of flattened cells that constitute the endothelium of the anterior chamber. This layer is in contact with the aqueous humour of the anterior chamber.

The cornea has no blood vessels or lymphatics. It receives nutrition from vessels around its periphery. The cornea has a rich nerve supply.

Questions:

1. What layers does the eyeball consist of?

2. Structural features of the sclera.

3. Structural features of the choroid.

4. Structural features of the retina.

5. Structural features of the cornea.

______________________________________________________________________________________

Не знайшли потрібну інформацію? Скористайтесь пошуком google:

Генерація сторінки за: 0.005 сек.