Transcription

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19 Spinal Cord Tracts DESCENDING SPINAL TRACTS: Are concerned with somatic motor function, modification of ms. tone, visceral innervation, segmental reflexes. Main tracts arise form cerebral cortex and others from the brain stem.

20 Supra-spinal motor neurons are also known as upper motor neurons, while the spinal anterior grey horn motor neuron are known as lower motor neuron. Motor pathway has 1st order neuron in cerebral cortex (and supra-spinal areas), 2nd order are the Internuncial in spinal grey, 3rd order are the anterior grey horn motor neurons. Spinal Cord Tracts

21 PYRAMIDAL SYSTEM

22

23

24 Brodmann areas Brain cortex

25 Spinal Cord Tracts CORTICOSPINAL TRACTS: Formed by fibers arising from cells in cerebral cortex in the V (5th) layer i.e. mainly large pyramidal cell of Betz. Fibers arise from pre-central primary motor area (4) 31%, Secondary (pre-motor) area 29%(6), Post central gyrus area (3a, 3b, 1,2) and adjacent parietal area (40%)(5). The brain parts

26

27

28 Fibers converge down in corona radiata, enters the post limb of internal capsule Spinal Cord Tracts Descends to form the crus (leg like) cerebri at midbrain level, Here they lie close to the roots of III, VI and VII cranial nerves CR IC Pyr ACST LCST

29

30 At medulla, the fibers form a swelling called pyramid (pyramidal tract). Spinal Cord Tracts At the junction of medulla and spinal cord most of the fibers dissociate and divides into three separate tracts i.e.

31 Spinal Cord Tracts 1. Lateral Corticospinal Tract: 90% of the fibers decussate at caudal medullary level to form this tract which enters the lateral funiculus Lies medial to post. spinocerebellar tract and lateral to the fasciculus proprius.

32 Spinal Cord Tracts This tract descends throughout the spinal cord, In the lower L. and sac. regions it becomes close to the dorsolateral surface (because post. sp. cereb. is absent). Fibers terminate in the intermediate zone (in Lamina IV, V, VI, VII)

33 Spinal Cord Tracts 2. Anterior Corticospinal Tract: About 8% of the fibers descend uncrossed and occupies an oval area close to the anterior median fissure, This tract is present mainly in cervical segments. Most of the fibers cross at the upper cervical spinal levels in anterior white commissure and terminate in Lamina VII.

34 3. Anterolateral Corticospinal Tract: 2% of fibers remain uncrossed, lying close to ventral part of crossed lateral corticospinal tract Spinal Cord Tracts Terminates in intermediate grey and root of post horn. Although some corticospinal fibers form synaptic contact with anterior horn cells, majority terminate on internuncial neurons in Lamina VII. Corticospinal neurons in the motor cortex have multiple axonal branches that project to different spinal segments, specifically in the cervical and lumbar enlargements innervating diff: muscles, this indicates that corticospinal tract is not somatotopically organized. Glutamate and / or Aspartate may be the excitatory neuro transmitter.

35 Key points Descending Tracts Corticospinal Tract Origin: Cerebral Cortex Brodmann Area 4 (Primary Motor Area, M I) Brodmann Area 6 (Premotor Area, PM ) Brodmann Area 3,1,2 (Primary Somesthetic Area, S I) Corona Radiata lnternal Capsule, Posterior Limb Crus Cerebri, Middle Portion Longitudinal Pontine Fiber Pyramid - pyramidal decussation Corticospinal Tracts: - Lateral (crossed) - 90% - Anterior ( uncrossed) - 08% - Anterolateral (uncrossed ) 02% Termination: Spinal Gray (Rexed IV-IX)

36 Spinal Cord Tracts Concerned with voluntary, discrete (separate) and skilled (rapid) movements) Lession results in paralysis i.e. Hemiplegia, paraplegia, quadriplegia. All other descending tracts (other than corticospinal) arise from brain stem or sub-cortical area (extra-pyramidal tracts). Those which arise from midbrain are

37

38

39

40 Tracts from Midbrain

41 Tracts from Midbrain 1. Tectospinal Tract: Fibers arise from deeper layer of sup colliculus, run ventromedially, cross in dorsal tegmental decussation and descends in the brain stem anterior to the MLF. Spinal Cord Tracts

42 Spinal Cord Tracts In the spinal cord it lies in the anterior funiculus close to the anterior median fissure. Majority of the fibers terminate in the upper four (C1 C4) cervical segments (L: VI, VII, VIII). Concerned with reflex postural movements in response to visual stimuli (and perhaps auditory stimuli)

43 Spinal Cord Tracts 2. Rubrospinal Tract: Arise from red nucleus situated at the level of sup: colliculus in the midbrain. Red nucleus consists of rostral (parvicellular) part and caudal (magnocellular) part. Rubrospinal tract arises from the caudal part, Somatotopically arranged (meaning cell in the particular part of the nucleus project to defined spinal levels) so Fibers to cervical region arise from dorsal and dorsomedial part To lumbo-sacral region from ventral and ventro-lateral part and To thoracic region from intermediate part of the R. Nucleus.

44 Spinal Cord Tracts Fibers cross in ventral tegmental decussation, descend down, lies in the lateral funiculus, terminates in lateral half of L: V, VI, VII. Red nucleus also receives fibers from cerebral cortex and crossed cerebellar afferent fiber via sup: cerebellar peduncle. ( glubose and emboliform nuclei) Stimulation of R. Nucleus facilitates flexor ms. activity on the contralateral side. Most important function of R. Sp. tract is the control of tone in flexor ms. group (static tone)

45 Spinal Cord Tracts 3. Interstitiospinal Tract: Arises from the cell in the interstitial nucleus of cajal (in lateral wall) of third ventricle Descends via the MLF into the anterior funiculus of spinal cord, terminate in VII and VIII lamina upto the lumbosacral levels. The exact function is not known.

46 Tracts from Pons.

47 Spinal Cord Tracts Two major descending spinal tracts arise from pons. 1. Vestibulospinal Tract: Nuclei of this tract are situated in pons and medulla in the floor of fourth ventricle. The four nuclei receive aff fibers from ear through vestibular nerve and cerebellum through inf. cereb: peduncle.

48 Spinal Cord Tracts (i). Lateral vestibulo. sp: tract arise mainly from the lateral vest: nucleus, Descends ipsilaterally in lateral part of anterior funiculus and terminates on internuncial neurons in L: VI, VIII, IX. Stimulation of the tract facilitate the activity of extensor ms. and inhibit the activity of flexor ms. to maintain balance of the body.

49 Spinal Cord Tracts (ii) Medial vestibulospinal tract arises mainly from medial vest: Nucleus, descends via MLF into anterior funiculus, Lies close to midline, is mainly uncrossed fibers, runs upto mid thoracic level, Inhibit motor neurons innervating axial ms. of neck and upper part of back.

50 Reticulospinal Tract (Pons and medulla)

51 Spinal Cord Tracts 2. Reticulospinal Tract: (Pons and medulla) A. Pontine reticulospinal tract: Arises from cell in the medial pontine tegmentum known as nuclei reticularis pontis Fibers descends ipsilaterally in medial part of anterior funiculus in entire length of spinal cord and terminates in L: VII and VIII,

52 Spinal Cord Tracts B. Medullary Reticulospinal Tract: Fibers arise from medial 2/3 of medullary reticular formation lying dorsal to inferior olivary complex, Some of the fibers cross the opposite side with in medulla and descends in the anterior part of lateral funiculus terminates in L: VII and IX.

53 Spinal Cord Tracts The reticulospinal tract can facilitate or inhibit the (gama or alpha motor neuron) voluntary movement and reflex activity. Brain stem reticular formation also receives fibers from cerebral cortex mainly the motor area and form a pathway from cortex to spinal level. Olivospinal spinal tract : Doubt that it exists.

54 Spinal Cord Tracts Descending Autonomic Fibers: Fibers in the spinal cord terminates on ( intermediolateral cell column and sacral pre ganglionic cell groups) supply smooth muscles, cardiac muscle, glands and body viscera. Principle nuclei of these fibers are (i) In hypothalamus (ii) Occulomotor complex (iii) Locus cerulus (Pons) and reticular formation, They probably form parts of reticulospinal tract and run in the anterior and lateral funiculus.

55 Spinal Cord Tracts( Inter segmental) Fasciculi proprii Formed by short ascending and descending fibers which begins and end in spinal cord. Connect cell groups at various level and with in the same level. These fibers take part in inter segmental reflexes

56 Medial Longitudinal Fasciculus (MLF) This bundle lies in the posterior part of anterior funiculus, Fibers originate at different levels of brain stem mainly from, (1) Vestibular nuclei (2) Pontine reticular formation (3) Superior colliculus (4) Interstitial Nucleus of cajal (Interstitio spinal). MLF is well defined in cervical regions (to L: VII and VIII) Spinal Cord Tracts