14.0 Introduction: Central Nervous System
Chapter Objectives
After studying this chapter, you will be able to:
- Describe the connections of the diencephalon and cerebellum on the basis of patterns of embryonic development
- Explain how a disruption in circulation would result in a stroke
- Describe the connections between the cerebrum and brain stem through the diencephalon, and from those regions into the spinal cord
- Explain the initiation of movement from the neurological connections
- Compare different descending pathways, both by structure and function
The central nervous system, composed of the brain, brainstem, and spinal cord, coordinates the body’s responses to internal and external stimuli. During development, a portion of the ectoderm differentiates and forms the neural tube that undergoes a series of changes to eventually form the brain from the anterior end of the neural tube and the spinal cord from the posterior end, while the open space within the neural tube becomes the cerebrospinal fluid-filled ventricles of the brain. Cerebrospinal fluid circulates to remove metabolic waste from nervous tissue while acting as a liquid cushion. A robust and redundant blood supply to provide oxygen and glucose to the brain and the blood-brain barrier which regulates which contents of the blood can pass into the central nervous system. Oxygen deprivation to the brain due to a loss of blood flow, known as a stroke, can cause neural deterioration within 1 or 2 minutes. Three meninges, membranous coverings of varying thickness, protect the brain.
The brain, composed of the cerebrum, diencephalon, brainstem, and cerebellum, is responsible for a person’s consciousness, regulation of homeostasis, and coordination. All conscious sensation, memory, language, and reasoning occur in the cerebral cortex. Other cerebral structures form connections between neurons and control subconscious processes. The brainstem connects the cerebrum to the spinal cord and also forms the connection to cranial nerves of the peripheral nervous system and the cerebellum which helps refine and coordinate motor commands based on sensory feedback. The spinal cord, unlike the brain, maintains the tube structure of its embryonic origins. Synapses in the gray horns of the spinal cord are responsible for sensory processing and sending out motor signals while white columns are organized axon tracts carrying sensory and motor information. Emerging from the spinal cord are a series of paired spinal nerves which contribute to the peripheral nervous system. Central nervous system health is tested through the spinal and cranial nerve exams which can reveal problems in the spinal cord and brainstem.
