ANIMAL TISSUES:

A group of cells in which cells are similar in structure, function and origin is called TISSUE.

In a tissue cells may be dissimilar in structure and function but they are always similar in origin.

Word animal tissue was coined by – Bichate (Plant tissue by – N Grew).

Study of tissue – Histology. Histology word was given by – Mayer Father of Histology – Bichate

Detail study of tissue is called Microscopic anatomy. Founder of microscopic anatomy – Marcello Malpighi

Tissue

Epithelial Tissue Connective Tissue Muscular Tissue Nervous Tissue EPITHELIAL TISSUE:

Word Epithelium was given by – Ruysch.

A tissue which grows upon another tissue is called EPITHELIUM.

Due to absence of intercellular spaces blood vessels, lymph vessels & capillaries are unable to pierce this tissue.

Cells depend for their nutrients on underlaying connective tissue.

Basement membrane

Basal Lamina Fibrous Lamina

• Non – cellular layer between • Towards connective tissue, in epithetical and connective tissue. which collagen and reticular • Towards epithelium it is made up fibres are suspended in of glycoprotein. mucopolysaccharide.

So basement membrane is secreted by both epithelium and connective tissue.

Mucopolysaccharide composed of N actyl D-glucosamine & glucuronic acid. Intercellular junctions:

 Interdigitation – Finger like processes of plasma membrane which enter into cytoplasm of adjacent cell.mainly found in transitional epithelium.

 Desmosomes/(ADHERING JUNCTIONS: Macula Adherens) consists of protein plate with fibre known as tonofibrils . These provide mechanical support to stratified epithelium.  Tight Junction - Plasma membrane of adjacent cells become fused to form tight Junction.

 Gap Junction - Connect cytoplasm of adjoining cells for rapid transfer of ions, small molecules and big molecules. EPITHELIAL TISSUE:SIMPLE SQUAMOUS TISSUE-

Simple Epithelium Tissue

Simple Squamous Simple Cuboidal Pseudostratified Simple Columnar

Simple Squamous It is also called pavement epithelium due to its tile like appearance, Epithelium also called tessellated epithelium due to its wavy appearance associated with filtration & diffusion.

It is found in the lining of Bowman's capsule (Podocyte), Descending limb & thin part of ascending limb of loop of Henle, Rete Testis, Alveoli, Small bronchioles, Mesothelium, (Visceral & Parietal peritonium, Visceral and parietal pleura, Visceral and Parietal pericardium), Endothelium – Inner lining of blood vessels and lymph vessels. SIMPLE CUBOIDAL EPITHELIUM: Cells are cube like in shape. This helps in absorption, secretion & excretion, gamete formation.

Exocrine part of sweat gland is composed of acini & cuboidal cells of acini produce pancreatic juice.

Coiled part of this gland is secretory unit in which simple cuboidal epithelium is present while in secretory duct of this gland stratified cuboidal epithelium is present.

This is also present in Iris, Choroid, Ciliary body of eye, ascending limb of loop of Henle, DCT of nephron.

It is found in peripheral region of & lining of seminiferous tubules in Testis, where it divides to form egg and sperm, also known as Germinal epithelium.

Modifications • Brush bordered cuboidal epithelium :- microvilli are present on cell surface , Found in PCT of nephron. • Ciliated cuboidal epithelium: cilia present on cell surface, Found in collecting duct. SIMPLE COLUMNAR EPITHELIUM:

 Cells are pillar like in shape.

 Nucleus is present at the base of cell.

 It helps in absorption and secretion.

Modifications Of Simple Columnar Epithelium

 Brush Bordered Columnar epithelium: When microvilli are present on free end E.g.Gall bladder

 Glandular columnar epithelium:mucous secreting goblet cells are in between columnar cells. Eg. Stomach, Colon, Rectum

 Glandular Brush bordered columnar epithelium: When microvilli present on free end of columnar cells and goblet cells are also present.  Eg. Duodenum, Ileum, Caecum.

 Ciliated columnar epithelium: Cilia are present on free end of columnar cells. Eg. , ependymal epithelium PSEUDOSTRATIFIED EPITHELIUM:

 Long cells nucleus present at the base of cell and in short nucleus is at centre of cell.

 It is unilayered. Eg. Middle part of male

Modification - Pseudostratified ciliated glandular epithelium, Eg.Trachea, Bronchi

Respiratory epithelium of nasal chambers Compound Epithelium:

Compound Epithelium

Transitional epithelium:– Stretchable. Stratified epithelium:– Non-stretchable.

Transitional Epithelium (Urothelium)

It is only tissue in which basement membrane is absent.

These different shape of cells appears only in resting stage. When this tissue is stretched, all the cells become flattened.

Cells are interconnected by interdigitation.

Eg.– Renal Pelvis

– Ureter – Urinary Bladder – Proximal part of male urethra. STRATIFIED SQUAMOUS EPITHELIUM:

These cells have high mitotic index.

These cells are interconnected with Desmosomes.

Keratinized Stratified squamous epithelium. Keratin present non nucleated dead cells. Eg.–Epidermis of skin, Scale, Horn, Nails, Feathers etc.

Non Keratinized Stratified squamous epithelium. Keratin absent. nucleated and Living cells. Eg.– Buccal cavity or oral cavity of mammals, Inner lining of cheeks, Inner lining of lips, Lining of hard palate, Lining of tonsils, Lower part of soft palate, Pharynx, Oesophagus, Anal canal, Lining of , Cornea of eye STRATIFIED CUBOIDAL AND COLUMNAR EPITHELIUM:

Middle layer - polygonal shaped cells

 Eg.–Secretory duct of sweat glands,  mammary glands and sebaceous gland,  Secretory duct of sebaceous gland,  Secretory duct of salivary glands,  Submandibular – Whartson's duct,  Parotid – Stenson's duct,  Sublingual – Bartholin duct or duct of Rivinus- Pancreatic duct, Female Urethra, Conjunctiva of eye.

Stratified Columnar Epithelium

Ciliated stratified Non-ciliated stratified columnar epithelium. columnar epithelium

Eg. Buccopharyngeal cavity Cilia absent on free end. of Frog, Upper part of soft Eg.Distal part of male palate towards nasopharynx, urethra, Epiglottis. Larynx, CONNECTIVE TISSUE:

Connective Tissue

Connective Tissue Proper- Connective Tissue Skeleton- Connective tissue Vascular- Matrix soft and fibrous Dense and mineralised matrix. Liquid and fibres free matrix.

Connective Tissue Proper

(A) Cells Of Connective Tissue Proper

Fibroblast Cells – Plasma Cell: - Cart Wheel Cell Branched cytoplasmic process irregular Around rounded nucleus chromatin material is in shape. Cytoplasm is rich in rough ER. arranged like spokes (radial rows) in wheel so Fibroblast can be modified into they are also hence called as Cart wheel cells Osteoblast & Chondroblast Function: (1) formed by the division of lymphocytes. Function: To produce fibres (2) To secrete matrix To produce, Secrete & transport of antibody. Cells Of ConnectiveMast Cells Tissue(Mastocytes) Proper – MastThey Cells haveand Lymphocyte) centralized nucleus. Cytoplasm basophilic granules are present which can be stained with Methylene Blue.

Mast Cells Releases: a) Histamine: vasodilator, It also increase permeability of blood capillaries. Histamine stimulate inflammatory reactions. b) Serotonin or 5 Hydroxy tryptamine vasoconstrictor increase blood pressure, reduces blood loss. c) Heparin: Is a mucopolysaccharide. It is a natural anti-coagulant.

Artificial Anticoagulants: E.g. Soduim Anticoagulants Organisms citrate, Sodium oxalate, EDTA Hirudin Found in leech. (Ethylene diamine tetra acetic acid) Anophelin Found in female anophelese. LYMPHOCYTES: Lampredin Found in peteromyzon. Cumerin Obtain from plants. Warfarin Obtain from plants

A large nucleus is present It's function is to produce, transport & secretes antibodies. Adipose Cells, Mesenchymal Cells and Macrophages:

Adipose Cells Stores fat in fat globule.

Adipocytes

Monolocular adipocytes Multilocular adipocytes single large and central fat globule, many small fat globules, form form white fat. brown fat.

Mesenchymal Cells These are undifferentiated cells of connective tissue because they can transform into any cell of connective tissue proper. E.g. interstitial cells of hydra, totipotent in nature.

Macrophages (Histeocyte) Lung Dust cells Amoeboid in shape with kidney Liver Kupffer cells shaped nucleus. Blood Monocytes

Cytoplasm is agranular but appears Brain Microglial cells granular due to more lysosomes Thymus gland Hessel's granules Spleen Reticular cells They are phagocytic in nature. ConnectiveCollagen fibres (WhiteTissuefibres) Proper – Fibres and Matrix Composed of collagen protein (Tropocollagen). They are wavy & tough fibrescalled . On boiling they convert into gelatine. Digestible by pepsin enzyme

Elastic fibres — (Yellow fibres)

They composed of elastin protein .In these fibres maximum elasticity is present. They are digestible by trypsin enzyme.

Reticular Fibres

Arzyrophil fibre stained by silver dalt. They are composed of reticulin protein. They are delicate and non elastic fibres. These are mainly distributed in lymphoid organs AREOLAR CONNECTIVE TISSUE:

Most widely distributed tissue in the body.

Few elastic fibres but reticular fibres are completely absent.

Mast cells, macrophage & fibroblast are more in number.

Eg. (1) Tela Subcutaneous: - A thin continuous layer which connect skin with underlaying skeletal muscles (Panniculus carnosus)

(2) Endomysium – Around single muscles fibre.

Perimysium – Around bundle of muscle fibres.

Endoneurium – Around single nerve fibre.

Outside of seminiferous Tubules.

Medulla of ovary Sub mucosa of Trachea, Bronchi, Intestine ADIPOSE CONNECTIVE TISSUE:

A modification of areolar connective tissue. Adipocytes which store fats.. White fat: - Panniculus adiposus continuous layer of white fat which is also called hypodermis of skin, absent in rabbit. Blubber: - Thick layer of white fat found in whale, seal elephants. • Hump of camel • Yellow bone marrow.

Brown fat - It produces 20 times more energy than white fat. colour of fat is due to cytochrome Pigment.

Cold resistance device in new born baby is due to presence of brown fat.

When fat is oxidised it produce water & energy. WHITE FIBROUS CONNECTIVE TISSUE:

Yellow fibres & reticular fibres are completely absent.

Fibroblast and mast cells are more in number.

Cord:- Bundle of collagen fibres & matrix are distributed in regular pattern

 Fibroblast cells are arranged in a series. Mast cells are scattered in matrix. E.g. Tendon:- A structure which connects muscles & bones.

 Strongest tendon of the body is Tendocalcaneus tendon connects gastrocnemius muscle of shank with calcaneum bone of ankle.

Sheath: - no regular pattern of fibres & matrix.

Eg. – Pericardium

Periosteum -- outer covering of bone. Perichondruim -- outer covering of cartilage SKELETON CONNECTIVE TISSUE:

Sketeton Connective Tissue  Matrix is dense & mineralised

Cartilage Bone they are supporting Tissue

Cartilage  Outer most covering of cartilage is called Perichondrium

 Cartilage producing cells known as Chondroblast.

 Mature cells of cartilage are called Chondriocytes.

 Chondrioclast are cartilage destroying cells.Matrix of chondrin composed of chondromucoprotein Chondrotin-6-sulphate and mucopolysaccharide (Hyaluronic acid)

Type of Cartilage

Hyaline Cartilage. Fibrous Cartilage Calcified Cartilage. Elastic cartilage White fibrous cartilage HYALINE CARTILAGE:

Embryonic skeleton is composed of this cartilage.

Matrix of this cartilage is glass like clear or hyaline matrix fibres are completely absent

Eg. (a) Nasal septum. (b) 'C' shaped rings of trachea and bronchi. (c) Sternal part of ribs. (Coastal cartilage) (d) Larynx: Thyroid, Cricoid, Arytenoid.

Articular cartilage:- At the end of long bone FIBROUS CARTILAGE:

Fibrous Cartilage

Elastic cartilage White fibrous cartilage Calcified cartilage

Elastic Cartilage Matrix of this cartilage yellow fibres is highly flexible cartilage of body.

Eg. a. Tip of Nose b. Ear Pinna c. Epiglottis d. Larynx — Cartilage of Santorini of larynx e. Wall of eustachian tube

White Fibrous Cartilage Perichondrium is absent In matrix bundle of collagen fibres strongest cartilage.

Eg.Pubic symphysis, Intervertebral disc

Calcified cartilage It is modified hyaline cartilage but due to deposition of calcium salts its matrix becomes hard like bones. Ca salt deposits in the

form of Hydroxy apatite Ca10(PO4)6 (OH)2. Eg. – Pubis of frog's pelvic girdle. – Supra scapula of pectoral girdle. - Head of femur & humerus. BONE:

Study of Bone – Osteology

 Process of bone formation – Ossification

 Outermost covering of bone is Periosteum

 Bone producing cell is called Osteoblast.

 Mature cell of bone is called as Osteocyte Long Bone

 Bone destroying cells are Osteoclast cells. Epiphysis Diaphysis Metaphysis Matrix

 Inorganic Part:- 65 - 68%

 Ca3(PO4)2 – 80% max. rest 20% CaCO3 (10%), Mg3(PO4)2 (10%), Flourides

 Organic part:- 32 - 35% Ossein in which bundle of collagen fibres suspended in sulphated mucopolysaccharide.

 Sharpay's fibre:- extra bundle of collagen fibres which are present in the outermost layer of matrix STRUCTURE OF BONE-

 Epiphysis :

 Ends of long bone composed of spongy tissue.  At the joint periosteum is absent & articular cartilage (Hyaline cartilage) is present.

 Trabeculae filled with red bone marrow.  Composed of myeloid tissue, produce blood corpuscles

 Diaphysis :

 MIDDLE part composed of compact bone.  Bone marrow cavity filled with yellow bone marrow composed of white fat.

 Metaphysis :

 Epiphyseal plate is present, made up of osteoblast cells. They divide to form osteocyte and also synthesize matrix of bone.  After complete development of long bone this plate is destroyed. Internal Structure of Mammalian Bone

 PERIOSTEUM : Outermost covering consists of two layers

Outer layer Inner layer

consist of WFCT in which blood circulation is present consists osteoblast cells

 MATRIX

Haversian Canal Volkmann’s Canal

Longitudinal canals Transverse/horizontal or oblique canals Lamellae

Matrix of bone is synthesized in the form of layer. These layers of matrix are called Lamellae.

Haversian Interstitial Circumferential Lamellae Lamellae Lamellae  Haversian  Concentric layers of matrix present around Haversian Canal. Lamellae : Between these lamellae osteocyte are present.

 Haversian canal, Haversian lamellae & Osteocyte form Haversian system or Osteon.

 Interstitial  Each osteocyte is inter connected Lamellae :  These layers of matrix are present between two Haversian systems.

 Circumferential Lamellae :

Outer circumferential Inner circumferential lamellae lamellae

• Present around all • Present around Haversian system bone marrow cavity

ENDOSTEUM  Towards bone marrow lined with reticular fibrous connective tissue.  Towards matrix of bone endosteum lined with layer of osteoblast cells.  Growth of bone is bidirectional. While Growth of cartilage is unidirectional. Vascular Connective Tissue:BLOOD :  Packed cell volume :- (PCV) % volume or Total number of blood corpuscles in blood.  Hematocrit Volume :- % volume or only number of RBC in blood.

 PLASMA :  Matrix of blood, pale yellow in colour due to urobillinogen. Composition of Plasma: COMPOSITION OF PLASMA

Water Inorganic part Organic part

Ions Salts Gases

+ + ++ • Na , K , Ca NaCl, KCl, NaHCO3, KHCO3 • O2, CO2, N2 − − −− −−− • Cl , HCO3 , SO4 , PO4 • Cl− > Na+ Proteins

Albumin – 4% (Max.) Globulin – 2 – 2.5%

Responsible to maintain BCOP • α − Globulin – Produced by liver (28 – 32 mm Hg) E.g. : Ceruloplasmin – Cu carrying protein • β − Globulin – Produced by liver E.g. : Transferin – Fe carrying protein • γ − Globulin – Produced by lymphoid organs, also called as immunoglobulins Blood Plasma -

 Prothrombin :  0.3%  Produced by liver.

 Fibrinogen :  0.3%  Produced by liver  Help in blood clotting

 Digested Examples : Amino acid, Glucose(Blood glucose level – 80 – Nutrients : 100 mg %), Fatty acid, Glycerole, Cholesterol, Vitamins

 Waste  Urea Products :  Uric acid  Creatine  Creatinine

 Anticoagulant Example : Heparin

 Defence  Lysozyme Compounds  Properdin or anti-toxin  Hormones Blood Corpuscles: Erythrocytes:

 Erythrocytes (Red blood Corpuscles) :

 At the time of origin nucleus is present in the RBC but it degenerates during maturation process.

 Biconcave shape of RBC increases surface area.

 Exception: - Camel & Lama are mammals with biconvex, oval shaped.

 Endoskeleton is composed of stromatin which is a spongy cytoskeleton.

 Plasma membrane of RBC is called Donnan's - - membrane, permeable to ions like Cl & HCO 3 and impermeable to Na+ & K+ ions. It is called Donnan's phenomenon.

 In RBC enzyme of glycolysis process are present, while enzyme of Krebs cycle is absent.

 Rh Antigen is also found on the surface of RBC. Haemoglobin: Haemoglobin – Respiratory pigment

Haem Globin

 5% Lipid part (Iron and Porphyrin)  95% Protein part

 Haem  Iron present in the form of Fe+2 but in muscles it is present in the form of Fe+3.

 1 gm Hb carries 1.34 mL O2.

 Each globin is α polypeptide chain having 141 amino acids composed of 4 polypeptide chains. β polypeptide chain having 146 amino acids

γ polypeptide chain having 146 amino acids

δ polypeptide chain having 146 amino acids

Hemoglobin

Hb A (Adult Hb) – 2α + 2β Hb A2 (Adult – 2) – 2α + 2δ Hb F (Foetal Hb) – 2α + 2γ Red Blood Cells:

 Due to Vit. B12 deficiency RBC become larger (Macrocytes).

 Due to Fe deficiency RBC become smaller (Microcytes).

 Shapes of RBC is Biconcave.  0.8 – 1% NaCl solution is isotonic for RBC. (0.9% of NaCl)

 Average life span of RBC in human is 120 days

 RBC count :  Human (Male) – 5.5 million/mm3  Human (Female) – 4.5 million/mm3

 Increase in the RBC count condition is called polycythaemia.

 Decrease in RBC count condition is called Anaemia.

 Formation of RBC is called Erythropoiesis.

 During embryonic life RBC are produced by Liver, Spleen, Placenta, Thymus gland.

 In adult stage RBC is produced by Red Bone Marrow.

 Destruction of RBC occur in spleen, called Graveyard of RBC.

 Spleen stores excess blood corpuscles called Blood Bank of body. Leucocytes:

 Leucocytes or WBC  Total leucocyte count : 8000 – 11000/mm3

Acidophils – 4% of TLC

Basophils – 0.5% – 1% TLC

Total leucocyte count Neutrophils – 65 – 70% TLC

Monocytes – 4 – 8% TLC

Lymphocytes – 25 – 30% TLC

 Leucocytosis :- Increase in TLC, in bacterial & viral infection.

 Leukocytopenia :- Decrease in TLC, in typhoid & AIDS.

 Leukemia :- Abnormal increase in TLC in blood cancer.

Leucocyte

Granulocytes Agranulocytes

• In their cytoplasm granules are present. • Cytoplasm is clear & granular. • Nucleus is multilobed • Nucleus do not divide in lobes so called • Polymorph nuclear WBC. as mononuclear WBC. • Example : Monocytes, Lymphocytes Granulocytes

ACIDOPHILS /  All granulocytes are amoeboid in shape. EOSINOPHILS  protect body against allergy & parasitic infection.  In allergy they synthesize histamine.  In parasitic infection they act as lysosome.  Increase in number of Acidophils occurs in Taeniasis, Ascariasis, Hay fever (Parasitic infection).

BASOPHILS  Smallest granulocytes.  Main function is to secrete & transport heparin, histamine & serotonin.

NEUTROPHILS /  They can squeeze & comes out from the wall of blood capillaries HETEROPHILS in tissue. This phenomenon is called Diapedesis.

 Phagocytic in nature called as Micro police man.  In female neutrophils barr body is attached with lobe of nucleus which is formed by the modification of X chromosomes.  Barr body is absent in male. Agranulocytes:

 MONOCYTES :  Nucleus kidney shaped/bean shaped.  Phagocytic nature called as Macro police man.  Scavenger of blood because they engulf damaged or dead & minute bits of blood corpuscles.

 LYMPHOCYTES :  Large nucleus is present.

Lymphocytes

T – lymphocytes B – lymphocytes

T – killer/Cytotoxic : Direct kill bacteria or viruses

 T – lymphocytes : T – Helper : Stimulate B – lymphocytes to produce antibody

T –Suppressor: Suppress T – killer and protect immune system

 B – lymphocytes :  Its function is to produce, synthesize & transport antibodies. Blood Corpuscles Diagram: Platelets or Thrombocytes:

 They are non-nucleated and derived from megakaryocyte cells of bone marrow.

 Critical count of thrombocytes is 40,000/mm3. If number is less than critical count then red spot or rashes appears on the skin called Purpura disease.

 Their Count is 1.5 - 4.5 lakh/mm3.  Decrease in number of blood platelets is called Thrombocytopenia. Blood Clotting:

Blood Clotting  Clotting time: 2 – 8 mins.

Thrombus Clot Embolus Clot

 Static clots which grow bigger & bigger & ultimately  Moving clots. block the blood vessels.  Mechanism of blood clotting  If this clot is formed in the coronary vessels then proposed by Macfarlane & called as coronary thrombosis. Co-workers.  If found in brain, then called as cephalic thrombus

 Releasing of  Injured tissue synthesizes exothromboplastin and platelets Thromboplastin synthesize endothromboplastin.  These react with plasma proteins in the presence of Ca++ ions to form Prothrombinase enzymes. (Thrombokinase)

 Conversion of Prothrombin  Prothrombinase enzyme convert inactive into Thrombin prothrombin into active thrombin in the presence of Ca++ ion.

 Conversion of  Thrombin protein polymerise monomers of fibrinogen fibrinogen into fibrin to form insoluble fibrous protein fibrin in which blood corpuscles got trapped.

 Blood – Corpuscles = Plasma  Plasma –fibrinogen and large proteins = Serum Muscular Tissue:

 Study of muscles is called as myology or sarcology.

 It is mesodermal in origin, except iris and ciliary blood muscles, which are ectodermal.

 Conductivity and contractility are properties of muscular tissue.

 Skeletal (Voluntary or Striated) Muscles :

 These are under control of will power. These are striated muscle fiber.

 Tendon attach muscle and bone.

 Striated muscle fibres are cylindrical, unbranched, multinucleate and controlled by CNS.

 Plasma membrane of muscle fibre is called as sarcolemma.

 Contains myoglobin, mitochondria (sarcosome), nucleus (synctial), myofibrils (actin and myosin filaments) and endoplasmic reticulum (sarcoplasmic reticulum).

 In myofibrils dark and light bands are present. Unstriated Muscles:

 Unstriated (Smooth or Visceral) muscles

 These are found in posterior part of esophagus, stomach, intestine, lungs, urinogenital tract, urinary bladder, blood vessels, iris of eye, dermis of skin and erector pilli muscle of hair.

 These are under control of ANS.

 Cells are spindle shaped and pointed at ends.

 Striations are absent.

 Actin and myosin filaments are present in myofibrils. Cardiac Muscles:

 These are present in the wall of heart, pulmonary veins and superior vena cava.

 These are involuntary and are supplied by both CNS and ANS.

 Lateral branches are connected by oblique bridges to form contractile network.

 These are uninucleate and branched. They show striations. Nervous Tissue:

 Neural Tissue :  Ectodermal in origin.

 Excitability and conductivity are properties of cells.

 Inside CNS, supporting cells are called as neuroglia and in PNS, these are called as Schwann cells.

Process of Neuron or Neuritis

Dendrons Axon

Neuron  Cyton :  Its cytoplasm is called as neuroplasm.

 Nissl’s granules (Trigoid Granules) are modified RER and Ribosomes.

 Centrioles are absent.

 Dendrons :  Dendrites – are fine branches of Dendrons.

 Telodendria – very fine branches from dendrites

 Axon :  Axon hillock – part of Cyton, from which axon rises.

 Terminal arborization (axon endings or presynaptic knobs), where axon ends.

 Collateral fibres – side branches from certain axons.

 Axolemma – plasma membrane of axon.

 Axoplasm – neuroplasm of axon, which contains abundant neurofibrils and mitochondria, but Nissl’s granules, golgi bodies, ribosomes and fat globules are absent.

 Synapse – region of union of terminal arborization of axon of one neuron with dendrite of another neuron. Transmission occurs through neurotransmitter.