This chapter should help the student to:

• List the features distinguishing nerve tissue from other basic tissue types.
  
• List the nerve tissue cell types and describe the structure, function, location, and embryonic origin of each.
  
• Describe in detail how neurons receive, propagate, and transmit signals.
  
• Describe a neuron’s organelles in terms of their location and roles in impulse transmission and neuronal repair.
  
• Describe synapses in terms of their structural components, function, and classification.
  
• Describe nervous system organization in terms of the structure, functions, location, and distinguishing features of its subsystems.
  
• Describe the structure and function of the meninges.
  
• Describe the response of nerve tissue to injury.
  
• Recognize the type of nerve tissue displayed in a micrograph and identify its cells and cell processes.

1. List the basic functions of nerve tissue (I.A.1; VII.B).

2. Compare the central nervous system (CNS) and peripheral nervous system (PNS) (I.D.1; Table 9–1) in terms of:

1. 
   

   Major components (organs)

   
   
2. 
   

   Names given to a collection of nerve cell bodies

   
   
3. 
   

   Names given to a collection of nerve cell fibers

   
   
4. 
   

   Supporting cells present

   
   
5. 
   

   Cells responsible for myelination

   
   
6. 
   

   Cells that invest unmyelinated fibers

   
   
7. 
   

   Embryonic origin

3. Compare gray matter and white matter (Table 9–1) in terms of:

1. 
   

   Predominant neuronal components (cell bodies, axons, dendrites)

   
   
2. 
   

   Amount of myelin present

   
   
3. 
   

   Predominant astrocyte type (III.A.1)

   
   
4. 
   

   Abundance of synapses

4. Name two basic subdivisions of the autonomic nervous system (ANS) (I.D.2; Table 9–2).

5. Compare the sympathetic and parasympathetic nervous systems (I.D.2; Fig. 9–1; Table 9–2) in terms of the locations of cell bodies of preganglionic and postganglionic neurons, the neurotransmitter released by their postganglionic neurons, and their primary function (sensory or motor).

6. Beginning with neural plate formation, list the basic steps in nervous system development (I.E; Fig. 9-2).

7. List the cell types derived from the embryonic neural crest (I.E).

8. Compare the dura mater, arachnoid, and pia mater (I.G) in terms of:

1. 
   

   Location

   
   
2. 
   

   Attachments (eg, periosteum, brain, spinal cord)

   
   
3. 
   

   Tissue type

   
   
4. 
   

   Presence of blood vessels

9. Describe the blood–brain barrier in terms of its structural correlates and its function (I.H;III.A.1).

10. Compare multipolar, bipolar, and pseudounipolar neurons (II. D; Table 9–3) in terms of their number of axons and dendrites, typical function, and location in the body (include examples).

11. Compare axons (II.C) and dendrites (II.B) in terms of:

1. 
   

   Number per neuron

   
   
2. 
   

   Relative length

   
   
3. 
   

   Presence of surface projections

   
   
4. 
   

   Primary function

   
   
5. 
   

   Presence of Nissl bodies (RER and ribosomes)

   
   
6. 
   

   Degree of branching

   
   
7. 
   

   Variation in diameter as a function of distance from the perikaryon

   
   
8. 
   

   Content of synaptic vesicles

12. Draw a terminal bouton and its associated synapse (see Fig. 9–3) and label the synaptic vesicles, mitochondria, presynaptic membrane, synaptic cleft, and postsynaptic membrane.

13. Compare protoplasmic astrocytes and fibrous astrocytes in terms of their location and the length and diameter of their cell processes (III.A.1).

14. Compare astrocytes, oligodendrocytes, and microglia (III.A.1–3) in terms of:

1. 
   

   Nuclear shape, size, and staining intensity

   
   
2. 
   

   Relative number of cell processes

   
   
3. 
   

   Ability to form myelin

   
   
4. 
   

   Relationship to the mononuclear phagocyte system

15. Describe ependymal cells in terms of their embryonic origin and location (III.A.4).

16. Compare neurons (II) and neuroglia (III) in terms of:

1. 
   

   Cytoplasmic staining properties and visibility (II.A; III.A)

   
   
2. 
   

   Nuclear size (III.A)

   
   
3. 
   

   Relative number in the CNS (III.A)

   
   
4. 
   

   Capacity for proliferation in adults (VIII.A and B.1)

   
   
5. 
   

   Embryonic origin (I.E)

   
   
6. 
   

   General function (I.A.1 and 2)

17. Which part of a Schwann cell forms the myelin sheath, and what is the predominant biochemical constituent of myelin (III.B.1)?

18. Compare myelinated and unmyelinated axons of the peripheral nervous system in terms of:

1. 
   

   Impulse conduction velocity (I.B)

   
   
2. 
   

   Diameter (Table 9–5)

   
   
3. 
   

   Presence of nodes of Ranvier (III.B.1)

   
   
4. 
   

   Action potential (diffusion versus saltatory conduction) (VII.B.2 and 5)

19. Compare Schwann cells (III.B.1) and oligodendrocytes (III.A.2) in terms of:

1. 
   

   Location

   
   
2. 
   

   Number of axons each can myelinate

   
   
3. 
   

   Number of cells per internode

   
   
4. 
   

   Whether they ensheathe unmyelinated axons

20. Compare craniospinal and autonomic ganglia (V; Table 9–4) in terms of:

1. 
   

   Location

   
   
2. 
   

   Primary function (motor or sensory)

   
   
3. 
   

   Class of neurons present

   
   
4. 
   

   Distribution of ganglion cell bodies

   
   
5. 
   

   Nuclear shape and position in ganglion cell bodies

   
   
6. 
   

   Completeness of satellite cell layer

21. How do the ganglion cells of the spiral (acoustic) ganglion differ from those in craniospinal ganglia (Table 9–4)?

22. How do intramural ganglia differ from other autonomic ganglia (Table 9–4)?

23. Draw a peripheral nerve cross-section (VI; Fig. 9–4) and label the epineurium, perineurium, endoneurium, myelin sheaths, and axons.

24. Compare the inside and outside of a resting-state neuron in terms of K+ and Na+ ion concentrations and approximate resting membrane potential in millivolts (VII.B.1).

25. How does a neuron maintain its resting membrane potential (VII.B.1)?

26. Beginning with an excitatory synaptic stimulus, list the events leading to the generation of an action potential (VII.B.2).

27. After depolarization, how does a neuron reestablish its resting membrane potential (VII.B.2 and 3)? Does this process require ATP? How long does it take?

28. Beginning with the spread of an action potential into a terminal bouton, list the sequence of events leading to depolarization of a postsynaptic membrane (IV.A–C).

29. What happens to acetylcholine after it binds to receptors in the postsynaptic membrane (IV.C)?

30. List several neurotransmitters (Table 9–3). Which one is inhibitory?

31. Compare nerve fibers (types A, B, and C) in terms of myelination, fiber diameter, and internode length (Table 9–5).

32. What happens to the following after a nerve is cut (VIII.A, B.1 and 2)?

1. 
   

   Distal stumps of injured axons

   
   
2. 
   

   Myelin distal to the cut

   
   
3. 
   

   Schwann cells distal to the cut

   
   
4. 
   

   Nissl bodies of perikarya

   
   
5. 
   

   Volume of perikarya

   
   
6. 
   

   Position of nuclei in perikarya

   
   
7. 
   

   Proximal stumps of injured axons

33. If a large gap exists between the proximal and distal cut ends of a nerve (VIII.B.2), what may happen to the neurites and the effector organ?

I. General Features of Nerve Tissue & the Nervous System

A. Two Classes of Cells

Nerve tissue consists of neurons that transmit electrochemical impulses and the supporting cells that surround them. It contains little extracellular material.

1. 
   

   Neurons (II). These cells are specialized to receive, integrate, and transmit electrochemical messages. Each has a cell body, also called the soma (“body”) or perikaryon (“around the nucleus”), comprising the nucleus, the surrounding cytoplasm, and the plasma membrane. Each neuron has a variable number of dendrites (cytoplasmic processes that collect incoming messages and carry them toward the soma) and a single axon (a cytoplasmic process that transmits messages to the target cell). Axons of most neurons have a myelin sheath formed by supporting cells and interrupted by gaps called nodes of Ranvier. Axon segments between the gaps are called internodes.

   
   
2. 
   

   Supporting cells (III) are called neuroglia (“nerve glue”) or glial cells. Their functions include structural and nutritional support of neurons, electrical insulation, and enhancement of impulse conduction velocity (VII.B.2 and 5).

B. Impulse Conduction

Signals (impulses) are propagated as a wave of depolarization along the plasma membrane of the dendrites, soma, and axon. Depolarization involves channels (ionophores) in the membrane, which allow ions (e.g., Na+, K+) to enter or exit the cell. In unmyelinated axons, depolarization occurs in waves over the entire surface. In myelinated axons, depolarization occurs only at nodes of Ranvier, jumping from node to node (saltatory conduction). Impulse conduction is therefore faster in myelinated axons.

C. Synapses

Signals pass from neuron to target cell by specialized junctions called synapses. A target may be another neuron or a cell in the end-organ (e.g., gland or muscle). At chemical synapses (IV), signals are transmitted by the exocytosis of neurotransmitters—chemicals such as acetylcholine that cross a narrow gap (synaptic cleft) between cells to initiate target cell depolarization. At the less common electrical synapses, signals are transmitted by ions flowing through a gap-junction–like complex.

D. Subsystems of the Nervous System