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MCAT

Unit 4: Lesson 1

Foundations of behavior passages

Structure of the central nervous system

Problem

One method scientists use to classify parts of the brain is to look at the developmental origins of those parts. As the fetus grows, the neural tube develops into three primary vesicles and the spinal cord. These three vesicles are the prosencephalon, the mesencephalon, and the rhombencephalon – more commonly known as the forebrain, midbrain, and hindbrain, respectively.
The forebrain develops into the diencephalon and the telencephalon. These contain, among others, the thalamus, cerebral cortex, and basal ganglia. Structures arising from the forebrain are responsible for higher thought, motor coordination, and homeostasis. The midbrain is associated with eye and body movement. The vesicle that gives rise to the midbrain is the only one of the three that does not divide further. The hindbrain develops into the myelencephalon and metencephalon, which contain the cerebellum, pons, and medulla oblongata. These sections of the brain are responsible for autonomic functions, attention and sleep, and complex muscle movement. The midbrain, pons, and medulla oblongata are considered part of the brainstem, which connects the brain to the spinal cord.
The brain sends and receives signals from the body via cranial and spinal nerves. The twelve cranial nerves innervate the head and face, and emerge from the brain, while the spinal nerves emerge from the spinal cord, and innervate the rest of the body.
Figure 1. Developmental vesicles of the brain. Attribution: modified from Surachit, CC-BY-SA 3.0
Septo-optic dysplasia is a condition that affects the optic nerve, hypothalamus, pituitary, and corpus callosum. In some cases, the disorder appears to have a genetic basis, including mutations of the HESX1 gene. Based on the affected structures, HESX1 is important in the development of which of the following?
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