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Human Physiology

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Human Physiology PDF Notes, Important Questions and Formulas

BODY FLUIDS AND CIRCULATION
  1. INTRODUCTION
  • An expanded pipe line system is present in human body. It is called closed circulatory system. A continuous chemical exchange of materials between animal body and environment among different tissues of the body is done through this system. In this way digested nutrients from digestive system, oxygen from respiratory organs, hormones from endocrine glands are distributed to all the cells of body. Also the transport of CO2 from body cells to respiratory organs, NH3, urea etc. excretory substances to excretory organs is the function of circulatory system. The whole circulatory system is formed by the mesoderm of embryo. Except the inner lining of blood vessels and heart which are of endodermal origin. Types of circulatory system on basis of complexity and evolution.

 

Open type

 

Closed type

1.

Blood is filled in coelomic channel and sinus coelom is called haemocoel. Fluid is called haemolymph.

1.

Blood is circulates in closed vessels

2.

Tissues are in direct contact with circulating fluid.

 

Tissues are not in  direct contact with circulating fluid

 

eg. Arthropodes. Non cephalopod mollucs

 

eg. Annelids, Cephaloped molluscs, Chordates

In human beings (on the basis of circulating fluid)
Two types of circulatory system are observed.

 

Fishes

Amphibians

Reptiles

Crocodiles, Aves, Mammals

No. of heart Chambers

2

3

3

4

Atria

1

2

2

2

Ventricles

1

1

1

2

Type of circulation

Single

Incomplete

Incomplete

Double Circulation

 

 

Double

Double

 


1)  Blood circulatory system : It consist of :-
      Blood, Blood vessels, Heart.
2)   Lymphatic system : It consist of lymph, lymph capillaries, lymph vessels , lymph nodes, lymphoid tissues/organs

  • The study of blood vascular system or circulatory system is called–Angiology
    William Harvey is known as father of angiology. He called heart as the "Pumping station of body"

2.  BLOOD

  • Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements.

A.  Plasma

  • Plasma is a straw colored, viscous fluid constituting nearly 55 per cent of the blood.
  • 90-92 per cent of plasma I water and proteins contributes 6-8 percent of it.
  • Fibrinogens, globulins and albumins are the major proteins
  • Fibrinogens are needed for clotting or coagulation of blood.
  • Globulins primarly are involved in defense mechanisms of the body and the albumins help in osmotic balance.
  • Plasma also contains small amounts of minerals like Na+, Ca++, Mg++, HCO3 , Cl, etc. Glucose, amino acids, lipids, etc., are also present in the plasma as they are always in transit in the body.
  • Factors for coagulation or clotting of blood are also present in the plasma in an inactive form. Plasma without the clotting factors is called serum

B.  Formed Elements

  • Erythrocytes, leucocytes and platelets are collectively called formed elements and they constitute nearly 45 percent of the blood.
  • Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood.
  • A healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs mm–3 of blood.
  • RBCs are formed in the red bone marrow in the adults.

 

  • RBCs are devoid of nucleus in most of the mammals and are biconcave in shape. They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these cells.
  •  A healthy individual has 12-16 gms of haemoglobin in every 100 ml of blood.
  •  These molecules play a significant role in transport of respiratory gases.
  •  RBCs have an average life span of 120 days after which they are destroyed in the spleen (graveyard of RBCs).
  • Leucocytes are also known as white blood cells (WBC) as they are colourless due to the lack of haemoglobin.
  • They are nucleated and are relatively lesser in number which averages 6000-8000 mm–3 of blood. Leucocytes are generally short lived.
  • Two main categories of WBCs – granulocytes and agranulocytes.
  • Neutrophils, eosinophils and basophils are different types of granulocytes, while lymphocytes and monocytes are the agranulocytes.
  • Neutrophils are the most abundant cells (60-65 per cent) of the total WBCs and basophils are the least (0.5-1 per cent) among them. Neutrophils and monocytes (6-8 per cent) are phagocytic cells which destroy foreign organisms entering the body.
  • Basophils secrete histamine, serotonin, heparin, etc., and are involved in inflammatory reactions.
  • Eosinophils (2-3 per cent) resist infections and are also associated with allergic reactions.
  • Lymphocytes (20-25 per cent) are of two major types – ‘B’ and ‘T’ forms. Both B and T lymphocytes are responsible for immune responses of the body.
  • Platelets also called thrombocytes, are cell fragments produced from megakaryocytes (special cells in the bone marrow).
  • Blood normally contains 1,500, 00-3, 500, 00 platelets mm–3.
  • Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood.
  • A reduction in their number can lead to clotting disorders which will lead to excessive loss of blood from the body.

 

BREATHING AND EXCHANGE OF GASES

  1. INTRODUCTION
    Respiration –
  • A process in which oxidation of organic compounds occurs in cell and energy is released is called as respiration.

 2.   RESPIRATORY ORGANS

Respiratory organs

General body surface

Moist cuticle(skin)

Tracheal tubes

Gills

Lungs

Examples

Sponges, Coelenterates,

Flatworms

Earthworm Frogs

Insects

Aquatic arthropods

-Molluscs

-Fishes

-Reptiles

-Birds

-Mammals

 i.  External Respiration (ventilation)-Gaseous exchange between environment and lung.

ii.  Internal Respiration-

  1. Gaseous exchange between lungs and blood.
  2. Gaseous exchange between blood and tissue fluid.

iii.   Cellular Respiration- Oxidation of organic compounds in cell in which energy is released.

3.  HUMAN RESPIRATORY SYSTEM

 

  • Respiratory Tract (Conducting zone)
  • Lungs (Exchange zone)

Respiratory tract
– A passage from external nostrils to lungs
                     Or
– A passage by which air enters into lungs

Lungs – Anatomical organ which is the actual site for exchange of gases. 

A.  Nose and Nasal-passage-

  • The respiratory path begins from the Nose and the Nasal passage. Each external nare opens into a nasal passage or Nasal Chamber. Both the Nasal Chamber are separated from each other by hyaline cartilage. The anterior small part of each Nasal Chamber is called Nasal vestibule.
  • It is formed by the invagination of the skin in embryonic stages; so this part contains hair and sebaceous glands. In this manner dust particles cannot enter in. The remaining part of the nasal-passage is surrounded by 3 types of bones, namely the nasal, maxilla & ethamoid.
  • At several places in the nasal-passage these bones form out growths. These outgrowths are called Turbinal bones or Turbinates or conchae. Due to these outgrowths the nasal-passage is long and spiral. This helps in making the temperature of air equal to the body temperature before it reaches the lungs and does not allow unwanted materials like dust to reach the lungs. A coat of epithelium is present on the turbinal bones of maxilla and ethmoid.
    This is pseudo stratified columnar ciliated glandular epithelium = PSCCGE.
  • PSCCGE is a simple epithelium i.e., made up of only 1 layer of cells; but it appears to be stratified because it has cells of varying length. This epithelium has Goblet Cells, which secrete mucous. This mucous binds the dust particles and bacteria. The cilia present on the epithelium continuously propel the mucous into the pharyngeal cavity. On the turbinal bone of nasal-bone a hair less cillialess membraneous covering is present, known as Schneiderian membrane. This membrane is Olfactory. Both the nasal-passages, through a pair of internal-nares or choanae open into the naso pharyngeal cavity.
    Functional division of Nasal Passage
  1. Vestibular Region: - skin, hairs, sebaceous glands.
  2. Respiratory Region: - PSCCGE, Goblet cells.
  3. Olfactory Region: - Schneidarian membrane or neuro sensory epithelium.

 B.   Bucco-pharyngeal cavity-

  • It is divided into two parts. Anterior part is called the Buccal-cavity and the posterior part is called Pharyngeal-cavity. Between the buccal and the Nasal cavity hard palate followed by soft palate is present. The terminal part of soft plate is called Uvula. Uvula is bent towards the pharyngeal cavity. This divides the pharyngeal-cavity incompletely into two chambers. Upper chamber is the Nasopharyngeal chamber and the Lower chamber is Oropharyngeal chamber.
  • At the time of swallowing of food, the Uvula lifts up and covers the internal-nares and so prevents the food from entering the nasal-passage. In the pharyngeal chamber, 2 slit like apertures are present. Dorsal-pore is called the gullet which opens into the oesophagus, so this is the path of food. Ventralpore is called the glottis; and it opens into the Larynx; and so this is the respiratory-passage.
  • Near the glottis a flat cartilage called the Epiglottis is present. At the time of swallowing food this cartilage covers the glottis, so the breathing stops. Pharynx is the only part where food and air passage mix together.

 

CHEMICAL COORDINATION & INTEGRATION

  1.  INTRODUCTION
  • The branch of biology which deals with the study of endocrine system and its physiology is known as "Endocrinology".
  • ‘‘Thomas Addison’’ is known as father of Endocrinology.
  • Whereas the gland with duct is called exocrine gland which secretes enzyme etc. Endocrine glands pour their secretion directly into blood. These glands lack ducts, so these glands are called ductless glands.
  • Co-ordination in the body of almost all the higher vertebrates is controlled by two systems Nervous system and endocrine system.
  • Nervous system and endocrine system are called Integrative system of the body.
  • Nervous system carries informations in the form of impulses to the different parts of body. High speed services are offered by this system.
  • Where as, the work of co-ordination by endocrine system is done slowly by secretion of some chemical substances.
  • Substances secreted by these glands are known as hormones. The meaning of word ' hormone' in Greek is " to excite " = horman

 

Differences between Nervous and Endocrine coordination

Nervous Co-Ordination

Endocrine Co-ordination

(Chemical Co-ordination)

1. Information passes as electrical impulses along nerve fibers.

1. Information passes as a chemical substance through the blood and lymph.

2. There is rapid transmission of information.

2. There is slow transmission of   information.

3.Response is immediate

3. Response is usually slow.

4. Response is very exact

4. Response is usually widespread.

5. Response is short lived

5. Response is long-lasting.


HORMONE:

  • The term hormone was coined by Starling.
  • Hormones are also called “Primary messengers" or " chemical messengers".
  • First discovered hormone is secretin. It was discovered by Bayliss & Starling in 1902.

Nature

Harmone

Gland

A.   Proteinaceous

  i.      Amino acid derivatives

Thyoxine (Icxlothyronine)

Epinephrine Non-epineprine

Thyroid gland adrenal medulla

 ii.    Short peptides

Vasopressin, oxytocin MSH

Hypothalamus Adenohypophysis

iii. Long peptides

Parathyroid hormone Insulin Thyrocalcitonin

ACTH

Parathyroid Pancreas Thyroid

iv. Glyco-Proteins

TSH, FSH, LH

Adenohypophysis

B.  Steroids

Mineralocoirticoids
Glucocoericoids
Testosterone
Oestrogen
Progesterone

Adrenal cortex
Adrenal cortex
Tests
Ovary
Ovary

  • Thyroxine is exception in this regards.
  • Liver and kidneys separate hormones from blood and decompose them. The product formed after decomposition is excreted with urine. It cannot be reutilized.

 Physical & Chemical Specialties of Hormones:–

  • The molecules of most of the hormones are small, and their molecular weight is low.
  • Hormones are soluble in water and are easily diffusible in tissues.
  • The secretion of hormone is always in very small quantity because these are most reactive substances.
  • Hormones are destroyed after use i.e. hormones cannot be stored in the body.
  • Hormones are non- antigenic & non species specific substances.
  • Usually, hormones do not participate in the metabolic activities of target cells but they affect and control the activity level of these target cells. Due to the effect of hormones, not only the rate of metabolic activities is affected but also the permeability of cell membrane is changed so the nature of reactions is also changed.

Differences between Hormone & Enzyme

Hormones

Enzymes

1. They are produced at one site and are passed by blood to another site for action.

1. They may act at site where they are produced or carried to another site for action.

2. They have low molecular weight.

2. They have very high molecular weight.

3. Hormones may be steroids, proteins, peptides or amino acid derivatives.

3. Enzymes are proteins.

 

4. They are used up in their action.

4. They are not used up in their action.

5. They are effective in low concentration. Their excess or deficiency may cause disorders.

5. They also act in low concentration. However, the rate of enzyme catalyzed reactions steadily increase with an increase in their concentration

6. They may act slowly or quickly.

6. They act slowly.

 

DIGESTION AND ABSORPTION 

Introduction –
The process of conversion of complex indiffusible food material into simple and diffusible food by mechanical and biochemical (hydrolysis) process, is termed as Digestion. Human Digestive gland cansis of Alimentry canal and accessory digestive gland.

  1. ALLIMENTRY CANAL
  • The alimentary canal is tubular structure which extends from mouth to anus. It develops from ectoderm & endoderm.
  • The alimentary canal is divided into following parts –

 

Ectoderm-upto hard palate       IIeum            Rectum

 

A.   Mouth
Mouth is a horizontal transverse slit like aperture which is surrounded by upper and lower lip, a specific muscle is associated with lip called orbicularis oris muscle.

B.   Buccopharyngeal Cavity -
Mouth opens into Buccopharyngeal cavity, this cavity is divided into two parts.

  1. Buccal vestibule – The space between the gums and cheeks where the food is stored temporarily for some time. It is a peripheral part.
  2. Oral cavity – It is inner & central part which is surrounded by upper and lower jaw. Lined by stratified squamous epithelium. It is inner and central part. Upper Jaw is Fixed and Lower Jaw is Movable. Oral cavity consist varius part.

a.  Palate
The roof of oral cavity is called as Palate.

Palate is differentiated into two parts:

i.  Hard Palate –

  • It is the anterior part of the palate. It is made up of Maxilla and palatine bone in human.
  • On the ventral surface of hard palate, some projection or transverse ridges are present which are called as palatine rugae.
  • These rugae prevent slip out of the food from buccal cavity during mastication, these rugae are well developed in carnivorous animals.

ii.  Soft Palate –

  • It is the posterior part of palate. It is made up of involuntary muscle fibrous connective tissues and mucous epithelium. (Stratified squamous epithelium)

  •  The posterior out growth of soft palate which hangs down in the form of finger like process called as Uvula or Velum palati. On the dorsal side of Uvula internal nasal pores are present.
  • Uvula or Velum palati covers the opening of internal nasal pores during ingestion of food, so food particle can not move inside nasal chamber.
  •  One pair of large lymph node is present on the posterolateral surface of soft palate, called as Palatine tonsil or Tonsils.

(b) Tongue

  • On the floor of oral cavity a muscular, flat, fleshy plate like structure is present which is called Tongue. The anterior part of tongue is free while posterior part of Tongue is connected to the Hyoid bone.

                

  • The surface of tongue is connected to the floor of buccal cavity through a very flexible membrane/ ligamentous fold called as Frenulum linguae.
  • On the Dorsal surface of tongue, it is divided into two unequal parts by a V shaped sulcus, called as sulcus terminalis.
  • The two limbs of the 'V' meet at a median pit named Foramen Caecum. It is divided into two parts –
  1. Pharyngeal Part – It is the posterior 1/3 part of the tongue. Many small lymph nodes are present in this part which are called Lingual tonsil.

 

EXCRETORY PRODUCTS AND THEIR ELIMINATION

  1. INTRODUCTION
    Animals accumulate ammonia, urea, uric acid, carbon dioxide, water and ions like Na+, K+, Cl–, phosphate, sulphate, etc., either by metabolic activities or by other means like excess ingestion: These substances have to be removed totally or partially.

    Excretion:
    Removal of mainly nitrogenous substances from the body which are end product of metabolic activity.
    OR
    The process which is concerned with removal of nitrogenous waste materials (e.g.. urea, uric acid, CO2, Ammonia, salts, excess water etc.) is termed excretion.

  2. TYPE OF ANIMALS ON THE BASIS OF NITROGENOUS WASTE MATERIALS
    Animals on the basis of excretory matter are divided into three categories: -

 

Characters

Type of animals

 

 

Ammonotelic

Ureotelic

Uricotelic

1.

Excretory

Ammonia

Urea

Uric acid

2.

Requirement of water

Very large

Less than ammonia

Least

3.

Mechanism of excretion

By diffusion across body surfaces or through gill surfaces (in fish) as ammonium ion.

Ammonia produced by metabolism is the liver and released into the blood which is filtered and excreted out by the kidneys.

 

4.

Toxicity

Highest

Less than ammonia

Least

5.

Example

Teloests, Tadpoles, Aquatic insect

Mammals, Sharks.

Birds, Insects, Land snails, many reptiles

 3.  EXCRETORY ORGANS IN ANIMAL

Excretory

organs

Protonephridia

(Flame cells)

Nephridia

Malpighian

tubules

Green glands or

Antennal glands

Kidneys

Example

-Platyheliminthes

-Rotifers

-Cephalochordate

(Amphioxus)

-some annelids

Annelids

(Earthwors)

Most of the insects (Cockroache)

Crustaceans

(Prawn)

All vertebrates

4.  HUMAN EXCRETORY SYSTEM
Hunan excretory system consists of:
– A pairs of kidneys
– A pair of ureters
– A urinary bladder
– A urethra

A.  Kidneys

  • Mammalian kidneys are bean shaped, reddish brown coloured with a tough fibrous connective tissue covering called renal capsule.
  • Kidneys are located lateraly on either side of vertebral column levels between the last thoracic and third lumber vertebra close to the dorsal inner wall of the abdominal cavity.
  • In humans right kidney is at slightly lower level than left kidney.
  • Dorsal surface of the kidney is attached to the dorsal abdominal wall, so only its ventral surface is covered by peritoneum, therefore this type of kidney is called retro-peritoneal kidney or extra peritoneal kidney.

 

Each kidney measures 10-12 cm in length, 5-7 cm in breadth and 2-3 an in thickness, weighing about 120-170 gm in an adult. Lateral surfaces of kidney are convex while medial surfaces are concave.

  • On the concave margins of the kidney longitudinal opening called Hilum (Hilus renalis) is present. Through this, renal artery and nerve enter while renal vein and ureter leave the kidney.
  • The Hilum leads to a funnel shaped space called the renal pelvis.
  • The kidney tissue surrounding the pelvis is arranged in an outer renal cortex and inner renal medulla.
  • The renal medulla funs conical pyramid shaped masses which project into the renal pelvis. These are called as medullary pyramids or renal pyramids (8 to 12 in humans, while only one pyramid is present in kidney of rabbit)
  • The cortex extends in between the medullary pyramids as renal columns called columns of Bertini.
  • Each kidney has nearly one million complex tubular structures called Nephrons which are the functional units.

These nephrons are arranged in a radiating fashion within the renal pyramids. Urine produced by each nephron empties into collecting duct. The collecting duct passes through a papilla into the renal calyx (Pleural-calyces).
The renal calyces drain urine in the central cavity of renal pelvis.

B.  Ureters
Urine passes from the pelvis into the ureter. Both the ureters open through separate oblique openings into the urinary bladder. The obliquity of the openings prevent the backflow of urine.

 

 

LOCOMOTION & MOVEMENT

  1. INTRODUCTION
    Study of muscles known as myology (Sarcology).

 

  • Muscle of Iris, ciliary body & myoepithelial cell of sweat gland develop from ectoderm. Conductivity & contractility are the two main characteristics of muscle.

2.  TYPES OF MOVEMENT

  1. Ciliary
  2. Flagellate
  3. Amoeboid
    Except iris & ciliary body all muscles of body develop from mesoderm.

3.   TYPES OF MUSCLES
Three types of muscles are found in the body.

 

  1. Voluntary of skeletal muscles.
  2. Involuntary or smooth muscles.
  3. Cardiac muscles.  

i. Voluntary Muscle-

  • It develops from the epimeric layer of myotome.
  • Skeletal muscles constitutes around 40% of adult body mass in an average healthy person.
  • They are related to the skeletal system. So also called as skelatal muscles.
  • Transverse lines are found at regular interval. Hence these muscles are also called as striped or striated muscle
  • Their contractions are controlled by will power of animal so also called voluntary muscles.
  • a.  Structure of Muscle Fibre

 

Fine structure of muscle fibre:-

  • The outer membrane of muscle fibre is called sarcolemma.
  • This cell membrane contain collagen fibres.
  • Each muscle fibre contain multinucleated sarcoplasm.
  • Nucleus & sarcoplasm are found in peripheral part.
  • Myofibril are arranged in parallel row & form the dark & light line.
  • These lines are found in alternate order.
  • These lines are made up of actin & myosin protein. Both proteins are filamentous proteins.
  • Actin filaments are thin while myosin filaments are thick.
  • Light line or band is made up of only actin filament, these band are monorefractive in polarised light so it is called   Isotropic band (I band).
  • Actin filaments are connected with a disc of Z– line protein (Actinin) which is called as Z line (Zweichenschiebe) or (Doble's membrane) or (Krause's membrane).
  • Dark line is made up of actin & myosin filament so it is double monorefractive in polarised light due to overlaping so it is called Anisotropic band.
  • The terminal end of actin filament are embedded among the myosin filament so peripheral part of a band is darker as compared to the middle part of a band which is called as H-Zone or Hensen zone.
  • A dark line is also found in the central part of H-zone which is called as M line or mesogramme line.
  • The distance between two Z–lines is called as Sarcomere.
  • It is structural unit or functional unit of voluntary muscle fibre.

Sarcomere = 1A band + two half I band
The Length of Sarcomere is 2.5 μm.
(I band = 1μm, myosin = 1.5 μm)

  • 1 Myosin filament is surrounded by 6 Actin filaments & 1 Actin filament is surrounded by 3 Myosin filaments.
  • Muscle fibre is covered by a layer of connective tissue which is called Endomysium.
  • Many muscle fibres are combined to form a group which is called fasciculi.
  • Each fasciculus is covered by a layer of connective tissue which is called Perimysium.
  • Many fasciculi combined to form a muscle.
  • Muscle is also covered by a layer of connective tissue which is called as Epimysium.
  • Muscle fibre is a cylindrical or tubular shape.
  • The muscle fibres attached to a tough cord of connective tissue called Tendon & Tendon is further attached with a bone.

 

 

NEURAL CONTROL & COORDINATION

  1. INTRODUCTION
  • In human body the neural system and the endocrine system jointly coordinate and integrate all the activities of the organs so that they function in a synchronised fashion. The neural system provides an organised network of point-to-point connections for a quick coordination. The endocrine system provides chemical integration through hormones. Co-ordination is the process through which two or more organs interact & complement the functions of one another.

A.   Neural System

  • The neural system of all animals is composed of highly specialised cells called neurons which can detect, receive and transmit different kinds of stimuli.
  • The neural organisation is very simple in lower invertebrates. For example, in Hydra it is composed of a network of neurons.
  • The neural system is better organised in insects, where a brain is present along with a number of ganglia and neural tissues.
  • The vertebrates have a more developed neural system.

 

The human neural system is divided into two parts:

  1. The central neutral system (CNS)
  2.  The peripheral neutral system (PNS)
    The CNS includes the brain and the spinal cord and is the site of information processing and control. The PNS comprises of all the nerves of the body associated with the CNS (brain and spinal cord). The nerve fibers of the PNS are of two types:

a.  Afferent fibres
b.  Efferent fibres

  • The afferent nerve fibres transmit impulses from tissues/organs to the CNS and the efferent fibres transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs. The PNS is divided into two divisions :-

a. Somatic neural system (SNS)
b. Autonomic neural system (ANS)

  • The somatic neural system relays impulses from the CNS to skeletal muscles while the autonomic neural system transmits impulses from the CNS to the involuntary organs and smooth muscles of the body. The autonomic neural system is further classified into sympathetic neural system and parasympathetic neural system.
  • Nervous tissue originates from ectoderm and is specialized for receiving stimuli (Excitability or Inrritability) and transmit message (conductivity).

 

B.  Neutron as Structure and Functional Unit of Neutral System Structure of a neuron
Structure of a neutron: Nerve cell is made up of cell body & cell process – (Dendron And Axon =Neuritis)

 

  1.  Cell body or Cyton or soma or perikaryon:-
  • It contains uninucleated cytoplasm.
  • Except centriole, all cell organelles are found in cytoplasm.
  • Centriole is absent or immaturely present in the nerve cell thus cell division is absent.
  • Some other cell organelles like Nissl's granule and Neurofibril are also found in nerve cell.

Nissl's granules:

  • Endoplasmic reticulum coils around the ribosome and form granule like structure called as Nissl's granules or Tigroid body.
  • It is the centre of protein synthesis.
  • Chemically – Ribonucleoprotein containing Iron.
  • Site – Cyton & dendron (Rod shape)
  • Many small fibrils are found in the cytoplasm called neurofibrils, these help in internal conduction in the cyton.

Cell processes:

  1.   Dendron :–
    It is small cell process. It's fine branches are called dendrites. Some receptor's are found on the dendrites, so dendron receive the stimuli & produce centripetal (towards the cell body) conduction.
  2. Axon (Long process = Axon = Nerve fibre) It is longest cell process of cyton, its diameter is uniform. It contain axoplasm.
  • Nissl's granules are absent in the axoplasm.
  • (Axoplasm of axon contains only neurofibrils and mitochondria).
  • Axon is covered by axolemma. Part of cyton where axon arises called axon hillock.
  • The axon hillock is the neuron's trigger zone, because it is the site where action potential are triggered.
  • The terminal end of axon is branched in button shape branches which are called as Telodendria.
  • More mitochondira are found in the telodendria which synthesize Acetylcholine (Ach) with the help of choline acetyl transferase enzyme.
  • Ach is stored in the vesicles.
  • Axon is the functional part of nerve cell, therefore term nerve fibre usually refer to Axon.

 

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