PANTOMATH

SPINAL CORD

INTERESTING FACTS ABOUT SPINAL CORD

• Spinal cord consists of :
  • 1 billion neurons,
  • Over 120 muscles
  • Around 220 ligaments and
  • 100 joints.

CLINICAL SCENARIO

• A 62 year old man, who was a heavy drinker and smoker, consulted his physician about feeling a strong pulse in his abdomen. He said it felt like second heart. He also complained about pain in his abdomen, back and groin. The physician arranged for radiographic studies, including CT scans.
• Radiologist Report:
  • The plain radiographs showed calcium deposits in the wall of the abdominal aorta and an apparent aneurysm. The CT scans revealed an abdominal aortic aneurysm that was 11 cm in diameter. Before he could be admitted to hospital for repair of his abdominal aortic aneurysm, the patient passed out on his home and was involved in a minor car accident. He was rushed to hospital and admitted  for surgery for repair of the ruptured aneurysm.
  • During Surgery for repair of the ruptured aortic aneurysm, there was extensive mobilization of the aorta and several segmental arteries were ligated. Although the aorta was successfully repaired using a Dacron graft, the patient was paraplegic, impotent and his bladder and bowel functions were no longer under voluntary control.

PROBLEMS

1. What arteries supply the spinal cord?
2. what is the most likely anatomical basis for the patient’s paraplegia?
3. Name the important artery supplying the spinal cord that was likely deprived of blood?
4. what are predisposing factors for developing aneurysms?
5. why arterial supply of spinal cord so important?

LEARNING OBJECTIVES

• Knowledge about Spinal cord features, Coverings and Blood supply.
• Application of Knowledge gained,  in clinical practice and procedures like LP.
• Internalisation about Organisation of Spinal cord.
• Prevention of Complications by better orientation.

Spinal cord

• Part of Central Nervous System.
• Length – 42 to 45 cms.
• Located within the vertebral canal – occupying upper two thirds of the vertebral column.
• Extent – From upper border of C1(atlas) to lower border of L1 vertebra in adults. During 3rd month of foetal life, it extends throughout the vertebral canal. At birth, the lower limit of spinal cord is at L3 vertebra. These changes occur due to growth difference between spinal cord and vertebral column.

Functions of spinal cord

• It acts as a conduit for motor information ( from centre to the periphery).
• It acts as a conduit for sensory information (from periphery to the centre).
• It is the centre for coordinating simple reflexes.

Coverings of spinal cord

• Spinal meninges : these are Connective tissue membranes
• Spinal Dura mater: outermost layer; it is the prolongation of cranial dura; continuous with epineurium of the spinal nerves.
• It extends from foramen magnum to lower border of S2.
• Arachnoid mater: thin transparent vascular membrane. Above, its continuous with arachnoid surrounding brain and below it extends upto S2.
• Pia mater: vascular membrane; bound tightly to surface of spinal cord. It is modified at some places – processes of piamater.

Modifications of Pia mater

• Filum terminale – delicate thin prolongation of spinal cord beyond the conus medullaris; 20 cms long; extends from the tip of conus medullaris to the base of the coccyx (after piercing the dura).
• It has two parts
  • Filum terminale Internum – 15 cms long within the dural sac
  • Filum terminale Externum – 5 cms long, outside the dural sac.

    

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• Ligamentum Denticulata – These are lateral extensions (21 teeth like projections) of pia mater between the attachments of ventral and dorsal nerve roots.

Ligamentum Denticulata

• Linea splendens – thickened band of pia along the anterior median fissure of spinal cord.
• Subarachnoid septum -  fenestrated pial septum in the midsagittal plane, which connects the pia mater (over the posterior median fissure) with arachnoid mater posteriorly.

Spaces related to the spinal cord

• Epidural space / Extradural space : It lies between the spinal dura and the periosteum lining the vertebral canal.  Contents - loose areolar tissue and semiliquid fat, minute spinal arteries, internal vertebral venous plexus
• Subdural space : It is a potential space between the spinal dura and arachnoid mater containing a thin film of serous fluid, which acts as a lubricant

Subarachnoid space:

• It is a relatively large space between arachnoid mater and pia mater filled with cerebrospinal fluid (CSF).
• It communicates with the subarachnoid space around the brain at the foramen magnum.
• Below the level of conus medullaris, the space is quite roomy (called lumbar cistern) and contains only cauda equina and filum terminale in a pool of CSF.

Clinical importanceEpidural anesthesia:

• The anesthetic solution is injected through a catheter into the epidural space at the desired site without piercing the dura mater to numb the spinal nerves that traverse the epidural space.
• It is used for the purpose of painless labour, postoperative pain relief and to relieve pain in cancer patients.

Lumbar puncture :

•  It is performed to obtain samples of cerebrospinal fluid for various diagnostic and therapeutic purposes.
• A LP needle is introduced into the subarachnoid space through the interval between the third and fourth lumbar vertebrae.

Spinal anesthesia:

• To give spinal anesthesia, the anesthetic solution is injected into the subarachnoid space. It mixes up with CSF surrounding the spinal nerve roots which get anaesthetized.

External Features of Spinal cord

• The spinal cord is cylindrical structure, somewhat flattened anteroposteriorly. Its lower end tapers into a cone forming the conus medullaris.
• Cauda equina - It is a bunch of lumbar (except L1), sacral, and coccygeal nerve roots around the filum terminale in the pool of CSF (cauda = tail, equina = horse).
• It gives rise to 31 pairs of spinal nerves (cervical 8, thoracic 12, lumbar 5, sacral 5, coccygeal 1).
• Spinal segment – the length of the spinal cord giving origin to one spinal nerve constitutes one spinal segment.
• Spinal segments that contribute to the nerves of the upper limb are enlarged to form the cervical enlargement. The segments innervating the lower limbs form the lumbar enlargement.
• The anterior aspect of spinal cord possesses a deep midline groove called anterior median fissure.
• It extends along the entire length of the spinal cord.
• On either side of anterior median fissure it presents anterolateral sulci.
• where the ventral roots of spinal nerves emerges.
• The posterior aspect of the spinal cord presents a shallow posterior median sulcus, from which a posterior median septum of neuroglial tissue extends into the substance of the cord to a variable extent. On either side of posterior median sulcus, it presents posterolateral sulcus where dorsal roots of spinal nerves emerges.

• The anterior and posterior roots of the spinal nerve unite within the intervertebral foramina. (The anterior root & posterior roots are formed by union of many rootlets).
• The anterior and posterior roots pass to their appropriate intervertebral foramina, where each evaginates dura mater separately before uniting to form the nerve trunk. At all levels from C1 to L1 vertebrae, the anterior and posterior nerve roots pass in front of and behind the ligamentum denticulatum, respectively.

Blood supply of spinal cord Arterial supply :

• Anterior spinal artery - formed by the union of two spinal branches of the right and left vertebral arteries in the upper cervical canal. It runs caudally in the anterior median fissure of the spinal cord and terminates along the filum terminale.

• Posterior spinal arteries - each arising from either the vertebral or posterior inferior cerebellar artery and runs down in the posterolateral sulcus along the line of attachment of posterior nerve roots and usually divides into two collateral arteries along the medial and lateral side of the posterior nerve roots.

• These Spinal arteries are reinforced by the segmental arteries (feeder arteries).
• The anterior spinal artery supplies the anterior two-third of the cord, while two posterior spinal arteries together supply the posterior one-third of the cord.
• Segmental arteries: These are spinal branches of deep cervical, ascending cervical, posterior intercostal, lumbar, and lateral sacral arteries. They reach the spinal cord as the anterior and posterior radicular arteries along the corresponding roots of the spinal nerves, respectively. They mainly nourish the nerve roots.
• The largest segmental (radicular) arteries at the 1st (T1) and 11th thoracic (T11) segmental levels are often termed arteria radicularis magna (arteries of Adamkiewicz).

The veins draining the cord form six longitudinal venous channels:

1. Two median longitudinal, one in the anterior median fissure and the other in the posteromedian sulcus.
2. Two anterolateral, one on either side, posterior to the anterior nerve roots.
3. Two posterolateral, one on either side, posterior to the posterior nerve roots.

• These longitudinal venous channels communicate with the internal vertebral venous plexus and drained by veins, which leave through the intervertebral foramina to empty into the vertebral, posterior intercostal, lumbar, and lateral sacral veins. The internal vertebral venous plexus communicates above with the basilar venous plexus.

Clinical importance

• Anterior spinal artery syndrome: It occurs due to occlusion (thrombosis or compression of the anterior spinal artery).
• Signs and symptoms:
  • (a) Motor symptoms due to involvement of corticospinal tracts and anterior grey columns.
  • (b) Sensory symptoms (viz. bilateral loss of pain and temperature sensation) due to ischemia of spinothalamic tracts.
• The conscious proprioceptive sensations are preserved because the region of posterior white column is supplied by posterior spinal arteries.

SUMMARY

• Length- 42 to 45 cms.
• Extent : Adult- upto lower border of L1.
• Infants upto L3 level.
• Spinal Meninges extent upto S2 level.
• Blood supply by Anterior Spinal and Posterior Spinal artery.
• Spaces related.

CLINICAL SCENARIO

• A 21 Year old man was involved in head on collision. When removed from his sports car, he complained of loss of sensation and voluntary movements in his lower limbs. There was also impaired ability of upper limb movements, particularly in his hands. The patient was kept warm and immobilized until the ambulance arrived. After examination at the hospital, radiographs of his vertebral columns were taken.
• Radiologist reports: Dislocation of c6 vertebra on C7 and a chip fracture of the anterosuperior corner of body of C7.

PROBLEMS

1. What Joints of the cervical region of vertebral column were dislocated?
2. What ligaments binding the vertebrae together were probably strained or torn?
3. What was the most likely cause of the patient’s paralysis?
4. What other physiological functions would no longer be under voluntary control?