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The Course>English Textbook>part Ⅵ nervous system>Chapter 1 General Description
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PART Ⅵ NERVOUS SYSTEM
Content
Introduction
Learining Conditions
Chapter 1 General Description
English Textbook
Ⅰ. Composition of Nervous System
Ⅱ Reflex and reflex archs
PART Ⅰ LOCOMOTOR SYSTEM
PART Ⅱ SPLANCHNOLOGY
PartⅢ ANGIOLOGY
Ⅲ Terminology
Chapter 2 Central Nervous System
Section 1 Spinal Cord
PART IV SENSORY ORGANS
Ⅰ. External Features of Spinal Cord
PART V ENDOCRINE SYSTEM
Ⅱ. Internal Structure of Spinal Cord
part Ⅵ nervous system
Section 2 Brain Stem
Chapter 1 General Description
I. External Features
Chapter 2 Central Nervous S…
II. Internal Structure
Chapter 3 Nervous Pathways
III. Transverse Sections of Brain Stem
IV 1esions of Brain Stem
Chapter 4 Meninges and Blo…
Section 3 Cerebellum
Chapter 5 Peripheral Nervous
I. Lobes of Cerebellum
II. Cerebellar Cortex
III. Central Nuclei of Cerebellum
IV. Cerebellar Cortex and Cerebellar Peduncles
V. Functions
Section4. Diencephalon
I . Dorsal Thalamus
II . Epithalamus
III. Subthalamus
IV. Metathalamus
V. Hypothalamus
VI. Third Ventricle
Section 5. Telencephalon
I . External Features
II . Limbic System
III. Cerebral Cortex
IV. Internal Structures
Chapter 3 Nervous Pathways
Section 1.. Sensory (Ascending)Pathways
Ⅰ.Superficial Sensory Pathways
Ⅱ.Deep Sensory (or the proprioceptive) Pathways
Ⅲ. Visual Pathways
Ⅳ. Auditory Pathway
Ⅴ. Equilibratory Pathway
Section 2.. Motor (Descending)Pathways
Ⅰ. Pyramidal System
Ⅱ. Extrapyramidal System
Chapter 4 Meninges and Blood Vessels of Brain and Spinal Cord, and the Cerebrospinal Fluid
Section 1... Meninges of Brain and Spinal Cord
I. Dura mater
II. Arachnoid
III. Pia Mater
Section 2.. Blood Vessels of Brain and Spinal Cord
Ⅰ. Arteries of Brain
Ⅱ. Veins of Brain
Ⅲ. Blood Vessels of Spinal Cord
Section3. Circulation of the Cerebrospinal Fluid
Section 4. Brain Barriers
Ⅰ. Morphologic Basis for Blood-Brain Barrier
Ⅱ. Morphologic Basis for Blood-Cerebrospinal Fluid Barrier
Ⅲ. Morphologic Basis for Cerebrospinal Fluid-Brain Barrier
Chapter 5 Peripheral Nervous System
Section 1 Spinal Nerves
Ⅰ. Anterior Branches of Thoracic Nerves
Ⅱ. Cervical Plexus
Ⅲ. Brachial Plexus
Ⅳ. Lumbar Plexus
Ⅴ. Sacral Plexus
Section 2 Cranial Nerves
Ⅰ. Sensory Cranial Nerves
Ⅱ. Motor Cranial Nerves
Ⅲ. Mixed Cranial Nerves
Section 3 Autonomic Nervous System
I. Visceral Efferent Nerve
II. Visceral Afferent Nerves
III. Central Centers of Visceral Nerves
IV. Referred Pain
part Ⅵ NERVOUS SYSTEM
Introduction
The nervous system controls and coordinates most of the activities of the body, matching them to the
continuously changing circumstances of the world around. In order to carry out these functions, the nervous system
monitors events in the external environment and within the body, coordinates all this information and matches it
against past experience, and instructs other systems, such as somatic muscle, to produce an appropriate response.
This response will in turn alter the information coming from the body and the external environment.
Nervous system can be divided into peripheral nervous system and central nervous system(FigⅥ-1).
1. Peripheral nervous system (PNS) is formed by the cranial and spinal nerves and the peripheral part of the visceral
nervous system. it collects the information from specialized sensory receptors throughout the body and transmits this information
to the central nervous system. The peripheral nervous system also carries commands from the central nervous system to
effectors.
2. Central nervous system (CNS) comprising the brain and spinal cord is wrapped in protective coverings, the
former lies in the cranial cavity, and the latter located in the vertebral canal.
FigⅥ-1. The structure of the CNS and the PNS.
Chapter 1 General Description
I．Composition of Nervous System
The nervous system is basically formed by the nervous tissue which consists of two principal cellular constituents, the nerve
cells or neurons, and neuroglial cells or glia. The neuron is the structural and functional unit of the nervous system and the glia
provide structural and metabolic support for neurons.
Ⅰ) Neurons
1. Structure of neurons (FigⅥ-1-1).
Although neurons are different in shapes and sizes, each has four morphologically specialized regions (FigⅥ2): cell body, dendrites, axon, and axon terminals. A neuron can be defined, functionally, as 3 zones: ① Receptor
zone — (cell body and dendrites) at where the afferent or incoming impulses arrive. ② Conducting zone — (axon)
specialized for conduction of the nervous impulse. ③ Effector zone— (axon terminals) where electrical or
chemical signals are transmitted across specialized junction (synapse).
PART Ⅵ NERVOUS SYSTEM
Introduction
Chapter 1 General Description
Ⅰ. Composition of Nervous System
Ⅱ Reflex and reflex archs
Ⅲ Terminology
Chapter 2 Central Nervous System
Section 1 Spinal Cord
Ⅰ. External Features of Spinal Cord
Ⅱ. Internal Structure of Spinal Cord
Section 2 Brain Stem
I. External Features
II. Internal Structure
III. Transverse Sections of Brain Stem
IV 1esions of Brain Stem
Section 3 Cerebellum
I. Lobes of Cerebellum
II. Cerebellar Cortex
III. Central Nuclei of Cerebellum
IV. Cerebellar Cortex and Cerebellar Peduncles
V. Functions
Section4. Diencephalon
I . Dorsal Thalamus
II . Epithalamus
III. Subthalamus
IV. Metathalamus
V. Hypothalamus
VI. Third Ventricle
Section 5. Telencephalon
I . External Features
II . Limbic System
III. Cerebral Cortex
IV. Internal Structures
Chapter 3 Nervous Pathways
Section 1.. Sensory (Ascending)Pathways
Ⅰ.Superficial Sensory Pathways
Ⅱ.Deep Sensory (or the proprioceptive) Pathways
Ⅲ. Visual Pathways
Ⅳ. Auditory Pathway
Ⅴ. Equilibratory Pathway
Section 2.. Motor (Descending)Pathways
Ⅰ. Pyramidal System
Ⅱ. Extrapyramidal System
C
Meninges and Blood Vessels of Brain and Spinal Cord, and the Cerebrospinal Fluid
Section 1... Meninges of Brain and Spinal Cord
I. Dura mater
II. Arachnoid
III. Pia Mater
Section 2.. Blood Vessels of Brain and Spinal Cord
Ⅰ. Arteries of Brain
Ⅱ. Veins of Brain
Ⅲ. Blood Vessels of Spinal Cord
Section3. Circulation of the Cerebrospinal Fluid
Section 4. Brain Barriers
Ⅰ. Morphologic Basis for Blood-Brain Barrier
Ⅱ. Morphologic Basis for Blood-Cerebrospinal Fluid Barrier
Ⅲ. Morphologic Basis for Cerebrospinal Fluid-Brain Barrier
Chapter 5 Peripheral Nervous System
Section 1 Spinal Nerves
Ⅰ. Anterior Branches of Thoracic Nerves
Ⅱ. Cervical Plexus
Ⅲ. Brachial Plexus
Ⅳ. Lumbar Plexus
Ⅴ. Sacral Plexus
Section 2 Cranial Nerves
Ⅰ. Sensory Cranial Nerves
Ⅱ. Motor Cranial Nerves
Ⅲ. Mixed Cranial Nerves
Section 3 Autonomic Nervous System
I. Visceral Efferent Nerve
II. Visceral Afferent Nerves
III. Central Centers of Visceral Nerves
IV. Referred Pain
part Ⅵ NERVOUS SYSTEM
Introduction
The nervous system controls and coordinates most of the activities of the body, matching them to the
continuously changing circumstances of the world around. In order to carry out these functions, the nervous system
monitors events in the external environment and within the body, coordinates all this information and matches it
against past experience, and instructs other systems, such as somatic muscle, to produce an appropriate response.
This response will in turn alter the information coming from the body and the external environment.
Nervous system can be divided into peripheral nervous system and central nervous system(FigⅥ-1).
1. Peripheral nervous system (PNS) is formed by the cranial and spinal nerves and the peripheral part of the visceral
nervous system. it collects the information from specialized sensory receptors throughout the body and transmits this information
to the central nervous system. The peripheral nervous system also carries commands from the central nervous system to
effectors.
2. Central nervous system (CNS) comprising the brain and spinal cordis wrapped in protective coverings, the
former lies in the cranial cavity, and the latter located in the vertebral canal.
FigⅥ-1. The structure of the CNS and the PNS.
Chapter 1 General Description
I．Composition of Nervous System
The nervous system is basically formed by the nervous tissue which consists of two principal cellular constituents, the nerve
cells or neurons, and neuroglial cells or glia. The neuron is the structural and functional unit of the nervous system and the glia
provide structural and metabolic support for neurons.
Ⅰ) Neurons
1. Structure of neurons (FigⅥ-1-1).
Although neurons are different in shapes and sizes, each has four morphologically specialized regions (FigⅥ2): cell body, dendrites, axon, and axon terminals. A neuron can be defined, functionally, as 3 zones: ① Receptor
zone( — (cell body and dendrites) at where the afferent or incoming impulses arrive. ② Conducting zone— (axon)
specialized for conduction of the nervous impulse. ③ Effector zone — (axon terminals) where electrical or
chemical signals are transmitted across specialized junction (synapse).
FigⅥ-1-1. A schematic nerve cell is shown, illustrating the dendrites,
cell body, axon, and axon terminals.
FigⅥ-1-1. A schematic nerve cell is shown, illustrating the dendrites,
cell body, axon, and axon terminals.
(1) Cell body
The cell body, or perikaryon is the metabolic and genetic center of a neuron (Fig. Ⅵ -1-1,2). It contains a nucleus with a
prominent nucleolus. After appropriate staining procedures, one can demonstrate within the cytoplasm of nerve cells neurofibrils,
chromophil substance(Nissl bodies), Golgi apparatus, mitochondria, at times a central body, and various inclusions such as pigment,
and lipids. Neurofibrils are uniquely characteristic of nerve cells, whereas the other cytoplasmic constituents are observed in other
tissue cells. Most of these constituents are visualized simultaneously with the electron microscope.
Fig VI-1-2
(2)Dendrites
Most neurons usually have many dendrites. The cytoplasm of dendrites resembles that of the perikaryon, with
granular endoplasmic reticulum(Nissl bodies) in their proximal trunks and at points of branching. The surface area
of the dendrites is usually far larger than that of the cell body. In some neurons, the smaller branches bear large
numbers of minute mushroom-shaped projections, called dendritic spines, which receive the nerve impulses coming
from the other neurons(Fig.Ⅵ-1-1).
(3) Axons and axon terminals
A neuron has a single axon, which is a cylindrical tube of cytoplasm covered by a membrane, the axolemma.
The axon conducts electrical signals from the cell body to the axon terminals. In large neurons, the initial segment of
axon form a cone-shaped portion， the axon hillock, which is free of Nissl bodies. Distally each axon breaks up into
simple or extensive terminal arborizations which end as synaptic terminals (also known as terminal button) in
contact with other cells(FigsⅥ-1-1,3)to form the synapses. Collateral branches may be given off from the axon.
FigsⅥ-1-1,3
2．Classification of neurons(FigsⅥ-1-3,4)
(1). Based on number of processes arising from cell body, neurons are classed as unipolar(or pseudounipolar),
bipolar, and multipolar. The multipolar neurons is different greatly in shape.
(2). Based on length of axons, neurons are also classified into three types(FigⅥ-1-4): Golgi typeⅠneurons
have long axons. The longest axons in the central nervous system (CNS) of humans extend from the cerebral cortex
to the caudal tip of the spinal cord, a distance of 50—70 cm.； Golgi type Ⅱ neurons have short axons. The
shortest axons terminate only a few micra from the perikaryon； Amacrine neurons, an unusual neuron type, lack
axons.
FigⅥ-1-4. Variety of neuron shapes
(3). Based on their function, all neurons fall into three types(FigⅥ-1-5):
Sensory neurons receive stimuli and transmit afferent impulse to the CNS； Association neurons(also called
nterneurons) lies in the central nervous system forming the complex nervous circuits. Motoneurons deliver
efferent impulses from the central nervous system to the peripheral nervous system (PNS) to activate effectors.
(4) Based on classification of neurotransmitters chemistry, neurons may also grouped as monoaminergic,
cholinergic, amino acidergic, peptidergic, and so on.
FigⅥ-1-2. The diaphragm of neuron cell body
FigⅥ-1-3. Morphological classification of neurons: A. bipolar neuron; B. unipolar neuron; c. multipolar neuron.
FigⅥ-1-5. Functional classification of neurons: A. a sensory neuron;
B. a association neurons C. a motor neuron.
Ⅱ) Synapses and Neurotransmitters
Communication between neurons usually occurs at specialized junctions called synapses. where excitation is
transmitted from one nerve cell to another. We call the neuron sending information the presynaptic neuron and the
other is called the postsynaptic neuron which receives the information.
1. synapses
Synapses can be formed between almost any regions of the two participating neurons. The most common type
of synapses occurs between a terminal of an axonal branch of a neuron and a dendrite or a soma of another(FigsⅥ1-1,5). The synapses may be divided into two kinds: the chemical synapses and electrical synapses. The chemical
synapses is the most common type in the mammalian nervous system, which transmits the nervous impulse by the
chemical substance—Neurotransmitters. Electrical synapses are only present in invertebrates and fishes. The
chemical synapses can be classified, according to the neuronal regions that participate in forming the synapse, into
axodendritic synapses and axosomatic synapses (most common), or, less often, dendrodendritic synapses and
axoaxonal synapses.
FigsⅥ-1-6
Typical chemical synapses may be divided into 3 parts(FigsⅥ-1-6)： ① the presynaptic part with the dense
thickening presynaptic membrane；② the postsynaptic part with the postsynaptic membrane(；③the synaptic
cleft ， a narrow gap about 20 nm wide which separates the presynaptic and postsynaptic membrane. The
presynaptic part contains numerous vesicles, Synaptic vesicles in which the chemical substances --neurotransmitter
is present.
2. Neurotransmitters
Neurotransmitters are small molecular weight compounds; among these are acetylcholine and monoaminergic compounds
such as norepinephrine and serotonin. Amino acids(e.g., glutamate, glycine, and γ-aminobutyric acidγ-, or GABA) and larger
molecules, such as peptides (e.g., enkephalin and substance P) also function as neurotransmitters. When an impulse arrives at the
presynaptic element, the neurotransmitter diffuses across the synaptic cleft and bind to the receptor molecules in the postsynaptic
membrane. As a result, the postsynaptic neuron is activated and the impulse is conducted from one neuron to the others.
II.Reflex and Reflex arcs
1. Basic components of reflex arc
A reflex arc is the basic functional unit of the nervous system. The reflex arc has five basic components: ①
a receptor respond to stimuli and produce nervous impulse, ② a sensory neuron transmits the impulse to the
CNS, where the axons usually synapse with ③ interneurons; which synapse with motor neurons in the CNS; ④ a
motor neuron carry action potentials out of the CNS and through the PNS to ⑤ effector organs, such as
muscles or glands, respond to the action potentials(FigⅥ-1- 7).
The response produced by the reflex arc is called a reflex.
FigⅥ-1-7. A schematic monosynaptic reflex arc.
III. Terminology
1. Nerve fiber
A nerve fiber in the central nervous system consists of the axon and the surrounding myelin sheath or of the axon
only in the case of unmyelinated fibers. In the peripheral nervous system both myelinated and unmyelinated fibers
have, in addition, an outer delicate nucleated membrane, the sheath of Schwann or nurolemmal sheath. The peripheral
myelinated fiber is structurally the most differentiated, consisting of axon, myelin and sheath of Schwann(Fig.Ⅵ-1- 8).
Fig.Ⅵ-1- 8
Myelinated fibers conduct more rapidly than unmyelinated ones. Speed of conduction is proportional to the
diameter of the fiber and the thickness of the myelin sheath. The myelin sheath may be regarded as insulation, while
the extracellular space at the nodes of Ranvier and the periaxonal space provide ready avenues for ionic diffusion.
2. Nucleus and grey matter
A nucleus is a aggregation of neuronal cell bodies and dendrites, of more or less similar shape and function,
located inside the central nervous system. Nuclei is various in sizes and shapes, commonly spherical and oval, and
sometimes in small flattened sheets.
The neuronal cell bodies and dendrites may form more extensive layers or masses in the central nervous system
collectively called grey matter. The grey matter looks grey because it consists of masses of nerve cell bodies that
contain pigment and organelles. Neuronal dendrites and synaptic activity are mostly confined to nuclei and areas of
grey matter.
3. Tracts and white matter
Bundles of nerve fibres in the central nervous system tend to be grouped to form the tracts, or fasciculi. In the
brain and spinal cord, concentrations of tracts constitute the white matter, so called because the axons are often
ensheathed in myelin which glistens white in the fresh state.
4. Cortex and medullary substance
The continuous sheet of grey matter covering the surface of the cerebrum and cerebellum is called the cortex.The
medullary substance, or medulla is a central core of white matter beneath the cortex of the cerebrum and cerebellum.
5. Ganglion
In the peripheral nervous system （ PNS ） , the cell bodies are grouped together to form the ganglia. Sensory
ganglion cells in dorsal roots of spinal nerves and some cranial nerves give off both central and peripheral processes, and
do not have synapses on their cell bodies, whilst ganglionic neurons of the viscersl nervous system receive synaptic
contacts from various sources.
6. Nerve
In the peripheral nervous system , a nerve is a bundle of nerve fibers together with supporting connective tissue.
Most of nerves have a whitish appearance because of their myelin content. There are three connective tissue sheaths in
peripheral nerves. They are, from inside out, the endoneurium, perineurium, and epineurium. Each nerve fiber is
surrounded by a re-enforcing sheath of delicate connective tissue, the endoneurium. It is continuous with the more
abundant connective tissue of the perineurium, which envelops both small and large bundles of fibers within a
peripheral nerve trunk and divides the nerve into fascicles. The epineurium is the outermost sheath. This dense,
collagenous layer forms an external connective tissue ensheathment for all peripheral nerves.
Huang Yaode : Shanghai Second Medical University