human physiology by Yigizie Y, University of Gondar, Ethiopia,2017

1. 03/19/17 1
Introduction to Human Physiology
By
Yigizie Yeshaw(MSc)
University of GondarUniversity of Gondar
College of Medicine & Health SciencesCollege of Medicine & Health Sciences
Department of PhysiologyDepartment of Physiology
yigizieyeshaw29@gmail.comyigizieyeshaw29@gmail.com

2. 03/19/17 2
Objectives
At the end of this chapter the student will be able to:
1. Define what physiology mean
2. Explain homeostasis.
3. Discuss negative & positive feed back mechanism.
4. Discuss cell physiology.
5. Enumerate the cell organelles with their function.
6. . Body fluids
7. Describe PM components and transport across
8. Define membrane potential and its causes
9. Action potential

3. 3
What is Physiology?
Physiology is the study of the normal functioning of a
living organism and its component parts, including all its
chemical and physical processes
Fields of physiology
Ranges from simple viral physiology, bacterial physiology, cellular
physiology to the most complex human physiology
03/19/17

4. Human physiology
Explain the specific characteristics and mechanisms of the
human body that make it a living being.
The fact that we remain alive is the result of complex
control systems.
Example
– Hunger makes us seek food, and
– fear makes us seek refuge.
– Sensations of cold make us look for warmth.
these special attributes allow us to exist under widely varying
conditions, which otherwise would make life impossible.03/19/17 4

5.  An important part of physiology is understanding
 how different parts of the body are controlled,
 how they interact, and
 how they adapt to changing conditions
03/19/17 5

6. 1. William Harvey in 1628
 Blood was pumped out of the heart through one set of vessels and
returned to the heart through another set.
2. Claud Bernard, in the 19th
C
Described that every cell in body is bathed with the fluid environment
called extracellular fluid(ECF).
He called ECF is the internal environment of the body.
3. Walter cannon-
Define homeostasis as maintenance of constant conditions in the ECF
Historical background
603/19/17

7. Relationship b/n Physiology and other sciences
Physiology has a strong link with other disciplines
It is Highly related to
Anatomy
 Biochemistry
Pathology
Pharmacology etc
Physiology as a quantitative science
All physiological parameters are expressed in numbers
03/19/17 7

8. Levels of the Organization of the Human Body
 chemical level cell  tissue organ  system organism
03/19/17 8

9. 1. Cell
The basic structural and functional unit of an organism.
It is the smallest living unit of the human body
But play a big role in making our body function
properly.
03/19/17 9

10. The entire body contains about 100,000,000,000,000 cells.
Each type of cell is specially adapted to perform one or
a few particular functions. e.g. RBC- transport oxygen
from the lungs to the tissues
Each cell has basic requirements to sustain it and
The body's organ systems are providing these many
cells with those basic needs (oxygen, food) and
remove waste products.
03/19/17 10

11.  There are many different types of cells in the body including:
Nerve cells
Blood cells
Epithelial cells and
Muscle cells
03/19/17 11

12. 2. Tissue
 When many identical cells are organized together it is called a tissue
 There are four types of tissues in the body:
1. Epithelial tissue
2. Connective tissue
3. Muscle tissue
4. Nervous tissue
3. Organ
 Organs are structures that are made of two or more different types of
tissues.
03/19/17 12

13. 4. System
Consists of related organs that have a common function.
There are 11 organ systems in the body:
1. Respiratory System
2. Cardiovascular System
3. Digestive System
4. Urinary System
5. Reproductive System
6. The Skeletal System
7. Muscular System
8. The Integumentary System
9. Nervous System
10. Endocrine System
11. Lymphatic & Immune System
03/19/17 13

14. 5. organism –it is the highest level of organization.
e.g human
03/19/17 14
CVS GIT RS
Renal
System
Skeletal
System
Muscular
system

15. Homeostasis
 Homeostasis is maintenance of nearly constant conditions in the
internal environment (ECF).
But this does not mean that its composition are absolutely
unchanging.
Both external and internal factors continuously threaten to
disrupt homeostasis.
Factor disrupting homeostasis:
External stimuli
heat, cold,
lack of 02,
pathogens & toxins
 Internal stimuli
 abnormalities in visceral organs03/19/17 15

16. When any factor starts to move the internal environment
away from optimal conditions,
the body systems initiate appropriate counter reactions to
minimize the change.
For example, Exposure to a cold/to warm environmental
temperature tends to decrease/ increase the body’s internal
temperature.
– Shivering in response to cold environment
– Sweating in response to high temperature
03/19/17 16

17. 17
 Essentially all organs of the body perform their functions to
maintain constant conditions in the ECF. For example
 Respiratory system(RS)
The blood picks up oxygen in the alveoli, thus acquiring the
oxygen needed by the cells
Carbon dioxide is released from the blood into the lung alveoli
for exhalation
So RS help to maintain the normal concentration of respiratory
gases in blood.
03/19/17

18. 03/19/17 18
Cardiovascular System(CVS)
CVS-provides
nutrients(glucose,aa,lipids),
gases (O2)
signaling molecules
(hormones) and
Removal of wastes (urea,
creatinine, CO2),

19.  Gastrointestinal system
 different dissolved nutrients are absorbed from the ingested food
into the extracellular fluid of the blood.
 some waste products of metabolism are eliminated in the
feces
 Renal system
Passage of the blood through the kidneys removes substances
that are not needed by the cells from the plasma.
The kidneys maintain constant ionic concentration
 Musculoskeletal System
Provides motility for protection against adverse surroundings
Allow movement to obtain the foods required for nutrition
Hemopoiesis and Mineral storage
1903/19/17

20.  Immune System
protect the body from pathogens
 Integumentary System.
provide a boundary b/n the body’s internal environment and the
outside world.
cover, cushion, and protect the deeper tissues and organs of the
body
temperature regulation and excretion of wastes
 Reproductive system
Have less role for homeostasis
help maintain homeostasis by generating new beings to take the
place of those that are dying.
2003/19/17

21. 03/19/17 21
Regulatory Systems of Homeostasis
• The nervous
system and the
endocrine system
are the two
controlling bodies
of homeostasis
Effector cell
NTs
Receptor
Nerve Impulse
Hormone
Receptor

22. 22
Regulatory systems of homeostasis
1. The nervous regulatory mechanism
 The nerves system is composed of three major components the
I. Sensory portion- The sensory receptor detects any change in
the body (BGC, BT, ABP, pain etc) and send impulse to the
CNS(brain, spinal cord).
II. Integrative portion -The CNS associate the information store
some, generate thought.
III. Motor portion - send appropriate response to the effecter
organs (muscle + glands).
03/19/17

23. 23
Regulatory systems of homeostasis…
2. The hormonal regulatory mechanism
 Hormones are chemical messengers secreted by endocrine glands,
and transported in blood to the target organs.
Examples:
• PTH act on the kidney, bone, and intestine = [Ca2+]
• Aldosterone  to the kidney   [Na+]
 An organism is said to be in homeostasis when its internal
environment contains an optimum amount of
1. Nutrients
2. Gases
3. Electrolytes
4. Water
5. Hormones
6. Enzymes and temperature.03/19/17

24. To stabilize the physiological factor being regulated,
homeostatic control systems must be able to detect and
resist change.
03/19/17 24

25. Homeostatic control systems…
1. Feed-forward control
The term feed forward is used for responses made in
anticipation of a change.
• The regulatory processes established before the change is
developed.
 Correction is by anticipation- Example
-  HR and RR before actual exercise
-  Digestive juice before food inter
into GIT
03/19/17 25

26. • When meal is still in the GIT, there is an increase insulin
– that will promote the cellular uptake and storage
glucose after absorption.
– This anticipatory response helps limit the rise in
[BGC] after absorption.
• Used to adapt and rapid rate of response to the change.
03/19/17 26

27. II. Feedback control
 It refers to responses made after a change has been
detected;
– The regulatory processes established after the change is
developed.
• These feedback systems alter the function of organs by
increasing or decreasing their activities.
• There are two types of feed back mechanisms:
1.Negative feedback mechanism
2.Positive feedback mechanism
03/19/17 27

28. 28
Negative Feedback Mechanism (NFM)
 It works by producing an effect which opposes the previous
condition (the initiating stimulus) of the organ.
 A negative feedback control system contains the following
elements:
1. A set point value, which is at the center of the normal range of
a variable and is treated by the control system as the target
value
2. Sensors that continuously monitor the controlled variable
3. A comparator (control center), which interprets input from
the sensors to determine when deviations from the set point
have occurred
• The comparator initiates a counter response
1. Effectors are the mechanisms that restore the set point to its
normal level
03/19/17

29. 03/19/17 29

30. Stimulus:
Produces
change
in variable
1
2
3
Change
detected
by receptor
Input:
Information
sent along
afferent
pathway to
5 Response of
effector feeds
back to influence
magnitude of
stimulus and
returns
variable to
homeostasis
Variable (in homeostasis)
Imbalance
Imbalance
Receptor (sensor)
Control
center 4 Output:
Information sent
along efferent
pathway to
Effector
Homeostatic Control Mechanisms
3003/19/17

31.  Most homeostatic values of the body are controlled by NFM.
Example :
1. Control of Blood Glucose Level
2. Control of Body Temperature
3. Control of Calcium
4. Control of Arterial Blood Pressure etc.
3103/19/17

32. 03/19/17 32
Control of Blood Glucose Level

33. 33
Ca2+-
homeostasis
03/19/17

34. 03/19/17 34
Control of Arterial Blood Pressure

35. Human Thermoregulation
35
Brain senses change in blood temperature
 if overheating, vessels dilate in the skin and sweating begins
 if too cold, vasoconstriction in the skin and shivering begins
03/19/17

36. 36
The Positive Feedback Mechanism (PFM)
It works by producing an effect which enhances or
repeats the same action like that of the starting stimulus.
 “Positive” implies that when a deviation from a normal
value occurs, the response of the system is to make the
deviation even greater
Positive-feedback mechanisms are not homeostatic and
are rare in healthy individuals.
Examples of the PFM
1. Blood clotting
2. Labor during child birth
3. Generation and propagation of the action potential.
03/19/17

37. PFM..
1. Blood clotting is an example of a very valuable use of PFM.
3703/19/17

38. 2. Labor during child birth
3803/19/17

39. 39
PFM..
03/19/17
3. Generation and propagation of the action potential.
Stimulated nerve fiber
opening of Na+ channels
entry of few Na+
stimulates the opening of more and more Na+ channels

40. Why do essentially all control systems of the body operate
by NFM rather than PFM?
– B/c positive feedback does not lead to stability but to instability
and often death. Example
03/19/17 40

41.  Heart of a healthy human being pumps about 5L of blood per minute.
If the person is suddenly bleed 2L blood
The amount of blood in the body is decreased to such a low level that
not enough blood is available for the heart to pump effectively.
As a result, the arterial pressure falls
coronary vessels blood flow diminishes
weakening of the heart, further diminished pumping, a further decrease
in coronary blood flow
still more weakness of the heart; the cycle repeats itself again and again
until death occurs.
4103/19/17

42. 42
Homeostatic values
1. Body fluid volume(TBW) = 42 L
ICF = 28L(2/3rd
of TBW)
ECF = 14L(1/3rd
of TBW)
Interstitial fluid = 11 L(3/4th
of ECF)
 Plasma fluid = 3 L (1/4th
of ECF)
2. Osmolality = 300 mosm/L, (285 – 300 mosm/L)
3. Body T. = 36.5 – 37.4O
C
4. pH = 7.35 – 7.45
5. Blood Gases - PCO2 = 35 – 45 mm Hg
PO2 = 40 – 104 mm Hg
6. Electrolytes (ECF)
Ca2+
= 10 mg/dL or 5 meq/L
K+
= 4 meq/L
Na+
= 142 meq/L
Cl-
= 103 meq/L
HCO3
-
= 27 meq/L
03/19/17

43. 43
Homeostatic values
7. Waste Products
Bilirubin = 0.5 mg/dl
Creatinine = 0.6 – 1.5 mg/dL
Blood urea nitrogen (BUN) = 8 – 25 mg/dL
Uric acid (s): Women = 2.3 – 6.6 mg/dL
Men = 3.6 – 8.5 mg/dL
8. Blood Glucose level (fasting): 70 – 110 mg/dL
9. Arterial Blood pressure (systemic circulation).
Systolic pressure = 120 mm Hg (90 – 140 mm Hg)
Diastolic pressure = 80 mm Hg (60 – 90 mm Hg)
Pulse pressure = 40 mm Hg
Mean BP = 96 mm Hg
Pulmonary AP = 25/10 mm Hg
Cardiac output = 5 L/min
Blood Flow = 5 L /min
10. RBC count = 4-6 millions/mm3
11. WBC count = 4000-11,000/mm3
12. Hb = 12-18 g/dl in F, 14-20 g/dl in M
13. Platelets = 150,000-450,00003/19/17

44. 03/19/17 44
Disturbances of homeostasis
When there is lose in homeostasis, the organism tries to
compensate it.
– If compensation succeeds, wellness happens
– If compensation fails, illness or diseases happens
• Deviations from normal ranges = PATHOLOGY
• Disease: a state of disrupted homeostasis.
– Hypo/ Hyperthermia ….. ↓or↑ Temperature
– Hypo/ Hypercapnea ….. ↓or↑ PCO2
– Acidosis/Alkalosis ….. ↓or↑ PH
– Hypoxia/ Hyperoxia …. ↓or↑ PO2
– Hypo/ Hypercalcemia …. ↓or↑ Ca 2+
– Hypo/ Hyperglycemia … ↓or↑ Glucose

45. 45
Structural levels of organization of human body
Muscle cells
Nerve cells
Cells: 4 types Epithelial cells
Cells in the connective tissues
Muscle tissue
Tissues 4 types Nerve tissue
Epithelial tissue
connective tissues
Organs: Example: Heart, lungs
Organ system: Example: Respiratory system, CVS
Organism: Human organism
03/19/17

46. 46
Generalized cell
Components of cells
 A typical cell has two parts: nucleus and cytoplasm.
 The nucleus is separated from the cytoplasm by a nuclear
membrane and
 The cytoplasm is separated from the surrounding fluid (ECF) by
the plasma membrane
 The different substances that make up the cell are collectively
called protoplasm.
 Protoplasm is composed mainly of five basic substances: water,
electrolytes, proteins, lipids, and carbohydrates.03/19/17

47. Cell Physiology
» Two types of cells:
A. cells without typical nucleus = prokaryotes
B. cells with nucleus = eukaryotes
4703/19/17

48. Comparision b/n Prokaryotic and Eukaryotic cells
Eukaryotes
1.Have nucleus
2. Larger (10-100 µ m)
3.Cytoskeleton present
4.Membrane-bound organelles
present
5.RNA synthesis in nucleus,
protein synthesis in the
cytoplasm
6. Multiple linear chromosomes
Prokaryotes
1.No nucleus
2.Smaller (1-10 µm)
3.No cytoskeleton
4.Generally no membrane-
bound organelles
5.RNA and protein
synthesis occur in
cytoplasm.
6.Small circular
chromosome
03/19/17 48

49. 49
The plasma membrane
It is a sheet-like structure that surround (enclose) the cell,
It separates the cellular contents from the ECF.
Regulates the passage of substances in and out.
03/19/17

50. 50
The nucleus
 The nucleus is the control center for the cells.
 It contains the genes, which are units of heredity.
 Chemically each gene consists of highly compressed DNA in the
form of chromosomes
 Genes control cellular activity by determining the type of
proteins,
enzymes, and
other substances that are made by the cell.
03/19/17

51. 51
The nucleus (cont’d)
Nucleoli- site for Ribosomal RNA is synthesis.
The nuclear contents are surrounded by a double walled
nuclear membrane.
The pores present in this membrane allow fluids,
electrolytes, RNA, and other materials to move between
the nuclear and cytoplasmic comportments.
03/19/17

52. the nucleus with DNA the double strand genetic code
that stores and transmits genetic material, and
coordinates protein synthesis in ribosomes
Undertakes its transcription phase of protein synthesis
in the nucleus.
Following transcription, the mRNA leaves the nucleus
and travels to the cell's ribosomes, where translation
occurs
transcription translation
DNA RNA Protein synthesis
03/19/17 52

53. 53
Cellular organelles
• Embedded within the cytoplasm are organelles or inner
organs of the cell.
These include
– the ribosomes,
– endoplasmic reticulum (ER)
– Golgi apparatus,
– mitochondria,
– lysosomes, and
– the cytoskeletal system (microtubules and microfilaments).
03/19/17

54. 03/19/17 54

55. Cell organelles may be:
Non-membrane-limited
Nucleoli
Ribosomes
Microtubules
Microfilaments
Centrioles
Membrane-limited
Nucleus
Endoplasmic reticulum
 Golgi apparatus
Lysosomes
Mitochondria
03/19/17 55

56. 56
Ribosomes:
Are the sites of protein synthesis in the cell
Found in two forms:
1. Attached to the wall of ER or
2. As free ribosomes. They are found in two forms
I. Scattered in the cytoplasm and
II. Clustered (aggregated) to form functional units
called polyribosomes
03/19/17

57. 57
Endoplasmic reticulum (ER)
 It is an extensive membranous structure that connects various
parts of the inner cell.
 ER is also connected with the nuclear membrane.
 There are two types of ER:
– rough ER and
– smooth ER.
 rER is the site of protein synthesis
03/19/17

58. 58
Endoplasmic reticulum (ER)
• The sER is free of ribosome.
• Function of sER varies in different cells.
• The sarcoplasmic reticulum of skeletal and
cardiac muscle cells are forms of sER.
• In the liver, the sER is involved in glycogen
storage and drug metabolism.
• ER can synthesize a group of drug metabolizing
enzymes called microsomal system.
Function of sER:-
1. Glycogen storage
2. Calcium storage
3. Lipid biosynthesis
4. Drug metabolism (detoxify)
Endoplasmic reticulum (rER and sER)
03/19/17

59. 59
Golgi Complex
 The Golgi complex communicate
with the ER and acts as a
receptacle/container for hormones
and others substances that the ER
produces.
 It then modifies and packages
these substances ( proteins) into
secretary granules.
03/19/17

60. 60
Rough ER and Golgi complex
03/19/17

61. 61
Mitochondria-power house
 The mitochondria are literally the
“power plants-factory” of the cell, b/c
many of the reactions that produce
energy take place in mitochondria.
 Major site of
ATP production
Oxygen utilization
 CO2
formation.
 Contains enzymes of krebs cycle and
oxidative phosphoryiation03/19/17

62. Lysosomes
 Lysosomes are vesicular organelles that form by breaking off from
the Golgi apparatus and then dispersing throughout the
cytoplasm.
 Contains aggregates of enzymes.
 Well developed in macrophages.
 Are called suicide bags
 The lysosomes provide an intracellular digestive system that
allows the cell to digest
– damaged cellular structures
– harmful substances such as bacteria.
6203/19/17

63. Lysosomes …cont’d
Membrane bound organelles that contain
hydrolases(Hydrolytic enzymes)
 Hydrolytic enzymes;
lipases,
proteases,
glycosidases,
nucleases etc )
 The membrane surrounding the lysosome prevents the enclosed
hydrolytic enzymes from coming in contact with other substances in
the cell and, therefore, prevents their digestive actions.
6303/19/17

64. Peroxisomes
 Also called small bodies and they are spherical in shape
 Are membrane bound organelles containing enzymes; oxidases and
catalases
– Surrounded by single membrane
 Have protective role in that they secrete chemical that converts
harmful substances into harmless
 E.g. Catalase is a type of oxidase produced by peroxisomes and
converts:
» H2O2 catalase H2O + O2
6403/19/17

65. Peroxisomes
 Are similar physically to lysosomes, but they are different in two
ways:
  They formed by self-replication (or perhaps by budding off
from the sER) rather than from the golgi apparatus
  They contain oxidases rather than hydrolases
6503/19/17

66. Cell to Cell communication
 Cell to cell communication very important for multicellular
organisms.
1. Endocrine signals
produced by endocrine cells
travel through the blood to reach all parts of the body.
1. Paracrine signals
target only cells in the surrounding area of the releasing
cell. E.g Neurotransmitters
1. Autocrine signals
Affect only cells that are of the same cell type as the
emitting cell. E.g. immune cells
1. Juxtacrine signals(Paracrine signals+Autocrine signals)
are capable of affecting either the emitting cell or cells
immediately adjacent03/19/17 66

67. 67
Intercellular signaling
03/19/17

68. Junctions between Cells
• Multicellular organisms
requires specific interaction
b/n cells to hold the cells
together and to
communicate in order to
coordinate activities.
• Five kinds of junctions
– Tight junctions
– Adherens junctions
– Gap junctions
– Desmosomes
– Hemidesmosome
03/19/17 68

69. 03/19/17 69

70. 03/19/17 70

71. a. Tight junctions(occluding junctions)
Help plasma membranes of adjacent cells to fuse together,
forming an impermeable junction that encircles the cell.
They prevent molecules from passing through the
extracellular space between adjacent cells
So most materials must actually enter the cells (by
diffusion or active transport) in order to pass through the
tissue
For example, tight junctions b/n epithelial cells lining the
digestive tract keep digestive enzymes and
microorganisms in the intestine from leaking into the
bloodstream
03/19/17 71

72. b. Gap Junctions(communicating junction)
 It is a communicating junction b/n adjacent cells
 At gap junctions the adjacent plasma membranes are very
close, and the cells are connected by hollow cylinders
called connexons.
 Allow ions and small molecules to pass for intercellular
communication
 Present in electrically excitable tissues, such as smooth
muscle and the heart, where ion passage from cell to cell
helps synchronize their electrical activity and contraction.
03/19/17
72

73. c. Anchoring junctions
These junctions are most abundant in tissues that are
subject to constant mechanical stress such as skin and
heart
1. Adherens Junctions
 Provide strong mechanical attachments between adjacent cells
 Ties cells with other cells or EC matrix
 They hold cardiac muscle cells tightly together as the heart
expands and contracts
 They hold epithelial cells together
7303/19/17

74. 2.Desmosomes
 Desmosomes are localized patches that hold two cells tightly
together
 They are common in epithelia (e.g, the skin).
3. Hemidesmosomes
 These are similar to desmosomes but attach epithelial cells to the
basal lamina ("basement membrane" instead of to each other
03/19/17 74

75. Human Body fluid
 The approximate composition of an average adult human per body
weight is that:
– Water = 60%
– Proteins = 18%
– Fats = 15%
– Minerals = 7%
What is Body Fluid(BF)?
The term BF refers to the body water + its dissolved substances
BF comprises an average of 60% of total body weight
The TBW in a 70kg adult man averages about 42 L, distributed
as: ICF and ECF
03/19/17 75

76. 76
The fluid environment of the body
 This 60% of human BF(42 L) is distributed in 2 compartments
1. Intracellular fluid compartment (ICF)
-Fluid inside the cell (28L) -which is 2/3rd
of TBW
2. Extracellular fluid compartment (ECF)
-fluid out side the cell(14 L) –which is 1/3 of TBW.
-2 Subdivisions:
I. Blood plasma (1/4th
of the ECF) =3.5L
II. Interstitial fluid (3/4th
of the ECF )=10.5L
III. transcellular fluid(1% to 3% of body weight)
03/19/17

77. 7703/19/17

78. Transcellular fluid include
CSF,
aqueous and vitreous humor of the eye,
secretions of the digestive tract and associated organs
(saliva, bile, pancreatic juice),
renal tubular fluid and bladder urine,
synovial fluid, and sweat
03/19/17 78

79. Extracellular fluid compartment (ECF)
• Contain ions and nutrients needed by the cells to
maintain life.
• This ECF is in constant motion throughout the body.
 It is transported rapidly in the circulating blood and then
mixed between the blood and the tissue fluids by
diffusion through the capillary walls.
Thus, all cells live in essentially the same
environment(the ECF,milieu intérieur or internal
enviroment).
Cells are bathed with ECF.
This fluid contains an optimum amount of nutrients,
gasses, hormones, enzymes, water and electrolytes03/19/17 79

80. Cells are capable of living and performing their special
functions as long as the proper concentrations of
oxygen,
glucose,
different ions,
amino acids,
fatty substances and other constituents
are available in this internal environment(ECF).
8003/19/17

81. ICF
Water
High K+,Po4
3-
,Mg2+,
proteins
Nutrients,
gases
Hormones
ECF
Water
High Na+
, Cl-
, Ca2+
and
HCO3
Nutrients
Gases: O2, CO2
Hormones
Enzymes
81
Special mechanisms for transporting ions through the cell
membranes maintain the ion concentration differences between the
extracellular and intracellular fluids.
03/19/17

82. Normal values of ECF & ICF
03/19/17 82

83.  These two fluid compartments differ strikingly in terms of their
electrolyte composition
 The blood plasma, interstitial fluid, and lymph are nearly
identical in composition, except for the higher protein
concentration in the plasma
 But the fluid compartments solute concentrations (osmolarity)
are normally equal (no an osmotic difference between cells
cytoplasm/ICF and ECF)
8303/19/17

84. Disturbances of Water Balance
• Disturbances of body fluid volume may be
hypervolemia (excess fluid retention) or
 hypovolemia (loss of fluid or dehydration)
8403/19/17

85. Disturbances of body fluid volume
– Hypervolemia may be caused due to:
1. Liver disease
2. kidney disease
3. Heart disease
4. Mismanagement of IV fluid
– Hypovolemia may be caused due to:
1. Excessive diarrhea
2. Excessive vomiting
3. Excessive sweating
4. Hemorrhage
5. Mismanagement of IV fluid
8503/19/17

86. Edema
• A typical (Abnormal) accumulation of fluid in the interstitial
space
– tissue swelling
• Causes:
– Caused by anything that increases flow of fluids out of the
bloodstream or hinders their return
1. Increase capillary hydrostatic pressure: as in obstruction of
venous system as in congestive heart failure
2. Decrease in the plasma colloid osmotic pressure: as in excess
loss of protein, in kidney diseases or decrease production, in
liver diseases or malnutrition
3. Obstruction of lymph vessel: accumulation of proteins in the
interstitial spaces
8603/19/17

87. Membrane Physiology
87

88. 88
The plasma membrane
It composed of proteins, lipids and carbohydrates in
proportion of
 Proteins- 55 %
Phospholipids 25 %
 Lipids- 42 % Cholesterol 13 %
Neutral fats 4 %
Carbohydrate-3%
 cholesterol determines rigidity of the membrane and
used to stabilizes the cell membrane

89. 89
Function of the plasma membrane
1. Separates cellular contents from the ECF
2. Regulates the passage of substances in and out.
It is semi-permeable allowing some subs to pass
through it excluding others. This creates unequal
distribution of ions on both sides of the membrane.
it allows oxygen and nutrients to enter the cell while
keeping toxins and waste products out

90. Function of the plasma membrane…
3. It provides receptors for NTs, hormones and
drugs.
4. It is a means of cell to cell contact.
5. Plays an important role in the generation and
transmission of electrical impulse in nerves &
muscle.
6. Involved in the regulation of cell growth and 90

91. 91
Components of cell membrane
 A plasma membrane is a
fluid in its nature.
 Lipids form the basic
structure of the membrane.
 The lipid molecules are
arranged in two parallel
raws, forming a lipid
bilayer.
ECF ICF
1. Lipid

92. Cont,d
• The lipid bilayer portion of the
cell membrane is impermeable to
water and water soluble
substances such as
– ions,
– glucose,
– urea and others.
• On the other hand, fat soluble
substances such as
– O2,
– CO2,
– alcohol and drugs
can penetrate this portion of the
membrane.
92

93. Phospholipids
Fatty acid
Phosphate
• Phosphate head
– hydrophilic
• Fatty acid tails
– hydrophobic
• Arranged as a bilayer “repelled by water”
“attracted to water”

94. Arranged as a Phospholipid bilayer
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
polar
hydrophilic
heads
• Serves as a cellular barrier / border
H2Osugar
lipids
salt
waste
impermeable to polar molecules

95. Permeability to polar molecules?
 Membrane becomes semi-permeable via protein
channels
– specific channels allow specific material across cell
membrane
inside cell
outside cell
sugaraaH2O
saltNH3

96. 96
• The lipid molecules (primarily
phospholipids) contain a
– polar phosphate heads, soluble in water
(hydrophilic) and
– a non-polar tails that does not mix with
water (hydrophobic).
• The physical orientation of the lipid
bilayer structures is that the
hydrophilic ends of the lipid
molecules line up facing the ICF and
ECF.
• The hydrophobic tails of the
molecules face each other in the
interior of the bilayer.

97. 97
2. Proteins (Membrane proteins)
A. Integral or intrinsic proteins
 Exist as globular units running through the width of the cell
membrane;
 Partly hydrophilic (polar and protruding to cell surface) and
partly hydrophobic (non-polar and embedded in the lipid
bilayer).
 Protruding part may often carry CHO chains or lipids attached
to their tips like flags.
 Tightly associated with membrane and
 Account for about 70% of the membrane proteins.

98.  Many of them provide structural channels through w/c
polar substances can diffuse in and out of the cell.
Trans membrane proteins serve as:
 Channels through which ions pass
 Carriers which actively transports material across the
bilayer e.g. glucose
 Pumps which actively transport ions
 Receptors for neurotransmitters and hormones
98

99. 99
B. Peripheral or extrinsic proteins:
 Hydrophilic and readily dissociated from membrane.
 Free, floating on the surface (stud the inside and the outside of the
membrane)
 Account for about 30% of the membrane proteins.
 Bind specific hormones and proteins on cell membrane.
 Peripheral proteins that bind to the intracellular surface contribute
to the cytoskeleton.

100. 100

101. 101

102. 102
3. Carbohydrates(Membrane carbohydrates)
 Attached on the outside surface of the membrane, binding with
protruded integral proteins(forming glyco-proteins)
and lipid(forming glyco-lipid )
Function
– It is the site of receptors for NTs, hormones and drugs.
– Cell to cell attachment

103. Transport through cell membrane
What needs to cross the PM?
Nutrients and wastes
Signaling molecules
Fluid
Certain ions
The PM is a very important structure which functions
to allow certain substances to enter or leave the cell
still excluding others to cross the membrane
103

104. Transport through cell membrane…
Such a membrane is referred to as "selective
permeable“ ("semipermeable")
It can "pump" other substance into or out of the
cell against the concentration gradient
Both the protein portion and the phospholipids
portion of the membrane are involved in the
membrane permeability.
104

105. Transport through the cell membrane…
I. Cells have two categories of transport for the movement of ions and
small solute molecules across the plasma membrane. These are
1. Passive transport
 transport process that happens without the cell needing to
expend any energy. It includes
 Simple diffusion
 Facilitated diffusion
 Osmosis
1. Active transport
 transport processes require energy (ATP) from the cell's reserves to
"power" them. It includes
 primary active transport
 secondary active transport
105

106. Transport through the cell membrane
II. The movement of large molecules across cell membrane
takes place by vesicular transport
1. Endocytosis
2. Exocytosis
106

107. 107
Transport through the cell membrane
ECF
ICF

108. 108
1.Simple Diffusion
• Diffusion is passive movement of substances down their
concentration gradient.
Factors affecting the net rate of diffusion
– Lipid solubility of the subs
– Membrane permeability
– Concentration difference or Pressure difference
Membrane permeability is affected by
– Membrane Thickness
– No of ion channels per unit area
– Temperature: T =  thermal motion of molecule
permeability
– MW (molecular weight)

109. 109
Simple Diffusion…
• Rate of diffusion is determined by the following factors
summarized in the formula shown below.
C.A. T.S
• Rate of diffusion = D
Where, C = Change of concentration
S = Solubility in lipid of the sub.
A = Surface area of the membrane
T = Temperature
D = Distance or membrane thickness
MW = Molecular wgt of substances
• Examples: Substances that are transported by simple diffusion are
CO2, O2, alcohol, lipid soluble drugs and ions through specific
channels.
MW

110. 110
2. Facilitated diffusion
 Carrier mediated transport
 Do not need energy
 Transports substances down
their concentration gradient
Is more rapid than simple
diffusion.
 Is carrier-mediated and
therefore exhibits specificity
and saturation
 Examples: transport of glucose,
proteins. (Macromolecules)
Glucose
Carrier protein
Cell membrane
ECF
ICF

111. Facilitated diffusion…
 Unlike simple diffusion the
rate of facilitated diffusion
increases as the
concentration gradient
increases until all of the
carrier sites are filled.
 At this point, the rate of
diffusion can no longer
increase with increasing
particle concentration.
 This is called saturation,
111
Fig. Effect of concentration of a substance on
rate of diffusion by simple diffusion and
facilitated diffusion.
This shows that facilitated diffusion
approaches a maximum rate called the Vmax.

112. 112
3. Osmosis
• It is the power of movement of
H2O from an area of higher
amount of water to an area of
lower amount of water through
the semi permeable membrane.
• The direction of movement of
water is governed by the amount
of osmoticaly active particles
(solutes).
• The pressure that opposes osmosis
of water is called osmotic
pressure
• H2O molecules can not traverse
the lipid bilayer simply.
– Instead they pass through specific
water channels called aquaporins:

113. 2 requirements for osmosis:
Must be difference in solute concentration on the
2 sides of the membrane.
Membrane must be impermeable to the solute.
• Osmotically active solutes:
– Solutes that cannot pass freely through the
membrane.
113

114. Tonicity
Tonicity is defined as the ability of a solution to change
the shape of a cell immersed in it due to changes in the
cell’s water volume.
A solution with the same concentration of non-penetrating
solutes( as those found in cells) are isotonic, i.e., “the
same tonicity.
Cells exposed to such solution retain their normal shape
and exhibit no net gain or loss of water.
Most IV solutions are isotonic (e.g., 0.9% saline or 5%
glucose).
114

115. Direction of osmosis is determined by comparing
total solute concentrations.
A cell is
Hypertonic – if it has more solute, less water than
surrounding solution cell swelling
Hypotonic - if it has less solute, more water than
surrounding solution cell shrinking
Isotonic - equal solute, equal water to surrounding
solution
no change on cell volume
Movement of water out of the cell is exactly115

116. 116
Active transport
 Substances are transported against concentration gradient, up hill
direction.
 Consumes energy in the form of ATP
 Used for the transport of Na+
, K+
, Ca2+
, Fe2+
, H+
, Cl-
1. Primary active transport
- Carrier protein in involved
- Consumes energy from ATP
Common examples
1. Na+ - K+ ATPase
2. Ca2+ ATPase(In the sarcoplasmic reticulum (SR).
3. H+
, k+
-ATPase(proton pump)
 In gastric parietal cells transports H+
into the lumen of the
stomach against its electrochemical gradient.
 It is inhibited by Omeprazole.

117. 117
Active transport: Na+ - K+ ATPase
Na-K-Pump
Na+ - K+ pump is a carrier protein that is
made up of two subunits. It has 3 binding
sites for Na+ inside and 2 binding sites for
K+ on the outside
It pumps 3Na+
outward and 2K+
inward
 It maintains electropositive outside and
electro negation, inside.
Both Na and k are transported against their
electrochemical gradients.
It has ATPase activity inside.
ATP = ADP + ---P + energy.
Energy brings conformational change of
the pump so that Na+ pumped outward and
K+ inward.

118. Importance of Na+
-K+
Pump
Creates an electrical potential across the cell
membrane
118

119. 119
2. Secondary active transport
Carrier protein is
involved
Consumes energy
The movement of a molecule down its concentration gradient(
usually Na+) provides energy for the "uphill" transport of the
other solute(s). i.e. metabolic energy is not directly used but
indirectly from the Na gradient .

120. Binding of more than one molecule in one
direction – symport (cotransport).
e.g. -Na+ glucose cotransport in small intestine
- Na-K-2Cl- cotransport in the kidney.
 If the solutes move in opposite directions across
the cell membranes, it is called countertransport,
exchange, or antiport.
• Examples are Na+
/H+
exchange and Na+
/Ca2+
exchange systems
120

121.  Depending on the number of substances that carriers
transport, carrier proteins may be referred to as (Fig7a):
Uniport carriers: Carry single substance to one
direction
Antiport carriers: Carry two substances in opposite
directions, facilitating exchange of substances
Symport carriers: Carry two substances into the same direction
121

122. 122

123. Vesicular
transport For transport of macromolecules. Two types
1.Endocytosis:-
cells internalize extracelluar material
Engulfing of materials by invaginating the outer part of a
cell membrane until it buds off within the cytoplasm
a.Phagocytosis: cell eating
Is the process by which bacteria, dead tissue, or other material are
engulfed by cells.
substance is a solid
Phagocytic cell(macrophages)
Are almost =to engulfed sub.
123

124. 124
b. Pinocytosis- cell drinking :
 Is a similar process like phagocytosis but
the vesicles are much smaller in size
the substances ingested are in solution.
Invagination occurs into cell and pinches off to form
boundary of an intracellular vesicle, vacuole or
tubule.

125. phagocytosis
pinocytosis
receptor-mediated
endocytosis
fuse with
lysosome for
digestion
non-specific
process
triggered by
molecular signal
125
C. Receptor-mediated endocytosis
Requires the substance to bind to a membrane-
bound receptor

126. 126
2. Exocytosis - “Cell vomiting”
E.g. Releases of NTs, digestive
enzymes and some hormones.

127. 127

128. Resting Membrane Potential
128

129. Tissues which are capable of generation and
transmission of electrochemical impulses
along the membrane
E.g.- nerve and muscle
129
Excitable Tissues

130. • Neurons are functional & structural units of
the nervous system.
• Specialized to conduct information from one
part of the body to another
130

131. 131
Neurons
 A neuron has 3 distinct parts. These
are:
Cell body , Dendrites and Axon
1. Dendrites
Are thin, branched processes whose
main function is to receive incoming
signals.
Convey info towards the soma through
the use of graded potentials.

132. 132
2.Soma( cell body)
 Contains a very active & developed
rough endoplasmic reticulum
which is responsible for the
synthesis of NTs.
– The neuronal RER is referred
to as the Nissl body.
Acts as a receptive service
for interaction with other
neurons.

133. 133
3. Axons:
Convey info away from soma
Originates from axon hillock
( special region of soma)
Transmit APs from the soma
toward the end of the axon where
they cause NT release.
Often branch sparsely which end
in a synaptic knob, which contains
synaptic vesicles(membranous bags
of NTs).
Neuronal Processes…cont’d

134. 134

The tips of most axon terminals swell into synaptic
end bulbs.

These bulb-shaped structures contain synaptic
vesicles, tiny sacs that store chemicals called NTs .

The NT molecules released from synaptic vesicles are
the means of communication at a synapse.

135. 135
Membrane potential
All cells have a voltage difference across their
plasma membrane. This is called membrane
potential.
 Changes in membrane potential are due to
changes in ion movement across the membrane.
The membrane potential (VM) at rest is called resting
membrane potential (RMP).
At rest, there are electropositivity out and

136. An average value for the resting membrane
potential of neurons is -70 mV
That is, the potential inside the fiber is 70mv more
negative than the potential in the ECF on the outside
of the fiber.
136

137. 137
What are the causes of the RMP?
1. An outward diffusion of K+
through K+
leak channels. The
ECF is very high in Na+
while the ICF is very high in K+
. As a
result, K+
is constantly leaking out of the cell.
2. The Na+
/K+
pump is constantly pumping 3 Na+
ions out and 2
K+
ions in for every ATP used. Thus more positive charge is
leaving than entering.
3. There are protein anions (i.e., negatively charged proteins)
within the ICF that cannot travel through the PM.

138. Ion channels
Are integral proteins that span the membrane and,
when open, permit the passage of certain ions.
May be
open (leak channels)
closed(gated channels)
When the channel is open, the ion(s) for which it
is selective can flow through.
When the channel is closed, ions cannot flow
through.
Opening and closing of channels are controlled by
gates 138

139. Four kinds of gated channels
1. Voltage-gated channels
-Are opened or closed by changes in membrane
potential.
2. Chemically gated channels
-Are opened or closed by hormones, second
messengers, or neurotransmitters.
3. Mechanically gated channels- respond to stretching
or other mechanical deformation
4. Thermally gated channels-respond to local changes
139

140. 140
Basic Electrophysiological Terms I
 Stimulus : any change in the environment (internal or external
environmental condition of the cell).
 Excitable cells: cells that generate action potential during
excitation-nerve and muscle cells.
 Excitability: the ability to respond to a stimulus and convert it
into an action potential.
 Threshold stimulus:
Any stimulus strong enough to initiate an action
potential (nerve impulse).
At threshold potential, net inward current becomes
larger than net outward current

141. Depolarization:
- the membrane potential becomes less negative
than the resting potential (-70 mV) (due to the
rapid opening of Na+ channel)
Repolarization:
- when the membrane returns to RMP after
depolarization (due to the slower opening of
K+channels and the closing of Na+ channels).
Hyperpolarization:
- membrane potential become more negative than
the resting potential (due to the out flow of K+
may be so great)
- Undershoot, or hyperpolarizing after potential 141

142. • There are two basic forms of electrical
signals:
1.Graded potentials
 Graded potentials in neurons are depolarization's or
hyperpolarization's that occur in the dendrites and cell body or,,
near the axon terminals(less frequently).
 If stimulus is not strong enough to depolarize the cell to
threshold at the trigger zone, and the graded potential dies out
without triggering an action potential
 stronger initial stimulus that initiates a stronger depolarization142

143. 143
2. Action Potentials
An immediate change of the RMP
in to depolarization that is
followed by re-establishment of
the RMP (re polarization) is called
action potential (nerve impulse).
Action potential is a rapid,
conductive, and reversible
change of the membrane potential
after the cell is stimulated.

144. AP is a brief, rapid, & large changes in membrane
potential that conveys information within the
nervous system and in all types of muscle.
Action potential occurs only if the change in membrane
potential at the axon hillock is above threshold.
 Unlike graded potentials, Aps are conducted, or propagated,
throughout the entire membrane in none decremental fashion
AP has 3 phases
1.Resting phase
2.Depolarization
3.Repolarization
144

145. 145
Action Potentials1. Resting potential: all voltage-
gated channels closed
2. When the change in membrane
potential reaches threshold level
Voltage-gated Na channels open
(Na+ activation gate opens) and
Na influx will occur( b/c Na
conc. outside is more than the
inside) causes
depolarization(This is the rising
phase of an AP)
3. When it reaches +35, Na
channels closes/
inactivated(Na+ inactivation
gate closes)
4. Then Voltage-gated K channels

146. 5. On return to resting potential, Na+ activation gate
closes and inactivation gate opens, resetting
channel to respond to another depolarizing
triggering event
6. Further outward movement of K+ through still-
open K+ channel briefly hyperpolarizes
membrane, which generates after
hyperpolarization.
7. K+ activation gate closes, and membrane returns
to resting potential.
 K+
channels are slow to open and slow to close. This
causes hyperpolarization
146

147.  But ionic distribution has become unequal
 Na/K pump restores Na and K conc. slowly
– By pumping 3 Na ions outward and 2 K ions inward
147

148. 148
Phases of action
potential:
1. Resting phase
2. Depolarization
3. Repolarization

149. 149
2 gates
1. Activation gates
Voltage-dependent
Opens with
depolarization
Fast opening
––
1
Voltage-Gated Na+
Channels

150. 150
2. Inactivation gates
 Voltage-dependent
Closes with depolarization
Slow opening
Voltage-Gated Na+
Channels

151. 151
Voltage-Gated K+
Channels
• One gate
• Voltage-dependent (sensitive to
depolarization)
• Time-dependent
– Opens more slowly than Na
channels
• Slow closing results in
hyperpolarization

152. 152
Refractory Periods

Two types refractory period
1. Absolute refractory period( ARP)
 The period during which a second action potential cannot be
elicited, even with a strong stimulus, is called the ARP
 A new AP cannot occur in an excitable fiber as long as the
membrane is still depolarized from the preceding AP.
 - A Na+
channel cannot be involved in another AP until the
inactivation gate has been reset.

153. ARP…
 The reason for this restriction is
that after the AP is initiated, the
sodium channels become
inactivated and no amount of
excitatory signal applied to these
channels at this point will open
the inactivation gates.
– Because of the closure of
inactivation gate
outside
inside
153

154. 2.Relative refractory period
 Follows ARP
 VG K+
channels are open.
 During this period nerve membrane
can be excited by supra threshold
stimuli
 At the end of repolarization phase
inactivation gate opens and
activation gate closes
 Some Na* channels that have not
quite returned to their resting
position can be opened by stronger
stimulus(Some Na channels still
inactivated will be opened with
greater stimulus.
-90
+35
outside
inside
154

155.  Action potential is an ALL OR NONE EVENT (It happens
completely or it does not occur at all).
 The AP fails to occur if the stimulus is sub threshold in
magnitude (it does not occur at all), OR
 it occurs with constant amplitude regardless of the strength of
the stimulus if the stimulus is at or above threshold
intensity(It happens completely).
Once threshold intensity is reached, a full-fledged
action potential is produced .Further increases in the
intensity of a stimulus produce no increment or other
change in the action potential
155

156. Action potential vs Graded
potentialAction Potential
1. Amplitude is independent
of the initiating event.
2. Action potential can not be
summated
3. Has refractory period
4. Not affected by distance
5. Is depolarization with an
overshoot
6. Initiated by membrane
depolarization.
Graded potential
1. Amplitude varies with
condition of the initiating
event
2. Graded responses can be
summated
3. Has no refractory period
4. Is conducted decrementally,
amplitude decreases with
distance
5. Can be depolarization or
repolarization
6. Initiated by NTs, drugs,
hormones or spontaneously.

157. 157
Conduction of Action Potential
• If an AP is generated at the axon hillock, it will
travel all the way down to the synaptic knob.
• The manner in which it travels depends on whether
the neuron is myelinated or unmyelinated.
Unmyelinated neurons undergo the Sweeping
/continuous conduction/ of an AP whereas
Myelinated neurons undergo jumping /saltatory
conduction/ of an AP.

158. 158
1. Continuous (Sweeping) Conduction
• Occurs in
unmyelinated axons.
• The whole length of
the membrane is
depolarized (AP
occurs on whole length
of the axon membrane)
• Velocity of conduction
is slow
• Consumes large
amount of energy

159. 159
2. Saltatory (Jumping) Conduction
 Occurs in myelinated axons.
 AP occurs at the axon of nodes
of Ranvier.
 Velocity of conduction is faster
(50 times faster than the fastest
unmyelinated fibers).
 Consumes few amount of energy
(Economizes ATP)

160. 160
Saltatory Conduction
 Nodes of Ranvier
• Region of concentrated voltage-gated Na channels.

161. 161
Factors Affecting Rates of AP Conduction
1. presence or absence of myelination
Myelinated axons faster rate of AP conduction than
unmyelinated axons
2. Diameter of fiber (size of nerve fiber)
An axon with a large diameter conduct an AP faster than
axon with a small diameter .
3. Age
Slower in babies and elderly
4. Temperature
When warmed, nerve fibers conduct impulse at highest speed;
when cooled at lower speed.

162. 162
Synapses
- The junction between two cells in which one must be a neuron.
- The region where there is a transfer of message from a neuron
to the next.
There are 3 types of synapses
1. Neuroneuronal junction
-the junction b/n two neuron Presynaptic and postsynaptic neuron
2. Neuromuscular junction
- the junction between neuron & muscle.
3. Neuroglandualr junction
-the junction b/n neuron & gland

163. 163
 There are 3 types of neuroneuronal junctions
1. Axo-dendritic junctions
2. Axo-somatic junctions
3 Axo-axonic junctions

164. 164
Synaptic Transmission
 Two types of synapses:
– Electrical synapses and
– Chemical synapses
1.Electrical synapses
Allow current to flow from one excitable cell to the next
via gap junctions(b/n the pre- and postsynaptic
neurons)
These gap junctions allow the transmission of the
depolarization wave directly from the pre- to the
postsynaptic membrane
Gap junctions are more numerous in smooth muscle and

165. Electrical synapses…
Characteristics
Are extremely rapid,
relatively rare and
have very little physiological
significance .
An AP in one neuron always
leads to an AP in the
connected neuron
165

166. 166
2. Chemical Synapses
More common than electrical synapse
One neuron will transmit impulse to
another neuron or
muscle or by releasing chemicals(NTs)
 gland cell
 Acts slower than electrical synapses
b/c the NT must diffuse across the synaptic cleft to
bind the receptor.

167. 167
Components of AxoSomatic synapse
1. Presynaptic terminal
 contains neurotransmitter
(NT)
1. Synaptic cleft
 contains ECF and Enzymes
1. Postsynaptic neuron
 contains receptor for the
action of NT

168. 168
Mechanism of Chemical Synaptic Transmission
• An AP reaches the presynaptic axon terminal of the
presynaptic cell and causes V-gated Ca2+
channels to open.
• Ca2+
rushes in, binds to regulatory proteins & initiates NT
release by exocytosis.
• NTs diffuse across the synaptic cleft and then bind to specific
receptors on the postsynaptic membrane and initiate
postsynaptic potentials.
• NT-Receptor interaction results in either EPSP or IPSP.

169. 169
Mechanism of Chemical Synaptic Transmission…cont’d
• When the NT-R combination
triggers the opening of ligand
gated Na-channels, this leads to
membrane depolarization,
EPSP.
e.g. Ach on Nicotinic receptor
• When the NT-R combination
triggers the opening of ligand
gated K or Cl-channels, this
leads to membrane
hyperpolarization, IPSP.
e.g. GABA on GABAb receptor

170. 170
Excitatory Vs Inhibitory
Synapses
• Excitatory
- more likely to have action potential of postsynaptic cell
- depolarization
• Inhibitory
• Neurotransmitter binds to receptor, channels for either K or Cl
open
 hyperpolarizes the cell (less likely to have action potential)
• If K channels open
– K moves out -IPSP
• If Cl channels open, either
– Cl moves in -IPSP

171. 171
Excitatory Synapses Inhibitory Synapses

172. 172
Properties of synaptic transmission
Unidirectional conduction
Synaptic delay (0.5 -1.0m/s)
o The time required for the multiple steps in chemical
neurotransmission to occur.
Fatigue
- Decrease in response of postsynaptic neurons after
repetitive stimulation by the presynaptic neurons
possibly resulting from Depletion of NT stores from
the presynaptic terminal.
Synaptic potentiation (facilitation)
- Increase in postsynaptic responses caused by previous post
synaptic stimulation

173. 173
PH
- Alkalosis ↑ Synaptic transmission
- Acidosis ↓ Synaptic transmission
Hypoxia ↓ Synaptic transmission
Drugs
- Caffeine, Theophylline, Theobromine
↑Synaptic transmission
- Strychnine
↑ Synaptic transmission
- Hypnotics, Anesthetics, tranquilizers
↓ Synaptic transmission
Factors Affecting Synaptic transmission

174. THANK YOU!!
174