Nervous System Introduction

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Nervous System Introduction

• Biology 2121
• Chapter 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 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 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

• Myelinated fibers
• Unmyelinated fibers
• Schwann Cells

• 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 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
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How Nerve Impulses Are Produced

• Resting or polarized membranes (-70 mV)
  membrane potential
• 2. Changes occur
• Membranes are stimulated
• Ion movement into and out of cells

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Types of Channels
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Depolarization

• 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

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Not All Membranes Produce APs
(1). A short-lived change in the membrane
potential. (2). Occurs in all membranes (3).
Strength depends on stimulus strength (4). Lose
magnitude with distance (5). Occurs in
dendrites
Graded Potentials
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Conduction Velocities

• The conduction velocity of a neuron depends on
  the following factors
• Axon Diameter
• Greater the diameter, faster the conduction speed
  
• Degree of Myelination
• Greater the mylenation, faster the conduction
  speed

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Nodes of Ranvier