No. 21No. 21

1. Introduction of Nervous System1. Introduction of Nervous System

2. Spinal Cord (1)2. Spinal Cord (1)

PART THE ⅥPART THE ⅥNERVOUS SYSTEMNERVOUS SYSTEM

Chapter 1 IntroductionChapter 1 Introduction

The nervous system is a master system in The nervous system is a master system in the living body; it regulates and integrates the living body; it regulates and integrates the activities of all the bodily systems for the activities of all the bodily systems for the benefit of the organism as a whole.the benefit of the organism as a whole.

ⅠⅠ.. Divisions of the Nervous Divisions of the Nervous SystemSystem

The nervous system consists of central The nervous system consists of central part (central nervous system) and part (central nervous system) and peripheral part (peripheral nervous peripheral part (peripheral nervous system).system).

The The central nervous systemcentral nervous system is is composed of brain and spinal cord.composed of brain and spinal cord.

The The peripheral nervous systemperipheral nervous system includes cranial nerves (12 pairs), spinal includes cranial nerves (12 pairs), spinal nerves (31 pairs), and visceral nerves.nerves (31 pairs), and visceral nerves.

The somatic and visceral nervesThe somatic and visceral nerves:: According to the functions of organs According to the functions of organs

innervated by the nerves, the peripheral innervated by the nerves, the peripheral nervous system is also divided the nervous system is also divided the somatic nervessomatic nerves and and visceral nervesvisceral nerves..

The somatic nerves supply the body The somatic nerves supply the body surface, bones, joints, and skeletal muscle.surface, bones, joints, and skeletal muscle.

The visceral nerves are distributed in the The visceral nerves are distributed in the viscera, heart, vessels, and smooth viscera, heart, vessels, and smooth muscles.muscles.

In the peripheral nerves (the somatic and visceral In the peripheral nerves (the somatic and visceral nerves), there are two nerve fibers called nerves), there are two nerve fibers called afferent nervesafferent nerves ( (sensory nervessensory nerves)) and and efferent nervesefferent nerves ( (motor nervesmotor nerves))..

The efferent (motor) part of visceral nerves is The efferent (motor) part of visceral nerves is called the called the vegetative nervous systemvegetative nervous system or or autonomic nervous systemautonomic nervous system..

The The autonomic nervous systemautonomic nervous system innervates the innervates the smooth muscle and the glands of viscera, and the smooth muscle and the glands of viscera, and the smooth muscle of blood vessels, together with smooth muscle of blood vessels, together with the cardiac muscle, and further divided into the cardiac muscle, and further divided into sympathetic nervesympathetic nerve and and parasympathetic parasympathetic nervenerve..

ⅡⅡ. Organization of nervous system. Organization of nervous system

The nervous system is composed of nervous tiThe nervous system is composed of nervous tissue that consists of billions of nerve cells (ssue that consists of billions of nerve cells (neneuronsurons) and supported by a special variety of c) and supported by a special variety of connective tissue known asonnective tissue known as neuroglianeuroglia..

ⅠⅠ) ) NeuronsNeurons The neurons are independent structural The neurons are independent structural

unit of the nervous system and are unit of the nervous system and are functional specialized for reception, functional specialized for reception, integration, and transmission of coded integration, and transmission of coded information.information.

1. Morphology1. Morphology Each neuron possesses a nucleated Each neuron possesses a nucleated cell cell

bodybody and two types of and two types of processesprocesses; an ; an axon which conducts impulse away from axon which conducts impulse away from the cell body and one or morethe cell body and one or more dendritedendrite which conduct impulses towards the cell which conduct impulses towards the cell body.body.

2. Structure2. Structure ① ① Cell bodyCell body Like other cells, the cell body of the neuron serves as Like other cells, the cell body of the neuron serves as

metabolic center of the entire unit and consists of a lametabolic center of the entire unit and consists of a large, pale rge, pale nucleusnucleus and and cytoplasmcytoplasm, , organellesorganelles, , cell mecell membranembrane, and , and Nissl bodyNissl body..

Nissl body and neurofibril:Nissl body and neurofibril: The organelles contained within the cytoplasm are coThe organelles contained within the cytoplasm are co

mmon to other cell in the body, but there are abundammon to other cell in the body, but there are abundant granular endoplasmic reticulum which constitutes tnt granular endoplasmic reticulum which constitutes the he Nissl bodyNissl body, a protein synthesis apparatus., a protein synthesis apparatus.

NeurofibrilsNeurofibrils have role of supporting neuron and invol have role of supporting neuron and involved in transmission of substance in the cell.ved in transmission of substance in the cell.

② ② ProcessesProcesses TheThe axonaxon:: It is a slender process. It may transfer the nerve impulIt is a slender process. It may transfer the nerve impul

ses from the beginning part (axon hillock) to the end ses from the beginning part (axon hillock) to the end (axon terminal). Because the axoplasm does not cont(axon terminal). Because the axoplasm does not contain RNA and ribosome, proteins synthesis cannot take ain RNA and ribosome, proteins synthesis cannot take place in the axon. All axonal proteins, therefore, must place in the axon. All axonal proteins, therefore, must come from the cell body, and the products are transpcome from the cell body, and the products are transported by a perpetual axoplasmic motion. Some organorted by a perpetual axoplasmic motion. Some organelles, structural protein and neurotransmitters contaielles, structural protein and neurotransmitters contained within cytoplasm are carried by axoplasmic flow ned within cytoplasm are carried by axoplasmic flow which moves in both directions and with varying velocwhich moves in both directions and with varying velocity. This phenomenon is called ity. This phenomenon is called axoplasmic transportaxoplasmic transport..

The The dendritesdendrites:: The main or primary dendrites arise from the cThe main or primary dendrites arise from the c

ell body and then branch repeatly in a tree –likell body and then branch repeatly in a tree –like manner to form a complex dendrite tree. Dee manner to form a complex dendrite tree. Dendrite spines are on the dendrites, which are sndrite spines are on the dendrites, which are structures specialized for synaptic contact, recetructures specialized for synaptic contact, receiving nerve impulses.iving nerve impulses.

3. Classification of neurons3. Classification of neurons ① ①According to the number of their processes, they are According to the number of their processes, they are

described as:described as: Unipolar neuron,Unipolar neuron, Bipolar neuron,Bipolar neuron, Multipolar neuron.Multipolar neuron. ② ②According to their functions and the direction of tranAccording to their functions and the direction of tran

sportation, they are described as:sportation, they are described as: Sensory (afferent) neuronSensory (afferent) neuron Motor (efferent) neuronMotor (efferent) neuron Intermediate (association) neuron.Intermediate (association) neuron.

4. Nerve fiber4. Nerve fiber The nerve fibers are the longer processes The nerve fibers are the longer processes

of neurons which are enveloped by of neurons which are enveloped by myelin sheathmyelin sheath and nerve membrane. and nerve membrane.

5. The synapses5. The synapses Within the nervous system impulses are conducted froWithin the nervous system impulses are conducted fro

m one part to another along a chain of neurons. The tm one part to another along a chain of neurons. The terminal arborizations of the axon of one neuron ramiferminal arborizations of the axon of one neuron ramify in close contact with the cell body or dendrites, less y in close contact with the cell body or dendrites, less frequently with axonic terminals of many others. Thesfrequently with axonic terminals of many others. These structural and functional areas of contact are termee structural and functional areas of contact are termed d synapsessynapses..

Chemical synapse transports the impulses through thChemical synapse transports the impulses through the chemical substancee chemical substance neurotransmitterneurotransmitter. The chemic. The chemical synapse is the most common type in the mammaliaal synapse is the most common type in the mammalian nervous system.n nervous system.

The chemical synapse includes three parts:The chemical synapse includes three parts: Presynaptic element,Presynaptic element, Postsynaptic element.Postsynaptic element. Synaptic cleft.Synaptic cleft. The presynaptic element contains numerous sThe presynaptic element contains numerous s

ynaptic vesicles in which the neurotransmitter ynaptic vesicles in which the neurotransmitter is present and presynaptic membrane.is present and presynaptic membrane.

When an impulse arrives at the presynaptic eleWhen an impulse arrives at the presynaptic element, the neurotransmitter diffuse cross the sment, the neurotransmitter diffuse cross the synaptic cleft and bind to the receptor moleculynaptic cleft and bind to the receptor molecules in the postsynaptic membrane. As a result, tes in the postsynaptic membrane. As a result, the postsynaptic neuron is activated and impulhe postsynaptic neuron is activated and impulse is conducted from one neuron to the others.se is conducted from one neuron to the others.

ⅡⅡ). Neuroglia). Neuroglia It includes the central and peripheral nervous systemiIt includes the central and peripheral nervous systemi

c neuroglia.c neuroglia. 1. In the central nervous system1. In the central nervous system The neuroglial cells is the interstitial cells or supportinThe neuroglial cells is the interstitial cells or supportin

g cells.g cells. According to their shape, they are divided into four tyAccording to their shape, they are divided into four ty

pes, i.e.:pes, i.e.: MacrogliaMacroglia, , includingincluding AstrocytesAstrocytes,, OligodendrocyteOligodendrocyte,,MicrogliaMicroglia,, Ependymal cell Ependymal cell.. 2. In the peripheral nervous system2. In the peripheral nervous system Schwann cellSchwann cell,,Satellite cellSatellite cell..

ⅢⅢ. Activated Way of Nervous . Activated Way of Nervous SystemSystem

The way of activity of nervous system is The way of activity of nervous system is reflex.reflex.

ReflexReflex:: A reflex is an automatic, stereotyped A reflex is an automatic, stereotyped

reaction, such as movement, that is reaction, such as movement, that is performed without conscious volition in performed without conscious volition in response to an appropriate stimulus.response to an appropriate stimulus.

The basic structure is reflex arc.The basic structure is reflex arc.

Reflex ArcReflex Arc:: The reflex arc, a linkage of afferent and efferent neuroThe reflex arc, a linkage of afferent and efferent neuro

ns, is defined as the entire neural pathway that is involns, is defined as the entire neural pathway that is involved in a reflex. The effector, e. g. a muscle, is supplied ved in a reflex. The effector, e. g. a muscle, is supplied by an efferent nerve, and between the afferent and effby an efferent nerve, and between the afferent and efferent components there may be one or more connecterent components there may be one or more connector or interneuron. These elements-or or interneuron. These elements-afferent neuronsafferent neurons,, iinterneuronsnterneurons and and efferentefferent neuronsneurons-are the basis of re-are the basis of reflex nervous activities.flex nervous activities.

Receptor→afferent (sensory) nerve →center→efferent Receptor→afferent (sensory) nerve →center→efferent (motor) nerve→effector. (motor) nerve→effector.

3. Gray matter and white matter3. Gray matter and white matter Gray matterGray matter:: In the CNS the part that contains In the CNS the part that contains

aggregations of nerve cell bodies aggregations of nerve cell bodies embedded in a network of delicate nerve embedded in a network of delicate nerve processes is known as gray matter, it has processes is known as gray matter, it has a gray color during the fresh condition.a gray color during the fresh condition.

White matterWhite matter:: In the CNS the part that contains mainly In the CNS the part that contains mainly

bundles of nerve fibers are white matter bundles of nerve fibers are white matter and the white color is due to a rich content and the white color is due to a rich content of fatty myelin sheath.of fatty myelin sheath.

4. Cortex and medullary substance4. Cortex and medullary substance CortexCortex:: The cortex is the outermost layer of gray mattThe cortex is the outermost layer of gray matt

er in the cerebral hemispheres or in the cerebeer in the cerebral hemispheres or in the cerebellum. The cell bodies in the cortex are arrangellum. The cell bodies in the cortex are arranged in more or less well-defined laminae or layerd in more or less well-defined laminae or layers.s.

Medullary substanceMedullary substance:: It a central core of white matter beneath the cIt a central core of white matter beneath the c

ortex of the cerebrum and cerebellum.ortex of the cerebrum and cerebellum.

ⅣⅣ. Some Usual Terminology of . Some Usual Terminology of nervous systemnervous system

The neuroanatomical terms in common usage are as fThe neuroanatomical terms in common usage are as follows:ollows:

1. Nucleus and ganglion1. Nucleus and ganglion NucleusNucleus:: Nerve cells with the same shape, function and connecNerve cells with the same shape, function and connec

tions within the central nervous system (CNS) are groutions within the central nervous system (CNS) are grouped together into nucleus.ped together into nucleus.

The nucleus may originate, relay, modify, or amplify nThe nucleus may originate, relay, modify, or amplify neural signal within the nervous system.eural signal within the nervous system.

GanglionGanglion:: Nerve cells with the same shape, function and connecNerve cells with the same shape, function and connec

tions outside the CNS often are grouped together into tions outside the CNS often are grouped together into ganglion.ganglion.

2. Nerve and nerve fiber2. Nerve and nerve fiber Nerve fiberNerve fiber:: Nerve fibers are mainly axons, some of which are enveNerve fibers are mainly axons, some of which are enve

loped by myelin sheath. loped by myelin sheath. FasciculusFasciculus: In CNS, a distinct : In CNS, a distinct collection of nerve fibers with common origins, destincollection of nerve fibers with common origins, destinations and functions are referred to fasciculus, or ations and functions are referred to fasciculus, or tractractt..

NerveNerve:: In the peripheral nervous system (PNS), the nerve fibeIn the peripheral nervous system (PNS), the nerve fibe

rs are grouped into bundles to form the nerve trunk. Mrs are grouped into bundles to form the nerve trunk. Most of nerves have a whitish appearance because of thost of nerves have a whitish appearance because of their myelin content.eir myelin content.

Chapter 2 The Central Chapter 2 The Central Nervous SystemNervous System

Section 1 The Spinal CordSection 1 The Spinal Cord

Ⅰ Ⅰ. Location and Length. Location and Length The spinal cord, a long cylindrical structure, is The spinal cord, a long cylindrical structure, is

located in the vertebral canal and invested by located in the vertebral canal and invested by meninges.meninges.

It extends from the foramen magnum, where it It extends from the foramen magnum, where it continues with the medulla oblongata, to the lcontinues with the medulla oblongata, to the lower border of the first lumbar vertebra, abouower border of the first lumbar vertebra, about 40t 40 ～～ 45 cm in length. Diameters of the spinal 45 cm in length. Diameters of the spinal cord are not equal at various levels.cord are not equal at various levels.

Ⅱ Ⅱ. External Features. External Features Ⅰ Ⅰ) Two enlargements and conus medullaris) Two enlargements and conus medullaris The spinal cord displays two prominent enlargements.The spinal cord displays two prominent enlargements. The The cervicalcervical enlargementsenlargements,, The The lumbosacral enlargementslumbosacral enlargements.. Each enlargement associates with the nerve roots that Each enlargement associates with the nerve roots that

make up the brachial plexus and lumbosacral plexus, make up the brachial plexus and lumbosacral plexus, which innervate the upper and lower extremities, respwhich innervate the upper and lower extremities, respectively. Caudal to the lumbosacral enlargement, the ectively. Caudal to the lumbosacral enlargement, the spinal cord tapers gradually and becomes the conical spinal cord tapers gradually and becomes the conical termination known as termination known as conus medullarisconus medullaris..

Ⅱ Ⅱ) Film terminale and cauda equina) Film terminale and cauda equina A condensation of pia mater forms the A condensation of pia mater forms the film terminalefilm terminale

which descends the conus medullaris to the level of thwhich descends the conus medullaris to the level of the second sacral vertebra, from here it is enveloped by e second sacral vertebra, from here it is enveloped by the dura mater and continues to the posterior surface the dura mater and continues to the posterior surface of the coccyx.of the coccyx.

Since the spinal cord is markedly shorter than the vertSince the spinal cord is markedly shorter than the vertebral column, the lumbosacral roots descend for varyiebral column, the lumbosacral roots descend for varying distances within the terminal cisterna before reachng distances within the terminal cisterna before reaching their corresponding intervertebral foramina. They ing their corresponding intervertebral foramina. They form a divergent sheaf of spinal roots surrounding the form a divergent sheaf of spinal roots surrounding the film terminale, and is called the film terminale, and is called the cauda equinacauda equina..

Ⅲ Ⅲ) Fissure and sulci) Fissure and sulci Six longitudinal sulci are shown on the surface of the Six longitudinal sulci are shown on the surface of the

naked spinal cord.naked spinal cord. TheThe anterior median fissureanterior median fissure is on the median line of t is on the median line of t

he anterior surface, where the anterior spinal artery ahe anterior surface, where the anterior spinal artery and the companion vein are lodged.nd the companion vein are lodged.

On the posterior surface there is the shallow On the posterior surface there is the shallow posterioposterior median sulcusr median sulcus. .

On each side of the posterior median sulcus there is a On each side of the posterior median sulcus there is a pair of pair of posterior lateral sulciposterior lateral sulci into which filaments of t into which filaments of the he posterior rootsposterior roots enter the spinal cord and a pair of enter the spinal cord and a pair of posterior spinal arteries and veins run along the sulci.posterior spinal arteries and veins run along the sulci.

On each side of anterior median fissure there is a pair On each side of anterior median fissure there is a pair of of anterolateral sulcianterolateral sulci which mark the exit of the anter which mark the exit of the anterior root fibers.ior root fibers.

ⅢⅢ. External segments. External segments Thirty-one pairs of spinal nerves arise from the spinal Thirty-one pairs of spinal nerves arise from the spinal

cord and pass through the intervertebral froamina betcord and pass through the intervertebral froamina between adjacent vertebrae of the vertebral column.ween adjacent vertebrae of the vertebral column.

Each portion of the cord that gives rise to a pair of spiEach portion of the cord that gives rise to a pair of spinal nerves is called a spinal segment. Each spinal segnal nerves is called a spinal segment. Each spinal segment is functionally correlated with the related cutanment is functionally correlated with the related cutaneous area, skeletal musculature and viscera.eous area, skeletal musculature and viscera.

Because the vertebral column grows at a faster rate thBecause the vertebral column grows at a faster rate than the spinal cord, so the spinal segments are not equan the spinal cord, so the spinal segments are not equal to the vertebral segments except for the CS1-4.al to the vertebral segments except for the CS1-4.

Table 1. The correlation between spinal Table 1. The correlation between spinal segments (PS) and vertebraesegments (PS) and vertebrae

Spinal segments (SS) Spinal segments (SS) VertebraeVertebrae

CSCS1-41-4 CVCV1-41-4 CSCS5-85-8, ST, ST1-41-4 -1 -1

TSTS5-8 5-8 -2-2

TSTS9-129-12 -3 -3

LSLS1-5 1-5 TVTV10-12 10-12

SSSS1-51-5, CoS , CoS TVTV1212, LV, LV1 1