Download Functions of the Nervous System

Functions of the
Nervous System
NERVOUS SYSTEM
CENTRAL NS
BRAIN
GRAY MATTER
SPINAL CORD
PERIPHERAL NS
CRANIAL
SPINAL
NERVES
NERVES
(12 pairs)
(31 pairs)
AUTONOMIC
NERVES
WHITE MATTER
SYMPATHETIC
NERVES
PARASYMPATHETIC
NERVES
Section 1 General Function of Neuron and Neuroglia
1. Neuron
The structure and
function unit of
nervous system,
including the soma,
axon and dendrites
Classification of neuron by function
Function and Classification of Nerve Fiber
Nerve Fiber: Axons or Dendrites

Function
 Conducting AP
 Nerve
impulse
Characteristics of Excitement
Conduction

Intact

Bidirectional conduction

Not easy to be fatigue

Insulation
The affecting factors of conduction velocity




Diameter of the axon
myelin sheath or no myelin sheath
Thickness of myelin sheath
Temperature
Erlanger /Gasser classification of nerve fibers
Function
Avg. fiber
diameters
(μm)
Avg. cond.
Velocity
(m/s)
Aα
Primary muscle spindle afferents, motor to
skeletal muscle
15
100 (70-120)
Aβ
Cutaneous touch and pressure afferents
8
50 (30-70)
Aγ
motor to muscle spindle
5
20 (15-30)
Aδ
Cutaneous temperature and pain afferents
<3
15 (12-30)
B
Sympathetic preganglionic
3
7 (3-15)
C
Cutaneous pain
postganglionic
1
1 (02-2)
Fiber
types
afferents
sympathetic
Lloyd/Hunt classification of nerve fibers
Group
Function
Avg. fiber
diameters
(μm)
Avg. cond.
Velocity
(m/s)
Ia,Ib
Primary muscle spindle afferents
and afferents from tendon organs
13
75 (70120)
II
Cutaneous mechanoreceptors
9
55 (25-70)
III
Deep pressure sensors in muscle
3
11(10-25)
IV
Unmyelinated pain fibers
1
1
Axoplasmic transport of nerve fiber
Conception:: Axoplasm in axon often keep flow, the
flow of axoplasm play the role to transport material, it is
called axoplasmic transport.
Anterograde axoplasmic transport
~ fast
~ slow
Retrograde axoplasmic transport
dynein
kinesin
Fig. Axopasmic transport
Fig. The method of horseraidish peroxidase
Trophic action of nerve
Conception: Nerve endings often release some trophic
factors, continuously to regulate metabolic activity of the
tissue that controlled by the nerve, then affecting its the
structure, biochemical and physiological changes, this
effect is called trophic action of nerve.
Mechanism: anxoplasmic transport
Phenomenon:
Neurotrophin
Conception: a kind of protein molecules that produced by
the tissue( such as muscle ) and astrocytes, and is the
necessary substance to the neuron survival and growth.
Action mode: Neurotrophin enter into the terminal of axon
by endocytosis, then reach to cell body by retrograde
axoplasmic transport.
Significance: to promote protein synthesis in the cell body.
so play important roles in supporting neuron growth,
development and functional integrity.
Types:
Types of Neuroglia

CNS
 Astrocyte
 Microglia
 Oligodendrocyte
Ependymal Cell
Characteristics of Neuroglia
Quantity
Protrusion:
Gap junction:
Membrane receptor
Membrane potential:
Function of Neuroglia
1.Supporting and inducting neuron migration:
2. Repair and.
3: Immune response.
4. Insulation and barrier：
5. Metabolism and nutrition
6. Keeping the stability of potassium concentration
7.Uptaking and secreting the neurotransmitter
Section 2 synaptic transmission
1. Several important synaptic transmission
*Classical synaptic transmission
*Non-directed synaptic transmission
*Electrical synaptic transmission
2. Neurotransmitter and receptor
*Neurotransmitter
*Receptor
*The main transmitter and receptor system
Classical synaptic transmission
 Synaptic
microstructure
Presynaptic membrane
 Voltage-gated
 Transmitter
Ca2+ channels
vesicles
Synaptic cleft
Postsynaptic
 Receptors
membrane
Classical synaptic transmission
 Classification
of Synapse
Main: A-D、A-S、A-A
Other:
D-D、D-S、D-A、S-D、S-S、S-A
Classical synaptic transmission
 Process
of synaptic transmission
 1. AP
 2.
Ca2+ channel open
 3.
Neurotransmitter release

Exocytosis
 4.
Neurotransmitter + receptor
 5.
Postsynaptic potential (AP)
Electric - Chemical - Electric
Synaptic Transmission
• AP travels down axon to bouton.
• VG Ca2+ channels open.
• Ca2+ activates calmodulin, which activates
protein kinase.
• Protein kinase phosphorylates synapsins.
– Synapsins aid in the fusion of synaptic vesicles.
Synaptic Transmission (continued)
• NTs are released and diffuse across synaptic
cleft.
• NT (ligand) binds to specific receptor proteins
in postsynaptic membrane.
• Chemically-regulated gated ion channels open.
– EPSP: depolarization.
– IPSP: hyperpolarization.
• Neurotransmitter inactivated to end
transmission.
Classical synaptic transmission

Postsynaptic Potential
 Excitatory
postsynaptic potential(EPSP)
 Inhibitory postsynaptic potential(IPSP)
depolarization
hyperpolarization
Excitatory postsynaptic potential (EPSP)
• No threshold.
• Decreases resting
membrane potential.
– Closer to threshold.
• Graded in magnitude.
• Have no refractory
period.
• Can summate.
Inhibitory postsynaptic potential (IPSP)
–No threshold.
–Hyperpolarize
postsynaptic membrane.
–Increase membrane
potential.
–Can summate.
–No refractory period.
Summation of EPSP or IPSP
The processes by which the multiple EPSPs (IPSPs) from
presynaptic neurons summate over time and space are called
temporal and spatial summation
Classical synaptic transmission

Excitation and inhibition of postsynaptic
neuron
Classical synaptic transmission

Modulation of synapse
Regulating NT release
Ca2+ inflow, AP frequency or amplitude, presynaptic
receptor.
Regulating
the uptake and inactivation
Regulating the receptors

Synaptic Plasticity
Classical synaptic transmission
 The
types of synaptic plasticity
Posttetanic
potentiation
Habituation
sensitization
long-term potentiation( LTP)
long-term depression(LTD)
Non-directed synaptic transmission
The postganglionic autonomic
neuron innervate the smooth
muscle and cardiac muscle .
The multiple branches are beaded
with enlargements (varicosity)
that are not covered by Schwann
cells and contain synaptic vesicles;
Fig. : Ending of postganglionic
autonomic neurons on smooth muscle
Electrical synaptic transmission
• Structure: Gap junctions:
– Each gap junction is
composed of 12 connexin
proteins.
– The 12 connexin proteins
form a water channel.
– the charged small
molecules and the local
current are allowed
through.
• Distribution
Electrical synaptic transmission
• Functional characteristics:
– the charged small molecules
and the local current are
allowed through the channel.
– low resistance
– Rapid
– Bidirectional transmission
• significance:
Electrical Synapse
Chemical Synapse
Neurotransmitter
Conception: small molecules that synthesized by the neurons,
can be released from presynaptic terminals into the synaptic
cleft and combined with the receptor of postsynaptic
membrane, cause postsynaptic potential.
Conception of neuromodulator:
In addition to neurotransmitter, neuron can synthesize and
release some chemical substances, they are not directly
transmit information between neurons, but can enhance or
impair neurotransmitter effects, this kind of substance is
called neuromodulator.
Neurotransmitter coexistence :
Two or more than two (including neuromodulator) have
been found in the same neuron, this phenomenon is called
neurotransmitters coexistence.
Neurotransmitter
Neurotransmitter metabolism:
• Synthesis
• Storage
• Release
• Degradation
• Reuptake
Receptor
Subtype of receptor: each receptor has multiple subtypes
Cholinergic receptor：muscarinic receptor (M receptor)
and nicotinic receptor (N receptor), N1 and N2
Adrenergic receptor: α (α1, α2) and β (β1, β2, β3)
Receptor
Presynaptic receptor: also called autoreceptor
Usually, the presynaptic receptor activation can inhibit
neurotransmitter release, realize the negative feedback
control.
noradrenergic receptor
noradrenalin
Receptor
Mechanism of receptor :



Activation : Binding with the neurotransmitter
Signal transduction pathways
Biological effects(changing postsynaptic neuron
activity or making target cells to produce effects
Classification of receptor :


Ion channel receptors
G protein-coupled receptor : most
Main neurotransmitter and receptor system
Acetylcholine(Ach) :
Cholinergic neuron: widely distributed in the CNS
Somatic motor nerve fibers
Cholinergic fiber All autonomic preganglionic fibers
Most parasympathetic postganglionic fibers
A few sympathetic postganglionic fibers
The Life Cycle of Acetylcholine
Choline acetyltransferase
Acetylcholinesterase
Acetylcholine(Ach) receptor:
According to pharmacological properties, acetylcholine
receptor can be divided into two categories
•Muscarinic receptors(M receptor):
M1 to M5, G protein-coupled receptor
•Nicotinic receptors(N receptor):
N1 and N2, ion channel receptor
G protein-coupled receptor
M receptor
Ion channel receptor
N Receptor
Acetylcholine(Ach) receptor:
Receptor
M
N1
N2
Distribution
Autonomic effector
(cardiac muscle，smooth muscle）
Autonomic ganglion
Endplate membrane of
skeletal muscle
Antagonist
Atropin
Curare,
hexamethonium
Curare,
decamethonium
Noradrenaline(NA) or norepinephrine(NE):
•Noradrenergic neuron: In both PNS and CNS
PNS: Smooth muscles, cardiac muscle and glands.
CNS: General behavior.
•Adrenergic fibers: most sympathetic postganglionic fibers
•Adrenergic receptors: G protein-coupled receptor
Distribution and antagonist of adrenergic receptor in
the peripheral nervous system
2
Distribution
Most sympathetic
effector(excitation)
Presynaptic receptor (regulate
neurotransmitter release)
1
cardiac muscle(excitation)
Propranolol, Practolol
2
Most sympathetic
effector(inhibition)
Propranolol, Butaxamine
1
Antagonist
Phentolamine, Prazosin
Phentolamine,Yohimbine
Mechanism of Action ( receptor)
Dopamine and receptor:
•Dopaminergic neuron:
Distributed in the CNS:
•Dopaminergic receptors:
1.Nigrostriatal system, participate in
the movement regulation.
2.Mesolimbic system,participate in the
mental activities.
3.Tuberoinfundibular system, involved
in neuroendocrine regulation.
Serotonin and receptor:
•Serotonergic neuron :
mainly in the raphe nucleus of the lower brainstem
•Receptors:
There are 7 types of serotonin receptor: Serotonin1-7.
There are 14 subtypes of Serotonin receptors:
Histamine and receptor:
•Histaminergic neuron :
mainly in the tuberomammillary nucleus of posterior hypothalamus,
its fiber projection is very wide, almost reach all parts of CNS.
•Receptors:
Histamine system has three kinds of receptors, H1,H2, and H3
All receptors are a G- protein-coupled receptor
Amino acid neurotransmitter and receptor:
•Excitatory amino acid:
Mainly include the glutamate and aspartate, and glutamate is the
major excitatory neurotransmitter in the brain and spinal cord
•Inhibitory amino acid:
Section 3 The basic rule of reflex activity
What is Reflex?
Reflex refers to the regularity response of body to various
stimulus from internal and external environment under
the central nervous system involvement.
Classification of reflex
Classification
Obtain
Quantity
Form
Unconditioned reflex
innate
limited
fixed and low-class
Conditioned reflex
acquire
infinite
Changeable and high-class
Section 3 The basic rule of reflex activity
Central Control of Reflex
Reflex arc: Receptor→Afferent neuron→CNS→ Efferent
neuron→ Effector
Monosynaptic reflex: only a synaptic transmission in the central.
This is the simplest reflected, only monosynaptic reflex in vivo is
tendon reflex.
Polysynaptic reflex: Multiple synaptic transmission in the central.
This is the simplest reflected, Most reflexes are polysynaptic reflex.
The basic process of reflex
Contact Ways of Central Neurons
 Single line connection
 Divergent connection
Contact Ways of Central Neurons
 Convergent connection
 Chain connection
 Recurrent connection
Characters of Central Excitation Conduction
 One-way conduction
 Central delay
 Summation of excitation
.
 Change of excitatory rhythm
 After discharge
 Susceptibility & Fatigue
Characteristics of and nerve fiber conduction and
synaptic transmission
Nerve fiber conduction
Synaptic transmission
Conduction direction
Bidirectional
monodirectional
Time delay
no
have
Potential change
all or nothing
changes of Summation and
rhythm
After discharge
no
have
Integrity
requirement
requirement
Fatigue
not easy
easy
Environmental
factors
insulation
susceptible
Central Inhibition and Facilitation
 Postsynaptic inhibition
*afferent collateral inhibition
After afferent nerve to the central, not only can excite a interneuron
though synaptic connection, but can excite a inhibitory interneuron
through its collateral branch, further inhibit another neuron, this kind
of inhibition is called afferent collateral inhibition.
*recurrent inhibition
When the central neuron is excited, the efferent impulse is conducted
outward along the axon, at the same time, also can excite a inhibitory
interneuron though its collateral branch, then cause the release of
inhibitory neurotransmitter, which inhibit the previously excited
neurons, this kind of inhibition is called recurrent inhibition.
Central Inhibition and Facilitation
 Presynaptic inhibition
 Postsynaptic facilitation
 Presynaptic facilitation