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Practical Physiology Central Nervous System Sensory Disturbances Syringomyelia ◊Definition It is a disorder of unknown cause which is characterized by progressive damage of the gray m...

Practical Physiology Central Nervous System Sensory Disturbances Syringomyelia ◊Definition It is a disorder of unknown cause which is characterized by progressive damage of the gray matter around the spinal central canal. ◊Site: The most common site is the lower cervical and upper thoracic segments of the cord. ◊Manifestations: a)1st : There is a cavitation and enlargement of the spinal central canal → destroys the crossing axons of the 2nd order neurons of pain and thermal sensations from both sides. It is manifested by bilateral dissociated sensory loss (loss of pain and temperature with intact other sensations) which takes jacket distribution. b) With progression of the disease; The central cavitation expands and other neurons in the gray matter become destroyed;  AHCs → flaccid paralysis of ms in both upper limbs of the LMNL type.  LHCs →Horner's syndrome. c) At a later stage of the disease: The white matter is destroyed → damage of the ascending and descending tract→ leads to; i) Interruption of the dorsal columns → loss of fine touch and proprioceptive sensations, ii)Interruption of the spinothalamic tracts → loss of pain , temperature, and crude touch sensations. All these sensory losses occur in the body regions innervated by the spinal cord below the level of the lesion. 23 Practical Physiology Central Nervous System ii)Interruption of the descending motor pathways→ spastic paralysis of the UMN lesion type of ms innervated by the spinal cord below the level of the lesion. Tabes Dorsalis ◊Cause It occurs as a complication of syphilis. ◊Mechanism The essential lesion in tabes dorsalis is a constrictive fibrosis around the spinal dorsal roots at their point of entry into the spinal cord, central to their ganglia. This causes degeneration of the dorsal root fibers, especially the mechanoreceptive fibers which ascend in the dorsal columns, as well as fibers of pain. ◊Manifestations; a) Loss of tactile and proprioceptive sensations: -1st there is a loss of fine touch, vibration, and proprioceptive sensations. -loss of proprioceptive sensations results in failure of ms co-ordination→ sensory ataxia → movements become jerky, exaggerated, and irregular. Sensory ataxia in manifested by; 24 Practical Physiology Central Nervous System  Incordination of voluntary movements  Stamping gait.  Romberg's Sign→ when the patient closes his eyes during standing he tends to sway from side to side and may fall. b) Loss of pain sensation Loss of pain in the regions supplied by the degenerated pain fibers. c)Loss of reflex actions: Damage of the afferent limb of the reflex arcs causes loss of the spinal reflex actions including somatic and visceral reflexes. The flexion withdrawal and the stretch reflexes are lost, ms are hypotonic, and the tendon jerks become weak. Bilateral damage of the sacral dorsal roots causes loss of micturition, defecation and erection reflexes. 25