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
• Motor – initiates impulses to effectors [muscles or
glands] that do work)
Organization
Fig. 11.2, p. 388
Cells
Neurons and Supporting Cells
• neurons
– produce impulses to transfer information
– amitotic (mostly), high metabolic rates, longlived
• 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 CNS
• Astrocytes – connect neurons to blood supply
• Microglia – phagocytic
Fig. 11.3, p. 389
Supporting 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 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 (Myelin 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 Sheath
Fig. 11.5, p. 393
Neurons
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
Neuron
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 Processes
Dendrites (d)
• bring depolarization toward
cell body
• no myelin
Axons (a)
• generally take action
potential (impulse) away
form cell body
• myelinated or unmyelinated
• axon hillock
• telodendria
– synaptic end bulb
d
Fig. 11.4, p.
a
Classification 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
Unipolar neurons
Unipolar neurons
° dendrites short, lead to
myelinated axon (central and
peripheral processes) before cell
body
° generally sensory neurons within
peripheral nervous system
Table 11.1, p. 395
Major Structural Classes
Bipolar Neurons
Bipolar neurons
° one axon, one
dendrite
° sensory,
including retina
of eye and
olfactory
mucosa
Table 11.1, p. 395
Major Structural Classes
Multipolar Neurons
Multipolar :
° one axon, several dendrites
° interneurons, motor neurons
° may be myelinated or
unmyelinated
Table 11.1, p. 395
Functional Classes of Neurons
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
Other 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 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 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