1. Neurons: Cellular and Network Properties
Chapter 8a
Neurons: Cellular and Network Properties

2. Organization of Nervous System Cells of the nervous system
About this Chapter
Organization of Nervous System
Cells of the nervous system
Electrical signals in neurons
Cell-to-cell communication in the nervous system
Integration of neural information transfer

3. Physiologically: Anatomically: Afferent (Sensory) receptors
Efferent (Motor)
somatic
autonomic
Sympathetic
Parasympathetic
Anatomically:
Central:
Brain
Spinal Cord
Peripheral:
Nerves
Receptors
Ganglia

5. Organization of the Nervous System
Figure 8-1

6. The Neuron

7. Dendrites receive incoming signals; axons carry outgoing information
Model Neuron
Input
signal
Dendrites
Dendrites receive incoming signals; axons carry outgoing information
Integration
Cell body
Nucleus
Axon hillock
Axon (initial segment)
Myelin sheath
Presynaptic axon terminal
Output signal
Synaptic cleft
Synapse
Postsynaptic dendrite
Postsynaptic neuron
Figure 8-2

8. Anatomic and Functional Categories of Neurons
Sensory neurons
Somatic senses
Neurons for smell and vision
Neurons can be classified according to function or structure
Dendrites
Neurons can be categorized by the number of processes and function
Schwann cell
Axon
Pseudounipolar
Bipolar
(a)
(b)
Figure 8-3a-b

9. Anatomic and Functional Categories of Neurons
Interneurons of CNS
Axon
Dendrites
Axon
Anaxonic
Multipolar
(c)
(d)
Figure 8-3c-d

10. Anatomic and Functional Categories of Neurons
Efferent neuron
Dendrites
Axon
Axon terminal
Multipolar
(e)
Figure 8-3e

11. Cells of NS: Glial Cells and Their Functions
Glial cells provide physical and biochemical support for neurons.
are found in
Peripheral nervous system
contains
Satellite cells
Schwann cells
forms
Myelin sheaths
secrete
Support cell bodies
Neurotrophic factors
(b) Glial cells and their functions
Figure 8-5b (1 of 2)

12. Cells of NS: Glial Cells and Their Functions
are found in
Central nervous system
contains
Oligodendrocytes
Microglia (modified immune cells)
Ependymal cells
Astrocytes
forms
act as
Myelin sheaths
Scavengers
provide
help form
secrete
take up
create
Blood- brain barrier
Source of neural stem cells
Barriers between compartments
Substrates for ATP production
Neurotrophic factors
K+, water, neurotransmitters
(b) Glial cells and their functions
Figure 8-5b (2 of 2)

13. Amyotrophic Lateral sclerosis (ALS
ALS has been linked to a mutation on the gene coding for superoxide dismutase.
Microglia use reactive oxygen species (superoxides) to destroy, may lead to oxidative stress and neurodegeneration
A-myo-trophic comes from the Greek language. "A" means no or negative. "Myo" refers to muscle, and "Trophic" means nourishment–"No muscle nourishment." When a muscle has no nourishment, it "atrophies" or wastes away.

14. Cells of NS: Glial Cells and Their Functions
Ependymal cell
Interneurons
Microglia
Capillary
Astrocyte
Myelin (cut)
Axon
Section of spinal cord
Node
Oligodendrocyte
(a) Glial cells of the central nervous system
Figure 8-5a

15. Cells of NS: Schwann Cells
Schwann cell nucleus is pushed to outside of myelin sheath.
Nucleus
Axon
Myelin consists of multiple layers of cell membrane.
(a) Myelin formation in the peripheral nervous system
Schwann cell wraps around the axon many times.
Sites and formation of myelin
Figure 8-6a

16. Cells of NS: Schwann Cells
Cell body
1–1.5 mm
Node of Ranvier is a section of unmyelinated axon membrane between two Schwann cells.
Schwann cell nucleus is pushed to outside of myelin sheath.
Axon
Myelin consists of multiple layers of cell membrane.
(b) Each Schwann cell forms myelin around a small segment of one axon.
Figure 8-6b

17. Multiple Sclerosis
Nystagmus - involuntary eye movement

18. Electrical Signals: Nernst Equation
Describes the membrane potential that a single ion would produce if the membrane were permeable to only that ion
Membrane potential is influenced by
Concentration gradient of ions
Membrane permeability to those ions

19. Electrical Signals: GHK Equation
Predicts membrane potential that results from the contribution of all ions that can cross the membrane

20. Electrical Signals: Ion Movement
Resting membrane potential determined primarily by
K+ concentration gradient leak channels open
Cell’s resting permeability to K+, Na+, and Cl–
Gated channels control ion permeability
Mechanically gated
Pressure or stretch
Chemical gated
Ligands, NTs
Voltage gated
Membrane potential change
Threshold voltage varies from one channel type to another (minimum to open or close)

21. Electrical Signals: Channel Permeability
Table 8-3

22. Electrical Signals: Graded Potentials
Graded potentials decrease in strength as they spread out from the point of origin
Figure 8-7

23. Electrical Signals: Graded Potentials
Subthreshold and (supra)threshold graded potentials in a neuron
Figure 8-8a

24. Electrical Signals: Graded Potentials
Figure 8-8b

25. Electrical Signals: Action Potentials1
Resting membrane potential 2
Depolarizing stimulus 3
Membrane depolarizes to threshold. Voltage-gated Na+ channels open quickly
and Na+ enters cell. Voltage-gated K+ channels begin to open slowly. 4
Rapid Na+ entry depolarizes cell. 5
Na+ channels close and slower K+ channels open. 5 6
K+ moves from cell to extracellular fluid. 7
K+ channels remain open and additional K+ leaves cell, hyperpolarizing it. 6 8 4
Voltage-gated K+ channels close, less K+ leaks out of the cell. 9
Cell returns to resting ion permeability and resting membrane potential.
Threshold 3 1 2 7 9 8
Figure 8-9 (1 of 2)

26. Electrical Signals: Action Potentials
Figure 8-9 (2 of 2)

27. Electrical Signals: Voltage-Gated Na+ Channels
Na+ channels have two gates: activation and inactivation gates
Na+
ECF
ICF
Activation gate
Inactivation gate
(a) At the resting membrane potential, the activation gate closes the channel.
Figure 8-10a

28. Electrical Signals: Voltage-Gated Na+ Channels
Figure 8-10b

29. Electrical Signals: Voltage-Gated Na+ Channels
Figure 8-10c

30. Electrical Signals: Voltage-Gated Na+ Channels
Figure 8-10d

31. Electrical Signals: Voltage-Gated Na+ Channels
Figure 8-10e

32. Electrical Signals: Ion Movement During an Action Potential
Figure 8-11

33. Electrical Signals: Refractory Periods
Both channels closed
Na+ channels open
Both channels closed
Na+ channels close and K+ channels open
Na+ channels reset to original position while K+ channels remain open
Na+
Na+ and K+ channels K+ K+ K+
Absolute refractory period
Relative refractory period
Action potential
Na+
Membrane potential (mV)
Ion permeability K+
High
High
Excitability
Increasing
Zero
Time (msec)
Figure 8-12

34. Electrical Signals: Coding for Stimulus Intensity
Na+ and K+ [ ]’s change very little
1 in K+ leave to shift from +30 to -70mVolts
Na/K pump will re-establish, but neuron without pump can still 1000x
Figure 8-13a

35. Electrical Signals: Coding for Stimulus Intensity
Figure 8-13b

36. Electrical Signals: Trigger Zone
Graded potential enters trigger zone
Voltage-gated Na+ channels open and Na+ enters axon
Positive charge spreads along adjacent sections of axon by local current flow
Local current flow causes new section of the membrane to depolarize
The refractory period prevents backward conduction; loss of K+ repolarizes the membrane

37. Electrical Signals: Trigger Zone
Figure 8-14

38. Electrical Signals: Conduction of Action Potentials
Trigger zone 1
A graded potential above
threshold reaches the
trigger zone.
Axon 2
Voltage-gated Na+ channels
open and Na+ enters the axon. 3
Positive charge flows into adjacent
sections of the axon by local current flow. 4
Local current flow from the
active region causes new sections
of the membrane to depolarize. 5
The refractory period prevents backward
conduction. Loss of K+ from the cytoplasm
repolarizes the membrane.
Refractory
region
Active region
Inactive region
Figure 8-15

39. Electrical Signals: Conduction of Action Potentials
Trigger zone 1
A graded potential above
threshold reaches the
trigger zone.
Axon
Figure 8-15, step 1

40. Electrical Signals: Conduction of Action Potentials
Trigger zone 1
A graded potential above
threshold reaches the
trigger zone.
Axon 2
Voltage-gated Na+ channels
open and Na+ enters the axon.
Figure 8-15, steps 1–2

41. Electrical Signals: Conduction of Action Potentials
Trigger zone 1
A graded potential above
threshold reaches the
trigger zone.
Axon 2
Voltage-gated Na+ channels
open and Na+ enters the axon. 3
Positive charge flows into adjacent
sections of the axon by local current flow.
Figure 8-15, steps 1–3

42. Electrical Signals: Conduction of Action Potentials
Trigger zone 1
A graded potential above
threshold reaches the
trigger zone.
Axon 2
Voltage-gated Na+ channels
open and Na+ enters the axon. 3
Positive charge flows into adjacent
sections of the axon by local current flow. 4
Local current flow from the
active region causes new sections
of the membrane to depolarize.
Refractory
region
Active region
Inactive region
Figure 8-15, steps 1–4

43. Electrical Signals: Conduction of Action Potentials
Trigger zone 1
A graded potential above
threshold reaches the
trigger zone.
Axon 2
Voltage-gated Na+ channels
open and Na+ enters the axon. 3
Positive charge flows into adjacent
sections of the axon by local current flow. 4
Local current flow from the
active region causes new sections
of the membrane to depolarize. 5
The refractory period prevents backward
conduction. Loss of K+ from the cytoplasm
repolarizes the membrane.
Refractory
region
Active region
Inactive region
Figure 8-15, steps 1–5

44. Electrical Signals: Action Potentials Along an Axon
Figure 8-16b

45. Electrical Signals: Speed of Action Potential
Speed of action potential in neuron influenced by
Diameter of axon
Larger axons are faster
Resistance of axon membrane to ion leakage out of the cell
Myelinated axons are faster

46. Electrical Signals: Myelinated Axons
Saltatory conduction
Figure 8-18a

47. Electrical Signals: Myelinated Axons
Figure 8-18b

48. Electrical Signals: Chemical Factors
Effect of extracellular potassium concentration of the excitability of neurons
Figure 8-19a

49. Electrical Signals: Chemical Factors
Figure 8-19b

50. Electrical Signals: Chemical Factors
Figure 8-19c

51. Electrical Signals: Chemical Factors
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Figure 8-19d