Topic: descending pathways, functions of cerebellum, basal ganglia
Question: With the help of a diagram, describe the corticospinal tract from origin to termination. Write briefly on upper motor neuron paralaysis
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The corticospinal tract, also known as the pyramidal tract, is a neural pathway that originates in the cerebral cortex and descends to the spinal cord, where it synapses with lower motor neurons. It’s responsible for controlling voluntary movements.
Here’s a description of the corticospinal tract from origin to termination:
- Origin: The corticospinal tract originates from the primary motor cortex (located in the precentral gyrus of the frontal lobe), the premotor cortex, and the supplementary motor area.
- Course: The fibers of the corticospinal tract descend through the corona radiata and the internal capsule, then pass through the cerebral peduncles of the midbrain, the pons, and the medulla oblongata. In the medulla, about 85-90% of the fibers cross over to the contralateral side at the pyramidal decussation, forming the lateral corticospinal tract. The remaining 10-15% of the fibers continue down ipsilaterally in the anterior corticospinal tract.
- Termination: The fibers of the corticospinal tract terminate by synapsing with lower motor neurons in the anterior horn of the spinal cord. The lateral corticospinal tract controls movements of the distal muscles of the limbs, while the anterior corticospinal tract controls movements of the axial and proximal limb muscles.
Upper motor neuron paralysis is a type of paralysis that results from damage to the corticospinal tract or other upper motor neurons. It’s characterized by the following features:
- Spasticity: This is a condition in which the muscles are abnormally stiff and resistant to movement. It’s caused by the loss of inhibitory signals from the corticospinal tract.
- Hyperreflexia: This is a condition in which the deep tendon reflexes are exaggerated. It’s caused by the loss of inhibitory signals from the corticospinal tract.
- Babinski sign: This is a condition in which stroking the sole of the foot causes the big toe to extend and the other toes to fan out. It’s a sign of damage to the corticospinal tract.
- Weakness or paralysis: This can occur on the contralateral side of the body, depending on the location and extent of the damage.
- Clonus: This is a series of rapid muscle contractions and relaxations that occur when a muscle is stretched. It’s a sign of damage to the corticospinal tract.
Upper motor neuron paralysis can be caused by various conditions, such as stroke, spinal cord injury, multiple sclerosis, and cerebral palsy. The treatment depends on the underlying cause and may include physical therapy, medications, and surgery.
