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Chapter 12, 13
Nervous Tissue, Spinal Cord
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Divisions of NS1. CNS-central nervous system
A. Brain
B. Spinal Cord
2. PNS-peripheral nervous system- primarily nerves of body
A. Spinal nerves- 31 pairs
B. Cranial nerves- 12 pairs
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Divisions of PNS
a. Somatic- controls skeletal muscle, skin
b. Autonomic-controls smooth, cardiac muscle
1. Sympathetic- fight/flight, emergencies
2. Parasympathetic-relaxation, “vegetative”
reflexes
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3 Basic Functions
1. Sensory (afferent)
Receptors send impulses to CNS
2. Motor (efferent)
CNS sends impulses to effectors (muscles or glands)
3. Integrated Functions- intelligence, creativity, personality, etc.
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Organelles in a neuron
1. Nucleus
2. Granular ER(Nissl bodies)
3. Mitochondria
4. Neurofibrils(microtubules)
5. No centrioles
-
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Classification of Neurons
• P365
1. Anaxonic- located in brain, special sense organs
2. Bipolar-special sense organs
3. Unipolar-sensory neurons of PNS
4. Multipolar- most common
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Neuroglia
2. Neuroglia in PNS
A. Satellite Cells- similar to astrocytes
B. Schwann Cells- similar to oligodenedrocytes, produce myelin sheath in PNS
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Neuroglia
1.Neuroglia in CNS A. Astrocyte- function in creating blood-brain barrier, provide structureB. Oligodendocyte- produce myelin sheathC. Microglia- immune cells of CNS, similar to macrophagesD. Ependymal- found in ventricles of brain, produce cerebrospinal fluid
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Synapse
• A specialized site where neurons communicate with one another
• http://faculty.washington.edu/chudler/synapse.html
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Myelin
• Acts like electrical insulation• Nodes of ranvier-gaps between schwann
cells on axon; allows nerve impulse to jump between nodes; leads to high conduction speeds= 100m/s
• Locations-A. All motor neuronsB. All spinal nervesC. 99% of brain
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Unmyelinated
• Slow conductions speed, .5 m/s
• Located
A. In autonomic nervous system
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Spinal Cord- Chapter 13• Length= 18”, width=.5”• Extends from
base(foramen magnum) of skull to 2nd lumbar vertebra
• “carrot shaped”• Ends @ conus
medullaris- many nerves exit and form cauda equina
• 2 enlargements=cervical and lumbar- where more nerves enter and leave the cord
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# of spinal nerves-31
• Cervical- 8
• Thoracic-12
• Lumbar-6
• Sacral-5
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Organization
1. White matter- myelinated sections on outermost parts
• can be ascending- going to brain
-carry sensory info
-called afferent
• Can be descending- coming from brain - carry motor info
- called efferent
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• Root- where nerve enters or exits cord
dorsal root=sensory/afferent
ventral root= motor/efferent
** In back door out front door**
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Organization
1. Gray matter- unmyelinated sections forming H pattern in the interior
• posterior horns- contain afferent neurons
• anterior horns- contain efferent neurons
• “cross bar”=commissure
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Plexuses
• Plexus- interwoven network of nerves
1. Cervical plexus
2. Brachial plexus
3. Lumbar plexus
4. Sacral plexus
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Reflexes• Rapid automatic response to a specific
stimuli
• Work through a reflex arc- a simple neural
pathway
1. reception
2. transmission via sensory neuron
3. integration
4. transmission via motor neuron
5. response
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Classifying Reflexes p 424
1. By response
A. Somatic reflex- involves skin, skeletal muscle, function in protection
B. Visceral reflex- involves cardiac, smooth muscle, glands, bl.v, function in homeostasis
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2. By development
A. Innate- w/drwal fr. pain, suckling, tracking objects w/ eye
B. Acquired- driving, sports
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3. By processing siteA. Spinal- patellar reflexB. Cranial- sudden noise, bright light,
respiration
4.Complexity of circuitA. Monosynaptic-B. Polysynaptic
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