Chapter 14 - The Brain and Cranial Nerves - Study Guide - Testing Your Comprehension - Page 556: 3

The outcomes of the two experiments, where different structures in the medulla oblongata were selectively transected, would lead to distinct neurological deficits due to the different functions of these structures. Here's how the outcomes of the two experiments would differ: **Experiment 1: Selective Transection of the Pyramids (Anterior Side of Medulla Oblongata):** - The pyramids are white matter tracts in the anterior part of the medulla oblongata, primarily composed of corticospinal fibers. - These fibers are responsible for carrying motor signals from the cerebral cortex (upper motor neurons) to the spinal cord (lower motor neurons), ultimately controlling voluntary muscle movements. - Transection of the pyramids in the medulla would disrupt the descending motor pathways. - Outcome: This experiment would lead to a loss of voluntary motor control below the level of the lesion. This condition is known as "spastic paralysis" or "upper motor neuron syndrome." The individual would have difficulty executing voluntary movements and may experience muscle weakness or spasticity (involuntary muscle contractions). **Experiment 2: Selective Transection of the Gracile and Cuneate Fasciculi (Posterior Side of Medulla Oblongata):** - The gracile and cuneate fasciculi are sensory pathways located in the posterior part of the medulla oblongata. - These pathways carry sensory information, such as proprioception (awareness of limb position), fine touch, and vibration sensations, from the lower limbs and trunk (gracile fasciculus) and upper limbs and trunk (cuneate fasciculus) to the brain. - Transection of these sensory pathways would disrupt the ascending sensory pathways. - Outcome: This experiment would result in sensory deficits. The individual would lose the ability to perceive fine touch, vibration, and proprioceptive sensations from the parts of the body served by these pathways, depending on the level of the lesion. This condition is known as "posterior column syndrome" or "sensory ataxia." It can lead to difficulty with balance, coordination, and an impaired sense of limb position. In summary, Experiment 1 (transection of the pyramids) would primarily affect motor function, leading to spastic paralysis, while Experiment 2 (transection of the gracile and cuneate fasciculi) would predominantly affect sensory function, resulting in sensory deficits and impaired coordination. These experiments demonstrate the critical role of different structures in the medulla oblongata for motor and sensory functions in the human brainstem.

The outcomes of the two experiments, where different structures in the medulla oblongata were selectively transected, would lead to distinct neurological deficits due to the different functions of these structures. Here's how the outcomes of the two experiments would differ: **Experiment 1: Selective Transection of the Pyramids (Anterior Side of Medulla Oblongata):** - The pyramids are white matter tracts in the anterior part of the medulla oblongata, primarily composed of corticospinal fibers. - These fibers are responsible for carrying motor signals from the cerebral cortex (upper motor neurons) to the spinal cord (lower motor neurons), ultimately controlling voluntary muscle movements. - Transection of the pyramids in the medulla would disrupt the descending motor pathways. - Outcome: This experiment would lead to a loss of voluntary motor control below the level of the lesion. This condition is known as "spastic paralysis" or "upper motor neuron syndrome." The individual would have difficulty executing voluntary movements and may experience muscle weakness or spasticity (involuntary muscle contractions). **Experiment 2: Selective Transection of the Gracile and Cuneate Fasciculi (Posterior Side of Medulla Oblongata):** - The gracile and cuneate fasciculi are sensory pathways located in the posterior part of the medulla oblongata. - These pathways carry sensory information, such as proprioception (awareness of limb position), fine touch, and vibration sensations, from the lower limbs and trunk (gracile fasciculus) and upper limbs and trunk (cuneate fasciculus) to the brain. - Transection of these sensory pathways would disrupt the ascending sensory pathways. - Outcome: This experiment would result in sensory deficits. The individual would lose the ability to perceive fine touch, vibration, and proprioceptive sensations from the parts of the body served by these pathways, depending on the level of the lesion. This condition is known as "posterior column syndrome" or "sensory ataxia." It can lead to difficulty with balance, coordination, and an impaired sense of limb position. In summary, Experiment 1 (transection of the pyramids) would primarily affect motor function, leading to spastic paralysis, while Experiment 2 (transection of the gracile and cuneate fasciculi) would predominantly affect sensory function, resulting in sensory deficits and impaired coordination. These experiments demonstrate the critical role of different structures in the medulla oblongata for motor and sensory functions in the human brainstem.