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. 10.2: General Functions of the Nervous System
The three general functions of the nervous system:
Receiving stimuli = sensory function
Deciding about stimuli = integrative function
Reacting to stimuli = motor function

7. Functions of Nervous System
Sensory Function
Sensory receptors gather information
Information is carried to the CNS
Motor Function
Decisions are acted upon
Impulses are carried to effectors
Integrative Function
Sensory information used to create:
Sensations
Memory
Thoughts
Decisions

8. 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

9. 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

10. 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)

11. 10.2 Clinical Application
Multiple Sclerosis

12. 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

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

14. 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)

15. 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 20

16. 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

17. 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)

18. Animation: Chemical Synapse
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19. 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.

20. 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.

21. 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

22. 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

23. 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)

24. 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

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

26. Animation: Action Potential Propagation in Myelinated Neurons
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27. Animation: Action Potential Propagation in Unmyelinated Neurons
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28. 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

29. 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

30. Animation: The Nerve Impulse
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31. Factors Affecting Impulse Conduction
10.3 Clinical Application
Factors Affecting Impulse Conduction

32. 10.7: Synaptic Transmission
This is where released neurotransmitters cross the synaptic cleft and react 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.

33. Neurotransmitters

34. Neurotransmitters

35. Neuropeptides
Neurons in the brain or spinal cord synthesize neuropeptides.
These neuropeptides act as neurotransmitters.
Examples include:
Enkephalins
Beta endorphin
Substance P