Chapter 10 central nervous system, spinal nerves, and cranial nerves
Nervous System Cells. The Nervous System The Nervous system is responsible for communication...
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Transcript of Nervous System Cells. The Nervous System The Nervous system is responsible for communication...
Nervous System Cells
The Nervous System
• The Nervous system is responsible for communication
• Composed of the:• Brain • Spinal Cord • Nerves
Organization of the Nervous System • Central Nervous System
(CNS) • Brain • Spinal Cord
• Peripheral Nervous System (PNS)• Cranial Nerves • Spinal Nerves
Afferent and Efferent Divisions
• Afferent Division – consists of all of the incoming sensory pathways
• Efferent Division – Consists of all of the outgoing motor pathways
Somatic and Autonomic Divisions
• Somatic Nervous System (SNS) • Somatic Motor Division – carries
information to the somatic effectors (skeletal muscles)
• Somatic Sensory Division – carries feedback information to somatic integration centers in the CNS
Autonomic Nervous System (ANS)
• Efferent division of the ANS carries info to the autonomic or visceral effectors (smooth and cardiac muscle)• Sympathetic division – “fight-or-flight” response• Parasympathetic division – “rest-and-repair”
division
• Visceral Sensory division carries feedback info to autonomic integrating centers of the CNS
Cells of the Nervous System
• Neurons – excitable cells that conduct the impulses that make possible all nervous system functions
• Glia – (glial cells) support the function of neurons in various ways
Glia (Neuroglia)
• 900 billion in the human nervous system
• Retain their capacity for division (makes them susceptible to cancer)
Astrocytes
• Found only in the CNS
• Largest and most numerous
• Feed the neurons
• “Blood-brain barrier”
Microglia
• Small, stationary cells found in the CNS
• In inflamed tissue they enlarge and move about in order to carry out phagocytosis of microorganisms and cellular debris
Ependymal Cells
• Resemble epithelial cells
• Form thin sheets that line the fluid cavities of the brain
• Some secrete the fluid
• Cilia to circulate fluid
Oligodendrocytes
• Cell with few branches
• Help hold nerve fibers together
• Produce the fatty myelin sheath around nerve fibers in the CNS
Schwann Cells
• Found only in the PNS
• Functional equivalent of oligodendrocytes
• Wrap around nerve fiber
Nodes of Ranvier
• Short space in the myelin sheath between adjacent Schwann cells
Multiple Sclerosis
Neurons
• The human brain contains about 100 billion neurons
• All neruons consist of a cell body and at least two processes–an axon and a dendrite
Structural Classification of Neurons• Multipolar – have only one axon but several
dendrites
• Bipolar – have only one axon and only one highly branched dendrite
• Unipolar – have only a single process extending from the cell body
Structural Classification
Functional Classification
• Neurons can be classified according to the direction in which they conduct impulses• Afferent neurons – transmit to the spinal cord
or brain• Efferent neurons – transmit away from the
brain or spinal cord• Interneurons – conduct impulses toward motor
neurons (entirely within the CNS)
Reflex Arc
Nerves and Tracts
• Nerves are bundles of peripheral nerve fibers held together by several layers of connective tissue • Endoneurium – surrounds each nerve fiber• Perineurium – surrounds each fascicle • Epineurium – surround the nerve
• In the CNS bundles of nerve fibers are called tracts
Nerve Structure