Question

This patient’s ependymoma was located in the tapered caudal end of the spinal cord, which is supplied by branches of the aorta and spinal arteries. Ependymomas in this region are particularly vulnerable to vessel damage due to higher mobility and vascularization, and movement can lead to vessel rupture and hemorrhage, as occurs in this case. In this case, the patient suffered from a sudden onset of symptoms, presumably following hemorrhage. Answer the following questions regarding the loss of motor and sensory function observed.

Justify the patient’s sudden onset of lower limb paralysis by answering the following questions:

a. Using words and/or drawings, be sure to describe the structure of the corticospinal pathway. Identify the location of the upper and lower somatic motor neurons, decussation, and white matter tracts in the spinal cord. Then, describe how the patient’s ependymoma and subsequent hemorrhage impacted excitability of somatic neurons in this pathway.

b. Justify the patient’s paralysis in both lower limbs. Describe how changes in excitability in lower motor neurons leads to changes in excitability in a skeletal muscle fiber (cell). In your answer, be sure to briefly describe the structure and function of the neuromuscular junction (NMJ), identifying any membranebound proteins and the sequence of events required for skeletal muscle excitation and subsequent force generation. State how ependymoma hemorrhage changes graded and action potentials in a skeletal muscle fiber (cell), the concentration of intracellular calcium, and cross-bridge formation in the muscle.

Answer 1

Ans a) The corticospinal tract is a white matter motor pathway starting at the cerebral cortex that terminates lower motor neurons and interneurons in the spinal cord which controls movement of the limbs and trunk. The tract conducts impulses from the brain to the muscles in a voluntary manner. The corticospinal tract mainly controls our upper and lower limbs.

The cell bodies of the upper motor neurons are located in the cortex of the brain and the cell bodies of the lower motor neurons are located in the grey matter of the spinal cord and brain stem. The decussation is located just before the junction between the medulla oblongata and the spinal cord. The white matter is located in the deeper tissues of the brain (subcortinal) .

Ans b) Since the patients all four limbs are affected by paralysis, it affects both legs, hips, sexuality etc. It refers to paraplegia and paraplegia refers to substantial impairment in functioning and movement. Spinal cord injuries are the most common cause of paraplegia. These injuries impede the brains ability to send and receive signals below the site of injury.

The neuromuscular junction is a type of synapse where neuronal signals from the spinal cord or brain interact with skeletal muscle fibres, causing them to contract. The function of NMJ is to transmit signals from the motor neuron to the skeletal muscle fibre quickly and reliably, to ensure precise control of skeletal muscle contraction and hence voluntary movement.