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Spinal cord
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Spinal cord

  1. 1. The spinal cord • The spinal cord, enclosed in the vertebral column, extends from the foramen magnum of the skull to the first or second lumbar vertebra, just inferior to the ribs. • About 42 cm (17 inches) long and 1.8 cm (3/4 of an inch) thick and the spinal cord provides a two-way conduction pathway to and from the brain.
  2. 2. • The spinal cord is protected by bone, meninges, and cerebrospinal fluid. • Cerebrospinal fluid fills the subarachnoid space between the arachnoid and pia mater meninges.
  3. 3. Gross Appearance • Cylindrical in shape • Foramen magnum  L1/L2 (adult) • L3 (newborn) • Occupies upper ⅔ of vertebral canal • Surrounded by 3 layers of meniges: – dura mater – arachnoid mater – pia mater • CSF in subarachnoid space
  4. 4. Longitudinal depressions a. Posterior Median Sulcus - PMS b. Anterior Median Fissure - AMF Enlargements of the spinal cord a. Cervical enlargement (biggest) - pectoral girdle – C4-C8 b. Lumbar enlargement - supplies and innervates lower limbs
  5. 5. • Conus medullaris:- the spinal cord terminates in a tapering cone-shaped structure called the conus medullaris. • Filum termniale • Anterior median fissure • Posterior median sulcus • 31 pairs of spinal nerves attached to it by the anterior roots & posterior roots
  6. 6. • The filum terminale:- a fibrous extension of the conus covered by pia mater, extends inferiorly from the conus medullaris to the coccyx, where it anchors the spinal cord so it is not jostled by body movements
  7. 7. • Denticulate ligaments:- The pia mater of the spinal cord has a pair of denticulate ligaments with 21 attachments per side which attach it to the arachnoid and dura mater.
  8. 8. Gray Matter • H-shaped pillar with anterior & posterior gray horns • United by gray commissure containing the central canal • Lateral gray column (horn) present in thoracic & upper lumbar segments • Amount of gray matter related to the amount of muscle innervated • Consists of nerve cells, neuroglia, blood vessels
  9. 9. Nerve cells in the anterior gray columns • Large and multipolar – Axons pass out in the anterior nerve roots as α-efferents • Smaller nerve cells are multipolar – Axons pass out in anterior roots as ɣ- efferents
  10. 10. Nerve cells in the posterior gray columns • 4 nerve cell groups 1. Substantia gelatinosa 2. Nucleus proprius 3. Nucleus dorsalis (Clark’s column) 4. Visceral afferent nucleus
  11. 11. 1. Substantia gelatinosa – situated at the apex – throughout the length of spinal cord – composed mainly of Golgi Type II neurons – receives afferent fibres concerning with pain, temperature & touch from posterior root
  12. 12. • Nucleus proprius – anterior to substantia gelatinosa – present throughout the whole length of spinal cord – main bulk of cells in posterior gray column – receives fibers from posterior white column that are assoc with proprioception, 2-point discrimination & vibration
  13. 13. • Nucleus dorsalis (Clark’s column) – base of posterior column – C8 – L3 / L4 – associated with proprioceptive endings (neuromuscular spindles & tendon spindles) • Visceral afferent nucleus – lateral to nucleus dorsalis – T1 – L3 – receives visceral afferent informations
  14. 14. The gray matter • The gray matter of the cord looks like the letter H or like a butterfly. It consists of mirror image lateral gray masses connected by a crossbar of gray matter, the gray commissure, that encloses the central canal. The two dorsal projections of the gray matter are the dorsal (posterior) horns, and the ventral pair are the ventral (anterior) horns. The thoracic and superior lumbar segments of the cord have an additional pair of gray matter columns, the small lateral horns.
  15. 15. Lateral horns • Formed by the intermediolateral group of cells • T1 – L2 / L3 • Cells give rise to preganglionic sympathetic fibres • In S2, S3, S4; they give rise to preganglionic parasympathetic fibres
  16. 16. • The gray commissure and central canal – connects the gray on each side – central canal in the centre – posterior gray commissure – anterior gray commissure – central canal present throughout – superiorly continuous with the central canal of medulla oblongata – inferiorly, expands as terminal ventricle – terminates within the root of filum terminale
  17. 17. a. Dorsal Root - posterior - sensory nerves b. Dorsal Root Ganglion (contains sensory nerve cell bodies). c. Ventral Root - anterior - motor neurons "AMPS" anterior/motor and posterior/sensory. Spinal nerves start where the dorsal root ganglia and ventral root fuse or come together and join to become a mixed nerve/exit the spine at the intervertebral foramen.
  18. 18. • The spinal gray matter can be divided further according to its neurons’ relative involvement in innervating the somatic and visceral regions of the body. • Spinal gray matter has the following four zones. – Somatic sensory (SS) – Visceral sensory (VS) – Visceral (autonomic) motor (VM) – Somatic motor (SM).
  19. 19. White Matter • The white matter of the spinal cord is composed of myelinated and nonmyelinated nerve fibers that allow communication between different parts of the spinal cord and between the cord and brain. These fibers run in three directions: – Ascending — up to higher centers (sensory inputs) – Descending — down to the cord from the brain or within the cord to lower levels (motor outputs) – Transverse — across from one side of the cord to the other (commissural fibers) • Consists of nerve fibres, neuroglia, blood vessels
  20. 20. • The white matter on each side of the cord is divided into three white columns, or funiculi named according to their position as – Dorsal (posterior) funiculi – Lateral funiculi – Ventral (anterior) funiculi
  21. 21. Tracts • Ascending • Descending • Transverse
  22. 22. Ascending Tracts • Fibres that ascend from spinal cord to higher centres • Conduct afferent information which may or may not reach consciousness • Information may be – exteroceptive (pain, temperature, touch) – proprioceptive (from muscles & joints)
  23. 23. • The nonspecific and specific ascending pathways send impulses to the sensory cortex – These pathways are responsible for discriminative touch (2 pt. discrimination) and conscious proprioception (body position sense). • The spinocerebellar tracts send impulses to the cerebellum and do not contribute to sensory perception
  24. 24. Ascending Pathway
  25. 25. Lateral spinothalamic tract • Pain & temp pathways • 1st-order neurons • Pain conducted by A- type fibres & C-type fibres • 2nd-order neurons – decussate to the opposite side – ends in thalamus (ventral posterolateral nucleus • 3rd-order neurons – ends in sensory area in postcentral gyrus
  26. 26. Anterior (ventral) spinothalamic tracts • Light (crude) touch and pressure pathways
  27. 27. Posterior (Dorsal) spinocerebellar tract • Muscle joint sense pathways to cerebellum • Unconscious proprioception • Muscle joint info from muscle spindles, GTO, joint receptors of the trunk & lower limbs • Info is used by the cerebellum in the coordination of movements & maintenance of posture
  28. 28. Anterior (Ventral) spinocerebellar tract • Majority of 2nd-order neurons cross to the opposite side • Enter cerebellum through superior cerebellar peduncle • Info from trunk, upper & lower limbs • Also carries info from skin & subcut tissue
  29. 29. Posterior (Dorsal) white column • Discriminative touch, vibratory sense, conscious muscle joint sense (conscious proprioception)
  30. 30. Descending Tracts • Descending tracts deliver motor instructions from the brain to the spinal cord • Divided into two groups – Pyramidal, or corticospinal tracts:- concerned with voluntary, discrete, skilled movements – Indirect pathways, essentially all others • Motor pathways involve two neurons – Upper motor neuron (UMN) – Lower motor neuron (LMN) • aka ‘anterior horn motor neuron” (final common pathway)
  31. 31. Pyramidal (Corticospinal) Tracts • Originate in the precentral gyrus of brain (aka, primary motor area) – I.e., cell body of the UMN located in precentral gyrus • Pyramidal neuron is the UMN – Its axon forms the corticospinal tract • UMN synapses in the anterior horn with LMN – Some UMN decussate in pyramids = Lateral corticospinal tracts – Others decussate at other levels of s.c. = Anterior corticospinal tracts • LMN (anterior horn motor neurons) – Exits spinal cord via anterior root – Activates skeletal muscles • Regulates fast and fine (skilled) movements
  32. 32. Corticospinal tracts 1. Location of UMN cell body in cerebral cortex 2. Decussation of UMN axon in pyramids are at exit level of LMN 3. Synapse of UMN and LMN occurs in anterior horn of s.c. 4. LMN axon exits via anterior root
  33. 33. Extrapyramidal Motor Tracts • Includes all motor pathways not part of the pyramidal system • Upper motor neuron (UMN) originates in nuclei deep in cerebrum (not in cerebral cortex) • UMN does not pass through the pyramids! • LMN is an anterior horn motor neuron • This system includes – Rubrospinal – Vestibulospinal – Reticulospinal – Tectospinal tracts • Regulate: – Axial muscles that maintain balance and posture – Muscles controlling coarse movements of the proximal portions of limbs – Head, neck, and eye movement
  34. 34. Reticulospinal tract • The two recticulospinal tracts have differing functions: • The medial reticulospinal tract arises from the pons. It facilitates voluntary movements, and increases muscle tone. • The lateral reticulospinal tract arises from the medulla. It inhibits voluntary movements, and reduces muscle tone
  35. 35. Tectospinal tract • This pathway begins at the superior colliculus of the midbrain. The superior colliculus is a structure that receives input from the optic nerves. The neurones then quickly decussate, and enter the spinal cord. They terminate at the cervical levels of the spinal cord. • The tectospinal tract coordinates movements of the head in relation to vision stimuli.
  36. 36. Rubrospinal tract • The rubrospinal tract originates from the red nucleus, a midbrain structure. As the fibres emerge, they decussate (cross over to the other side of the CNS), and descend into the spinal cord. Thus, they have a contralateral innervation. • Its exact function is unclear, but it is thought to play a role in the fine control of hand movements
  37. 37. Vestibulospinal Tracts • There are two vestibulospinal pathways; medial and lateral. They arise from the vestibular nuclei, which receive input from the organs of balance. The tracts convey this balance information to the spinal cord, where it remains ipsilateral. • Fibres in this pathway control balance and posture by innervating the ‘anti-gravity’ muscles (flexors of the arm, and extensors of the leg), via lower motor neurones.
  38. 38. Other Tracts • Spinotectal tract – The tectospinal tract (also known as colliculospinal tract) is a nerve pathway that coordinates head and eye movements. This neural tract is part of the indirect extrapyramidal tract. To be specific, the tectospinal tract connects the midbrain tectum and cervical regions of the spinal cord. • Spinoreticular tract – The spinoreticular tract is an ascending pathway in the white matter of the spinal cord, positioned closely to the lateral spinothalamic tract. The tract is from spinal cord to reticular formation to thalamus. – It is responsible for automatic responses to pain, such as in the case of injury. • Spino-olivary tract – This is a non-specific indirect ascending pathway and is connected to olivary nuclei in the brain. It is located in the ventral funiculus of the spinal cord. This tract carries proprioception information from muscles and tendons as well as cutaneous impulses to the olivary nucleus.
  39. 39. Spinal Meninges • Dura mater • Arachnoid mater • Pia mater
  40. 40. Dura mater • Dense, strong fibrous membrane • Encloses the spinal cord & cauda equina • Continuous above with meningeal layer of dura covering the brain • Ends at the level of S2 • Separated from wall of vertebral canal by the extradural space • Contains loose areolar tissue and internal vertebral venous space
  41. 41. Arachnoid mater • Delicate impermeable membrane • Lies between pia and dura mater • Separated from pia mater by subarachnoid space • Continuous above with arachnoid mater covering the brain • Ends on filum terminale at level of S2
  42. 42. Pia mater • Vascular membrane • Closely covers spinal cord • Thickened on either side between nerve roots to form the ligamentum denticulatum
  43. 43. Blood supply Arteries of the spinal cord • Anterior spinal artery • Posterior spinal artery • Segmental spinal arteries
  44. 44. Anterior spinal artery • Formed by the union of 2 arteries • From vertebral artery • Supply anterior ⅔ of spinal cord Posterior spinal arteries • Arise from vertebral artery or posterior inferior cerebellar arteries (PICA) • Descend close to the posterior roots • Supply posterior ⅓ of spinal cord
  45. 45. Segmental spinal arteries • Branches of arteries outside the vertebral column • Gives off the anterior & posterior radicular arteries • Great anterior medullary artery of Adamkiewicz • Arise from lateral intercostal artery or lumbar artery at any level from T8 – L3
  46. 46. Venous drainage • Venous drainage largely follows arterial supply. That is, there are anterior and posterior spinal veins and anterior and posterior radicular veins, which freely communicate with the internal vertebral plexus in the epidural space. This is in turn drains to the cerebral dural venous sinuses and cerberal veins as well as the external vertebral plexus. • The veins of the spinal cord and vertebral column are valveless.
  47. 47. Applied anatomy Spinal shock • Follows acute severe damage to the spinal cord • All cord functions below the level of the lesion become depressed or lost • Sensory impairment and flaccid paralysis occur • Segmental spinal reflexes are depressed • Persists for less than 24 hours (may be as long as 1 – 4 weeks)
  48. 48. Poliomyelitis • Acute viral infection of the neurones of anterior gray column • Motor nuclei of cranial nerves • Death of motor neurone cells → paralysis & wasting of muscles • Muscles of lower limb more often affected
  49. 49. Spinal Nerves • A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. • These are grouped into the corresponding – Cervical nerves 8 pairs – Thoracic nerves 12 pairs – Lumbar nerves 5 pairs – Sacral nerves 5 pairs – Coccygeal nerves one pair • The spinal nerves are part of the peripheral nervous system.
  50. 50. Structure of spinal nerve • 3 layers of Connective tissues – Epineurium • Outermost layer • Consists of dense network of collagen fibers – Perineurium • Middle layer • Divide nerve into series of compartments which contain bundles of axons (fascicles) – Endoneurium • Innermost layer • Surround individual axons
  51. 51. • Spinal nerves consist of two types of nerves: – Sensory nerves – Motor nerves
  52. 52. • Sensory nerves deliver information to spinal cord from muscles and joints about body position and also transmit sensations such as touch, pressure, pain and temperature.
  53. 53. Motor nerves Motor nerves pass information received from brain through spinal tracts to the skeletal muscles to direct precise voluntary movements. Spinal nerves are linked to specific muscles: • Cervical spinal nerves supply the muscles of neck, shoulders, arms and hands, and diaphragm. • Thoracic spinal nerves supply truck muscles and muscles involved with breathing. • Lumbar and sacral spinal nerves supply hip, leg and foot muscles. • Sacral nerves supply anal and urethral sphincters.
  54. 54. Distribution of Spinal Nerves Spinal Nerves: – Consist of dorsal root and ventral root – Branch to form pathways to destination – Includes motor and sensory nerves Dermatomes: a. Each pair of spinal nerves controls a region of body surface sensation - the exception to this is C1, which does not. b. From dorsal and ventral rami fibers c. Damage to the spinal nerve results in loss of sensation to a region of skin d. This is a helpful diagnostic tool, sometimes pain is referred from one nerve to a corresponding region of skin.
  55. 55. Spinal Nerves: Rami • The short spinal nerves branch into three or four mixed, distal rami – Small dorsal ramus – to back – Larger ventral ramus – to plexuses/intercostals – Tiny meningeal branch – to meninges – Rami communicantes at the base of the ventral rami in the thoracic region – to/from ANS
  56. 56. Nerve Plexuses • All ventral rami except T2-T12 form interlacing nerve networks called plexuses • Plexuses are found in the cervical, brachial, lumbar, and sacral regions • Each resulting branch of a plexus contains fibers from several spinal nerves • Fibers travel to the periphery via several different routes • Each muscle receives a nerve supply from more than one spinal nerve • Damage to one spinal segment cannot completely paralyze a muscle
  57. 57. Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall • The back is innervated by dorsal rami via several branches • The thorax is innervated by ventral rami T1-T12 as intercostal nerves • Intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wall
  58. 58. The 4 Major Plexuses of Ventral Rami 1. Cervical plexus 2. Brachial plexus 3. Lumbar plexus 4. Sacral plexus
  59. 59. Cervical Plexus • The cervical plexus is formed by ventral rami of C1-C4 (C5) • Most branches are cutaneous nerves of the neck, ear, back of head, and shoulders • The most important nerve of this plexus is the phrenic nerve • The phrenic nerve is the major motor and sensory nerve of the diaphragm
  60. 60. Brachial Plexus • Formed by C5-C8 and T1 (C4 and T2 may also contribute to this plexus) • It gives rise to the nerves that innervate the upper limb
  61. 61. Trunks and Cords of Brachial Plexus • Nerves that form brachial plexus originate from: – superior, middle, and inferior trunks – large bundles of axons from several spinal nerves – lateral, medial, and posterior cords – smaller branches that originate at trunks
  62. 62. Brachial Plexus: Nerves • Axillary – innervates the deltoid and teres minor • Musculocutaneous – sends fibers to the biceps brachii and brachialis • Median – branches to most of the flexor muscles of forearm • Ulnar – supplies the flexor carpi ulnaris and part of the flexor digitorum profundus • Radial – innervates essentially all extensor muscles
  63. 63. Lumbar Plexus • Arises from (T12) L1-L4 and innervates the thigh, abdominal wall, and psoas muscle • The major nerves are the femoral and the obturator
  64. 64. Sacral Plexus • Arises from L4-S4 and serves the buttock, lower limb, pelvic structures, and the perineum • The major nerve is the sciatic, the longest and thickest nerve of the body • The sciatic is actually composed of two nerves: the tibial and the common fibular (perineal) nerves
  65. 65. Nerve plexuses - Summary • Cervical – C1-C4 – Phrenic nerve • Brachial – C5 – T1 (roots/trunks/divisions/cords) – Axillary, MC, median, ulnar, radial • Lumbar – L1-L4 – Femoral, obturator • Sacral – L4-S4 – Sciatic (common peroneal/tibial), pudendal
  66. 66. Figure 13–13a 5 Patterns of Neural Circuits in Neuronal Pools 1. Divergence: – spreads stimulation to many neurons or neuronal pools in CNS 2. Convergence: – brings input from many sources to single neuron
  67. 67. Figure 13–13c 3. Serial processing: – moves information in single line 4. Parallel processing: – moves same information along several paths simultaneously 5 Patterns of Neural Circuits in Neuronal Pools
  68. 68. Figure 13–13e 5. Reverberation: – positive feedback mechanism – functions until inhibited
  69. 69. Reflex activity • 5 components of a reflex arc – Receptor – Sensory neuron – Integration center (CNS) – Motor neuron – Effector
  70. 70. 4 Classifications of Reflexes 1. By early development – Innate or Acquired 2. By type of motor response – Somatic or Visceral 3. By complexity of neural circuit – Monosynaptic or Polysynaptic 4. By site of information processing – Spinal or Cranial
  71. 71. Spinal Reflexes • Range in increasing order of complexity: – monosynaptic reflexes – polysynaptic reflexes – intersegmental reflex arcs: • many segments interact • produce highly variable motor response
  72. 72. Monosynaptic Reflexes • Have least delay between sensory input and motor output: – e.g., stretch reflex (such as patellar reflex) • Completed in 20– 40 msec
  73. 73. Muscle Spindles • The receptors in stretch reflexes • Bundles of small, specialized intrafusal muscle fibers: – innervated by sensory and motor neurons • Surrounded by extrafusal muscle fibers: – which maintain tone and contract muscle
  74. 74. Postural Reflexes • Postural reflexes: – stretch reflexes – maintain normal upright posture • Stretched muscle responds by contracting: – automatically maintain balance
  75. 75. Polysynaptic Reflexes • More complicated than monosynaptic reflexes • Interneurons control more than 1 muscle group • Produce either EPSPs or IPSPs
  76. 76. The Tendon Reflex • Prevents skeletal muscles from: – developing too much tension – tearing or breaking tendons • Sensory receptors unlike muscle spindles or proprioceptors
  77. 77. Withdrawal Reflexes • Move body part away from stimulus (pain or pressure): – e.g., flexor reflex: • pulls hand away from hot stove • Strength and extent of response: – depends on intensity and location of stimulus
  78. 78. Reciprocal Inhibition • For flexor reflex to work: – The stretch reflex of antagonistic (extensor) muscle must be inhibited (reciprocal inhibition) by interneurons in spinal cord
  79. 79. Crossed Extensor Reflexes • Occur simultaneously, coordinated with flexor reflex • e.g., flexor reflex causes leg to pull up: – crossed extensor reflex straightens other leg – to receive body weight – maintained by reverberating circuits
  80. 80. Integration and Control of Spinal Reflexes • Though reflex behaviors are automatic: – processing centers in brain can facilitate or inhibit reflex motor patterns based in spinal cord • Higher centers of brain incorporate lower, reflexive motor patterns • Automatic reflexes: – can be activated by brain as needed – use few nerve impulses to control complex motor functions – walking, running, jumping
  81. 81. Superficial reflexes • Stroking of the skin elicits muscle contraction – Involves functional upper motor pathways as well as cord level reflex arcs • Plantar reflex (L4-S2) Babinski is normal in infants – Usually indicative of CNS damage in adults • Abdominal reflex (T8-T12) – Absent with corticospinal lesion
  82. 82. Spinal Cord Trauma: Transection • Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut • Paraplegia – transection between T1 and L1 • Quadriplegia – transection in the cervical region
  83. 83. Applied anatomy/physiology Peripheral Neuropathies • Regional loss of sensory or motor function • Due to trauma or compression • Example: if your foot “falls asleep” Shingles • Caused by varicella-zoster virus (chickenpox) • After chickenpox, virus hides in neurons of spinal cord • Later in life, attacks neurons in dorsal roots of nerves = painful rash/blisters • Distribution of rash corresponds to dermatome nerves affected
  84. 84. THANK YOU