PHYSIOLOGY OF SENSORY AND MOTOR SYSTEMS OF THE SPINAL CORD (Part 2)

NOMENCLATURE IN THE DESCRIPTION OF PAIN AND ABNORMAL SENSATION

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Any abnormal sensation described as unpleasant

Dysesthesia

Exaggerated pain response from a normally painful stimulus 

Usually includes aspects of summation c repeated stimulus of constant intensity and after sensation 

Increased sensitivity and lowered threshold to painful stimuli 

Hyperalgesia
Ex. inflammation or burns

Exaggerated perception of touch stimulus

Heightened cutaneous sensitivity

Hyperesthesia (hypesthesia)

Abnormal perception of pain from a normally non-painful mechanical or thermal stimulus 

Usually has elements of delay in perception and of aftersensation 

Allodynia

Ex. Trigeminal neuralgia

Decreased sensitivity and raised threshold to painful stimuli

Hypoalgesia (hypalgesia)

Reduced perception of all sensation

Anesthesia

Spontaneous positive, pricking sensation that is not unpleasant 

“Pins and needles” 

Parasthesia

Burning pain in distribution of one or more peripheral nerves 

Causalgia

PAIN SENSATIONS

SKIN AND DEEP PAIN

SKIN PAIN

Two types:

• Pricking pain → evoked immediately on penetration of skin by needle 

• Followed by stinging or burning pain

• “Double response” → pricking followed by stinging or burning 

DEEP PAIN

From visceral and skeletomuscular structures 

Aching; can be sharp, knife-like, burning

Diffuse, purely localized 

• Pain at location other than site of stimulus 

• Deep pain → has infinite boundaries and location is distant from the visceral structures involved 

  • Tends to be referred to other areas innervated by the same spinal segments of the viscera affected 

REFERRED PAIN

• Possible explanation: 

  • Small-caliber pain afferents from deep structures and cutaneous afferents project to a wide range of lamina V neurons in the dorsal horn 

  • Convergence of deep and cutaneous afferents on the same dorsal horn cells, and the fact that there are a lot more cutaneous afferents than visceral afferents and have direct connections with the thalamus, is probably the reason for the phenomenon 

• Unmyelinated sprouts of A-delta and C fibers of an injured nerve become capable of spontaneous ectopic excitation and afterdischarge and are susceptible to ephatic activation 

• Injured nerves are also sensitive to locally applied or intravenously administered catecholamines because of an overabundance of adrenergic receptors on regenerating fibers 

CHRONIC PAIN

• Sensory neurons in dorsal horns of SC or thalamus, if chronically bombarded with pain impulses, may become autonomously overactive (being maintained in this state perhaps by excitatory amino acids) and may remain so even after the peripheral pathways have been interrupted  

MOTOR EXAMINATION

Observation, Inspection, Palpation, Muscle Tone Testing, Functional Testing, Strength Testing of Individual Muscle Groups

MUSCLE STRENGTH

Muscle strength → rated on a scale of 0/5 to 5/5

0/5: no contraction

1/5: muscle flicker, but no movement

2/5: movement possible, but not against gravity (test joint in its horizontal plane

3/5: movement possible against gravity, but not against resistance by examiner

4/5: movement possible against some resistance by the examiner (subdivided into 4-/5, 4/5, 4+/4)

5/5: normal strength

FUNCTIONAL TESTING

Rhythmic thumb and index finger tapping

 Rhythmic heel tapping

Closed eyes, forward flex arms, maintain

SENSORY EXAMINATION

Sensory examination → performed in all extremities, including face and trunk; eyes closed

correlate and recheck to improve objectivity

Light touch → cotton tipped swab or fine light touch

Pain → Sharp or dull end of safety pin or broken wooden swab 

• Ask patient to identify sharp or dull

Temperature Sense - Cold metal i.e. end of a tuning fork

Vibration Sense - Low frequency tuning fork 128 Hz on ball of large toes or fingers

Joint Position Sense - Moving toe or finger up or done

Two-Point Discrimination -Special calipers or bent paper clip or Alternately touching with one or two points

DEEP TENDON REFLEX