Chapter 12: Neural Tissue

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Chapter 12 Neural Tissue
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The Nervous System

• One of 2 systems maintaining homeostasis
• Includes all neural tissue in the body
• 3 Basic functions
• Sensory function
• Integrative function
• Motor function

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Neural Tissue

• Contains 2 kinds of cells
• neurons
• cells that send and receive signals
• neuroglia (glial cells)
• cells that support and protect neurons

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Organs of the Nervous System

• Brain and spinal cord
• Sensory receptors of sense organs (eyes, ears,
  etc.)
• Nerves connect nervous system with other systems

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What are the anatomical of the nervous system?
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• Central nervous system (CNS)
• Consists of the spinal cord and brain
• Peripheral nervous system (PNS)
• Includes all neural tissue outside the CNS

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Functions of the CNS

• Are to process and coordinate
• sensory data
• motor commands
• higher functions of brain

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Functions of the PNS

• Deliver sensory information to the CNS
• Carry motor commands to peripheral tissues and
  systems

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Nerves

• Also called peripheral nerves
• bundles of axons with connective tissues and
  blood vessels
• carry sensory information and motor commands in
  PNS
• cranial nerves connect to brain
• spinal nerves attach to spinal cord

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Functional Divisions of the PNS

• Afferent division
• carries sensory information
• from PNS sensory receptors to CNS
• Receptors
• Efferent division
• carries motor commands
• from CNS to PNS muscles and glands
• Effectors

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Components of Efferent Division

• Somatic nervous system (SNS)
• Controls skeletal muscle contractions
• Autonomic nervous system (ANS)
• Controls subconscious actions

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Divisions of the ANS

• Sympathetic division
• has a stimulating effect
• Parasympathetic division
• has a relaxing effect

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What is the structure of a typical neuron, and
the function of each component?
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The Structure of Neurons

• Cell body (soma)
• Large nucleus and nucleolus
• Perikaryon
• Nissl Bodies
• Lack centrioles

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• Dendrites
• Highly branched processes
• Extend from soma
• Dendritic spines
• 8090 of neuron surface area
• Receives info from other neurons

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• Axon
• Long cytoplasmic processes
• Carries action potential
• Axolemma
• myelination
• Collaterals
• Telodendria

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Figure 121
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Synapse

• Area where a neuron communicates with another
  cell
• Presynaptic cell
• neuron that sends message
• Synaptic Cleft
• Postsynaptic cell
• cell that receives message

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• Synaptic Knob
• expanded area of axon
• Contains synaptic vesicles of neurotransmitters
• chemical messengers
• Types of Synapses
• Neuromuscular junction
• Neuroglandular junction

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Figure 122
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How are neurons classified by structure and
function?
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4 Structural Classifications of Neurons

• Anaxonic neurons
• Bipolar neurons
• Unipolar neurons
• Multipolar neurons

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Anaxonic Neurons

• All cell processes look alike
• brain and sense organs

Figure 123 (1 of 4)
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Bipolar Neurons

• 1 dendrite, 1 axon
• special sensory organs

Figure 123 (2 of 4)
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Unipolar Neurons

• Fused dendrites and axon
• Cell body to 1 side
• sensory neurons of PNS

Figure 123 (3 of 4)
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Multipolar Neurons

• Multiple dendrites, 1 axon
• common in the CNS
• motor neurons

Figure 123 (4 of 4)
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3 Functional Classifications of Neurons

• Sensory neurons
• afferent neurons of PNS
• Motor neurons
• efferent neurons of PNS
• Interneurons
• association neurons

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3 Types of Sensory Receptors

• Interoceptors
• monitor internal systems and senses
• Exteroceptors
• external senses
• Proprioceptors
• monitor position and movement

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What are the locations and functions of
neuroglia?
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Neuroglia

• Cells that nurture and support neurons
• Half the volume of the nervous system
• Many types of neuroglia in CNS and PNS
• Abundant and diverse

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4 Types of Neuroglia in the CNS

• Ependymal cells
• Line central canal of spinal cord and ventricles
  of brain
• Secrete cerebrospinal fluid (CSF)
• Astrocytes
• Maintain blood-brain barrier
• Maintain structural framework for CNS
• Stabilize damaged neural tissue
• Guide neuron development

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• Oligodendrocytes
• Wrap around axons to form myelin sheaths
• Myelination insulates axons
• Increases speed of action potentials
• Internodes and Nodes
• Microglia
• Clean up cellular debris, waste products, and
  pathogens

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Neuroglia of the Central Nervous System
Figure 124
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Ganglia

• Masses of neuron cell bodies in the PNS
• Surrounded by neuroglia

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Neuroglia of the Peripheral Nervous System

• Satellite cells (amphicytes)
• Insulate soma
• Schwann cells (neurilemmacytes)
• Form myelin sheath (neurilemma) around peripheral
  axons

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Schwann Cells
Figure 125a
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Schwann Cells
Figure 125b
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• Neurons perform all communication, information
  processing, and control functions of the nervous
  system
• Neuroglia preserve physical and biochemical
  structure of neural tissue, and are essential to
  survival and function of neurons