1. Chapter 10 Nervous System I: Basic Structure and Function
Hole’s Human Anatomy and Physiology Twelfth Edition Shier w Butler w Lewis
Chapter 10
Nervous System I: Basic Structure and Function
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2. 10.1: Introduction Cell types in neural tissue: Neurons
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Cell types in neural tissue:
Neurons
Neuroglial cells (also known as neuroglia, glia, and glial)
Dendrites
Cell body
Nuclei of
neuroglia
Axon
© Ed Reschke

3. Divisions of the Nervous System
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Brain
Central Nervous System (CNS)
Brain
Spinal cord
Peripheral Nervous System (PNS)
Cranial nerves
Spinal nerves
Cranial
nerves
Spinal
cord
Spinal
nerves
(a)

4. Divisions of Peripheral Nervous System
Sensory Division
Picks up sensory information and delivers it to the CNS
Motor Division
Carries information to muscles and glands
Divisions of the Motor Division:
Somatic – carries information to skeletal muscle
Autonomic – carries information to smooth muscle, cardiac muscle, and glands

5. Divisions Nervous System
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Central Nervous System
(brain and spinal cord)
Peripheral Nervous System
(cranial and spinal nerves)
Brain
Cranial
nerves
Sensory division
Sensory receptors
Spinal
cord
Spinal
nerves
Motor division
Somatic
Nervous
System
Skeletal muscle
Autonomic
Nervous
System
Smooth muscle
Cardiac muscle
Glands
(a)
(b)

6. Functions of Nervous System
Sensory Function (receiving information)
Sensory receptors gather information
Information is carried to the CNS
Integrative Function (deciding what to do about information)
Sensory information used to create:
Sensations
Memory
Thoughts
Decisions
Motor Function (acting on information)
Decisions are acted upon
Impulses are carried to effectors

7. 10.3: Description of Cells of the Nervous System
Neurons vary in size and shape
They may differ in length and size of their axons and dendrites
Neurons share certain features:
Dendrites
A cell body
An axon

8. Neuron Structure Chromatophilic substance (Nissl bodies) Dendrites
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Chromatophilic
substance
(Nissl bodies)
Dendrites
Cell body
Nucleus
Nucleolus
Neurofibrils
Axonal
hillock
Impulse
Axon
Synaptic knob of
axon terminal
Nodes of Ranvier
Myelin (cut)
Nucleus of
Schwann cell
Axon
Schwann
cell
Portion of a
collateral

9. Myelination of Axons White Matter Contains myelinated axons
Considered fiber tracts
Gray Matter
Contains unmyelinated structures
Cell bodies, dendrites
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Dendrite
Unmyelinated
region of axon
Myelinated region of axon
Node of Ranvier
Axon
Neuron
cell body
Neuron
nucleus
(a)
Enveloping
Schwann cell
Schwann
cell nucleus
Longitudinal
groove
Unmyelinated
axon
(c)

10. 10.4: Classification of Neurons and Neuroglia
Neurons vary in function
They can be sensory, motor, or integrative neurons
Neurons vary in size and shape, and in the number of axons and dendrites that they may have
Due to structural differences, neurons can be classified into three (3) major groups:
Bipolar neurons
Unipolar neurons
Multipolar neurons

11. Classification of Neurons: Structural Differences
Multipolar neurons
99% of neurons
Many processes
Most neurons of CNS
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Dendrites
Peripheral
process
Bipolar neurons
Two processes
Eyes, ears, nose
Axon
Direction
of impulse
Unipolar neurons
One process
Ganglia of PNS
Sensory
Central
process
Axon
Axon
(a) Multipolar
(b) Bipolar
(c) Unipolar

12. Classification of Neurons: Functional Differences
Sensory Neurons
Afferent (approach)
Carry impulse to CNS
Most are unipolar
Some are bipolar
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Central nervous system
Peripheral nervous system
Cell body
Dendrites
Sensory
receptor
Interneurons
Link neurons in CNS
Aka association neurons
Multipolar
Cell body
Axon
(central process)
Axon
(peripheral process)
Sensory (afferent) neuron
Interneurons
Motor (efferent) neuron
Motor Neurons
Efferent (exit)
Carry impulses away from CNS to effectors
Multipolar
Axon
Effector
(muscle or gland)
Axon
Axon
terminal

13. Types of Neuroglial Cells in the PNS
1) Schwann Cells
Produce myelin found on peripheral myelinated neurons
Speed up neurotransmission
2) Satellite Cells
Support clusters of neuron cell bodies (ganglia)

14. Types of Neuroglial Cells in the CNS
1) Microglia
CNS
Phagocytic cell
3) Oligodendrocytes
CNS
Myelinating cell
4) Ependyma or ependymal
CNS
Ciliated
Line central canal of spinal cord
Line ventricles of brain
Keep CSF moving
2) Astrocytes
CNS
Scar tissue
Mop up excess ions, etc.
Induce synapse formation
Connect neurons to blood vessels

15. Types of Neuroglial Cells
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Fluid-filled cavity
of the brain or
spinal cord
Neuron
Ependymal
cell
Oligodendrocyte
Astrocyte
Microglial cell
Axon
Myelin
sheath (cut)
Capillary
Node of
Ranvier

16. Regeneration of A Nerve Axon
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Motor neuron
cell body
Skeletal
muscle fiber
Changes
over time
Site of injury
Schwann cells
Axon
(a)
Distal portion of
axon degenerates
(b)
Proximal end of injured axon
regenerates into tube of sheath cells
(c)
Schwann cells
degenerate
(d)
Schwann cells
proliferate
(e)
Former connection
reestablished 16

17. 10.5: The Synapse
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Nerve impulses pass from neuron to neuron at synapses, moving from a pre-synaptic neuron to a post-synaptic neuron.
Synaptic
cleft
Impulse
Dendrites
Axon of
presynaptic
neuron
Axon of
postsynaptic
neuron
Axon of
presynaptic
neuron
Cell body of
postsynaptic
neuron
Impulse
Impulse

18. Synaptic Transmission
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Direction of
nerve impulse
Neurotransmitters are released when impulse reaches synaptic knob
Synaptic
vesicles
Axon
Presynaptic neuron
Ca+2
Ca+2
Synaptic knob
Cell body or dendrite
of postsynaptic neuron
Mitochondrion
Synaptic
vesicle
Ca+2
Vesicle releasing
neurotransmitter
Axon
membrane
Neurotransmitter
Synaptic cleft
Polarized
membrane
Depolarized
membrane
(a)

19. Animation: Chemical Synapse
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20. 10.6: Cell Membrane Potential
A cell membrane is usually electrically charged, or polarized, so that the inside of the membrane is negatively charged with respect to the outside of the membrane (which is then positively charged).
This is as a result of unequal distribution of ions on the inside and the outside of the membrane.

21. Distribution of Ions
Potassium (K+) ions are the major intracellular positive ions (cations).
Sodium (Na+) ions are the major extracellular positive ions (cations).
This distribution is largely created by the Sodium/Potassium Pump (Na+/K+ pump).
This pump actively transports sodium ions out of the cell and potassium ions into the cell.

22. Resting Potential Resting Membrane Potential (RMP):
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Resting Membrane Potential (RMP):
70 mV difference from inside to outside of cell
It is a polarized membrane
Inside of cell is negative relative to the outside of the cell
RMP = -70 mV
Due to distribution of ions inside vs. outside
Na+/K+ pump restores
High Na+
Low Na+
Impermeant
anions
High K+
Low K+
Cell body
Axon
Axon terminal + + + + – – –
(a) – + + – + + + – – – – – – – – – + + – + – – – + + + + + +
–70 mV
(b) + + + + – – –
High Na+ –
Low Na+
Na+ + + – – + +
Pump – – – – – K+
High K+ – + – –
Low K+ – + + + + + + – +
–70 mV 22
(c)

23. Local Potential Changes
Caused by various stimuli:
Temperature changes
Light
Pressure
Environmental changes affect the membrane potential by opening a gated ion channel
Channels are 1) chemically gated, 2) voltage gated, or 3) mechanically gated
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Gatelike mechanism
Protein
Cell
membrane
Fatty acid
tail
Phosphate
head
(a) Channel closed
(b) Channel open

24. Local Potential Changes
If membrane potential becomes more negative, it has hyperpolarized
If membrane potential becomes less negative, it has depolarized
Graded (or proportional) to intensity of stimulation reaching threshold potential
Reaching threshold potential results in a nerve impulse, starting an action potential

25. Local Potential Changes
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Na+
Na+
–62 mV
Chemically-gated
Na+ channel
Neurotransmitter
Presynaptic
neuron
(a)
Voltage-gated
Na+ channel
Trigger zone
Na+
Na+
Na+
Na+
Na+
–55 mV
(b)

26. Action Potentials At rest, the membrane is polarized (RMP = -70)
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Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+ K+ K+ K+ K+ K+ K+ K+ K+ –0
Threshold stimulus reached (-55) K+ K+ K+ K+ K+ K+ K+ K+
–70
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
(a)
Sodium channels open and membrane depolarizes (toward 0)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+ channels open
K+ channels closed K+
Na+
Na+
Na+ K+ K+ K+ K+ K+ K+ K+ –0
Threshold
stimulus K+ K+ K+
Na+
Na+
Na+ K+ K+ K+ K+ K+
–70
Potassium leaves cytoplasm and membrane repolarizes (+30)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Region of depolarization
(b) K+ K+ K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+ channels open
Na+ channels closed K+
Na+
Na+
Na+ K+ K+ K+ K+ K+ –0
Brief period of hyperpolarization (-90) K+
Na+
Na+
Na+ K+ K+ K+ K+ K+
–70 K+ K+ K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Region of repolarization
(c)

27. Action Potentials +40 Action potential +20 –20 Resting potential
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+40
Action potential
+20
–20
Resting potential
reestablished
Membrane potential (millivolts)
–40
Resting
potential
–60
–80
Hyperpolarization 1 2 3 4 5 6 7 8
Milliseconds

28. Action Potentials Region of action potential + + + + + + + + + + + – –
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Region of
action potential + + + + + + + + + + + – – – – – – – – – + + – – – – – – – – – + + + + + + + + +
(a) + + + + + + + + + – – – + + – – – – – –
Direction of nerve impulse – – – + + – – – – – – + + + + + + + + +
(b) + + + + + + + + + – – – – – – – + + – – – – – – – – – + + – – + + + + + + + + +
(c)

29. Animation: Action Potential Propagation in Unmyelinated Neurons
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30. Animation: Action Potential Propagation in Myelinated Neurons
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31. All-or-None Response
If a neuron responds at all, it responds completely
A nerve impulse is conducted whenever a stimulus of threshold intensity or above is applied to an axon
All impulses carried on an axon are the same strength

32. Refractory Period Absolute Refractory Period
Time when threshold stimulus does not start another action potential
Relative Refractory Period
Time when stronger threshold stimulus can start another action potential

33. Impulse Conduction

34. Animation: The Nerve Impulse
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35. 10.7: Synaptic Transmission
This is where released neurotransmitters cross the synaptic cleft and reacts with specific molecules called receptors in the postsynaptic neuron membrane.
Effects of neurotransmitters vary.
Some neurotransmitters may open ion channels and others may close ion channels, making it more likely or less likely for an action potential to occur.

36. Synaptic Potentials EPSP Excitatory postsynaptic potential Graded
Depolarizes membrane of postsynaptic neuron
Action potential of postsynaptic neuron becomes more likely
IPSP
Inhibitory postsynaptic potential
Graded
Hyperpolarizes membrane of postsynaptic neuron
Action potential of postsynaptic neuron becomes less likely

37. Summation of EPSPs and IPSPs
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EPSPs and IPSPs are added together in a process called summation
More EPSPs lead to greater probability of an action potential
More IPSPs lead to lower probability of an action potential
Neuron
cell body
Nucleus
Presynaptic
knob
Presynaptic
axon 37

38. Neurotransmitters

39. Neurotransmitters

40. 10.8: Impulse Processing
The way the nervous system processes nerve impulses and acts upon them.
Neuronal pools of interneurons
Convergence
Divergence

41. Neuronal Pools
Groups of interneurons that make synaptic connections with each other
Interneurons work together to perform a common function – may be excitatory or inhibitory
Each pool receives input from other neurons
Each pool generates output to other neurons

42. Convergence Neuron receives input from several neurons
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Neuron receives input from several neurons
Incoming impulses represent information from different types of sensory receptors
Allows nervous system to collect, process, and respond to information
Makes it possible for a neuron to sum impulses from different sources 2 1 3 42
(a)

43. Divergence
One neuron sends impulses to several neurons via its branched axon
Can amplify an impulse
Impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction or glandular secretion
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(b)

44. Important Points in Chapter 10: Outcomes to be Assessed
10.1: Introduction
Describe the general functions of the nervous system.
Identify the two types of cells that comprise nervous tissue.
Identify the two major groups of nervous system organs.
10.2: General Functions of the Nervous System
List the functions of sensory receptors.
Describe how the nervous system responds to stimuli.
10.3: Description of Cells of the Nervous System
Describe the three major parts of a neuron.
Define neurofibrils and chromatophilic substance.

45. Important Points in Chapter 10: Outcomes to be Assessed
Describe the relationship among myelin, the neurilemma, and the nodes of Ranvier.
Distinguish between the sources of white matter and gray matter.
10.4: Classification of Neurons and Neuroglia
Identify structural and functional differences among neurons.
Identify the types of neuroglia in the central nervous system and their functions.
Describe the Schwann cells of the peripheral nervous system.
10.5: The Synapse
Define presynaptic and postsynaptic.
Explain how information passes from a presynaptic to a postsynaptic neuron.

46. Important Points in Chapter 10: Outcomes to be Assessed
10.6: Cell Membrane Potential
Explain how a cell membrane becomes polarized.
Define resting potential, local potential, and action potential.
Describe the events leading to the conduction of a nerve impulse.
Compare nerve impulse conduction in myelinated and unmyelinated neurons.
10.7: Synaptic Transmission
Identify the changes in membrane potential associated with excitatory and inhibitory neurotransmitters.
10.8: Impulse Processing
Describe the basic ways in which the nervous system processes information.