nervous system introduction biology 2121 chapter 11
TRANSCRIPT
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Nervous System Introduction
Biology 2121Chapter 11
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Nervous System Overview • Sensory input
– Environmental stimulus
– PNS to CNS – Afferent NS
• Integration– Processing of
information
• Motor output– CNS via PNS to the:
– Effector organs
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Divisions of the Nervous SystemDivisions of the Nervous System
1. Central Nervous System (CNS)• Brain and Spinal Cord
2. Peripheral Nervous System (PNS)–Cranial and Spinal Nerves
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Neurons of the CNS and PNSNeurons of the CNS and PNS
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Heart and Soul of the Nervous System – The Neuron
• 1. Cell Body– Organelles
• Nissl Bodies • Golgi • Pigment inclusions
• 2. Processes – Dendrites – Axons
• 3. Axon Terminals – Secretory Region
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Neuron
• 4. Axon Hillock
• 5. Axon – Mylenated or
unmylenated – Axon Terminals – NT – Motor neurons (3-4 feet)
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Myelination Myelination
Myelination:
• Increases the transmission speeds of neurons
• PNS nerves that serve voluntary organs (example skeletal muscles) have more myelination
• Nerves that serve visceral organs (involuntary or smooth muscle organs) have less myelination.
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Characteristics of Nerve CellsCharacteristics of Nerve Cells• 1. Long lifespan
• 2. Amitotic
• 3. High Metabolic Rate
• 4. Large and Complex
• 5. Excitable Neurons– Muscle and nerve cells
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Neuroglia Cells Neuroglia Cells
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1. Resting or polarized membranes – (-70 mV) membrane potential
2. Changes occur: • Membranes are stimulated • Ion movement into and out of cells
How Nerve Impulses Are Produced How Nerve Impulses Are Produced
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Types of Channels Types of Channels
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1. Sodium moves in -------- depolarization (0 to +30mV). • Leads to an action potential
(AP)
2. Potassium gates slowly open as sodium gates close quickly. • Leads to Hyper-polarization
3. Potassium gates close. • Repolarization
Depolarization Depolarization
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Not All Membranes Produce AP’s Not All Membranes Produce AP’s
Graded Potentials
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• The conduction velocity of a neuron depends on the following factors:
1. Axon Diameter• Greater the diameter, faster the conduction speed
2. Degree of Myelination • Greater the mylenation, faster the conduction speed
Conduction Velocities Conduction Velocities
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Node of Ranvier Node of Ranvier