• Nervous tissue contains densely packed nerve cell ( neuron),which are specialized for nerve impulse conduction.
• Origin- ectoderm
• Nervous tissue consists of

1. Neuron or nerve cell (functional unit of Nervous system)
2. Neuroglia (glial cell)

Neuron:

• About 100 billions of neurons are present in nervous system.
• They are Specialised type of cell, they vary in shape and size, all neurons contains three principle parts- cell body, dendrites and an axon

Cell body

• Has a large nucleus, which contain prominent nucleolus, as well as other several structures (Nissl bodies, ER,lysosome, mitochondria, neuroflament), responsible for metabolism, growth and repair of neuron
• Nissl bodies- made up of RNA, RER and free ribosome, help in protein synthesis
• Neurofilament and neurotubules are thread like protein, runs parallel to long process
• Neurofilament- semisolid structure that provide skeletal framework to axon
• Neurotubules- transport intracellular proteins between cell body and the processes

Dendrites-

• Many thread cytoplasmic extension arises from cell body called dendrites
• It conducts nerve impulse toward the cell body
• They are myelinated and have Nissl’s granule and neurofibril

Axon-

• Usually one of the cytoplasmic extension is long and unbranched called axon.
• It is covered by lipid sheath called myelin sheath
• Myelin sheath is formed by specialized non-neural cell called schwann cell (neurolemmocytes) in PNS and by Oligodendrocytes in CNS. The outer sheath of these cell is known as neurolemma
• It conduct nerve impulse away from cell body
• It lacks nissl’s granules

Types of neuron:

I. Types of neuron based on structure-

1. Unipolar- have single processes, very common sensory neuron in PNS,
2. Bipolar- two processes- a dendrires and an axon, eg. Retina, cochlea, smell receptor
3. Multi polar-many processes- many dendrites but one axon eg. Brain and spinal cord

II. Types of neuron based on function-

1. General somatic afferent (sensory)- carry sensory impulse from skin, skeletal muscles, joints and connective tissue to CNS
2. General visceral afferent- impulse from visceral organ to CNS
3. General somatic efferent(motor)- CNS to skeletal muscles
4. General visceral efferent- CNS to visceral organs
5. Special visceral efferent- brain to muscles of jaws, pharynx, facial expression, larynx
6. Special afferent- receptor cell (olfactory, optics, auditory, vestibule, gustation) to CNS

2. Neuroglia

• Glial cells are non conducting cells that protect and nurture as well as support cells of nervous tissue.
• There are 4 types of neuroglia cells

i) Astrocytes–

• largest,most numerous glial cell, with long star like processes, help form the blood –brain barrier.
• Function: structural support, transport of substance between blood vessels and neurons, mop up excess ions (k) and neurotransmitters.

ii) Oligodendrocytes-

• relatively small, with several branching processes,found in grey and white matter of CNS,
• function: produce myelin sheath

iii) Microglial cell–

• smallest glial cell, cuboidal or columnar shaped, it is a macrophage, engulf damaged neuron

iv) Ependymal cell-

• elongated cell, arranged in single layer in inner lining of spinal cord and ventricle of brain.

Nervous tissue: Neuron and Neuroglia

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• Muscles are made up of highly specialized thin and elongated cells called muscle fibres. The muscle fibres contains specialized cytoplasm called sarcoplasm that contain network of the membrane called sarcoplasmic reticulum. The muscle fibres may be bounded by the cell membrane called sarcolemma. Each muscle fibre may contain numerous longitudinal fibrils called myofibrils.

Basic physiological property of muscle tissue

1. Contractibility
2. Excitability
3. Extensibility
4. Elasticity

Types of muscle

1. skeletal muscle
2. smooth muscle
3. cardiac muscle

1. Skeletal muscle:

• It acquires its name because most of the muscles involved are attached to skeleton, and make it move.
• Also known as Striated muscle -because it cell (fibre) are composed of alternating light and dark band (stripe).
• Also known as voluntary muscle

Structure-

• Composed of muscle fibres. Each muscle fibre is long, cylindrical shaped with numerous nuclei.
• Each fibre is 1.2 inch long and 0.004 inch in diameter ( longest fibre-Sartorius muscle;12 inch, shortest fibre- stapedius muscle;0.04 inch)
• Each fibre contains numerious myofibrils, which are made up of thick and thin threads called
• Thick myofilament is composed of larger protein-
• Thin myofilament is composed of smaller protein- actin
• When viewed with light microscope, skeletal tissue shows a pattern of alternating light and dark bands. The bands are caused by th earrangement of actin and myosin myofilament in the muscle fibre.
• An overlapping of thick myosin and actin myofilaments produce- dark A band (anisotropic band);doesnot allow light to pass
• Thin actin myofilament alone produce- light I band(isotropic band);allow light to pass.
• Cutting across each I band is a dark Z line
• Within A band is a somewhat light H zone( Hensen’s disc), which consists only myosin myofilament
• The area between two Z line is known as sarcomere, which is the fundamental contractile unit of myofibril

Functions: Voluntary in functions. They bring about the movement of the organs and locomotion of the body

• Skeletal muscles undergo powerful and rapid contractions with short rest periods and hence get fatigued easily.
• They are supplied by voluntary Nervous system (CNS and PNS).
• They require large amount of energy, so are supplied with blood vesssels and numerous elongated mitochondria and glycogen granules.
• Found- attached to head, trunk, limbs, also in body wall, tongue, pharynx, oesophagus

2. Smooth muscle:

• It get its name because it is not striated, and appear smooth under microscope.
• Also called involuntary muscle because it is controlled by ANS

Structure

• Muscle fibre is long (but not nearly as long as skeletal muscle fibre),spindle shaped and slender. Contain only one nucleus, situated at the centre of the fibre at the broadest part
• Smooth muscle fibre is enclosed by sarcolemma, and contain numerous longitudinal myofibrils
• Actin and myosin myofilaments within myofibrils are very thin and are arranged more randomly than in skeletal muscle, so there is no stripes.
• 2 main characterstics
• Its contraction and relaxation period are slower
• Its action is rhythemical. Its contraction may last for 3o sec or more, but it doesnot tired easily. Such sustained contraction puls the ability to stretch made it suitable to muscular control of stomach, intestine, urinary bladder, uterus

3. Cardiac muscle:

• It is present only in heart

Structure-

• Under microscope, they have similar striation as skeletal muscle
• Cardiac muscle cells are closely packed but each cell are nucleated and separated from each other
• The cells are joined end to end by the specialised cell junctions called intercalated disks that attach one cell to another with desmosomes, connect the myofibril filaments of adjacent cells and contain gap junctions that help to syncronise the contraction of cardiac muscle, by allowing impulse transmission from one cell to another.
• They contain light I and dark A band, the intercalated disk always occur at the location of Z-line
• Supplied with central and autonomous nervous system
• The rhythmic contraction on its own
• They don’t get fatigue, so called as fatigue less muscle.

Muscular tissue: skeletal, smooth and cardiac muscle

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Types of proper connective tissue

I. loose connective tissue

II. Dense connective

I. Loose connective tissue:

• The cells in the matrix are widely distributed and the fibres are loosely woven.
• It generally connects and support various tissues and organs and helps them to resist strain and displacement.
• types-

1. Areolar connective tissue
2. Adipose connective tissue
3. Reticular tissue

1. Areolar connective tissue:

• These are simplest and most widely distributed connective tissues. It has homogenous, transparent, semi-fluid and gelatinous matrix. (glycoprotein, mucin, hyaluronic acid and chondroitin sulphate).
• Matrix contain various types of cells (fibroblast, macrophages, mast cells, lymphocytes, fat cells, plasma cells) and fibres (white collagen fibres, yellow elastic fibres)
• Fibres are loosely arranged and there is space between fibres, areolae, which derives its name.
• Found in continuous layers beneath skin, space between many organs, between muscles, peritoneum and mesentries.

Functions:

• They binds tissues together
• They engulf bacteria and damaged and dead cells
• They secrete heparin and histamine. Heparin is an anticoagulant while histamine causes inflammation reaction
• They produces antibodies

2. Adipose connective tissue:

• It is a modified form of areolar tissue that contain large number of fat cells ( Adipocytes cells).
• Adipocyte is a large, spherical or oval shaped cell, with large fat droplet causing shifting of nucleus to periphery of the cell
• 2 types of adipocytes- white adipocyte- contain a single large fat droplet and Brown adipocyte- contain number of small fat droplets
• Found beneath skin in dermis, mesentries, around kidney, heart and eye balls

• 

Functions:

• As it synthesise, stores and metabolises fat, it is a considerable sourse of energy
• It acts as a shock absorbers around kidney, heart, and eye balls
• It prevent heat loss by forming insulating layer

3. Reticular tissue:

• It is a modified areolar tissue that contains large number of stellate shape reticular cells floating in fluid matrix.
• Reticular cells has number of cytoplasmic processes which are interconnected to form reticular network.
• Reticular cells secretes reticular fibres
• Found-lymph glands, spleen, liver , bone marrow, thymus and tonsils.

Function:

• they are mostly phagocytic cells, helps in defense mechanism of the body

II. Dense (fibrous) connective tissue:

• The fibres dominate over the cells and the matrix in quantity.
• The fibres may be regularly or irregularly arranged
• types:

1. White fibrous tissue ( tendon and sheath)
2. Yellow elastic tissue (Ligament

1. White fibrous tissue:

• It contains fibroblast cells and collagen fibres and very few amount of matrix.
• The dense network of collagen fibres gives great strength.
• it occur in two form- i) tendon and Sheath
• Tendon is the thick bundle of collagen fibres running parallel to each other, giving strong, flexible but inextensible strength. It joins skeletal muscles to bones.
• Sheath is the bundles of collagen fibres lies in a criss-cross manner. It is present in pericardium of heart, dura matter, cornea, capsule of kidney, spinal cord. It also forms covering of cartilage and bones.

2. Yellow elastic tissue:

• These tissues contains numerous and closely packed yellow elastic fibres.
• Elastic fibre are long, straight and branched, they are elastic and flexible.
• They are present in Ligament, also present in wall of blood vessel, vocal cords, respiratory passage and lungs.
• Ligament– It is composed of yellow elastic fibres and some collagen fibres. It join two bone together.

 Proper connective tissue: Areolar, Adipose, Reticular, white fibrous and yellow elastic tissue

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• They are supporting tissue, forms endoskeleton of vertebrates, protect vital organs
• types-

1. Cartilage: Hyline cartilage, elastic cartilage and fibrous cartilage
2. Bone: spongy bone and compact bone

1. Cartilage:

• It is tough, hard but a flexible connective tissue. It can resist strain and can absorb mechanical shock.
• It consists of solid or semisolid matrix in which cartilage cell (chondrocytes) and fibres are embedded.

Structure:

• cartilage is enclosed in a sheath of white fibrous connective tissue called Below the perichondrium, there is layer chondroblast cell, which form chondrocytes.
• Chondrocytes are dispersed in the matrix and occur in the fluid filled space called lacunae.
• Each lacunae contain 2-4 chondrocytes. Each chondrocytes is a large, angular cell with distinct nucleus.
• The matrix lacks the blood vessels.

types:

• Depending upon matrix, cartilage are of 3 types

i. Hyaline cartilage:

• The matrix is glass like semi transparent, homogenous and has fine collagen fibres
• It is slightly elastic and compressible.
• Found in- nose, larynx, trachea, ends of bone. It forms skeleton of cartilage fish

ii. Elastic cartilage:

• The matrix is semi opaque and has network of yellow elastic fibres
• It is highly elastic and flexible. The tissue recover the shape quickly
• Found in-external ear, epiglottis, and pharynx (Eustachian tube)

iii. Fibrous cartilage:

• The matrix has bundles of densely packed white collagen fibres
• It provides great strength and little degree of flexibility
• It acts as a shock absorber by giving a cushioning effect
• Found in- intervertebral discs and at pubis symphysis

2. Bone:

• It is supportive and protective tissue.
• The matrix is solid and calcified. (70% salts of calcium and phosphate: hydroxyapatite-Ca10(PO4)6(OH)2, 30 %fibrous protein; Ossein).
• Bone cell (Osteocyte) and collagen fibre are embedded in solid matrix

Structure:

• Each bone is enclosed in a layer of white fibrous connective tissue, called periosteum.
• Matrix is arranged in concentric circles called lamellae.
• Number of osteoblast cell and osteocytes are arranged in between the lamellae, in the fluid filed space called Lacunae.
• Each lacunae has fine cytoplasmic processes called canaliculi, which connect with other lacunae.
• Osteoblast are active bone cell, while osteocytes are inactive osteroblats

types:

i. Compact bone:

• Compact bone is arranged in concentric ring structures called osteons (Haversian canal system) in the center of each ring is a structure called a Haversian canal. This canal carries blood vessels through
  the bone to nourish the cells embedded within the tissue.
• Around the Haversian canal, rings of bone tissue are found called lamellae. Within these rings, are space called lacunae that contain osteocytes
• Radiating out from the lacunae are tiny channels that allow interaction of the cells with the blood supply,exchanges of nutrients, gases, called canaliculi.
• Canal of Volkman connects various Haversian canal systems together
• In the centre of compact bone, bone marrow cavity is present, filled with yellow bone marrow

ii. Spongy bone:

• The matrix is web like rather than solid with number of space in between.
• Also known as trabeculae
• Found in epiphysis of long bone
• It lacks Haversian canal system and Volkman canal
• It contains red bone marrow, which forms RBC and WBC.

Supportive connective tissue: Cartilage and Bone

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1. Blood

• Blood is composed of blood corpuscles (45%) and blood plasma(55%)
• An average person has 5-6 ltr of blood.

Blood Plasma:

• It is pale yellow liquid, composed of 90% water and 10% inorganic and organic substances. It contains different proteins(albumin, fibrinogen, globulin), hormones, inorganic salts etc

Blood cells: 3 types-i) erythrocytes, Leucocytes and Thrombocytes

i. Erythrocytes (RBC)

• small,biconcave, non nucleated (fish, amphibian, reptiles,birds, camel;nucleated)
• Number varies from 4.5-5 million per mm3
• Cytoplasm has haemoglobin, hence appear red in color.
• Transpart O2 and CO2

ii. Leucocytes (WBC)

• These are larger than erythrocytes and are present in much smaller amount, their ratio to RBC is 1:600
• 5000-10000 per mm3
• They are devoid of hb, colourless
• They have prominent nucleus
• They are produced in red bone marrow and in lymphatic glands
• Life span is of few days
• They are immune cells
• 2 Types- Agranulocytes and Granulocytes
• Agranulocyte: 2 types- i) Monocytes– larger cell with bean shaped nucleus ii) Lymphocytes- larger spherical cell with oval nucleus.
•  Granulocyte: 3 types- i) Eosinophil- spherical cell with bilobed nucleus, stained with acidic dye. Main function to neutralize toxins and have anti-histamine property ii) Basophils- spherical cell with multi lobbed nucleus( S-shaped), stained with basic dye. Produce histamine and heparine iii) Neutrophil- spherical cell with multi lobbed nucleus, stained with neutral dye. Phagocytic function

iii. Thrombocytes (platelets)

• These are irregular cells, even smaller than RBC
• They are often without nucleus, but cytoplasm contains distinct granules
• They are the fragments of protoplasm broken from large bone marrow cell; megakaryocytes
• Their life span is of 7 days
• They release platelet releasing factors which help in blood cloting.

2. Lymph:

• Lymph is similar in composition to blood plasma except that it lacks red blood cells, platelets, plasma protein required for clotting and other macromolecules found in blood.
• It flows through lymphatic vessel
• helps in immunity.

Fluid or liquid connective tissue: blood and lymph

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• Connective tissues are the major supporting tissue of the body. It is composed of variety of cells, fibre (non-living products of cell) and semi-solid matrix between cells.

Characteristics of connective tissue:

• Connective tissue ranges from avascular to highly vascular.
• Composition: Composed mainly of nonliving extracellular matrix that separates the cells of the tissue.
• Location: It is present in between different tissue and organs. It can be found in and around the body organs. skeletal tissue present in the form of bone and cartilage, and fluid connective tissue as blood and lymph are connective tissue.

Function of connective tissue:

• It binds various tissue together like skin with the muscles and muscles with bones
• It form inter cellular substance between cells of different types of tissue, so that help in friction less movement of the body organ
• It forms sheaths around the body organs and make a kind of packaging tissue
• The areolar tissue protects the body against wound and infection
• The adipose tissue stores fats and insulates the body against heat loss
• The supportive tissue forms shape and the frame work of the body
• The haemopoitic tissue produce blood
• The lymphatic tissue helps in body immunity

Types of connective tissue

I. Proper connective tissue: types-

1. Loose connective tissue:

• Areolar connective tissue
• Adipose connective tissue
• Reticular tissue

2. Dense (fibrous) connective tissue: 

• White fibrous tissue ( tendon and sheath)
• Yellow elastic tissue (Ligament)

II. Supporting connective tissue: types-

1. Cartilage:

• Hyline cartilage
• Elastic cartilage
• Fibrous cartilage

2. Bone:

• Spongy bone
• compact bone

III. Fluid or liquid connective tissue:

• Blood
• lymph

Connective tissue: characteristics, functions and types

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II. compound epithelium 

III. Specialized Epithelium

I. Simple epithelium tissue

1. Simple squamous epithelium
2. Simple cuboidal epithelium
3. Simple columnar epithelium
4. Pseudo-stratified epithelium

1. Simple squamous epithelium

• consist of a single layer of flattened cells
• Margin of squamous cells are irregular
• Occur as tiles on a floor, also known as pavement epithelium
• Comprises lining of body cavity, cardiovascular and lymphatic systems,
• surface of coelom, buccal cavity, nasal cavity, alveolar lining of lungs lung and bowman’s capsule of kidneys (gas and liquid exchange)
• Function = protection, absorption, diffusion and filtration

2. Simple cuboidal epithelium

• -consists of a single layer of cells that are roughly square in shape when cut in cross-section. Each cell has a spherical nucleus in the centre
• forms lining many ducts and tubules of the body.
• Functions of secretion and absorption e.g. kidney
• Cuboidal epithelium is commonly found in secretive or absorptive tissue: for example;
• (secretive); exocrine gland the pancreas.
• (absorptive); lining of the kidney tubules.
• in the ducts of the glands.
• germinal epithelium; lining of ovary and testis.

3. Simple columnar epithelium

• Cells are elongated and column-shaped. Their nuclei are elongated and are usually located near the base of the cells.
• Columnar epithelium is found in the following:
• The lining of the stomach and intestines.
• Some columnar cells are specialized for sensory reception such as in the nose, ears and the taste buds of the tongue.
• Also have surface modifications such as cilia and microvilli and
• Goblet cells (unicellular glands) are found between the columnar epithelial cells of the duodenum.
• Function: secretion and absorption.

4. Pseudo-stratified epithelium:

• These are simple columnar epithelial cells whose nuclei appear at different heights, giving the misleading (hence “pseudo“) impression that the epithelium is stratified when the cells are viewed in cross section.
• Found in lining of respiratory tract, urinary tract, vas deferentia, epididymis
• Pseudo-stratified epithelium also possess fine hair-like extensions of their apical (luminal) membrane called cilia. In this case, the epithelium is described as “ciliated” pseudostratified epithelium.
• Ciliated epithelium is found in the:
• Airways (nose, trachea and bronchi).
• Uterus and Fallopian tubes of females.

II. Compound or Stratified epithelium:

1. Stratified squamous epithelium
2. Stratified cuboidal epithelium
3. Stratified columnar epithelium
4. Transitional epithelium

1. Stratified squamous epithelium

• Stratified squamous epithelium consists of multiple layers, with squamous cells at the apical surface.
• The primary function of this type of epithelium is protection.
• Aeas subject to abrasion, like mouth, esophagus and skin, have stratified epithelium.
• Stratified Squamous epithelium are of 2 types
• i. Keratinized stratified epithelium
• ii. Non-keratinized stratified epithelium

i. Keratinized Stratified epithelium:

• The Epidermis (most superficial layer) of the skin is composed of stratified squamous epithelial cells that contain large quantities of the protein
• Keratin is a tough fibrous protein that offers protection from abrasion and water loss.
• New cells are produced at the basal membrane of the epithelium and are gradually pushed towards the apical surface. As they move upwards, they become filled with keratin and eventually die, forming a layer of dead, keratin filled cells on the apical surface of the epidermis.
• The dermis, which lies deep to the epidermis, is composed of connective tissue.
• Functions- Impervious to water, resistant to mechanical damage.

ii. Non-keratinized stratified epithelium:

• These are Layers of living squamous epithelium formed by cuboidal cells
• Found in moist surface like, buccal cavity, oesophagus, vagina
• Functions– protection from mechanical damage

2. Stratified cuboidal epithelium:

• Stratified cuboidal epithelium consists of multiple layer of cell where the outermost layer of cells is cuboidal in shape.
• Found in conjunctiva of eyes, lining of ducts of sweat glands, salivary gland, mammary glands and urethra.
• Function– Protection against mechanical and chemical stress

3. Stratified Columnar epithelium:

• Stratified columnar epithelium consists of multiple layers of cells where the outermost layer of cells are columnar in shape, Middle layer is cuboidal.
• It forms lining of vasa-differentia, respiratory tract and mammary gland.
• Function– secretion of fluids and protection from mechanical and chemical stress.

4. Transitional epithelium:

• Transitional epithelium consists of layers of cells which are similar in size and may be flattened at the top and have the capability to modify the shape.
• Cells are living, large and stretch to change its thickness.
• Found in areas that are subjected to stress condition such as- urinary bladder, ureter, renal pelvis.
• Function-expansion of the organ, prevent loss of water form blood and prevent escape of urine to surrounding tissue.

III. Specialised Epithelium

1. Glandular epithelium
2. Germinal epithelium
3. Sensory epithelium
4. Ciliated epithelium

1. Glandular epithelium:

• Glands are composed of cuboidal and columnar epithelium and are specialized for secretion. They secrete enzymes, hormones, mucus etc.
• Based on the no. of cells, glands are of two types;
• Unicellular gland- individual cell is modified into glandular cell, eg. Goblet cell
• Multi cellular gland- Number of glandular cells are aggregated to form multicellular gland

2. Germinal epithelium:

• These are cuboidal or columnar epithelium layer found in the gonads. Eg, ovary and seminiferous tubules

 3. Sensory epithelium:

• These are modified columnar epithelium having sensory hair (cilia) at the free surface lies between columnar epithelium.
• They perceive the stimulus,. Found in nasal cavity and tongue

4. Ciliated epithelium:

• These are elongated columnar epithelium having numerous cilia at the free end.
• Found in Ureter, respiratory passage, spinal cord, oviduct etc.

Types of epithelial tissue:  simple, compound and specialized

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epithelial tissue

• An epithelium is a sheet of cells that covers a body surface or lines a cavity.
• Epithelium forms the coverings of surfaces of the body such as Skin, Mouth, Nasal cavity (Ectodermal), Lines internal body surface such as GI tract, Lungs, Urinary bladder and vagina (Endodermal) and Lining of blood vessels, lymphatic and heart (Endothelial cells derived from Mesoderm).
• It serves many purposes, including protection, adsorption, excretion, secretion, filtration, and sensory reception.
• Epithelium also serves as glandular epithelium.
• There are two functional types of epithelium: lining epithelium and glandular epithelium.

Characteristics of epithelium tissue

1. Polarity- Epithelium is arranged so there is one free surface (apical surface) and one attached surface (basal surface)
2. Cellular nature– Cells in epithelium fit closely together side by side and sometimes atop each other to form sheets of cells. These sheets are held together by specialized junctions.
3. Supported by connective tissue– Attachment to a layer of connective tissue at the basal surface forms a layer called the basement membrane, an adhesive layer formed by secretions from the epithelial cells and the connective tissue cells.
4. Avascular– Epithelium typically lacks its own blood supply.
5. Regeneration– Epithelium cells can regenerate if proper nourished.
6. Absence of nerves (except for a few axons in the deeper layers)

Classification scheme of epithelial tissue:

Typically epithelial tissue is classified on the basis of arrangement and shape of cells. For naming the tissue types, the arrangement of the cells is stated first, then the shape, and is followed by “epithelium” to complete the naming. For example; Simple Squamous Epithelium.

1. Classification scheme of epithelial tissue on the basis of arrangement of cells

i. Simple epithelium:

• Cells are found in a single layer attached to the basement membrane.

ii. Compound or Stratified epithelium:

• Cells are found in 2 or more layers stacked atop each other.

iii. Pseudo-stratified epithelium:

• Pseudo-stratified epithelium appears to be more than one cell thick since the nuclei lie at different heights, but in fact it is single layer of cells, in contact with the basement membrane

iv. Transitional epithelium:

• cells are rounded and can slide across one another to allow stretching

2. Classification scheme of epithelial tissue on the basis of shape

i. Squamous epithelium: (Latin, squama- scale)

• flat, thin, scale-like cells,
• eg. Endothelium, mesothelium, pericardium, peritonium

ii. Cuboidal epithelium:

• cells that have a basic cube shape.
• Typically the cell’s height and width are about equal.
• Eg. Kidney tubules, thyroid glands, duct of sweat gland

iii. Columnar epithelium:

• tall, rectangular or column shaped cells.
• Typically cells are longer than width.
• Eg. Intestinal lining, gall bladder, ducts of glands

Types of epithelium tissue:

1. simple epithelium tissue
2. compound epithelium tissue
3. Specialized Epithelium

Simple epithelium tissue

1. Simple squamous epithelium
2. Simple cuboidal epithelium
3. Simple columnar epithelium
4. Pseudo-stratified epithelium

Compound or Stratified epithelium:

1. Stratified squamous epithelium
2. Stratified cuboidal epithelium
3. Stratified columnar epithelium
4. Transitional epithelium

Specialised Epithelium

1. Glandular epithelium
2. Germinal epithelium
3. Sensory epithelium
4. Ciliated epithelium

Epithelial tissue: characteristics and classification scheme and types

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• The air molecule under pressure causes vibration of tympanic membrane. Low frequency sound wave causes slow vibration while high frequency wave causes rapid vibration.
• The vibration of tympanic membrane moves the malleus in middle ear.
• The vibrating malleus produce vibration to incus and vibrating incus moves stapes in and out of oval window causing vibration of perilymph in scala vestibuli.
• Vibration of perilymph are transmitted across the vestibular membrane to endolymph in scala media (cochlear duct) and also up the scala vestibuli and down the scala tympani.
• The vibration of scala tympani are dissipated out of cochlea through round window into Eustachian tube.
• During transmission of vibration from perilymph to endolymph in scala media, the basilar membrane ripples. This ripple is concern with frequency and intensity of sound.
• The vibration causes bending of receptor of hair cells of organ of corti to generate potential.
• These potential excites the cochlear nerves to generate action potential.
• When the hair or microvilli of hair cells are displaced toward the basal body, hair cells get excited and when the hair are displaced away from basal body hair cells are inhibited.
• The nerve impulse from cochlear nerve are conveyed to auditory area of CNS via common vestibule-cochlear nerve. The auditory area is located in temporal lobe where sound is perceived.

Physiology of hearing

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1. Refraction of light entering the eye
2. Focusing of image on the retina by accommodation of lens
3. Convergence of image
4. Photo-chemical activity in retina and conversion into neural impulse
5. Processing in brain and perception

Refraction of light entering the eye:

• Light wave travels parallel to each other but they bend when passes from one medium to another. This phenomenon is called refraction.
• Before light reach retina it passes through cornea, aqueous humor, lens vitrous humor, so refraction takes place in every medium before it falls on retina.
• In normal eye, light wave focused on retina.
• However in myopic eye (short sightedness) light focused in front of retina. So this defect can be treated by using cancave lens.
• In case of far sightedness light focused behind retina, so no image is formed. This defect can be treated by using convex lens.

Accommodation of lens to focus image:

• Accommodation is a reflex process to bring light rays from object into perfect focus on retina by adjusting the lens.
• When an object lying less than 6 meter away is viewed, image formed behind retina. But due to accommodation of lens image formed in retina and we can see the object.
• For accommodation to view closer object, ciliary muscle contract and lens become thick which causes focus on closer object.
• Similarly, when distant object is viewed, ciliary muscles relaxes, so the tension of ligament become greater which pull lens and lens become thinner, due to which image forms on retina.
• The normal eye is able to accommodate light from object about 25 cm to infinity.

Focus on nearer object:

Ciliary muscle contract——-ciliary body pull forward and inward ———tension on suspensory ligament of lens reduced ——lens become thicker and round due to its elasticity ——possible to focus near object

Focus on distant object:

Ciliary muscles relaxes——ciliary body return to its normal resting state—–tension on suspensory ligament of lens increases——-lens become thinner and flat———possible to focus distant object

Convergence of image:

• Human eye have binocular vision, it means although we have two eye, we perceive single image
• In binocular vision, two eye ball turns slightly inward to focus a close object so that both image falls on corresponding points on retina at same time. This phenomenon is called convergence.

Photo-chemical activity in retina and conversion into neural impulse

1. Photochemical activity in rods:

• Each eye contains 125 million rods which are located in neuro-retina.
• Rods contains light sensitive pigment-rhodopsin.
• Rhodopsin is a molecule formed by combination of a protein scotopsin and a light sensitive small molecule retinal (retinene).
• Retinene (retinal) is a carotenoid molecule and is derivative of vitamin A (retinol).
• Retinal exists in two isomeric form- cis and trans according to light condition.
• The extra cellular fluids surrounding rod cells contains high concentration of Na+ ion and low concentration of K+ ions while concentration of Na+ is low and K+ is high inside rod cells. The concentration is maintained by Na-K pump.
• In resting phase, K+ tends to move outside the rod cells creating slightly –ve charge inside.
• When light is falls on rod cell, it is absorbed by rhodopsin and it breaks into scotopsin and 11 cis- retinal. The process is known as bleaching.
• 11 cis-retinal absorb photon of light and change into all trans-retinal which inturn activates scotopsin into enzyme.
• This reaction produces large amount of transducin which activates another enzyme phosphodiesterase.
• Phosphodiesterase hydrolyses cGMP which causes to cease the flow of Na+ ion inside rod cell. This causes increased negative charge inside cell creating hyperpolarized state.
• Hyperpolarized rod cells transmit the neural signal to bipolar cell.
• Bipolar cell, amacrine cell and ganglion cell process the neural signal and generate action potential to transmit to brain via optic nerve.

2. Photochemical activity in cones:

• Each eye contains 7 million cone cells.
• The neural activity in cone cell is similar to that of rod cell but there are three different types of cone cells and each cone cell contains different photo-pigment and are sensitive to red, green and blue.
• Like rod, cone cell contains iodopsin as photo-pigment which is composed of 11 cis-retinal and photopsin.
• The perception of color depends upon which cone are stimulated.
• The final perceived color is combination of all three types of cone cell stimulated depending upon the level of stimulation.
• The proper mix of all three color produce the perception of white and absence of all color produce perception of black.

Processing of image in brain and perception:

• All visual information originates in retina due to stimulation of rods and cones are conveyed to brain.
• Retina contains 5 types of cells and they are interconnected by synapse. These cells are photoreceptor cells (rod and cone), bipolar cell, ganglion cell, horizontal cell and amacrine cell.
• Photoreceptor cells, bipolar cells and ganglion cells transmit impulse directly from retina to brain.
• The nerve fiber of ganglion cells from both eyes carries impulse along two optic nerve.
• The optic nerves meets at optic chiasma where fibers from nasal half of each retina cross-over but fibers from temporal half of each retina do not cross-over.
• The optic nerve after crossing the chiasma is called as optic tract.
• Each optic tract continues posteriorly until it synapse with neuron in thalamus called lateral geniculate body which project to primary visual cortex in occipital lobe of cerebrum and image is perceived.

Physiology of vision

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