The Nervous System ——The Spinal Cord Liu jiao Binzhou Medical University Department Of Anatomy

Divisions Central nervous system (CNS) Peripheral nervous system (PNS)

Central nervous system (CNS) Brain Telencephalon Diencephalon Cerebellum Brain stem Midbrain Pons Medulla oblongata Spinal cord

Reflex and reflex arc 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 Moter neurons Effector

The Spinal Cord 脊髓 Position It is located in the vertebral canal Continuous above with medulla oblongata at level of foramen magnum Ends below at lower border of L1 in adult; at birth at level of L3

External features A long cylindrical structure and slightly flattened anteroposteriorly, Conus medullaris（conical termination） Filum terminale （formed by a condensation of pia mater） Cauda equina Diameters of the spinal cord are not equal at various level. Two enlargements Cervical enlargement : corresponds to the C4 to the T1 segments Lumbosacral enlargement : corresponds to the L2 to the S3 segments

Fissure and sulci Anterior median fissure Posterior median sulcus 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

Relationship of segments of spinal cord to vertebrae 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 segments of spinal cord to vertebrae 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

Internal structures Central canal Gray matter Lateral horn (column) Anterior horn (column) Posterior horn (column) Intermediate zone Lateral horn (column) Anterior gray commissures Posterior gray commissures White matter Anterior funiculus lateral funiculus Posterior funiculus Anterior white commisure

Posterior horn (column): Marginal layer Substantia gelatinosa Nucleus proprius Nucleus thoracicus in segments C8~L3

Intermediate zone Intermediaolateral nucleus (lateral horn or column): lies in segments T1~L3, containing sympathetic preganglionic neurons Sacral parasympathetic nucleus: lies in segments S2~S4, containing parasympathetic preganglionic neurons Intermediomedial nucleus : for sensation of viscera

Anterior horn (column): contain motor neurons Three kinds of neuron α-motor neuron: larger multipolar neuron, innervates extrafusal fibers of skeletal m., producing contraction of m. γ-motor neuron: smaller neuron, innervates intrafusal fibers regulating muscular tonus Renshaw’s cell: negative feedback mechanism Two groups of nuclei 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 板层 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 Intermediate zone Ⅶ Nucleus thoracicus (C8~L3) Intermediolateral nucleus (T1~L3) Sacral parasympathetic nucleus (S2~S4) Intermediomedial nucleus Anterior horn Ⅸ Motor neuron

Ⅲ) White matter White matter contains three kinds of fibers: ascending, descending, and fasciculus proprius

Ascending tracts Fasciculus gracilis Fasciculus cuneatus Posterior spinocerebellar tract Anterior spinocerebellar tract Spinothalamic tract

Fasciculus gracilis and fasciculus cuneatus Fasciculus gracilis and fasciculus cuneatus enter the ipislateral posterior funiculus of the spinal cord The fiber arising from sacral, lumbar and lower 8 thoracic segements make up the fasciculus gracilis. While the fiber arising from the upper 4 thoracic and cervical segements make up the fasciculus cuneatus. The two tracts conduct impuls of the discriminating tactle (ability to recognize the size, shape, and texture of an object) and kinesthetic (sense of position, movement and vibration) T3 T4 T5 Spinal ganglion T6

Ascending tracts Spinothalamic tract 脊神经节 It includes lateral and anterior spinothalamic tracts, and its fibers associated with pain and thermal senses. The fibers cross in the anterior commissure and ascend in the opposite lateral funiculus They transmit impulses associated with rough touch, pain and thermal senses on the opposite side of the body. 脊神经节

Ascending tracts Tract Site of origin Funiculus Termination Function Fasciculus gracilis Spinal ganglia below segment T5 Posterior Gracile nucleus Convey proprioceptive and fine touch sensation of trunk and limbs Fasciculus cuneatus Spinal 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 simple touch sensation of trunk and limbs

Descending tracts Fasciculus proprius Lateral corticospinal tract Rubrospinal tract Reticulospinal tract Vestibulospinal tract Tectospinal tract Medial longitudinal fasciculus Anterior corticospinal tract

Corticospinal tract This tract arises from the cerebral cortex, descends through the internal capsule and brain Stem, and is divided into: 1) Lateral corticospinal tract It decussates obliquely in the medulla oblongata and descends in lateral funiculus. 2) Anterior corticospinal tract It occupies a strip adjacent to the anterior median fissure, terminating in the bilateral anterior horns.

Descending tracts Tract Site of origin Funiculus Termination Function Lateral corticospinal Cerebral cortex Lateral Laminae Ⅳ~Ⅸ anterior horn Voluntary movement Anterior corticospinal Anterior Rubrospinal Red nucleus Ⅶ~Ⅶ Excitatory of flexors Vestibulospinal Homolateral vestibular nuclei Ⅶ~Ⅷ Excitatory of extensors Reticulospinal Reticular formation Anterior and lateral Medial longitudinal fasciculus Vestibular nuclei Coordinate neck with eye movement Tectospinal Superior colliculus Ⅵ~Ⅷ Fasciculus proprius Spinal cord Anterior, lateral and posterior Intrinsic reflex mechanism of spinal cord

Main functions of spinal cord Conduction of excitations Reflex activity

Reflex arc

Reflex arc

The clinical consideration Pathologic lesion in the spinal cord can produce characteristic syndromes (abnormal masses compression, mechanical injury). Complete hemisection of spinal cord produce Brown-sequard syndrome.

Brown-sequard syndrome. the signs and symptoms of patient include ipislateral motor neuron paralysis in the segments of the lesion (resulting from damage to corticospinal tract), ipislateral loss of propriceptive, vibratory, and two point discrimination senses (resulting from damage to fasciculus gracilis and cuneatus ). A contralateral loss of pain and temperature senses below one or two segments at the damaged level (resulting from damage to the spinothalamic tracts).

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