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Chapter 3

CH3 Nervous System.doc

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Paul Mallet

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PS263: Chapter 3:Anatomy of the Nervous System • Main themes in this chapter: The clinical implications: ◦ Discussions of the importance of the cranial nerves in neurological diagnosis, ◦ The role of blockage of cerebral aqueducts in hydrocephalus, and the involvement of damage to the pathway from the substantia nigra to the striatum in Parkinson’s disease. ◦ Also, the evolutionary perspective was evident when the text noted inter-species differences in cortical convolutions. • Central Nervous System(CNS): is the division of the nervous system that is located within the skull and the spine. ◦ Is composed of 2 divisions: the brain and the spinal cord. • Peripheral Nervous System(PNS): is the division that is located outside the skull and spine. ◦ Is composed of 2 divisions: ◦ Somatic Nervous System(SNS): the part if the PNS that interacts with the external environment. ▪ It is composed of Afferent nerves that carry sensory signals from the skin, skeletal muscles, joints, eyes, ears, and etc to the CNS. ▪ Also the Efferent Nerves that carry motor signals from the central nervous system to the skeletal muscles. ◦ Autonomic Nervous System(ANS): the part of the PNS that regulates the body's internal environment. ▪ It is composed of the afferent nerves carrying sensory signals from internal organs to the CNS, and the efferent nerves carrying motor signals from the CNS to the internal organs. • TheAutonomic nervous System(ANS) has two kinds of efferent nerves: ◦ Sympathetic and Parasympathetic. ▪ Sympathetic nerves are those autonomic motor nerves that project from the CNS in the lumbar and the thoracic regions of the spinal cord. ▪ Parasympathetic nerves are those autonomic motor nerves that project from the brain and sacral(lower back) region of the spinal cord. • Conventional view of the respective functions of the sympathetic and the parasympathetic systems stresses 3 important principals • 1)that sympathetic nerves stimulate, organize, and mobilize energy resources in threatening situations, whereas parasympathetic nerves act to conserve energy; • (2) that each autonomic target organ receives opposing sympathetic and parasympathetic input, and its activity is thus controlled by relative levels of sympathetic and parasympathetic activity; • (3) that sympathetic changes are indicative of psychological arousal, whereas parasympathetic changes are indicative of psychological relaxation. • Cranial Nerves: there are 12 pairs of them in the brain: ◦ Olfactory ◦ Optic ◦ Vagus (longest cranial nerve) ◦ etc.. • The brain and spinal cord are protected by 3 membranes: ◦ Three Meniniges: ▪ Dura mater: the outer meninx, is a tough membrane ▪ Arachnoid membrane: immediately inside the dura mater, it is a spider-like membrane. ▪ Subarachnoid space: beneath the arachnoid membrane in a space; it contains large blood vessels and cerebrospinal fluid. ▪ Pia mater: the innermost meninx, which adheres to the surface of the CNS • Cerebrospinal fluid: it fills the sub-arachnoid space;,the central canal of the spinal cord and the cerebral ventricles of the brain. • Central Canal : small central channel that runs the length of the spinal cord rd • Cerebral Ventriclesth4 large internal chambers of the brain; the 2 lateral ventricles, the 3 ventricle and the 4 ventricle. • Choroid plexuses networks of capillaries (small blood vessels) that protrude into the ventricles from the pia mater. The excess cerebrospinal fluid is continuously absorbed from the subarachnoid space into large blood filled spaces, or dural sinuses, which run through the dura mater and drain into the large jugular veins of the neck. • The brain is a finely tuned electrochemical organ whose function can be severely disturbed by the introduction of certain kinds of chemicals. Fortunately, there is a mechanism that impedes the passage of many toxic substances from the blood into the brain: the blood brain barrier. • Fill In the blanks: ◦ 1. The Central Nervous system is composed of the brain and the spinal cord. ◦ 2. The part of the peripheral nervous system that regulates the body s internal environment is the autonomic nervous system. ◦ 3. Nerves that carry signals away from a structure, such as the CNS, are efferent nerves. ◦ 4. TheANS nerves that project from the thoracic and lumbar regions of the spinal cord are part of the sympathetic nervous system. ◦ 5. Sympathetic nerves stimulate, organize, and mobilize energy resources in threatening situations. ◦ 6. The vagus nerves are the longest Cranial Nervous. ◦ 7. The olfactory nerves and optic nerves are the only two purely sensory Cranial Nervous. ◦ 8. The innermost meninx is the pia mater. ◦ 9. The cerebral ventricles, central canal, and subarachnoid space are filled with cerebrospinal fluid. ◦ 10. Cerebrospinal Fluid is continuously produced by the choroid plexuses. ◦ 11.Atumor near the cerebral aqueduct can produce hydrocephalus. ◦ 12. The blood brain barrier blocks the entry of many large molecules into brain tissue from the circulatory system. • Neurons: are cells that are specialized for the reception, conduction, and transmission of electrochemical signals. They come in an incredible variety of shapes and sizes ◦ Major external features: ▪ Cell membrane. The semipermeable membrane that encloses the neuron. ▪ Dendrites. The short processes emanating from the cell body, which receive most of the synaptic contacts from other neurons. ▪ Cell body. The metabolic center of the neuron; also called the soma. ▪ Axon hillock. The cone-shaped region at the junction between the axon and the cell body. ▪ Axon. The long, narrow process that projects from the cell body. ▪ Myelin. The fatty insulation around many axons. ▪ Nodes of Ranvier :The gaps between sections of myelin. ▪ Buttons. The buttonlike endings of the axon branches, which release chemicals into synapses. ▪ Synapses. The gaps between adjacent neurons across which chemical signals are transmitted. ◦ Major Internal Features ▪ Endoplasmic reticulum. Asystem of folded membranes in the cell body; rough portions (those with ribosomes) play a role in the synthesis of proteins; smooth portions (those without ribosomes) play a role in the synthesis of fats. ▪ Mitochondria. Sites of aerobic (oxygen-consuming) energy release. ▪ Nucleus. The spherical DNA-containing structure of the cell body. ▪ Cytoplasm. The clear internal fluid of the cell. ▪ Ribosomes. Internal cellular structures on which proteins are synthesized; they are located on the endoplasmic reticulum. ▪ Golgi complex. Aconnected system of membranes that packages molecules in vesicles. ▪ Microtubules. Tubules responsible for the rapid transport of material throughout neurons. ▪ Synaptic vesicles. Spherical membrane packages that store neurotransmitter molecules ready for release near synapses. ▪ Neurotransmitters. Molecules that are released from active neurons and influence the activity of other cells. • Neuron Cell membrane is composed of a lipid bilayer. • Aneuron with more than two processes extending from its cell body is classified as: ◦ Multipolar neuron; most neurons are multipolar. ◦ Aneuron with one process extending from its cell body is classified as a unipolar neuron. ◦ a neuron with two processes extending from its cell body is classified as a bipolar neuron. ◦ Neurons with a short axon or no axon at all are called interneurons; their function is to integrate the neural activity within a single brain structure, not to conduct signals from one structure to another. • In the central nervous system, clusters of cell bodies are called nuclei (singular nucleus); in the peripheral nervous system, they are called ganglia. • Glial cells do predominate in some brain structures, but overall the numbers of glial cells and neural cells are approximately equal. • There are several kinds of glial cells: ◦ Oligodendrocytes, for example, are glial cells with extensions that wrap around the axons of some neurons of the central nervous system. These extensions are rich in myelin, a fatty insulating substance, and the myelin sheaths that they form increase the speed and efficiency of axonal conduction.Asimilar function is performed in the peripheral nervous system by ◦ Schwann cells, a second class of glial cells, can guide axonal regeneration (regrowth) after damage. That is why effective axonal regeneration in the mammalian nervous system is restricted to the PNS. ◦ Microglia make up a third class of glial cells. Microglia are smaller than other glia thus their name. They respond to injury or disease by multiplying, engulfing cellular debris, and triggering inflammatory responses. ◦ Astrocytes constitute a fourth class of glial cells. They are the largest glial cells and they are so named because they are star-shaped (astron means star ). The extensions of some astrocytes cover the outer surfaces of blood vessels that course through the brain; they also make contact with neuron cell bodies. These particular astrocytes play a role in allowing the passage of some chemicals from the blood into CNS neurons and in blocking other chemicals. ◦ The greatest blessing to befall neuroscience in its e
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