The Nervous System

SHANDONG UNIVERSITY

Liu Zhiyu

Organizations

Central nervous system (CNS)

Peripheral nervous system (PNS)

Major Division of the Central Nervous System (CNS)

Brain Telencephalon

Diencephalon

Cerebellum

Brain stem

Midbrain

Pons

Medulla oblongata

Spinal cord

Major Division of the Peripheral Nervous System (PNS)

Cranial nerves (12 pairs)

Spinal nerves (31 pairs)

Visceral nerves Visceral sensory nerve

Visceral motor nerve

Sympathetic part

Parasympathetic part

Cellular Organization

Neuron Cell body

Axon

Dendrites

Neuroglia － glial cel

l

Classification of Neurons

Structural classification Bipolar neuron

has an axon and a dendrite Pseudounipolar neuron

has a central branch and a peripheral branch

Multipolar neuron has an axon and two or more dendri

tes

Classification of Neurons

Functional classification Sensory (afferent) neuron Motor (efferent) neuron Association neuron

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

Reflex and Reflex Arc

Basic Terminology in Nervous System

In the CNS 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 Nucleus:

a collection ( group ) of cell bodies which have the same shape and function

Fasciculus ( tract ): a bundle of nerve fibers which have the same origin, termination, pathway and function

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 Ganglion: a collection of

neuronal cell bodies outside the CNS

Nerve: a bundle of nerve fibers held together by connective tissue sheath

The Spinal Cord

Position of the Spinal Cord

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

A long cylindrical structure and slightly flattened anteroposteriorly

Two enlargements Cervical enlargement correspon

ds to the C4 to the T1 segments Lumbosacral enlargement corresponds t

o the L2 to the S3 segments

Conus medullaris Filum terminale Cauda equina

External Features of Spinal Cord

External Features of Spinal Cord

Fissure and sulci Anterior median fissure Posterior median sulcus

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

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 Vertebral levels (spines)

Upper cervical region (C1~C4) Lie opposite the corresponding vertebrae

Lower cervical and upper thoracic region (C5~T4)

One lower in number than corresponding vertebrae

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 Vertebral levels (spines)

Upper cervical region (C1~C4) = C1 ~ C4

Lower cervical and upper thoracic region (C5~T4)

－ 1 = C4 ~ T3

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

Gray matter White matter Central canal

Gray Matter of Spinal Cord Anterior horn (column) Posterior horn (column) Lateral horn (column) is present in th

e thoracic and upper lumber segments of the cord (T1-L3)

Intermediate zone Anterior gray commissures Posterior gray commissures

Gray Matter of Spinal CordPosterior horn (column): Marginal layer Substantia gelatinosa

Situated at the apex of posterior horn throughout the length of spinal cord

Concerns the sensations of pain and temperature

Nucleus proprius Situated anterior to the substantia gel

ationnosa throughout the length of spinal cord

Receives fibers that are associated with the senses

Nucleus thoracicus Situated at the base of posterior horn

and extending from segments C8~L3 Associated with proprioceptive endin

gs

Gray Matter of Spinal Cord

Intermediate zone Intermediaolateral nucleus (later

al horn) Extents from segments T1~L3, Containing sympathetic preganglioni

c neurons Sacral parasympathetic nucleus

Extents from segments S2~S4, Containing parasympathetic pregan

glionic neurons Intermediomedial nucleus

Throughout the length of spinal cord Associated with receiving viscera aff

erent information

Gray Matter of Spinal Cord Anterior horn (column): Two kinds of motor neurons

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 Medial nuclear group: present in mo

st segments of spinal cord, innervating axial muscles

Lateral nuclear group: present only in cervical and lumbosacral enlargements, innervating limb muscles

Rexed’s lamina

Posterior horn is formed by lamina to Ⅰ Ⅵ ；

Intermediate zone corresponding to lamina Ⅶ ；

Anterior horn is composed laminae and Ⅷ Ⅸ ；

lamina is the gray mattⅩer 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

Intermediate zone

Ⅶ Nucleus thoracicus (C8~L3)

Ⅶ Intermediolateral nucleus (T1~L3)

Ⅶ Sacral parasympathetic nucleus (S2~S4)

Ⅶ Intermediomedial nucleus

Anterior horn Ⅸ Motor neuron

White Matter of Spinal Cord White matter contains three kinds of fibers: ascending, d

escending, and fasciculus proprius

Anterior funiculus

Lateral funiculus

Posterior funiculus

Anterior white commissure

Ascending Tracts

Fasciculus gracilis

Fasciculus cuneatus

Posterior spinocerebellar tract

Anterior spinocerebellar tract

Spinothalamic tract

Fasciculus gracilis

Fasciculus cuneatus

Spinothalamic tract

Ascending tracts

Tract Site of origin Funiculus Termination Function

Fasciculus gracilis

Spinal ganglia below segment T5

Posterior Gracile nucleus

Conscious proprioceptive (vibratory sense, and muscle joint sense) and fine touch sensation of trunk and limbsFasciculus cu

neatusSpinal ganglia above segment T4

Cuneate nucleus

Posterior spinocerebellar

Homolateral nucleus thoracicus

Lateral Cerebellum Unconscious proprioception from lower limb and lower portion of trunk

Anterior spinocerebellar

Contralateral Laminae Ⅴ~Ⅶ

Spinothalamic Laminae , ~Ⅰ Ⅳ Ⅶ

Lateral and anterior

Dorsal thalamus

Pain, temperature and crude touch sensation of trunk and limbs

Descending Tracts

Lateral corticospinal tract

Anterior corticospinal tract

Rubrospinal tract

Vestibulospinal tract

Reticulospinal tract

Medial longitudinal fasciculus

Tectospinal tract

Fasciculus proprius

Descending tractsTract Site of origin Funiculus Termination Function

Lateral corticospinal

Cerebral cortex Lateral Laminae Ⅳ~Ⅸanterior horn

Voluntary movement

Anterior corticospinal

Cerebral cortex Anterior

Rubrospinal Red nucleus Lateral Laminae Ⅴ~Ⅶ

Facilitates activity of flexor muscles

Vestibulospinal 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

Conduction of excitations Reflex activity