Clinical Relevance

Clinical Relevance: Upper motor neuron lesions are also known as supranuclear lesions.

Damage to the Corticospinal Tracts

The pyramidal tracts are susceptible to damage, because they extend almost the whole length of the central nervous system. As mentioned previously, they particularly vulnerable as they pass through the internal capsule – a common site of cerebrovascular accidents (CVA).

If there is only a unilateral lesion of the left or right corticospinal tract, symptoms will appear on the contralateral side of the body. The cardinal signs of an upper motor neurone lesion are:

Hypertonia – an increased muscle tone

Hyperreflexia – increased muscle reflexes

Clonus – involuntary, rhythmic muscle contractions

Babinski sign – extension of the hallux in response to blunt stimulation of the sole of the foot

Muscle weakness

Damage to the Corticobulbar Tracts

Due to the bilateral nature of the majority of the corticobulbar tracts, a unilateral lesion usually results in mild muscle weakness. However, not all the cranial nerves receive bilateral input, and so there are a few exceptions:

  • Hypoglossal nerve – a lesion to the upper motor neurones for CN XII will result in spastic paralysis of the contralateral genioglossus. This will result in the deviation of the tongue to the contralateral side.
    • Note: this is in contrast to a lower motor neurone lesion, where the tongue deviates towards the damaged side.
  • Facial nerve – a lesion to the upper motor neurones for CN VII will result in spastic paralysis of the muscles in the contralateral lower quadrant of the face.

Damage to the Extrapyramidal Tracts

Extrapyramidal tract lesions are commonly seen in degenerative diseases, encephalitis and tumours. They result in various types of dyskinesias or disorders of involuntary movement.

Notes to remember:
  • Amyotrophic lateral sclerosis (ALS)
Amyotrophic lateral sclerosis (ALS), also known as motor neurone disease(MND), or Lou Gehrig’s disease, is a specific disease which causes the death of neurons controlling voluntary muscles. Some also use the term motor neuron disease for a group of conditions of which ALS is the most common.

  • The outer ear includes: auricle (cartilage covered by skin placed on opposite sides of the head), auditory canal (also called the ear canal), eardrum outer layer (also called the tympanic membrane)

  • The middle ear is the part of the ear between the eardrum and the oval window. The middle ear transmits sound from the outer ear to the inner ear. The middle ear consists of three bones: the hammer (malleus), the anvil (incus) and the stirrup (stapes), the oval window, the round window and the Eustrachian tube.
  • Inner ear. Inner ear, also called labyrinth of the ear, part of the ear that contains organs of the senses of hearing and equilibrium. The bony labyrinth, a cavity in the temporal bone, is divided into three sections: the vestibule, the semicircular canals, and the cochlea.