1. The Nervous System SHANDONG UNIVERSITY Liu Zhiyu

2. Organizations Central nervous system (CNS) Peripheral nervous system (PNS)

3. Major Division of the Central Nervous System (CNS) Brain  Telencephalon  Diencephalon  Cerebellum  Brain stem Midbrain Pons Medulla oblongata Spinal cord

4. 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

5. Cellular Organization Neuron  Cell body  Axon  Dendrites Neuroglia － glial cell

6. 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 dendrites

7. Classification of Neurons Functional classification Sensory (afferent) neuron Motor (efferent) neuron Association neuron

8. 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

10. 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

11. 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

12. 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

13. The Spinal Cord

14. 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

16. A long cylindrical structure and slightly flattened anteroposteriorly Two enlargements  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

17. 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

18. 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

19. Relationship of spinal Cord Segments to Vertebral Numbers Spinal segmentsVertebral 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 segmentsT10~T12 Sacral and coccygeal segmentsL1

20. Relationship of spinal Cord Segments to Vertebral Numbers Spinal segmentsVertebral 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

21. Structure of Spinal Cord Gray matter White matter Central canal

22. Gray Matter of Spinal Cord Anterior horn (column) Posterior horn (column) Lateral horn (column) is present in the thoracic and upper lumber segments of the cord (T1-L3) Intermediate zone Anterior gray commissures Posterior gray commissures

23. Gray Matter of Spinal Cord Posterior 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 gelationnosa 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 endings

24. Gray Matter of Spinal Cord Intermediate zone Intermediaolateral nucleus (lateral horn)  Extents from segments T1~L3,  Containing sympathetic preganglionic neurons Sacral parasympathetic nucleus  Extents from segments S2~S4,  Containing parasympathetic preganglionic neurons Intermediomedial nucleus  Throughout the length of spinal cord  Associated with receiving viscera afferent information

25. 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 most segments of spinal cord, innervating axial muscles  Lateral nuclear group: present only in cervical and lumbosacral enlargements, innervating limb muscles

26. Rexed’s lamina 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.

27. Important Subdivision of Spinal Cord Gray Matter RegionLaminaNucleus 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

28. White Matter of Spinal Cord White matter contains three kinds of fibers: ascending, descending, and fasciculus proprius Anterior funiculus Lateral funiculus Posterior funiculus Anterior white commissure

29. Ascending Tracts Fasciculus gracilis Fasciculus cuneatus Posterior spinocerebellar tract Anterior spinocerebellar tract Spinothalamic tract

30. Fasciculus gracilis Fasciculus cuneatus

31. Spinothalamic tract

32. 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 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 crude touch sensation of trunk and limbs

33. Descending Tracts Lateral corticospinal tract Anterior corticospinal tract Rubrospinal tract Vestibulospinal tract Reticulospinal tract Medial longitudinal fasciculus Tectospinal tract Fasciculus proprius

35. Descending tracts TractSite of originFuniculusTerminationFunction Lateral corticospinal Cerebral cortexLateralLaminae Ⅳ ~ Ⅸ anterior horn Voluntary movement Anterior corticospinal Cerebral cortexAnterior RubrospinalRed nucleusLateralLaminae Ⅴ ~ Ⅶ Facilitates activity of flexor muscles VestibulospinalHomolateral vestibular nuclei AnteriorLaminae Ⅶ ~ Ⅷ Facilitates activity of extensor muscles ReticulospinalReticular formation Anterior and lateral Laminae Ⅶ ~ Ⅷ Voluntary movement Medial longitudinal fasciculus Vestibular nucleiAnteriorLaminae Ⅶ ~ Ⅷ Coordinate neck with eye movement TectospinalSuperior colliculus AnteriorLaminae Ⅵ ~ Ⅷ Fasciculus proprius Spinal cordAnterior, lateral and posterior Spinal cordIntrinsic reflex mechanism of spinal cord

36. Main functions of spinal cord Conduction of excitations Reflex activity