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