The Nervous System Anatomy and Physiology Nervous System Functions 1. Sensory-receptors gather...
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![Page 1: The Nervous System Anatomy and Physiology Nervous System Functions 1. Sensory-receptors gather information and pass it on toward the CNS 2. Integrative-in.](https://reader035.fdocuments.us/reader035/viewer/2022070401/56649f205503460f94c38a18/html5/thumbnails/1.jpg)
The Nervous System
Anatomy and Physiology
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Nervous System Functions
• 1. Sensory-receptors gather information and pass it on toward the CNS
• 2. Integrative-in the spinal cord or brain, we put information together and make sense of it
• 3. Motor-carry impulses to effectors such as muscles and glands
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Basic Structures
• Central nervous system (CNS) consists of brain and spinal cord only
• Peripheral nervous system (PNS) are nerves outside the CNS
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Basic Structures
• Neurons are the nerve cells that can transmit the electrical impulse
• Neurons are surrounded by support cells called neuroglial cells
• There are 5 types of neuroglial cells
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Neuron Structure
• Cell body with nucleus
• Dendrites: branching fibers that RECEIVE impulses
• Axon: long fiber that SENDS the impulse on
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Neuron Structure
• Axon is often wrapped in cells called Schwann cells
• A Schwann cell has its own nucleus and is made of myelin
• Nodes of Ranvier are the spaces between Schwann cells
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Types of Neurons
• Sensory neurons carry information from sensory receptors to the CNS (AFFERANT)
• Interneurons relay impulses within the CNS
• Motor neurons carry impulses from CNS to effectors ( EFFERENT)
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Types of Neurons
• Bipolar: only two fibers—one dendrite and one axon
• Unipolar: single fiber from the cell body which splits into dendrite and axon
• Multipolar: many dendrites; one axon
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Identify which neuron is unipolar, bipolar, and multipolar.
Identify which is the sensory neuron, the interneuron, and the motor neuron
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The Nerve Impulse• The membrane of
a resting neuron is POLARIZED
• This means that there is a different electrical charge on the outside of the membrane as compared to the inside
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Resting Potential
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Resting Potential• More positive ions outside than inside• Result of actively pumping out sodium ions (Na+)• Potassium ions are also involved (K+)• Three Na+ ions are pumped out for every two K+ ions
pumped in.
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Becoming Polarized
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Sodium Potassium Pump
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Resting Potential• More positive outside the membrane than inside
(POLARIZED)
• This charge difference is called a potential difference
• Holds potential energy which can be released in the form of an electrical impulse
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Action Potential
• When stimulated, the membrane of the neuron opens the channels and lets the Na+ rush inside
• This is DEPOLARIZATION
• This releases the potential energy in the form of a current down the neuron membrane
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Like a Wave
Depolarization of one section stimulates the next section of membrane
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Action Potential
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Back to Resting Potential
After the wave, or current, of depolarization has passed, ions are restored to resting potential
This means Na+ are again pumped out, setting up a more positive charge outside the neuron
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Odds and Ends
• Threshold must be reached to trigger depolarization
• Each nerve fiber has an ALL OR NONE RESPONSE
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Reflex Arc
• Minimum of three neurons
• Sensory to inter to motor neuron
• Fastest responses go only to the spinal cord, not all the way to the brain
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Reflex Arc
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Reflex Arc
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Reaction Time
• Is the time between stimulation and the beginning of the response
• Sensory neuron to interneurons in brain, then motor neuron
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Reaction Time
• Can get shorter, as we practice
• Use the same pathway over and over
• Learned behavior
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Bell Ringer
• Which nerve would be faster at transmitting an impulse: 2 mm in diameter, or 4.5 mm in diameter
• Which neuron would be faster at transmitting an impulse: one with Schwann Cells, or a bare axon with no Schwann cells
• How is multiple sclerosis related to Schwann cells?