Neuroanatomy: Pyramidal Tracts Overview

Which statement is true regarding upper motor neurones for the facial nerve (CN VII)?

Upper motor neurones for the hypoglossal (CN XII) nerve provide bilateral innervation.

Where do the corticobulbar fibres synapse with lower motor neurones?

The upper motor neurones from the left primary motor cortex act as upper motor neurones for the _____ and _____ trochlear nerves.

Match the cranial nerve with its innervation type:

What is the primary function of the pyramidal tracts?

The corticobulbar tracts supply the musculature of the body.

From which part of the brain do the corticospinal tracts originate?

The fibers in the lateral corticospinal tract _______ (cross over to the other side of the CNS).

Where do the lower motor neurones from the ventral horn supply muscles?

Match the following areas of the brain with their related function:

The anterior corticospinal tract decussates in the medulla.

What condition is associated with compression of the internal capsule?

Pyramidal Tracts Overview

Named after the medullary pyramids in the medulla oblongata.
Responsible for voluntary control of body and facial musculature.

Functional Subdivisions

Corticospinal Tracts: Supply musculature of the body.
Corticobulbar Tracts: Supply musculature of the head and neck.

Corticospinal Tracts

Originate from the cerebral cortex, incorporating:
- Primary motor cortex
- Premotor cortex
- Supplementary motor area
Receive input from the somatosensory area, influencing ascending tract activity.
Neurons converge and descend through the internal capsule, a white matter pathway between thalamus and basal ganglia.
Internal capsule is vulnerable to compression, leading to potential 'capsular stroke' and lesions of descending tracts.
Tracts progress through:
- Crus cerebri of the midbrain
- Pons
- Medulla
In the caudal medulla, the tract bifurcates:
- Lateral corticospinal tract: Fibers decussate (cross over), descend into the spinal cord, and end in the ventral horn. Lower motor neurons: supply body muscles.
- Anterior corticospinal tract: Remains ipsilateral initially, decussates later, terminating in the ventral horn at cervical and upper thoracic segments.

Corticobulbar Tracts

Arise from the lateral aspect of the primary motor cortex.
Share inputs with corticospinal tracts, converging through the internal capsule to the brainstem.
Neurons terminate at motor nuclei of cranial nerves, synapsing with lower motor neurons that innervate muscles of the face and neck.
Many corticobulbar fibers innervate lower motor neurons bilaterally:
- Example: Left primary motor cortex influences both sides of the trochlear nerves.
Exceptions:
- Upper motor neurons for facial nerve (CN VII) provide contralateral innervation affecting lower facial muscles (below the eyes).
- Upper motor neurons for hypoglossal nerve (CN XII) exclusively offer contralateral innervation.

This quiz examines the structure and function of the pyramidal tracts in neuroanatomy. It focuses on the corticospinal and corticobulbar tracts, highlighting their roles in voluntary muscle control for the body and face. Test your understanding of these vital neural pathways.