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OBJECTIVES

Objectives

After studying this chapter, the student should be able to:

  • Distinguish the 3 components of the brainstem and their general functions.

  • Outline the cranial nerves and describe their overall motor, sensory and/or autonomic functions.

  • Diagram the connections from the forebrain to and from the cerebellum and describe the functions of the cerebellum.

  • Identify the gray and white matter regions of the spinal cord, explain their functions, and define the spinal cord segments.

  • Outline the spinal nerves and their dorsal and ventral roots, main branches, and peripheral nerves.

  • Delineate the meninges and describe its locations and 3 membrane components.

  • Define the ventricular system and the flow of cerebrospinal fluid.

  • Distinguish and describe the main central nervous system arteries and their origins and branches and venous drainage.

INTRODUCTION

The forebrain is highly interconnected with the midbrain, hindbrain, and spinal cord. These regions also provide the connections to the peripheral nervous system (PNS); the PNS includes the cranial nerves, spinal nerves, peripheral nerves, and ganglia located outside of the brain and spinal cord. The midbrain, pons, and medulla oblongata (hereafter medulla) compose the brainstem, which contains nuclei that are critical for survival through automatic responses such as breathing and reflexes such as coughing. The brainstem also contains nuclei for cranial nerves (CNs) III to XII. Emerging from the brainstem, CNs III to XII serve somatic and autonomic motor and sensory functions in the face, head and neck, special senses, and autonomic innervation of the heart, lungs, and other organs. The other region of the hindbrain is the cerebellum, which is connected to the rest of the brain and spinal cord via the pons. The cerebellum functions in motor functions including coordination, precision, timing, and motor learning and has been implicated in cognition and emotion.

Caudal to the medulla is the spinal cord. The spinal cord contains both ascending and descending white matter tracts and neurons involved in motor output, sensory relay, integration, and spinal reflexes. Spinal cord gray matter contains the cell bodies of somatic motor neurons, preganglionic autonomic neurons, and sensory relay neurons, as well as spinal interneurons involved in integration and spinal reflexes. The spinal cord is the origin of the 31 pairs of spinal nerves and their branches, called peripheral nerves, which contain axons that innervate the skin, muscles, tendons, joints, and organs (viscera). The circuitry within the spinal cord generates spinal reflexes and contributes to central pattern generators. Another component of the PNS is the enteric nervous system (ENS); located in the gastrointestinal (GI) tract, the ENS functions in peristalsis and secretions.

The central nervous system (CNS) is protected on the outside by the skull and meninges, membranes that prevent the movement of the brain within the skull and contain cerebrospinal fluid (CSF) that helps cushion the CNS. Inside the CNS lies the ventricular system and central canal, with the main function of production and circulation of ...

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