Transcript PNS
The Nervous System http://www.youtube.com/watch?v=Q4uh2r1djWw The Nervous System - General organization - The basic units- the cells - Neurophysiology - Neural interactions Brain, Spinal cord, Neuronal pathways, Special senses The Human Nervous System The Central Nervous System (CNS) The Peripheral Nervous System (PNS) The Nervous System Monitors changes Processes and interprets Causes a response PNS CNS Central Nervous system sensory Peripheral Nervous system Sensory (Afferent) motor Motor (Efferent) Somatic (skin, skeletal muscle and joints) Visceral (internal organs) Somatic Autonomic Skeletal muscles Smooth and cardiac muscles; Glands Neurons “The Mysterious Butterflies of the Soul” Santiago Ramón y Cajal (1852-1934) “As the entomologist chasing butterflies of bright colors, my attention was seeking in the garden of gray matter, those cells of delicate and elegant forms, the mysterious butterflies of the soul, whose fluttering wings would someday—who knows?— enlighten the secret of mental life” Neurons “The Mysterious Butterflies of the Soul” Santiago Ramón y Cajal Nobel prize in physiology and medicine 1906 The neuron Dendrites Cell body Axon Nissl bodies Telodendria Most of our wiring is insulated Myelin sheath Myelin sheath • Whitish, fatty (protein-lipoid), segmented sheath around most long (NOT ALL) axons • It functions to: - Protect the axon - Electrically insulate fibers from one another - Increase the speed of nerve impulse transmission Myelin sheath • Formed by Schwann cells in the PNS • A Schwann cell: - Envelopes an axon in a trough - Has concentric layers of membrane that make up the myelin sheath Axons are bundled together to form fascicles CNS: axon bundles form tracts PNS: axon bundles form nerves Neurons are not alone Neurons are Not Alone: The supporting neuroglia CNS Astrocytes - Support and brace neurons - Anchor neurons to their nutrient supplies - Guide migration of young neurons - Control the chemical environment Microglia The “Immune System” of the CNS - Small, ovoid cells with spiny processes - Turn into phagocytes upon inflammation (monitor the health of neurons, in the absence of macrophages, due to the BBB) Ependymal cells - Ciliated epithelial cells lining the central cavities of the brain and spinal column - Forming a permeable barrier between the CSF and nervous tissue - Beating cilia helps circulating the CSF CSF (cerebrospinal fluid) -Beating cilia helps circulating the CSF A B Banizs et al. Development (2005) What could happen in B? Neurons are Not Alone: The supporting neuroglia CNS Oligodendrocytes - Insulators of the thick neurons of the CNS - A single oligodendrocyte can form myelin sheaths around several axons The supporting neuroglia in the CNS The supporting neuroglia in the PNS - Schwann cells surround and insulate axons (the “oligodendrocytes” of the PNS) - Satellite cells Support an nourish cell bodies (“astrocytes” of the PNS) Summary Central Nervous system sensory Peripheral Nervous system Sensory (Afferent) motor Motor (Efferent) Somatic (skin, skeletal muscle and joints) Visceral (internal organs) Somatic Autonomic Skeletal muscles Smooth and cardiac muscles; Glands Summary Not all neurons look like that outside+ Neurophysiology inside + + + ++ + - - -- - - - Opposite electrical charges attract each other In case negative and positive charges are separated from each other, their coming together liberates energy Thus, separated opposing electrical charges carry a potential energy Neurophysiology • Voltage (V) measure of differences in electrical potential energy generated by separated charges • Current (I) the flow of electrical charge between two points ++ + ++ + • Resistance (R) + outside hindrance to charge flow inside - - -- - - - Ohm’s law + + + + + + + + + + Current: ions - - - - - - outside inside Voltage: potential across the membrane Resistance: membrane permeability + + + + + + + + + + - - - - - - Resistance: membrane permeability outside inside How can ions move across the membrane?