1. NERVOUS SYSTEM

2. NERVOUS FUNCTIONS Body’s master controlling and communicating system
Three functions
Sensory input
Gathers information from sensory receptors
Integration
Processes and interprets sensory input
Motor output
Activates effector organs to cause a response

3. Nervous System Organization

4. ORGANIZATION Two Principal Parts of the System
Central nervous system (CNS)
Brain and spinal cord
Integrating and command center
Interprets sensory input
Dictates motor responses
Peripheral nervous system (PNS)
Nerves extending from brain and spinal cord
Carry impulses to and from the CNS

5. PERIPHERAL DIVISIONS Two Functional Subdivisions of the PNS
Sensory division
“afferent division”
Nerve fibers conveying impulses to the CNS
Somatic afferent fibers convey impulses from the skin, muscles, and joints
Visceral afferent fibers convey impulses from visceral organs
Motor division
, “efferent division”
Nerve fibers conveying impulses from the CNS

6. ORGANIZATION

7. HISTOLOGY Nervous system consists mainly of nervous tissue
Highly cellular
e.g., <20% extracellular space in CNS
Two principal cell types
Neurons
Excitable nerve cells that transmit electrical signals
Supporting cells
Smaller cells surrounding and wrapping neurons
“Neuroglia”

8. NEURONS Nerve cells Structural units of nervous system
Billions are present in nervous system
Conduct messages throughout body
Nerve impulses
Extreme longevity
Can function optimally for entire lifetime
Amitotic
Ability to divide is lost in mature cells
Cannot be replaced if destroyed
Some (very few) exceptions
e.g., stem cells present in olfactory epithelium can produce new neurons
Stem cell research shows great promise in repairing damaged neurons
High metabolic rate
Require large amounts of oxygen and glucose

9. Dendrites of another neuron
Neurons
Cell Body
Dendrites
Axon
Myelin Sheath
Dendrites of another neuron
Axon of another neuron

10. Collins I 4 lines
Based on the diagram, what do you think each part does to receive and pass along an impulse toward the brain

11. Agenda 11/3/11 – Day 1
Take more notes
HW- vocab

12. NEURONS Generally large, complex cells
Structures vary, but all neurons have the same basic structure
Cell body
Slender processes extending from cell body
Plasma membrane is site of signaling

13. NEURON CELL BODY Most neuron cell bodies are located in the CNS
Protected by bones of skull or vertebral column
Clusters of cell bodies in the CNS are termed “nuclei”
Clusters of cell bodies in the PNS are termed “ganglia”

14. NEURON CELL BODY Major biosynthetic (control) center of neuron
Other usual organelles present except CENTRIOLES
-Why?
What do centrioles do?

15. NEURON PROCESSES Extend from the neuron’s cell body
Two types of neuron processes
Dendrites
Axons

16. NEURON PROCESSES Typical Dendrite
Short, slender, branching extensions of cell body
Generally hundreds clustering close to cell body
Most cell body organelles also present in dendrites
Main receptive / input regions
Large surface area for receiving signals from other neurons
Convey incoming messages toward cell body

17. NEURON PROCESSES Typical Axon Single axon per neuron
The axon forms from the narrowing of the cell body. The region between the large cell body and the axon is the “axon hillock”
Sometimes very short
Sometimes very long
e.g., axons controlling big toe are 3 – 4 feet long

18. NEURON PROCESSES Typical Axon Single axon may branch along length
“Axon collaterals” extend from neurons at ~ 90o angles
Usually branches profusely at end
10,000 or more terminal branches is common
Distal endings termed “axonal terminals”

19. NEURON PROCESSES Typical Axon Conducting component of neuron
Generates nerve impulse
Transmits nerve impulses away from cell body towards the
axonal terminals

20. NEURON PROCESSES Typical Axon terminal
Axonal terminals are secretory component of neuron
Sequence of events
Signal reaches terminals
Membranes of vesicles fuse with plasma membrane
Neurotransmitters released
Neurotransmitters interact with either other neurons or effector cells
Excite or inhibit

21. Vocabulary Either in flash card form OR in list
CNS
PNS
Neuron
Stimulus
Afferent division
Efferent division
neuroglia
Amitotic
Dendrite
Cell body
Axon
Axon terminal
Ganglia
Nuclei (in terms of clusters)

22. Collins I 2 lines
What is the difference between the PNS and the CNS?

23. Agenda 11/4/11 -- Day 2 Remember quiz 11/9 Take notes
Complete labeling and coloring of neuroglia
HW-complete ALL vocab terms

24. MYELIN SHEATH Whitish, fatty covering the axons of many neurons
Protects and electrically insulates fibers
Increases speed of nerve impulse transmission
Some axons and all dendrites are unmyelinated

25. MYELIN SHEATH
In PNS, Schwann cells Continually wrap around the axon of a neuron
Result is many concentric layers of plasma membrane surrounding the axon
Thickness depends on number of wrappings
Nucleus and most of cytoplasm exist as a bulge external to the myelin sheath

26. Myelin sheath and schwann cells
Node of Ranvier
Schwann Cells

27. MYELIN SHEATH Adjacent Schwann cells on axon do not touch each other
Gaps in sheath occur at regular intervals
“Nodes of Ranvier”
Axon collaterals can emerge at these nodes

28. MYELIN SHEATH In CNS, there are both myelinated and unmyelinated axons
Oligodendrocytes, not Schwann cells, form CNS myelin sheaths
Numerous processes that can coil around numerous (up to 60) axons at once

29. NEUROGLIA “Nerve glue”
Six types of small cells associated with neurons
4 in CNS
2 in PNS
Several functions
Supportive scaffolding for neurons
Electrical isolation of neurons
Neuron health and growth

30. CNS NEUROGLIA
Astrocytes
Microglia
Ependymal cells
Oligodendrocytes

31. CNS NEUROGLIA Astrocytes Facilitate nutrient delivery to neurons
Anchor neurons to capillary blood supply
Facilitate nutrient delivery to neurons
(blood  astrocyte  neuron)

32. CNS NEUROGLIA Microglia Small ovoid cells; thorny looking
Transform into macrophage
Phagocytize microorganisms, debris
(Cells of immune system cannot enter the CNS)

33. CNS NEUROGLIA Oligodendrocytes
Wrap processes tightly around thicker neuron fibers in CNS
Makes “Myelin sheath”
Insulating covering

34. CNS NEUROGLIA Ependymal Cells
Line central cavities of brain and spinal cord
Many are ciliated
Beating helps circulate cerebrospinal fluid cushioning brain and spinal cord

35. PNS NEUROGLIA Schwann cells
Surround and form myelin sheaths around larger neurons of PNS
Functionally similar to oligodendrocytes

36. PNS NEUROGLIA
Satellite cells
Surround cell bodies of PNS ganglia

37. HW- Vocab Terms Myelin sheath Schwann cells Nodes of ranvier
Oligodendrocytes
Neuroglea
Astrocyte
Microglia
Ependymal cell
Satalite cell

38. MYELIN SHEATH White matter Gray matter
Regions of the brain and spinal cord containing dense collections of myelinated fibers
Gray matter
Regions of the brain and spinal cord containing mostly nerve cell bodies and unmyelinated fibers

39. NEURON CLASSIFICATION
Structural classification based upon number of processes
Multipolar neurons
Bipolar neurons
Unipolar neurons
Functional classification based upon direction nerve impulse travels
Sensory (afferent) neurons
Motor (efferent) neurons
Interneurons (association neurons)

40. NEURON CLASSIFICATION
Unipolar neurons
Single short process
Process divides into proximal and distal branches
Distal process often associated with a sensory receptor
“Peripheral process”
Central process enters CNS
Most are sensory neurons in PNS
Structural Classification
Multipolar neurons
Three or more processes
Most common neuron type in humans
(> 99% of neurons)
Bipolar neurons
Two processes – axon and dendrite
Found only in some special sense organs
e.g., retina of eye
Act as receptor cells

41. Classification of neurons by shape

42. NEURON CLASSIFICATION
Functional Classification
Sensory (afferent) neurons
Transmit impulses toward CNS
From sensory receptors or internal organs
Most are unipolar
Cell bodies are located outside CNS
Motor (efferent) neurons
Carry impulses away from CNS
Toward effector organs
Multipolar
Cell bodies generally located in the CNS
Interneurons
a.k.a., association neurons
Lie between motor and sensory neurons in neural pathways
Shuttle signals through CNS pathways where integration occurs
> 99% of neurons in body
Most are multipolar
Most are confined within the CNS

43. NEUROPHYSIOLOGY Neurons are highly irritable
Responsive to stimuli
Response to stimulus is action potential
Electrical impulse carried along length of axon
Always the same regardless of stimulus
The underlying functional feature of the nervous system

44. ION CHANNELS Plasma membranes contain various ion channels
Passive channels (leakage channels)
Always open
Active channels (gated channels)
Ligand-gated channels
Open when specific chemical binds
Voltage-gated channels
Open and close in response to membrane potential
Mechanically-gated channels
Open in response to physical deformation of receptor
e.g., touch and pressure receptors

45. MEMBRANE POTENTIALS A voltage exists across the plasma membrane
Due to separation of oppositely charged ions
Potential difference in a resting membrane is termed its “resting membrane potential”
~ -70 mV in a resting neuron
Membrane is “polarized”

46. MEMBRANE POTENTIALS
Neurons use changes in membrane potentials as signals
Used to receive, integrate, and send signals
Changes in membrane potentials produced by
Anything changing membrane permeability to ions
Anything altering ion concentrations
Two types of signals
Graded potentials
Short-distance signals
Action potentials
Long-distance signals

47. MEMBRANE POTENTIALS Graded Potentials
Short-lived local changes in membrane potential
Either depolarizations or hyperpolarizations
Cause current flows that decrease in magnitude with distance
Magnitude of potential dependent upon stimulus strength
Stronger stimulus  larger voltage change
Larger voltage change  farther current flows

48. MEMBRANE POTENTIALS Graded Potentials
Triggered by change in neuron’s environment
Change causes gated ion channels to open
Small area of neuron’s plasma membrane becomes depolarized (by this stimulus)
Current flows on both sides of the membrane
+ moves toward – and vise versa

49. MEMBRANE POTENTIALS Graded Potentials
Inside cell: + ions move away from depolarized area
Outside cell: + ions move toward depolarized area
(+ and – ions switch places)
Membrane is leaky
Most of the charge is quickly lost through membrane
Current dies out after traveling a short distance

50. MEMBRANE POTENTIALS Graded Potentials
Act as signals over very short distances
Important in initiating action potentials

51. MEMBRANE POTENTIALS Action Potentials
Principal means by which neurons communicate
Brief reversal of membrane potential
Total amplitude of ~ 100 mV (-70  +30)
Depolarization followed by repolarization, then brief period of hyperpolarization
Time for entire event is only a few milliseconds
Events in generation and transmission of an action potential identical between neurons and skeletal muscle cells

52. ACTION POTENTIALS

53. ACTION POTENTIALS
Not all local depolarizations produce action potentials
Depolarization must reach threshold values
Brief, weak stimuli produce sub threshold depolarizations that are not translated into nerve impulses
Stronger threshold stimuli produce depolarizing events

54. ACTION POTENTIALS Action potential is all-or-nothing phenomenon
Happens completely or doesn’t happen
Independent of stimulus strength once generated
Strong stimuli generate more impulses of the same strength per unit time
Intensity is determined by number of impulses per unit time

55. ACTION POTENTIALS Multiple Sclerosis (MS)
Autoimmune disease mainly affecting young adults
Myelin sheaths in CNS are gradually destroyed
Interferes with impulse conduction
Visual disturbances, muscle control problems, speech disturbances, etc.
Some modern treatments showing some promise in delaying problems

56. SYNAPSE Nerve impulse reaches axonal terminal
Voltage-gated Ca2+ channels open in axon
Ca2+ enters presynaptic neuron
Neurotransmitter is released via exocytosis
Vesicles fuse with axonal membrane
Neurotransmitter binds to postsynaptic receptors
Ion channels open in postsynaptic membrane
Result is excitation or inhibition

57. SYNAPSE Binding of neurotransmitter to its receptor is reversible
Permeability affected as long as neurotransmitter is bound to its receptor
Neurotransmitters do not persist in the synaptic cleft
Degraded by enzymes associated with postsynaptic membrane
Reuptake by astrocytes or presynaptic terminal
Diffusion of neurotransmitters away from synapse

58. NEUROTRANSMITTERS More than fifty neurotransmitters identified
Most neurons make two or more
Can be released singly or together
Classification by Structure
Acetylcholine (ACh)
Biogenic amines
Amino acids
Peptides
ATP
Dissolved gases
Classification by Function
Excitatory/Inhibitory
Direct/Indirect