Physiology Handout made by Mr J Kamaloni from EHC.

1. JOSEPH KAMALONI
Contact: 0977453292
Email: josephkamaloni@yahoo.com

2. ASSESSMENT
60% = Final Exam
Continuous Assessment (CA)
40% = Total CA
25% = Tests
Test One = 12.5% (8th August,2018)
Test Two = 12.5% (6th September,2018)
Assignment = 5% (8th August, 2018)
5% Quiz One
5% Quiz Two

3. INTRODUCTION TO PHYSIOLOGY
What is physiology?
Why learn physiology?
What is the relevance of physiology to health practice?
LESSON 1

4. INTRODUCTION
- Physiology is the science that deals with the
functions of the living organism and its parts
- The term is a combination of 2 words;
physis=nature and logos=study
- As a science, physiology can be subdivided
according to;
1. Type of organism involved, such as human
physiology or plant physiology
2. Organizational level studied, such as molecular
or cellular physiology
3. A specific systematic function being studied such
as neurophysiology, respiratory physiology, or
cardiovascular physiology

5. INTRODUCTION
Characteristics of life
- As opposed to non living organisms, living
organisms have the following characteristics
1. Responsiveness
2. Growth
3. Respiration
4. Digestion
5. Absorption
6. Secretion
7. Excretion
8. Reproduction, etc

6. CELLULAR PHYSIOLOGY

7. CELLULAR PHYSIOLOGY
- A cell is the basic biological and structural unit of
the body consisting of a nucleus surrounded by
cytoplasm and enclosed by a plasma membrane
- Almost all human cells are microscopic in size
- The exact size and shape of specific cells is such
that it suits the function of that cell
- Despite the differences in size and shape, a
typical or composite cell describes the structures
that are found in almost all cells

8. Composite cell...
Cell structure and function
- Each cell is surrounded by a plasma membrane
that separates the cell from its surrounding
- The inside of the cell is composed largely of
cytoplasm which is made up of various organelles
and molecules suspended in a watery fluid called
cytosol or sometimes intracellular fluid
- The nucleus is at the centre of the cell – usually
considered to be part of the cytoplasm

9. Composite cell...
Cell structure and function
- The main cell structures are:
1. The plasma membrane
2. Cytoplasm (including all cell organelles)
3. The nucleus

12. CELLULAR PHYSIOLOGY
Cell membranes
- A typical cell contains a variety of membranes
- The outer boundary of the cell, plasma
membrane, is just one of these membranes
- All organelles are surrounded by membranes
- Membranes are made in such a way that they
are selectively permeable

13. CELLULAR PHYSIOLOGY
Membrane function
- Serves as the boundary of the cell
- Maintains its integrity
- Proteins embedded in the plasma membrane
perform various functions such as markers,
receptors, transport mechanisms

14. CELLULAR PHYSIOLOGY
Cytoplasm and organelles
- Cytoplasm is the gel-like internal substance of
the cell that contains many suspended
structures called organelles

15. CELLULAR PHYSIOLOGY
Cell organelles and their functions
1. Endoplasmic Reticulum (ER)
- Two types, rough and smooth ER
- Ribosome are attached to rough ER
- Function as circulatory system for the cell,
proteins move through the canals of ER
- Ribosome attached to ER synthesise proteins
which enter the canals of ER and move to the
golgi apparatus, some leave the cell
- Smooth ER synthesize certain lipids and
carbohydrates, transport Calcium ions

16. CELLULAR PHYSIOLOGY
2. Ribosomes
- Protein synthesis
- Ribosomes attached to ER synthesise proteins
mainly for export to other areas
- Ribosomes free in the cytoplasm synthesise
proteins for use within that cell

17. CELLULAR PHYSIOLOGY
3. Golgi Apparatus
- Synthesis of carbohydrates
- Processing and packaging of proteins for export
from the cell
4. Lysosomes
- These contain digestive enzymes which break
down defective cell parts and ingested particles

18. CELLULAR PHYSIOLOGY
5. Proteasomes
- Found throughout the cytoplasm
- Responsible for breaking down abnormal and
misfolded proteins from ER, as well as
destroying normal regulatory proteins in the
cytoplasm that are no longer needed
- Unlike lysosomes which destroy large groups
of proteins all at once, proteasomes destroy
protein molecules one at a time

19. CELLULAR PHYSIOLOGY
6. Peroxisomes
- Also contain enzymes
- Detoxify harmful substances that may enter the
cell
- Often seen in kidney and liver cell
- Contain the enzymes peroxidase and catalase
which are important in metabolic reactions
involving hydrogen peroxide ( a chemical toxic to
cells)

20. CELLULAR PHYSIOLOGY
7. Mitochondria
- ATP synthesis
- Called the cell’s power house because of this function
- Found in abundance in cells that need more energy to
do their work, such as muscle cells,
- They increase in number in some cells when energy
consumption increases e.g. Frequent aerobic exercise
can increase the number of mitochondria in skeletal
muscle cells

21. CELLULAR PHYSIOLOGY
8. Nucleus
- One of the largest cell structures
- The functions of the nucleus are primarily
functions of DNA
- DNA molecules dictate both the structure and
function of cells

22. CELLULAR PHYSIOLOGY
9. Cytoskeleton
- Is the cell’s internal supporting framework
- Made up of rigid, rod-like pieces that provide
support and allow movement

23. Plasma Membrane
Structure and Function

24. Outline
• Phospholipid Bilayer
• Fluid Mosaic Model
• Membrane Proteins
• Diffusion
• Facilitated Diffusion
• Osmosis
• Bulk Transport
• Active Transport

25. Characteristics of Plasma Membrane
• The plasma membrane (cell membrane) is made of
two layers of phospholipids
• The plasma membrane has many proteins
embedded in it
• The plasma membrane regulates the entry and exit
of the cell
• Many molecules cross the cell membrane by
diffusion and osmosis
• The fundamental structure of the membrane is
phospholipid bilayer and it forms a stable barrier
between two aqueous compartments
• The proteins present in the plasma membrane, act
as pumps, channels, receptors, enzymes or
structural components

26. Membrane Functions
• Protection
• Communication
• Selectively allow substances in/out
• Respond to environment
• Recognition

27. Plasma Membrane
• Boundary that separates
the living cell from it’s
non-living surroundings.
• Phospholipid bilayer
• Amphipathic - having
both:
hydrophilic
heads
hydrophobic
tails
• ~8 nm thick
• Is a dynamic structure
Phospholipid

28. Fluid-Mosaic Model

29. Proteins—Functions
• Transport
• Receptors
• Enzymes
• Signal Transducers
• Support

30. PROTEINS CAN
MOVE IN THE
MEMBRANE,
TOO!
Plasma Membrane Proteins

31. Channel protein

32. Carrier protein

33. Cell recognition protein

34. Receptor protein

35. Permeability of the Cell Membrane-
Differentially Permeable

36. Permeability of the Cell Membrane

37. Movement of Substances Across
Cell Membranes

38. Definitions
• Solution – mixture of dissolved molecules in a liquid
• Solute – the substance that is dissolved
• Solvent – the liquid in which a solute will dissolve

39. CELLULAR PHYSIOLOGY
- If a cell is to survive, it must be able to move
substances to places where they are needed
- Both within the cell and outside the cell across
the plasma membrane
1. Passive transport processes – no energy is
required, substances move down their
concentration gradient
2. Active transport processes – energy is required,
substances move against their concentration
gradient

40. Passive vs Active Transport

41. CELLULAR PHYSIOLOGY
1. Passive Transport Processes
a) Simple diffusion - movement of particles through a phospholipid
bilayer or through channels from an area of high concentration to
an area of low concentration – i.e. Down the concentration
gradient
b) Osmosis - diffusion of water molecules through a selectively
permeable membrane – there is al least one impermeable solute
c) Channel-mediated passive transport ( facilitated diffusion) –
diffusion of a particle through a membrane by means of channel
structures in the membrane (particles move down their
concentration gradient)
d) Carrier-mediated passive transport – diffusion of particles through
a membrane by means of carrier structures in the membrane
(particles move down their concentration gradient)

42. DIFFUSION
• Diffusion
– the passive movement of molecules from a
higher to a lower concentration until
equilibrium is reached.
–How can we explain diffusion?
–Gases move through plasma membranes by
diffusion.
• Osmosis– A special case of diffusion

43. Process of diffusion

46. Gas exchange in lungs by diffusion

47. Question:
What’s in a Solution?
Answer:
• solute + solvent  solution
• NaCl + H20  saltwater

48. Osmotic Solutions – Tonicity
(tonos = tension)
• Isotonic – equal solute on each side of the membrane
• Hypotonic – less solute outside cell, water rushes into cell and
cell bursts
• Hypertonic – more solute outside cell, water rushes out of cell
and cell shrivels

49. Hypertonic
• A solution with a greater solute concentration
compared to another solution.
3% NaCl
97% H2O
Red Blood Cell
5% NaCl
95% H2O
solution
Which
way
will
the
water
move?

50. Hypotonic
• A solution with a lower solute concentration
compared to another solution.
3% Na
97% H2O
Red Blood Cell
1% Na
99% H2O
solution
Which
way
will
the
water
move?

51. Isotonic
• A solution with an equal solute concentration
compared to another solution.
3% Na
97% H2O
Red Blood Cell
3% Na
97% H2O
solution
Which
way
will
the
water
move?

52. Osmosis
• The movement of water from region of low solute
concentration (high water concentration) to an area of
high solute concentration (low water concentration)
• Driving force is the osmotic pressure caused by the
difference in water pressure

53. ISOTONIC SOLUTION

54. HYPOTONIC SOLUTION

55. HYPERTONIC SOLUTION

56. Carrier Proteins
• Function—Transport. Are specific,
combine with only a certain type of
molecule.
• Types
–Facilitated transport--passive
–Active transport—requires energy

57. Facilitated Transport

58. Active Transport

60. CELLULAR PHYSIOLOGY
2. Active transport processes
a) Pumping – movt of solute particles against their
concentration gradient by means of an energy-
consuming pump structure in the membrane
b) Phagocytosis (endocytosis) – movt of cells or
other large particles into the cell by trapping it in
the section of plasma membrane that pinches
off to form an intracellular vesicle – a type of
vesicle-mediated transport
c) Pinocytosis (endocytosis) – same as
phagocytosis, except it involves movt of fluids
d) Exocytosis – same as phagocytosis, except
substances move out of the cell

61. 61
2. Active Transport
Active transport
• Requires energy – ATP is used directly or
indirectly to fuel active transport
• Able to moves substances against the
concentration gradient - from low to high
concentration
- allows cells to store concentrated substances
• Requires the use of carrier proteins

62. 62
Active Transport
• Carrier proteins used in active transport
include:
-uniporters – move one molecule at a
time
-symporters – move two molecules in
the same direction
-antiporters – move two molecules in
opposite directions

63. 63
Active Transport
Sodium-potassium (Na+-K+) pump
• An active transport antiport mechanism
• Uses an antiporter to move 3 Na+ out of the
cell and 2 K+ into the cell
• ATP energy is used to change the
conformation of the carrier protein
• The affinity of the carrier protein for either
Na+ or K+ changes so the ions can be carried
across the membrane

64. 64
Active Transport
Sodium-potassium (Na+-K+) pump
• Used by animal cells to maintain a high
internal concentration of K+ ions and a low
internal concentration of Na+ ions
• Maintains a concentration gradient that is
used to power many other important
physiological process

65. Fig. 5.15-1

67. Fig. 5.15-3

68. 68

69. The sodium-potassium pump

70. Bulk Transport (Transport in vesicles)
• Polypeptides and proteins, as well as many
other molecules, are too large to be
transported through a membrane by carrier
proteins
• Examples of protein molecule excreted in
vesicle include hormones, lipoproteins, and
neurotransmitters

71. Bulk transport
• There are three main types of bulk flow
(a) EXOCYTOSIS
(b)ENDOCYTOSIS
i. Phagocytosis
ii. Pinocytosis
iii. Receptor mediated endocytosis
(c) TRANCYTOSIS

72. (a) Exocytosis
• Bulk movement of substances out of the cell into
extracellular environment by fusion of secretory
vesicles with the plasma membrane
• The material for secretion is packaged within
intracellular transport vesicles, which move
toward the plasma membrane.
• When the vesicle and plasma membrane come
into contact, the lipid molecules of the vesicle
and plasma membrane bilayers re-arrange
themselves so that the two membranes fuse.

73. (a)Exocytosis
• The fusion of these lipid bilayers requires the
cell to expend energy in the form of ATP
• Following fusion, the vesicle contents are
released to the outside of the cell
• E.g. the release of digestive enzymes by
pancreatic acini into the pancreatic duct for
transport to the small intestine.
• E.g. the release of neurotransmitters into the
synaptic cleft by neurons.

74. (a)Exocytosis
• The fusion of these lipid bilayers requires the
cell to expend energy in the form of ATP
• Following fusion, the vesicle contents are
released to the outside of the cell
• E.g. the release of digestive enzymes by
pancreatic acini into the pancreatic duct for
transport to the small intestine
• E.g. the release of neurotransmitters into the
synaptic cleft by neurons.

75. Exocytosis

76. (b)Endocytosis
• Extracellular macromolecules and large
particulate matter are packaged in a vesicle that
forms at the cell surface for internalization into
the cell
• A small area of plasma membrane folds inward to
form a pocket(invagination)which deepens and
pinches off as the lipid bilayer fuses
• New intracellular vesicle is formed containing
material that was formerly outside the cell

77. Endocytosis
• Three types of endocytosis :
• Phagocytosis
• Pinocytosis
• Receptor-mediated endocytosis

78. (i)Phagocytosis(Cell eating)
• Is a nonspecific process that occurs when a
cell engulfs a large particle external to the cell
by forming membrane extensions
(pseudopodia) or false feet,to surround the
particle
• the particle is engulfed then packaged within an
enclosed membrane sac
• The contents of the vesicle are broken down
(digested) after it fuses with a lysosome which
contains specific digestive enzymes that split
large molecules into smaller ones

79. (i)Phagocytosis
• Process by which bacteria, dead tissue, or
other bits of microscopic material are
engulfed by cells such as the
polymorphonuclear (multi lobed nucleus)
leukocytes of the blood and macrophages in
connective tissue

82. (ii) Pinocytosis(cell drinking)
• Nonspecific process that occurs when the
cell internalizes a very small droplet of ECF
into tiny internal vesicles
• Within the cell, the vesicle fuses with a
lysosome, where enzymes degrade the
engulfed solutes
• The resulting smaller molecules, e.g amino
acids and fatty acids, leave the lysosome
to be used elsewhere in the cell

83. (ii)Pinocytosis
• Occurs in cells of capillary wall, where vesicles
fill with a fluid droplet containing small
solutes from the blood , carry this droplet to
the other side of the cell, and then expel its
contents outside the capillary wall e.g.
transportation of fatty acids from plasma into
adipose tissue(fatty cells).

86. (iii) Receptor mediated endocytosis
• Movement of specific molecules from the
extracellular environment into a cell by way of a
newly formed vesicle
• It begins when molecules in the ECF bind to
their specific integral membrane protein
receptors.
• It is a specific mechanism because endocytosis
is stimulated by binding of the specific
molecules to their specific membrane receptors

87. (iii) Receptor mediated endocytosis
• The receptor proteins then cluster in one
region of the membrane to begin the process
of endocytosis
• The plasma membrane housing the bound
specific molecules from the ECF folds inward
to form a pocket(invagination)
• This membrane pocket deepens and pinches
off as the lipid bilayers fuse.

88. (iii) Receptor mediated endocytosis
• E.g.
• Human cells contain receptors that bind to and
internalize cholesterol, which is required for
new membrane synthesis
• Cholesterol travels in our blood bound to
proteins called low-density lipoproteins (LDLs)
• LDL particles bind to LDL receptors in the
membrane

91. (c) Trancytosis
• This is transport in vesicles which involve successive
movement of a substance into, across, and out of a
cell.
• In this active process, vesicles undergo endocytosis
on one side of a cell, move across the cell, and then
undergo exocytosis on the opposite side
• Occurs most often across the endothelial cells that
line blood vessels and is a means for materials to
move between blood plasma and interstitial fluid e.g.
movement of maternal antibodies cross the placenta
into the fetal circulation.

92. Receptor-mediated Endocytosis

98. BODY FLUID COMPARTMENTS

99. OBJECTIVES
a)Discuss the distribution of total body H2O in the
body
b) List the ionic composition of different body
compartments
c) Explain the principles of measurements
(home work)

100. Body fluid compartments
• About 60 per cent of the adult human body is
fluid, mainly a water solution of ions and other
substances
• Body cells exist in an “internal sea” of
extracellular fluid (ECF)enclosed within the
integument of the animal
• From this fluid, the cells take up O₂ and
nutrients; into it, they discharge metabolic
waste products

101. Divisions of Body fluid compartments
• Body fluids are divided into two major
compartments
(a) Extracellular fluid(ECF)→All fluids outside
cells
(b)Intracellular fluid(ICF)→All fluid inside cells
• The body fluid compartments are separated
from each other by cell membrane highly
permeable to water but not to most of the
electrolytes in the body

102. (a) Extracellular fluid(ECF)
• Account for 20 per cent of the body weight
• Divided into;
(i) Interstitial fluid
• Fluid in the intercellular spaces, i.e. outside
vascular system bathing cells
• Makes 75% of the ECF and 15% of body weight
(i) Circulating blood plasma
• Fluid within vascular system
• 25% of the ECF and 5% of body weight

103. (iii) Transcellular fluid
• Very small special type of ECF, about 1 to 2
litres altogether
• It includes fluid in the synovial, peritoneal,
pericardial, and intraocular spaces, as well as
the cerebrospinal fluid(CSF).

104. (b) Intracellular Fluid (ICF)
• All the fluid inside the body cells
• Account for 40% of total body weight
• The fluid of each cell contains its individual
mixture of different constituents, but the
concentrations of these substances are similar
from one cell to another.
• For this reason, the intracellular fluid of all the
different cells together is considered to be
one large fluid compartment

105. Composition and differences between
ECF and ICF
The ECF contains large amounts of chloride,
sodium and bicarbonate ions, nutrients for
cells,(glucose, fatty acids and amino acids),
carbon dioxide and other cellular products
The ICF contains large amounts of potassium,
magnesium and phosphate ions

106. FLUID COMPARTMENTS
EXTRA CELLUAR INTRA CELLULAR
FLUID (cytosol)FLUID
PLASMA INTERSTITIAL TRANSCELLULAR
FLUID FLUID
1. CSF
2. Intra ocular
3. Pleural
4. Peritoneal
5. Synovial
6. Digestive Secretions

107. Composition and differences
between ECF and ICF
• Body fluid compartmentalization is achieved by
barriers between compartments
• Properties of the barriers determine which
substances can move between the compartments
• ICF and ECF are separated by membranes which
surround the cells
• ECF compartments are separated by cellular walls
of the smallest blood vessels and capillaries

109. Composition and differences between
ECF and ICF
Substance ECF (mmol/kg water) ICF (mmol/kg water)
Na⁺ 142 10
K⁺ 4 140
Ca⁺⁺ 1.3 0.0001
Mg⁺⁺ 1.2 58
Cl⁻ 114 7
HCO₃⁻ 28 10
Phosphate
SO₄⁻

110. Semester assignment question
Describe types of glial cells in details and explain the functions
of each of them
Instructions/format:
- introduction
- main body
-conclusion
- reference list (at least 5, using Harvard referencing style)
- include in-text citations
- not more than three (3) pages (excluding cover page and
reference list)
- should be typed, hand-written will not be accepted
- font size 12, style Times New Roman, spacing 1.5
note: a clean and neat write-up with images will attract more
marks

111. Resting membrane potential

112. OBJECTIVES
• At the end of this lecture you should
be able to describe:
• 1. Ionic distribution across the cell
membrane
• 2. Different types of channels present
in the cell membrane.
• 3. Role of different ions in the
development of Resting Membrane
Potential

113. Excitable Tissues
Definition:
Tissues which are capable of responding to
stimuli to highest degree than other tissues
of the body in the form of electrical signals.
Imp.
Excitable tissues have LOW Threshold of
Stimulation
-Nerve
-Muscle

114. Resting Membrane Potential
• Definition
Potential difference existing across the cell
membrane under resting condition due to
difference in voltage between the inside
and the outside (potential difference)

115. Potentials
• All potentials result from ions moving across
membranes
• Two forces on ions: Diffusion (from high to low
concentration); Electrical (toward opposite charge and
away from like charge).
• Each ion that can flow through channels reaches
equilibrium between two forces
• Equilibrium potential for each ion determined by Nernst
Equation.
• K+ make - potentials; Na+ make + potentials

116. Cell in the body are:
• In electrical disequilibrium – few extra
negative ions inside cells and their matching
positive ions are outside

117. Na+
Cl-
Organic anions
K+
Na+
Cl-
Organic
Anions
K+
Distribution of main ions

118. Na+
Cl-
Organic anions
K+
Na+
Cl-
Organic
Anions
K+
ATPase
3 Na+
2 K+
Electrical disequilibrium across the cell membrane
 membrane potential difference
Anionic proteins
are trapped
Inside the
cell

119. There are more positive charges outside and more negative charges inside
The cell membrane
Is an insulator

120. Na+
Cl-
Organic anions
K+
Na+
Cl-
Organic
Anions
K+
Electrochemical gradient
is a combination of the electrical and chemical gradients

121. Electrochemical gradient
• Electrical gradients and chemical gradients
across the cell membrane
• Electrical force moves K+ into the cell (cell has
more neg. charges)
• Chemical gradient favors K+ to leave the cell
(K+ concentration is low outside)
• These forces reach a steady state

122. Membrane Resting Potential
• The voltage difference across the cell
membrane when there is an electrochemical
gradient at a steady state
• There is a voltage difference between the
inside and the outside (potential difference)

123. Resting Membrane Potential
• Is the difference in electrical charge on the outside and
inside of the plasma membrane in a resting neuron (not
conducting a nerve impulse).
• The outside has a positive charge and the inside has a
negative charge.
• We refer to this as a polarized membrane.
• A resting neuron is at about -70mV
• The resting membrane potential is determined by K+

124. Why is there a difference?
1. There is 30 times more K+ inside the cell than outside
and about 15 times more Na+ outside than inside
2. are also large negatively charged proteins trapped
inside the cell. (This is why it is negative inside.)

126. Would you expect to see so
much K+ inside and so
much Na+ outside?

127. Why so much K+ inside?
• Special protein channels called sodium-potassium
pumps moving 3 Na+ out and bringing 2 K+ back in,
when the cell is at rest.
• In a resting cell there are no open channels for Na+
to easily move back into the cell. However, there are
some K+ channels open at all time.
• Na+ causes the outside to be positive forcing
more K+ into the cell. (Lots of potassium ions inside
the resting cell.)

128. The value for the resting membrane
potential

129. K+ channels are open during the resting
membrane potential.

130. If K+ channels are open.

131. Equilibrium Potential
• The membrane potential when the channels for a
particular ion are open is called the equilibrium
potential for that particular ion.
• At EK+ the rate of ions moving in due to the electrical
gradient equals the rate of ions moving out because
of the concentration gradient.
• EK+ is close to the resting membrane potential

132. Factors that are important for the
equilibrium potential for an ion:
• Only channels for that ion are open
• The charge of the ion
• Concentration of the ion inside the cell
• Concentration of the ion outside the cell

133. At the equilibrium potential for Na+
Artificial cell, Na+ is leaving because the inside became + after the inward
Movement of Na+

134. Currents during resting membrane
potential
K+ outward current is much stronger than Na+ inward current.
Lots of K+ channels are open, few Na+ channels are open at rest.

135. Currents during resting membrane
potential
K+ outward current is much stronger than Na+ inward current.
Lots of K+ channels are open, few Na+ channels are open at rest.

136. The value for the resting membrane
potential

137. ACTION POTENTIAL (AP)

138. outline
• Structure of a nerve cell (neuron)
• definition
• Depolarization
• Repolarization
• Hyperpolarization
• All-or-none principle
• Conduction of electrical impulses (Continuous
and Saltatory conduction)

139. Function of neurons
Primary function of neurons is conduction of
electrical impulses

140. STRUCTURE
They have three distinct
parts:
• (1) Cell body,
• (2) Dendrites, and
• (3) the Axon
The particular type of
neuron that stimulates
muscle tissue is called a
motor neuron.
Dendrites receive
impulses and conduct
them toward the cell
body.

141. Myelinated Axons
The axon is a single long, thin extension
that sends impulses to another
neuron.
They vary in length and are surrounded
by a many-layered lipid and protein
covering called the myelin sheath,
produced by the schwann cells.

144. Action Potential
When the cell membranes
are stimulated, there is a
change in the
permeability of the
membrane to sodium
ions (Na+).
The membrane becomes
more permeable to Na+
and K+, therefore
sodium ions diffuse into the cell down a concentration gradient. The entry of
Na+ disturbs the resting potential and causes the inside of the cell to become
more positive relative to the outside.

145. DEPOLARISATION
As the outside of the cell has
become more positive
than the inside of the cell,
the membrane is now
DEPOLARISED.
When enough sodium ions
enter the cell to
depolarise the membrane
to a critical level
(threshold level) an action
potential arises which
generates an impulse.
In order for the neuron to
generate an action potential
the membrane potential
must reach the threshold of
excitation.

146. AP
Definition: the brief reversal of electric polarization of
the membrane of a nerve cell (neuron) or muscle cell
• In the neuron an action potential produces the nerve
impulse
• In the muscle cell it produces the contraction
required for all movement
• Sometimes called a propagated potential because a
wave of excitation is actively transmitted along the
nerve or muscle fibre

147. AP
• An AP is conducted at a speeds that range from 1 to
100 metres (3 to 300 feet) per second, depending on
the properties of the fibre which is conducting that
AP

148. AP
• Depolarization- a decrease in the potential
difference between the inside and outside of the cell
• Hyperpolarization- an increase in the potential
difference between the inside and outside of the cell
• Repolarization- returning to the RMP from either
direction.

149. Changes in membrane potential
• Resting membrane is polarized
• Depolarization positive charges move in
membrane potential moves toward 0
0
-70
mV
time

150. Changes in membrane potential
• Repolarization membrane potential returns
to polarized state (+ charges move out of the
cell)
• Hyperpolarizationmembrane potential
becomes more negative than at rest (extra +
charges move out of the cell)

151. Before Depolarization

152. Action potentials: Rapid depolarization
• When partial depolarization reaches the activation threshold,
voltage-gated sodium ion channels open.
• Sodium ions rush in.
• The membrane potential changes from -70mV to +40mV.
Na+
Na+
Na+
-
+
+
-

153. Action potentials: Repolarization
• Sodium ion channels close and become refractory.
• Depolarization triggers opening of voltage-gated potassium ion channels.
• K+ ions rush out of the cell, repolarizing and then hyperpolarizing the
membrane.
K+ K+
K+
Na+
Na+
Na+
+
-

154. AP

155. Steps in an AP
1. The neuron gets stimulated (ex. receives a signal from
another neuron). This stimulation causes a change in
the resting membrane potential.
2. If a neuron is stimulated enough the inside of the cell
will reach a critical level called threshold (about -
55mV).
3. At this point sodium ion channels will open.

156. What do you think will
happen now?

157. Depolarization
4. Sodium ions rush into the neuron because of diffusion
forces (high to low) and charge attraction (+ and -).
5. The charge inside the cell eventually reaches about
+30mV. (Relative to the outside of the cell the inside is
now positive and the outside is negative.) At this point
the sodium ion channels close.
• This change in polarization (- inside to +) is called
depolarization (step 4 and 5)

158. Repolarization
6. Next, potassium ion channels open up. This
causes K+ to rush out of the cell
6. As the K+ leaves it causes the inside of the cell
to become negative again (-70mV). This is
referred to as repolarization (step 6 and 7).

160. All-or-None Principle
Throughout depolarisation, the Na+ continues to rush
inside until the action potential reaches its peak and
the sodium gates close.
If the depolarisation is not great enough to reach
threshold, then an action potential and hence an
impulse are not produced.
This is called the All-or-None Principle.

161. All-or-None Principle
• If a stimulus is strong
enough to generate an
action potential (reaches
threshold), the impulse is
conducted along the entire
length of the neuron at the
same strength.

162. All-or-None Principle
• The action potential is “all-or-none”.
• It is always the same size.
• Either it is not triggered at all - e.g. too little
depolarization, or the membrane is
“refractory”;
• Or it is triggered completely.

163. Course of the Action Potential
• The action potential begins with a partial depolarization (e.g. from
firing of another neuron ) [A].
• When the excitation threshold is reached there is a sudden large
depolarization [B].
• This is followed rapidly by repolarization [C] and a brief
hyperpolarization [D].
• There is a refractory period immediately after the action potential
where no depolarization can occur [E]
Membrane
potential
(mV)
[A]
[B] [C]
[D] excitation threshold
Time (msec)
-70
+40
0
0 1 2 3
[E]

164. Refractory Period
There are two types of
refractory period:
Absolute Refractory Period –
Na+ channels are
inactivated and no matter
what stimulus is applied
they will not re-open to
allow Na+ in &
depolarise the membrane to the threshold of an action potential.
Relative Refractory Period - Some of the Na+ channels have re-opened but the
threshold is higher than normal making it more difficult for the activated Na+ channels
to raise the membrane potential to the threshold of excitation.

165. Conduction of the action potential
• Passive conduction will ensure that adjacent
membrane depolarizes, so the action potential
“travels” down the axon.
• But transmission by continuous action potentials is
relatively slow and energy-consuming (Na+/K+
pump).
• A faster, more efficient mechanism has evolved:
saltatory conduction.
• Myelination provides saltatory conduction.

166. Myelination
• Most mammalian axons are myelinated.
• The myelin sheath is provided by oligodendrocytes and
Schwann cells.
• Myelin is insulating, preventing passage of ions over the
membrane.

167. Saltatory Conduction
• Myelinated regions of axon are electrically insulated.
• Electrical charge moves along the axon rather than across the membrane.
• Action potentials occur only at unmyelinated regions: nodes of Ranvier.
Node of Ranvier
Myelin sheath

168. Continuous conduction
• Occurs in unmyelinated neurons.
• It is a step-by-step
depolarization of each adjacent
area of the axon (or dendrite)
membrane.
• It results form one area
depolarizing causing the next
area to reach threshold and
depolarize.

169. Saltatory conduction
• Occurs in myelinated neurons.
• Depolarization only occurs at the nodes of Ranvier.
• The action potential jumps from one node to the next.
• Saltatory conduction will conduct the signal much
faster than continuous conduction.

170. Speed of Nerve Impulses • Imp
• The
inc
con
• In u
me
is s

171. Quiz 1
Duration:6 minutes
1.Explain what happens during the depolarization
phase of an action potential? [3 marks]
2.Explain what happens during the repolarization
phase of an action potential? [3 marks]
3.Explain what happens during the hyperpolarization
phase of an action potential? [2 marks]
4.Explain the meaning of “all-or-none” principle [2 marks]

172. Physiology of synapses,
interneuronal connections

173. What is a synapse?
• A synapse is the junction between 2
neurones.
A specialized junction that transfers
nerve impulse information between
neurons

174. Structure of a synapse

175. The Synapse

177. • A junction that mediates information transfer from one
neuron:
– To another neuron
• Called neuro-synapses or just synapse
– To an effector cell
• Neuromuscular synapse if muscle involved
• Neuroglandular synapse if gland involve
• Presynaptic neuron – conducts impulses toward the
synapse
• Postsynaptic neuron – transmits impulses away from
the synapse
• Two major types:
– Electrical synapses
– Chemical synapses
Synapses

178. Anatomical Types of Synapses
• Axo-dendritic – synapses between the axon of
one neuron and the dendrite of another
• Axo-somatic – synapses between the axon of one
neuron and the soma of another
• Other types of synapses include:
– Axo-axonic (axon to axon)
– Dendro-dendritic (dendrite to dendrite)
– Dendro-somatic (dendrites to soma)

179. Functional classification
or Types of comnication
• A.Chemical synapse
• Almost all synapses used for signal transmission
in the CNS of human being are chemical
synapses.
• First neuron secretes a chemical substance called
neurotransmitter at the synapse to act on receptor
on the next neuron to excite it, inhibit or modify
its sensitivity.

180. The chemical synapse is a specialized junction that
transfers nerve impulse information from a presynaptic
membrane to a postsynaptic membrane using
neurotransmitters.
Axo-dendritic synapse Axo-somatic synanpse Axo-axonic synapse

181. The Chemical Synapse

182. 183
Neurotransmitters
• Properties of neurotransmitters:
1) synthesized in the presynaptic neuron
2) Localized to vesicles in the presynaptic neuron
3) Released from the presynaptic neuron under
physiological conditions
4) Rabidly removed from the synaptic cleft by uptake or
degradation
5) Presence of receptor on the post-synaptic neuron.
6) Binding to the receptor elicits a biological response
R.E.B, 4MedStudents.com, 2003

183. 184
Neurotransmitters found in the
nervous system
• EXCITATORY
• Acetylcholine
• Dopamine
• Histamine
• Nonepinephrine
• Epinephrine
• Glutamate
• Serotonin
• INHIBITORY
• GABA
• Glycine

184. • NT affects the postsynaptic membrane potential
• Effect depends on:
–The amount of neurotransmitter released
–The amount of time the neurotransmitter is
bound to receptors
• The two types of postsynaptic potentials are:
–EPSP – excitatory postsynaptic potentials
–IPSP – inhibitory postsynaptic potentials
Postsynaptic Potentials

185. Excitatory postsynaptic potential (EPSP)
• If positive ion gates open (which allow more Na+ and
Ca2+ to enter than K+ to exit), the membrane becomes
depolarized
• This results in an excitatory postsynaptic potential
(EPSP)
• If the threshold potential is exceeded, an action
potential is generated.

186. Excitatory postsynaptic potentials
(EPSPs)
• Opening of ion channels which leads to depolarization
makes an action potential more likely, hence “excitatory
PSPs”: EPSPs.
– Inside of post-synaptic cell becomes less negative.
– Na+ channels
– Ca2+
inside
outside
Na+ Ca2+
+
-

187. Inhibitory postsynaptic potential (IPSP)
• If K+ or chlorine ion (Cl−) gates open (allowing K+ to
exit or Cl− to enter), the membrane becomes more
polarized (hyperpolarized)
• This results in an inhibitory postsynaptic potential
(IPSP)
• As a result, it becomes more difficult to generate an
action potential on this membrane

188. Inhibitory postsynaptic potentials
(IPSPs)
• Opening of ion channels which leads to hyperpolarization
makes an action potential less likely, hence “inhibitory
PSPs”: IPSPs.
– Inside of post-synaptic cell becomes more negative.
– K+ (NB remember termination of the action potential)
– Cl- (if already depolarized)
K+
Cl- +
- inside
outside

189. • Neurotransmitter binding to a receptor at
inhibitory synapses:
– Causes the membrane to become more permeable to
potassium and chloride ions
– Leaves the charge on the inner surface more negative
(flow of K+ out of the cytosol makes the interior more
negative relative to the exterior of the membrane
– Reduces the postsynaptic neuron’s ability to produce
an action potential
Inhibitory Synapses

190. Inhibition occurs at
synapses where transmitter
release results in the
hyperpolarisation of the
post-synaptic membrane
During hyperpolarisation, the
post-synaptic membrane
potential becomes more negative
than its resting potential and
results from either the efflux of
positive charge or the influx
of negative charge
The nature of the
neurotransmitter determines
the response of the
post-synaptic membrane

191. Muscle Physiology

192. Muscular System Functions
• Body movement (Locomotion)
• Maintenance of posture
• Respiration
– Diaphragm and intercostal contractions
• Communication (Verbal and Facial)
• Constriction of organs and vessels
– Peristalsis of intestinal tract
– Vasoconstriction of b.v. and other structures (pupils)
• Heart beat
• Production of body heat (Thermogenesis)

193. Properties of Muscle
• Excitability: capacity of muscle to respond
to a stimulus
• Contractility: ability of a muscle to shorten
and generate pulling force
• Extensibility: muscle can be stretched back
to its original length
• Elasticity: ability of muscle to recoil to
original resting length after stretched

194. Muscle Tissue
• Skeletal Muscle
• Cardiac Muscle
• Smooth Muscle

195. Types of Muscle
• Skeletal
– Attached to bones
– Makes up 40% of body weight
– Responsible for locomotion, facial expressions, posture, respiratory
movements, other types of body movement
– Voluntary in action; controlled by somatic motor neurons
• Smooth
– In the walls of hollow organs, blood vessels, eye, glands, uterus, skin
– Some functions: propel urine, mix food in digestive tract, dilating/constricting
pupils, regulating blood flow,
– In some locations, autorhythmic
– Controlled involuntarily by endocrine and autonomic nervous systems
• Cardiac
– Heart: major source of movement of blood
– Autorhythmic
– Controlled involuntarily by endocrine and autonomic nervous systems

196. Cardiac Muscle
• Branching cells
• One/two nuclei per cell
• Striated
• Involuntary
• Medium speed contractions

197. Smooth Muscle
• Fusiform cells
• One nucleus per cell
• Nonstriated
• Involuntary
• Slow, wave-like
contractions

198. Skeletal Muscle
• Long cylindrical cells
• Many nuclei per cell
• Striated
• Voluntary
• Rapid contractions

199. Skeletal Muscle
• Produce movement
• Maintain posture & body position
• Support Soft Tissues
• Guard entrance / exits
• Maintain body temperature
• Store nutrient reserves

200. Skeletal Muscle Structure

201. Skeletal Muscle Fiber

202. Sarcomere

205. Z line Z line

206. Sarcomere Relaxed

207. Sarcomere Partially Contracted

208. Sarcomere Completely Contracted

217. Neuromuscular Junction

222. Single Fiber Tension
The all–or–none principle
As a whole, a muscle fiber is
either contracted or relaxed
Tension of a Single Muscle Fiber
Depends on
The number of pivoting cross-
bridges
The fiber’s resting length at
the time of stimulation
The frequency of stimulation
Length–tension relationship
-Number of pivoting cross-
bridges depends on:
amount of overlap between
thick and thin fibers
-Optimum overlap produces
greatest amount of tension:
too much or too little reduces
efficiency
-Normal resting sarcomere length:
is 75% to 130% of optimal length

225. Muscle Contraction Types
Isotonic contraction
Isometric contraction

226. Muscle Contraction Types
Isotonic contraction
Isometric contraction

227. Muscle Contraction Types
Isotonic contraction
Isometric contraction

228. ATP as Energy Source

229. Creatine
Molecule capable of storing ATP energy
Creatine + ATP Creatine phosphate + ADP
ADP + Creatine phosphate ATP + Creatine

230. Metabolism
• Aerobic metabolism
– 95% of cell demand
– Kreb’s cycle
– 1 pyruvic acid molecule  17 ATP
• Anaerobic metabolism
– Glycolysis  2 pyruvic acids + 2 ATP
– Provides substrates for aerobic metabolism
– As pyruvic acid builds converted to lactic acid

234. Muscle Fatigue
• Muscle Fatigue
– When muscles can no longer perform a required activity,
they are fatigued
• Results of Muscle Fatigue
– Depletion of metabolic reserves
– Damage to sarcolemma and sarcoplasmic reticulum
– Low pH (lactic acid)
– Muscle exhaustion and pain

235. Muscle Hypertrophy
• Muscle growth from
heavy training
• Increases diameter of
muscle fibers
• Increases number of
myofibrils
• Increases mitochondria,
glycogen reserves

236. Muscle Atrophy
– Lack of muscle
activity
• Reduces muscle size, tone,
and power

237. Steroid Hormones
• Stimulate muscle growth and hypertrophy
– Growth hormone
– Testosterone
– Thyroid hormones
– Epinephrine

238. Muscle Tonus
• Tightness of a muscle
• Some fibers always contracted

239. Tetany
• Sustained contraction of a muscle
• Result of a rapid succession of nerve impulses

240. Tetanus

241. Refractory Period
• Brief period of time in which muscle cells will
not respond to a stimulus

242. Refractory

243. Skeletal Muscle Cardiac Muscle
Refractory Periods