[Neurology] Posturing

Posturing is a medical sign which provides information about central nervous system (CNS) dysfunction.
This is a feature of the motor section of the Glasgow Coma Scale scoring system.

Physiology

The CNS contains many structures which, in earlier mammals, coordinated voluntary and involuntary skeletal muscle activity. In humans, the cerebral cortex has developed to become the master controller of these structures. The cortex and associated structures regulate the passive muscle tone throughout the body. The cerebral cortex is also necessary for fine motor control. It sends signals to the muscles directly through the corticospinal tract.

When there is brain dysfunction, the cortex and corticospinal tract can fail to output neuronal signals. This removes the corticospinal component of muscle tone. However, the subordinate nuclei, which are lower down in the brain, can continue to send signals.

Cross-section of midbrain and cross-section of pons.
Red: red nuclei and rubrospinal tracts
Blue: corticospinal tracts

 

Decorticate posturing

The red nuclei sit in the midbrain. If the dysfunction occurs at a level above the red nuclei, then the red nuclei are able to send signals and modulate the tone of the muscles.

• The flexor muscles in the upper limb draw the upper limbs into flexion.
• The extensor muscles at the neck draw the head into hyperextension.
• The extensor muscles in the legs draw the legs into a hyperextended, internally rotated position.

This is decorticate (no-cortex) posturing. 
GCS score: -3

 

Left: Cross-section of midbrain, red nuclei. Right: decorticate posturing.

 

Decerebrate posturing

The pons (latin: bridge) is in the brainstem situated below the midbrain, above the medulla oblongata, and in front of the cerebellum.

If dysfunction occurs at a level below the red nuclei, the rubrospinal component of passive muscle tone is lost. The pontine nuclei are able to send signals and modulate the tone of the muscles.

• The extensor muscles in the upper limb draw the upper limbs into extension.
• The extensor muscles at the neck draw the head into hyperextension.
• The extensor muscles in the legs draw the legs into a hyperextended, internally rotated position.

This is decerebrate (no-cerebrum) posturing.
GCS score: -4

 

Left: Cross-section of pons. Right: decerebrate posturing.

 

Global hypotonia

If dysfunction occurs at a level below the pontine nuclei, then there are no brain nuclei sending signals to the spinal cord. In the short-term, the global muscle tone will fall, leading to a state of hypotonia.

• All flexor muscles are flaccid and paralysed.
• All extensor muscles are flaccid and paralysed.

GCS score: -5

 

Causes

• Raised intracranial pressure  
• Cerebrovascular infarction (stroke)  
• Intracranial haemorrhage 
• Severe traumatic brain injury 
• Brain, Other CNS & Intracranial Tumours
• Brain herniation 
• Transient posturing called 'fencing response' is often seen in sports, when athletes sustain mild traumatic brain injuries (concussions).