Chapter 7 Part 1

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Janelle Leboutillier

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The Structure of the Nervous System o Nervous system sees, hears, feels, moves, remembers, and dreams o Human brain is extremely complicated. However, our brain is merely a variation on a plan that is common to the brains of all mammals.  The human brain appears complicated because it is distorted as a result of the selective growth of some parts within the confines of the skull o The nervous system of all mammals has two divisions: 1. The Central Nervous System (CNS) 2. The Peripheral Nervous System (PNS) o Anatomical references describe the location in the brain and points of references in the human o Rat is used to describe brain anatomical references since it is a simplified version that has all the general features of mammalian nervous system organization  Pointing to the rats nose is known as the anterior or rostral - toward the nose  Pointing to the rats tail is known as the posterior or caudal - toward the tail  The direction pointing up is referred to as dorsal - toward the back  The direction pointing down is referred to as ventral – toward the belly  The spinal cord runs anterior to posterior  The top side of the spinal cord is the dorsal side  The bottom side of the spinal cord is the ventral side o When we look down on the nervous system, it may be divided into two equal halves. The right side of the brain of the brain and the spinal cord is the mirror image of the left side which is known as bilateral symmetry  With a few exceptions, most structures come in pairs one of the right side of the brain and one on the left side of the brain  The invisible line running down the middle of the nervous system is called the midline  Gives us another way to describe anatomical references  Structures closed to the midline of the brain are medial  Structures that are away from the midline are lateral  The nose of a rat is medial to the eyes  In additional, two structures that are on the same side of midline are said to be ipsilateral, example: the right ear is ipsilateral to the right eye  Structures that are on the opposide sides of the midline are said to be contralateral, example: the right ear is contralateral to the left ear o To view the internal structure of the brain, it is usually necessary to slice it up.  A slice is called a section – to slice is to section o The standard approach is to make cuts parallel to one of the three anatomical planes of section 1. The plane of section resulting from splitting the brain into equal right and left halves is called the “midsagittal plane”  Sections that are parallel to this plane are in the sagittal plane 2. The horizontal plane is parallel to the ground.  Single section in this plane could pass through both the eyes and the ears. Thus this plane splits into a dorsal and ventral part 3. The coronal plane is perpendicular to the ground and to the sagittal plane  Single section in this plane could pass through both eyes or both ears, but not through all four at the same time  Thus splits brain into anterior and posterior parts o The Central Nervous System (CNS) consists of the parts of the nervous system that are encased in bone: the brain and the spinal cord. The side view of a rat’s brain reveals three parts that are common to all mammals: a. Cerebrum – rostral-most and largest part of the brain  Can be split into two cerebral hemispheres which is separated by the deep sagittal fissure  The cerebrum works contralaterally – the right cerebral hemisphere receives sensations from, and controls movements of, the left side of the body b. Cerebellum – lying behind the cerebrum; little brain  Contains as many neurons as both cerebral hemispheres combined  Primarily a movement control center that has extensive connections with the cerebrum and the spinal cord  The cerebellum works ipsilaterally – the left side of the cerebellum is concerned with movements of the left side of the body, and the right side is concerned with the right c. Brain stem – forms the stalk from which the cerebral hemispheres and the cerebellum sprout  Brain stem is a complex nexus of fibers and cells that in part serves to relay information from the cerebrum to the spinal cord and cerebellum, and vice versa  It is also a site where vital functions are regulated, such as breathing, consciousness, and the control of body temperature  It is considered a primitive part, but even so it is the most important to life  One can survive damage to both the cerebrum and cerebellum, but damage to the brain stem usually means rapid death d. Spinal cord – encased in the bony vertebral column and is attached to the brain stem, major conduit of information from the skin, joints, and muscles of the body to the brain, and vice versa.  A transection of the spinal cord results in anesthesia (lack of feeling) in the skin and paralysis of the muscles in parts of the body caudal to the cut  Spinal cord communicates with the body via the spinal nerves which are a part of the PNS  Spinal nerves exit the spinal cord through notches between each vertebra of the vertebral column. Each spinal nerve attaches to the spinal cord by means of two branches, the dorsal root and the ventral root  Magendie showed that the dorsal root contains axons bringing information into the spinal cord; example: entry of thumbtack into foot  Bell showed that ventral root contains axons carrying information away from the spinal cord; example: muscle jolt when thumbtack enters foot o All the parts of the nervous system other than the brain and spinal cord comprise the Peripheral Nervous System (PNS)
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