1. Chapter 10 *Lecture Outline
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2. 10.1: Introduction Cell types in neural tissue:
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Cell types in neural tissue:
Neurons – transmit impulses
Neuroglial cells – many other functions
Dendrites
Cell body
Nuclei of
neuroglia
Axon
© Ed Reschke

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

4. 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)

5. 10.2: General Functions of the Nervous System
Sensory Function
Sensory receptors gather information
Information is carried to the CNS
Integrative Function
Sensory information used to create sensations, memory, thoughts, decisions
Motor Function
Decisions are acted upon
Impulses are carried to effectors
Divisions of motor functions of PNS
Somatic – transmits impulses to skeletal muscles
Autonomic – transmits impulses to smooth muscles, cardiac muscle, and glands

6. 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 – receiving ends
A cell body – contains nucleus
An axon – transmits impulses and releases neurotransmitters to another neuron or effector

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

8. Myelination of Axons
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Axons which are tightly wrapped by neuroglial cells are termed myelinated.
White Matter
Contains myelinated axons
Considered fiber tracts
Gray Matter
Contains unmyelinated structures
Cell bodies, dendrites
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)

9. 10.4: Classification of Cells of the Nervous System
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

10. 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

11. Classification of Neurons: Functional Differences
Sensory Neurons
Afferent
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
Multipolar
Located in CNS
Cell body
Axon
(central process)
Axon
(peripheral process)
Sensory (afferent) neuron
Interneurons
Motor (efferent) neuron
Axon
Effector
(muscle or gland)
Axon
Motor Neurons
Multipolar
Carry impulses away from CNS
Carry impulses to effectors
Axon
terminal

12. Types of Neuroglial Cells in the CNS
1) Astrocytes
CNS
Scar tissue
Aid metabolism of certain substances
Induce synapse formation
Connect neurons to blood vessels
Part of Blood Brain Barrier
3) Microglia
CNS
Phagocytic cell
4) Ependyma or ependymal
CNS
Ciliated
Line central canal of spinal cord
Line ventricles of brain
2) Oligodendrocytes
CNS
Myelinating cell

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
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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

15. Neuroglia and Axonal Regeneration
Neurons cannot divide
If cell body is injured, the neuron usually dies
If a peripheral axon is injured, it may regenerate

16. Neuroglia and Axonal Regeneration
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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

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 hillock 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. 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) but also by ion channels in the cell membrane.

21. 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
negative ions
High K+
Low K+
Cell body
Axon
Axon terminal
(a) If we imagine a cell before the membrane potential
diffusion of potassium ions out of the cell exceeds
is established, concentration gradients are such that
diffusion of sodium ions into the cell, causing a net
loss of positive charge from the cell. + + + – + – – – + + + – – – + + – – – – – – – + + – – + + + + – + + – +
–70 mV
(b) The net loss of positive charges from the inside
of the cell has left the inside of the cell membrane
slightly negative compared to the outside of the
difference (an electrical “potential difference”) is
membrane, which is left slightly positive. This
measured as –70 millivolts (mV) in a typical neuron,
and is called the resting membrane potential. + + – – + + –
High Na+ –
Low Na+
Na+ – + – +
Pump + – + – K+ + – – –
Low K+
High K+ + + + – + – – + + – + –
–70 mV
is now aided, and potassium diffusion opposed, by the negative charge on
(c) With the membrane potential established, sodium diffusion into the cell
the inside of the membrane. As a result, slightly more sodium ions enter the
cell than potassium ions leave, but the action of the sodium/potassium pump
balances these movements, and as a result the concentrations of these ions,
and the resting membrane potential, are maintained.

22. 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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Gate-like mechanism
Protein
Cell
membrane
Fatty acid
tail
(a) Channel closed
Phosphate
head
(b) Channel open

23. Local Potential Changes
Environmental changes can cause gated ion channels to open
As ions then flow through the membrane, the membrane 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 triggers voltage gated channels to open, causing an action potential
Subthreshold depolarization will not result in action potential

24. 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 (axon hillock)
Na+
Na+
Na+
Na+
Na+
–55 mV
(b)

25. 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+
Threshold
stimulus K+ K+ –0 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)

26. Action Potentials
Trigger zone at first part of axon contains many voltage gated sodium channels
Voltaged gated Na+ channels open in response to threshold
As Na+ moves in the membrane depolarizes until it reaches +30 mV (action potential)
Na+ channels close and K+ channels open
K+ moves out and membrane repolarizes
As membrane potential drops below -70mV, the membrane is hyperpolarized
Active transport reestablishes the resting potential of -70mV as Na+ and K+ concentrations are maintained

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
A nerve impulse is the propagation of action potentials down the length of an axon.
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Region of action potential + + + + + + + + + + + – – – – – – – – – + + – – – – – – – – – + + + + + + + + +
(a) + + + + + + + + + – – – + + – – – – – –
Direction of nerve impulse – – – + + – – – – – – + + + + + + + + +
(b) + + + + + + + + + – – – – – – – + + – – – – – – – – – + + – – + + + + + + + + +
(c)

29. All-or-None Response
If a neuron axon responds at all, it responds completely – with an action potential (nerve impulse)
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

30. 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

31. Impulse Conduction
The speed of impulse conduction varies on different types of neurons.
Myelinated axons transmit impulses through saltatory conduction, which is faster than impulses along unmyelinated axons.
Thick axon fibers transmit faster impulses than thin axon fibers.

33. 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.
Chemically gated ion channels respond to neurotransmitter, creating synaptic potentials.

34. 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

35. 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
Summation usually occurs at the trigger zone
Neuron
cell body
Nucleus
Presynaptic
knob
Presynaptic
axon

36. Neurotransmitters

37. Neurotransmitters

38. Neuropeptides
Neurons in the brain or spinal cord synthesize neuropeptides.
Some neuropeptides act as neurotransmitters.
Other neuropeptides act as neuromodulators (substances which alter a neuron’s response to a neurotransmitter or block the release of a neurotransmitter)
Examples of neuropeptides include:
Enkephalins
Beta endorphin
Substance P

39. 10.8: Impulse Processing
The way the nervous system processes nerve impulses and acts upon them reflects the organization of neurons and axons in the CNS

40. Neuronal Pools
Groups of interneurons that make synaptic connections with each other
Interneurons work together to perform a common function
Each pool receives input from other neurons
Each pool generates output to other neurons
Facilitation may occur

41. 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
(a)

42. Divergence One neuron sends impulses to several neurons
Can amplify an impulse
Impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction
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(b)

43. 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 parts of a neuron.

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

45. Important Points in Chapter 10: Outcomes to be Assessed
10.6: Cell Membrane Potential
Explain how a cell membrane becomes polarized.
Describe the events leading to the generation of an action potential.
Explain how action potentials move down an axon.
Compare impulse conduction in myelinated and unmyelinated neurons.
10.7: Synaptic Transmission
Identify the changes in membrane potential associated with excitatory and inhibitory neurotransmitters.
Explain what prevents a postsynaptic cell from being continuously stimulated.

46. Important Points in Chapter 10: Outcomes to be Assessed
10.8: Impulse Processing
Describe the basic ways in which the nervous system processes information.