Pyramidal Tracts PDF

Pyramidal Tracts DR. DOHA AL-AFIFI Objectives At the end of this lecture the student will be able to: Describe the course, origin, subdivisions and the termination of the pyramidal tract. Describe the functions of the pyramidal tract Describe the dysfunction of the pyramidal tracts. D...

Pyramidal Tracts DR. DOHA AL-AFIFI Objectives At the end of this lecture the student will be able to: Describe the course, origin, subdivisions and the termination of the pyramidal tract. Describe the functions of the pyramidal tract Describe the dysfunction of the pyramidal tracts. Descending tracts Tracts originating from the brain and descending in to the spinal cord. These tracts are concerned with various motor activity with the body. Two main tracts: Pyramidal tracts Extrapyramidal tracts Pyramidal tract The pyramidal system is composed of the upper motor neurons in the cerebral cortex. Their axons pass without interruption to lower motor neurons or their interneuronal pools for the purpose of initiating and regulating voluntary movements (especially the more skilled movements). Axons of the pyramidal system destined for the spinal motor nuclei form the pyramidal or corticospinal tract; those destined for brainstem motor nuclei form the corticobulbar tract.  Pyramidal tract Definition: They derived their name from medullary Pyramids of medulla oblongata which they pass through. The pyramidal system originate in cerebral cortex and terminate at A.H.C of different levels of spinal cord. It control the opposite side of the body.  Origin and subdivisions: Origin: It originates in multiple areas of the brain, mainly in the primary motor cortex called Betz cell (area 4) and in premotor areas ( area 6) Subdivisions: It divides into two tracts: 1) The corticospinal tract : Lateral corticospinal tract( Crossed pyramidal tract): supply the musculature of the body Anterior corticospinal tract( Un Crossed pyramidal tract): supply the musculature of the head and neck. 2) The corticobulbar tract:  Course After leaving the cortex, the pyramidal tract axon descend through the corona radiata to reach posterior limb of internal capsule. After the internal capsule, the neuron pass through the crus cerebri of the midbrain, the pons and into the medulla. In the most inferior (caudal) part of the medulla it divided in two: The fibers with in the lateral corticospinal tract decussate ( cross over to the other side of the CNS), then they descend to the spinal cord, terminating in to the ventral horn(at all segmental levels). From the ventral horn the lower motor neuron go to supply the muscles of the body. The anterior corticospinal tract, remain ipsilateral descending into the spinal cord, then they decussate and terminating in to the ventral horn of the cervical and upper thoracic segment levels.  Function Transmit impulses that control most of motor function of the body They are responsible for initiating and regulating voluntary movements (especially the more skilled movement ).  The pathway starting from the cells of the cortex down the spinal cord called the pyramidal (∆) tract or corticospinal tract.  The corticospinal tract Origin: It originates in primary motor cortex (area 4) and in premotor areas ( area 6). The fibers with in the lateral corticospinal tract decussate ( cross over to the other side of the CNS), then they descend to the spinal cord, terminating in to the ventral horn(at all segmental levels). From the ventral horn the lower motor neuron go to supply the muscles of the body. The anterior corticospinal tract, remain ipsilateral descending into the spinal cord, then they decussate and terminating in to the ventral horn of the cervical and upper thoracic segment levels.  Pyramidal decussation: In the lower medulla about 85 to 90% of the fibers will cross over or “decussate” at the pyramidal decussation to descend in the white matter of the opposite side of the spinal cord to form the lateral corticospinal tract, while the remaining fibers (10 to 15 % ) descend directly in the white matter of the same side. B- Corticobulbar tract The fiber Converge and pass through the internal capsule to the brain Stem. The neuron terminates on the motor nuclei of cranial nerves, they synapse with lower motor nucleus to supply the muscles of the face and neck. At the brain stem corticobulbar supply the motor nuclei of cranial nerve on both sides except the lower half of facial Nucleus and the hypoglossal nucleus which supplied only from the opposite pyramidal Tract. These fibers are called corticobulbar as they do not reach the spinal cord. Corticobulbar tract Corticobulbar tract conduct impulses from the brain to the nuclei of the cranial nerves which control the muscle of the face and neck and are involved in facial expression , mastication , swallowing and other motor functions. Corticobulbar tract Dysfunction or lesion of pyramidal tract Upper motor neuron syndrome Lesions involving the pyramidal system, especially the pyramidal tract, are common. This is because the pyramidal tract extends through the entire brain and spinal cord, thereby making it susceptible to vascular and traumatic damage at any central nervous system (CNS) level. A lesion of the upper motor neuron is also called a supranuclear lesion because damage occurs in the pathway carrying impulses to the lower motor neuron. The principal signs of the upper motor neuron syndrome include the absence of volitional movements (paralysis), increased muscle tone, exaggerated myotatic reflexes, and an extensor plantar response—all of these in the contralateral limbs. Function of the pyramidal system Dysfunction or lesion of pyramidal tract Dysfunction or lesion of pyramidal tract To classify LMN lesion based on the basis of anatomical station affected: Case study Upper motor neuron syndrome