No. 22

1. No. 22 • Spinal cord (2) • Brain stem (1)

2. Ⅱ. Internal Structure • In transverse section, the spinal cord is seen to consist of the gray matter and the whitematter. The gray matter of the spinal cord is centrally located and is surrounded by the white matter.

4. Ⅰ) Gray Matter • The gray matter forms a butterfly-shaped core of the spinal cord, roughly in the form of a letter H. • The transverse bar of gray matter that connects the two lateral gray areas is the gray commissure. • Within the gray commissure is the narrow, fluid-filled central canal, which is continuous with the fourth ventricle. The anterior and posterior to the gray matter are respectively anterior gray commissure and posterior gray commissure. The anterior and posterior gray commissures are also called central gray.

5. The vertical bars of the gray H, on either side of the gray commissure, are separated into: • a pair of posterior horns (columns), • a pair of anterior horns (columns). • In the thoracic and upper lumbar (L1-3) regions, the spinal cord also has a pair of lateral horns (columns). The area located between the anterior and posterior horns is the intermediate zone. • The gray matter of the spinal cord contains an enormous number of neurons of varying size and shape.

6. Rexed lamina structure of gray matter of spinal cord. 1. Lamina Ⅰ • It is also called marginal layer or Walderyer layer.Thenucleus posteromarginalisis in this lamina, forming a thin layer of cells covering the tip of the posterior horn. 2. Lamina Ⅱ • It is also named the substantia gelatinosa anterior to marginal area and is the correlation between the spinal segments. 3. Lamina Ⅲ

7. 4. Lamina Ⅳ • In lamina Ⅲ and Ⅳ, there are larger cell groups—nucleusproprius. They receive the numerous afferent fibers from posterior root. • Fibers from the nucleus proprius, crosses in the anterior white commisure and contribute to the spinothalamic tract. 5. Lamina Ⅴ • It is equivalent to the neck of posterior horn. It has reticular nucleus. 6. Lamina Ⅵ • It lies the base part of posterior horn. • Lamina Ⅴ and Ⅵ receive the afferent fibers of proper sensation from the posterior roots.

8. 7. Lamina Ⅶ • It occupies the great part of the intermediate zone. 1) The nucleus thoracicus (nucleus dorsalis of Clarke) is situated in the medial portion of the base of posterior horn. It is well defined in the segments of C8—L3. The axons contribute fibers to the posterior spinocerebellar tracts of ipsilateral side.

9. 2) Theintermediomedial nucleuslies in the most medial portion of lamina Ⅶ, lateral to the lamina Ⅹ, anterior to the nucleus thoracicus., receiving the • It receives the visceral afferent fibers from the posterior roots and gives rise to fibers which constitute the anterior spinocerebellar tract of both sides of the spinal cord.

10. 3) The intermediolateral nucleus • It is located between the anterior and posterior horns, lateral to the intermediomedial nucleus. The intermediolateral nucleus of the lateral horn from C8—L3) segments, is the lower center of sympathetic nerve. It is the site where the bodies of sympathetic neurons lie. • In segments S2—S4, the site equivalent to the intermediolateral nucleus, the sacral parasympathetic nucleus is the lower center of parasymthetic nerve.

11. 8. Lamina Ⅷ • It is in the base part of anterior horn, consisting of intermediate neurons. In cervical and lumbosacral enlargements it is only located in the medial part of anterior horn. • It receives the fibers from joining laminae and some descending funiculi and sends out fibers to the lamina Ⅸ.

12. 9. Lamina Ⅸ • It is composed of anterior horn motor neurons and intermediate neurons. • In the cervical and lumbosacral enlargements, the anterior horn motor neurons are divided into two great groups. The medial group is also called medial nucleus of anterior hornresponsible for innervating the intrinsic muscles of the and trunk. • While the lateral group is also called the lateral nucleus of anterior horn responsible for supplying the muscles of the limbs.

13. The composition of anterior horn motor neurons: 1) Theα-motor neuron • It is large multipolar neuron. Its axon passes through the white matter to contribute to the respective anterior rootlet of the spinal nerve, which innervates the extrafusal fibers of the skeletal muscle and produces the motion of joints.

14. 2) Theγ-motor neuron • The smaller γ-motor neuron gives rise to γ-efferent fiber which also emerges via the anterior rootlet and supplies the intrafusal muscle fibers of neuromuscular spindles, which play important role in the reflex regulation of muscle tonus. • TheRenshaw cell • This recurrent inhibitory pathway from motor axon collaterals via Renshaw cell back to α-motor neuron is regarded as a negative feed-back mechanism.

15. 10. Lamina Ⅹ • It is located around the central canal, including anterior and posterior commissures.

16. Ⅱ) White Matter • The white matter completely surrounds the gray matter. It is composed of longitudinal fibrous tracts. • Anterior to the gray commissure is a bundle of transverse fibers, called the anterior white commissure. • In each half of the spinal cord the white matter is divided by the gray matter into three areas: the anterior, posterior, and lateral funiculi.

17. The anterior funiculus lies between the anterior median fissure and the posterolateral sulcus. • The posterior funiculus lies between the posterolateral sulcus and posterior median sulcus. • The lateral funiculus lies between the anterolateral and posterolateral sulci. • Each funiculus is composed of many tracts orfasciculi.

18. The main tracts contained within the white matter are as follows: 1. Ascending (sensory) spinal tracts • The ascending tracts carry sensory impulses from spinal cord to the supeasegmental structures.

19. 1) Fasciculus gracilis and fasciculus cuneatus • Location: • They are in the posterior funiculus. The fasciculus gracilis is lateral to the fasciculus cuneatus. • Arision: • They are both composed of the central processes (branches) of pseudounipolar neurons in spinal ganglion. • The fibers arising from the lower half body (under T5, sacral, lumbar and lower six thoracic segments) make up the fasciculus gracilis, while the fibers arising from the upper half body (above T4, upper six thoracic and cervical segments) make up the fasciculus cuneatus.

20. Termination: • After reaching the medulla oblongata, the fasciculi gracilis and cuneatus, terminate upon the nuclei gracilis and cuneatus, respectively. • Functions: • These two tracts conduct the deep senses (position, vibration and movement) and the discriminating tactile (ability to recognize the size, shape and texture of an object). • Symptom after lesion: • Lesion of posterior funiculus naturally abolishes or diminishes discriminating tactile and kinesthetic senses (sensory ataxia) and the symptoms appear and vibratory sense are lost or diminished.

21. 2) Spinocerebellar tract • It includes posterior and anterior spinocerebellar tract. ①Posterior spinocerebellar tract • Location: • It is situated along the posterolateral periphery of the spinal cord. • Journey: • It arises from the ipsilateral dorsal nucleus of lamina Ⅶ and ascends through the spinal cord to the medulla oblongata in which it becomes incorporated in the inferior cerebellar peduncled. • Function: It conveys subconscious proprioceptive impulses to the cerebellum.

22. ②Anterior spinocerebellar tract • Location: It is situated along the lateral periphery of the spinal cord, anterior to the posterior spinocerebellar tract. • Journey: Its fibers arise from the scattered cells in the intermediate zone of lamina Ⅴ--Ⅶ, cross the spinal cord and ascend through the spinal cord, medulla oblongata and pons, then enter the cerebellum by coursing along the dorsal surface of the superior cerebellar peduncle. • Function: Its function is the same as that of the posterior spinocerebellar tract.

23. 3) Spinothalamic tract • It includes lateral and anterior spinothalamic tracts. • Location: • They are situated in the lateral funiculus and anterior funiculus. • Arision and route and function: • The fibers of tracts arise from the nucleus proprius (laminaeⅠand Ⅳ--Ⅶ). • Most fibers of the tract cross obliquely in the anterior white commissure to opposite side, ascend within the anterior and lateral funiculus, terminate to the ventral posterolateral nucleus of thalumus.

24. Fibers ascending in the opposite (ascending one to two segments before crossing) lateral funiculus are called as lateral spinothalamic tract. • The lateral spinothalamic tract transmits the impulses of pain and thermal sense. • Fibers of the lateral spinothalamic tract are somatotopically arranged, those originating from the most caudal segments of the spinal cord are situated laterally with respect to those from more rostral spinal segments.

25. Fibers ascending in the opposite anterior funiculus (including undecussating fibers) are called as anterior spinothalamic tract. It transmits the impulses associated with what is called “light touch”. • Clinical points: • In the patient with hemisection of the spinal cord (Brown-Sequard’s Syndrome), there is loss of pain and thermal senses on the opposite half of the body below 1-2 segments of the level of the lesion, while the senses of position and movement, two-point discrimination and vibration are lost on the same side as the lesion.

26. 2. Descending (motor) spinal tracts 1) Corticospinal tract • This tract arise from the cerebral cortex (precentral gyrus, anterior part of paracentral lobule), descends through the internal capsule and brain stem, and divides into two tracts: • The lateral corticospinal tract: • The most fibers (75-90%) of corticospinal tract decussate in the medulla oblongata and descend medial to the posterior spinocerebellar tract in the spinal cord, forming the lateral corticospinal tract. The tract extends to the most caudal part of the spinal cord and progressively diminishes in size as more and more fibers leave to terminate in the anterior horn of the gray matter. • This tract has somatotopical arrangement from medial to lateral in cervical, thoracic, lumbar and sacral order.

27. The anterior corticospinal tract: • It occupies a strip adjacent to the anterior median fissure. It normally extends only to the upper thoracic spinal segments. Most of these fibers decussate in the anterior white commissure before they terminate in the anterior horn. • The corticospinal tract control the voluntary movements of skeletal muscles. 2) Tectospinal tract 3) Rubrospinal tract 4) Vestibulospinal tract 5) Reticulospinal tract

28. 3 Short ascending and descending tracts • The short ascending and descending tracts are restricted in the spinal cord; they connect the various segments of the spinal cord and make them act as a whole. 1) Fasciculus proprius • It surrounds the grey matter of the spinal cord and takes part in the intrinsic reflex mechanism of the spinal cord.

29. 2) Dorsolateral fasciculus (of Lissauer) • Locaciton: • It is situated between the tip of the posterior grey column and the surface of the spinal cord, close to the posterior rootlets. • It belongs to one of the segmental apparatus and relates to transmit impulses of pain and thermal senses.

30. Reticular formation: It appears mainly in the upper cervical cord, lying laterally between posterior and anterior horns. The fibers contributing to the reticular formation interlace each other to form widespread network.

31. Ⅲ. Functions of Spinal Cord ①One of the principal functions of the spinal cord is to convey afferent impulses which initiates from the somatic and visceral receptors to the brain and to conduct efferent impulses from the brain to the effectors. ②A second principal function is related to the reflexes. It plays the part of the center of the segmental reflex arc, e. g. the stretch reflex, the reflex of bladder and rectal emptying.

32. Section 2 The Brain • The brain (encephalon) is one of the organs of the body, weighing about 1,400g. • It is divided into four principal parts: • brain stem,consisting of the: medulla oblongata, pons and midbrain. • cerebellum, • diencephalon, • telencephalon.

33. Ⅰ. The Brain Stem • Brain stem is the stalk-like part of the brain, which connects the cerebrum, cerebellum with the spinal cord. Ⅰ) External Features 1. The medulla oblongata • The shape of inferior part of the medulla oblongata is familiar with the spinal cord. The central canal of the spinal is prolonged upwards into the lower half of the medulla oblongata, and then it expands to form the lower half of the floor of fourth ventricle, the medulla oblongata may therefore be divided into a lower closed part and an upper open part.

34. 1) Ventral surface of medulla obongata ①Anterior median fissure and anterolateral sulci ②Pyramid and decussation of pyramid: • On each side of the anterior median fissure is an oblongated elevation, the pyramid. Near the lower extremity of the medulla oblongata a great number of fibers leave the pyramids in successive bundles, and decussate with those of the opposite side in anterior median fissure. These interdigitating bundles of fiber are known as the decussation of pyramid.

35. ③Olive • Posterolateral to the pyramid is an oval elevation, called olive. Embed in it is inferior olivary nucleus. ④Emerging of the cranial nerves: • Four pairs of cranial nerves emerge from the surface of the medulla oblongata. Hypoglossal nerve emerges in the anterolateral sulcus. • Glossopharyngeal, vagus, andaccessorynerve emerge in the posterolateral sulcus. ⑤bulbopontine sulcus: the bounary between the medulla oblongata and pons.

36. 2) Dorsal surface of medulla oblongata ①Gracile tubercle and cuneate tubercle • At the lower angle of the fourth ventricle, the fasciculus gracilis ends in an elongated swelling, the gracile tubercle. Lateral and adjacent to it, there is another swelling, the cuneate tubercle, in which the fasciculus cuneatus ends.

37. ②Inferior cerebellar peduncle Rostral to the gracile and cuneate tubercles a thick rounded ridge is the inferior cerebellar peduncle. ③Posterior median sulcus and posterolateral sulcus ④The lower half of the rhomboid fossa

38. 2. The pons 1) The ventral surface of the pons • The ventral surface (basilar part of pons) of the pons is markedly convex from side to side and shows many broad transverse bands of nerve fibers across the median plane. ①Basilar sulcus: • A marked shallow median groove on the ventral surface of the pons is called the basilar sulcus in which the basilar artery is lodged. ②Middle cerebellar peduncle: • The transverse fibers converge on each side into a compact mass which forms the middle cerebellar peduncle and finally enter the corresponding hemisphere of the cerebellum.

39. ③Cranial nerves emerging in the pons • Four pairs of the cranial nerves make their exits in the ventral surface of the pons. • In the bulbopontine sulcus there emerge the abducent, facial and vestibulocochlear nerves ranged medial laterally. • The trigeminal nerves emerge from the junction of the basilar part of pons and middle cerebellar peduncles.

40. 2) The dorsal surface of the pons • Superior cerebellar peduncles • The dorsal part of the pons is opened to form the upper half of the floor of fourth ventricle, along the lateral borders of which there are two prominent and rather large strands of nerve fiber called the superior cerebellar peduncles.

41. 3.The rhomboid fossa • The floor of the fourth ventricle is rhomboidal in shape, named rhomboid fossa. • It is formed by the posterior surface of both the pons and the open part of medulla oblongata.

42. 1) The boundaries: • Superolateral boundary: the superior cerebellar peduncles. • Inferolateral boundary: the inferior cerebellar peduncle, the cuneate and gracile tubercles from above downwards. • The caudal angle of rhomboid fossa is continuous with the central canal in the closed part of medulla oblongata, the rostral angle with the mesencephalic aqueduct of midbrain.

43. 2) Morphology: • Median sulcus: • Sulcus limitans: • Mmedial eminence: • Striae medullares: • Facial colliculus: • At the middle of the medial eminence above the striae medullares a rounded swelling is referred to as facial colliculus.

44. Hypoglossal and vagal triangle: • Below the striae medullares on each side of the median sulcus there are two triangular there are two triangular areas. Of these the most medial one is called the hypoglossal triangle; the lateral one is the vagal triangle. • Vestibular area: • There is a triangular field to the sulcus limitans, called the vestibular area. • Acoustic tubercle:

45. 4. The fourth ventricle 1) Location: • The fourth ventricle lies behind the pons and upper half of the medulla oblongata and in front of the cerebellum. 2) Formation: • It possesses a roof and a floor. • The floor: the rhomboid fossa • The roof : • Anterior part—superior cerebellar peduncle and superior (or anterior) medullary velum. • Posterior part—inferior medullary velum and tela choroidea of fourth ventricle. • In the inner surface of the inferior medullary velum is lined with pia matter andependyma. • Choroids plexus of fourth ventricle:

46. 3) Communications: • It gets into the subarachnoid space through one median aperture of fourth ventricle and two lateral apertures of fourth ventricle (Luschka aperture). • Its tapering upper and lower ends become continuous, respectively, with the mesencephalic aqueduct and the central canal in the lower half of the medulla oblongata.

47. 5. The midbrain (mesencephalon) 1) Ventral surface of the midbrain ① Cerebral peduncles and interpeduncular fossa • The ventral surface of the midbrain is a pair of longitudinal columns of nerve fibers, the cerebral peduncles. • A deep depression bounded by the cerebral pedunclesis known as interpeduncular fossa. ② Posterior perforated substance ③ Cranial nerve emerging in the midbrain: • The oculomotor nerve emerges from a groove on the medial side of each peduncle.

48. 2) The dorsal surface of the midbrain • Superior and inferior colliculi, • Brachium of superiorandinferior colliculi: getting to the lateral geniculate and medial bodies.