unit iv nervous system histology
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Biology 220 Anatomy & Physiology. Unit IV NERVOUS SYSTEM HISTOLOGY. Chapter 11 pp. 387-396. E. Gorski/ E. Lathrop-Davis/ S. Kabrhel. Functions. Sensory – recognize changes in environment [stimuli] Integration – analysis of sensory information, storage of information, decisions - PowerPoint PPT PresentationTRANSCRIPT
Unit IVUnit IVNERVOUS SYSTEM NERVOUS SYSTEM
HISTOLOGYHISTOLOGY
Chapter 11
pp. 387-396
Biology 220Anatomy & Physiology
E. Gorski/ E. Lathrop-Davis/ S. Kabrhel
FunctionsFunctions
• Sensory – recognize changes in environment [stimuli]
• Integration – analysis of sensory information, storage of information, decisions
• Motor – initiates impulses to effectors [muscles or glands] that do work)
OrganizationOrganization
Fig. 11.2, p. 388
CellsCellsNeurons and Supporting Cells• neurons
– produce impulses to transfer information– amitotic (mostly), high metabolic rates, long-
lived• supporting cells – support, protect, nurture neurons
– neuroglia (glial cells)• astrocytes, oligodendrocytes, ependymocytes,
microglia, satellite cells, Schwann cells (neurolemmocytes)
– in CNS, tumors arise from abnormal divisions of glial cells
Supporting Cells in the CNSSupporting Cells in the CNS
• Astrocytes – connect neurons to blood supply• Microglia – phagocytic
Fig. 11.3, p. 389
Supporting Cells in the CNSSupporting Cells in the CNS• Oligodendrocytes – produce myelin sheath• Ependymal cells – epithelial lining of brain
ventricles and central canal of spinal cord– produce cerebrospinal fluid
Fig. 11.3, p. 389
Supporting Cells in PNSSupporting Cells in PNS
• Satellite cells – surround neuron cell bodies in ganglia
• Schwann cells (neurolemmocytes)– form myelin sheaths around larger nerve fibers– play role in regeneration of nerve fibers
Fig. 11.3, p. 389
Myelination (Myelination (Myelin Myelin Sheath)Sheath)• formed by oligodendrocytes (CNS), Schwann cells
(PNS)• surrounds some axons (fibers) in CNS and PNS• composed of lipids and proteins (neurolemma = cell
membrane of Schwann cell in PNS)• nodes of Ranvier = spaces between sheath cells• importance of myelin sheath:
– increase speed of impulse conduction– decrease energy required (Na+/K+ pump only
active at nodes)Multiple sclerosis – destruction of myelin sheath in
CNS diminishes impulse conduction
Development of Myelin SheathDevelopment of Myelin Sheath
Fig. 11.5, p. 393
NeuronsNeurons
General:• most are amitotic (no cell division)
– communicate with each other at synapses– neuron-neuron– neuroeffector junction (NEJ)
• neuromuscular junction (NMJ)• neuroglandular junction (NGJ)
• high rate of aerobic respiration
NeuronNeuron
Cell body (perikaryon)• contains nucleus• rich in ribosomes & rough ER (Nissl bodies)• produces proteins for export to axon or dendrite• lots of mitochondria• neurofibrils
Neuron ProcessesNeuron ProcessesDendrites (d)• bring depolarization toward
cell body• no myelinAxons (a)• generally take action
potential (impulse) away form cell body
• myelinated or unmyelinated• axon hillock• telodendria
– synaptic end bulb
Fig. 11.4, p. d
a
Classification of NeuronsClassification of Neurons
• Based on structure – number of processes extending from cell body– unipolar– bipolar– multipolar
• Based on function – type & direction of information– sensory– motor– association (interneurons)
Major Structural Classes Major Structural Classes Unipolar neuronsUnipolar neurons
Table 11.1, p. 395
Unipolar neurons° dendrites short, lead to
myelinated axon (central and peripheral processes) before cell body
° generally sensory neurons within peripheral nervous system
Major Structural Classes Major Structural Classes Bipolar NeuronsBipolar Neurons
Table 11.1, p. 395
Bipolar neurons ° one axon, one
dendrite° sensory,
including retina of eye and olfactory mucosa
Major Structural Classes Major Structural Classes Multipolar NeuronsMultipolar Neurons
Table 11.1, p. 395
Multipolar : ° one axon, several dendrites
° interneurons, motor neurons
° may be myelinated or unmyelinated
Based on type and direction of information (impulse) transmission• Sensory:
° afferent (brings sensory info to CNS)° most unipolar or bipolar
• Interneurons: ° integration between sensory & motor in CNS° most multipolar
• Motor: ° efferent (goes toward/to effector)° most multipolar
Functional Classes of NeuronsFunctional Classes of Neurons
Other DefinitionsOther Definitions• Nerve fiber: long axon (primarily in PNS)• Nerve: bundle of neuron processes (fibers) in PNS• Tract: bundle of neuron processes in CNS• Ganglion (ganglia): cluster of cell bodies in PNS• Nucleus (nuclei): cluster of cell bodies in CNS• White matter: myelinated nerve processes in CNS
– outside in spinal cord; inside in brain• Gray matter: unmyelinated nerve processes in CNS
– inside in spinal cord, outside in brain
Nerve StructureNerve Structure• Nerves = bundles of neuron
processes (axons) in PNS• Coverings:
– endoneurium: wraps individual fibers (over myelin sheath); composed of areolar CT
– perineurium: groups fibers into bundles called fascicles; composed of dense irregular CT
– epineurium: encloses fascicles, arteries, veins; composed of dense irregular connective tissue
Fig. 13.2, p. 481
Peripheral Nerve TypesPeripheral Nerve Types
• Sensory nerves carry afferent fibers only• Motor nerves carry efferent fibers only• Mixed nerves carry both kinds of fibers
1 = epineurium
2 = perineurium
3 = endoneurium