1. Nervous System and Nervous Tissue

2. Nervous System Master control and communication
Functions (system level and cell level)
Sensory input – monitoring stimuli
Integration – interpretation of sensory input
Motor output – response to stimuli

3. Cellular v. System level
PNS
Dendrites: input
Cell body: integration
Axon: output
CNS
PNS

4. Nervous System Organization
Central nervous system (CNS)
Form: Brain and spinal cord
Function: Integration and command center
Peripheral nervous system (PNS)
Form: Paired spinal and cranial nerves
Function: Carries messages to and from the spinal cord and brain

5. Central Nervous System Peripheral Nervous System
Motor (efferent)
Sensory
(afferent)
Somatic
(voluntary)
Autonomic
(involuntary)
Parasympathetic
(Stop! )
Sympathetic
(Action! Go!)

6. Peripheral Nervous System (PNS)
INPUTS: Sensory (afferent) division
Sensory afferent fibers – from skin, skeletal muscles, and joints to the brain
Visceral afferent fibers – from visceral organs to the brain
OUTPUTS: Motor (efferent) division
Transmits impulses from the CNS to effector organs

7. Motor Division Organization
Somatic nervous system (SNS)
Conscious control of skeletal muscles
Autonomic nervous system (ANS)
Regulates involuntary muscle (smooth and cardiac) and glands
Sympathetic (Stimulates = Go!)
Parasympathetic (Conserves = Stop!)

8. The Autonomic Nervous System
Is part of the CNS
Is part of the PNS 25

9. The Central Nervous System
Includes only the brain
Includes the brain and spinal cord
Includes the brain, spinal cord and all peripheral nerves 25

10. Nervous System Cell Types
Neurons
Transmit electrical signals
Neuroglia (“nerve glue”)
Supporting cells
Neuroglia in the CNS
Astrocytes
Microglia
Ependymal cells
Oligodendrocytes
Neuroglia in the PNS
Satellite cells
Schwann cells

11. Neurons Structural units of the nervous system Long-lived (100+ years)
Amitotic (no centrioles = can’t divide)
High metabolic rate (glucose gobblers!)

12. Neuron Classification (function)
Sensory (afferent)
transmit impulses toward the CNS
Motor (efferent)
transmit impulses away from the CNS
Interneurons (association neurons)
shuttle signals through CNS pathways

13. Neuron (nerve cell) Neuron cell body Cell body Dendrites Dendritic
(a)
Dendrites
Cell body
Nissl bodies
Axon terminals
(secretory component)
Axon hillock
Node of Ranvier
Impulse
direction
Schwann cell
Neuron cell body
Dendritic
spine

14. Nerve Cell Body (Soma) Contains nucleus and nucleolus
Major biosynthetic center
Focal point for the outgrowth of neuronal processes (dendrites and axons)
Axon hillock – where axons arise

15. Neuronal processes (fibers)
Dendrites
Numerous
Short and tapering
Diffusely branched
Contain “spines” where synapses form
Axons
One per cell
Long (up to 4 ft. in length)
Form synapses at terminals (release neurotransmitters)
Anterograde and retrograde transport (out and back!)

16. Supporting Cells: Neuroglia
Provide a supportive scaffolding for neurons
Segregate and insulate neurons
Guide young neurons to the proper connections
Promote health and growth
Help regulate neurotransmitter levels
Phagocytosis

17. Astrocytes Most abundant and versatile
Cling to neurons and synaptic endings
Cover capillaries (blood-brain barrier)
Support and brace neurons
Guide migration of young neurons
Control the chemical environment

18. Microglia Monitor health of neurons
Transform into macrophages to remove cellular debris, microbes and dead neurons
NOTE: Normal immune system cells can’t enter CNS

19. Ependymal Cells Shape: squamous to columnar (often ciliated)
Location: Line the central cavities of the brain and spinal column
Function: Circulate cerebrospinal fluid

20. Oligodendrocytes Wrap CNS axons like a jelly roll
Form insulating myelin sheath

21. Schwann Cells and Satellite Cells
Surround axons of the PNS
Form insulating myelin sheath
Satellite cells
Surround neuron cell bodies
Nodes of Ranvier

22. Myelin Sheath and Neurilemma
White, fatty sheath protects long axons
Electrically insulates fibers
Increases the speed of nerve impulses
Neurilemma
remaining nucleus and cytoplasm of a Schwann cell

23. Axons of the CNS Both myelinated and unmyelinated fibers are present
Oligodendrocytes insulate up to 60 axons each
White matter: dense collections of myelinated fibers
Gray matter: mostly soma and unmyelinated fibers

24. Which cell myelinates CNS neurons?
Schwann cells
Ependymal cells
Oligodendrocytes 25

25. The inputs to a neuron are the…
Cell body (soma)
Dendrites
Axons 25

26. Which cell forms the blood-brain barrier?
Schwann cells
Ependymal cells
Astrocytes
Microglia 25

27. Which is NOT found in the CNS?
Schwann cells
Ependymal cells
Astrocytes
Microglia 25

28. Action Potentials (nerve impulse)
Electrical impulses carried along the length of axons
Always the same regardless of stimulus
Based on changes in ion concentrations across plasma membrane
This is HOW the nervous system functions

29. Electricity Definitions
Voltage (V)
potential energy from separation of charges (+ and -)
For neurons, measured in millivolts
Current (I)
the flow of electrical charge between two points
Insulator
substance with high electrical resistance
Think myelin sheath!

30. Ion Channels Passive (leakage) channels: always open
Voltage-gated channels: open and close in response to membrane potential
Ligand-gated (chemically gated) channels: open when a specific neurotransmitter binds
Mechanically gated channels: open and close in response to physical forces

31. Let’s review! The sodium-potassium pump

32. Voltage-Gated Channels

33. Chemically Gated Channels

34. Gated Channels When gated channels are open:
Ions move along electro-chemical gradients
Takes into account charge differences
Takes into account concentration differences
An electrical current is created
Voltage changes across the membrane

35. Measuring Membrane Potential

36. Resting Membrane Potential
Resting membrane potential (–70 mV)
The inside of a cell membrane has more negative charges than outside the membrane
Major differences are in Na+ and K+

37. Changes in Membrane Potential
Depolarization
the inside of the membrane becomes less negative
Hyperpolarization
the inside of the membrane becomes more negative than the resting potential
Repolarization
the membrane returns to its resting membrane potential

38. Action Potentials = nerve impulse
Principal means of neural communication
A brief reversal of membrane polarity
All or nothing event
Maintain their strength over distance
Generated only by muscle cells and neurons

39. Phases of an Action Potential
Resting state
Depolarization
Repolarization
Hyperpolarization
Return to resting potential

40. Action Potential: Resting State
Na+ and K+ GATED channels are closed
Each Na+ channel has two voltage-regulated gates
Activation gates
Inactivation gates

41. Action Potential: Depolarization
Na+ permeability increases; membrane potential reverses
Na+ gates are opened, but K+ gates are closed
Threshold: critical level of depolarization (-55 to -50 mV)
Once threshold is passed,action potential fires

42. Action Potential: Repolarization
Sodium inactivation gates close
Voltage-sensitive K+ gates open
K+ rushes out
Interior of the neuron is negative again

43. Action Potential: Hyperpolarization
Potassium gates remain open
Excess K+ leaves cell
Membrane becomes hyperpolarized
Neuron is insensitive to stimuli until resting potential is restored

44. Return to resting potential: Sodium-potassium pump
Repolarization
ONLY restores the electrical differences across the membrane
DOES NOT restore the resting ionic conditions
Sodium-potassium pump restores ionic conditions
More sodium outside
More potassium inside

45. Resting state Hyperpolarization Depolarization Repolarization Sodium
channel
Na+
Potassium
channel
Activation
gates K+
Inactivation gate
Na+
Na+ 1
Resting state K+ K+ 4
Hyperpolarization
Na+ 2
Depolarization K+ 3
Repolarization

46. ACTION! http://outreach.mcb.harvard.edu/animations/actionpotential.swf

47. Absolute and Relative Refractory Periods

48. Refractory Periods Absolute refractory period (NO WAY! NO HOW!)
Neuron CANNOT generate an action potential
Ensures that each action potential is separate event
Enforces one-way transmission of nerve impulses
Relative refractory period (Well, maybe…)
Threshold is elevated
Only strong stimuli can generate action potentials

49. Propagation of an Action Potential
–70
+30
(a) Time = 0 ms
(b) Time = 2 ms
(c) Time = 4 ms
Voltage
at 2 ms
at 4 ms
at 0 ms
Resting potential
Peak of action potential
Hyperpolarization
Membrane potential (mV))

50. Action Potential Frequency
Stronger stimuli generate more frequent action potentials

51. How fast does a signal travel?
Velocity determined by
Axon diameter
the larger the diameter, the faster the impulse
Presence of a myelin sheath
Myleinated neurons have much faster impulses
Why? Node-jumping! (Saltatory conduction)

52. Saltatory Conduction

53. Sodium rushes into the cell during…
Depolarization
Repolarization
Hyperpolarization

54. Hyperpolarization means…
The inside is more negative
The cell has crossed threshold
The inside is more positive

55. During an absolute refractory period…
Action potentials absolutely fire
Action potential can never fire
The cell is hyperpolarized

56. Multiple Sclerosis (MS)
Cause: Autoimmune disease with symptoms appearing in young adults (women at highest risk)
UNKNOWN environmental and genetic factors
Symptoms: visual disturbances, weakness, loss of muscular control, incontinence
Physiology
Myelin sheaths in the CNS are destroyed, producing a hardened lesion (scleroses)
Shunting and short-circuiting of nerve impulses occurs
Alternating periods of relapse and remission

57. Multiple Sclerosis Treatment Prognosis
Drugs that modify immune response
Prognosis
Medications can prevent symptoms from worsening
Reduce complications
Reduce disability
HOWEVER, not all drugs work long-term in all patients

58. Synapses Junction for cell  cell communication Presynaptic neuron
Neuron neuron
Neuron  effector cell
Presynaptic neuron
Conducts impulses toward the synapse
Postsynaptic neuron/cell
Receives signal
May/may not act on signal

59. Synapses

60. Electrical Synapses (fast)
Less common
Resemble gap junctions
Allow direct ion flow cell  cell
Important in the CNS
Neural development
Synchronization of activity
Emotions and memory

61. Electrical Synapses

63. Chemical Synapses (slower)
Most common
Excitatory or inhibitory
Communication by neurotransmitters
Presynaptic neuron releases neurotransmitter
Postsynaptic neuron has membrane-bound receptors
Neurotransmitters must be recycled, removed or degraded after release

64. Chemical Synapses
vesicles
containing
Neurotransmitter
Synaptic
cleft
Ion channel
(closed)
Ion channel (open)
Axon terminal of
presynaptic neuron
Postsynaptic
membrane
Ion channel closed
Ion channel open
Receptor
Degraded
neurotransmitter
Na+
Ca2+ 1 2 3 4 5
Action potential
NOTE: Ion channels are chemically gated, not voltage-gated

65. Neurotransmitter Diversity
Acetylcholine (ACh)
Biogenic amines (dopamine, serotonin)
Amino acids (glutamate, GABA)
Peptides (endorphins, enkephalins)
Novel messengers
ATP
Nitric oxide (why Viagra works!)
Carbon monoxide

66. Neurotransmitter Actions
Direct
Alter ion channels
Rapid response
Important in sensory-motor coordination
Ex.) ACh, GABA, glutamate
Indirect
Work via second messengers and G-proteins
Slower action
Important in memory, learning, and autonomic nervous system
Ex.) dopamine, serotonin, norepinephrine

67. Postsynaptic Potentials
EPSP: excitatory postsynaptic potentials
Cell is depolarized
Ex.) glutatmate
IPSP: inhibitory postsynaptic potentials
Cell is hyperpolarized
Ex.) GABA

68. Postsynaptic Potentials
Will the postsynaptic cell fire? It depends on…
Which neurotransmitter is released
The amount of neurotransmitter released
The length of time the neurotransmitter is bound to receptors
If threshold isn’t reached, no action potential

69. Summation Spatial summation Temporal summation
Multiple potentials arrive at the same time
Number of IPSPs v. EPSPs determine if action potential is generated
Temporal summation
Multiple potentials arrive at different times
Time intervals determine if action potential is generated

70. Summation
NOTE: This is oversimplified. One neuron can receive inputs from thousands of other neurons.

71. Neuronal signaling and health
Depression
Often linked to altered levels of serotonin
Treated with SSRIs (selective serotonin reuptake inhibitors)
Provides greater signal from less neurotransmitter
WARNING: Suicide risk can actually increase in some patients, particularly adolescents and young adults.

72. Neuronal signaling and health
Addiction
Dopamine is essential in “reward” pathways
Triggers pleasurable sensations
Involved in both drug and alcohol addiction
Glutamate is essential in memory pathways
May trigger relapses

73. Neuronal signaling and health
BoTox = botulinum toxin
Works by blocking acetylcholine release at neuromuscular junction
Facial muscles can’t contract, wrinkles disappear
Also used for many spastic disorders
Local anaesthesia
Most block sodium channels, so action potentials aren’t generated

74. Chemical synapses are faster than electrical synapses
True
False 25

75. An inhibitory neurotransmitter will hyperpolarize the postsynaptic cell
True
False
Too confused to even guess! 25

76. Spatial summation involves…
Multiple stimuli from one neuron
Multiple stimuli from multiple neurons
Stimuli separated by time 25

77. Which neurotransmitter is associated with depression?
Dopamine
GABA
Glutatmate
Serotonin 25

78. Which neurotransmitter is associated with addiction?
Dopamine
GABA
Nitric oxide
Acetylcholine 25