Download The nervous system

The nervous system
Chapter one introduction
一、Division of the nervous system
the central part : brain and spinal cord
the peripheral part: cranial , spinal and visceral (autonomic nervous system) nerves
二、Composition of the nervous system
nerve cells (neurons) and neuroglia
(一) Neurons
independent structural and functional units of the nervous sytem
1 Structure : consists of cell body and processes (an axon and one or more dendrite)
2 Myelinated and nonmyelinated nerve fibres
①Myelinated nerve fibres: The nerve fibres (mainly axon) enveloped by myelin sheath which is
formed by Schwann cell in the PNS and oligodendrocyte in the CNS)
②Unmyelinated nerve fibres: The nerve fibres not enveloped by myelin sheath.
3 Synapses : One neuron contacts with another neuron to form synapse. Synapse consists of
presynaptic membrane , postsynaptic membrane and synaptic cleft. The axodendritic synapse is
most common , and the axosomatic is quite common.
4 Classify :
according to the number of the processes :
a.
pseudounipolar neuron
b.
bipolar neuron
c.
multipolar neuron
according to function of the neuron
a.
sensory neuron
b.
motor neuron
c.
interneuron
Others, Golgi I and II, et al.
(二) Neuroglia ( glial cells)
large neuroglia ( oligodendrocyte , Schwann cell and astrocyte) and small neuroglia
( microglia)
三、The reflex and reflex arch
1 conception of the reflex
2 composition of the reflex arch
sensory receptors, afferent neurons, interneurons , efferent neurons and effectors
四、Terminology
1 gray matter and white matter , cortex and medulla
①gray matter: Groups of nerve cell bodies and their dendrites in the CNS are termed gray matter.
②white matter: Bundles of nerve fibres in the CNS are termed white matter.
2 nucleus and ganglion
①nucleus: Nerve cells with the same shape and function in the CNS are grouped together to form
nucleus.
②ganglion: Nerve cells with the same shape and function in the PNS are grouped together to form
ganglion.
3 fasciculus , funiculus and nerves
①fasciculus: A group of nerve fibres with common origins, destinations and functions in the CNS
is termed fasciculus.
②funiculus: A group of nerve fibres with different origins, destinations and functions in the CNS
is termed funiculus.
③nerves: Nerve fibres are grouped together in the PNS are termed nerves.
Chapter 2 The central nervous system
Section one the spinal cord
一、Location
in the vertebral canal and between the foramen magnum and the lower border of the first lumbar
vertebra
二、External features
six sulci, two enlargements and one filum terminale, thirty-one segments
1 six sulci: anterior median fissure and posterior median sulcus, two anterolateral sulci , two
posterior lateral sulci
2 two enlargements: cervical enlargement and lumbosacral enlargement
3 one filum terminale: formed by pia mater
4 conus medullaris
5 cauda equina
6 thirty-one segments
三、Internal structure
consists of the grey matter , white matter and central canal.
(一) Grey matter
1 anterior horn:
①large neuron →α-motor neuron : innervates the extrafusal fibres of the skeletal muscle
②small neuron →γ-motor neuron : innervates the intrafusal fibres of the skeletal muscle
2 posterior horn : the nucleus posteromarginalis, substantia gelatinossa (of Rolando), nucleus
proprius, nucleus thoracicus ( nucleus dorsalis of Clarke)
3 lateral horn (intermediate zone)
①the intermediolateral nucleus: extends from C8 - L2 or L3 . It is the center of the sympathetic
system
② the sacral parasympathetic nucleus: extends from S2 - S4. It is one center of the
parasympathetic system.
③the intermediomedial nucleus
(二) White matter
1 Long ascending tracts : carry sensory impulses
① Gracile fasciculus and cuneate fasciculus
location: in the posterior funiculus
function: conduct the ipsilateral fine touch,two-point discrimination,proprioception
② Lateral spinothalamic tract
location: in the lateral funiculus
function: conduct the contralateral pain and temperature sense below one or two segments of the
original level
③ Anterior spinothalamic tract
location: in the anterior funiculus
function: conduct the contralateral crude touch below one or two segments of the original level
④ Anterior and posterior spinocerebellar tracts : conveys the subconscious proprioceptive sense
to the cerebellum
⑤Spinoreticular tract
2 Long descending tracts : carry motor impulses
① Corticospinal tract
a.
lateral corticospinal tract
location: in the lateral funiculus
function: innervate the muscle of the extremities by influencing the spinal cord
b.
anterior corticospinal tract
location: in the anterior funiculus
function: innervate the muscle of the neck and trunk by influencing the spinal cord
② Tectospinal tract: regulates the influence of optical reflexes on the muscle of the neck
③ Rubrospinal tract: helps flexor motor neurons
④ Vestibulospinal tract: increases the extensor muscle tone
⑤ Reticulospinal tract: play a role in moderation of the muscle tone.
3 Short ascending and desending tracts
①Fasciculus proprius: take part in the intrinsic reflex mechanism of the spinal cord
②Dorsolateral fasciculus (of Lissauer): consists of fine myelinated and unmyelinated posterior
root fibers and relates to transmit pain and temperature sense.
Ascending fiber systems in the spinal cord
Name
Location in cord
Gracile and cuneate
Post. funiculus
Origin
Spinal ganglion
fasciculi
Ending
Function
Gracile and cuneate
Fine touch,two-point
nuclei of medulla
discriminiation,
prorioception
Lateral spinothalamic
Lateral funiculus
Laminae I,II,V
Ventral posterolateral
Pain and temperature
tract
nucleus of thalamus
Anterior
Anterior funiculus
Laminae I,II,V
Ventral posterolateral
Crude touch
spinothalamic tract
nucleus of thalamus
Posterior
Lateral funiculus
Dorsal nucleus
Cerebellar
(Clarke’s nucleus)
paleocortex
LaminaeV,VI
Cerebellar
spinocerebellar tract
Anterior
Subconscious
proprioception
Lateral funiculus
spinocerebellar tract
Subconscious
proprioception
and VII
paleocortex
Spinoreticular tract
Lateral funiculus
Post. horn
Reticular formation
Deep
and
chronic
pain
of brain stem
Descending fiber systems in the spinal cord
Name
Location in cord
Lateral corticospinal
Lateral funiculus
Origin
Motor
Ending
and
Function
Anterior horn cells
Control
premotor cortex
tract
distal
musculature
(interneurons and lower
motor neurons)
Anterior corticospinal
Anterior funiculus
Motor
and
Anterior horn cells
Proximal and axial
(interneurons and lower
musculature
premotor cortex
tract
motor neurons)
Vestibulospinal tract
Anterior funiculus
Vestibular
Anterior horn
Postural reflexes
nucleus
(for extensors)
Rubrospinal
Lateral funiculus
Red nucleus
Anterior
horn
Motor function
interneurons(for flexor)
Reticulospinal
Anterior funiculus
Brain
stem
Posterior and anterior
reticular
formation
horn
Modulation of
sensory
transmission
(especially pain)
Tectospinal
Anterior funiculus
Midrain
Anterior
horn
Reflex head turning
interneurons
Medial
longitudinal
Anterior funiculus
Vestibular nuclei
Cervical gray
Coordination of head
fasciculus
and eye movement
四、Functions of spinal cord
1 reflex
2 conduction
Section two the brain
The brain consists of four parts: the brain stem, cerebellum, diencephalon and telencephalon.
一、The brain stem
includes the medulla oblongata, pons and midbrain
(一) External features
1 The ventral surface of brain stem
① the medulla oblongata
pyramid, decussation of pyramid, olive, four pairs of cranial nerves emerge from the medulla
oblongata ( IX-XII, the glossopharyngeal N, vagus N, accessory N and hypoglossal N)
② the pons
the basilar sulcus, middle cerebellar peduncles , four pairs of cranial nerves emerge from the
pons ( V- VIII, the trigeminal N, abducent N, facial N and vestibulocochlear N)
③ the midbrain
the cerebral peduncles, two pairs of cranial nerves emerge from the midbrain ( III – IV, the
oculomotor N and trochlear N)
2 The dorsal surface of brain stem
① the medulla oblongata
the gracile tubercle, the cuneate tubercle, striae medullares
② the pons
the median sulcus, sulcus limitans, medial eminence, facial colliculus, vestibular area, locus
ceruleus, superior cerebellar peduncles and superior medullary velum
③ the midbrain
the superior and inferior colliculi ( quadrigeminal body ). the superior colliculi are involved in
visual reflexes and the inferior involved the auditory reflexes. the brachium of superior colliculus
(pass to the lateral geniculate body), the brachium of inferior colliculus (pass to the medial
geniculate body)
3 The rhomboid fossa
① the boundaries
4 The fourth ventricle
① location: among cerebellum, the dorsal surface of the medulla oblongata and pons
② communication: continuous below with the central canal and above with the mesencephalic
(cerebral ) aqueduct
(二) Internal structure
1 Features
①The fourth ventricle appears
②Relation of between the motor nucleus and sensory nucleus is medial and lateral relationship
③Gray and white matters are not continuous
④Cranial nerve nuclei have seven functional components
⑤The region of reticular formation is widely
2 Cranial nerve nuclei
①General somatic efferent(motor) nuclei:hypoglossal nucleus of XII,oculomotor nucleus of
III,trochlear nucleus of IV, and abducens nucleus of VI
②General visceral efferent(motor) nuclei:accessory oculomotor nucleus(Edinger-Westphal) of III,
superior salivatory nucleus of VII, inferior salivatory nucleus of IX and dorsal motor nucleus of X
③ Special visceral efferent(motor) nuclei:trigeminal motor nucleus of V,facial nucleus of
VII,ambiguous nucleus of IX,X,and XI, and spinal accessory nucleus of XI
④General visceral afferent(sensory) nuclei: nucleus of solitary tract of VII,IX, and X
⑤Gpecial visceral afferent(sensory) nuclei: the same as the ④
⑥General somatic afferent(sensory) nuclei:mesencephalic nucleus of V, pontine nucleus of V,
nucleus of spinal trigeminal tract
⑦Special somatic afferent(sensory) nuclei:four vestibular nuclei and two cochlear nuclei
3 Other nerve nuclei
①Medulla: gracile nucleus and cuneate nucleus
②Pons:pontine nucleus
③Midbrain:superior and inferior colliculi; red nucleus; substantia nigra
4 Ascending tracts
①Medial lemniscus: gracile and cuneate nuclei give rise to a crossed fiber bundle to form medial
lemniscus.
②Spinal lemniscus: It is continuous with the spinothalamic tract in the spinal cord.
③Lateral lemniscus: The fibers arising from the contralateral anterior and posterior cochlear
nuclei, and superior olivary nucleus, and the ipsilateral olivary nucleus make up the lateral
lemniscus.
④Trigeminal lemniscus: The pontine nucleus of V, nucleus of spinal trigeminal tract give rise to a
crossed fiber bundle to form the trigeminal lemniscus.
5 Descending tracts
①Pyramidal system: consists of the corticospinal tract(pyramidal tract) and corticonuclear tract
6 Reticular formation
① Definition(term): is localized in the tegmentum of the brain stem (with exception of the
conspicuous fiber bundles and nuclei of the brain stem), the lateral hypothalamic area, and the
medial, intralaminar, and reticular nuclei of the thalamus.This area is characterized by a diffuse,
seemingly unorganized structure with interlacing cells and fibers.Scattered through the reticular
formation lie some cell accumulations with ill defined boundaries(reticular nuclei: unpaired raphe
nuclei,paired medial nuclei , paired lateral nuclei). Most reticular neurons are fairly large, and it is
notable that the larger neurons are found more medially while the smaller ones are located more
laterally.
② Function: control respiration
consciousness,sleep, and alertness.
;
cardiovascular
system
functions;
and
二 The cerebellum
(一) Location:
Behind the pons and medulla oblongata and located in the posterior cranial fossa
(二) External structure
states
of
The cerebellum consists of cerebellar hemispheres joined by a vermis.
1 Structure: superior, middle and inferior peduncles; folia; primary fissure; anterior and posterior
lobes; tonsil; nodulus, uvula and pyramis of vermis; flocculus
2 Division:
① According to phylogenesis:
a. archicerebellum ( flocculonodular lobe)
b. paleocerebellum ( ant. lobe and uvula and pyramis )
c. neocerebellum (post. lobe exception the uvula and pyramis)
② According to function
a.vestibulocerebellum (archicerebellum):concerned with equilibrium and connects with
vestibular system
b. spinocerebellum(paleocerebellum):involoved with propulsive, stereotyped movements, such
as swimming and walking ,and connects with the spinal cord
c. pontocerebellum(neocerebellum): concerned with the coordination of fine movement , and
connects with cerebral cortex.
Recent work suggests that the cerebellum may be involved in the mechanism of memory for
motor activities.
(三) Internal structure
includes cerebellar cortex, medullary substance and four pairs of cerebellar nuclei
1 Cerebellar cortex: the molecular layer , the Purkinje cell layer and the granular layer
2 cerebellar nuclei:fastigial, globose, emboliform and dentate
(四) Clinical correlations: ataxia; asynergy; dysmetria; adiadochokinesis ;
三 The diencephalon
located between the brain stem and telencephalon , and entirely surrounded by the
telencephalon. It includes the thalamus, the hypothalamus, the epithalamus, the subthalamus and
the metathalamus. The third ventricle lies between the halves of the diencephalon
(一) The thalamus (dorsal thalamus)
1 Landmarks
the pulvinar, the anterior thalamic tubercle, the interthalamic adhesion
2 White matter: internal and external medullary laminae
3 Thalamic nuclei
① Anterior nuclear group:anterior nucleus
② Medial nuclei:dorsal medial nucleus
③ Lateral nuclear group: dorsal:dorsolateral nuclei
ventral: ventral anterior , lateral and posterior nuclei(ventral posterolateral
and posteromedial nuclei which receive fibers from the medial lemniscus and the spinothalamic
and trigeminal tracts)
④ Nuclei of the midline :
4 Functional divisions of thalamic nuclei
①Specific sensory nuclei: ventral posterolateral and posteromedial nuclei, medial and lateral
geniculate bodies
②Motor nuclei: ventral anterior and lateral nuclei
③Nonspecific nuclei:intralaminar nuclei, periventricular nuclei and reticular nucleus
④Associative nuclei:pulvinar, dorsolateral nuclei
⑤Limbic nuclei:dorsomedial nucleus and anterior nucleus
(二) The metathalamus
consists of the medial and lateral geniculate bodies
(三) The epithalamus
comprises the habenular nucleus, the pineal body, and the habenular and posterior
commissure
(四) The subthalamus
(五)The hypothalamus
1 Location: lies below and in front of the thalamus , and surrounds the third ventricle beneath
the hypothalamic sulcus.
2 Boundary: Anterior→optic chiasm and lamina terminalis ; inferior →the tuber cinereum ,
infundibulum and mamillary bodies ; superior → the hypothalamic sulcus ; posterior →
subthalamus
3 Nuclei: the supraoptic , paraventricular , suprachiasmatic and mamillary nuclei, et al.
4 Relation of the hypothalamus with the hypophysis
① The hypothalamohypophyseal tract: runs from the suraoptic and paraventricular nuclei to
the neurohypophysis (posterior pituitary)
②The tuberohypophyseal tract:goes from the tuberal portion of the hypothalamus to the
neurohypophysis
5 Function
the highest regulatory center of homeostatic and endocrine mechanism
四 The telecephalon
consists of two cerebral hemispheres jointed by the corpus callosum.
(一) External structure
1 Three constant fissures(sulci) and five lobes
① Three constant fissures: the lateral cerebral fissure( of Sylvius), the central sulcus( of
Rolando) and the parietooccipital fissure
② Five lobes: the frontal lobe, the parietal lobe, the occipital lobe, the temporal lobe and the
insula
2 The main gyri and sulci on the dorsolateral surface of the hemisphere
① The frontal lobe
the precentral sulcus and the precentral gyrus, the superior and middle suci and the superior,
middle and inferior frontal gyri
② The parietal lobe
the postocentral sulcus and the postocentral gyrus, the intraparietal sulcus and the superior
and inferior parietal lobues, the supramarginal gyrus and the angular gyrus
③ The temporal lobe
the superior and inferior sulci and the superior, middle and inferior gyri, two transverse
temporal gyri
3 The main gyri and sulci on the medial surface of the hemisphere
the paracentral lobule, corpus callosum, cingulated gyrus , parietooccipital fissure, calcarine
fissure, cuneus, lingual gyrus, hippocampal fissure and dentate gyrus , and hippocampus
4 The main gyri and sulci on the inferior surface of the hemisphere
① The frontal lobe
the olfactory bulb, the olfactory tract and the olfactory trigone
② The temporal lobe
parahippocampal gyrus, uncus
(二) Internal structure
is composed of the cerebral cortex, the cerebral medullary substance, the basal ganglia and two
lateral ventricles.
1 Lateral ventricles
① Location: one in each cerebral hemisphere
② Division: the anterior horn, posterior horn, inferior horn and central part(body)
③ Communication: communicate with the third ventricle through the two interventricular
foramens( of Monro)
2 The basal ganglia (basal nuclei)
include the lentiform nucleus, the caudate nucleus, the claustrum and the amygdaloid body.
① Corpus striatum: lentiform nucleus
globus →
paleostriatum
putamen
caudate nucleus
neostriatum
② Function: the basal ganglia and some nuclei of the brain stem(such as the substantia nigra)
form the extrapyramidal system which controls the movement and posture.
3 The cerebral cortex
According to phylogenesis, the cerebral cortex can be divided into archicortex(hippocampus,
dentate gyrus), paleocortex(rhinencephalon), neocortex. The former two contain three layers, and
the neocortex contains six layers. The pyramidal cells are the most important cells in the cortex.
① Classification of principal areas
According to Brodmann’s classification system (based on cytoarchitecture), the cerebral
cortex can be divided into 52 areas.
② Functional localizations of the cerebral cortex
A. the somesthetic area(primary sensory area)
I. Location: the postcentral gyrus and the posterior part of the paracentral lobule (parietal
lobe-area 3,1, and 2)
II. Features : a the primary sensory area are discussed
B the somatotopic representation is inverted.
C the size of the cortical area for the body parts is determined by the its need for
sensitivity
B. the primary motor area
I. Location: the precentral gyrus and the anterior part of the paracentral lobule (frontal lobe-area 4.
Area 6 is the premotor area)
II. Features : a the primary motor area are discussed
b the somatotopic representation is inverted.
c the size of the cortical area for the body parts is determined by the its need for
importance and dexterity of the movement
C. Visual area
Surrounds the calcarine sulcus of the occipital lobe (occipital lobe-area 17) . The visual cortex
is also termed the striate area. Each visual area receives data from the temporal half of the
ipsilateral retina and the nasal half of the contralateral retina.
D. The acoustic area ( auditory area)
In the transverse temporal gyri( temporal lobe-area 41 and 42). Each auditory area receives the
auditory radiation from the cochlea of the both ears.
E. The taste area (gustatory area) : close to the facial sensory and extends onto the opercualr
surface of the lateral cerebral fissure(parietal lobe-area 43)
F. The language areas ( dominant hemisphere)
I. The motor speech area (Broca’s area) : in the opercular and triangular portion of the inferior
frontal gyrus ( frontal lobe-area 44 and 45)
II. The auditory speech area ( Wernicke’s area) : in the posterior portion of the superior temporal
gyrus( temporal lobe-area 22)
III. The written word area : in the posterior portion of the middle frontal gyrus (frontal lobe-area
8).
IV. The visual speech area : in the angular gyrus( parietal lobe-area 39)
4 The medullary substance
① The association fibers: connect the gyri in one hemisphere.
② The commissural fibers: connect the gyri in one hemisphere to in the other hemisphere.Such as
the corpus callosum and fornix
③ The projection fibers: connect the cortex with the subcortical structures.
A The internal capsule : is a broad band of myelinated fibers that between the lentiform nucleus
and the medial caudate nucleus, thalamus.
B Division of the internal capsule: The anterior limb, the posterior limb and genu.
The anterior limb is between the lentiform nucleus and the medial caudate nucleus. It contains
the anterior thalamic radiation and frontopontine tract.
The posterior limb is between the lentiform nucleus and the thalamus. It contains the
corticospinal
tract,
thalamocortical
tract,
optic
radiation,
acoustic
radiation,
parieto-occopito-temporo-pontine tract, corticorubral tract
The genu: in the junction of the anterior and posterior limbs. It contains the corticonuclear tract.
C The lesion of the internal capsule
Anesthesia and hemiplegia on the opposite side of the body, and blindness in the opposite
visual field
5 The limbic system
①Composition: the limbic lobe(parahippocampal, cingulated, and subcallosal gyri), the amygdala,
and hippocampal formation and associated structure.
②Function:contributes to the preservation of the individual and the continuation of the species.
Section 4 The meninges and blood vessels of brain and spinal cord, and the cerebrospinal fluid
一、The meninges (or coverings) of brain and spinal cord
Three meninges envelop the brain (from outer to inner): the dura, the arachnoid and the pia
maters.
(一) The dura mater
1 The spinal dura mater
① The epidural space: A space between the spinal dura and the periosteum of the vertebral canal,
which contains the loose areolar tissue, lymphatic vessels and venous plexuses. The spinal nerves
pass through the space.
2 The cerebral dura mater
(1)Characteristics:
①loose contact with the calvaria, closely attached at the base of skull;
②form dura septa: the cerebral falx and the cerebellar tentorium
③form dura venous sinuses(lack smooth muscle): Inferior sagittal sinus→straight sinus→
(superior sagittal sinus→)confluence of sinuses→(cavernous sinuses→) transverse sinuses→
sigmoid sinuses→internal jugular vein
(2) The cavernous sinuses
①Location: on either side of the sella turcica
②Communication: with the facial vein via the ophthalmic vein, and with the pterygoid plexus
through the foramen ovale
③Structures passing through the sinuses: the internal carotid artery, the oculomotor nerve (III),
trochlear nerve (IV) ,the ophthalmic and the maxillary divisions of the trigeminal nerve(V), and
the abducens nerve(VI)
(二) The arachnoid mater
is a avascular membrane.
1 The subarachnoid space: between the arachnoid and the pia maters, filled with the cerebrospinal
fluid(CSF).
2 The subarachnoid cisterns: these widened the subarachnoid space.
3 The arachnoid granulations: berry-like clumps of the arachnoid protruding into superior sagittal
sinus and other sinuses.
(三) The pia mater
contains rich blood vessels. And combines with the ependyma and choroids vessels to form the
choroid plexus of the third , fourth and lateral ventricles. Between the dorsal and ventral nerve
roots of the spinal cord to form the denticulate ligment.
二、The blood vessels of the brain and spinal cord
(一) The arteries of brain
come from two pairs of large vessels: the internal carotid arteries and vertebral arteries . The
internal carotid arteries supply the anterior two-thirds of the cerebral hemisphere and parts of the
diencephalon, the posterior one-third of the cerebral hemispheres and the remainder of the
diencephalons are supplied by the vertebral arteries.
1 The internal carotid artery
main branches:
①The anterior cerebral A.
②The middle cerebral A.: runs in the lateral sulcus and supply most of the dorsolateral surface of
the cerebral hemisphere and the lentiform nucleus, caudate nucleus, the internal capsule.
③The posterior communicating A.
④The anterior choroidal A.
⑤The ophthalmic A.
2 The vertebral artery
Two vertebral arteries unit to form the basilar artery.
(1) Main branches of the vertebral A.
①The anterior and posterior spinal A.
②The posterior inferior cerebellar A.
(2) Main branches of the basilar artery
①The anterior inferior cerebellar A.
②The pontine A.
③The superior cerebellar A.
④The posterior cerebral A.
3 The circle of Willis(cerebral arterial circle)
formed by the anterior and posterior cerebral arteries, the anterior and posterior communicating
arteries, and a segment of internal carotid arteries. This is important for the functionally adequate
anastomosis to occur.
(二) The veins of the brain
do not run together with the arteries, and usually are divided into superficial and deep groups.
(三) The blood vessels of spinal cord
The blood of the spinal cord comes from the anterior and posterior spinal arteries of the
vertebral artery, and also from the posterior intercostal and the lumbar arteries.
三、Cerebrospinal fluid(CSF)
Normal CSF is clear, colorless, and odorless.And fills with ventricles, the subarachnoid space
and the central canal of the spinal cord. And produced by the choroids plexuses of the ventricles.
1 Function:play a role like lymph in the central nervous system, has function of the support,
protection, nutrition, and carries away metabolites.
2 Circulation: Lateral ventricles (through the interventricular foramens) → the subarachnoid
space the third ventricle(through the cerebral aqueduct) →the fourth ventricle(through lateral and
medial apertures) →the subarachnoid space (through the arachnoid granulations)→ dura sinuses
→ veins
四、Barriers in the nervous system
1 Blood-brain barrier(BBB): consists of the endothelial cell and basement membrane of capillaries,
and the processes of astrocyte.This barrier is absent in several specialized regions of the brain:
the basal hypothalamus, the pineal gland, the small area near the third ventricle, and area
postrema of the fourth ventricle.
2 Blood-CSF barrier
3 CSF-brain barrier
Chapter 3 The peripheral nervous system
According to the origin and distribution, the peripheral nervous system can be divided into three
parts: spinal nerves, cranial nerves and the autonomic nervous system (visceral nervous system or
vegetative nervous system).
Section 1 the spinal nerves
一、Introduction
There are 31 pairs of spinal nerves, which are divided into 8 pairs of cervical (C1-8), 12 pairs of
thoracic(T1-12), 5 pairs of lumbar(L1-5), 5 pairs of sacral(S1-5), and 1 pair of coccygeal
nerves(Co 1).
1 Spinal nerve roots
Each nerve consists of an anterior(ventral) root and a posterior(dorsal) root.. The anterior root
contains motor fibers arising from the anterior and lateral horn of the spinal cord. The posterior
root contains sensory fibers originating in the pseudounipolar neurons in the spinal ganglion that is
interposed in the course of the posterior root.
2 Branches of typical spinal nerves
(1) The dorsal branch: is distributed to the muscles and skin of the posterior part of the body.
(2) The communicating branch
(3) The meningeal branch
(4) The anterior branch : is distributed to the limbs, the lateral and ventral trunk. The anterior
branches form the cervical, brachial, lumbar and sacral plexuses with exception of the thoracic
nerves(they remain segmental).
二、The cervical plexus
1 The formation: C1-4
2 Location:deeply in the sternocleiodmastoid muscle.
3 Branches: superficial and deep branches
(1) The superficial (cutaneous) branches
emerge near the middle of the posterior border of the sternocleiodmastoid muscle.
①The lesser occipital nerve
②The greater auricular nerve
③The transverse nerve of neck
④The supraclavicular nerve
(2) The deep branches
innervate the deep muscles of the neck, the infrahyoid muscles the levator scapulae and
diaphragm.
①The phrenic nerve
A. Course
B. Distribution: supply the diaphragm, the sensory fibers supply the pericardium, the mediastinal
pleurae and diaphragmatic peritoneum. The right phrenic nerve is also distributed to the liver, the
gallbladder and the biliary sytem.
三、The brachial plexus
1 The formation: C5-8 and T1
2 Branches
(1) The branches above the clavicle
①The long thoracic N.:innervates the serratus anterior. The lesion of the N causes the “wing” of
the scapula.
②The dorsal scapular N: innervates the levator scapulae and rhomboideus
③The suprascapular N: innervates the supraspinatus and the infraspinatus.
(2) The branches below the clavicle
①The thoracodorsal N:supplies the latissimus dorsi.
②The lateral and medial pectoral nerves(anterior thoracic N): supplies the pectoralis major and
pectoralis minor.
③The musculocutaneous N:supplies the coracobrachialis, biceps, and brachialis muscle.It ends as
the lateral antebrachial cutaneous N.
④The median N
A.Course
B.Branches: the forearm →muscular branches, the hand→a recurrent branch,three common
palmar digital nerves and proper palma digital nerves
C.Distribution:
Motor branches: in the forearm → the pronators and flexor muscles except the
brachioradialis, the flexor carpi ulnaris and the medial half of the flexor digitorum profundus; in
the hand→the first and second lumbricales and the thenar muscles except the adductor pollicis.
Sensory branches: the skin of the palmar surface of the radial half of the hand and thumb and
the lateral 21／2 fingers , and the dorsal surface of the middle ,distal ends of the same fingers .
D.Clinical features of the N. lesion: easily injured at the wrist and causes “ape hand”
⑤The ulnar N
A Course
B Branches: the forearm →muscular branches, the hand→a superficial and a deep branches, a
dorsal branch
C Distribution:
Motor branches: in the forearm→the flexor carpi ulnaris and the medial half of the flexor
digitorum profundus; in the hand→the adductor pollicis, the third and fourth lumbricales,
interossei.
Sensory branches:hand→ the skin of the ulnar half of the hand, and the ulnar one and half
fingers.
D.Clinical features of the N. lesion: easily injured at the sulcus for unlar nerve or the wrist and
causes “clawhand”
⑥The radial N
A Course
B Branches: at the elbow joint→the superficial and deep branches
C Distribution:
Motor branches: in the forearm→all extensors; the arm→all extensors and the brachioradialis
Sensory branches: hand→the dorsal surface of the radial half of the hand, and the proximal
digits of the lateral two and half fingers.
D Clinical features of the N. lesion: easily injured in the upper or middle part of the arm and
causes “Wristdrop”
⑦The axillary N
A Course
B Distribution : supply the deltoid and teres major
C Clinical features of the N. lesion: easily injured in fracture of the humeral neck or in dislocation
of the shoulder joint and causes “quadrate” shoulder.
四、The anterior branches of thoracic nerves
1 Number: 12 pairs. Among them, 11 pairs are the intercostals nerves, 1 pairs are the subcostal
nerves.
2 Course
3 Segmental distribution:
T2→the sternal angle
T4→the nipple
T6→the xiphoid process
T8→the costal arch
T10→the umbilicus
T12→the anterior superior iliac spine
五、The lumbar plexus
1 Formation: part of T12(inconstant),L1-3 and part of L4
2 Location: situated in the psoas major
3 Main branches
(1) The iliohypogastric N: supply the skin of the hypogastric region and inguinal region.Its
muscular branch supplies the muscles of the lower part of the abdominal wall.
(2) The ilioinguinal N: supply the skin of the inguinal region, the scrotum( or the greater lip of
pudendum). Its muscular branch supplies the muscles of the lower part of the abdominal wall.
(3) The lateral femoral cutaneous
(4) The femoral N
①Course:descends beneath the inguinal ligment to enter the femoral trigone on the lateral side of
the femoral atery
②Main branches: saphenous N (cutaneous N)
③Distribution:suppies the quadriceps femoris, sartorius and pectineus. The sensory branches
supply the anterior and medial surfaces of the thigh and the saphneous nerve to the medial side of
the leg and foot.
④Clinical features of the N. lesion: impossible to flex the thigh . The extension of the leg and the
knee jerk are lost.
(5)The obturator N: distributed to the muscles and skin of the medial side of the thigh.
(6) The genitofemoral N: distributed to the cresmater and skin over the scrotum( or the greater lip
of pudendum).
六、The sacral plexus
1 Formation: L4-5(the lumbosacral trunk), the anterior branches of the sacral and coccygeal
nerves.
2 Location:situated in front of the piriformis on the posterior wall of the pelvis.
3 Main branches:
(1) The superior gluteal N:supplies the gluteus medius and minimus and the tensor fasciae latae.
(2) The inferior gluteal N:supplies the gluteus maximus.
(3) The posterior femoral cutaneous N
(4) The pudendal N: ①The anal N(inferior rectal N);②The perineal N;③The dorsal N of penis or
clitoris
(5) The sciatic N
①Course: leaves the pelvis through the greater sciatic foramen below the piriformis, and descends
between the greater trochanter of the femur and the ischial tuberosity along the posterior surface
of the thigh to the popliteal fossa, where it terminates by dividing into the tibial and common
peroneal nerves.
②Distribution:supplies the muscles and skin of the posterior side of the thigh.
③Branches:
A. The tibial N
a.
Course: descends between the superficial and deep layers of the posterior muscles of the leg
and enters to the sole of the foot.
b.
Branches: in the back of the leg→the medial sural cutaneous N.; in the sole of the foot→the
medial and lateral plantar nerves
c.
Distribution: supplies the posterior muscles of the leg and the muscles of the sole of the foot.
d.
Clinical features of the N. lesion: causes a “hook-like” foot.
B. The common peroneal N
a.
Course:passes around the neck of the fibula to enter deep to the peroneus longus and is
divided into the superficial and deep peroneal nerves.
b.
Branches: in the back of the leg→the lateral sural cutaneous N.; in the anterior and lateral
sides of the leg→the superficial and deep peroneal nerves.
c.
Distribution: the superficial peroneal nerve supplies the lateral muscles of the leg; the deep
peroneal nerve supplies the anterior muscles of the leg and the muscles of the dorsal foot.
d.
Clinical features of the N. lesion: causes a “foot-drop” or “taplies equinovarus”.
Section two the cranial nerves
一、Introduction
1. The names and orders of the cranial nerves
I olfactory N; II optic N; III oculomotor N; IV trochlear N; V trigeminal N; VI
abducent N; VII facial N; VIII vestibulocochlear; IX glossopharyngeal N; X vagus N;
XI accessory N; XII hypoglossal N
2. Functional components of the cranial nerves
(1) Somatic efferent(motor) fibers: involved in eye and tongue movements;
(2) Special visceral efferent fibers: involved in chewing, making facial expressions, swallowing,
producing vocal sounds, and turning the head;
(3) General visceral efferent fibers: involved in movements of smooth muscles of the inner eye,
glands and the muscles of the heart, lung, and bowel that involved in movement and secretion;
(4) General somatic afferent(sensory) fibers: convey sensation from the skin and the mucous
membrane of the head;
(5) Special somatic afferent(sensory) fibers: involved with the vision, hearing and equilibrium;
(6) General visceral afferent fibers: convey sensation from the alimentary tract, heart, vessels, and
lungs;
(7) Special visceral afferent fibers: involved with the sense of taste and smell .
二、12 pairs of the cranial nerves
Cranial nerve I: olfactory nerve
The olfactory nerves(olfactory filaments) are the central processes of the olfactory cells in the
olfactory mucosa of the nase and perforate the cribriform plate , end in the olfactory bulb.
Cranial nerve II: optic nerve
Arise from the ganglion cells in the retina and converge on the optic disc, pass through the
optic canal into the cranial fossa .after forming the optic chiasm, it changes its name to optic tract.
Cranial nerve III: oculomotor nerve
Arise from the oculomotor nucleus and the accessory oculomotor nucleus(Edinger-Westphal
nucleus). It enters the orbit through the superior orbital fissure and supplies the levator palpebrae
superioris, superior , medial, and inferior rectus muscles, and the inferior oblique muscle, the
ciliary and the constrictor pupillae muscles.
The ciliary ganglion is a parasympathetic ganglion. The preganglionic fibers of the
oculomotor nerve are relayed in the ganglion. The cells in the ganglion give rise to fibers which
supplies the ciliary and the constrictor pupillae muscles
Cranial nerve IV: trochlear nerve
Originates from the trochlear nucleus . It enters the orbit through the superior orbital fissure
and supplies the superior oblique muscle.
Cranial nerve IV: abducent nerve
Originates from the abducent nucleus . It enters the orbit through the superior orbital fissure
and supplies the lateral rectus muscle.
Cranial nerve V: trigeminal nerve
1 Roots of the trigeminal nerve: contains a large sensory root, which originates in the trigeminal
ganglion , and a smaller motor root, which originates in the. motor nucleus of V
2 Three divisions: the ophthalmic, maxillary and mandibular nerves
(1) The ophthalmic N: sensory distribution in the face above the fissure of the eye.
①The lacrimal N
②The frontal N
③The nasocilliary N
(2) The maxillary N: sensory distribution in the face between the fissures of the eye and the mouth
①The infraorbital N
②The zygomatic N
③The pterygopalatine
④The superior alveolar nerves
(3) The mandibular N: sensory distribution in the face below the fissure of the mouth, the motor
fibers to supply the masticatory muscles, mylohyoid, tensor tympani muscle
①The auriculotemporal N
②The buccal N
③The lingual N
④The inferior alveolar N
⑤The nerve of masticatory muscles
Cranial nerve VII the facial nerve
1 Components: (l ) the somatic efferent fibers take origin from the facial nucleus and supply the
muscles of expression, (2) the visceral efferent fibers arise from the superior salivatory nucleus
and control the secretion of the lacrimal gland, the submandibular and sublingual salivary glands
and the mucous membrane of the nose and palate, and (3) the visceral afferent fibers arise from
the cells of the geniculate ganglion. The periphery processes of the ganglionic cells are distributed
to the taste buds on the anterior 2/3 of the tongue.
2 Course:The facial nerve passes through the internal acoustic meatus, and enters the facial canal.
The nerve leaves the facial canal through the stylomastoid foramen, then runs forward into the
parotid gland. Finally, it is distributed to muscles of expression .
3 The branches within the facial canal
(1) The greater petrosal nerve: distributed to the lacrimal gland and the glands of the nose and
palate.
(2) The chorda tympani: distributed to the mucous membrane covering the anterior 2/3 of the
tongue, the submandibular and sublingual glands.
(3) The stapedial nerve
4 The branches outside the facial canal
supply the muscles of expression:
(1) The temporal branches
(2) The zygomatic branches
(3) The buccal branches
(4) The marginal mandibular branch
(5) The cervical branch
5 The parasyrnpathetic ganglia
(l) The pterygopalatine ganglion: The fibers of the greater petrosal.nerve enter and are relayed in
the ganglion. The cells in the ganglion send the postganglionic fibers to distribute to the lacrimal
gland and the mucous membrane of the nasal cavity and palate and control their secretion .
(2) The submandibular ganglion: The fibers of the chorda tympani enter and are relayed in the
ganglion. The cells in the ganglion send the postganglionic fibers to distribute to the
submandibular and sublingual glands and control their secretions.
6 The clinical features of the facial nerve lesion
(1) Lesion in the facial canal : ①wrinkles on the forehead are smoothed out, the eye can not shut
voluntarily, the nasolabial fold becomes smooth on the affected side; ② when a smile is
attempted ,the angle of mouth draw to the unaffected side; ③there is a loss of taste in the anterior
2/3 of the tongue;④reduced salivation;⑤the sounds are very loud in the affected ear due to the
paralysis of the stapedius
(2) Lesion outside the facial canal : there is paralysis of the muscles of expression only.
Cranial nerve VIII The vestibulocochlear ( acoustic) nerve
It consists of choclear nerve and vestibular nerve.
1 The cochlear nerve(for hearing): Fibers from bipolar cells in the cochlear(spiral) ganglion
consist of peripheral processes that are distributed to the spiral organ (organ of Corti). And central
processes form the cochlear nerve and end in the ventral and dorsal cochlear nuclei.
2 The vestibular nerve(for equilibrium): Fibers from bipolar cells in the vestibular ganglion
consist of the peripheral processes that are distributed to the ampullae of the semicircular canals
and the maculas of the utricle and saccule, and the central processes form the vestibular nerve and
end in the vestibular nuclei.
Cranial nerve IX
The glossopharyngeal nerve
1 Components:①the somatic efferent fibers arise from the ambiguous nucleus and supply the
stylopharyngeus;②the visceral efferent fibers arise from inferior salivatory nucleus and control
the secretion of the parotid gland;③he visceral afferent fibers arise from the inferior ganglion to
supply the mucous membrane of the pharynx, the tonsil, the middle ear, the posterior 1/3 of the
tongue, and the carotid glomus and the carotid sinus;④the somatic afferent fibers arise from the
superior ganglion and supply the skin of the posterior surface of the auricle.
2 Course: The nerve leaves the skull through the jugular foramen, and passes forwards between
the internal jugular vein and internal carotid artery to reach the root of the tongue.
3 The main branches
(l) The tympanic nerve :It enters the tympanic cavity to form the tympanic plexus. The plexus
gives off many branches to the mucous membrane of the middle ear. The lesser petrosal nerve
arises from this plexus and enters the otic ganglion and is relayed in the ganglion. The cells in the
ganglion send the postganglionic fibers to distribute to the parotid gland.
(2) The carotid sinus branch (often double): descends along the internal carotid artery to the
wall of carotid sinus and the carotid glomus.
(3) The lingual branches : distributed to the posterior 1/3 of the tongue. They contains both fibers
of special sense (taste) and of general sensations.
(4) The pharyngeal branches: distributed to the pharynx and the stylopharyngeus.
4 The otic ganglion: its preganglionic fibers come from the lesser petrosal nerve. The
postganglionic fibers pass through a communicating branch to the auriculotemporal nerve which
supplies the parotid gland.
Cranial nerve X The vagus nerve
1 Components :①The visceral efferent fibers arise from the dorsal nucleus of vagus nerve, and
end in the paraorganic or interorganic parasympathetic ganglions in the throacic and abdominal
cavities. The postganglionic fibers supply the smooth muscles, cardiac muscles and glands of the
viscera.②The visceral afferent fibers arise from the inferior ganglion of vagus nerve and terminate
in the nucleus of solitary tract. The peripheral processes of this ganglionic cells are dlstributed to
the viscera of the neck, thorax and abdomen.③The somatic afferent fibers originate from the
superior ganglion of vagus nerve and end in the spinal nucleus of trigeminal nerve. The peripheral
processes of this ganglionic cells supplies the skin of the auricle and external acoustic meatus
and cerebral dura mater.④The somatic efferent fibers arise from the ambiguous nucleus and
supply the muscles of the larynx and the pharynx.
2 Course: It leaves the skull through the jugular foramen and descends within the carotid sheath.
The vagus nerve enters the thorax and forms the pulmonary plexus and the esophageal plexus.
Left vagus descends in front of the esophagus to form the anterior vagal trunk, right vagus
descends behind the esophagus to form the posterior vagal trunk. The vagal trunks enter the
abdominal cavity through the esophageal hiatus of the diaphragm and divide into their terminal
branches. The anterior vagal trunk divides into the anterior gastric branches and the hepatic
branches; the posterior vagal trunk divides into the posterior gastric branches and the celiac
branches.
3 The branches of the vagus nerve
(1)The branches in the neck
①The superior laryngeal nerve : distributed to the mucous membrane of the larynx above the
level of the fissure of glottis and the cricothyroid .
②The cervical cardiac branches: form the cardiac plexuses and distributed to the heart and the
wall of the aorta.
③The pharyngeal branch
(2)The branches in the thorax
①The recurrent laryngeal nerve: enters the larynx and then is named the inferior laryngeal nerve.
The nerve supplies all the muscles of larynx except for the cricothyroid, and is distributed to the
mucous membrane of the larynx below the level of glottis.
②The broncheal branches,and the esophageal branches
(3)The branches in the abdomen
①The anterior gastric branches and posterior gastric branches : are distributed to the stomach. The
branch reaching to the pyloric canal and pylorus is named the “crowls foot".
②The hepatic branches: join the hepatic plexus and supply the liver and gallbladder to regulate
the bile secretion.
③The celiac branches: join the celiac plexus and supply most viscera of the abdomen and
alimentary tract anterior to transverse colon.
4 Clinical feature of the vagus lesion
Unilateral injury of the recurrent laryngeal nerve produce the paralysis of vocal fold on the
same side, resulting in a weak hoarse voice. Bilateral injury of the recurrent laryngeal nerves
produce aphonia and even apnea.
Cranial nerve XI The accessory nerve
1 Root :consists of the cranial and spinal roots. The smaller cranial root arises from the ambiguous
nucleus. The cranial root arises from the accessory nucleus in the anterior horn of the upper 5-6
cervical segments.
2 Course: leave the skull through the jugular foramen.
3 Distribution: The cranial root is distributed to the sternocleidomastoid and the trapezius.The
spinal root joins the vagus and supplies the muscles of the larynx and pharynx.
Cranial nerve XII The hypoglossal nerve
1 Origin: arises from the hypoglossal nucleus.
2 Course: leaves the skull through the hypoglossal canal.
3 Distribution: supplies the all the extrinsic and intrinsic muscles of .the tongue (with the
exception of the palatoglossus).
4 Clinical feature of the hypoglossal nerve lesion
Injury to the hypoglossal nerve results in paralysis and atrophy of the affected side of
the tongue. The tongue deviates to the paralyzed side during protrusion.
Section 3 The Autonomic Nervous System
The autonomic (or visceral or vegetative) nervous system innervates the viscera ,
cardiovascular system and glands. And contains two groups of fibers: afferent fibers and efferent
fibers. The afferent fibers are divided into the sympathetic and parasympathetic divisions.
一、The sympathetic division(system)( or thoracolumbar division)
the lateral horn of T1 (or C8) -L2 (or L3) segments of.the spinal cord(preganglionic neurons)
→preganglionic fibers→sympathetic ganglia(postganglionic neurons) →postganglionic fibers→
vicera
1.Sympathetic ganglia: include the paravertebral ganglia and the prevertebral ganglia
(1) The paravertebral ganglia: on either side of the spinal column, and to form the sympathetic
trunk. The cervical portion contains the superior, the middle and inferior cervical ganglia. The
inferior cervical ganglion fuses with the first thoracic ganglion to form the cervicothoracic
(stelllate) ganglion. There are11 or 12 thoracic, 3 or 4 lumbar and 4 or 5 sacral ganlia on each
trunk.
(2) The prevertebral ganglia: include the celiac, the aorticorenal, the superior and inferior
mesenteric ganglia.
2. The communicating branches: connect the sympathetic ganglion with the corresponding spinal
nerve . and include the white and grey communicating branches .
3. The general distributions of the sympathetic nerves
(1) the lateral horn of T1 –T5→preganglionic fibers →the corresponding sympathetic ganglia
(C1-3 and T1-5 paravertebral ganglia) → postganglionic fibers→vicera of the head ,neck and
thorax; blood vessels, sweat gland and arrectores pilorum of the upper limb.
(2) the lateral horn of T5 –T12→preganglionic fibers→the corresponding sympathetic ganglia
(T5-12 paravertebral ganglia and the celiac, the aorticorenal ganglia ) → postganglionic fibers→
vicera of the abdomen ; the alimentary tract anterior to the left colic flexure.
(3) the lateral horn of L1 –L2(orL3)ganglia → preganglionic fibers → the corresponding
sympathetic ganglia (L1-L4, S1-S5 paravertebral ganglia and the superior and inferior mesenteric
ganglia ) → postganglionic fibers → vicera of the pelvis; blood vessels, sweat gland and
arrectores pilorum of the lower limb.
二、 The parasympethetic division(system)
consists of the cranial portion and sacral portion
1. The cranial portion of the parasympathetic system
(l ) The parasympathetic preganglionic fibers in the oculomotor nerve :
Edinger-Westphal nucleus→ preganglionic fibers(oculomotor N.) →the ciliary ganglion→
the postganglionic fibers→ the ciliary muscle and sphincter pupillae.
(2) The parasympathetic preganglionic fibers in the facial nerve:
① superior salivatory nucleus → preganglionic fibers(greater petrosal N.) → the
pterygopalatine ganglion→the postganglionic fibers→the lacrimal gland, mucosa of the nasal
cavity and palate
②superior salivatory nucleus→ preganglionic fibers(chorda tympani) → the submandibular
ganglion →the postganglionic fibers→the submandibular and the sublingual glands.
(3) The parasympathetic preganglionic fibers in the glossopharyngeal nerve
inferior salivatory nucleus → preganglionic fibers(lesser petrosal nerves) → the otic
ganglion→the postganglionic fibers→ the parotid gland.
(4) The parasympathetic preganglionic fibers in the vagus nerve
dorsal nucleus of vagus→ preganglionic fibers(vagus) →ganglia which are situated in or near
the organs innervated→the postganglionic fibers→ viscera of the neck, thorax and abdomen, the
alimentary tract anterior to the left colic flexure.
2. The sacral portion of the parasympathetic nerve
S2-S4 segments of the spinal cord→ preganglionic fibers (pelvic splanchnic nerve) →ganglia
which are situated in or near the organs innervated →the postganglionic fibers→ the pelvic
organs , the descending and sigmoid colon and rectum
三、 The main differences between the sympathetic and parasympathetic systems
1. The different central center
2. The different locations of the peripheral ganglia
3. The different ratio of the preganglionic fibers to the postganglionic
4. The different distributions
5. The different actions to a visceral organ
四、 The. autonomic plexuses
the sympathetic nerves, parasympathetic nerves and the afferent fibers of the the autonomic
system are interweave into extensive plexuses .Such as : the cardiac plexus, the pulmonary plexus,
the celiac plexus, the abdominal aortic plexus,et al.
五、The visceral afferent (sensory) nerves
1. Features of the visceral sensation
①insensitive to cutting, crushing or burning
②sensitive to the excessive tension and contraction of smooth muscle
③sensitive to certain pathological conditions
④location of the visceral pain is poorly
六、The referred pain
In pathological condition, visceral pain radiates to cutaneous areas and is therefore assumed by the
patient to arise mainly or exclusively in surface areas of the body. The kind of pain is called
referred pain.
Section 3
The Nervous Pathways
The nervous pathways are classified into: sensory (ascending) pathways and motor
(descending) pathways.
一、The sensory (ascending) pathways
The sensation may be divided into 4 groups: superficial, deep, visceral and special . Superficial
sensation is concerned with touch, pain, temperature,et al. Deep sensation, with muscle and joint
position and motion senses, muscle pain, and vibration sense. Visceral sensation, with nausea,
hunger, blood pressure, osmotic pressure, et al. Special sensation, with smell, taste, vision,
equilibrium and hearing. The sensory pathways mainly include the deep and superficial sensory,
visual and acoustic pathways. Most sensory pathways contain three orders of neurons: ①the first
order neurons in the spinal ganglia;②the second neurons in the spinal cord or brain stem;③the
third neurons in the ventral posterior nucleus of the thalamus .
1. The deep sensory (or the proprioceptive) pathways
convey the deep sensations and fine touch sensation (discriminatory sensation).
(1) The conscious deep sensory pathways
①The deep sensory pathway of trunk and limbs
the receptors of the muscle, tendon, periosteum and joint, and skin→the spinal ganglia(the first
neurons)→gracile fasciculus and cuneate fasciculus→ the gracile and cuneate nuclei(the second
neurons) × medial lemniscus →the ventral posterolateral(VPL) nucleus of the thalamus( the
third neurons) →superior and middle parts of the postcentral gyrus and the postetior part of the
paracentral lobule
②The deep sensory pathways of head and face: is not known
(2). The unconscious deep sensory pathway
the receptors of the muscles, tendon, periosteum and joint→the spinal ganglia (the first order
neurous) →the central processes of the first order neurous→ the thoracic nucleus and posterior
grey horn(the second neurons)→the anterior or posterior spinocerebellar tract→the cerebellum
2. The superficial sensory pathways
convey the sensation of pain, temperature and rude tactile from the skin and mucosa to the
centers
(1). The superficial sensory pathway of trunk and limbs
①The pain and thermal(temperature) pathway
the cutaneous exteroceptor of the trunk and limbs→ the spinal ganglia (the first
neurons) →the dorsolateral fasciculus( upward within one or two segments ) →Laminae I, IV
and V of the posterior horn( the second neurons)
the anterior and lateral spinothalamic
tracts →the ventral posterolateral(VPL) nucleus of the thalamus( the third neurons)→the upper
and middle parts of the postcentral gyrus, and the posterior part of the paracentral lobule
(2). The superficial sensory pathway of head and face
the superficial receptor in the skin and mucosa of the head and face→the trigeminal
ganglion(the first neurons) → the central processes→the spinal and pontine nuclei of the
trigeminal nerve (pain and temperature sensation→spinal nucleus, touch sensation→pontine
nucleus, the second neurons ) × the trigeminal lemniscus→ the ventral posteromedial(VPM)
nucleus of the thalamus(the third neurons) →the inferior part of the postcentral gyrus.
3 The visual pathways
(l) The visual pathway
The receptors (rods and cones) →the bipolar cells (the first order neurons) →the ganglion
cells (the second neurons) →optic nerve →the optic chiasma(fibers from the nasal halves of the
retinae cross)→ the optic tract→ Within the chiasma a partial decussation→the lateral geniculate
nucleus→the optic radiation(geniculocalcarine tract)→the calcarine sulcus of the occipital lobe
(2) Pupillary light reflexes
①Pathway
②Direct and indirect(or consensual)papillary light reflexes
③Clinical features of visual pathway lesion
4 The acoustic(auditory) pathway
Receptors(spiral organ of Corti) →the bipolar cells in the spiral ganglion(the first order
neurons) →the cochlear nerve→the cochlear nuclei(the second neurons)×the lateral lemniscus
(also receive the fibers from the ipsilateral superior olivary nucleus and the cochlear nuclei) →the
medial geniculate body(the third neurons)→the acoustic radiation→the transverse temporal gyri
5 The equilibratory pathway
Receptors (the cristae ampullae, maculae of the utricle and saccule)→bipolar neurons in the
vestibular ganglion (the first order neurons) →the vestibular nerve →the vestibular nucleus ( the
second neurons) →①the medial longitudinal fasciculus;②the vestibulospinal tract;③entering the
cerebellum via the inferior cerebellar peduncle;④connecting with the reticular formation of brain
stem, vagus and glossopharyngeal nuclei;⑤connecting with the temporal, parietal and frontal
cortex of the hemisphere.
二、The Motor (descending) Pathways
They are concerned with motor function, and include pyramidal and extrapyramidal systems.
1 The pyramidal system
It is concerned with the voluntary movement of the skeletal muscles and is composed of two
orders of neurons: the upper and lower motor neurons. The upper motor neurons are composed of
the giant pyramidal cells (Betz cells) and other pyramidal cells in the precentral gyrus and
paracentral lobule, and their axons (the corticonuclear tract and the corticospinal tract). The lower
motor neurous include the cranial motor cells of the brain stem and motor cells of the anterior
horn of the spinal cord., and their axons(cranial nerves and spinal nerves).
(l) The corticonuclear(corticobulbar) tract
pyramidal neurons in the inferior part of the precentral gyrus→ the corticonuclear tract→
through the genu of internal capsule→the bilateral motor nuclei of the cranial nerves(oculomotor,
trochlear, trigeminal motor, ambiguous, accessory nuclei and superior part of the facial nucleus,
and to the contralateral hypoglossal nucleus and the inferior part of the facial nucleus)
(2) The corticospinal tract
pyramidal cells of the superior and middle parts of the precentral gyrus and the paracentral lobule
→the corticospinal tract →through the posterior limb of internal capsule→ the intermediate 3/5
of the cerebral crus→ the basilar part of the pons→ the ventral part of the medulla oblongata
× the lateral corticospinal tract→ipsilateral and contralateral anterior horns of spinal cord
→ the anterior corticospinal tract (above the mid-thoracic segments) →the anterior horn
(3) Clinical features of the upper and lower motor neurons lesion
Upper motor neuron
Or supranuclear lesion
Structures involved
cerebral cortex or corticospinal
and corticonuclear tracts
Lower motor neuron
infranuclear lesion
motor nuclei of the cranial nerves and
the cranial N
motor cells of the anterior horn of the spinal cord and spinal N
Muscle tone
Myotatic(Deep) reflex
increased
hyperactivite
Cutaneous(Superficial) reflex decreased or absent
Pathological reflex
existed(Babinski sign)
Muscle bulk
slight atrophy
Classical description
spastic paralysis
decreased
decreased or absent
absent
absent
pronounced atrophy
flaccid paralysis
2 The extrapyramidal system
It is the nervous pathways which influence and control the movement of body except the
pyramidal system. The system includes the corpus striatum, together with the subthalamic nucleus,
substantia nigra, red nucleus, and brain stem reticular formation.The main functions of the
extrapyramidal system in man are to regulate the muscles tone, coordinate the muscular activities,
maintain the normal body posture and produce habitual and rhythmic movements.
(l). The cortico-pallidal system
the frontal, parietal, occipital and temporal lobes→ the caudate nucleus and putamen →the
globus pallidus→the thalamus,substantia nigra, subthalamic nucleus,red nucleus and the reticular
formation of brain stem→the cerebral cortex
(2). The corticoponto-cerebellar system
the frontal, parietal, occipital and temporal lobes → the frontopontine, parietopontine,
occipitopontine and temporopontine tracts → the pontine nuclei × the neocortex of the
cerebellum→the dentate nucleus ×
the ventrolateral nucleus of the thalamus →the precentral motor area of the cerebral cortex
and red nucleus→ rubrospinal tract