nervous system (BAI GIANG HE THAN KINH)

Physiology of the nervous system- Neurophysiology
Objectives:
Part 1: basic concepts in nerous system
•The Divisions of the nervous system. Central nervous system (CNS), Peripheral nervous system
(PNS), sensory (afferent) nervous system, motor (efferent) nervous system, somatic nervous
system, autonomic nervous system: sympathetic and parasympathetic nervous system
• Neuron, the structural unit of the nervous system. Types of neurons
• Glial cells and their function
•Resting membrane potential and action potential. Role of Na+, K+ and ion channels in generating
an action potential
• Myelinated and unmyelinated nerve fibers
thuùc ñaåy
•Transmission of nerve impulse in myelinated and unmyelinated axons
• Synapse Daãn truyeàn
• Synaptic transmission of nerve impulse
• Excitatory postsynaptic potential (EPSP). Inhibitory postsynaptic potential (IPSP).
•Spatial and temporal summation of postsynaptic potential
•Neurotransmitters
•Divergent and convergent pathway in the nervous system
Part2: major structures of the central nervous system and their main function
• Spinal cord
• brain stem
•Thalamus and hypothalamus
•Cerebellum
•Cerebrum
Part 3.The autonomic nervous system. Structural organization of sympathetic and
parasympathetic systems and their function


Specific terms and keywords
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Neuron
Neuro– Neurology
– Neurologist
– Neuropathology/neuropathy
– Neurophysiology
– Neuroscience

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Resting membrane potential
Ion channels. Voltage-gated ion channels
Threshold
Action potential/nerve signal/nerve impulse
Action potential propagation/ transmission/conduction
Synapse
Synaptic transmission


Neurons and nervous systems in different phyla
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Nerve net (cnidarians: jellyfish,
anemones,
hydra) neurons are
phaân taùn
dispersed in a thin layer
Centralized and cephalized nervous
system (flatworm, squid)
Haïch
Ganglionic central nervous system
(anthropods, annelids, molluscs)
Hình oáng
Columnar nervous system
(vertebrates)
– Nervous systems of all animals
originate from ectoderm
– Neurons of all animals are quite
similar in their functional properties
– Changes in evolutionary history of
nervous systems: changes in the
complexity of organization of
neurons into systems, rather than
changes in neurons themselves

AHill, Wyse , Andersonn ingly. Aimal physiology . 2nd


The divisions of the nervous system

• central nervous system- CNS
– Brain
– Spinal cord

• peripheral nervous system- PNS
– Nerve fibers: 12 pairs of cranial nerves , 31 pairs of spinal
nerves
– Ganglion/ganglia
– 2 subdivions :
• Afferent /sensory division
• Efferent/motor division:
– somatic motor nervous system: skeletal muscles
– autonomic nervous system-ANS: smooth muscles, glands, heart
muscle
» sympathetic nervous system
» parasympathetic nervous system


Fig.7.1 C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Cellular components of the
nervous system
• Neuron
• Glial cells (70-90%)


Neuron
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Neuron:
– Cell body (soma):
receive information
• nucleus, rough
endoplasmic
reticulum, free
ribosomes (Nissl
bodies) golgi
apparatus,
• Mature neurons
Trung theå
lack centrioles
– Dendrites Sôïi nhaùnh, ñuoâi gai
– Axon: send information
• Some mm ->1m
• Transport materials
to presynaptic
membrane
• neural impulse
transmission:
– Axon hillock
– Axon terminal

•
C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

Mature neurons can not
divide

Structural classification of neurons

C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Classification of neuron types
• Functional classification
– afferent/sensory neuron
– efferent/ motor neuron
– interneuron

• Structural classification
– unipolar neuron
• one axon
• sensory neuron

– bipolar neuron
• one axon and one axon-like dendrite
• Sensory neuron in the eyes, roof of the nasal cavity, and inner ear

– multipolar neuron
• Many dendrites and one axon
• Interneuron and motor neuron


Teỏ baứo than kinh ủeọm

Neuroglia (glial cells)
Rudolf Virchow (1821-1902) coined the term (1846)
Large number (75-90% cells of the CNS, >1/2 brain mass)

Functions:







Structural/physical support to neurons
Metabolic support to neurons
Component of blood-brain barrier
Protection of neurons from pathogens and removal of dead neurons
Production of cerebrospinal fluid
Formation of myelin sheath surrounding axons

Types of glial cells:
+
+
+
+
+

Astrocyte:CNS
Ependymal: CNS: cerebrospinal fluid
Microglia: macrophages differentiated in CNS,
Oligodendrocyte: CNS
Schwann cells: PNS


C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

Astrocyte and microglia

www.physoc.org/.../article.asp?ARTICLE_ID=95

Astrocytes (star-shaped cells)
- metabolic support to neuron: provide lactate and glycogen
- component of the blood–brain barrier
- regulate the external chemical environment of neurons:
removal of excess ions (K+), recycling excess
neurotransmitters
- Direct neuron migration, modulate the growth of dendrites
and axons
-Remove excess neurotransmitters

Microglia


Oligodendrocyte

CNS

Oligodendrocytes:
-Forming myelin sheath
surrounding axons in the CNS
- Cytoplasmic processes of one
cell wrapping/surrounding
several axons

homepage.psy.utexas.edu/.../Cells/Cells.html


Schwann cells

PNS

fig.cox.miami.edu/.../neuro/neurophysiology.htm
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Forming myelin sheath surrounding axons in the PNS
One Schwann cell forms one myelin sheath surrounding a small portion of an axon
Myelinated axons: myelin sheath and nodes of Ranvier


Unmyelinated axons

• a series of Schwann cells cover
the length of several axons
• abutting Schwann cells are
tightly joined -> no Ranvier nodes
•Axons invaginate Schwann cells
plasma membrane
•Axons are connected to extra
cellular fluid through channels


How do neurons function?

• Receive information (dendrites)
•Integrate information (cell body)
• Send information (axon):
+ down along the axon
+ out to other neurons
• information = electrical signal

C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Electrical properties of living cells
-Negatively and positively charged ions
-Negatively and positively organic molecules
-Ion channels
-Permeability of membrane for ions


Localization of ion channels in neurons
• Each region (in a neuron) has specific types of ion channels
• Most of the ion channels are gated (can open or close)
• The opening or closing of ion channels changes the
permeability of the plasma membrane for a specific ion
leading to a change in electrical properties of the cell or the
release of neurotransmitters.
• Leak channels (none gated channels): always open, found
throughout a neuron -> resting membrane potential
• Ligand-gated channels: open or close in response to the
binding of a chemical messenger to a specific receptor in the
plasma membrane

• Voltage-gated channels: open or close in response to
changes in membrane potential:
– voltage-gated Na+ and K+ channels mostly found in axon and axon
hillock
– Ca2+ channels in axon terminals


Resting membrane potential of a neuron
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A cell at rest has a potential difference across its membrane: inside of the
cell is negative charge (relative to the outside): resting membrane potential
(resting Vm)
For a neuron Vm= -70mV
Membrane potential is defined as the potential inside the cell relative to
outside
Neuron communicate by generating electrical signals in the form of
changes in membrane potential. Some of these changes in membrane
potential trigger the release of neurotransmitters which then carries signal
to another cells.
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What causes the resting membrane potential ?
What causes the membrane potential to change ?

What causes the resting membrane potential?
solute

ICF (mM)

ECF (mM)

K+

140

4.0

Na+
Cl-

15.0
4.0

145.0
115.0

• Concentration gradients (created by Na+/K+ pump) of ions
(sodium and potassium ions) across the plasma membrane
• The presence of ion channels (leaking channels) in the
plasma membrane (mainly K+ channels when cells are at
rest)
• The differences in the permeability of the plasma membrane

to these 2 ions
• Chemical and electrical forces for moving sodium and
potassium ions across the plasma membrane


Establishing a steady-state resting membrane potential

Fig.7.8 C.L. Standfield.2011. Principles of Human Physiology, 4th edition.


Nernst Equation :
to calculate the equilibrium potential across a cell’s
membrane for one ion given its concentrations inside and
outside the cell are known

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C.L. Standfield.2011. Principles of Human Physiology, 4th edition.

Ei: equilibrium potential
for ion I
Z: the valence of the ion
(I)o: Concentration of I
ion outside the cell
(I)i: concentration of I ion
inside the cell

Goldman-Hodgkin-Katz (GHK) Equation
To calculate membrane potential in case only K+ and Na+ are
permeant and their concentration inside and outside the cell
are known


Electrical signal: changes in membrane
potential
Gated-ion channels open or close in
response to a stimuli -> change the
membrane permeability for ions
-> change in membrane potential


Change in membrane potential is defined based on the
direction of change relative to the resting membrane potential
• hyperpolarization
a change to more
negative value:
• Depolarization: a
change to less
negative/positive
value
• Repolarization:
potential returns
to the resting
membrane
potential following
a depolarization

AHill, Wyse , Andersonn. Aimal physiology . 2nd e,2008.