Sensory vs Motor Pathways - Anatomy and Physiology

1. Where do most fibers of the lateral corticospinal tract decussate?

   In the pyramids of the medulla oblongata, so each motor cortex controls the opposite side of the body.

2. Where does the dorsal column-medial lemniscus pathway cross to the opposite side?

   In the medulla oblongata, where second-order neurons from the gracile and cuneate nuclei decussate.

3. A hemisection of the right half of the spinal cord at T10 abolishes pain and temperature below the lesion on which side?

   The left side. Spinothalamic fibers cross near their entry level, so the right cord carries pain from the left body.

4. Which type of motor neuron lesion produces spasticity, hyperreflexia and a positive Babinski sign?

   An upper motor neuron lesion. Lower motor neuron lesions cause flaccid weakness, atrophy and reduced reflexes.

5. In which structure do most ascending sensory pathways synapse before reaching the cerebral cortex?

   The thalamus, where second-order neurons synapse on third-order neurons.

6. A stroke damages the primary motor cortex of the left hemisphere. Which side of the body becomes weak?

   The right side, because the corticospinal tract decussates in the medulla.

7. How many neurons typically make up an ascending pathway from receptor to the somatosensory cortex?

   Three: first-order (receptor to CNS), second-order (to the thalamus), and third-order (thalamus to cortex).

8. Which sensations does the dorsal column-medial lemniscus pathway carry?

   Fine (discriminative) touch, vibration and conscious proprioception.

9. Which sensations does the spinothalamic (anterolateral) tract carry, and where does it cross?

   Pain, temperature and crude touch. It crosses in the spinal cord, near the level where the fibers enter.

10. What is the difference between an upper and a lower motor neuron?

    Upper motor neurons lie in the cortex or brainstem; lower motor neurons lie in the anterior horn or cranial nerve nuclei and directly innervate muscle.

11. What is the difference between afferent and efferent pathways?

    Afferent (sensory) pathways carry signals toward the CNS; efferent (motor) pathways carry commands from the CNS to effectors.

Study these flashcards