Chapter 2
Cell Physiology
Chunling Jiang(姜春玲)
MD, PhD
Professor of Physiology
Dalian Medical University
§1 The cell and its function
I Membranous Structures of the Cell
1.Most organelles of the cell are covered by membranes
composed primarily of lipids and proteins.
2. These membranes include the cell membrane, nuclear
membrane, membrane of the endoplasmic reticulum, and
membranes of the mitochondria, lysosomes, and Golgi
apparatus.
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Cell membrane lipids
Proteins
42%
Phospholipids 25%
Cholesterol
13%
other lipids
4%
55%
Carbohydrates 3%
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3. Function
(1) function of the lipids
(2) cell membrane proteins
(3) Function of the carbohydrate
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4. structure of the cell membrane
---- the fluid mosaic model (Fig.1)
It is composed of a lipid bilayer of phospholipids molecules,
but with large numbers of protein molecules protruding throug
h the layer( globular masses floats in the lipid bilayer).
Also carbohydrate moieties are attached to the protein molec
ules, the outside of the membrane.
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III Transport of substances through the cell membrane
1. Simple diffusion
(1) Concept ：
(2) Example：
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2. Facilitated diffusion
(1) Concept
◇ Some substances which are insoluble in lipids (water-soluble)
through the cell membrane
◇ Down concentration gradient
(2) Types
carrier-mediated diffusion
channel-mediated diffusion
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① Carrier-mediated diffusion
Concept:
Example:
Features:
② channel-mediated diffusion
Example:
Features:
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3. Active transport
(1) Concept
(2) Features
(3) Types
Primary Active Transport
Secondary Active Transport
(4) Example of Primary Active Transport
Na pump
② Function:
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§3 Electrical phenomena
1.Excitability
(1) Concept:
(2) Signicance:
2. Excitable tissue ------ muscle, nerve or gland
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3.threshold
(1)Exp.
(2)Concept:
(2)significance
4.The relation between the excitability and the threshold
5.subthreshold and superthreshold
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1.Resting potential (RP)
(1) Exp. (Fig.1 and Fig.2)
Animal: Calamary
(2) Concept: Difference in voltage across the membrane of a cell,
with the inside being negative relative to the outside of the cell
at rest.
(3) Normal Value: In neurons, it is usually about -70 mV,
in muscle cells, it is about -90 mV.
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2. Action potential (AP)
(1) Exp. (Fig.3 and Fig.4)
(2) Concept:
rising phase --- depolarization phase
Spike potential
falling phase --- repolarization phase
AP
after- depolarization
After potential
after-hyperpolarization
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The Action Potential
Action Potential: a rapid depolarization and slight reversal
of the usual potential (- 70 mV)
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(3) All or None phenomenon
A stimulus of threshold or suprathreshold intensity applied to a s
ingle nerve fibers, the size, amplitude and velocity of an action
potential are independent of the intensity of the stimulation that
caused it .
A stimulus of threshold or suprathreshold intensity applied to a s
ingle nerve fibers always produces an action potential of
constant amplitude and the amplitude remains constant along
the propagation path. The propagation velocity of a single nerve
fiber also remains constant.
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4. Mechanism of RP genesis
RP and equilibrium potential of K+ (EK).
5.Mechanism of AP genesis
AP and ENa+
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6. Action potential propagation
an unmyelinated axon ------ the Local Circuit Flow
or Local Current theory
(Fig.5)
a myelinated axon -----------the “Saltatory Conduction “ theory
(Fig.6)
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7. Local response
(1)Concept: With a subthreshold stimulus, a localized
membrane depolarization appears at the site of stimulation,
which is called a local response.
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(2)Features:
It is nonpropagated local depolarizaition that only spread a
few mm to either sides of the point of stimulation, which is
called an electronic conduction.
During the local response, the excitability of the nerve is
increased and two local responses , elicited by two
subthreshold stimuli in rapid succession, can summate
and initiate an AP.
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8. Refractory Period:
1.Exp. (Fig.7)
2.Phases
(1)绝对不应期 (Absolute refractory period, ARP)
① Concept:The period during which a second action potential
can not be elicited, even with a strong stimulus, is called the a
bsolute refractory period.
② Features:
③ Significance:
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（2）Relative refractory period, RRP
（3）supernormal period,SNP
（4）Subnormal period
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§4 Neuromuscular transmission
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Neuromuscular Junction (Fig.8)
APs reaches the motor nerve terminals
↓
Ca2+ influx
↓
Liberation of ACh into synaptic cleft
↓
ACh acts on N2 receptors (on muscle cell membrane)
↓
It increases membrane permeability to Na+ and K+
↓
Producing end plate potential
↓
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Generation of AP in the muscle fiber
excitation contraction coupling
Causing muscle contraction
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• ACh is quickly destroyed by cetylcholinesterase
• 终板电位(End-plate potential, EPP)
1. Concept：
2. Features:
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§2 Signaling
I Receptor – channel 偶联系统
Example 1：Neuromuscular junction
Example 2: IPSP
Structure of the Neuromuscular Junction
N-Ach R:
MW:290KD, 5 units,
Neuromuscular Junction (Fig.8)
APs reaches the motor nerve terminals
↓
Ca2+ influx
↓
Liberation of ACh into synaptic cleft
↓
ACh acts on N2 receptors (on muscle cell membrane)
↓
It increases membrane permeability to Na+ and K+
↓
Producing end plate potential
↓
Generation of AP in the muscle fiber
excitation contraction coupling
Causing muscle contraction
II Receptor-G protein-effector enzyme =
Signal transduction mediated by G-protein-linked receptor

Receptor-G protein –AC pathway
Receptor-G protein –PLC pathway

1. receptor =G protein –linked receptor

2.G protein

3. Effector enzyme

4. Pathways
(1)Receptor-G protein –AC pathway
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First messenger
↓
receptor
↓
Gs protein
↓
(+) AC
↓
ATP
cAMP
↓
PKA
↓
Cell’s response
(P30 Fig.2-9)
(2)Receptor-G protein –PLC pathway (P32 Fig.2-10)
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First messenger
↓
receptor
↓
G protein
↓
(+) PLC
↓
PIP2
IP3 + DG
↓
Ca2+
↓
PKC
Ca2+-CaM
↓
Cell’s response
III Signal transduction mediated by enzyme-linked receptor
1.酪氨酸激酶受体（Tyrosine kinase receptor, Tk受体）
( P34 Fig.2-12 )

(1) Function:
(2) Example:

(3)pathway

cell proliferation and differentiation
insulin
NGF,EGF,FGF,GSF
2.鸟苷酸环化酶受体（Guanylyl cyclase receptor,GC受体）

(1)Function: the receptor functions both as a receptor and as a guanylyl
cyclase to catalyse the formation of cyclic GMP
(cGMP) in the cytoplasm.

(2)Example : ANP and NO

(3) Pathway