Functions of the

Nervous System

NERVOUS SYSTEM

CENTRAL NS PERIPHERAL NS

BRAIN SPINAL CORD CRANIAL SPINAL AUTONOMIC

NERVES NERVES NERVES (12 pairs) (31 pairs)

SYMPATHETIC PARASYMPATHETIC NERVES NERVES

GRAY MATTER WHITE MATTER

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

Function

Conducting AP

Nerve impulse

Nerve Fiber: Axons or Dendrites

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

Fiber types

FunctionAvg. fiber diameters (μm)

Avg. cond. Velocity (m/s)

Aα Primary muscle spindle afferents, motor to skeletal muscle

15100 (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 afferents sympathetic postganglionic

1 1 (02-2)

Erlanger /Gasser classification of nerve fibers

Group FunctionAvg. fiber diameters (μm)

Avg. cond. Velocity (m/s)

Ia,IbPrimary muscle spindle afferents and afferents from tendon organs 

1375 (70-120)

II Cutaneous mechanoreceptors 

9 55 (25-70)

III Deep pressure sensors in muscle 

3 11(10-25)

IV Unmyelinated pain fibers 1 1

Lloyd/Hunt classification of nerve fibers

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

Fig. Axopasmic transport Fig. The method of horseraidish peroxidase

dynein

kinesin

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 transportPhenomenon:

Trophic action of nerve

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:

Neurotrophin

Types of Neuroglia

CNS

Astrocyte

Microglia

Oligodendrocyte

Ependymal Cell

Characteristics of Neuroglia

Quantity

Protrusion:

Gap junction:

Membrane receptor

Membrane potential:

Function of Neuroglia1.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 Ca2+ channels Transmitter vesicles

Synaptic cleftPostsynaptic membrane

Receptors

Classification of SynapseMain: 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 transmission1. AP

2. Ca2+ channel open

3. Neurotransmitter release Exocytosis

4. Neurotransmitter + receptor

5. Postsynaptic potential (AP)

Classical synaptic transmission

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.

Postsynaptic PotentialExcitatory postsynaptic potential(EPSP)Inhibitory postsynaptic potential(IPSP)

Classical synaptic transmission

depolarization hyperpolarization

• No threshold.• Decreases resting

membrane potential.– Closer to threshold.

• Graded in magnitude.• Have no refractory

period.• Can summate.

Excitatory postsynaptic potential (EPSP)

–No threshold.

–Hyperpolarize postsynaptic membrane.

–Increase membrane potential.

–Can summate.

–No refractory period.

Inhibitory postsynaptic potential (IPSP)

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

Excitation and inhibition of postsynaptic neuron

Classical synaptic transmission

Classical synaptic transmission Modulation of synapse

Regulating NT releaseCa2+ 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

NeurotransmitterConception: 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.

NeurotransmitterNeurotransmitter metabolism:

• Synthesis

• Storage

• Release

• Degradation

• Reuptake

ReceptorSubtype of receptor: each receptor has multiple subtypesCholinergic receptor ： muscarinic receptor (M receptor) and nicotinic receptor (N receptor), N1 and N2 Adrenergic receptor: α (α1, α2) and β (β1, β2, β3)

ReceptorPresynaptic receptor: also called autoreceptor

Usually, the presynaptic receptor activation can inhibit neurotransmitter release, realize the negative feedback control.

noradrenergic receptor

noradrenalin

ReceptorMechanism of receptor :

Classification of receptor :

Activation : Binding with the neurotransmitter Signal transduction pathways Biological effects(changing postsynaptic neuron

activity or making target cells to produce effects

Ion channel receptors G protein-coupled receptor : most

Main neurotransmitter and receptor system

Acetylcholine(Ach) :

Cholinergic fiber

Somatic motor nerve fibersAll autonomic preganglionic fibersMost parasympathetic postganglionic fibersA few sympathetic postganglionic fibers

Cholinergic neuron: widely distributed in the CNS

The Life Cycle of Acetylcholine

Choline acetyltransferase

Acetylcholinesterase

Acetylcholine(Ach) receptor:

•Muscarinic receptors(M receptor):

M1 to M5, G protein-coupled receptor

•Nicotinic receptors(N receptor):

N1 and N2, ion channel receptor

According to pharmacological properties, acetylcholine receptor can be divided into two categories

G protein-coupled receptor

M receptor

Ion channel receptorN Receptor

Acetylcholine(Ach) receptor:

Receptor Distribution Antagonist

MAutonomic effector

(cardiac muscle ， smooth muscle）

Atropin

N1 Autonomic ganglion Curare,

hexamethonium

N2Endplate membrane of

skeletal muscle

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

1Most sympathetic

effector(excitation)Phentolamine,

Prazosin

2

Presynaptic receptor (regulate neurotransmitter

release)

Phentolamine,Yohimbine

1 cardiac muscle(excitation)Propranolol,

Practolol

2Most sympathetic effector(inhibition)

Propranolol, Butaxamine

Distribution Antagonist

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

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

What is 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

Reflex arc: Receptor→Afferent neuron→CNS→ Efferent neuron→ Effector

Central Control of Reflex

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

Nerve fiber conduction Synaptic transmission

Conduction direction Bidirectional monodirectional

Time delay no have

Potential change all or nothingchanges of Summation and

rhythm

After discharge no have

Integrity requirement requirement

Fatigue not easy easy

Environmental factors

insulation susceptible

Characteristics of and nerve fiber conduction and synaptic transmission

Central Inhibition and Facilitation Postsynaptic inhibition*afferent collateral inhibitionAfter 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 inhibitionWhen 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