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+ HUMAN BRAIN= 100 BILLION NEURONS SPINAL CORD = 13.5 MILLION NEURONS HUMAN BRAIN = 1 TO 10 TERABYTES OF INFORMATION STORED 1 TERABYTE= 1024 GIGABYTES 1 GIGABYTE = 1024 MEGABYTES SO……. 1 TERABYTE = 1,048,576 MEGABYTES Organization of the Nervous System and the Neuron Organization of the Nervous System The Nervous System “maintains body homeostasis with electrical signals; provides for sensation, higher mental functioning, and emotional response; and activates muscles and glands.” 3 Overlapping Functions of Nervous System SENSORY INPUT- INTEGRATION- MOTOR INPUT- Works with the Endocrine System to maintain homeostasis. 1.Nervous System2.Endocrine System- Organization of the nervous system can be based on: 1. Structural ClassificationA. CNSB. PNS2.Functional ClassificationA. AfferentB. Efferent- STRUCTURAL CLASSIFICATION FUNCTIONAL CLASSIFICATION Nervous Tissue Nervous tissue is made up of two types of cellsSupporting and Neurons Supporting cells of the CNS are called Neuroglia or “nerve glue”. Neuroglia includes many types of cells that generally support, insulate, and protect neurons. Types of Neuroglial cells•Astrocytes- •Microglia•Ependymal cells•Oligodendrocytes- What about “gliomas”??? Supporting Cells of the Peripheral Nervous System •Satellite cells•Schwann cellsMyelin Neurilemma is found covering the neuronsof the Peripheral Nervous System and helps regenerate damaged nerve fibers Which brings us to bundles of nerve fibers•Tracts•Nerves- And gray matter vs. white matter- THE NEURON THE NEURON •Nerve fibers may be microscopic •May extend 3 to 4 feet •Neurons never touch each other •Axonal terminals release neurotransmitters into the synapse Neurons classified according to structure and function 1. FunctionalSensory or AfferentMotor or EfferentAssociative or Interneurons- 2. Structural- based on # of processes extending from cell body Physiology of Neurons Neurons have two major functions 1.Irritability- 2. Conductivity- Irritabililty- the short version •Resting or inactive neuron is polarized •A stimulus excites the neuron to become and generate an impulse active •The stimulus changes the permeability of the neuron’s membrane • Sodium gates open and Na diffuses into the cell •Neuron is now depolarized • Depolarization activates the neuron to transmit an action potential or nerve impulse Depolarization is followed almost immediately by repolarization Until the neuron repolarizes it cannot conduct another impulse= absolute refractory period There also exists a relative refractory period when a stronger than usual stimulus is required The Action Potential GENERATION OF AN ACTION POTENTIAL Alcohol, sedatives, anesthetics- Cold and continuous pressureWarm or remove pressure- Conductivity No contact between neurons except at electrical synapses (escape reflexes, retina, heart) Axonal terminals release neurotransmitters which cause depolarization of next neuron Neurotransmitter is removed from synapse by reuptake at axonal terminal or enzymatic breakdown YouTube - Neurotransmitter Synapse 3D Animation Peripheral Nervous System • Those nerves found outside the central nervous system • Each nerve is made of bundles of neuron fibers • Neuron fibers are surrounded by a delicate tissue sheath • Groups of fibers are bound by coarser connective tissue wrapping to form bundles called fascicles CRANIAL NERVES • • • • SPINAL NERVES • • • • Spinal Nerves DISORDERS AFFECTING NEURONS POLIOMYELITIS MULTIPLE SCLEROSISBELL’S PALSYSHINGLES- And then there’s… CARPAL TUNNEL SYNDROME- http://www.youtube.com/watch?v=SGyKQch SEJ4&feature=related