Biological Systems MCAT Practice Exam

Which structure is primarily responsible for primitive reflexes and basic behaviors like walking?

1. Cerebellum

2. Spinal cord

3. Hypothalamus

4. Cerebral cortex

The correct answer is: Spinal cord

The spinal cord plays a crucial role in coordinating primitive reflexes and basic motor behaviors, such as walking. Reflexes are automatic responses to stimuli, and many of these reflexes, including withdrawal reflexes and those involved in locomotion, are mediated directly through the spinal cord. This allows for rapid responses without the need for higher brain processing. In terms of walking, the spinal cord contains networks of neurons known as central pattern generators, which are responsible for generating the rhythmic patterns of movement for walking. Even in the absence of higher brain input, these networks can produce coordinated movements due to their intrinsic properties. Other structures, while they do contribute to motion and behavior, do not directly mediate these primitive reflexes. The cerebellum is primarily involved in the coordination and fine-tuning of movements rather than initiating basic reflexes. The hypothalamus plays key roles in homeostasis and emotional responses but is not directly responsible for motor behaviors. The cerebral cortex is essential for higher-order processing and voluntary control of movements but does not govern the primitive reflexive actions that are largely spinal cord-mediated.