Hypertonicity vs spasticity
Original Editors - Saeed Dokhnan
Hypertonicity or Spastic Dystonia
Spasticity is a term that is often used interchangeably with hypertonia. Spasticity, however, is a particular type of hypertonia in which the muscles' spasms are increased by movement.
Tone is the resistance of muscles to passive stretch or elongation, basically the amount of tension a muscle has at rest. Normal tone is high enough to resist the effects of gravity in both posture and movement yet low enough to allow freedom of movement
Hypertonia is resistance to passive movement, it is not dependent on velocity, can be with or without spasticity.Spasticity is an increase in resistance to sudden , passive movement and IS velocity dependent. The faster the passive movement the stronger the resistance. Spasticity is considered to be a form of sustained efferent muscular hyperactivity, dependent on the continuous supraspinal drive to the alpha motor neuron.
- Decorticate posture is a sign of damage to the nerve pathway in the midbrain, which is between the brain and spinal cord. The midbrain controls motor movement. Serious condition but not as severe as the below.
- Decerebrate posture is an abnormal body posture that involves the arms and legs being held straight out, the toes being pointed downward, and the head and neck being arched backward. The muscles are tightened and held rigidly. This type of posturing usually means there has been severe damage to the brain.
Spasticity is a velocity-dependent increase in muscle tone in response to passive movement. Pyramidal tract injury doesn't give rise to spasticity. Rather, the main symptoms are weakness and loss of dexterity which is greater in distal than in the proximal muscles. The pyramidal tract is the system which balances muscle tone.
Neural Component of Spasticity
- Dorsoreticulospinal tract (DRT) - has an inhibitory effect on MRT and VST
- Medial reticulospinal tract (MRT) and Vestibulospinal tract (VST) - have a facilitatory effect on extensor tone.
All three systems are thought to inhibit flexor reflex afferents responsible for flexor spasm.
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