Transcript The Nervous System

The Nervous System
SHANDONG UNIVERSITY
Liu Zhiyu
Organizations
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Central nervous system (CNS)
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Peripheral nervous system (PNS)
Major Division of the
Central Nervous System (CNS)
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Brain
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Telencephalon
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Diencephalon
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Cerebellum
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Brain stem
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Midbrain
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Pons
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Medulla oblongata
Spinal cord
Major Division of the
Peripheral Nervous System (PNS)
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Cranial nerves (12 pairs)
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Spinal nerves (31 pairs)
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Visceral nerves
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Visceral sensory nerve
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Visceral motor nerve
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Sympathetic part
Parasympathetic part
Cellular Organization
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Neuron
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Cell body
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Axon
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Dendrites
Neuroglia －glial cell
Classification of Neurons
Structural classification
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Bipolar neuron
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Pseudounipolar neuron
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has an axon and a dendrite
has a central branch and a
peripheral branch
Multipolar neuron
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has an axon and two or more
dendrites
Classification of Neurons
Functional classification
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Sensory (afferent) neuron
Motor (efferent) neuron
Association neuron
Reflex and Reflex Arc
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Reflex: a reaction of the organism by
the nervous system in response to a
stimulus
Reflex arc: has 5 basic components
Receptor
↓
Sensory neurons
↓
CNS
↓
Motor neurons
↓
Effector
Reflex and Reflex Arc
Basic Terminology in Nervous System
In the CNS
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Gray matter: collection of nerve cell
bodies and their dendrites, gray color
during fresh condition
Cortex: the outermost layer of gray
matter in cerebrum and cerebellum
White matter: collection of nerve
fibers, white color during fresh
condition
Medulla: a central core of white
matter beneath cortex of cerebrum
and cerebellum
Basic Terminology in Nervous System
In the CNS
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Nucleus:
a collection ( group ) of cell bodies
which have the same shape and
function
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Fasciculus ( tract ):
a bundle of nerve fibers which have the
same origin, termination, pathway and
function
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Reticular formation: an admixture
of cross-crossing fibers with larger or
smaller groups of nerve cells occupying
the meshes
Basic Terminology in Nervous System
In the PNS
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Ganglion: a collection of
neuronal cell bodies outside
the CNS
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Nerve: a bundle of nerve
fibers held together by
connective tissue sheath
The Spinal Cord
Position of the Spinal Cord
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Lies in vertebral canal
Continuous above with medulla
oblongata at level of foramen
magnum
Ends below at the lower border of
L1 in the adult; at birth the cord
ends at level of L3
External Features of Spinal Cord
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A long cylindrical structure and slightly
flattened anteroposteriorly
Two enlargements
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Cervical enlargement
corresponds to the C4 to the T1 segments
Lumbosacral enlargement corresponds to
the L2 to the S3 segments
Conus medullaris
Filum terminale
Cauda equina
External Features of Spinal Cord
Fissure and sulci
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Anterior median fissure
Posterior median sulcus
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Posterior median septum
Anterolateral sulcus －anterior
(motor) roots emerge serially
Posterolateral sulcus －posterior
(sensory) roots enter spinal cord,
each bear a spinal ganglion which
constitutes the first cell-station of the
sensory nerves
Segments of Spinal Cord
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A portion of the cord that
gives rise to a pair of spinal
nerve constitutes a segment.
There are 31 segments
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
Relationship of spinal Cord Segments
to Vertebral Numbers
Spinal segments
Upper cervical region (C1~C4)
Vertebral levels (spines)
Lie opposite the corresponding vertebrae
Lower cervical and upper thoracic One lower in number than corresponding vertebrae
region (C5~T4)
Middle thoracic region (T5~T8)
Two lower in number than corresponding vertebrae
Lower thoracic region (T9~T12)
Three lower in number than corresponding
vertebrae
Lumber segments
T10~T12
Sacral and coccygeal segments
L1
Relationship of spinal Cord Segments
to Vertebral Numbers
Spinal segments
Upper cervical region (C1~C4)
Vertebral levels (spines)
= C1 ~ C4
Lower cervical and upper thoracic －1 = C4 ~ T3
region (C5~T4)
Middle thoracic region (T5~T8)
－2 = T3 ~ T6
Lower thoracic region (T9~T12)
－3 = T6 ~ T9
Lumber segments
= T10 ~ T12
Sacral and coccygeal segments
= L1
Structure of Spinal Cord
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Gray matter
White matter
Central canal
Gray Matter of Spinal Cord
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Anterior horn (column)
Posterior horn (column)
Lateral horn (column) is present in
the thoracic and upper lumber segments
of the cord (T1-L3)
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Intermediate zone
Anterior gray commissures
Posterior gray commissures
Gray Matter of Spinal Cord
Posterior horn (column):
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Marginal layer
Substantia gelatinosa
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Nucleus proprius
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Situated at the apex of posterior horn
throughout the length of spinal cord
Concerns the sensations of pain and
temperature
Situated anterior to the substantia
gelationnosa throughout the length of
spinal cord
Receives fibers that are associated
with the senses
Nucleus thoracicus
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Situated at the base of posterior horn
and extending from segments
C8~L3
Associated with proprioceptive
endings
Gray Matter of Spinal Cord
Intermediate zone
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Intermediaolateral nucleus
(lateral horn)
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Sacral parasympathetic nucleus
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Extents from segments T1~L3,
Containing sympathetic
preganglionic neurons
Extents from segments S2~S4,
Containing parasympathetic
preganglionic neurons
Intermediomedial nucleus
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Throughout the length of spinal cord
Associated with receiving viscera
afferent information
Gray Matter of Spinal Cord
Anterior horn (column):
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Two kinds of motor neurons
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α-motor neuron: large multipolar
neuron, innervates skeletal muscles,
producing contraction of muscles
γ-motor neuron: smaller multipolar
neuron, innervates intrafusal muscle
fibers of neuromuscular spindles,
regulating muscular tonus
Interneuron —Renshaw’s cell:
negative feedback mechanism
Two groups of nuclei
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Medial nuclear group: present in
most segments of spinal cord,
innervating axial muscles
Lateral nuclear group: present only
in cervical and lumbosacral
enlargements, innervating limb
muscles
Rexed’s lamina
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Posterior horn is formed
by lamina Ⅰ to Ⅵ；
Intermediate zone
corresponding to lamina
Ⅶ；
Anterior horn is
composed laminae Ⅷ
and Ⅸ；
lamina Ⅹ is the gray
matter surrounding the
central canal.
Important Subdivision of Spinal Cord Gray Matter
Region
Lamina
Nucleus
Posterior horn
Ⅰ
Marginal layer
Ⅱ
Substantia gelatinosa
Ⅲ, Ⅳ
Nucleus proprius
Ⅶ
Nucleus thoracicus (C8~L3)
Ⅶ
Intermediolateral nucleus (T1~L3)
Ⅶ
Sacral parasympathetic nucleus (S2~S4)
Ⅶ
Intermediomedial nucleus
Ⅸ
Motor neuron
Intermediate
zone
Anterior horn
White Matter of Spinal Cord
White matter contains three kinds of fibers: ascending,
descending, and fasciculus proprius
Posterior funiculus
Lateral funiculus
Anterior funiculus
Anterior white commissure
Ascending Tracts
Fasciculus gracilis
Fasciculus cuneatus
Posterior spinocerebellar tract
Anterior spinocerebellar tract
Spinothalamic tract
Fasciculus cuneatus
Fasciculus gracilis
Spinothalamic tract
Ascending tracts
Tract
Site of origin Funiculus Termination
Function
Fasciculus
gracilis
Spinal ganglia
below segment
T5
Fasciculus
cuneatus
Spinal ganglia
above segment
T4
Conscious proprioceptive
(vibratory sense, and
muscle joint sense) and
fine touch sensation of
trunk and limbs
Posterior
spinocerebellar
Homolateral
nucleus
thoracicus
Anterior
spinocerebellar
Contralateral
Laminae
Ⅴ~Ⅶ
Spinothalamic Laminae
Ⅰ, Ⅳ~Ⅶ
Posterior
Gracile
nucleus
Cuneate
nucleus
Lateral
Cerebellum
Unconscious
proprioception from lower
limb and lower portion of
trunk
Lateral
and
anterior
Dorsal
thalamus
Pain, temperature and
crude touch sensation of
trunk and limbs
Descending Tracts
Lateral corticospinal tract
Fasciculus proprius
Rubrospinal tract
Medial longitudinal
fasciculus
Reticulospinal tract
Vestibulospinal tract
Tectospinal tract
Anterior corticospinal tract
Descending tracts
Tract
Site of origin
Funiculus
Lateral
corticospinal
Cerebral cortex
Lateral
Anterior
corticospinal
Cerebral cortex
Anterior
Rubrospinal
Red nucleus
Vestibulospinal
Termination
Function
Laminae
Ⅳ~Ⅸ
anterior horn
Voluntary movement
Lateral
Laminae
Ⅴ~Ⅶ
Facilitates activity of
flexor muscles
Homolateral
vestibular nuclei
Anterior
Laminae
Ⅶ~Ⅷ
Facilitates activity of
extensor muscles
Reticulospinal
Reticular
formation
Anterior and
lateral
Laminae
Ⅶ~Ⅷ
Voluntary movement
Medial
longitudinal
fasciculus
Vestibular nuclei
Anterior
Laminae
Ⅶ~Ⅷ
Coordinate neck with
eye movement
Tectospinal
Superior
colliculus
Anterior
Laminae
Ⅵ~Ⅷ
Fasciculus
proprius
Spinal cord
Anterior,
lateral and
posterior
Spinal cord
Intrinsic reflex
mechanism of spinal
cord
Main functions of spinal cord
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Conduction of excitations
Reflex activity