1. Chapter 12– Nervous Tissue

2. Ch. 12 Nervous Tissue– Study Guide
Critically read Chapter 12 pp before 12.5 Synapses.
Comprehend Terminology (those in bold in the textbook) within the reading scope above
Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions (within the reading scope above) . Before You Go On Questions.
Do end-of-chapter questions—
Testing Your Recall— 1-4, 7, 11-17
True or False– 1-4, 6, 8
10-2 2 2

3. 12.1 Overview of the nervous system

4. § Maintaining internal coordination by two body systems
Homeostasis? How?
Endocrine and nervous systems--
Endocrine sys. – slower
chemical messengers (hormones) delivered to the bloodstream
Example-- insulin
Nervous sys. – quicker
chemical and electrical means
Example– in cold environment, vasoconstriction/shivering

5. § Subdivisions of Nervous System
Two major ANATOMICAL subdivisions:
Central nervous system (CNS)
brain and spinal cord enclosed in bony coverings
Peripheral nervous system (PNS)– all nervous tissue outside the CNS; made up of:
Nerves-- bundles of axons in connective tissue; emerge from the CNS; carry signals
Ganglia-- knotlike swellings in nerves

6. Part of PNS (next slide)

7. § Functional divisions of PNS (SAME)
Sensory (Afferent) divisions (receptors to CNS)– carry signals to the CNS
somatic division—Ex.
visceral sensory division—Ex.
Motor (Efferent) division (CNS to effectors)
somatic motor division
Effectors: skeletal muscles
visceral motor division (also called ANS)
Effectors: glands and cardiac/smooth muscles
sympathetic division/parasympathetic division
Fig. 12.2

8. PNS CNS Brain Sensory division Spinal cord Motor division Somatic
Visceral
motor
division
Visceral
sensory
division
Somatic
motor
division
Sympathetic
division
Parasympathetic
division

9. 12.2 Properties of neurons

10. § Universal properties of neurons
Nerves made up of nerve cells (neurons); neurons’ properties include:
Excitability
ability to respond to stimuli by producing action potential
Conductivity
produce traveling electrical signals
Secretion
Where? Why?
What is secreted?

11. § Functional Classes of Neurons
Sensory (afferent) neurons
detect changes in body and external environment
Ex.
Interneurons (association neurons)
Confine ENTIRELY in CNS
90% of our neurons are interneurons
process, store and retrieve information
Motor (efferent) neuron
send signals out to muscles and gland cells (effectors carry out body responses)
Fig. 12.3

12. Fig.12.3 Three Classes of Neurons
Example--Detecting your own pulse at wrist

13. § Neuron Cell body = soma Nucleus Dendrites (1-many) Function
Axon (single; nerve fiber)
Fig c-d-e

14. Neurofibrils
Axon
(d)

15. Figure 12.4d

16. Schwann cell
nucleus
Axoplasm
Axolemma
Neurilemma
Myelin sheath
(c)

17. § Variation in Neuron Structure–
No. of processes from the soma: (Fig )
Multipolar neuron
most common
Bipolar neuron
one dendrite/one axon
Unipolar neuron
Ex. sensory from skin to spinal cord directly
Anaxonic neuron
many dendrites/no axon
Ex. help in visual processes

19. 12.3 Supportive cells (Neuroglia)

20. § Introduction
How many?! Neurons are outnumbered by neuroglia (1:50) in the nervous sys.
Functions- protect the neurons and help them function
Example– in the fetus, guide young migrating neurons to their destinations

21. § 4 Types of Neuroglial Cells (CNS)
Astrocytes (star-shaped)
most abundant glial cells - form framework of CNS
contribute to blood-brain barrier and regulate composition of brain tissue fluid
Oligodendrocytes form myelin sheaths in CNS; distinguish these from Schwann cells
Ependymal cells (epithelial cells) line ventricles of the brain and central canal of the spinal cord; produce CSF
Microglia formed from monocytes; engulf invading microbes
in areas of infection, trauma or stroke
Fig. 12.6

22. Neuroglial Cells of CNS

23. § 2 Types of Neuroglial Cells (PNS)
Schwann cells -- myelinate fibers of PNS; assist in the regeneration of damaged fibers
Satellite cells – surround cell bodies in ganglia; regulate the chemical environment of the neurons

24. § Myelin
Insulating layer around a nerve fiber; analogy– the rubber insulation on a wire
In CNS,
Each oligodendrocyte myelinate several fibers (Fig. 12.7a)
In PNS,
The ___________ cell wraps the nerve fiber
outermost coil is called neurilemma containing bulging body of the Schwann cell (nucleus and most of its cytoplasm) (Fig. 12.7b)

25. Myelin Sheath in CNS
Figure 12.7b

26. Myelin Sheath in PNS
Schwann cell
Axon
Myelin sheath
Neurilemma

27. Myelin Sheath in PNS
Node of Ranvier (gaps)-- between Schwann cells (also in CNS)
Internodes–
from one gap to the next

28. § Unmyelinated nerve fibers
Locations?
CNS, PNS, both (circle one)
One Schwann cell harbors ______ small fibers
The Schwann cell– folds once around each fiber
Fig. 12.8

29. Unmyelinated
nerve fibers
Schwann cell
Basal lamina

30. § Myelination and Speed of Nerve Signal
Diameter of fiber and presence of myelin
large fibers have more surface area for signal conduction
Speeds
small, unmyelinated fibers = m/sec
small, myelinated fibers = m/sec
large, myelinated fibers = up to 120 m/sec
Functions
slow signals supply the stomach and dilate pupil
fast signals supply skeletal muscles and transport sensory signals for vision and balance

31. 12.4A Electrophysiology of neurons
KEY issues–
How does a neuron generate an electrical signal?
Cellular mechanisms for producing electrical potential and currents

32. § Electrical Potentials & Currents
Electrical potential – a difference in the concentration of charged particles between one point and another
Electrical current– flow of charged particles from one point to another
Living cells have electrical potentials (are polarized)
resting membrane potential is -70 mV with a negative charge on the _______ of membrane; why? (next slide)

33. § Resting Membrane Potential of all cells (RMP; -70 mV)
Factors contribute to RMP: unequal distribution of electrolytes in ECF & ICF
Diffusion of ions down their conc. gradient
Selective permeability of the cell mem.
Cations and anions attract to each other
Details--
Membrane very permeable to K+
Membrane much less permeable to Na+
Cytoplasmic anions can not escape— EX. Proteins, phosphates etc.
Fig

34. Na+ more concentrated in the ECF K+ more concentrated in the ICF
Fig Ion basis of the resting membrane potential
Negative charge (-70 mV)
Na+ more concentrated in the ECF
K+ more concentrated in the ICF

35. § When a neuron is stimulated
Local potentials– changes in membrane potential when a neuron is stimulated
Causes– How?
Results– depolarization
Ionic bases--
Na+ rushes into/out of (circle one) the cell
Na+ diffuses for short distance inside membrane producing a local potential
Fig and X

36. For example– a chemical (pain signal; ligand) stimulates a neuron

37. Local potential-- Local, graded, and decremental
Resting mem.
Potential (-70 mV)
Time
Magnitude
of stimulus
Stimuli A B C D

38. § Action potentials if stimulus is strong (Fig. 12.13)
Threshold reached
Depolarization (sodium channels open)
Repolarization (Sodium channels close and K+ gates fully open)
Hyperpolarization
Resting membrane potential restores
12-38

39. Figure 12.13a

40. § Action potentials vs. local potentials (Table 12.5)?
Graded + reversible
Decremental

41. Ionic base

42. § The refractory period of the action potential (AP)
Period of resistance to stimulation for another AP
Absolute refractory period
as long as Na+ gates are open
no stimulus will trigger AP
Relative refractory period
as long as K+ gates are open
only especially strong stimulus will trigger new AP

43. 12.4B--Conduction of a nerve signal in an unmyelinated fiber

44. Where are ion gates?
First action potential occurs at?
The next action potential occurs at?
Chain reactions continue until _____

45. 12.4C--Conduction of a nerve signal in a myelinated fiber

46. § Saltatory conduction (Fig. 12.17a-b)
Most (99%) of the voltage-regulated ion gates are at the _______________.
Slow but nondecremental
At the internodes–
nerve signals travel very ______ (diffusion of ions) and decremental.
Most of the axon is covered with myelin (internodes)
nerve signal is faster at 120m/sec (than unmyelinated ones (up to 2 m/sec)

47. Action potentials occurs only at the _________________
It is called saltatory conduction meaning _____________.