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Nervous System Controls all other organ systems and is important for maintaining balance within those systems The nervous system is an organ system in charge of sending messages to and from the brain and spinal cord to and from all parts of the body. The ability of cells to respond to the environme...

Nervous System Controls all other organ systems and is important for maintaining balance within those systems The nervous system is an organ system in charge of sending messages to and from the brain and spinal cord to and from all parts of the body. The ability of cells to respond to the environment has evolved over billions of years Nervous systems show diverse patterns of organization  Nerve nets.  With cephalization come more complex nervous systems.  Basic division of the Nervous System  Central nervous system (“CNS”) – occupies cranium and vertebral column  Brain  Spinal cord  Peripheral nervous system (“PNS”)  Cranial nerves  Spinal nerves  Nervous tissue: 2 types of cells 1. Neurons  Excitable nerve cells  Transmit electrical signals 2. Supporting cells: neuroglia or just glia  Means “nerve glue”  29-7 CNS: Brain  Four sections  Cerebrum (cerebral hemisphere)  Diencephalons  Brain stem  Cerebellum  Cerebrum ‫المخ‬  Largest section  Composed of regions for  motor movement  sensations  auditory  vision  PNS neuroglia  Schwann cells: surround all axons of neurons in the PNS and creates myelin sheath around most axons of PNS  Satellite cells: Surround neuron cell body  Myelin  Lipoprotein  Increases speed of conduction, large axons  Are “insulation”  Prevent leakage of electric current  Layers with spaces (nodes of Ranvier) between cells  Impulse “jumps” from node to node  “Unmyelinated” axons – smaller, slower Myelin in the Peripheral and Central Nervous Systems In multiple sclerosis (MS), patches of myelin are destroyed in the brain and spinal cord  Gray and White Matter of the CNS  Gray matter: gray-colored  Where neuron cell bodies are clustered  White matter: white-colored  Where millions of axons are running between different part of CNS, in bundles of “tracts”  Remember, tracts are in CNS, vs nerves in PNS  White is from the myelin sheaths  Neuron Structure Cell body: with nucleus and cytoplasm. Cell bodies are in clusters CNS: clusters called nuclei PNS: clusters are called ganglia Dendrites (are outside the CNS) Dendrites – short Receive nerve impulses for the neuron Axons – long Schwann cells Send nerve impulses away from the cell body Axon Structure of Neuron Structural classification based on number of processes coming off of the cell body:  Neurons, continued  Can live for a lifetime (i.e. over 100 years)  Do not divide  (exception: recent neural stem cells identified)  Cannot replace themselves  High metabolic rate  Require continuous oxygen and glucose  Die within a few minutes without oxygen  Three types of neurons (function/direction)  Afferent or sensory nerves  Sensory information from environment or inside body to CNS for interpretation  Efferent or motor nerves  Impulses from CNS to PNS to allow for movement or action  Interneruons  Interpretive neurons between afferent and efferent nerves in the CNS  Reflexes Receptor Sensory Neurons Interneurons Effectors Motor Neurons  Terminology  Input: sensory = sensory input  Receptors monitor changes  Changes called “stimuli” (sing., stimulus)  Information sent by “afferent” nerves  Integration  Information processed  Decision made about what should be done  Output: motor = motor output  Effector organs (muscles or glands) activated  Effected by “efferent” nerves Remember the difference between the English words “affect” and “effect”  Synapses  Junctions between neurons  Information is passed (usually chemically)  Unidirectional  Presynaptic (toward synapse) vs postsynaptic (away from synapse): most neurons function as both  Synaptic cleft (tiny gap) Neurons can synapse with: 1. Neurons 2. Muscle 3. Glands  simplified  Information passed between neurons by chemicals  Can be excitatory or inhibitory  Along the axons, the information passes electrically  Central Nervous System  Composed of  spinal cord  brain  Meninges –membrane protect brain and spinal cord 29-24 Spinal cord  29-26 Spinal Cord  Slender structure continuous with the brain  Descends into the vertebral canal and ends around the level of the first or second lumbar vertebrae. Function: 1- The spinal cord is to carry sensory information to and from the brain 2- Another function of the spinal cord is to participate in reflexes (unpredictable, automatic response to stimuli )  29-28 Peripheral Nervous System  Nerves that branch off the CNS  Peripheral nerves two types:  Cranial nerves  Spinal nerves Cranial Nerves  Nerves emerging directly from the brain  12 pairs Some of these nerves bring information from the sense organs to the brain; control muscles; connected to glands or internal organs such as the heart and lungs. Spinal Nerves :  Peripheral nerves originating from the spinal cord. 31 pairs of spinal nerves