Chapter 3 Anatomy of the Nervous System Systems structures and cells that make up your nervous system 1 General lay out of the nervous system A Divisions of the nervous system i Central nervous system CNS is the division of the nervous system located with the skull as the brain and spine as the spinal column ii Peripheral nervous system PNS is the division located outside the scull and spine 1 Somatic nervous system SNS is the part that interacts with the external environment a Composed of afferent nerves that carry sensory signals from the skin skeletal muscles joints eyes ears etc to the central nervous system and efferent nerves that carry motor signals from the central nervous system to the skeletal muscles 2 Autonomic nervous system ANS as the part of the pretzel nervous system regulates the body s internal environment with afferent nerves carrying sensory signals from internal organs to the CNS and efferent nerves carry motor signals from the CNS to internal organs a Two kinds of efferent nerves as sympathetic automatic motor nerves that project from the CNS into the lumbar small of the back and thoracic chest area regions of the spinal cord and parasympathetic autonomic motor nerves that project from the brain and sacral lower back region of the spinal cord b Sympathetic nerves stimulate organize mobilize energy resources and threatening situations and parasympathetic nerves asked to conserve energy c Each autonomic target organ receives opposing sympathetic and parasympathetic input activity controlled by relative levels of each d Sympathetic changes are indicative of psychological arousal where is parasympathetic changes are indicative of psychological relaxation 3 Most peripheral nerves project from spinal cord but there are 12 pairs of cranial nerves which are exceptions and project from the brain a Some are purely sensory nerves but most contain both sensory and motor fibers b Longest is the vagus nerve 10 leading to heart lungs and other internal organs in the thoracic cavity B Meninges Ventricles and Cerebrospinal Fluid i The brain and spinal cord CNS are the most protecting organs in the body encased in three protective membranes meninges 1 The outer meninx is the dura mater tough mother followed by the fine arachnoid membrane spider web like membrane then a space called the subarachnoid space which contains many large blood vessels and cerebrospinal fluid then the innermost meninx as the delicate pia mater pious mother which it hears to the surface of the CNS 2 Cerebrospinal fluid CSF fills the subarachnoid space the central canal the spinal cord and the cerebral ventricles of the brain and cushions the brain thought to be produced by the choriod plexuses networks of capillaries that protrude into the ventricles from the pia mater a Access cerebrospinal fluid is absorbed into dural sinuses running through the dura mater to drain into the large jugular veins of the neck i Hydrocephalus Water buildup of fluid in the venture goals causes the entire brain to expand and is treated by dreaming this fluid and removing any obstructions b Central canal is this small central channel that runs the length of the spinal cord c Cerebral ventricles are the four large internal chambers of the brain C Blood brain barrier i The blood brain barrier is a mechanism that stops the passage many toxic substances from the blood into the brain in rest of body cells the compose walls of blood vessels are loosely packed but in brain the blood vessel walls are tightly packed forming a barrier are too many molecules like proteins large molecules 1 Large molecules critical to mumble brain function like glucose are actively transported through cerebral blood vessel walls ii Therapeutic recreational drugs influence brain activity depending on ease of penetration here 2 Cells of the nervous system A Anatomy of Neurons i Neurons are cells specialized for the reception conduction transmission of electrochemical signals and come in a variety of shapes and sizes 1 Cell membrane is a lipid bilayer with numerous embedded protein molecules including channel proteins through which certain molecules pass and signal proteins which transfer signals to the inside of the neuron when particular molecules bind to them on the outside of membrane 2 Multipolar neuron more than two processes extending from the cell body most multipolar 3 Unipolar neuron one process extending from its cell body 4 Bipolar neuron two processes extending from it s cell body 5 Interneurons short axis or no axis with a function to integrate the neural activity within a single brain structure not to conduct signals from one structure to another ii In the central nervous system clusters of cell bodies are called nuclei and in the peripheral nervous system they are called ganglia 1 In the CMS bundles of axons or call tracks and in the PNS they are called nerves B Glia the forgotten cells previously thought to provide support for neurons providing nutrients clearing waste forming physical matrix to hold neural circuits together but now shown to exchange chemical signals with neurons and other interneurons to control the establishment maintenance of synapses between neurons modulate nueral activity and to control the blood brain barrier i Oligodendrocytes are glial cells with extensions that wrap around the axons of some neurons of the central nervous system 1 extensions rich in myelin a fatty insulating substance and the mileage sheets they form increase the speed of efficacy of exile conduction often than more than one axon ii Schwann cells a second class of glia each constitute one myelin segment but more importantly can guide axonal regeneration regrowth after damage iii Microglia is a third class of the glia Smaller than the others but responds to injury or disease by multiplying engulfing cellular debris and triggering inflammatory responses iv Astrocytes are the largest glial cells and are star shaped 1 associated with the passage of chemicals from the blood into the CNS 3 Neuro anatomical techniques and directions A Neuroanatomical techniques i Key to studying their anatomy lies in preparing neural tissue in a variety of ways to permit clear viewing of different aspects of structure ii Golgi stain exposes tissue to potassium dichromate and silver nitrate Staining each invaded knurled entirely black offsets overall shape of neuron iii Nissl stain dying of cresyl violet penetrate cells but finds only two structures in neural cell