Nervous System Overview

1. ivyanatomy.com
Chapter 10

2. Sensory Function:
• Sensory receptors detect changes in the environment (stimuli)
• Information is carried to the CNS on sensory (afferent) neurons
Motor Function:
• Nerve impulses are transmitted from the CNS to PNS on motor
(efferent) neurons
• effectors (muscles or glands) within the PNS cause a change
(effect)
Integrative Function:
• Nervous system maintains homeostasis – detects and responds to
changes in blood pressure, body temp, heart rate, etc.
• Higher intellect: problem solving, thoughts, memory, judgment

3. The Central Nervous System (CNS)
• brain and spinal cord.
The Peripheral Nervous System (PNS)
• 12 pairs of cranial nerves and
• 31 pairs of spinal nerves
• Nerves may be motor (efferent), sensory
(afferent), or both (mixed)
The Central Nervous System is Red, while
the Peripheral Nervous System is Blue.

4. Sensory (Afferent) Division
• Transmits impulses from receptors in the PNS to CNS
Motor (Efferent) Division
• Transmits impulses from CNS to effectors in the PNS

5. Somatic Sensory
• Senses you’re consciously aware of
• Vision, taste, olfaction, smell, hearing
• Touch, vibration, pain
Somatic Motor
• Controls voluntary (skeletal) activities
• Skeletal muscles – voluntary control
Somatic Division is associated with voluntary (skeletal) activities and senses that
detect shapes, textures, sounds, and other external and internal forces acting on
the body.

6. Autonomic Sensory
• Senses that monitor vital conditions within the body
• O2/CO2 levels, pH, Blood Pressure, Body Temp
Autonomic Motor – involuntary control
• Smooth muscles
• Cardiac muscles
• glands
Autonomic Nervous System regulates functions of the internal organs
Heart rate, digestion, sexual arousal, urination

7. Sympathetic Division
• Fight-or-Flight Response
• Prepares body for emergency
Parasympathetic Divsion
• Rest-and-Digest
• Maintains body activities at rest
The Autonomic Nervous System (ANS) is divided into two branches

9. Neurons
• Integrate, regulate, and coordinate body functions
• Transmit nerve impulses (action potentials)
Neuroglia (glia = “glue”)
• Neuroglia provide neurons with nutritional,
structural, and functional support
Neural Tissue contains two Cell Types:

10. Neurons vary in shape and size
Dendrite
Cell Body (soma)
Nucleus
axon
axon terminal
Myelin sheath
Schwann Cell
3 Parts of a Neuron
• Dendrites – receive inputs from other
neurons or other stimuli
• Cell Body (Soma)
• Axon – transmit nerve impulses
away from the cell body towards
other neurons, muscles, or
glands

11. Dendrites
• Dendrites transmit information towards the cell body
• A cell may have many dendrites, few dendrites, or no dendrites
• Dendritic spines – additional contact points on dendrites
• A neuron may add more spines, increasing its sensitivity to incoming
stimuli, or It may remove spines to decrease its sensitivity to stimuli.
Segment of a dendrite (green) with dendritic spines (yellow)

12. Cell Body (Soma)
• Contains organelles such as nucleus, mitochondria, Golgi Apparatus,
neurofilaments, and Rough ER
• Chromatophilic Substances (Nissl Bodies) – mostly Rough ER, protein
synthesis
• Cell body produces proteins for the cell

13. Axon
• Transmits electrical impulses (action potentials)
away from the neuron
• Each neuron has only 1 axon, but it may divide
into several branches, called collaterals.
• Axon Hillock (trigger zone) – specialized site
connected to the cell body, where electrical
impulses (action potentials) are initiated
• Axon terminal – end of the axon.
• Contains enlarged synaptic knob (bouton)
• Neurotransmitters are stored within secretory
vesicles within the synaptic knob.

14. Axon
• Neurofibrils – microtubules that support long axons
• Neurofibrils aid in axonal transport – transports
proteins from the cell body through the axon
• Axoplasm – cytoplasm of the axon
• Axolemma – cell membrane of the axon

15. Myelin Sheath
• Thick fatty coating of insulation surrounding some axons
• Myelin sheath greatly enhances the speed of nerve
impulses
• Schwann Cells form the myelin sheath in the PNS
• Oligodendrocytes form the myelin sheath in the CNS
Schwann cell forming the myelin sheath around an axon within the PNS

16. Schwann Cells
• Schwann Cells myelinate neurons in the PNS
• Schwann Cells wrap around the axon in a jelly-roll
fashion, forming a thick layer of lipid insulation, called
the Myelin Sheath
• Neurilemma – The cytoplasm and nucleus of the
Schwann Cell are pushed outwards, forming an outer
layer, called the neurilemma
• Nodes of Ranvier – gaps of exposed axon between
adjacent Schwann Cells
Myelin sheathNeurilemma (at the nucleus)
Mitochondrion within axon
axon

17. ◊ Not all axons are myelinated
◊ Myelinated axons in the PNS
have a series of Schwann cells
lined up along the axon, each
having a wrapped coating of
myelin insulating the axon
◊ Unmyelinated axons in the PNS
are encased by Schwann cell
cytoplasm, but there is no
wrapped coating of myelin
surrounding the axons
Schwann Cell
axon
axon
Schwann Cell
Myelin sheath

18. Oligodendrocytes
• Oligodendrocytes myelinate
axons in the PNS
• Each oligodendrocyte myelinates
multiple axons
• White Matter – mass of
myelinated axons within the CNS
• Gray Matter – unmyelinated
nervous tissue in the CNS
Oligodendrocyte myelinating several axons.

19. Gray Matter of the Cerebral Cortex
- unmyelinated tissue
White Matter of the Cerebrum
- myelinated tissue

20. Multipolar Neuron
• Many dendrites and 1 axon
• Includes most neurons in the
CNS and motor neurons
dendrites
axon

21. Bipolar Neuron
• 1 dendrite and 1 axon
• Includes some special sensory neurons,
such as photoreceptors and olfactory
neurons.
dendrite
axon

22. Psuedounipolar Neuron
• Contains a single process that acts
as an axon
• Peripheral process – conducts
information from the PNS
• Central process – conducts
information toward the CNS
• Example includes sensory neurons
within the Dorsal Root Ganglia
(DRG)
peripheral process
central process

23. Sensory (afferent) neuron
• Transmit impulses from the PNS towards the CNS
• Most afferent neurons are unipolar. Some are Bipolar.
Motor (efferent) neuron
• Transmit impulses from the CNS towards effectors in the CNS
• Somatic Motor Neurons – voluntary control
• Autonomic Motor Neurons – involuntary control.
Interneuron (association)
• Completely within the CNS
• Interneurons link together in the CNS
• Interneurons connect sensory neurons to motor neurons

24. Peripheral Nervous System Central Nervous System
Sensory receptor Sensory neuron
interneuron
interneuronMotor neuronEffector
(muscle or gland)

25. General Functions of Neuroglia:
• Provide structural and metabolic support for neurons
• Guide developing neurons into position
• Remove excess ions and neurotransmitters
• Strengthen synapses
• Neuroglia outnumber neurons 10 to 1
Neuroglia in the CNS vs. PNS
• Neuroglia of the CNS include: astrocytes, ependymal cells,
microglia, and oligodendrocytes
• Neuroglia of the PNS include: satellite cells and Schwann
Cells

26. Astrocytes:
• Star-shaped cell
• Attaches neuron to blood vessels
• Astrocytes aid in metabolism, strengthen synapses,
and participate in the Blood-Brain-Barrier
Ependymal Cells
• Simple cuboidal epithelium with cilia
• Lines ventricles of the brain and central canal of spinal
cord
• Cover choroid plexuses (capillary networks within CNS)
• Regulate the composition of cerebrospinal fluid (CSF)

27. Microglia:
• Normally small cells until activated
• Enlarge into macrophages with infection
• Phagocytize foreign material
Microglia (green) surrounding nerve processes (red)
Oligodendrocytes:
• Form the myelin sheath within the CNS
• Provide structural support
Oligodendrocyte myelinating several axons within the CNS

28. Schwann Cells:
• Form the myelin sheath in the PNS
• Greatly increase nerve impulse speed
Satellite Cells:
• Surround and support clusters of cell
bodies (ganglia) within the PNS

29. • Mature neurons do not divide
• If cell body is injured, the neuron usually dies
Neuron Regeneration in the PNS:
• If a peripheral axon is injured, it may regenerate
• Axon separated from cell body and its myelin sheath will degenerate
• Schwann cells and neurilemma remain
• Remaining Schwann cells provide guiding sheath for growing axon
• If growing axon establishes former connection, function will return; if not,
function may be lost
Neuron Regeneration in the CNS:
• CNS axons lack neurilemma to act as guiding sheath
• Oligodendrocytes do not proliferate after injury
• Regeneration is unlikely

30. Multiple Sclerosis:
• Autoimmune disease that destroys the
myelin sheath of motor neurons.
• The damaged myelin sheath is replaced
with connective tissue, leaving behind
scars (scleroses)
• The scars block transmission of underlying
neurons, so muscles no longer receive
stimuli
• Muscles atrophy and wither over time
White matter lesions (scleroses) of Multiple Sclerosis

31. Neurons communicate with each other at synapses.
• A synapse is a site at which a neuron
transmits a nerve impulse to another neuron
• Presynaptic neuron sends
impulse (usually) by releasing neurotransmitters
into the synaptic cleft
• Postsynaptic neuron
receives impulse
• Synaptic cleft separates the
2 neurons

32. 1. A nerve impulse (action potential) travels
down the axon to the axon terminal.
2. The action potential opens calcium channels
causing calcium to diffuse into the synaptic
knob.
3. The calcium influx triggers the exocytosis
of neurotransmitters from synaptic
vesicles into the synapse.
4. The neurotransmitters diffuse across the
synapse and bind to receptors on the post-
synaptic cell
5. Neurotransmitter either exerts an excitatory
or inhibitory effect, depending on the
neurotransmitter and the receptor.

33. The cell membrane is usually polarized (charged)
• Inside the membrane is negatively charged relative to outside the membrane
• Polarization is due to unequal distribution of ions across the membrane
•Polarization is maintained by a series of ion pumps and ion channels
•All Cells have a membrane potential.
Cell membrane

34. • Potassium (K+) ions: major intracellular positive ions (cations).
• Sodium (Na+) ions: 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.
• Na+/K+ Pump transports Na+ ions out of cell and K+ ions into cell
• Ion channels, formed by membrane proteins, help regulate passage of
specific ions into or out of the cell
• Many chemical & electrical factors affect opening & closing of gated
channels

35. Non-Gated (Leak) Ion channels,
• Channels are always open, allowing specific
ions to “leak” down their concentration gradient.
• Cells have abundant K+ leak channels, making
them permeable to K+.

36. closed
open
Mechanically-Gated Ion channels,
• Open in response to physical deformation of
the cell membrane
• Touch, Hearing, Pressure, Vibrations, Etc.
Na+

37. Ligand
(molecule)
Ligand-Gated Ion channels,
• Open in response to a ligand
(neurotransmitter, hormone, or other
molecule)
Na+
closed open

38. Voltage-Gated Ion channels,
• Open and close due to small changes in the
membrane potential (millivolts = mV)
• Voltage-gated Na+ channels open when
membrane potential reaches -55mV.
• Voltage-gated K+ channels open as the
membrane potential approaches +35mV
openclosed
-70mV -55mV

39. Sodium-Potassium ATPase (Pump)
• Active Transport Mechanism (uses ATP)
• Pumps 3 Na+ out of the cell
• Pumps 2 K+ into the cell

40. 3 Factors Establish the Membrane Potential
1. Na+/K+ ATPase
2. Non-gated K+ channels
3. Negatively charged proteins and DNA within the cell
Sodium-Potassium ATPase (Pump)
• Pumps 3 Na+ out of the cell, but only 2 K+
into the cell.
• Net positive charges leaving the cell, making
inside negatively charged.
• The Na+/K+ pump only contributes a small
amount (-5mV) to the membrane potential

41. 3 Factors Help Maintain the Cell Membrane Potential
Non-gated Potassium Channels
• Cell has many K+ leak channels, making
it permeable to potassium.
• K+ continually leaks out of the cell,
making the inside of the cell more
negative.
Na+/K+ PumpK+ leak channel
K+
K+ Na+
ATP
ADP + P

42. Resting Membrane Potential (RMP)
• RMP = membrane potential of excitable
cells (neurons and muscles) while at rest.
• For a neuron at rest, the RMP is -70mV
inside the cell.

43. Opening/Closing gated-Ion channels cause changes in local membrane potential
Hyperpolarization
• membrane potential becomes more negative.
• e.g. -100 mV
Depolarization
• membrane potential becomes less negative.
• e.g. -60 mV
Resting Membrane Potential (RMP) of neuron = -70mV
-70mv (RMP)
-70mv (RMP)
Time (ms)

44. • Local potential changes are graded—the greater
the stimulus intensity, the greater the potential
change
• If degree of depolarization reaches threshold
potential of -55 mV, an action potential results
• If degree of depolarization does not reach threshold
potential, an action potential will not occur
subhreshold potential
Graded (Local) Potentials

45. Summation – Graded potentials may add together (summate)
• Spatial summation – stimuli from multiple neurons
• Temporal summation – high frequency stimulation from a presynaptic neuron
• Combination – stimuli from multiple neurons at a high frequency
• If summation reaches threshold potential (-55mV), it initiates an action potential
Example of Spatial Summation Example of Temporal Summation

47. Threshold potential
-70 mV
(RMP) stimulus Subthreshold
potentials
-55 mV
Action Potential
Hyperpolarization

48. Depolarization
• Voltage-Gated Na+ channels open at -55mV (threshold)
• Na+ diffuses into the cell
Repolarization
• Voltage-Gated K+ channels open as cell
depolarizes towards +30mV
• K+ diffuses out of the cell
• Na+ channels close
Hyperpolarization
• K+ channels remain open, causing an overshoot
• Na+/K+ pumps reestablish the RMP.

49. Na+
K+
At rest, the membrane is polarized
(RMP = -70mV). Sodium is mostly outside the
cell and potassium is within the cell.
Resting Membrane Potential

50. Na+
Na+
When a stimulus reaches threshold stimulus (-55mV),
voltage-gated Na+ channels open. Sodium rapidly diffuses
into the cell, depolarizing the membrane up to +30mV.
Depolarization

51. K+Na+
K+
Na+
Repolarization
As the membrane potential approaches +30mV, voltage-
gated K+ channels open and quickly repolarize the
membrane. Sodium channels also close at this point.

52. Na+
K+
Hyperpolarization
K+ channels remain open, causing an overshoot past RMP.
Following an action potential, Na+/K+ pumps actively
reestablish the Na+ and K+ concentration gradients.

53. High K+
High Na+
-70mV -70mV -70mV
Once an action potential is initiated it is propagated along the
entire axon at full strength. It does not weaken.
At rest, Na+/K+ pumps maintain a high
extracellular Na+ concentration and a high
intracellular K+ concentration.

54. • Action Potential begins when Axon Hillock
depolarizes to threshold potential (-55mV)
• Voltage-Gated Na+ channels open, Na+ diffuses
into the cell, depolarizing the region to +30mV
-70mV
+30mV
High Na+

55. High Na+
-55mV -70mV
• Sodium now within the cell diffuses to its
adjacent region, depolarizing it to threshold.

56. • Voltage-Gated Na+ channels in adjacent region
open. Na+ diffuses into the cell, causing another
action potential in the adjacent region.
Na+
K+
• Voltage-Gated K+ channels quickly repolarize the
axon, following the depolarization.

57. High Na+
-55mV -70mV
• Again Sodium diffuses to adjacent region,
depolarizing it to threshold. Another Action
potential follows.
• The action potential continues sequentially along
the entire axon, to the axon terminal.

58. 1. Resting Membrane Potential 1. Na+/K+ pumps, K+ leak channels, and negatively charged
proteins maintain RMP = -70mV
2. Graded Potential - Stimulus 2. Neuron receives stimulus initiating graded potentials
3. Threshold Potential 3. Graded potentials reach threshold, triggering an action
potential
4. Action Potential - Depolarization 4. Voltage-gated, Na+ channels open, sodium diffuses into cell.
5. Action Potential - Repolarization 5. Voltage-gated K+ channels open, potassium diffuses out of
the cell.
6. Action Potential - Hyperpolarization 6. Na+/K+ pumps re-establish RMP at region
7. Action Potential Propagation 7. Sodium diffusing into the cell generates an electrical current
that stimulates adjacent regions of the membrane.
Action potentials occur sequentially along the length of the
axon.
Action Potential propagated along the axon
is often called a nerve impulse.

59. All-or-None Response
• Action Potentials occur completely or they do not occur at all.
• A stronger stimulation does not produce a stronger impulse.
• Instead, a stronger stimulation produces a higher frequency
of nerve impulses (more impulses per second)
weaker stimulus stronger stimulus

60. Refractory Period: For a brief period following an action potential,
a threshold stimulus will not trigger another action potential.
Absolute Refractory Period
• no new action potentials can be produced
• Occurs while the membrane is changing in sodium permeability
• Between the depolarization and repolarization phases
Relative Refractory Period
• Action potential can be generated with a high intensity stimulus
• Occurs while membrane is reestablishing its resting membrane potential
• Lasts from the hyperpolarization phase, until RMP is reestablished

61. Speed of a Nerve Impulse Depends on
• Diameter of the axon: larger diameter = higher velocity
• Myelinated vs Unmyelinated: myelinated neurons are much
faster than unmyelinated neurons.
Unmeylinated Axons must generate action potentials across the entire
axon.
The impulse is slow (travels at 1 mile/hour)

62. Myelinated axons conduct impulses differently than unmyelinated axons.
Unmyelinated Axons
Generate a series of action potentials along the entire axon.
Nerve impulses are slow: travel around 1 mile/hour (0.4 meters/second)
Myelinated Axons
• Myelin is an electrical insulator
• Action potentials of myelinated axons are only generated
at the nodes of Ranvier.
• Nerve impulse through the myelinated portion travels by
electrical conduction
• This is called, salutatory conduction
• Saltatory conduction increases conduction velocity to
around 285 miles/hour (127 meters/second)

63. Unmeylinated Axons must generate action potentials across the entire
axon. The impulse is slow (travels at 1 mile/hour)
Meylinated axons conduct nerve impulses via salutatory conduction:
Electrical conduction through myelin sheath, action potentials only at nodes
of Ranvier. Appears as if nerve impulse “jumps” from node-to-node.
electrical conduction
Node of Ranvier
meyelin sheath

64. 1. A nerve impulse (action potential) travels
down the axon to the axon terminal.
2. The action potential opens calcium channels
causing calcium to diffuse into the synaptic
knob.
3. The calcium influx triggers the exocytosis
of neurotransmitters from synaptic
vesicles into the synapse.
4. The neurotransmitters diffuse across the
synapse and bind to receptors on the post-
synaptic cell
5. Neurotransmitter either exerts an excitatory
or inhibitory effect, depending on the
neurotransmitter and the receptor.

65. Synaptic Transmission
Most neuron communication occurs when a presynaptic neuron releases
neurotransmitters into the synaptic cleft, where the neurotransmitters
subsequently bind to receptors on a postsynaptic cell
Local potentials resulting from changes in
chemically gated ion channels are called synaptic
potentials

66. Excitatory postsynaptic potential (EPSP):
• Membrane change in which neurotransmitter opens Na+ channels (or
Ca2+) channels
• Depolarizes membrane of postsynaptic neuron, as Na+ enters axon
• Action potential in postsynaptic neuron becomes more likely
Inhibitory postsynaptic potential (IPSP):
• Membrane change in which neurotransmitter opens K+ channels (or Cl-
channels)
• Hyperpolarizes membrane of postsynaptic neuron, as K+ leaves axon
• Action potential of postsynaptic neuron becomes less likely

67. EPSPs and IPSPs are added together in a
process called summation
Summation occurs at axon hillock
(trigger zone)
The integrated sum of EPSPs and IPSPs
determines if an action potential occurs
If threshold stimulus is reached an action
potential is triggered.

68. Neurotransmitters
The nervous system produces at least thirty different types of neurotransmitters.
Examples:
1. Acetylcholine – skeletal muscle contractions
2. Monoamines
• Norepinephrine
- in CNS it creates a sense of well-being
- in PNS it may stimulate or inhibit autonomic nervous system
• Dopamine
- in CNS it creates a sense of well-being
- Amphetamines increase the levels of norepinephrine and dopamine
3. Amino Acids
• GABA – inhibitory neurotransmitter of the CNS
• Many sedatives and anesthesia enhances GABA secretions
• Schizophrenia is associated with a deficiency of GABA
4. Gases
• Nitric Oxide
• Vasodilation in PNS

69. Neurotransmitters
Examples:
5. Glutamate – primary excitatory neurotransmitter in the CNS
6. Serotonin – primarily inhibitory. Leads to sleepiness.
7. Substance P – pain perception
8. Endorphins & Enkaphalins – reduce pain by inhibiting substance P release

70. Enzymatic Degridation
• Acetylcholinesterase – decomposes Acetylcholine in the synaptic cleft.
• Monoamine Oxidase – decomposes Epinephrine and Norepinephrine.
• Limits the duration of your sympathetic (fight-or-flight) response.
Reuptake
• Neuroglia and enzymes transport neurotransmitters within the synaptic
cleft back to the synaptic knob of the presynaptic neuron.
• Neurotransmitters are repackaged into new secretory vesicles and used
again.

71. Cocaine
• Cocaine binds to Dopamine transporters, preventing the reuptake of
Dopamine.
• This results in excess dopamine in the synaptic cleft.
Nicotine
• Nicotine binds to Nicotinic receptors on dopaminergic neurons, causing
them to release dopamine.

72. Nerve impulses are processed by the CNS in a way that reflects
the organization of neurons in the brain and spinal cord.
Neuronal Pool
• Organized groups of interneurons within the CNS
• Pools are organized as neuronal circuits that
perform a common function, even though they
may be in different parts of the CNS.
• May have either excitatory or inhibitory effects on
effectors, or other neuronal pools.

73. Neuronal Pools
Convergence
• Several neurons synapse onto one post-synaptic
neuron
• Funnels impulses from several areas onto a
single neuron
• Information from various sensory receptors may
converge onto a single processing center.
Divergence
• Impulses spread from one axon to several post-
synaptic neurons
• May amplify a stimulus
• May send a one signal to multiple parts of the CNS.

74. • Neuron in tissue culture By GerryShaw (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via
Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/7/70/Neuron_in_tissue_culture.jpg
• Nervous System Divisions Diagram By This SVG image was created by Medium69. Cette image SVG a été créée par Medium69.
Please credit this : William Crochot (File:Nervous system diagram.png) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-
sa/4.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/5/5b/Nervous_system_diagram-en.svg
• Divisions of the Nervous System Diagram By Fuzzform at English Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or
CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/0/0b/NSdiagram.png
• Neural Tissue Illustration By Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine.
DOI:10.15347/wjm/2014.010. ISSN 20018762. (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via
Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/7/73/Blausen_0672_NeuralTissue.png
• Neuron Illustrated Hand-Tuned Quasar Jarosz at English Wikipedia [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-
sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/b/bc/Neuron_Hand-tuned.svg
• Dendritic Spines By Hotulainen P, Hoogenraad CC [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via
Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/2/26/Cytoskeletal_organization_of_dendritic_spines_%28ru%29.jpg
• Multipolar Neuron Illustration By BruceBlaus (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via
Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/1/10/Blausen_0657_MultipolarNeuron.png
• Microtubules Tangled High By ADEAR: "Alzheimer's Disease Education and Referral Center, a service of the National Institute
on Aging." [Public domain], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/5/51/TANGLES_HIGH.jpg
• Peripheral Nerve Myelination Illustration By CFCF (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)],
via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/a/a8/Periferal_nerve_myelination.jpg
Attribution

75. • TEM of myelinated neuron Roadnottaken at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-
BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/c/c1/Myelinated_neuron.jpg
• Oligodendrocyte Illustration By Artwork by Holly Fischer [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia
Commons https://upload.wikimedia.org/wikipedia/commons/2/2e/Oligodendrocyte_illustration.png
• Human Brain Sagittal Section By John A Beal, PhD Dep't. of Cellular Biology & Anatomy, Louisiana State University Health
Sciences Center Shreveport [CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/0/0c/Human_brain_right_dissected_lateral_view_description.JPG
• Multipolar Neuron Illustration By Artwork by Holly Fischer [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via
Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/b/bb/Multipolar_Motor_Neuron.png
• Bipolar Neuron Illustration By Artwork by Holly Fischer [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia
Commons https://upload.wikimedia.org/wikipedia/commons/9/9e/Bipolar_Interneuron.png
• Unipolar (pseudounipolar) Neuron By Artwork by Holly Fischer [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via
Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/b/b1/Unipolar_Sensory_Neuron.png
• Central Nervous System By Jordi March i Nogué [1] (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or
GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/f/f1/Central_nervous_system_2.svg
• Astrocyte By GerryShaw (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/6/63/Astrocyte5.jpg
• Ependyma By Martin Hasselblatt MD (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0
(http://creativecommons.org/licenses/by-sa/3.0/) or CC BY-SA 2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)],
via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/b/b7/Ependyma.png
Attribution

76. • Microglia By GerryShaw (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/0/0b/Microglia_and_neurons.jpg
• By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/c/c3/1210_Glial_Cells_of_the_PNS.jpg
• MRI of MS lesions By Veela Mehta, Wei Pei, Grant Yang, Suyang Li, Eashwar Swamy, Aaron Boster, Petra Schmalbrock, David Pitt [CC
BY 2.5 (http://creativecommons.org/licenses/by/2.5) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia
Commons https://upload.wikimedia.org/wikipedia/commons/d/d0/Journal.pone.0057573.g005.png
• Synapse Illustration By Edk006 (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/0/08/Neuronal_Synapse.jpg
• Synapse Illustration By Nrets [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-
sa/3.0/)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/e/e0/Synapse_Illustration2_tweaked.svg
• Resting Membrane Potential By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/d/de/1220_Resting_Membrane_Potential.jpg
• Summation By Sarahadam1 (Own work) [Public domain], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/6/6e/Spacial_and_Temporal_Summation.JPG
• Graded Potentials By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/e/ee/1223_Graded_Potentials-02.jpg
• Action Potential By Original by en:User:Chris 73, updated by en:User:Diberri, converted to SVG by tiZom (Own work) [GFDL
(http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/d/d1/Action_potential_%28no_labels%29.svg
• Action Potentials Stimulus By Original by Curtis Neveu Translated and modified by User:TnoXX [CC BY 3.0
(http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/7/71/Temporal_summation_uk.png
Attribution