Neuroscience 1 - Trans 6 - Spinal Cord and the Ascending Tracts.pdf

1A NUEROANATOMY THE SPINAL CORD AND THE ASCENDINDING TRACTS DR. A. VIADO, M.D....

1A NUEROANATOMY THE SPINAL CORD AND THE ASCENDINDING TRACTS DR. A. VIADO, M.D. arch articulate with the two inferior articular processes of the arch above, forming two synovial joints. Content Outline: Pedicles are notched on their upper and lower borders, forming I. Vertebral Column the superior and inferior vertebral notches. On each side, the A. Joints between two vertebral bodies B. Joints between two vertebral arches II. Spinal cord A. Structure of the Spinal Cord B. Gray Matter C. White Matter D. Spinal Pathways 1. Ascending Pathway 2. Descending Pathway E. Spinal Cord Segments III. Clinical Notes A. Lower Motor Neuron Lesion B. Clinical Syndromes Affecting the Spinal Cord IV. Sample Questions I. VERTEBRAL COLUMN -is the central bony pillar of the body -composed of 33 vertebrae 7 cervical 12 thoracic 5 lumbar 5 sacral (fused to form the sacrum) 4 coccygeal (the lower 3 are commonly fused) -Because it is segmented and made up of vertebrae, joints, and pads of fibrocartilage called intervertebral discs, it is a flexible structure. The intervertebral discs form about one-fourth the length of the column. - General Characteristics: Anteriorly: rounded body Posteriorly: vertebral arch Figure 1A: Lateral view of the vertebral column. B: General features of different kinds of vertebrae. -The vertebral arch consists of a pair of cylindrical pedicles,which form the sides of A. JOINTS BETWEEN TWO VERTEBRAL BODIES the arch,and a pair of flattened laminae, -Sandwiched between the vertebral bodies is an intervertebral disc which complete the arch posteriorly. of fibrocartilage. These enclose a space called the vertebral foramen, through which run the spinal cord and its coverings. Intervertebral Discs - Vertebral arch gives rise to seven processes: -are thickest in the cervical and lumbar regions,where the movements of the vertebral column are greatest one spinous - serve as shock absorbers when the load on the vertebral column is two transverse suddenly increased. four articular (Fig.4-2). -resilience is gradually lost with advancing age. Spinous process, or spine -is directed posteriorly from the junction of the two laminae. Transverse processes -are directed laterally from the junction of the laminae and the pedicles. Both the spinous and transverse processes serve as levers and receive attachments of muscles and ligaments. Articular processes -are vertically arranged and consist of two superior and two inferior processes. They arise from the junction of the laminae and the pedicles.The two superior articular processes of one vertebral Trans 4 | Andoy, Allida, Andam, Brul 1 of 7  Neuroanatomy THE SPINAL CORD AND THE ASCENDINDING TRACTS II. SPINAL CORD o Elongated cylindrical structure in vertebral canal o 35-40 cm in length o Extends from foramen magnum (continuous with medulla oblongata) to the lower border of L1 vertebra o With 2 enlargements o Cervical o Lumbar o Conus medullaris – conical termination o Filum terminale – connective tissue continuation of pia mater, penetrates dura mater at S1-S2 as coccygeal ligament o Cauda equina (“tail of the horse”) – formation of spinal nerve roots descending from the conus o surrounded by the three meninges, the dura mater, the arachnoid mater, and the pia mater. o cerebrospinal fluid- surrounds the spinal cord in the subarachnoid space. Figure 2 A: Joints in the cervical,thoracic,and lumbar regions of the vertebral column. B: Third lumbar vertebra seen from above showing the relationship between intervertebral disc and cauda equina. - consists of: 1. anulus fibrosus- peripheral part - composed of fibrocartilage, which is strongly attached to the vertebral bodies and the anterior and posterior longitudinal ligaments of the vertebral column. 2. nucleus pulposus- central part Figure 3 Spinal cord.A: Posterior view,showing cervical and lumbar enlargements.B:Three segments of the spinal cord showing the coverings of dura - in the young is an ovoid mass of gelatinous mater,arachnoid mater,and pia mater. material. - It is normally under pressure and situated A. STRUCTURE OF THE SPINAL CORD slightly nearer to the posterior than to the ▪ Foramen magnum to L1 or L2 anterior margin of the disc. ▪ Runs through the vertebral canal of the vertebral column ▪ Functions B. JOINTS BETWEEN TWO VERTEBRAL ARCHES 1. Sensory and motor innervation of entire body inferior to the -The joints between two vertebral arches consist of synovial joints head through the spinal nerves between the superior and inferior articular processes of adjacent 2. Two-way conduction ( Motor and Sensory ) pathway between vertebrae. the body and the brain ( ascending and descending ) Ligaments Major center for reflexes rd Supraspinous ligament:This runs between the tips of adjacent Fetal 3 month: ends at coccyx spines. Birth: ends at L3 Interspinous ligament: This connects adjacent spines. Adult position at approx L1-2 during childhood Intertransverse ligaments: These run between adjacent End: conus medullaris transverse processes. -This tapers into filum terminale of connective tissue, Ligamentum flavum: This connects the laminae of adjacent tethered to coccyx vertebrae. Denticulate ligaments: lateral shelves of pia mater anchoring to dura In the cervical region, the supraspinous and interspinous ligaments are greatly thickened to form the strong ligamentum nuchae. Spinal Cord coverings and spaces ▪ Dura mater ▪ Arachnoid mater S1T4 2 of 7  Neuroanatomy THE SPINAL CORD AND THE ASCENDINDING TRACTS ▪ Pia mater - In the spinal cord, grey matter is inside - "basal ganglia" deep within the cerebrum is a misnomer, corrected in more recent textbooks as "basal nuclei” C. WHITE MATTER - Represents predominantly the myelinated axons or nerve fibers, appearing white on unstained sections of the brain & SC - In the spinal cord, white matter is outside Tracts- Bundle of nerve fibers with a common origin and termination o Ascending tracts- carry nerve impulses towards the brain from the periphery. Example: anterior spinothalamic tract. - First part arises from the spinal cord and terminates in the thalamus. o Descending tracts- Carry nerve impulses away from the brain towards the periphery Example: lateral LP (lumbar puncure) = spinal tap corticospinal tract (needle introduced into subarachnoid space to collect CSF) - Starts from cerebral cortex going down to a -Lumbar spine needs to be flexed so can go between spinous processes specifc part of the spinal cord. -Epidural space is external to dura o By convention, tracts may be named according to -Anesthestics are often injected into epidural space common origin (1st stem) and termination (2nd Injection into correct space is vital; mistakes can be lethal stem); example: "spinocerebellar tract" is different from "cerebellospinal tract" Internal Spinal cord anatomy ( transverse axial ) Peduncles- stem-like connection between 2 areas of the ▪ Posterior median sulcus CNS (e.g. cerebral & cerebellar) ▪ Anterior median fissure Brachium/brachia- arm-like connection between 2 parts of ▪ Gray matter the CNS (e.g. brachia conjunctivum and brachium pontis) ▪ White matter Lemniscus/lemnisci- ribbon/band particularly part of the sensory tracts (e.g. medial, lateral, & spinal) Fasciculus/fasciculi-column, nerve bundle (e.g. cuneate & “P” gracile) Funiculus/funiculi-bigger column, cord-like bundle of “A” nerve fibers for the major divisions of SC white matter D. SPINAL PATHWAYS Gray/White Matter in spinal cord ▪ Hollow central cavity (“central canal”) ▪ Ascending pathways: sensory information by multi-neuron ▪ Gray matter surrounds central canal chains from body up to more rostral regions of CNS ▪ White matter surrounds gray matter (white: ascending and Dorsal column descending tracts of axons) Spinothalamic tracts ▪ “H” shaped on cross section Spinocerebellar tracts ▪ Dorsal half of “H”: cell bodies of sensory interneurons ▪ Ventral half of “H”: cell bodies of motor neurons ▪ Descending pathways: motor instructions from brain to more ▪ No cortex (as in brain) caudal regions of the CNS Pyramidal (corticospinal) most important to know All others (“extrapyramidal”) Gray commissure with central canal Columns of gray running the length of the spinal cord ▪ Most pathways cross (or decussate) at some point ( Take note - Posterior (dorsal) horns (cell bodies of where they decussate ) interneurons/sensory neurons) ▪ Most synapse two or three times along the way, e.g. in brain - Anterior (ventral) horns (cell bodies of motor stem, thalamus or other neurons) Lateral horns in thoracic and superior lumbar cord Major fiber tracts in white matter of spinal cord B. GRAY MATTER ( Ascending and Descending Pathways ) - Represents predominantly the nerve cell bodies (have no myelin Sensory Motor sheath) - These are the nuclei and cortex S1T4 3 of 7  Neuroanatomy THE SPINAL CORD AND THE ASCENDINDING TRACTS 5 basic modalities of sensation Lateral Spinothalamic Tract Posterior Columns Damage: to motor areas – paralysis Pain position to sensory areas - paresthesias Temperature vibration 1. ASCENDING PATHWAY / Tracts for the Somatic Senses Crude Touch Fine Touch Spinocerebellar tract: proprioception from skeletal muscles to cerebellum of same side (don’t cross) Posterior/Dorsal column: discriminative touch /joint position and vibration sensation through thalamus to somatosensory cortex (cross in medulla) Lateral Spinothalamic tract: carries nondiscriminative sensations (pain, temp, pressure, light/crude touch) through the thalamus to the primary somatosensory cortex (cross in spinal cord before ascending) NOTES The posterior column remains ipsilateral up to medulla where it crosses over. The spinothalamic tract crosses mostly within one or two segments of entry into the post column Joint position and vibration sense, fine touch ( Posterior column nd ): Ipsilateral during spinal cord course and then deccusates ( 2 order neuron ) in the medulla Pain, course touch and temperature sense ( anterior column ): nd Contralateral during spinal cord course and then decussates ( 2 order neuron ) immediately as it enters the spinal cord. Vibration, joint position and temperature senses are often lost without prominent symptoms Light touch and pinprick ( pain ) loss are usually symptomatic 2. DESCENDING PATHWAY -Synapse with ventral (anterior) horn interneurons S1T4 4 of 7  Neuroanatomy THE SPINAL CORD AND THE ASCENDINDING TRACTS Pyramidal tracts: By comparing the composition and proportion of the gray and Lateral corticospinal – cross in pyramids of medulla; voluntary motor white matter, one can differentiate the segments of the spinal to limb muscles cord: Ventral (anterior) corticospinal – cross at spinal cord; voluntary to o Ventral horns larger in cervical and lumbar segments: neurons that axial muscles innervate skeletal muscles (greater muscle mass on limbs than trunk) “Extrapyramidal” tracts: o More white matter relative to gray at cervical vs. lumbosacral eg: Rubrospinal tract , tectospinal,vestibulospinal, reticulospinal regions (all fibers connecting entire cord with the brain) tracts o The cervical segment is the final connection between the spinal cord and the brainstem, and thus it contains all axons from all nerve cell bodies from below going up into the brain, as compared to the lumbar section which only receives axons from those below o Ventral horns are larger in cervical compared to thoracic o Thoracic has the presence of lateral horns o In terms of proportion, the thoracic segment has a greater amount of white matter but in terns of absolute number, it is the cervical which has the greatest amount. III. CLINICAL NOTES A. LOWER MOTOR NEURON LESIONS Trauma, infection (poliomyelitis),vascular disorders, degenerative diseases, and neoplasms may all produce a lesion of the lower motor neuron by destroying the cell body in the anterior gray column or its axon in the anterior root or spinal nerve. The following clinical signs are present with lower motor neuron lesions: 1. Flaccid paralysis of muscles supplied. 2. Atrophy of muscles supplied. 3. Loss of reflexes of muscles supplied. 4. Muscular fasciculation. This is twitching of muscles seen only when there is slow destruction of the lower motor neuron cell. 5. Muscular contracture. This is a shortening of the paralyzed muscles.It occurs more often in the antagonist muscles whose action is no longer opposed by the paralyzed muscles.  If you look at the anatomy of the medulla in cross section, you will 6. Reaction of degeneration. Normally innervated muscles respond find these tracts ( tracts are collection of axons in the CNS, Nerves to stimulation by the application of faradic (interrupted) current, and are collection of axons in the PNS ) the contraction continues as long as the current is passing. Galvanic  Note that motor pathways are going away from the CNS and or direct current causes contraction only when the current is turned sensory pathways on the other hand ascends towards the CNS on or turned off. After 10 days, the response to direct current also ceases. This change in muscle response to electrical stimulation is E. SPINAL CORD SEGEMENTS known as the reaction of degeneration. S1T4 5 of 7  Neuroanatomy THE SPINAL CORD AND THE ASCENDINDING TRACTS cord is pressed on anteriorly by the vertebral bodies and posteriorly Types of Paralysis: by the bulging of the ligamentum flavum, causing damage to the 1. Hemiplegia is a paralysis of one side of the body and includes the central region of the spinal cord. Radiographs of these injuries often upper limb,one side of the trunk,and the lower limb. appear normal because no fracture or dislocation has occurred. 2. Monoplegia is a paralysis of one limb only. 3. Diplegia is a paralysis of two corresponding limbs (i.e.,arms or legs). 4. Brown-Séquard Syndrome or Hemisection of the Cord Paraplegia is a paralysis of the two lower limbs. Hemisection of the spinal cord can be caused by fracture dislocation 4. Quadriplegia is a paralysis of all four limbs of the vertebral column, by a bullet or stab wound, or by an expanding tumor.Incomplete hemisection is common; complete hemisection is rare. 5. Syringomyelia, which is due to a developmental abnormality in the formation of the central canal, most often affects the brainstem and cervical region of the spinal cord. At the site of the lesion, there is cavitation and gliosis in the central region of the neuroaxis. 6. Poliomyelitis is an acute viral infection of the neurons of the anterior gray columns of the spinal cord and the motor nuclei of the cranial nerves.Immunization has greatly reduced the incidence of poliomyelitis, which was once a feared disease 7. Multiple sclerosis is a common disease confined to the central nervous system,causing demyelination of the ascending and descending tracts. 8. Amyotrophic lateral sclerosis (Lou Gehrig disease) is a disease confined to the corticospinal tracts and the motor neurons of the anterior gray columns of the spinal cord. It is rarely familial and is inherited in about 10% of patients. Amyotrophic lateral sclerosis is a chronic progressive disease of unknown etiology. Typically, it occurs in late middle age and is inevitably fatal in 2 to 6 years. B. CLINICAL SYNDROMES AFFECTING THE SPINAL CORD 1. Complete Cord Transection Syndrome Complete cord transection *Tremors are rhythmic involuntary movements that result from the syndrome results in complete loss of all sensibility and voluntary contraction of opposing muscle groups. These may be slow,as in movement below the level of the lesion. It can be caused by fracture parkinsonism, or fast,as in toxic tremors from thyrotoxicosis.They dislocation of the vertebral column, by a bullet or stab wound, or by may occur at rest,as in parkinsonism,or with action,the so-called an expanding tumor. intention tremor,as seen in cerebellar disease. 2. Anterior Cord Syndrome Anterior cord syndrome can be caused by cord contusion during vertebral fracture or dislocation, from injury to the anterior spinal artery or its feeder arteries with resultant ischemia of the cord, or by a herniated intervertebral disc. 3. Central Cord Syndrome Central cord syndrome is most often caused by hyperextension of the cervical region of the spine. The S1T4 6 of 7  Neuroanatomy THE SPINAL CORD AND THE ASCENDINDING TRACTS drug, the doctor should know that the adult spinal cord terminates at which of the following intervertebral disc level? A. L1-L2 B. L2-L3 C. L3-L4 D. L4-L5 7. Which of the following structures is the distal end of the spinal cord? A. Cauda equina B. Conus medullaris C. Filum terminale D. Obex 8. Somatic nerve plexuses like brachial plexuses are formed by the merging of: A. Dorsal rami B. Dorsal root C. Ventral rami D. Ventral root 9. Which of the following statements best describes the PNS? A. It consists of 24 cranial nerves and 62 spinal nerves B. It contains bundle of fibers called tracts C. It its composed of the brain and the spinal cord D. Motor neurons convey impulses to the brain 10. Both paralysis of the muscle and numbness of the skin in the back may be attributed to the destruction of which of the following spinal rami? IV. SAMPLE QUESTIONS A. Gray 1. There are how many lumbar spinal nerves B. Dorsal A. 5 C. Ventral B. 8 D. White C. 10 D. 16 11. Referred pain results in the convergence of somatic and visceral 2. Into which spinal cord groups do the dorsal root fibers of afferent on the same segmental level of which part of the spinal spinal nerves enter? cord? A. Anterior median fissure A. Dorsal horn B. Anterolateral sulcus B. Dorsal root ganglion C. Posterior intermediate sulcus C. Gray rami D. Posterolaateral sulcus D. Ventral horn 3. The cranial nerves responsible for smell and taste carry which of the functional component 12. Which is a sign of a basal ganglia lesion? A. GSA A. dysdiadochokinesia B. SSA B. dysmetria C. SVA C. indefatigable horizontal nystagmus D. SVE D. resting tremors (present in Parkinson’s Disease) 4. Which regional vertebrae have the most number of articulating REFERENCES surfaces? th 1. Clinical Neuroanatomy 7 edition : Richard Snell A. cervical C. lumbar 2. Allan T. Viado, MD.,FAFN,FPCS Lecture on Spinal Cord and Spinal B. thoracic D. sacral Nerves 5. Which of the following cervical vertebrae has the longest spinous processes? A. C1 B. C2 C. C6 D. C7 6. A pregnant woman in labor would undergo a lumbar puncture during administration of spinal anesthesia. To safely administer the S1T4 7 of 7