Pyramidal system

Through which parts of the internal capsule do the corticonuclear and corticospinal tracts pass?

The corticonuclear and corticospinal tracts pass through the genu and the anterior two-thirds of the posterior limb of the internal capsule.

• Corticonuclear tract (tractus corticonuclearis) — passes through the genu of the internal capsule, where fibers to the face are located.
• Corticospinal tract (tractus corticospinalis) — passes through the anterior part of the posterior limb of the internal capsule, where fibers to the arm, trunk, and leg are located sequentially from front to back.

What clinical signs and symptoms are characteristic of central spastic paralysis?

Central spastic paralysis is characterized by a combination of muscle weakness with spastic hypertonia and reflex changes.

• Muscle weakness — decreased strength and difficulty in performing fine movements.
• Muscle hypertonia — spastic increase in muscle tone.
• Hyperreflexia — pathological increase in deep (tendon and periosteal) reflexes; clonus may appear.
• Pathological reflexes — appearance of extensor and flexor pyramidal signs (Babinski, Rossolimo, etc.).
• Reduction of superficial reflexes — weakening or loss of cutaneous (abdominal, cremasteric) reflexes.
• Syncinesias — involuntary associated movements.
• Absence of early atrophy — mild disuse hypotrophy develops only in later stages.

What clinical signs are characteristic of peripheral flaccid paralysis?

Peripheral flaccid paralysis is characterized by a triad of main clinical symptoms caused by damage to the peripheral motor neuron.

• Atonia or hypotonia — a sharp decrease or complete absence of muscle tone.
• Areflexia or hyporeflexia — reduction or complete loss of deep (tendon and periosteal) reflexes.
• Muscle atrophy — early-onset and pronounced thinning of muscle tissue.

Additionally, fascicular and fibrillary twitches may be observed (with lesions of the anterior horns), and when nerve plexuses or peripheral nerves are involved, paralysis is accompanied by sensory and autonomic disorders.

Which cranial nerve nuclei receive only unilateral cortical innervation?

Only contralateral cortical innervation is received by:

• Hypoglossal nerve nucleus (cranial nerve XII).
• Lower part of the facial nerve motor nucleus (cranial nerve VII), which innervates the lower half of the face.

The upper part of the facial nerve nucleus receives bilateral cortical innervation.

What pathological pyramidal reflexes occur in lesions of the pyramidal pathway?

Lesions of the pyramidal pathway result in pathological reflexes, which are subdivided into extensor and flexor reflexes.

• Babinski reflex (Babinski reflex) — extension of the great toe upon stroking the lateral aspect of the sole.
• Oppenheim sign — extension of the great toe when stroking down the anteromedial surface of the tibia.
• Gordon sign — extension of the great toe upon squeezing the gastrocnemius muscle.
• Rossolimo reflex (Rossolimo reflex) — plantar flexion of the toes when tapping their distal phalanges.
• Trömner reflex (Trömner reflex) — flexion of the fingers when tapping the palmar surface of the distal phalanx of the middle finger.
• Hoffmann sign — pathological finger flexor reflex.

What are alternating syndromes, and at what level of the pyramidal system lesion do they develop?

Alternating syndromes are crossed syndromes characterized by a combination of cranial nerve dysfunction on the side of the lesion (ipsilaterally) and limb muscle paralysis (hemiparesis) on the opposite side of the body (contralaterally).

They develop when the pyramidal system is damaged at the brainstem level. Due to the high density of cranial nerve nuclei and the adjacent descending motor pathways, even a small lesion in the brainstem (midbrain, pons, or medulla oblongata) causes combined damage to these structures. An example is Weber syndrome caused by a midbrain peduncle lesion.