Introduction to the Nervous System Chapter 12 Lecture Notes - PowerPoint PPT Presentation

1 / 127
About This Presentation
Title:

Introduction to the Nervous System Chapter 12 Lecture Notes

Description:

functional cell responsible for nervous system signaling. neuroglia ... The Nervous System Maintains Homeostasis and Integrates All Body Activities ... – PowerPoint PPT presentation

Number of Views:3820
Avg rating:3.0/5.0
Slides: 128
Provided by: there67
Category:

less

Transcript and Presenter's Notes

Title: Introduction to the Nervous System Chapter 12 Lecture Notes


1
Introduction to the Nervous SystemChapter 12
Lecture Notes
  • to accompany
  • Anatomy and Physiology From Science to Life
  • by
  • Gail Jenkins, Christopher Kemnitz, Gerard J.
    Tortora

2
Chapter Overview
  • 12.1 System Overview
  • 12.2 System Organization
  • 12.3 The Neuron
  • 12.4 Neuroglia
  • 12.5 Neural Communication
  • 12.6 Graded Potentials
  • 12.7 Action Potentials
  • 12.8 Impulse Propagation
  • 12.9 Synapse
  • 12.10 Repair and Regeneration

3
Essential Terms
  • neuron
  • functional cell responsible for nervous system
    signaling
  • neuroglia
  • supporting cells of the nervous system
  • nerve
  • bundle of neurons
  • neurotransmitter
  • chemical signal

4
Nervous System Overview
  • Role Maintain homeostasis
  • Sense changes (sensory neurons)
  • Integrate information (interneurons)
  • Respond (motor neurons)
  • Basic Anatomy
  • Mass 2 kg or 4.5 lbs 3 total body mass
  • Main Subdivisions
  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)

5
Concept 12.1The Nervous System Maintains
Homeostasis and Integrates All Body Activities
6
Nervous System Anatomy
  • Structures
  • brain
  • spinal cord
  • nerves
  • ganglia
  • enteric plexuses
  • sensory receptors

7
Brain
  • Part of CNS
  • Enclosed by the skull
  • Cranial nerve associations
  • Attached to spinal cord

8
Spinal Cord
  • Part of CNS
  • Connects to brain
  • Leaves skull through foramen magnum
  • Encircled by vertebrae
  • Spinal nerve associations

9
Nerves
  • Part of PNS
  • Cranial nerves
  • 12 pair
  • Emerge from base of brain
  • Spinal nerves
  • 31 pair
  • Emerge from spinal cord
  • Each nerve follows defined path
  • Each nerve serves specific region of body

10
Ganglia
  • Mass of nervous tissue in PNS
  • Collection of neurons
  • Closely associated with cranial and spinal nerves
  • Use of term
  • Ganglia is plural
  • Ganglion is singular

11
Enteric Plexuses
  • Located in walls of gastrointestinal tract
  • Help regulate digestive system function
  • Checkpoint
  • To which subdivision of the nervous system would
    the enteric plexuses belong?

12
Sensory Receptors
  • Monitor internal environment
  • Monitor external environment

13
Nervous System Physiology
  • Responsible for
  • Perceptions (five senses)
  • Behaviors
  • Memories
  • Movements
  • Three main functions
  • Sensory function
  • Integrative function
  • Motor function

14
1. Sensory Function
  • Sensory or Afferent neurons
  • Carry information from PNS to CNS
  • Signal travels through both cranial and spinal
    nerves
  • Detect stimuli
  • Internal (blood acidity)
  • External (raindrop on arm)

15
2. Integrative Function
  • Primarily Interneurons
  • Short axons in CNS
  • Contact nearby neurons in brain, spinal cord or
    ganglion
  • Most neurons are interneurons
  • Process information from afferent (sensory)
    neurons by
  • Analyzing information
  • Storing information
  • deciding appropriate response

16
3. Motor Function
  • Motor or Efferent neurons
  • Carry information from the CNS to the PNS
  • Respond to interneuron decisions
  • Cells responding are effectors
  • Examples include muscle fibers glandular cells

17
Concept 12.2 CNS consists of the Brain and
spinal cord- PNS consists of all other nervous
tissue
18
Nervous System Organization
  • Central Nervous System (CNS)
  • Brain
  • Spinal cord
  • Peripheral Nervous System (PNS)
  • Cranial nerves
  • Spinal nerves
  • Spinal nerve branches
  • Ganglia
  • Sensory receptors

19
Nervous System Organization
20
Central Nervous System
  • Integrates and correlates incoming sensory
    information
  • Source of thoughts, emotions, memories
  • Most motor signals originate in CNS

21
Peripheral Nervous System
  • Subdivisions of PNS
  • Somatic Nervous System (SNS)
  • Motor portion under voluntary control
  • Autonomic Nervous System (ANS)
  • Motor portion under involuntary control
  • Further subdivided
  • Sympathetic nervous system
  • Parasympathetic nervous system
  • Enteric nervous system (ENS)

22
1. Somatic Nervous System
  • A. Sensory input from somatic receptors
  • B. Motor output
  • voluntary control
  • carry impulses from CNS to skeletal muscles only

23
2. Autonomic Nervous System
  • A. Sensory input from autonomic receptors
  • B. Motor output to smooth muscle, cardiac muscle,
    glands
  • involuntary control
  • carry impulses to
  • sympathetic division
  • fight or flight response
  • parasympathetic divisions
  • return to normal

24
3. Enteric Nervous System
  • A. Sensory input from plexuses of GI tract
  • B. Motor output to plexuses of GI tract
  • innervate smooth muscle, glands, and endocrine
    cells of GI tract
  • involuntary control

25
Concept 12.3 Neurons Are Responsible For Most
Unique Functions Of The Nervous System
26
Neurons
  • Functional cell of nervous system
  • Bundled into nerves
  • Are excitable
  • Respond to stimuli
  • Can produce action potentials or impulses
  • Supported by neuroglia
  • Most are amitotic

27
Anatomy of a Neuron
28
Basic Anatomy of a Neuron
Cell Body
Dendrites
Axon
29
Collect signals
Dendrites
30
Dendrites
  • multiple processes
  • collect signals
  • usually short, tapering, highly branched

31
Cellular Metabolism
Cell Body
32
Cell Body of Neuron
  • Cellular Metabolism
  • Size from 5µm up to 135µm
  • Nucleus surrounded by cytoplasm
  • Typical cellular organelles
  • Lack centrioles (no mitosis)
  • Nissl bodies are prominent clusters of rough ER
  • Cytoskeletal elements
  • neurofibrils give cells shape and support
  • microtubules move materials to and through axon

33
Sends signal
Axon
34
Axon
  • single process
  • sends signal away toward target cell
  • long, thin, cylindrical
  • cytoplasm called axoplasm
  • membrane called axolemma
  • axon branches axon collaterals
  • end at axon terminals
  • some swell into synaptic end bulbs

35
Axon
  • axon joins cell body at axon hillock
  • first part called initial segment
  • trigger zone
  • where impulses arise at junction of hillock and
    initial segment
  • newly synthesized substances moved via motor
    proteins and microtubules
  • toward end bulbs process called anterograde
    transport
  • toward cell body process called retrograde
    transport

36
Cell Body
Dendrites
Axon Hillock (trigger zone)
Axon
Axon Terminals
Synaptic End Bulbs
37
Structural Classification
  • multipolar
  • several dendrites
  • one axon
  • most CNS neurons
  • bipolar
  • one main dendrite
  • one axon
  • retina of eye, inner ear, olfactory CNS
  • unipolar
  • embryonic sensory neurons

38
Structural Classification
39
Concept 12.4 Neuroglia Support, Nourish, And
Protect Neurons And Maintain Homeostasis
40
Neuroglia
  • Supporting cells of the nervous system
  • one-half of the volume of CNS
  • 5 to 50 times more numerous
  • smaller than neurons
  • no action potentials
  • highly mitotic

41
Neuroglia
  • CNS
  • astrocytes
  • oligodendrocytes
  • microglia
  • ependymal cells
  • PNS
  • Schwann cells
  • satellite cells

42
CNS - Neuroglia
  • Astrocytes
  • maintain chemical environment, support, and
    nourish
  • Oligodendrocytes
  • produce myelin sheath around adjacent axons
  • Microglia
  • migrating phagocytes
  • engulf invaders and injured tissue
  • Ependymal cells
  • form and circulate cerebrospinal fluid (CSF)

43
Astrocyte
44
Oligodendrocyte
45
Microglia
46
(No Transcript)
47
PNS - Neuroglia
  • Satellite cells
  • support cells within PNS ganglia
  • Schwann cells
  • produce myelin sheath around axons
  • participate in regeneration of PNS axons

48
Satellite Cells
49
Schwann Cells
50
Schwann Cells
51
Myelination
  • multilayered lipid and protein covering
  • insulates axons
  • greatly increases speed of impulse
  • produced by neuroglia
  • CNS oligodendrocytes
  • PNS Schwann cells
  • amount increases from birth to maturity
  • increasing coordination and speed of responses to
    stimuli as individual matures

52
Myelination Schwann Cells
  • begin formation in fetal development
  • each wraps 1mm of axon
  • cytoplasm and nucleus form outer layer
  • wraps approximately 100 times around
  • neurolemma is outermost layer
  • when axon is injured neurolemma aids regeneration
    tube guiding and stimulating regrowth of axon
  • spaces between nodes of Ranvier

53
Myelination
54
Unmyelinated Axons
  • Some axons are said to be unmyelinated
  • Schwann Cells are still present but do not wrap
    around and around process

55
Myelination Oligodendrocytes
  • each cell has approximately 15 processes that
    each mylenate axons
  • neurolemma is not present because cell body and
    nucleus not at processes
  • Nodes of Ranvier present, but fewer in number
  • Repair and regeneration of axons less in CNS than
    PNS due to absence of neurolemma and inhibitory
    influence of oligodendrocytes

56
Oligodendrocyte
57
Gray and White Matter of CNS
  • White matter consists primarily of myelinated
    axons
  • white color due to myelin
  • Gray matter consists primarily of neuronal cell
    bodies, dendrites, unmyelinated axons, axon
    terminals, and other neuroglia
  • Nissl bodies and absence of myelin lead to gray
    color

58
Gray and White Matter of CNS
  • Spinal cord
  • Gray matter surrounded by white matter
  • Centrally located H shape to gray matter
  • Brain
  • Mostly white matter surrounded by gray matter
  • Thin shell of gray matter on surface of cerebrum
    and cerebellum
  • Study Hint
  • Brain Spinal cord have opposite layer pattern
    for gray and white matter

59
Brain Gray over White
60
Spinal Cord White over Gray
61
See it?
62
Concept 12.5Neurons Communicate with Other Cells
63
Neuronal Communication
  • Excitable cells generate action potentials
  • electrical signals traveling cell membranes as a
    result of ionic movement into and out of cells
  • Graded potentials
  • used only for short-distance communication
  • Nerve action potential
  • both short and long-distance communication

64
Graded Potential
  • Vary in amplitude according to strength of
    stimulus
  • Travel short distances
  • Occur at
  • sensory receptors
  • dendritic connections
  • Can generate or trigger nerve action potentials

65
Nerve Action Potential
  • Amplitude fixed (all-or-none event)
  • Travel both short and long distances
  • Occur along axons
  • Triggered by
  • graded potentials at sensory receptors and
    dendritic connections

66
Graded Potential
67
Ion Channels
  • Ion channels open and close in response to
    stimuli
  • when open ions move down electrochemical gradient
  • chemical and electrical difference across
    membrane
  • movement constitutes flow of electrical current
    that flips the charge
  • Four main types of ion channels

68
Types of Ion Channels
  • Leakage channel
  • randomly alternate between open closed
  • voltage-gated channel
  • respond to change in voltage
  • ligand-gated channel
  • responds to chemicals stimulus
  • e.g. neurotransmitters, hormones, etc..
  • mechanically gated channel
  • responds to mechanical stimulation
  • e.g. vibration, pressure, stretching

69
Voltage and Ligand Gated Channels
70
Resting Membrane Potential
  • Recall that there is a separation of charges
    across the membrane of excitable cells.
  • Extracellular fluid contains more sodium ions
    than are found inside a cell
  • Cytosol contains more anions and negatively
    charged proteins
  • Thus sodium ions cling to the periplasmic cell
    surface

71
Resting Membrane Potential
  • Cell somewhat permeable to potassium
  • Much less permeable to sodium
  • Sodium quick to rush in when gates open
  • following both electrical and concentration
    gradients
  • Potassium not quick to rush out
  • only has concentration gradient to drive flow

72
Resting Membrane Potential
  • small build-up of anions in cytosol
  • equal build-up of cations in extracellular fluid

73
Change in Membrane Potential
  • Ligand-gated or mechanical-gated Na channels
    open
  • Fast Na influx
  • following electrical concentration gradients
  • Inside of cell becomes less negative

74
Concept 12.6Graded Potentials are the First
Response of a Neuron to Stimulation
75
Graded Potentials
  • Most occur at dendrites or cell body
  • When ligand-gated or mechanical-gated channels
    open or close
  • Slight deviation from resting membrane potential

76
Graded Potentials
  • Hyperpolarization
  • Increases charge difference between inside
    outside of cell
  • inside made even more negative
  • Depolarization
  • Reduces charge difference between inside
    outside of cell
  • inside made less negative

77
Graded Potentials
  • Graded because vary in amplitude (size) depending
    on strength of stimulus
  • larger or smaller signal depending on how many
    ion channels have opened or closed
  • alters the flow of ions
  • producing localized current that can trigger
    action potential when signal strong enough

78
Types of Graded Potentials
  • Postsynaptic potential
  • ligand-gated channel signal
  • neurotransmitters
  • hormones
  • Generator Potential
  • mechanical-gated channel signals
  • sensory receptors

79
Concept 12.7The Action Potential is an
All-or-None Electrical Signal
80
Action Potential Overview
  • Signals or impulses of communication
  • Travel along axons
  • Are all-or-none events
  • Unlike graded potentials
  • Threshold must be reached
  • Two phases
  • Depolarization
  • Repolarization
  • Refractory Periods
  • Absolute refractory period
  • Relative refractory period

81
Primary Location of Gates
Voltage-gated sodium and Potassium Ion channels
Voltage-gated CALCIUM ion channels
Ligand-gated and mechanical-gated channels
82
Events in Neural Signaling
Action Potentials
Synapses
Graded Potentials
83
Resting Membrane Potential
  • Review
  • Resting membrane potential in excitable cell is
    -70mV
  • Membrane positive outside negative inside
  • Anions inside cell that do pass
  • Na concentration high outside low inside
  • K concentration low outside high inside

84
Membrane Potential Changes
  • Graded potentials occur when
  • Ligand-gated or mechanical-gated Na channels
    open
  • Fast Na influx
  • following both electrical concentration
    gradients
  • Inside of cell becomes less negative
  • If change is 15mV action potential occurs

85
Depolarization
  • When graded potential signal is strong enough
    (15mV causing change to -55mV)
  • Trigger zone at axon hillock depolarizes opening
    voltage gated Na channels
  • Fast influx of Na at axon hillock
  • Triggering chain-reaction-like depolarization of
    entire axon as voltage-gated Na open
  • Depolarization peaks at 30mV
  • -70mV 15mV -55mV

86
Ion Gate Activity
  • All voltage-gates closed
  • Threshold reached (-55mV)
  • Fast responding voltage-gated Na channels open
    at activation gate
  • Slow responding voltage-gated K channels open
  • Fast Na influx
  • Membrane potential reaches 30mV
  • K outflow begins
  • Voltage-gated fast Na channels closed at
    inactivation gate
  • Fast Na influx stops
  • K outflow continues

87
(12.14)
88
Action Potential
89
Repolarization
  • Depolarization peaked at 30mV
  • Resting membrane potential must be restored
  • Hyperpolarization occurs first as Na influx
    stops and K outflow continues reducing membrane
    potential
  • When membrane potential reaches less than -55mV
    Na channels return to resting state and K
    channels close
  • Sodium potassium pump cleans up

90
Repolarization
  • At 30mV
  • Na influx stopped
  • K outflow continues until membrane potential is
    less than -55mV
  • After-hyperpolarization phase can occur because
    K gates are slow
  • Membrane potential even less than resting
    membrane potential of -70mV
  • All gates start to return to resting state when
    membrane potential is less than -55mV

91
Refractory Periods
  • Absolute refractory period
  • Second AP not possible
  • Na channels open until Na channels inactivated
  • During stimulus response and depolarization
  • Relative refractory period
  • Second AP possible with larger-than-normal
    stimulus
  • Na channels returned to resting state
  • K channels still open
  • During repolarization and hyperpolarization

92
Action Potential
93
Concept 12.8Nerve Impulses Travel as a Chain
Reaction of Action Potentials Along an Axon
94
Review Location of Gates
Voltage-gated sodium and Potassium Ion channels
Voltage-gated CALCIUM ion channels
Ligand-gated and mechanical-gated channels
95
Events in Neural Signaling
Action Potentials
Synapses
Graded Potentials
96
Events in Neural Signaling
Action Potential Impulse Propagation
Synapses
Graded Potentials
97
Impulse Propagation
  • AP continues as depolarization at one gate region
    triggers depolarization down axon
  • If axon is uninsulated by myelin sheath
  • impulse continues smoothly down axon
  • termed continuous conduction
  • If axon is insulated by myelin sheath
  • impulse jumps from node to node down axon
  • termed saltatory conduction
  • Faster than continuous conduction

98
Impulse Propagation
99
Axon Diameter
  • Recall that axons are also called nerve fibers
  • Larger fibers propagate impulses faster
  • Larger fibers usually myelinated
  • Smallest fibers are unmyelinated and therefore
    propagate impulses slower

100
A Fibers
  • Largest-diameter fibers
  • 5-20µm
  • Myelinated
  • Saltatory conduction
  • Speeds of 12-130m/sec (27-280 mph!)
  • Examples
  • Sensory fine touch, joint position
  • Motor impulses to skeletal muscles

101
B Fibers
  • Mid-size diameter fibers
  • 2-3µm
  • Myelinated
  • Saltatory conduction
  • Speeds of 15m/sec (32 mph!)
  • Examples
  • Sensory viscera to CNS
  • Motor ANS to cardiac muscle, smooth muscle, and
    glands

102
C Fibers
  • Smallest-diameter fibers
  • 0.5-1.5µm
  • Unmyelinated
  • Continuous conduction
  • Speeds of 0.5 to 2m/sec (1-4 mph!)
  • Examples
  • Sensory viscera to CNS, skin for pain, general
    touch, and pressure
  • Motor ANS cardiac muscle, smooth muscle, and
    glands

103
Sensory Stimulus Intensity
  • Frequency of impulses and receptor recruitment
    determines encoding of stimulus intensity
  • Light pressure generates low frequency impulses
    is perceived as low intensity stimulus
  • High pressure generates high frequency impulses
    is perceived as high intensity stimulus
  • A low number of sensory receptors stimulated
    perceived as low intensity stimulus
  • A high number of sensory receptors stimulated
    perceived as high intensity stimulus

104
Comparing Electrical Signals
  • Graded Potentials
  • cell body dendrites
  • ligand mechanical gates
  • shorter propagation
  • variable amplitude
  • longer lasting than AP
  • hyperpolarizing to depolarizing
  • no refractory period

Action Potentials axon hillock axon voltage
gated Na and K longer propagation all-or-none
amplitude shorter lasting than GP depolarization
to repolarization has refractory period
105
Concept 12.9The Synapse is a Special Junction
Between Neurons
106
Synapse
  • Functional junction
  • between two neurons or
  • between neuron and its effector
  • Focus this chapter on neuron-to-neuron
  • Site of action for many therapeutic and addictive
    chemicals

107
Synapse
108
Neuronal Synapse
  • Neural Synapse relationships
  • Axoanonic synapse axon to axon
  • Axodendritic synapse axon to dendrite
  • Axosomatic synapse axon to cell body
  • Presynaptic neuron sends signal
  • Postsynaptic neuron receives signal
  • Two types
  • Electrical Synapses
  • Chemical Synapses

109
Electrical Synapses
  • Direct cell-to-cell communication
  • Cell membranes connected by gap junctions
  • Act like tunnels to connect cytosol of cells
  • Found in smooth and cardiac muscle
  • Rare in CNS
  • Fast communication
  • Synchronized synapses coordinate effector tissue
    response

110
Chemical Synapses
  • Indirect communication between cells
  • Cell membranes separated by synaptic cleft
    between Presynaptic end bulb and postsynaptic
    cell membrane
  • Neurotransmitter released into cleft
  • Post synaptic cell responds with type of
    ligand-gated graded potential called postsynaptic
    potential
  • Exhibit synaptic delay of 0.5milliseconds

111
Chemical Synapses
  • Indirect communication between cells
  • Cell membranes separated by synaptic cleft
    between Presynaptic end bulb and postsynaptic
    cell membrane
  • Neurotransmitter released into cleft
  • Post synaptic cell responds with type of
    ligand-gated graded potential called postsynaptic
    potential
  • Exhibit synaptic delay of 0.5milliseconds

112
Chemical Synapse
  • AP arrives at synaptic end bulb of presynaptic
    neuron
  • Synaptic end bulb voltage gated Ca2 channels
    open resulting in fast Ca2 influx
  • Triggers fusion of synaptic vesicles plasma
    membrane and exocytosis of neurotransmitter into
    synaptic cleft
  • Neurotransmitter fuses with receptors on
    postsynaptic neuron

113
Chemical Synapse
  • Postsynaptic neuron ligand-gated channels open
  • Graded potential results as ions in synaptic
    cleft flow into postsynaptic cell
  • Depolarization occurs if channels are
    ligand-gated Na channels
  • Hyperpolarization occurs if channels are
    ligand-gated Cl- channels
  • If depolarization reaches threshold, action
    potential triggered

114
Signal Transmission
115
Postsynaptic Potentials
  • Excitatory Postsynaptic Potentials (EPSP)
  • Usually open ligand-gated Na, K, and Ca2
    channels
  • Na influx faster Ca2 influx or K outflow and
    depolarization results
  • Low intensity graded potential
  • Inhibitory Postsynaptic Potentials (IPSP)
  • Usually open ligand-gated K or Cl- channels
  • hyperpolarizing postsynaptic neuron
  • Preventing or inhibiting depolarization

116
Summation of Postsynaptic Potentials
  • Summation
  • Integration of input from thousands of synapses
    in CNS
  • Spatial Summation
  • Neurotransmitter released simultaneously by
    several presynaptic axon terminals
  • Temporal Summation
  • Neurotransmitter released by single presynaptic
    axon terminal two or more times in rapid
    succession

117
Summation of Postsynaptic Potentials
118
Net Summation Effects
  • Occurs when both inhibitory and excitatory
    effects are received by one postsynaptic neuron
  • Possible responses include
  • EPSP excitatory effect greater than inhibitory
    effects but no threshold reached
  • Nerve impulse excitatory effect greater than
    inhibitory effect and threshold reached
  • IPSP inhibitory effect greater than excitatory
    effect and membrane hyperpolarizes

119
Neurotransmitter Removal
  • Prevents prolonged or excessive influence of
    neurotransmitter on postsynaptic neuron or
    effector cell
  • Three mechanisms for removal
  • Diffusion of neurotransmitter away from synaptic
    cleft
  • Enzymatic degradation
  • Uptake by cells
  • Back into presynaptic neuron (reuptake)
  • Into nearby neuroglia (uptake)

120
Concept 12.10Neurons In The PNS Have Greater
Capacity For Repair And Regeneration Than Those
Of The CNS
121
Plasticity of Nervous System
  • neuronal plasticity
  • new dendrites
  • new proteins
  • change in synaptic contacts with effectors
  • very limited ability to regenerate
  • replicate or repair themselves

122
Damage and Repair in PNS
  • Neuron and nerve repair can occur if
  • damaged axons and dendrites are associated with
    neurolemma of functional Schwann cell
  • scar tissue formation does not block path

123
Neuronal Repair in PNS
  • Wallerian degeneration
  • Distal portion of axon myelin sheath
    degenerate
  • Debris phagocytized by macrophages
  • Chromatolysis
  • Nissl bodies break up into granular masses
  • Accelerating RNA and protein synthesis
  • Functional Schwann cells undergo mitosis and form
    regeneration tube across injured area
  • Bud of regenerating axon invades regeneration
    tube
  • can grow at rate of about 1.5mm per day
  • eventually connects to effector and some sensory
    or motor function returns

124
Axon Repair in PNS (12.19)
125
Neuronal Repair in CNS
  • Most injury in CNS is permanent
  • Little or no repair of damage to neurons occurs
  • Myelination occurs by oligodendrocytes
  • which do not form neurolemma
  • therefore no regeneration tubes form
  • Following axonal damage astrocytes move in
    quickly forming barrier scar tissue

126
Ongoing Research
  • Improve environment for spinal cord axons to
    bridge injury gap
  • Find ways to stimulate dormant stem cells to
    replace lost, damaged, or diseased neurons
  • Develop tissue cultured neurons that can be used
    for transplantation purposes.

127
End Chapter 12
Write a Comment
User Comments (0)
About PowerShow.com