Transcript 29 - IWS2.collin.edu

Nervous Tissue
Fundamentals
of the Nervous
P A R and
T A
System
Nervous
Tissue
1
Nervous System


The master controlling and
communicating system of the body
Functions
 Sensory input –the stimuli goes to
CNS
 Integration – interpretation of
sensory input
 Motor output – response to
stimuli coming from CNS
2
Nervous System
3
Figure 11.1
Organization of the Nervous
System


Central nervous system (CNS)
 Brain and spinal cord
 Integration and command center
Peripheral nervous system
(PNS)
 Paired spinal and cranial nerves
 Carries messages to and from the
spinal cord and brain
4
Peripheral Nervous System (PNS):
Two Functional Divisions

Sensory (afferent) division
 Somatic sensory fibers – carry
impulses from skin, skeletal muscles,
and joints to the brain
 Visceral sensory fibers – transmit
impulses from visceral organs to the
brain
5
Motor Division: Two Main Parts

Motor (efferent) division
 Somatic motor nervous
system (voluntary)- carries
impulses from the CNS to skeletal
muscles. Conscious control
6
Motor Division: Two Main Parts

Visceral motor nervous system
or Autonomic nervous system
(ANS) (involuntary) - carry
impulses from the CNS to smooth
muscle, cardiac muscle, and glands
 Sympathetic and
 Parasympathetic
 Enteric Nervous System (ENS)
7
Histology of Nerve Tissue

The two principal cell types of the
nervous system are:
 Neurons – excitable cells that
transmit electrical signals
 Neuroglias (glial) – cells that
surround and wrap neurons
8
Supporting Cells: Neuroglia

Neuroglia
 Provide a supportive scaffolding
for neurons
 Segregate and insulate neurons
 Guide young neurons to the
proper connections
 Promote health and growth
9
Neuroglia of the CNS



Astrocytes
Most abundant, versatile, and highly
branched glial cells
Maintain blood-brain barrier
 They cling to neurons and their
synaptic endings,
 They wrap around capillaries
 Regulate their permeability
10
Neuroglia of the CNS




Provide structural framework for the
neuron
Guide migration of young neurons
Control the chemical environment
Repair damaged neural tissue
11
Astrocytes
12
Figure 11.3a
Neuroglia of the CNS


Microglia – small, ovoid cells with
spiny processes
 Phagocytes that monitor the
health of neurons
Ependymal cells – range in shape
from squamous to columnar
 They line the central cavities of
the brain and spinal column
13
Microglia and Ependymal Cells
14
Figure 11.3b, c
Neuroglia of the CNS

Oligodendrocytes – branched cells
 Myelin
 Wraps of oligodendrocytes
processes around nerve fibers
 Insulates the nerve fibers
15
Neuroglia of the PNS


Schwann cells (neurolemmocytes) –
 Myelin
 Wraps itself around nerve fibers
 Insulates the nerve fibers
Satellite cells surround neuron cell
bodies located within the ganglia
 Regulate the environment around the
neurons
16
Oligodendrocytes, Schwann
Cells, and Satellite Cells
17
Figure 11.3d, e
Neurons (Nerve Cells)


Structural units of the nervous
system
 Composed of a body, axon, and
dendrites
 Long-lived, amitotic, and have a
high metabolic rate
Their plasma membrane function in:
 Electrical signaling
 Cell-to-cell signaling during
18
development
Neurons (Nerve Cells)
19
Figure 11.4b
Nerve Cell Body (Perikaryon or
Soma)






Contains the nucleus and a
nucleolus
Is the major biosynthetic center
Is the focal point for the outgrowth
of neuronal processes
Has no centrioles (hence its amitotic
nature)
Has well-developed Nissl bodies
(rough ER)
Contains an axon hillock – coneshaped area from which axons arise20
Processes



Arm like extensions from the soma
There are two types of processes:
axons and dendrites
Myelinated axons are called tracts
in the CNS and nerves in the PNS
21
Dendrites: Structure



Short, tapering processes
They are the receptive, or input,
regions of the neuron
Electrical signals are conveyed as
graded potentials (not action
potentials)
22
Neurons (Nerve Cells)
23
Figure 11.4b
Axons: Structure






Slender processes of uniform
diameter arising from the hillock
Long axons are called nerve fibers
Usually there is only one
unbranched axon per neuron
Axon collaterals
Telodendria
Axonal terminal or synaptic
knobs
24
Axons: Function



Generate and transmit action
potentials
Secrete neurotransmitters from the
axonal terminals
Movement along axons occurs in
two ways
 Anterograde — toward the axon
terminal
 Retrograde — toward the cell
body
25
Myelin Sheath


Whitish, fatty (protein-lipoid),
segmented sheath around most
long axons
It functions to:
 Protect the axon
 Electrically insulate fibers from
one another
 Increase the speed of nerve
impulse transmission
26
Myelin Sheath and Neurilemma:
Formation


Formed by Schwann cells in the PNS
A Schwann cell:
 Envelopes an axon
 Encloses the axon with its plasma
membrane
 Has concentric layers of
membrane that make up the
myelin sheath
27
Myelin Sheath and Neurilemma:
Formation
28
Figure 11.5a–c
Nodes of Ranvier (Neurofibral
Nodes)


Gaps in the myelin sheath between
adjacent Schwann cells
They are the sites where axon
collaterals can emerge
29
Unmyelinated Axons



A Schwann cell surrounds nerve
fibers but coiling does not take
place
Schwann cells partially enclose 15
or more axons
Conduct nerve impulse slowly
30
Axons of the CNS



Both myelinated and unmyelinated
fibers are present
Myelin sheaths are formed by
oligodendrocytes
Nodes of Ranvier are widely spaced
31
Regions of the Brain and Spinal
Cord


White matter – dense collections
of myelinated fibers
Gray matter – mostly soma,
dendrites, glial cells and
unmyelinated fibers
32
Neuron Classification

Structural:
 Multipolar — three or more
processes
 Bipolar — two processes (axon
and dendrite)
 Unipolar — single, short process
33
A Structural Classification of
Neurons
34
Figure 12.4
Neuron Classification

Functional:
 Sensory (afferent) — transmit
impulses toward the CNS
 Motor (efferent) — carry impulses
toward the body surface
 Interneurons (association
neurons) — any neurons between
a sensory and a motor neuron
35
Comparison of Structural
Classes of Neurons
36
Table 11.1.1
Comparison of Structural
Classes of Neurons
37
Table 11.1.2
Neurophysiology


Neurons are highly irritable
Action potentials, or nerve
impulses, are:
 Electrical impulses carried along
the length of axons
 Always the same regardless of
stimulus
38
Electricity Definitions




Voltage (V) – measure of potential
energy generated by separated
charge
Potential difference – voltage
measured between two points
Current (I) – the flow of electrical
charge between two points
Resistance (R) – hindrance to charge
flow
39
Electricity Definitions


Insulator – substance with high
electrical resistance
Conductor – substance with low
electrical resistance
40
Electrical Current and the Body


Reflects the flow of ions rather than
electrons
There is a potential on either side of
membranes when:
 The number of ions is different
across the membrane
 The membrane provides a
resistance to ion flow
41
Role of Ion Channels

Types of plasma membrane ion
channels:
 Nongated, or leakage channels
– always open
 Chemically gated channels –
open with binding of a specific
neurotransmitter
42
Role of Ion Channels
Voltage-gated channels – open
and close in response to
membrane potential.
 2 gates
 Mechanically gated channels –
open and close in response to
physical deformation of receptors

43
Gated Channels
44
Figure 12.13
Operation of a Chemically Gated
Channel



Example: Na+-K+ gated channel
Closed when a neurotransmitter is
not bound to the extracellular
receptor
 Na+ cannot enter the cell and K+
cannot exit the cell
Open when a neurotransmitter is
attached to the receptor
 Na+ enters the cell and K+ exits
the cell
45
Operation of a Voltage-Gated
Channel



Example: Na+ channel
Closed when the intracellular
environment is negative
 Na+ cannot enter the cell
Open when the intracellular
environment is positive
 Na+ can enter the cell
46
Gated Channels

When gated channels are open:
 Ions move quickly across the
membrane
 Movement is along their
electrochemical gradients
 An electrical current is created
 Voltage changes across the
membrane
47
Electrochemical Gradient



Ions flow along their chemical
gradient when they move from an
area of high concentration to an
area of low concentration
Ions flow along their electrical
gradient when they move toward an
area of opposite charge
Electrochemical gradient – the
electrical and chemical gradients
taken together
48
Resting Membrane Potential (Vr)


The potential difference (–70 mV)
across the membrane of a resting
neuron
It is generated by different
concentrations of Na+, K+, Cl, and
protein anions (A)
49
Resting Membrane Potential (Vr)

Ionic differences are the
consequence of:
 Differential permeability of the
neurilemma to Na+ and K+
 Operation of the sodiumpotassium pump
50
Measuring Membrane Potential
51
Figure 11.7
Resting Membrane Potential
(Vr)
52
Figure 11.8
Nervous Tissue
Fundamentals
P ANervous
RT B
of the
System and
Nervous Tissue
53
Membrane Potentials: Signals



Used to integrate, send, and receive
information
Membrane potential changes are
produced by:
 Changes in membrane
permeability to ions
 Alterations of ion concentrations
across the membrane
Types of signals – graded
potentials and action potentials
54
Changes in Membrane Potential

Changes are caused by three events
 Depolarization – the inside of
the membrane becomes less
negative
 Repolarization – the membrane
returns to its resting membrane
potential
 Hyperpolarization – the inside
of the membrane becomes more
negative than the resting
55
potential
Depolarization, Repolarization and
Hyperpolarization
56
Figure 12.15
Graded Potentials





Short-lived, local changes in
membrane potential
Decrease in intensity with distance
Magnitude varies directly with the
strength of the stimulus
Depolarization or hyperpolarization
Sufficiently strong graded potentials
can initiate action potentials
57
Graded Potentials
58
Figure 11.10
Graded Potentials



Voltage changes are decremental
Current is quickly dissipated due to
the leaky plasma membrane
Only travel over short distances
59
Action Potentials (APs)

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


A brief reversal of membrane
potential with a total amplitude of
100 mV
Action potentials are only generated
by muscle cells and neurons
They do not decrease in strength
over distance
They are the principal means of
neural communication
An action potential in the axon of a
neuron is a nerve impulse
60
Action Potential: Resting State



Na+ and K+ voltage gated channels
are closed
Leakage accounts for small
movements of Na+ and K+
Each Na+ channel has two voltageregulated gates
 Activation gates
 Inactivation gates
61
Figure 11.12.1
Action Potential: Resting State
Na channel is closed, but
capable of opening
62
Action Potential: Depolarization
Phase




Na+ permeability increases;
membrane potential reverses
Na+ gates are opened; K+ gates
are closed
Threshold – a critical level of
depolarization (-55 to -50 mV)
At threshold, depolarization
becomes self-generating
63
Figure 11.12.2
Action Potential: Depolarization
Phase
Both Na channels are opened
64
Action Potential: Repolarization
Phase




Sodium inactivation gates close
Membrane permeability to Na+
declines to resting levels
As sodium gates close, voltagesensitive K+ gates open
K+ exits the cell and internal
negativity of the resting neuron
is restored
65
Figure 11.12.3
Action Potential: Repolarization
Phase
Na activation channel is opened and
inactivation is closed.
66
Action Potential: Hyperpolarization


Potassium gates remain open,
causing an excessive efflux of K+
This efflux causes hyperpolarization
of the membrane (undershoot)
67
Figure 11.12.4
Action Potential:
Hyperpolarization
68
Action Potential:
Role of the Sodium-Potassium Pump


Repolarization
 Restores the resting electrical
conditions of the neuron
 Does not restore the resting ionic
conditions
Ionic redistribution back to resting
conditions is restored by the sodiumpotassium pump
69
Phases of the Action Potential
• 1 – resting state
• 2 – depolarization
phase
• 3 – repolarization
phase
• 4 –hyperpolarization
70
Figure 11.12
Action Potential
71
Propagation of an Action Potential
along an Unmyelinated Axon
72
Propagation of an action potential


Continuous propagation
 Unmyelinated axon
Saltatory propagation
 Myelinated axon
73
Propagation of an Action Potential
(Time = 0ms)- continuous propagation



Na gates open
Na+ influx causes a patch of the axonal
membrane to depolarize
Positive Na ions in the axoplasm move
toward the polarized (negative) portion
of the membrane
74
Propagation of an Action Potential
(Time = 2ms)- continuous propagation



A local current is created that depolarizes
the adjacent membrane in a forward
direction
Local voltage-gated Na channels are
opened
The action potential moves away from
the stimulus
75
Propagation of an Action Potential
(Time = 4ms)- continuous propagation





Sodium gates close
Potassium gates open
Repolarization
Hyperpolarization
 Sluggish K channels are kept opened
Resting membrane potential is restored
in this region
76
Saltatory Conduction




Current passes through a
myelinated axon only at the nodes
of Ranvier
Voltage-gated Na+ channels are
concentrated at these nodes
Action potentials are triggered only
at the nodes and jump from one
node to the next
Much faster than conduction along
unmyelinated axons
77
Saltatory Conduction
78
Figure 11.16
Types of stimuli


Threshold stimulus
 Stimulus strong enough to bring
the membrane potential to a
threshold voltage causing an action
potential
Subthreshold stimulus
 weak stimuli that cause
depolarization (graded potentials)
but not action potentials
79
Coding for Stimulus Intensity



Action potential are All-or-none
phenomenon
Strong stimuli can generate an
action potential more often than
weaker stimuli
The CNS determines stimulus
intensity by the frequency of
impulse transmission
80
Stimulus Strength and AP
Frequency
81
Figure 11.14
Absolute Refractory Period


Time from the opening of the Na+
activation gates until the closing of
inactivation gates
The absolute refractory period:
 Prevents the neuron from
generating an action potential
 Ensures that each action potential
is separate
 Enforces one-way transmission of
nerve impulses
82
Absolute and Relative
Refractory Periods
83
Figure 11.15
Relative Refractory Period


The interval following the absolute
refractory period when:
 Sodium gates are closed
 Potassium gates are open
 Repolarization is occurring
Stimulus stronger than the original
one cause a new action potential
84
Conduction Velocities of Axons


Conduction velocities vary widely
among neurons
Rate of impulse propagation is
determined by:
 Axon diameter – the larger the
diameter, the faster the impulse
 Presence of a myelin sheath –
myelination dramatically
increases impulse speed
85
Nerve Fiber Classification

Nerve fibers are classified according
to:
 Diameter
 Degree of myelination
 Speed of conduction
86
Axon classification



Type A fibers
 Diameter of 4 to 20 µm and myelinated
Type B fibers
 Diameter of 2 to 4 µm and myelinated
Type C fibers
 Diameter less than 2 µm and
unmyelinated
87
Multiple Sclerosis (MS)




An autoimmune disease that mainly
affects young adults
Symptoms: visual disturbances,
weakness, loss of muscular control,
and urinary incontinence
Nerve fibers are severed and myelin
sheaths in the CNS become
nonfunctional scleroses
Shunting and short-circuiting of
nerve impulses occurs
88
Synapses



A junction that mediates
information transfer from one
neuron:
 To another neuron
 To an effector cell
Presynaptic neuron – conducts
impulses toward the synapse
Postsynaptic neuron – transmits
impulses away from the synapse
89
Synapses
90
Figure 11.17
Types of Synapses



Axodendritic – synapses between
the axon of one neuron and the
dendrite of another
Axosomatic – synapses between the
axon of one neuron and the soma of
another
Others: Axoaxonic, etc
91
Electrical Synapses

Electrical synapses:
 Are less common than chemical
synapses
 Correspond to gap junctions found in
other cell types
 Very fast propagation of action
potentials
92
Electrical Synapses

Are important in the CNS in:
 Arousal from sleep
 Mental attention
 Emotions and memory
 Ion and water homeostasis
 Light transmitting (eye)
93
Chemical Synapses




Specialized for the release and
reception of neurotransmitters
Typically composed of:
Presynaptic neuron
 Contains synaptic vesicles
Postsynaptic neuron
 The receptors are located
typically on dendrites and soma
94
Chemical Synapses


Synaptic Cleft
 Fluid-filled space separating the
presynaptic and postsynaptic
neurons
Transmission across the synaptic
cleft:
 Is a chemical event (as opposed
to an electrical one)
 Ensures unidirectional
communication between neurons
95
Synaptic Cleft: Information
Transfer


Nerve impulses reach the axonal
terminal of the presynaptic neuron
and open Ca2+ channels
Neurotransmitter is released into
the synaptic cleft via exocytosis
96
Synaptic Cleft: Information Transfer


Neurotransmitter crosses the
synaptic cleft and binds to receptors
on the postsynaptic neuron
Postsynaptic membrane
permeability changes, causing an
excitatory or inhibitory effect
97
Synaptic Cleft: Information
Transfer
Ca2+
1
Neurotransmitter
Axon terminal of
presynaptic neuron
Postsynaptic
membrane
Mitochondrion
Axon of
presynaptic
neuron
Na+
Receptor
Postsynaptic
membrane
Ion channel open
Synaptic vesicles
containing
neurotransmitter
molecules
5
Degraded
neurotransmitter
2
Synaptic
cleft
Ion channel
(closed)
3
4
Ion channel closed
Ion channel (open)
98
Figure 11.18
Nervous Tissue
Fundamentals
ART C
of thePNervous
System and
Nervous
Tissue
99
Termination of Neurotransmitter
Effects

Neurotransmitter bound to a
postsynaptic neuron:
 Produces a continuous postsynaptic
effect
 Blocks reception of additional
“messages”
 Must be removed from its receptor
100
Termination of Neurotransmitter
Effects

Removal of neurotransmitters
occurs when they:
 Are degraded by enzymes
 Are reabsorbed by astrocytes or
the presynaptic terminals
 Diffuse from the synaptic cleft
101
Synaptic Delay



Neurotransmitter must be released,
diffuse across the synapse, and bind
to receptors
Synaptic delay – time needed to do
this
Synaptic delay is the rate-limiting
step of neural transmission
102
Postsynaptic Potentials

Neurotransmitter receptors mediate
changes in membrane potential
according to:
 The amount of neurotransmitter
released
 The amount of time the
neurotransmitter is bound to
receptors
103
Postsynaptic Potentials

The two types of postsynaptic
potentials are:
 EPSP – excitatory postsynaptic
potentials
 IPSP – inhibitory postsynaptic
potentials
104
Excitatory Postsynaptic Potentials


EPSPs are graded potentials that
can initiate an action potential in an
axon
 Use only chemically gated
channels
 Na+ and K+ flow in opposite
directions at the same time
Postsynaptic membranes do not
generate action potentials
105
Excitatory Postsynaptic
Potential (EPSP)
106
Figure 11.19a
Inhibitory Synapses and IPSPs

Neurotransmitter binding to a
receptor at inhibitory synapses:
 Causes the membrane to become
more permeable to potassium and
chloride ions
 Leaves the charge on the inner
surface negative
 Reduces the postsynaptic
neuron’s ability to produce an
action potential
107
Inhibitory Postsynaptic (IPSP)
108
Figure 11.19b
Summation



A single EPSP cannot induce an
action potential
EPSPs must summate temporally or
spatially to induce an action
potential
Temporal summation –
presynaptic neurons transmit
impulses in rapid-fire order
109
Temporal Summation
110
Summation


Spatial summation – postsynaptic
neuron is stimulated by a large
number of terminals at the same
time
IPSPs can also summate with
EPSPs, canceling each other out
111
Spatial Summation
112
EPSP – IPSP Interactions
113
Neurotransmitters



Chemicals used for neuronal
communication with the body and
the brain
50 different neurotransmitters have
been identified
Classified chemically and
functionally
114
Chemical Neurotransmitters





Acetylcholine (ACh)
Biogenic amines
Amino acids
Peptides
Novel messengers: ATP and
dissolved gases NO and CO
115
Neurotransmitters: Acetylcholine



First neurotransmitter identified,
and best understood
Released at the neuromuscular
junction
Synthesized and enclosed in
synaptic vesicles
116
Neurotransmitters: Acetylcholine


Degraded by the enzyme
acetylcholinesterase (AChE)
Released by:
 All neurons that stimulate skeletal
muscle
 Some neurons in the autonomic
nervous system
117
Neurotransmitters: Biogenic
Amines



Include:
 Catecholamines – dopamine,
norepinephrine (NE), and
epinephrine
 Indolamines – serotonin and
histamine
Broadly distributed in the brain
Play roles in emotional behaviors
and our biological clock
118
Synthesis of Catecholamines



Enzymes present in the cell
determine length of biosynthetic
pathway
Norepinephrine and dopamine are
synthesized in axonal terminals
Epinephrine is released by the
adrenal medulla
119
Figure
11.21
Synthesis of Catecholamines
120
Neurotransmitters: Amino Acids


Include:
 GABA – Gamma ()-aminobutyric
acid
 Glycine
 Aspartate
 Glutamate
Found only in the CNS
121
Neurotransmitters: Peptides




Include:
 Substance P – mediator of pain
signals
 Beta endorphin, dynorphin, and
enkephalins
Act as natural opiates; reduce pain
perception
Bind to the same receptors as
opiates and morphine
Gut-brain peptides – somatostatin,
122
and cholecystokinin
Neurotransmitters: Novel
Messengers

ATP
 Is found in both the CNS and PNS
 Produces excitatory or inhibitory
responses depending on receptor
type
 Induces Ca2+ wave propagation in
astrocytes
 Provokes pain sensation
123
Neurotransmitters: Novel
Messengers


Nitric oxide (NO)
 Activates the intracellular
receptor guanylyl cyclase
 Is involved in learning and
memory
Carbon monoxide (CO) is a main
regulator of cGMP in the brain
124
Functional Classification of
Neurotransmitters

Two classifications: excitatory and
inhibitory
 Excitatory neurotransmitters
cause depolarizations
(e.g., glutamate)
 Inhibitory neurotransmitters
cause hyperpolarizations (e.g.,
GABA and glycine)
125
Functional Classification of
Neurotransmitters

Some neurotransmitters have both
excitatory and inhibitory effects
 Determined by the receptor type
of the postsynaptic neuron
 Example: acetylcholine
 Excitatory at neuromuscular
junctions with skeletal muscle
 Inhibitory in cardiac muscle
126
Neurotransmitter Receptor
Mechanisms


Direct: neurotransmitters that open
ion channels
 Promote rapid responses
 Examples: ACh and amino acids
Indirect: neurotransmitters that
act through second messengers
 Promote long-lasting effects
 Examples: biogenic amines,
peptides, and dissolved gases
127
Channel-Linked Receptors



Composed of integral membrane
protein
Mediate direct neurotransmitter
action
Action is immediate, brief, simple,
and highly localized
128
Channel-Linked Receptors



Ligand binds the receptor, and ions
enter the cells
Excitatory receptors depolarize
membranes
Inhibitory receptors hyperpolarize
membranes
129
Channel-Linked Receptors
130
Figure 11.22a
G Protein-Linked Receptors



Responses are indirect, slow,
complex, prolonged, and often
diffuse
These receptors are transmembrane
protein complexes
First and Second messengers.
131
Neurotransmitter Receptor
Mechanism
Ions flow
Blocked ion flow
(a)
Channel closed
Adenylate
cyclase
Channel open
Neurotransmitter (ligand)
released from axon terminal
of presynaptic neuron
3
1
PPi
4
GTP
5
cAMP
ATP
5
3
Changes in
membrane
permeability
and potential
GTP
2
GDP
Protein
synthesis
Enzyme
activation
GTP
Receptor
G protein
(b)
Nucleus
Activation of
specific genes
132
Figure 11.22b
Neural Integration: Neuronal Pools

Functional groups of neurons that:
 Integrate incoming information
 Forward the processed
information to its appropriate
destination
133
Neural Integration: Neuronal Pools

Simple neuronal pool
 Input fiber – presynaptic fiber
 Discharge zone – neurons most
closely associated with the
incoming fiber
 Facilitated zone – neurons farther
away from incoming fiber
134
Simple Neuronal Pool
135
Figure 11.23
Types of Neuronal Pools
136
Types of Circuits in Neuronal
Pools

Divergent – information spreads
from one neuron to several neurons
or from one pool to several pools.
 One motor neuron of the brain
stimulates many muscle fibers
137 b
Figure 11.24a,
Types of Circuits in Neuronal
Pools

Convergent – input from many
neurons is funneled to one neuron or
neuronal pools
 Motor neurons of the diaphragm is
controlled by different areas of the
brain for subconscious and
conscious functioning
138 d
Figure 11.24c,
Types of Circuits in Neuronal
Pools


Reverberating –collateral
branches of axons extend back
toward the source of the impulse
Involved in rhythmic activities
 Breathing, sleep-wake cycle, etc
Figure139
11.24e
Types of Circuits in Neuronal
Pools


Parallel - incoming neurons
stimulate several neurons in parallel
arrays
Divergence must take place before
the parallel processing
 Response to a painfull stimuli
causes
 Withdrawal of the limb
 Shift of the weight
 Fell pain
 Shout “ouch!”
Figure140
11.24f
Patterns of Neural Processing

Serial
 Transmitting of the impulse from
one neuron to another or from
one pool to another
 Spinal reflexes
141
Development of Neurons



The nervous system originates from
the neural tube and neural crest
The neural tube becomes the CNS
There is a three-phase process of
differentiation:
 Proliferation of cells needed for
development
 Migration – neuroblasts become
amitotic and move externally
142
 Differentiation into neurons
Axonal Growth

Guided by:
 Scaffold laid down by older neurons
 Orienting glial fibers
 Release of nerve growth factor by
astrocytes
 Neurotropins released by other
neurons
 Repulsion guiding molecules
 Attractants released by target cells
143