Pyramidal Tract

Brief about pyramidal pathways

1. Descending Tracts: Pyramidal tract

2. Descending (motor) Tracts Are the pathways by which  motor signals  are sent from the brain to lower motor neurons. The lower motor neurons then directly innervate muscles to produce movement. Pyramidal tracts Extrapyramidal tracts

3. Pyramidal Tracts These tracts originate in the cerebral cortex , carrying motor fibers to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face. There are no synapses within the descending pathways . The neurons synapse with a lower motor neuron. Thus, all the neurons within the descending motor system are classed as  upper motor neurons . Their cell bodies are found in the cerebral cortex or the brain stem , with their axons remaining within the CNS.

4. Pyramidal Tracts Corticospinal tract  – supplies the musculature of the body (limbs & trunk). Corticobulbar tract  – supplies the musculature of the head and neck. Originate from: Premotor cortex (area 6): responsible for generating a plan of movement. Supplementary motor cortex (area 6): programs complex motor sequences, and is active during “mental rehearsal” of a movement. Primary motor cortex (precentral gyrus, Brodmann area 4): responsible for execution. Primary somatosensory cortex

5. Corticospinal tract The major function of this pathway is fine voluntary motor control of the limbs. The main effector or motor neurons (efferent neurons) for voluntary movement lie within layer V of the primary motor cortex and are a type of giant pyramidal cell called  Betz cells .  The cells have their bodies in the cerebral cortex. The nerve axons travel from the cortex through the  posterior limb of internal capsule (located between the thalamus and the basal ganglia). The neurons pass through the  crus cerebri   of the midbrain , the  pons  and into the  medulla . The axons form two prominences called the  pyramids of the medulla .

6. Corticospinal tract In the most inferior part of the medulla, the tract divides into two: The fibers within the  lateral corticospinal tract decussate (cross over to the other side), resulting in muscles being controlled by the opposite side of the brain. They then descend into the spinal cord, terminating in the ventral horn (at all segmental levels).  The  anterior corticospinal tract  remains ipsilateral, descending into the spinal cord. They then decussate and terminate in the ventral horn of the  cervical  and  upper thoracic segmental levels.

7. Corticobulbar tract The corticobulbar tracts arise from the lateral aspect of the  primary motor cortex . They receive the same inputs as the corticospinal tracts. The fibers converge and pass through the internal capsule to the  brainstem . The neurons terminate on the motor nuclei of the  cranial nerves . Here, they synapse with lower motor neurons, which carry the motor signals to the muscles of the  face  and  neck . Involved in control of facial and jaw musculature, swallowing and tongue movements.

8. Corticobulbar tract Many of these fibers innervate the motor neurons  bilaterally . Exceptions: Upper motor neurons for the  facial nerve  (CN VII) have a contralateral innervation. This only affects the muscles in the lower quadrant of the face – below the eyes. Upper motor neurons for the  hypoglossal  (CN XII) nerve only provide  contralateral innervation.