The Nervous System
- General organization - The basic units- the cells - Neurophysiology - Neural interactions Brain, Spinal cord, Neuronal pathways, Special senses
The Central Nervous System (CNS) The Peripheral Nervous System (PNS) The Human Nervous System
The Nervous System Monitors changes Processes and interprets Causes a response PNSCNS
Peripheral Nervous system Central Nervous system sensorymotor Autonomic Smooth and cardiac muscles; Glands Somatic Skeletal muscles Motor (Efferent) Sensory (Afferent) Somatic (skin, skeletal muscle and joints) Visceral (internal organs)
“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” Santiago Ramón y Cajal ( ) Neurons “The Mysterious Butterflies of the Soul”
Neurons “The Mysterious Butterflies of the Soul” Santiago Ramón y Cajal Nobel prize in physiology and medicine 1906
The neuron Axon Cell body Dendrites Telodendria Nissl bodies
Most of our wiring is insulated 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 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)
Banizs et al. Development (2005) What could happen in B? B A -Beating cilia helps circulating the CSF
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 Peripheral Nervous system Central Nervous system sensorymotor Autonomic Smooth and cardiac muscles; Glands Somatic Skeletal muscles Motor (Efferent) Sensory (Afferent) Somatic (skin, skeletal muscle and joints) Visceral (internal organs)
Summary Not all neurons look like that
Neurophysiology 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 inside outside
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) hindrance to charge flow Neurophysiology inside outside
Ohm’s law
inside outside Current: ions Resistance: membrane permeability Voltage: potential across the membrane
inside outside Resistance: membrane permeability How can ions move across the membrane?