12: Central and Peripheral Nervous System
The central nervous system (CNS) comprehends the brain and spinal cord, while the peripheral nervous system (PNS) comprises ganglia, cranial and spinal nerves. The focus of this chapter is on these organs. First you will learn the structures that support and protect the nervous system. Then you will focus on the various regions of the brain and spinal cord. At the end you will look at cranial and spinal nerves.
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- 12.1: Introduction to the Central and Peripheral Nervous System
- Different structures of the nervous system perform different functions. The structures of the nervous system were discovered through dissection, while functions of those regions were discovered through lesion case studies. In these studies, injuries or illnesses of the nervous system are studied to understand the relationship between the injured area and the function of it. One famous lesion case study was Phineas Gage, an American railroad worker.
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- 12.2: Support and Protection of the Brain
- The CNS is crucial to the operation of the body and any compromise of function in the brain and spinal cord can lead to severe difficulties. The CNS is protected by the skeletal system (skull and vertebral column), and underneath by membranes of connective tissue, called meninges. In addition, the CNS has a privileged blood supply, as suggested by the blood-brain barrier. Because of this privilege, the CNS needs specialized structures for the maintenance of circulation.
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- 12.3: Brain- Cerebrum
- The brain is divided into four major regions: cerebrum, diencephalon, brainstem, and cerebellum. The cerebrum is divided into different regions called lobes: frontal, parietal, occipital, temporal and insula. Each lobe performs a specialized function through their cerebral cortex. Overall, the functions of the cerebrum are motor initiation and coordination, processing of general and special senses, and high level functions such as judgment, reasoning, problem solving, and learning.
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- 12.4: Brain- Diencephalon, Brainstem, Cerebellum and Limbic System
- Deep and inferior to the cerebrum, the diencephalon, brainstem and cerebellum compose the rest of the brain. These regions are responsible for various functions including maintaining homeostasis, relaying sensory information, carrying vital functions through the autonomic system. Most of the cranial nerves originate from these regions. The limbic system comprehends structures from the cerebrum and diencephalon that are associated with emotions.
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- 12.5: Cranial Nerves
- The Peripheral Nervous System include nerves and ganglia. Nerves are organized into structures by layers of connective tissue that cover them. The epineurium covers the nerve, the perineurium covers the fascicles and the endoneurium covers the individual axon. Cranial nerves originate from the brain and carry sensory, motor or mixed information. There are twelve pairs of cranial nerves. Cranial nerve ganglia can be part of the somatic sensory NS or autonomic NS.
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- 12.6: Spinal Cord and Spinal Nerves
- The spinal cord transmits sensory information from the periphery to the brain and motor information from the brain to the periphery. The spinal cord is divided into grey horns that house interneurons, autonomic neurons and somatic motor neurons as well as glial cells, and white columns that house ascending and descending tracts of axons. Spinal nerves originate from the spinal cord, carry both sensory and motor information and connect to the skin to form a map of dermatomes.