1. Chapter 14 *Lecture Outline
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2. Chapter 14 Outline Organization of the Nervous System
Cytology of Nervous Tissue
Myelination of Axons
Axon Regeneration
Nerves
Synapses
Neural Integration and Neuronal Pools
Development of the Nervous System

3. Structural Organization of the Nervous System
Structurally, the nervous system is divided into two subdivisions:
Central nervous system (CNS)— includes the brain and spinal cord
Peripheral nervous system (PNS)— includes the cranial nerves, spinal nerves, and ganglia

4. Structural Organization of the Nervous System
Figure 14.1

5. Functional Organization of the Nervous System
The CNS and PNS perform three general functions:
Collecting information—receptors are PNS structures that detect changes in the internal and external environment (sensory input) and pass the information on to the CNS
Processing and evaluating information—CNS determines what, if any, response is required
Responding to information—CNS initiates specific nerve impulses, called motor output, to effectors (muscles or glands) to react to changes in the body’s environment

6. Functional Organization of the Nervous System
There are two functional divisions of the nervous system:
Sensory nervous system
Motor nervous system

7. Functional Organization of the Nervous System

8. Sensory Nervous System
Sensory nervous system (afferent) receives sensory information from receptors in the PNS and transmits it to the CNS
Subdivided into two systems:
Somatic sensory (voluntary)—touch, pain, pressure, vibration, and proprioception
Visceral sensory (involuntary)—impulses from viscera

9. Motor Nervous System
Motor nervous system (efferent) sends impulses from CNS to muscles and glands
Subdivided into two systems:
Somatic motor (voluntary)—impulses from the CNS that cause contraction of skeletal muscles
Autonomic motor (involuntary)—impulses from the CNS that regulate smooth and cardiac muscle and glands

10. Cytology of Nervous Tissue
There are two distinct types of cells within the nervous system:
Neurons (nerve cells)—electrically excitable cells that initiate, transmit, and receive nerve impulses
Glial cells—nonexcitable cells that support and protect the neurons

11. Neurons The basic structural unit of the nervous system
Conduct nerve impulses from one part of the body to another part
They have the following features:
High metabolic rate
Extreme longevity
Nonmitotic

12. Neuron Structure A neuron has three main structural regions: Cell body
Dendrites
Axon

13. Neuron Structure
Figure 14.3

14. Cell Body Contains typical organelles such as: Nucleus Nucleolus
Mitochondria !!!!!!
Free ribosomes and rough endoplasmic reticulum (Nissl bodies)!!!!

15. Dendrites Short processes that branch from the cell body
Receive nerve impulses and carry them to the cell body

16. Axon
Neurons have either one axon or no axon at all. Neurons without an axon are called anaxonic.
The region where the axon connects to the cell body is the axon hillock.
Axons transmit nerve impulses away from the cell body and transmit information to other cells.

17. Structures Associated with Axons
Axon collaterals—side branches of the main axon
Telodendria—fine terminal extensions at the end of the axon and its collaterals
Synaptic knobs—expanded regions at the tip of telodendria

18. Structural Classification of Neurons
Classified according to the number of processes emanating directly from the cell body of the neuron:
Unipolar—single, short process that branches like a T
Bipolar—two processes, one dendrite and one axon
Multipolar—many dendrites and a single axon, most common of all neurons

19. Structural Classification of Neurons
Figure 14.4

20. Functional Classification of Neurons
Functionally, neurons are classified according to the direction that the nerve impulse is traveling relative to the CNS:
Sensory (afferent)—transmit impulses from sensory receptors to the CNS
Motor (efferent)—transmit impulses from CNS to muscles or glands
Interneurons—facilitate communication between sensory and motor neurons

21. Functional Classification of Neurons
Figure 14.5

22. Glial Cells=Neuroglias
Sometimes referred to as neuroglia
Found in both CNS and PNS
Smaller than neurons and capable of mitosis
Physically protect and nourish neurons
More numerous than neurons
Brain tumors are more likely to be derived from glial cells than neurons

23. Glial Cells of the CNS
Figure 14.6

24. Glial Cells of the CNS There are four types of cells found in the CNS:
Astrocytes
Ependymal cells
Microglial cells
Oligodendrocytes
See Table 14.4 for the function of each of these glial cells.

25. Cellular Organization in Neural Tissue
Produce CSF
Regulate
Myelin
BBB
Clean lady
Repair-Myelin

26. Function of CNS Glial Cells

27. Astrocytes
Most abundant glial cells in the CNS, whose functions include:
Helping to form the blood-brain barrier (BBB)
Regulating tissue fluid composition
Forming a structural network
Replacing damaged neurons
Assisting neuronal development

28. Astrocytes
Figure 14.7

29. Ependymal Cells
Ciliated cuboidal epithelial cells that line the ventricles of the brain and the central canal of the spinal cord
In conjunction with other glial cells, the ependymal cells produce cerebral spinal fluid (CSF) and form the choroid plexus

30. Ependymal Cells
Figure14.7

31. Microglial Cells Small cells that are motile
Wander through the CNS and exhibit phagocytic activity, removing cellular debris from dead or dying cells

32. Microglial Cells
Figure 14.7

33. Oligodendrocytes Associated with CNS axons only
Wrap themselves around the axons like electrical tape wrapped around a wire
Produce myelin, which is an insulator of electrical activity

34. Oligodendrocytes
Figure 14.7

35. Function of PNS Glial Cells

36. Glial Cells of the PNS Satellite cells Neurolemmocytes=Schwann Cells
There are two types of cells found in the PNS:
Satellite cells
Neurolemmocytes=Schwann Cells
See Table 14.4 for the function of each of these glial cells.

37. Satellite Cells
Flattened cells arranged around neuronal cell bodies in ganglia
Figure 14.7

38. Neurolemmocytes Also called Schwann cells
Associated with PNS axons only
Wrap themselves around the axons like electrical tape wrapped around a wire
Produce myelin which is an insulator of electrical activity
Same structure and function as oligodendrocytes

39. Neurolemmocyte Development1
Neurolemmocyte
starts to wrap around
a portion of an axon. 2
Neurolemmocyte
cytoplasm and
plasma membrane
begin to form
consecutive layers
around axon.
Axon
Neurolemmocyte
Nucleus
Direction of
wrapping
Figure 14.8

40. Neurolemmocyte Development
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The overlapping inner
layers of the
neurolemmocyte
plasma membrane
form the myelin
sheath. 4
Eventually, the
neurolemmocyte
cytoplasm and
nucleus are pushed
to the periphery of
the cell as the myelin
sheath is formed.
Cytoplasm of the
neurolemmocyte
Myelin sheath
Myelin sheath
Neurolemmocyte
nucleus
Figure 14.8

41. Neurolemmocytes
Figure 14.7

42. Myelin Sheaths in the CNS and PNS
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Oligodendrocytes
Neurofibril
node
Axons
Myelin sheath
(a) CNS
Neurolemmocytes
(forming myelin sheath)
Neuron
cell body
Neurofibril
node
Figure 14.9
Axon
(b) PNS

43. Growth regeneration tube Remyelination accompanies
Axon Re ge ne ra tion
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Endoneurium
Neurolemmocytes
Trauma severs axon 1
Peripheral nerve injury
results in the severing
of axons (only one
axon is shown here).
Skeletal muscle fibers
Axon degenerates
in distal region 2
The proximal portion of each
severed axon seals off and
swells; the distal portion
degenerates.
Sealed, swollen end
Growth regeneration tube
formed by
neurolemmocytes 3
Neurolemmocytes form a
regeneration tube.
Remyelination accompanies
axon growth 4
Axon regenerates and
remyelination occurs.
Reconnection to effector 5
Reinnervation of the
effector (skeletal muscle
fibers) by the axon.
Figure 14.11

44. Nerves Cablelike bundle of parallel axons
Surrounded by three connective tissue wrappings
Endoneurium
Perineurium
Fascicles
Epineurium

45. Nerve Structure Figure14.12 Axon Perineurium Fascicle Myelin sheath
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Axon
Perineurium
Fascicle
Myelin sheath
Endoneurium
Fascicle
Perineurium
Endoneurium
Epineurium
Axon
Blood vessels
Myelin sheath
Blood vessels
SEM 450x
(b)
Myelin sheath
(a)
Axon
Neurolemmocyte
nucleus
Neurofibril node
LM 550x
(c)
Figure14.12
b: © Dr. Richard Kessel and Dr. Randy Kardon/ Tissues and Organs/ Visuals Unlimited; c: © Rick Ash

46. Synapses
Specialized junctions between one axon and another neuron, muscle cell, or gland cell
Presynaptic neuron
Postsynaptic neuron
Synaptic cleft

47. Electrical and Chemical Synapses
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Electrical
synapse
Smooth
muscle cells
Presynaptic
cell
Postsynaptic
cell
Nerve impulse
Axon of presynaptic neuron
Gap junction
Local current + + + + + + +
Mitochondria + + + +
Calcium
(Ca2+;)ions
Microtubules
of cytoskeleton + + + + + +
Voltage-regulated
calcium (Ca2+;)
channel
Synaptic vesicles
containing
acetylcholine (ACh) + + + +
Positively
charged ions
Connexons
Synaptic
cleft
Inner surface
of plasma
membrane
Plasma membrane
(a) Electrical synapse
Acetylcholine
Acetylcholine binds
to receptor protein,
causing ion gates
to open
Postsynaptic
membrane
Sodium
(Na+) ions
Receptor protein
Postsynaptic neuron
(b) Chemical synapse
Figure 14.14

48. Nervous System Development
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Cut edge of amnion
Neural fold
Neural groove
Primitive node
Primitive streak
Neural groove
Neural crest
Neural folds
Notochord 1
Neural folds and neural groove form from the neural plate.
Neural groove
Neural folds 2
Neural folds elevate and approach one another.
Neural groove
Ectoderm
Neural crest
cells 3
and form other structures.
Neural crest cells begin to "pinch off" from the neural folds
Neural tube
Developing
posterior root
ganglion
Developing
epidermis
Figure 14.16 4
Neural folds fuse to form the neural tube.