Spinal Cord Notes

Spinal Cord Introduction

Spinal Cord Situation And Extent: The spinal cord lies loosely in the vertebral canal. It extends from foramen magnum where it is continuous with medulla oblongata, above and up to the lower border of the first lumbar vertebra below.

Spinal Cord Coverings: The coverings of the spinal cord are membranous in nature and are called the meninges. The meninges are dura mater, pia mater, and arachnoid mater. These coverings continue as coverings of brain. The meninges are responsible for protection and nourishment of the nervous tissues. The length of the spinal cord is about 45 cm in males and about 43 cm in females.

Read And Learn More: Medical Physiology Notes

Spinal Cord Shape And Enlargements: Spinal cord is cylindrical in shape with two spindle-shaped swellings, the cervical and lumbar enlargements. These two portions of spinal cord innervate upper and lower extremities respectively. Below the lumbar enlargement, the spinal cord rapidly narrows to a cone-shaped termination called conus medullaris. A slender non-nervous filament called filum terminale extends from conus medullaris downward to the fundus of the dural sac at the level of second sacral vertebra.

• Segments of spinal cord: Spinal cord is made up of 31 segments
  • Cervical spinal nerves = 8
  • Thoracic spinal nerves = 12
  • Lumbar spinal nerves = 5
  • Sacral spinal nerves = 5
  • Coccygeal nerve = 1
• In fact, the spinal cord is a continuous structure. The appearance of the segment is given by the nerves arising from the spinal cord which are called spinal nerve.

Spinal Cord Nerves: The segments of spinal cord correspond to the 31 pairs of spinal nerves in a symmetrical manner: The spinal nerves are

• Cervical spinal nerves = 8
• Thoracic spinal nerves = 12
• Lumbar spinal nerves = 5
• Sacral spinal nerves = 5
• Coccygeal nerve = 1

Spinal Cord Nerve Roots

• Each spinal nerve is formed by an anterior (ventral) root and a posterior (dorsal) root. Both the roots on either side leave the spinal cord and pass through the corresponding intervertebral foramina. The first cervical spinal nerves pass through the foramen between the occipital bone and the first vertebra called the atlas.
• The cervical and thoracic roots are shorter whereas, the lumbar and sacral roots are longer. The long nerves descend in the dural sac to reach their respective intervertebral foramina. This bundle of descending roots surrounding the filum terminate resembles the tail of horse. Hence, it is called cauda equina.

Spinal Cord Fissure And Sulci

• On the anterior surface of spinal cord, there is a deep furrow known as anterior median fissure. The depth of this fissure is about 3 mm. Lateral to the anterior median fissure on either side, there is a slight depression called the anterolateral sulcus. It denotes the exit of anterior nerve root.
• On the posterior aspect, there is a depression called posterior median sulcus. The posterior median sulcus is continuous with a thin glial partition called the posterior median septum. It extends inside the spinal cord for about 5 mm and reaches the gray matter.
• On either side, lateral to the posterior median sulcus, there is posterior intermediate sulcus. It is continuous with posterior intermediate septum, which extends for about 3 mm into the spinal cord. Lateral to the posterior intermediate sulcus, is the posterolateral sulcus. This denotes the entry of posterior nerve root.

Internal Structure Of Spinal Cord: The neural substance of spinal cord is divided mt gray matter and outer white matter

Gray Matter Of Spinal Cord

• The gray matter of the spinal cord is the collection of nerve cell bodies, dendrites, and parts of axons. It is placed centrally in the form of wings of the butterfly and it resembles the letter H. Exactly in the center of gray matter, there is a canal called the spinal canal.
• The ventral and the dorsal portions of each lateral half of gray matter are called ventral (anterior) and dorsal (posterior) gray horns respectively. In addition, the gray matter forms a small projection in between the anterior and posterior horns in all thoracic and first two lumbar segments.
• It is called the lateral gray horn. The part of the gray matter anterior to central canal is called the anterior gray commissure and the part of gray matter posterior to the central canal is called the posterior gray commissure.

Neurons in Gray Matter of Spinal Cord: Gray matter contains of two types of multipolar neurons, Golgi 1 type neurons, and Golgi 2 type neurons.

1. Golgi 1 type neurons: Golgi 1 type cells have long axons and are usually found nor horns. Axons of these neurons form the long tracts of spinal cord.
2. Golgi 2 type neurons: Golgi 2 type neurons have short axons are found mostly in posterior horns. The axons from of these neurons pass towards the anterior horn of same side or opposite side.

Organization of Neurons in Gray Matter: Organization of neurons in the gray matter of spinal cord is described in two methods.

1. Nuclei or columns
2. Laminae or layers.
3. Nuclei: Clusters of neurons are identified in the form of nuclei or cell columns. The advantage of this method is that different nuclei are easily distinguished. The disadvantage is that some neurons like internuncial neurons which are outside the distinct nuclei are not included.
   • Nuclei in Posterior Gray Horn: The posterior gray horn contains the nuclei of sensory neurons which receive impulses from various receptors of the body through posterior nerve root fibers. There are four types of nuclei of sensory neurons.
     1. Marginal nucleus: It is also called posteromarginal nucleus, marginal zone nucleus, or border nucleus. It covers the very tip of the posterior gray horn and it is found in all levels of spinal cord.
     2. Substantia gelatinosa of Rolando: It is a cap-like gelatinous material at the apex of the posterior horn situated in all levels of spinal cord. It is formed by small neurons.
     3. Chief sensory nucleus or nucleus proprius: It is situated in the posterior gray horn ventral to substantial genatinosa. It is poorly defined cell column located in all segments of spinal cord.
     4. Dorsal nucleus of Clarke: It is also called Clarke’s column of cells and it is the collection of well-defined neurons. It occupies the basal portion of the posterior horn. This nucleus is found in spinal segments between C8 and L3 only.
   • Nuclei in Lateral Gray Horn: The lateral Gray Horn has a cluster of neurons called inter. less. The neurons of this nucleus give rise to preganglionic fibers, which leave the spinal cord through the anterior nerve root. Inter. nucleus extends between the T1 and L2 segments of spinal cord.
   • Nuclei in Anterior Gray Horn: Anterior gray horn contains the nuclei of lower motor neurons which are involved in motor function. These nuclei are present in almost all the levels of spinal cord. Three types of motor neurons are present in lower motor neuron nuclei
     1. Alpha motor neurons: Alpha motor neurons are large and multipolar cells. Axons of these neurons leave the spinal cord through the anterior root and end in groups of skeletal muscle fibers called extrafusal fibers.
     2. Gamma motor neurons: Gamma motor neurons are smaller cells scattered among alpha motor neurons. These neurons send axons to the intrafusal fibers of the muscle spindle.
     3. Renshaw cells: These cells are also smaller in size. Renshaw cells are the inhibitory neurons that play an important role in synaptic inhibition at the spinal cord.
4. Laminae: The neurons of the gray matter are distributed -h laminae or layers. Each lamina consists of neurons of different size and shape. This cytoarchitectural lamination was identified in 1950 by Bror Burke Rexed. He classified the neurons in 10 laminae based on his observation on sections of brain in a neonatal cat. The laminae are also called Rexed laminae. The advantage of this method is that all the neurons of gray horn are included. The disadvantage is that it is difficult to distinguish the laminae from one another.
   • Laminae in Posterior Gray Horn: Laminae 1 to 6 constitute the posterior gray horn. These laminae contain nuclei of sensory neurons which are concerned with sensory functions.
     • Nuclei present in the laminae of posterior gray horn
       1. Lamina 1: Marginal nucleus
       2. Laminae 2 and 3: Substantial gelatinosa of Rolando
       3. Laminae 3, 4, and 5: Chief sensory nucleus
       4. Lamina 6: Dorsal nucleus of Clarke.
   • Lamina in Lateral Gray Horn: Lateral gray horn contains only one lamina, the lamina 7. It contains an intermediolateral nucleus.
5. Laminae in Anterior Gray Horn: Laminae 8 and 9 form the anterior gray horn. These laminae contain nuclei of motor neurons which are concerned with motor functions.
   • Neurons present in the laminae of anterior gray horn:
     1. Lamina 8: Motor internuncial neurons which are also called interneurons
     2. Lamina 9: Motor neurons
6. Lamina around Central Canal: There is only one lamina around central of the spinal canal, the lamina 10. It contains neuroglia which form the supporting tissue.

White Matter Of Spinal Cord

• White matter of spinal cord surrounds the gray matter. It is formed by the bundles of both myelinated and nonmyelinated fibers, but predominantly the myelinated fibers.
• The anterior median fissure and the posterior median septum divide the entire mass of white matter into swo lateral halves. The band of white matter lying in front of anterior gray commissure is called the anterior white commissure.

Each half of the white matter is divided by the fibers us anterior and posterior nerve roots into three white columns or funicular:

1. Anterior or Ventral White Column: It lies between the anterior median fissure on one side and anterior nerve root and anterior gray horn on the other side. It is also called anterior or ventral funiculus.
2. Lateral White Column: It is present between the anterior nerve root and anterior gray horn on one side and posterior nerve root and posterior gray horn on the other side. It is also called lateral funiculus.
3. Posterior or Dorsal White Column: It is situated between the posterior nerve root and posterior gray horn on one side and posterior median septum on the other side. It is also called posterior or dorsal funiculus.

Tracts In Spinal Cord

The different collections of nerve fibers passing through the spinal cord are known as tracts of the spinal cord. Spinal tracts are divided into two main groups

1. Short Tracts: The fibers of the short tracts connect different parts of spinal cord itself. Short tracts are of two types:
   1. Association or intrinsic tracts which connect adjacent segments of spinal cord on the same side
   2. Commissural tracts, which connect opposite halves of same segment of spinal cord.
2. Long Tracts: The long tracts of spinal cord, which are also called projection tracts, connect the spinal cord with other parts of central nervous system. Long tracts are of two types
   1. Ascending tracts which carry sensory impulses from the spinal cord to brain
   2. Descending tracts, which carry motor impulses from brain to the spinal cord.

Ascending Tracts Of Spinal Cord

The ascending tracts of spinal cord carry the impulses of various sensations to the brain. The pathway for each sensation is formed by two or three groups of neurons, which are:

1. First-Order Neurons: First-order neurons receive sensory impulses from the receptors and send them to sensory neurons present in the posterior gray horn of spinal cord through their fibers. The nerve cell bodies of these neurons are located in the posterior nerve root ganglion.
2. Second-Order Neurons:
   • The second order neurons are the sensory neurons present in the posterior gray horn. The fibers from these neurons form the ascending tracts of spinal cord. These fibers carry sensory impulses from spinal cord to different brain areas below cerebral cortex (subcortical areas) such as thalamus.
   • All the ascending tracts are formed by fibers of second-order neurons of the sensory pathways except the ascending tracts in the posterior white funiculus which are formed by the fibers of first-order neurons.
3. Third-Order Neurons: Third-order neurons are in the subcortical areas. The fibers of these neurons carry the sensory impulses from subcortical areas to cerebral cortex. The ascending tracts situated in different white funiculi are listed in Table. The features of the ascending tracts are given in Table.

1. Anterior Spinothalamic Tract: Anterior spinothalamic tract is formed by the fibers of second-order neurons of the pathway for crude touch sensation.

• Anterior Spinothalamic Tract Situation: This tract is situated in anterior white funiculus near the periphery.
• Anterior Spinothalamic Tract Origin:
  • The fibers of anterior spinothalamic tract arise from the neurons of chief sensory nucleus of posterior gray horn which form the second-order neurons of the crude touch pathway. The first-order neurons are situated in the posterior nerve root ganglia.
  • These neurons receive the impulses of crude touch sensation from the pressure receptors. The axons of the first-order neurons reach the chief sensory nucleus through the posterior nerve root.
• Anterior Spinothalamic Tract Course
  • This contains crossed fibers. After taking origin, the libers cross obliquely in the anterior white commissure and enter the anterior white column of opposite side.
  • Here, the fibers ascend through other segments of spinal cord and brainstem (medulla, pons, and midbrain) and reach the thalamus.
  • A few fibers of this tract ascend in posterior gray horn for 2 or 3 segments in the same side and then cross over to the anterior white column of opposite side.
  • While ascending through the brainstem, the number of fibers is considerably reduced since some of the fibers form the collaterals and reach the reticular formation of brainstem.
• Anterior Spinothalamic Tract Termination: The fibers of anterior spinothalamic tract terminate in the ventral posterolateral nucleus of thalamus. The cells of this thalamic nucleus form the third-order neurons of the pathway. The fibers from thalamic nucleus carry the impulses to somesthetic area (sensory cortex) of cerebral cortex.
• Anterior Spinothalamic Tract Function: This tract carries impulses of crude touch (protopathic) sensation.
• Anterior Spinothalamic Tract Effect Of Lesion: The bilateral lesion of this tract leads to loss of crude touch sensation and loss of sensations like itching and tickling. The unilateral lesion of this tract causes loss of crude touch sensation in the opposite side below the level of lesion (because fibers of this tract cross to the opposite side in spinal cord).

2. Lateral Spinothalamic Tract: Lateral spinothalamic tract is formed by the fibers from the second order neurons of the pathway for the sensations of pain and temperature.

• Lateral Spinothalamic Tract Situation: This tract is situated in the lateral column towards medial side, i.e. near the gray matter.
• Lateral Spinothalamic Tract Origin: The fibers of Lateral spinothalamic tract take origin from two sources
  1. Marginal nucleus: Fibers arising from this nucleus transmit impulses of fast pain sensation
  2. Substantia gelatinosa of Rolando: Fibers arising from here transmit impulses of slow pain and temperature sensations.
• Lateral Spinothalamic Tract Course
  • This tract has crossed fibers. Axons from marginal nucleus and substantia gelatinosa of Rolando cross to the opposite side and reach the lateral column of same segment. Few fibers may ascend one or two segments, then cross to the opposite side, and then ascend in the lateral column.
  • All the fibers pass through medulla, pons, and midbrain and reach thalamus along with the fibers of anterior spinothalamic tract. Some of the fibers of lateral spinothalamic tract form collaterals and reach the reticular formation of brainstem.
  • The fibers of lateral spinothalamic tract form spinal lemniscus along with the fibers of anterior spinothalamic tract at the lower part of the medulla.
• Lateral Spinothalamic Tract Termination: The fibers of lateral spinothalamic tract terminate in the ventral posterolateral nucleus of the thalamus along with anterior spinothalamic tract fibers. From here, third-order neuron fibers relay to the somesthetic area (sensory cortex) of cerebral cortex.
• Lateral Spinothalamic Tract Function: The fibers of this tract carry impulses of pain and thermal sensations.
• Lateral Spinothalamic Tract Effect of Lesion: The bilateral section of this tract leads to total loss of pain and temperature sensations on both the sides below the level of lesion. The unilateral lesion or sectioning of the lateral spinothalamic tract causes loss of pain (analgesia) and temperature (thermoanesthesia) below the level of lesion in the opposite side.

3. Ventral Spinocerebellar Tract: Ventral spinocerebellar tract is also known as Gower’s tract, indirect spinocerebellar tract or anterior spinocerebellar tract. It is constituted by the fibers of second-order neurons of the pathway for subconscious kinesthetic sensation.

• Ventral Spinocerebellar Tract Situation: This tract is situated in lateral white column of the spinal cord along the lateral periphery.
• Ventral Spinocerebellar Tract Origin: The fibers of this tract arise from the marginal nucleus in posterior gray horn. Neurons of marginal nucleus form second-order neurons. The fibers from these neurons make the first appearance in lower lumbar segments of spinal cord.
  • The first-order neurons are in the posterior root ganglia and receive the impulses of proprioception from the proprioceptors in muscle, tendon, and joints. The fibers from the neurons of posterior root ganglia reach the marginal cells through the posterior nerve root.
• Ventral Spinocerebellar Tract Course
  • This tract contains both crossed and uncrossed fibers. Majority of the fibers from the marginal nucleus cross the midline and ascend in lateral white column of opposite side.
  • Some fibers ascend in the lateral white column of the same side also. These nerve fibers ascend through other spinal segments, medulla, pons, and midbrain. Finally, the fibers reach the cerebellum through the superior cerebellar peduncle.
• Ventral Spinocerebellar Tract Termination: These fibers terminate in the cortex of the anterior lobe of the cerebellum.
• Ventral Spinocerebellar Tract Function: This tract carries the impulses of subconscious kinesthetic sensation (proprioceptive impulses from muscles, tendons, and joints). The impulses of subconscious kinesthetic sensation are also called nonsensory impulses.
• Ventral Spinocerebellar Tract Effect Of Lesion: The lesion of this tract leads to loss of subconscious kinesthetic sensation in the opposite side.

4. Dorsal Spinocerebellar Tract: It is otherwise called Flechsig’s tract, direct spinocerebellar tract, or posterior spinocerebellar tract. Like the ventral spinocerebellar tract, this tract is also constituted by the second-order neuron fibers of the pathway for subconscious kinesthetic sensation. The first-order neurons are in the posterior nerve root ganglia. But, the fibers of this tract are uncrossed.

• Dorsal Spinocerebellar Tract Situation: The dorsal spinocerebellar tract is situated in the lateral column along the posterolateral periphery of spinal cord. It is situated posterior to ventral cerebellar tract and anterior to the entry of posterior nerve root.
• Dorsal Spinocerebellar Tract Origin: The fibers of this tract originate from the dorsal nucleus of Clarke situated in the posterior gray matter of the spinal cord. The first appearance of the fibers is in the upper lumbar segments. From lower lumbar and sacral segments, the impulses are carried upwards by the dorsal nerve roots to the upper lumbar segments.
• Dorsal Spinocerebellar Tract Course: This tract is formed by uncrossed fibers. The axons from neurons in dorsal nucleus of Clarke (second-order neurons) reach lateral column of same side. Then, they end through the other spinal segments and reach oblongata. From here, the fibers reach the through inferior cerebellar peduncle.
• Dorsal Spinocerebellar Tract Termination: The fibers of this tract end in the cortex of anterior lobe of cerebellum along with ventral spinocerebellar tract fibers.
• Dorsal Spinocerebellar Tract Function: Along with ventral spinocerebellar tract, the dorsal spinocerebellar tract carries the impulses of subconscious kinesthetic sensation, which are known as nonsensory impulses.
• Dorsal Spinocerebellar Tract Effect Of Lesion: Unilateral loss of the subconscious kinesthetic sensation occurs in lesion of this tract on the same side, as this tract has uncrossed fibers.

5. Spinotectal Tract: The spinotectal tract is considered as a component of anterior spinothalamic tract. It is constituted by the fibers of second-order neurons.

• Spinotectal Tract Situation: It occupies the lateral side of lateral white column, anterior to the lateral spinothalamic tract. It is bound anteriorly by anterior nerve root.
• Spinotectal Tract Origin: Fibers of this tract originate from the chief sensory nucleus (like anterior spinothalamic tract). The first appearance of the fibers is in upper lumbar segments. This tract is very prominent in the cervical segments.
• Spinotectal Tract Course: This tract contains crossed fibers. After taking the origin, the fibers cross to opposite side through anterior white commissure to the lateral column. Then, the fibers ascend to the midbrain along with anterior spinothalamic tract.
• Spinotectal Tract Termination: The fibers of spinotectal tract end in the superior colliculus of the tectum in the midbrain.
• Spinotectal Tract Function: This tract is concerned with spin visual reflex.

6. Fasciculus Dorsolateralis: It is otherwise called tract of Lissauer. It is considered as a component of lateral spinothalamic tract. And, it is constituted by the fibers of first-order neurons.

• Fasciculus Dorsolateralis Situation: This tract is situated in the lateral white column between the periphery of spinal cord and tip of the posterior gray horn
• Fasciculus Dorsolateralis Origin: It is formed by the fibers arising from the cells of posterior root ganglia and enters the spinal cord through the lateral division of posterior nerve root.
• Fasciculus Dorsolateralis Course: This tract contains uncrossed fibers. After entering the spinal cord, the fibers pass upwards or downwards for few segments on the same side and synapse with cells of substantia gelatinosa of Rolando. Axons from these cells (2-order neurons) join the lateral spinothalamic tract.
• Fasciculus Dorsolateralis Function: The fibers of the dorsolateral fasciculus carry impulses of pain and thermal sensations.

7. Spinoreticular Tract: Spinoreticular tract is formed by the fibers of second-order neurons.

• Spinoreticular Tract Situation: It is situated in the anterolateral white column.
• Spinoreticular Tract Origin: The fibers of this tract arise from the intermediolateral nucleus.
• Spinoreticular Tract Course: This tract consists of crossed and uncrossed fibers. After taking origin, some of the fibers cross the midline and then ascend upwards. Remaining fibers ascend up in the same side without crossing.
• Spinoreticular Tract Termination: All the fibers terminate in the reticular formation of the brainstem by three ways
  • Some fibers terminate in nucleus reticularis gigantocellularis and lateral reticular nucleus of medulla in the same side. Some fibers terminate in the nuclei present in the opposite side
  • Some fibers terminate in nucleus reticularis pontis caudalis of the pons in the same side or opposite side
  • Very few fibers terminate in midbrain.
• Spinoreticular Tract Function: The fibers spinoreticular tract are the components of ascending reticular activating system and are concerned With consciousness and awareness.

8. Spino-Olivary Tract: This tract is situated in anterolateral part of white column. The ongin of the fibers of this tract is not specific. However, the fibers terminate in the olivary nucleus of the medulla oblongata. From here, the neurons project into the cerebellum. This tract is concerned with proprioception.

9. Spinovestibular Tract: The spinovestibular tract is situated in the lateral white column of the spinal cord. The fibers of this tract arise from all the segments of spinal cord and terminate on the lateral vestibular nucleus. This tract is also concerned with proprioception.

10. Fasciculus Gracilis (Tract Of Goll) And

11. Fasciculus Cuneatus (Tract Of Burdach)

• These two tracts are together called ascending posterior colummn tracts. These tracts are formed by the fibers from posterior root ganglia. Thus, both the tracts are constituted by the fibers of first-order neurons of the sensory pathway.
• Fasciculus Gracilis And Fasciculus Cuneatus Situation:
  • These two tracts are situated in posterior white column of spinal cord hence the name posterior column tracts. In the cervical and upper thoracic segments of spinal cord, the posterior white column is divided by posterior intermediate septum into medial fasciculus gracilis and lateral fasciculus cuneatus.
  • Thus, the fasciculus gracilis is situated medially in between the posterior median sulcus and posterior median septum on one side and the posterior intermediate sulcus and posterior intermediate septum on the other side. The fasciculus cuneatus is situated laterally. It is bound medially by posterior intermediate septum and sulcus and laterally by posterior gray horn, tract of Lissauer, and posterior nerve root.
• Fasciculus Gracilis And Fasciculus Cuneatus Origin: Fibers of these two tracts are the axons of first order neurons. The cell body of these neurons is in the posterior root ganglia and, the fibers form the medial division (bundle) of the posterior nerve root.
• Fasciculus Gracilis And Fasciculus Cuneatus Course:
  • After entering the spinal cord, the fibers ascend through the posterior white column. These fibers do not synapse in the spinal cord. Some of the fibers of medial division of posterior nerve root descend through the posterior white column in the form of fasciculus interfascicularis or comma tract of Schultze.
  • The fasciculus gracilis contains the fibers from the lower extremities and lower parts of the body, i.e. from sacral, lumbar, and lower thoracic ganglia of posterior nerve root. Fasciculus cuneatus contains fibers from upper part of the body, i.e. from upper thoracic and cervical gangila of posterior nerve root.
  • Fasciculus Gracilis And Fasciculus Cuneatus Termination: These two tracts terminate in the medulla oblongata. The fibers of fasciculus gracilis terminate in the nucleus gracilis and the fibers of fasciculus cuneatus terminate in the nucleus cuneatus. The cells of these medullary nuclei form the second-order neurons.
  • The axons of the second-order neurons form the internal arcuate fibers. The internal arcuate fibers from both sides cross the midline forming sensory decussation and then ascend through pons and midbrain as medial lemniscus. The fibers of medial lemniscus terminate in ventral posterolateral nucleus of thalamus. From here, fibers of the third-order neurons relay to sensory area of cerebral cortex.
• Fasciculus Gracilis And Fasciculus Cuneatus Functions: The tracts of the posterior white column convey impulses of following sensations:
  1. Fine (epicretic) tactile sensation
  2. Tactile localization: It is the ability to locate the area of skin where the tactile stimulus is applied with closed eyes
  3. Tactile discrimination (two-point discrimination): It is the ability to recognize the two stimuli applied over the skin simultaneously with closed eyes
  4. Sensation of vibration: It is the ability to perceive the vibrations (from a vibrating tuning fork placed over bony prominence) conducted to deep tissues through skin
  5. Conscious kinesthetic sensation: It is the sensation or awareness of various muscular activities in different parts of the body
  6. Stereognosis: It is the ability to recognize known objects by touch with closed eyes.
• Fasciculus Gracilis And Fasciculus Cuneatus Effect of Lesion: The lesion in the fibers of these tracts or lesion in the posterior white column leads to the following symptoms on the same side below the lesion
  1. Loss of fine tactile sensation. However, crude touch sensation is normal
  2. Loss of tactile localization
  3. Loss of two-point discrimination
  4. Loss of sensation of vibration
  5. Astereognosis: It is the inability to recognize known objects by touch while closing the eyes
  6. Lack of ability to differentiate the weight of different objects
  7. Loss of proprioception: It is inability to appreciate the position and movement of different parts of the body
  8. Sensory ataxia or posterior column ataxia: It is the condition characterized by uncoordinated, slow, and clumsy voluntary movements because of the loss of proprioception.

12. Comma Tract Of Schultze: It is also called fasciculus interfascicularis. It is situated in between tracts of Goll and Burdach. This tract is formed by the short descending fibers, arising from the medial division of posterior nerve root. These fibers are also considered as the descending branches of the tracts of Goll and Burdach. The function of this tract is to establish intersegmental communications and to form short reflex arc.

Descending Tracts Of Spinal Cord

The descending tracts of the spinal cord are formed by motor nerve fibers arising from brain and descend into the spinal cord. These tracts carry motor impulses from brain to spinal cord. The descending tracts of the spinal cord are of two types:

1. Pyramidal tracts
2. Extrapyramidal tracts.

The descending tracts are listed in Table. The features of the descending are given in Table.

1. Pyramidal Tracts

• • The pyramidal tracts were the first tracts to be found in man. The pyramidal tracts of the spinal cord are the descending tracts concerned with voluntary motor activities of the body.
  • These tracts are otherwise known as corticospinal tracts. There are two corticospinal tracts, the anterior corticospinal tract and lateral corticospinal tract While running from cerebral cortex towards spinal coat fibers of these two tracts give the appearance of a pyramid on the upper part of anterior surface of medulla oblongata. Hence, these two tracts are called pyramidal tracts.
• Pyramidal Tracts Nerve Fibers
  • All the fibers of the pyramidal tracts are present since birth. However, myelination of these fibers is completed in about two years after birth. The pyramidal tracts on each side have more than a million fibers. About 70% of the fibers are large myelinated fibers having a diameter of 4-22 microns.
  • The larger fibers of pyramidal tracts have the tendency to disappear at old age. Since these tracts are concerned with control of voluntary movements, the disappearance of the fibers of pyramidal tracts causes automatic shivering movements in old age. The fibers of pyramidal tracts are the axons of upper motor neurons.
• Pyramidal Tracts Origin: Fibers of pyramidal tracts arise from the following nerve cells in the cerebral cortex
  1. Giant cells or Betz cells or pyramidal cells in precentral gyrus of the motor cortex. The giant cells are situated in area 4 (primary motor area) of frontal lobe
  2. Other areas of motor cortex namely, premotor area (area 6) and supplementary motor areas
  3. Other parts of frontal lobe
  4. Somatosensory areas of parietal lobe.
     • It is believed that 30% of pyramidal fibers arise from primary motor area (area 4) and supplementary motor areas, another 30% from premotor area (area 6), and the remaining 40% of fibers arise from somatosensory areas. All the above fibers form the fibers of upper motor neurons of motor pathway.
• Pyramidal Tracts Course
  • Corona radiata:
    • After taking origin, the nerve fibers run downwards in a diffused manner through white matter of cerebral hemisphere and converge in the form of a fan-like structure along with ascending fibers that project from thalamus to cerebral cortex.
    • The fan-like structure is called corona radiata. Thus, corona radiata contains both ascending fibers from thalamus and descending fibers from cerebral cortex.
  • Internal capsule: While passing down towards the brainstem the corona radiate converges in the form of internal capsule. It is situated in between thalamus and caudate nucleus on the medial side and lenticular nucleus on the lateral side.
  • In pons: The fibers descend down through internal capsule, midbrain and pons. While descending through pons, the fibers are divided into different bundles by the nuclei of pons. At the lower border of pons, the fibers are grouped once again into a compact bundle and then descend down into medulla oblongata.
  • In medulla:
    • This compact bundle of corticospinal fibers gives the appearance of a pyramid in the anterior surface of upper part of medulla. So, the corticospinal tracts are called the pyramidal tracts.
    • At the lower border of medulla, the pyramidal tract on each side is divided into two bundles of unequal sizes. About 80% of fibers from each side cross to the opposite side. While crossing the midline, the fibers of both sides form the pyramidal decussation.
  • In spinal cord
    • After crossing and forming pyramidal decussation, these fibers descend through the posterior part of lateral white column of the spinal cord. This bundle of crossed fibers is called the crossed pyramidal tract or lateral corticospinal tract or indirect corticospinal tract.
    • The remaining 20% of fibers do not cross to the opposite side but descend down through the anterior white column of the spinal cord. This bundle of uncrossed fibers is called the uncrossed pyramidal tract or anterior corticospinal tract or direct corticospinal tract. This tract is well marked in cervical region.
    • Since, the fibers of this tract terminate in different segments of spinal cord, this tract usually gets thinner while descending through the successive segments of spinal cord. The fibers of shm tract are absent mostly below the mid thoracic level Before termination, majority of the fibers of this anterior corticospinal tract cross to the opposite side at different levels of spinal cord.
• Pyramidal Tracts Termination
  • All the fibers of pyramidal tracts, both crossed and uncrossed fibers, terminate in the motor neurons of anterior gray horn either directly or through internuncial neurons. The pyramidal tract fibers terminate on both a motor neurons and α motor neurons. The axons of the motor neurons leave the spinal cord as spinal nerves through anterior nerve roots and supply the skeletal muscles.
  • The neurons giving origin to the fibers of the pyramidal tract are called the upper motor neurons. The anterior motor neurons in the spinal cord are called the lower motor neurons.
  • Pyramidal Tracts Function: The pyramidal tracts are concerned with voluntary movements of the body. Fibers of the pyramidal tracts transmit motor impulses from motor area of cerebral cortex to the anterior motor neurons of the spinal cord. These two tracts are responsible for fine, skilled movements.
  • Effects of lesion
    • The lesion in the neurons of motor cortex and the fibers of pyramidal tracts is called the upper motor neuron lesion. In human beings, pure pyramidal tract lesions do not occur. Lesion of pyramidal fibers occurs most commonly in stroke (cardiovascular accident) due to hemorrhage, thrombosis.
    • During such lesions, many extrapyramidal fibers are also damaged along with pyramidal fibers. Because of this reason, the neurologists often consider the lesion as upper motor neuron lesion and not as pyramidal tract lesion. The effects of lesion are:
      1. Voluntary movements: Voluntary movements of the body are very much affected. Initially, there is loss of voluntary movements in the extremities. Later, it involves the other parts of the body like hip and shoulder.
      2. Muscle tone: The muscle tone is increased leading to spasticity. The muscles are also paralyzed. This type of paralysis of muscles is called spastic paralysis. The spasticity is due to the failure of inhibitory impulses from upper motor neurons, particularly the neurons of the extrapyramidal system to reach the y motor neurons in the spinal cord. However, hypotonia occurs in pure pyramidal tract tester; which is very rare. In monkeys, the sectioning of pyramids tract fibers alone results in hypotonia.
      3. Reflexes: All the superficial reflexes are lost. And, the deep reflexes are exaggerated. The abnormal plantar reflex called Babinski’s sign is present (Babinski’s sign positive).
• Effects of Lesion at Different Levels
  • Cerebral cortex: Lesion of pyramidal tract fibers in cerebral cortex causes hypertonia, spasticity and contralateral monoplegia (paralysis of one limb) or contralateral hemiplegia (paralysis of one side of the body).
  • Internal capsule: Lesion of pyramidal tract fibers at posterior limb of internal capsule results in contralateral hemiplegia.
  • Brainstem: Lesion at brainstem involves not only pyramidal tract fibers but also other structures such as 6 and 7 cranial nerve nuclei. So the lesion results in contralateral hemiparesis (weakness of muscles in one side of the body) along with 6 and 7 cranial nerve palsies.
  • Spinal cord
    • Unilateral lesion of lateral corticospinal fibers at upper cervical segment causes ipsilateral hemiplegia and bilateral lesion causes quadriplegia (paralysis of all four limbs) and paralysis of respiratory muscles.
    • Bilateral lesion of these fibers in thoracic and lumbar segments results in paraplegia (paralysis of both lower limbs) without paralysis of respiratory muscles.

2. Extrapyramidal Tracts: The descending tracts of spinal cord other than the pyramidal tracts are called extrapyramidal tracts. Extrapyramidal tracts are listed in Table.

1. Medial Longitudinal Fasciculus
   • Medial Longitudinal Fasciculus Situation: Medial longitudinal fasciculus descends through posterior part of anterior white column of the spinal cord.
   • Medial Longitudinal Fasciculus Origin: Actually, this tract is the extension of medial longitudinal fasciculus of brainstem. The fibers of this tract take origin from four different areas in the brainstem
     1. Vestibular nuclei
     2. Reticular formation
     3. Superior colliculus
     4. Interstitial cells of Cajal.
   • Medial Longitudinal Fasciculus Course: After entering the spinal cord from the brainstem, the fibers of medial longitudinal fasciculus descend through the posterior part of anterior white column of the same side. In the spinal cord, this tract is well-defined only in upper cervical segments. Below this level, the fibers run along with the fibers of anterior vestibulospinal tract.
   • Medial Longitudinal Fasciculus Extent: The fibers of this tract extend up to the upper cervical segments of spinal cord.
   • Medial Longitudinal Fasciculus Termination: The fibers of this tract terminate in anterior motor neurons of the spinal cord along with fibers of anterior vestibulospinal tract either directly or through intornuncial neurons.
   • Medial Longitudinal Fasciculus Function: This tract helps in the coordination of reflex ocular movements and the integration of ocular and neck movements.
   • Medial Longitudinal Fasciculus Effects of Lesion: Reflex ocular movements and reflex neck movements are affected in the lesion of this tract.
2. Anterior Vestibulospinal Tract
   • Anterior Vestibulospinal Tract Situation: Anterior vestibulospinal tract is situated in the anterior white column, along the periphery of spinal cord lateral to the tectospinal tract.
   • Anterior Vestibulospinal Tract Origin: The fibers of this tract arise from the medial vestibular nucleus in medulla oblongata. In fact, the anterior vestibulospinal tract is the extension of medial longitudinal fasciculus. Most of the fibers are uncrossed.
   • Anterior Vestibulospinal Tract Extent: The fibers run up to thoracic segments of spinal cord.
   • Anterior Vestibulospinal Tract Course: The fibers of this tract run down from medulla into the anterior column of spinal cord along the periphery. All the fibers are uncrossed.
   • Anterior Vestibulospinal Tract Termination: Along with fibers of lateral vestibulospinal tract, the fibers of this tract terminate in anterior motor neurons directly or through internuncial neurons.
   • Anterior Vestibulospinal Tract Function: The function of this tract is explained along with the function of lateral vestibulospinal tract.
3. Lateral Vestibulospinal Tract
   • Lateral Vestibulospinal Tract Situation: This tract occupies the anterior part of lateral white column of spinal cord.
   • Lateral Vestibulospinal Tract Origin: The fibers of this tract take origin from the lateral vestibular nucleus in medulla. This nucleus is also called Deiter’s nucleus.
   • Lateral Vestibulospinal Tract Extent: The fibers of this tract are present throughout the spinal cord.
   • Lateral Vestibulospinal Tract Course: From Deiter’s nucleus, most of the fibers descend directly through lateral column. Very few fibers cross to the opposite side before descending.
   • Lateral Vestibulospinal Tract Termination: The fibers of this tract terminate in the anterior motor neuron, either directly or via internuncial neurons.
   • Lateral Vestibulospinal Tract Functions: The vestibular nuclei receive impulses concerned with muscle tone and posture from the vestibular apparatus and cerebellum. Vestibular nuclei in turn convey the impulses to different parts of the body through the anterior and lateral vestibulospinal tracts. The vestibulospinal tracts are concerned with adjustment of position of head and body during angular and linear acceleration.
   • Lateral Vestibulospinal Tract Effect of Lesion: The adjustment of head and body becomes difficult during acceleration when the vestibulospinal tracts are affected by lesion.
4. Reticulospinal Tract
   • Reticulospinal Tract Situation: The reticulospinal tract is situated in the anterior white column, posterior to anterior vestibulospinal tract.
   • Reticulospinal Tract Origin: Fibers of this tract arise from the reticular formation of pons and medulla. The pontine reticular fibers are uncrossed (direct) and descend in the medial part of anterior column. Fibers from medullary reticular formation are predominantly uncrossed and only few fibers are crossed. These fibers descend in lateral part of anterior column and to some extend in the anterior part of lateral column.
   • Reticulospinal Tract Extent: The fibers of reticulospinal tract extend up to thoracic segments.
   • Reticulospinal Tract Termination: The fibers of reticulospinal tract terminate in the gamma motor neurons of anterior gray horn through the internuncial neuron.
   • Reticulospinal Tract Functions: The reticulospinal tract is concerned with control of movements and maintenance of muscle tone, respiration, and diameter of blood vessels. The pontine and the medullary fibers have opposite effects on these functions, which are given in Table.
   • Reticulospinal Tract Effect of Lesion: Lesion of reticulospinal tract causes disturbances in respiration, blood pressure, movements of the body, and muscle tone.
5. Tectospinal Tract
   • Tectospinal Tract Situation: This tract is situated in the anterior white column of the spinal cord.
   • Tectospinal Tract Origin: The nerve fibers of this tract arise from superior colliculus of midbrain.
   • Tectospinal Tract Extent: The tectospinal tract extends only up to lower cervical segments.
   • Tectospinal Tract Course: After taking origin from the superior colliculus, the fibers cross the midline in the dorsal tegmental decussation and descend in anterior column.
   • Tectospinal Tract Termination: The fibers of tectospinal tract terminate in the anterior motor neurons of the spinal cord, directly or via internuncial neurons.
   • Tectospinal Tract Function: This tract is responsible for the movement of head in response to visual and auditory/ stimuli.
6. Rubrospinal Tract
   • Rubrospinal Tract Situation: The rubrospinal tract is situated in the lateral white column of the spinal cord.
   • Rubrospinal Tract Origin: The fibers of this tract arise from the large cells (nuclei magnocellularis) of red nucleus in midbrain.
   • Rubrospinal Tract Extent: The nerve fibers of this tract appear in the spinal worth only up to thoracic segments.
   • Rubrospinal Tract Course: After arising from the red nucleus, the fibers cross the midline in ventral tegmental decussation and descend into spinal cord through the reticular formation of pons and medulla.
   • Rubrospinal Tract Termination: The fibers of rubrospinal tract end in the anterior motor neurons of the spinal cord via the internuncial neurons.
   • Rubrospinal Tract Function: This tract exhibits facilitatory influence upon the flexor muscle tone.
7. Olivospinal Tract
   • Olivospinal Tract Situation: The olivospinal tract is present in the lateral white column of the spinal cord.
   • Olivospinal Tract Origin: The nerve fibers of the olivospinal tract take origin from the inferior olivary nucleus, which is present in the medulla oblongata.
   • Olivospinal Tract Termination: The fibers of this tract terminate in the anterior motor neurons of the spinal cord.
   • Olivospinal Tract Function: The functions of the olivospinal tract are not known clearly. It is believed that this tract is involved in reflex movements arising from the proprioceptors.

Applied Physiology

Spinal cord injury leads to either temporary or permanent dysfunction. It occurs because of:

1. Direct injury due to bullet firing or accidents (on road, in working place, during communal violence, etc.)
2. Compression by bone fragments, hematoma, or disk material.
3. Ischemia due to rupture of spinal arteries.

During the mechanical injury, the spinal cord may be cut Or one lateral half of the spinal cord may be damaged, or diffused crushing of several segments of spinal card may occur 4 Types.

1. Complete Transaction Of Spinal Cord: The complete transection of spinal cord occurs due to

• Bullet injury which causes dislocation of spinal cord
• Accidents that cause dislocation of spinal cord or occlusion of blood vessels.
  • The complete transection causes immediate loss of sensation and voluntary movement below the level of lesion. In quick transection of spinal cord, the patient feels himself cut into two. For a while, his mind remains clear but he feels as if his lower part of the body below the injury does not exist.
  • It is because his higher centers remain unaffected but the spinal centers below the level of injury loose the function.
  • Then the effects (symptoms) of complete transection of spinal cord start appearing. The effects occur in three stages:

1. Stage of Spinal Shock: It is the first stage of effects that occurs immediately after injury. It is also called stage of flaccidity. Signs and symptoms that develop during this stage:
   1. Paralysis of limbs: Paralysis occurs in two limbs or in all four limbs. Paralysis of limbs depends upon the level of Injury
      • Injury at the cervical region of the spinal cord leads to the paralysis of all four limbs. Paralysis of all the four limbs is called quadriplegia or tetraplegia
      • Injury at the thoracic, lumbar or sacral segments including cauda equina and conus medullaris causes paralysis of lower limbs. Paralysis of lower limbs is called paraplegia.
   2. Flaccid paralysis: The muscles, which are paralyzed, become flaccid, i.e. loose stiffness because of loss of tone. This type of paralysis is called flaccid paralysis.
   3. Loss of reflexes: All the reflexes are lost because of the injury to the anterior and posterior nerve roots.
   4. Loss of sensations: All the sensations are lost because of the injury to posterior nerve roots and sensory neurons in the posterior gray horn.
   5. Effect on visceral organs: Some of the visceral organs are also affected; especially, the urinary bladder and rectum are paralyzed.
   6. Heart rate: Heart rate is decreased and pulse becomes weak and thready.
   7. Venous return: Venous return is very much decreased. The venous return depends upon the muscle tone during resting conditions. During activity, it depends upon the contraction of skeletal muscle (muscle pump). But, in complete transection of spinal cord, muscle tone is lost and flaccid paralysis occurs. This leads to decrease in venous return. In addition, the limbs are immobile and smooth muscles of blood vessels loose the tone. So, the blood gets accumulated in blood vessels of limbs, particularly in lower limbs. And, the lower limbs become cold and blue.
   8. Effect on blood pressure: The effect on blood pressure depends upon the level of injury:
      1. Lesion anywhere below L₂ segment: The blood pressure is not affected much because the sympathetic vasoconstrictor fibers leave the spinal cord between and L₂ segments
      2. Lesion at or above T₁ segment: All the sympathetic vasoconstrictor fibers leaving the spinal cord from T₁, and L₂ segments are transected and are completely cut off from higher medullary cardiovascular centers which regulate the blood pressure. So the blood pressure falls drastically. The mean arterial pressure falls below 40 mm Hg.
         • Severity of complete transection depends upon the level of the lesion. The complete transection at the level of cervical region can be very fatal. Because the diaphragm and other respiratory muscles are cut off from the respiratory centers It causes paralysis of respiratory muscles leading to suciaan arrest of breathing.
         • The crushing injury at sacral segments of spinal cord results in atonic bladder and loss of micturition reflex. In human beings, the stage of spinal shock lasts for about three weeks. In animals the duration of spinal shock varies in different species. In amphibians like frog, it lasts only for few minutes. In mammals like dogs and cats, it lasts for few hours. In monkeys, it lasts for few days.
2. Stage of Reflex Activity: This stage is also called stage of recovery. After 3 weeks period, depending largely upon the general health of the patient, the reflex activity begins to return to the isolated segments of spinal cord below the level of lesion. Developments that take place in this stage
   1. First, the functional activities return to smooth muscles
   2. Next, the sympathetic tone to the blood vessels returns. As the neurons in the gray horn act independently of vasomotor center, the tone in blood vessels is restored and, the blood pressure is also restored to its normal level
   3. Lastly, after another 3 months, the tone in the skeletal muscle returns. The tone returns to the flexor muscles first. So, the flexor muscles of lower limb become less flabby and offer some resistance to the toes. Though the tonicity is returned, it is not complete even in flexor muscles. So, the muscles remain hypotonic The limbs in this condition tend to adopt a position of slight flexion, and, the paralysis is therefore called paraplegia in flexion. The limbs cannot support the weight of the body
   4. After few weeks, when the tone returns to more muscles, reflex movements can occur. The flexor reflexes appear first. To elicit the flexor reflex, a painful stimulus is required. The first reflex, which usually appears, is the Babinski’s reflex
   5. After a variable period of 1 -5 weeks of reappearance of flexor reflexes, the extensor reflexes return. Initially, the knee jerk returns, and then the ankle jerk
   6. In some cases, a widespread reaction can be elicited by scratching the skin over the lower limbs or the anterior abdominal wall, depending upon the level of lesion. This reaction constitutes the spasm in the flexor muscles of both the lower limbs, evacuation of the urinary bladder, and profuse sweating. This is known as the mass reflex.
3. Stage of Reflex Failure:
   • Though the reflex movements return, the muscles few the level of injury have less power and less resistance Usually, the general condition of the patient starts deteriorating.
   • General infection or toxemia becomes common. Due to this, the failure of reflex function develops. The reflexes become more difficult to elicit. The threshold for stimulus increases. Mass reflex is abolished and the muscles become extremely flaccid and undergo wasting.

2. Incomplete Transaction Of Spinal Cord: If the spinal cord is gravely injured, but does not suffer complete division, the condition is called as incomplete transection.

• Symptoms of Incomplete Transection: After incomplete transection of the spinal cord, all three stages of complete transection occur.
  1. Stage of Spinal Shock: The features are similar to those of complete transection.
  2. Stage of Reflex Activity: The features of this stare are:
     • The tone returns to the extensor muscles first and not to the flexor muscles. This is because, in incomplete transection, some of the descending fibers in the lateral column of the cord, especially the vestibulospinal and reticulospinal tracts may escape the injury. So, some connections persist between brainstem and spinal cord. The fibers of vestibulospinal and reticulospinal tracts mainly reinforce the activity of extensor motor neurons.
       Because of this, there is extensor hypertonia and so, the lower limbs are extended at hip and knee with toes pointing slightly downwards. This condition is known as paraplegia in extension.
     • The stretch reflex reappears first. The flexor reflexes return later. Phillipson’s reflex (clasp knife reflex) can be elicited.
     • In the upper limb, some resistance is offered when the arm is flexed at the elbow joint passively. That is, the arm cannot be flexed. This resistance is offered because of the stretch reflex developed in the triceps muscle. However, if forearm is flexed forcefully, the nsSfetance to flexion is abolished suddenly, leading to quick flexion of arm. This is called Phillipson’s traffic or clasp knife reflex.
     • The mass reflex, which is produced in complete transection, does not occur in incomplete transection of spinal cord.
  3. Stage of Reflex Failure: The features are similar to those of complete transection.

3. Hemisection Of Spinal Cord-Brown-Sequard Syndrome: The lesion involving one lateral half of the spinal cord is called hemisection. It can occur due to injury during accidents. It can also be produced experimentally in animals.

• Symptoms of Hemisection of Spinal Cord:
  • The signs and symptoms, which occur after hemisection of the spinal cord, constitute Brown-Sequard syndrome.
  • If the hemisection is due to injury, the spinal shock occurs immediately. The muscles loose the tone and become flaccid. The reflexes are abolished. In case the patient survives, this stage gradually passes off and certain signs and symptoms develop.
  • The effects are seen below the level of lesion and at the level of lesion. The effects in these places differ on the same side and on the opposite side. There are changes in sensory and motor functions.

4. Effects Of Hemisection Of Spinal Cord Below The Level Of Lesion

• On the Same Side
  • Sensory changes
    1. On the same side below the level of lesion, the following sensations are lost because, the’se sensations are carried by the uncrossed fibers of tracts of Goll and Burdach.
       1. Fine touch
       2. Tactile localization
       3. Tactile discrimination
       4. Sensation of vibration
       5. Conscious kinesthetic sensation
       6. Stereognosis.
    2. The following sensations are not affected because, these sensations are carried by the crossed fibers of spinothalamic tracts.
       1. Crude touch
       2. Pain
       3. Temperature.
  • Motor changes: The motor changes resemble the effects of upper motor neuron lesion.
    1. The muscle tone increases, leading to spastic paralysis
    2. The rigidity of limbs occurs
    3. Muscle wastage does not occur
    4. Superficial reflexes are lost
    5. Babinski’s sign is positive
    6. Deep reflexes are exaggerated
    7. Fall in blood pressure because of loss of vasomotor
• On the Opposite Side
  • Sensory changes
    1. On the opposite side, below the level of lesion, the following sensations are lost completely because, these sensations are carried by crossed spinothalamic tracts.
       1. Crude touch
       2. Pain
       3. Temperature.
    2. The following sensations are not affected because, these sensations are carried by the uncrossed tracts of Goll and Burdach.
       1. Fine touch
       2. Tactile localization
       3. Tactile discrimination
       4. Vibratory sense
       5. Conscious kinesthetic sensation
       6. Stereognosis.
  • Motor changes: Mostly there may not be any paralysis of muscles. If it occurs, it would be mild as only a few fibers of pyramidal tract are affected. This is because pyramidal fibers cross to the opposite side. The paralysis is of upper motor neuron lesion type. Thus, during hemisection of spinal cord, motor loss is extensive and sensory loss is less below the level of lesion on the same side. On the opposite side, the sensory loss is extensive and motor loss is less.

5. Effects Of Hemisection Of Spinal Cord At The Level Of Lesion

• On the Same Side:
  • Sensory changes: On the same side at the level of hemisection, there is complete anesthesia. That is, all the sensations are lost. This is because of complete destruction of the posterior nerve root.
  • Motor changes: The effects of lower motor neuron lesions occur because the motor neurons and their fibers leaving the spinal cord are affected. Motor changes of lower motor neuron lesion:
    1. Muscles loose their tone and become flaccid and paralyzed. This type of paralysis with loss of muscle tone is called flaccid paralysis
    2. All the reflexes are lost
    3. Muscles degenerate and undergo wastinq due to loss of tone
    4. The vasomotor tone is lost.
• On the Opposite Side
  • Sensory changes
    1. There is loss of pain, temperature and crude touch sensations because the crossed spinothalamic tracts are affected.
    2. But tracts of Goll and Burdach are not affected. So, the sensations carried by these two tracts are not affected.
  • Motor changes; No motor change occurs. If it occurs, it is very mild and is similar to the effects of lower motor neuron lesion.

6. Diseases Of Spinal Cord

1. Syringomyelia: Syringomyelia is spinal cord disorder characterized by the presence of fluid-filled cavities in the spinal cord. The gray matter around the central canal is the most affected part. So the sensory disturbances are more pronounced than the motor disturbances.
   • Syringomyelia Cause:
     • This disease of the spinal cord occurs due to the over growth of neuroglial cells in spinal cord accompanied by cavity formation and accumulation of fluid. Initially, the cavity appears in the gray matter near the central canal of the spinal cord. In later stages, the cavity extends and involves the surrounding white matter to a variable degree.
     • The disease usually starts in one or two segments. Then, it extends up and down for considerable distances. Lower cervical and upper thoracic regions are affected the most.
   • Syringomyelia Features: The characteristic features of this disease are the loss of pain and temperature sensations and muscular weakness. The severity of the loss of sensations depends upon the extent of disease in the spinal cord. Symptoms of syringomyelia
     • If the disease is only around central canal, there is loss of temperature, pain, and crude touch sensations only. It is due to lesion of the fibers crossing through the anterior gray commissure. Fine touch sensation is not affected because the fibers of the fine touch pathway are in the posterior white column.
     • If the lesion is unilateral, effect occurs only on the same side.
     • If the disease extends to the posterior gray horn, all the sensations are lost. Due to loss of pain and temperature sensations, the affected part is not withdrawn either reflexly or consciously from a painful stimulus. So, the affected persons become prone for injuries. Since the injury is not perceived it leads to severe damage to the tissues.
     • If the anterior gray horn is affected, there is flaccid paralysis of muscles. In later stages, both pyramidal and extrapyramidal tracts are also involved, if the disease spreads to white matter. It causes spastic paralysis of limbs, especially in lower limbs resulting in spastic paraplegia. Weakness and wasting of small muscle of limbs occur. Winging of scapula and scoliosis (lateral curvature of spine) develop.
2. Tabes Dorsalis: Tabes dorsalis is another disease of the spinal cord. It is a slowly progressive nervous disorder affecting both the motor and sensory functions of spinal cord.
   • Tabes Dorsalis Cause: It occurs due to the degeneration of posterior (sensory) nerve roots. It usually occurs in syphilis.
     • The posterior nerve roots are affected proximal to the posterior root ganglia. The ganglia are not affected. Among the liber; of the posterior root, the fibers of lateral division are affected much. The reason for this type of selective degeneration is not known. Along with lateral fibers of posterior root, the fibers in posterior white column of spinal cord are also affected.
   • Tabes Dorsalis Features: In tabes dorsalis, both sensory and motor functions are affected. The symptoms are
   • Tabes Dorsalis Sensations
     1. During the onset of degenerative changes, there is an exaggeration of pain sensation.
     2. Then, there is impairment and loss of all sensations.
     3. Loss of sensations, particularly pain sensation leads to deformities of joint. There is no proper support and movements at the joints become uncontrolled. It is called Charcot’s joint.
     4. The enlargement of joints occurs due to inflammation by the development of osteoarthritis.
   • Tabes Dorsalis Reflexes: Both superficial and deep reflexes are lost in tabes dorsalis mostly because of loss of sensations.
   • Tabes Dorsalis Voluntary Movements: There is lack of coordination of movements (ataxia). Normal movements like walking also become clumsy. The gait is awkward. Every movement of the limb is exaggerated while walking. The patient keeps the leg apart, raises the leg very high, and stamps it down forcibly. This is called stamping gait.
   • Tabes Dorsalis Urinary bladder: If the sacral segments are affected in tabes dorsalis, the smooth muscles of the urinary bladder become hypotonic. The micturition reflexes are lost. And, the urinary bladder becomes atonic bladder.
3. Multiple Sclerosis: Multiple sclerosis (MS) is a chronic and progressive inflammatory disease characterized by demyelination in brain and spinal cord. It affects the myelinated nerve fibers of the brain, spinal cord, and optic nerve and causes gradual destruction of the myelin sheath (demyelination). When the disease progresses, there is transection of axons in patches throughout the brain and spinal cord. The term sclerosis refers to scars (sclerosis) in the myelin sheath.
   • Multiple Sclerosis Cause: The cause of multiple sclerosis is unknown. It is hypothesized that multiple sclerosis occurs due to the combination and interaction of environmental factors (chemicals, bacteria, and virus) and genetic factors resulting in abnormal reactions of immune system. During the process, the immune system attacks the myelin sheath.
   • Multiple Sclerosis Signs And symptoms: The initial attack by multiple sclerosis is often mild or asymptomatic. As the disease progresses variety of symptoms start appearing. The symptoms become severe during further progress of the disease.
   • Common initial symptoms:
     1. Mild disturbance in the sensations on the face, arms, and legs
     2. Weakness and disturbances in maintenance of posture
     3. Double vision followed by partial blindness.
   • Other symptoms when the disease progresses:
     1. Tremor, fatigue, and muscle spasms
     2. Speech difficulty,
     3. Difficulty in performing day-to-day activities
     4. Bowel difficulties
     5. Bladder dysfunction
     6. Emotional outbursts like anxiety, anger and frustration
     7. Short-term memory loss
     8. Complete blindness
     9. Development of suicidal tendency.
4. Disk Prolapse:
   • The intervertebral or spinal disk is the cartilaginous structure of the vertebral column that separates each vertebra. It is made up of a tough outer fibrous layer and a soft inner part. The inner part acts as a shock absorber and cushions the vertebrae while moving. A small gap in between the adjacent vertebrae allows nerve roots to enter or leave the spinal cord.
   • The rupture of disk is called disk prolapse. During disk prolapse, the soft inner material bulges out through a weak area in the hard outer layer. The bulged disk material may irritate or compress or damage the nerve root that passes through the gap between the vertebrae. The severity of the condition depends upon the degree of bulging.
   • Disk Prolapse Causes: Common causes of disk prolapse are
     1. Injury to spinal cord, neck, or back
     2. Heavy weight lifting
     3. Sitting for a long time
     4. Sudden violent twisting of the body involving spine
     5. Aging – because of gradual degeneration of disk with age. After about 30 years of age, the disk starts dehydrating. So it is more susceptible for rupture at the age of 30-40 years.
   • Disk Prolapse Symptoms
     • The symptoms of disk prolapse include pain and weakness in the area of prolapse. The most common area of disk prolapse is the lower part of vertebral column.
     • If it compresses the sciatic nerve, the symptoms become more severe. The pain spreads down the back of leg to the ankle, heel, or toes of foot. The lower limb cannot be lifted sometimes.
     • There is numbness and tingling in the affected region. Sitting for long periods aggravates the pain and develops other symptoms such as sneezing, coughing, or voiding of urine. Prolonged compression of the sciatic nerve leads to weakness of leg muscles.
     • The next common area of disk prolapse is the neck. In this case, the pain is felt in the neck, shoulder blade, and armpit. If the nerves supplying upper limbs are compressed, the pain spreads through the arm up to the fingers. It also causes stiffness, weakness, or tingling in the upper limbs. Even the movements of fingers or arms are restricted.