Functions of the Nervous System

NERVOUS SYSTEM CENTRAL NS PERIPHERAL NS GRAY MATTER WHITE MATTER 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 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 Fiber types 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 afferents sympathetic postganglionic 1 1 (02-2)

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 (70-120) II Cutaneous mechanoreceptors 9 55 (25-70) III Deep pressure sensors in muscle 3 11(10-25) IV Unmyelinated pain fibers 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

Fig. Axopasmic 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 CNS Astrocyte Microglia Oligodendrocyte

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 Ca2+ channels Transmitter vesicles Synaptic cleft Postsynaptic membrane Receptors

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 : Classification 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 All autonomic preganglionic fibers Most parasympathetic postganglionic fibers A few sympathetic postganglionic fibers Cholinergic fiber

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: Distribution Antagonist M Autonomic effector (cardiac muscle，smooth muscle） Atropin N1 Autonomic ganglion Curare, hexamethonium N2 Endplate 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 Distribution Antagonist 1 Most sympathetic effector(excitation) Phentolamine, Prazosin 2 Presynaptic receptor (regulate neurotransmitter release) Phentolamine,Yohimbine 1 cardiac muscle(excitation) Propranolol, Practolol 2 Most sympathetic effector(inhibition) Propranolol, Butaxamine

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:

Changeable and high-class 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

Nerve fiber conduction Synaptic transmission Environmental factors 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 Integrity 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