Upon completing this study unit, you will be able to:
- Identify the two main components of the pyramidal tracts.
- Describe the course and the decussation of the pyramidal tracts.
- Understand the function of the pyramidal tracts.
The pyramidal tract is a descending white matter tract of the central nervous system that provides voluntary control of striated muscle movement. It is composed of 2 distinct tracts:
- Corticospinal tract, which mainly arises from the primary motor cortex in the brain. It receives additional contributions from the premotor, supplementary motor and the somatosensory cortex. This tract carries motor signals from the upper motor neurons (UMN) of the cerebral cortex to the lower motor neurons (LMN) of the spinal cord, which further relay them to the muscles of the trunk and limbs.
- Corticonuclear (corticobulbar) tract, which also arises from the upper motor neurons (UMN) in the primary motor cortex in the brain. Unlike the corticospinal tract, the lower motor neurons (LMN) of the corticonuclear tract are found in the motor cranial nerve nuclei of the brainstem, which innervate the muscles of the head, face and neck.
It’s important to note that according to the official terminologia anatomica (TA), the term ‘pyramidal tract’ refers only to the corticospinal tract, while the corticonuclear tract is regarded as a separate tract. However, most of the literature uses it as an umbrella term for both the corticospinal and corticonuclear tracts.
Learn more about the pyramidal tract by watching the video below!
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Take a closer look at the pyramidal tracts in the gallery below.
|Corticospinal tract||Primary motor cortex (UMN) → Corona radiata → Internal capsule → cerebral peduncle → Pons → Pyramids of medulla
→ 90% decussate → Lateral corticospinal tract → Lateral funiculus of spinal cord → Anterior horn of spinal cord (LMN) → Anterior root of spinal nerve → Spinal nerve → Muscles of the limbs
→ 10% remain ipsilateral → Anterior corticospinal tract → Anterior funiculus of spinal cord → Anterior horn of spinal cord (LMN) → Anterior root of spinal nerve → Spinal nerve → Muscles of the trunk
|Corticonuclear tract||Primary motor cortex (UMN) → Corona radiata → Internal capsule → Brainstem
→ Midbrain: Motor nuclei of oculomotor (CN III), trochlear (CN IV) and abducens (CN VI) nerves
→ Pons: Motor nuclei of facial (CN VII) and trigeminal (CN V) nerves
→ Medulla oblongata: Motor nuclei of glossopharyngeal (CN IX) and accessory (CN XI) nerves
Corticonuclear tract: Voluntary control of the muscles of face, head and neck
Corticospinal tract: Voluntary control of the muscles of the limbs and trunk
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