Download The Nervous System

7
The Nervous System
Yong Jeong, MD, PhD
Department of Bio and Brain Engineering
Functions of the Nervous System
• Sensory input—gathering information
• To monitor changes occurring inside and
outside the body
• Changes = stimuli
• Integration
• To process and interpret sensory input and
decide if action is needed
• Motor output
• A response to integrated stimuli
• The response activates muscles or glands
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© 2012 Pearson Education, Inc.
Figure 7.1
Structural Classification of the Nervous
System
•Central nervous system (CNS)
•Organs
•Brain
•Spinal cord
•Function
•Integration; command center
•Interpret incoming sensory information
•Issues outgoing instructions
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Structural Classification of the Nervous
System
• Peripheral nervous system (PNS)
• Nerves extending from the brain and spinal
cord
• Spinal nerves—carry impulses to and from
the spinal cord
• Cranial nerves—carry impulses to and from
the brain
• Functions
• Serve as communication lines among
sensory organs, the brain and spinal cord,
and glands or muscles
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Structural Classification
of the Nervous System
•Central nervous system
(CNS)
•Brain
•Spinal cord
•Peripheral nervous
system (PNS)
•Nerves outside the
brain and spinal cord
•Spinal nerves
•Cranial nerves
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Figure 7.2
Functional Classification of the Peripheral
Nervous System
•Sensory (afferent) division
•Nerve fibers that carry information to the
central nervous system
•Motor (efferent) division
•Nerve fibers that carry impulses away from
the central nervous system
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Figure 7.2
Functional Classification of the Peripheral
Nervous System
•Motor (efferent) division (continued)
•Two subdivisions
•Somatic nervous system = voluntary
• Consciously controls skeletal muscles
•Autonomic nervous system = involuntary
• Automatically controls smooth and
cardiac muscles and glands
• Further divided into the sympathetic and
parasympathetic nervous systems
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Nervous Tissue: Support Cells
•Support cells in the CNS are grouped together
as “neuroglia”
•General functions
•Support
•Insulate
•Protect neurons
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Nervous Tissue: Support Cells
•Astrocytes
•Abundant, star-shaped cells
•Brace neurons
•Form barrier between capillaries and
neurons
•Control the chemical environment of
the brain
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Capillary
Neuron
Astrocyte
(a) Astrocytes are the most abundant
and versatile neuroglia.
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Figure 7.3a
Nervous Tissue: Support Cells
•Microglia
•Spiderlike phagocytes
•Dispose of debris
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Neuron
Microglial
cell
(b) Microglial cells are phagocytes that
defend CNS cells.
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Figure 7.3b
Nervous Tissue: Support Cells
•Ependymal cells
•Line cavities of the brain and spinal cord
•Cilia assist with circulation of cerebrospinal
fluid
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Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue
(c) Ependymal cells line cerebrospinal
fluid-filled cavities.
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Figure 7.3c
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Nervous Tissue: Support Cells
•Oligodendrocytes
•Wrap around nerve fibers in the central
nervous system
•Produce myelin sheaths
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Myelin sheath
Process of
oligodendrocyte
Nerve
fibers
(d) Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
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Figure 7.3d
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Nervous Tissue: Support Cells
•Satellite cells
•Protect neuron cell bodies
•Schwann cells
•Form myelin sheath in the peripheral
nervous system
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Satellite
cells
Cell body of neuron
Schwann cells
(forming myelin sheath)
Nerve fiber
(e) Satellite cells and Schwann cells (which form
myelin) surround neurons in the PNS.
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Figure 7.3e
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Nervous Tissue: Neurons
•Neurons = nerve cells
•Cells specialized to transmit messages
•Major regions of neurons
•Cell body—nucleus and metabolic center
of the cell
•Processes—fibers that extend from the
cell body
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Nervous Tissue: Neurons
•Cell body
•Nissl bodies
•Specialized rough endoplasmic reticulum
•Neurofibrils
•Intermediate cytoskeleton
•Maintains cell shape
•Nucleus with large nucleolus
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Neuron Specific Function and
Structure
• Excitability: action potential
• Ion channels
• Long axon
• Cytoskeleton: microtubule etc.
• Myeline sheath
• Signal transmission
• Synapse
• Neurotransmitter
• Receptor
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Structure of Neuron
Dendrites, inputs
Soma, processing
Axon hillock, action potential (output)
Axon Signal
conduction
Presynaptic cell
Myelin sheath
Synapse
Postsynaptic cell
Synaptic terminals
neurotransmitter release
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Neuron cell body
Dendrite
(b)
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Figure 7.4b
Nervous Tissue: Neurons
•Processes outside the cell body
•Dendrites—conduct impulses toward the cell
body
•Neurons may have hundreds of dendrites
•Axons—conduct impulses away from the
cell body
•Neurons have only one axon arising from
the cell body at the axon hillock
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Mitochondrion
Dendrite
Cell
body
Nissl substance
Axon
hillock
Axon
Neurofibrils
Nucleus
Collateral
branch
One
Schwann cell
Axon
terminal
Node of
Ranvier
Schwann cells,
forming the myelin
sheath on axon
(a)
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Figure 7.4a
Nervous Tissue: Neurons
•Axons
•End in axon terminals
•Axon terminals contain vesicles with
neurotransmitters
•Axon terminals are separated from the next
neuron by a gap
•Synaptic cleft—gap between adjacent
neurons
•Synapse—junction between nerves
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Nervous Tissue: Neurons
•Myelin sheath—whitish, fatty material covering
axons
•Schwann cells—produce myelin sheaths in
jelly roll-like fashion around axons (PNS)
•Nodes of Ranvier—gaps in myelin sheath
along the axon
•Oligodendrocytes—produce myelin sheaths
around axons of the CNS
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Schwann cell
cytoplasm
Axon
Schwann cell
plasma membrane
Schwann cell
nucleus
(a)
(b)
Neurilemma
Myelin
sheath
(c)
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Figure 7.5
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Neuron Cell Body Location
•Most neuron cell bodies are found in the
central nervous system
•Gray matter—cell bodies and unmyelinated
fibers
•Nuclei—clusters of cell bodies within the
white matter of the central nervous system
•Ganglia—collections of cell bodies outside the
central nervous system
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Neuron Cell Body Location
•Tracts—bundles of nerve fibers in the CNS
•Nerves—bundles of nerve fibers in the PNS
•White matter—collections of myelinated fibers
(tracts)
•Gray matter—collections of mostly
unmyelinated fibers and cell bodies
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Functional Classification of Neurons
•Sensory (afferent) neurons
•Carry impulses from the sensory receptors
to the CNS
•Cutaneous sense organs
•Proprioceptors—detect stretch or tension
•Motor (efferent) neurons
•Carry impulses from the central nervous
system to viscera, muscles, or glands
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Central process (axon)
Cell
body
Sensory
neuron
Spinal cord
(central nervous system)
Ganglion
Dendrites
Peripheral
process (axon)
Afferent
transmission
Interneuron
(association
neuron)
Peripheral
nervous system
Receptors
Efferent transmission
Motor neuron
To effectors
(muscles and glands)
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Figure 7.6
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Figure 7.7a
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Figure 7.7b
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Figure 7.7c
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Figure 7.7d
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Figure 7.7e
Functional Classification of Neurons
•Interneurons (association neurons)
•Found in neural pathways in the central
nervous system
•Connect sensory and motor neurons
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Central process (axon)
Cell
body
Sensory
neuron
Spinal cord
(central nervous system)
Ganglion
Dendrites
Peripheral
process (axon)
Afferent
transmission
Interneuron
(association
neuron)
Peripheral
nervous system
Receptors
Efferent transmission
Motor neuron
To effectors
(muscles and glands)
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Figure 7.6
Structural Classification of Neurons
•Multipolar neurons—many extensions from the
cell body
•All motor and interneurons are multipolar
•Most common structure
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Cell body
Axon
Dendrites
(a) Multipolar neuron
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Figure 7.8a
Structural Classification of Neurons
•Bipolar neurons—one axon and one dendrite
•Located in special sense organs such as
nose and eye
•Rare in adults
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Cell body
Dendrite
Axon
(b) Bipolar neuron
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Figure 7.8b
Structural Classification of Neurons
•Unipolar neurons—have a short single
process leaving the cell body
•Sensory neurons found in PNS ganglia
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Dendrites
Cell body
Short single
process
Axon
Peripheral
process
Central
process
(c) Unipolar neuron
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Figure 7.8c
Functional Properties of Neurons
•Irritability
•Ability to respond to stimuli
•Conductivity
•Ability to transmit an impulse
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Nerve Impulses
•Resting neuron
•The plasma
membrane at rest is
polarized
•Fewer positive ions
are inside the cell
than outside the cell
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Resting Membrane Potential
[K+]
[K+]
[Na+]
[Ca2+]
[Cl-]
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Equilibrium Potential:
Selective Permeability


(Capacitance)
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Equilibrium Potential
Equilibrium potential:
Chemical driving force = Electrical driving force
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Nernst Equation
(Equilibrium potential in Squid Giant Axon)
RT
Ex =
zF
ln
[X]o
[X]i
Ex) RT/F = 25mV at 25oC
[K+]o = 20mM, [K+]i = 400mM
EK =
58mV
1
log
[20]
= -75mv
[400]
ENa = 55mV, [Na+]o = 440mM, [Na+]i = 50mM
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Goldman Equation
Vm =
RT PK[K]o + PNa[Na]o + PCl[Cl]i
ln
zF PK[K]i + PNa[Na]i + PCl[Cl]o
P: Permeability
Resting; PK:PNa:PCl = 1.0:0.04:0.45
= 1.0:20:0.45
(Action Potential)
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Nerve Impulses
•Resting neuron
•The plasma membrane at rest is polarized
•Fewer positive ions are inside the cell than
outside the cell
•Depolarization
•A stimulus depolarizes the neuron’s
membrane
•A depolarized membrane allows sodium
(Na+) to flow inside the membrane
•The exchange of ions initiates an action
potential in the neuron
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•Resting Membrane Potential
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•Action Potential
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[Na+]
+
–[K ]
–
+
+
© 2012 Pearson Education, Inc.
1 Resting membrane is polarized. In the resting state, the
external face of the membrane is slightly positive; its internal
face is slightly negative. The chief extracellular ion is sodium
(Na+), whereas the chief intracellular ion is potassium (K+).
The membrane is relatively impermeable to both ions.
Figure 7.9, step 1
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Nerve Impulses
•Depolarization
•A stimulus depolarizes the neuron’s
membrane
•The membrane is now permeable to sodium
as sodium channels open
•A depolarized membrane allows sodium
(Na+) to flow inside the membrane
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Na+
+
+
–
–
+
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2 Stimulus initiates local depolarization. A stimulus
changes the permeability of a local "patch" of the membrane,
and sodium ions diffuse rapidly into the cell. This changes the
polarity of the membrane (the inside becomes more positive;
the outside becomes more negative) at that site.
Figure 7.9, step 2
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Nerve Impulses
•Action potential
•The movement of ions initiates an action
potential in the neuron due to a stimulus
•A graded potential (localized depolarization)
exists where the inside of the membrane is
more positive and the outside is less positive
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Neuronal Signal (= Action Potential)
Excitation
Resting
K+
80
60
40
20 Leak channel
+
-
+
-
mV
-
-
+
-
Voltage-dependant
Na+ channel
+
-
-
-
-
-
+
0
-20
-40
-60
-80
+
-
-
-
-
Voltage-dependant
K+ channel
Resting
Excitation
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Na+
+
+
–
–
+
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3 Depolarization and generation of an action potential.
If the stimulus is strong enough, depolarization causes
membrane polarity to be completely reversed and an action
potential is initiated.
Figure 7.9, step 3
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Nerve Impulses
•Propagation of the action potential
•If enough sodium enters the cell, the action
potential (nerve impulse) starts and is
propagated over the entire axon
•Impulses travel faster when fibers have a
myelin sheath
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–
+
+
–
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4 Propagation of the action potential. Depolarization of
the first membrane patch causes permeability changes in the
adjacent membrane, and the events described in step 2 are
repeated. Thus, the action potential propagates rapidly along
the entire length of the membrane.
Figure 7.9, step 4
Nerve Impulses
•Repolarization
•Potassium ions rush out of the neuron after
sodium ions rush in, which repolarizes the
membrane
•Repolarization involves restoring the inside
of the membrane to a negative charge and
the outer surface to a positive charge
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+
K+
+
–
+
–
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5 Repolarization. Potassium ions diffuse out of the cell as
the membrane permeability changes again, restoring the
negative charge on the inside of the membrane and the
positive charge on the outside surface. Repolarization occurs
in the same direction as depolarization.
Figure 7.9, step 5
Nerve Impulses
•Repolarization
•Initial ionic conditions are restored using the
sodium-potassium pump.
•This pump, using ATP, restores the original
configuration
•Three sodium ions are ejected from the cell
while two potassium ions are returned to the
cell
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Na+
Na+
Na+ Diffusion
K+ Diffusion
Cell
exterior
Cell
interior
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Na+
Na+ – K+
pump
K+
K+
K+
Plasma
membrane
6 Initial ionic conditions restored. The ionic conditions
of the resting state are restored later by the activity of the
sodium-potassium pump. Three sodium ions are ejected for
every two potassium ions carried back into the cell.
K+
Figure 7.9, step 6
Transmission of a Signal at Synapses
•When the action potential reaches the axon
terminal, the electrical charge opens calcium
channels
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SYNAPTIC TRANSMISSION
• Electrical: gap junction
 Chemical
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Electrical synapse
•Gap junction
•Cytoplasmic continuity
•Bidirectional
•Instantaneous signal transmission
•Gap junction channel: connexon (6 connexin)
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Chemical synapse
•Amplify signal
•Cytoplasmic discontinuity
•Unidirectional ?
•Synaptic delay
•Active zone
•Neurotransmitter
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•Synaptic transmission
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Axon of
transmitting
neuron
Receiving
neuron
Dendrite
Axon terminal
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1 Action
potential
arrives.
Vesicles
Synaptic
cleft
Figure 7.10, step 1
Transmission of a Signal at Synapses
•Calcium, in turn, causes the tiny vesicles
containing the neurotransmitter chemical to
fuse with the axonal membrane
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2 Vesicle Transmitting neuron
fuses with
plasma
membrane.
Synaptic
cleft
Ion
channels
Neurotransmitter
molecules
Receiving neuron
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Figure 7.10, step 2
Transmission of a Signal at Synapses
•The entry of calcium into the axon terminal
causes porelike openings to form, releasing
the transmitter
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2 Vesicle Transmitting neuron
fuses with
plasma
3 Neurotransmembrane.
mitter is
released into
synaptic cleft.
Synaptic
cleft
Ion
channels
Neurotransmitter
molecules
Receiving neuron
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Figure 7.10, step 3
Transmission of a Signal at Synapses
•The neurotransmitter molecules diffuse across
the synapse and bind to receptors on the
membrane of the next neuron
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2 Vesicle Transmitting neuron
fuses with
4 Neurotransplasma
3 Neurotrans- mitter binds
membrane.
to receptor
mitter is
on receiving
released into
synaptic cleft. neuron's
membrane.
Synaptic
cleft
Ion
channels
Neurotransmitter
molecules
Receiving neuron
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Figure 7.10, step 4
Transmission of a Signal at Synapses
•If enough neurotransmitter is released, graded
potential will be generated
•Eventually an action potential (nerve impulse)
will occur in the neuron beyond the synapse
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Neurotransmitter
Receptor
Na+
5 Ion channel opens.
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Figure 7.10, step 5
Transmission of a Signal at Synapses
•The electrical changes prompted by
neurotransmitter binding are brief
•The neurotransmitter is quickly removed from
the synapse
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Neurotransmitter is
broken down and
released.
Na+
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6 Ion channel closes.
Figure 7.10, step 6
The Reflex Arc
•Reflex—rapid, predictable, and involuntary
response to a stimulus
•Occurs over pathways called reflex arcs
•Reflex arc—direct route from a sensory
neuron, to an interneuron, to an effector
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Stimulus at distal
end of neuron
Spinal cord
(in cross section)
Skin
2 Sensory neuron
1 Receptor
4 Motor neuron
5 Effector
3 Integration
center
Interneuron
(a) Five basic elements of reflex arc
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Figure 7.11a
The Reflex Arc
•Somatic reflexes
•Reflexes that stimulate the skeletal muscles
•Example: pull your hand away from a hot
object
•Autonomic reflexes
•Regulate the activity of smooth muscles, the
heart, and glands
•Example: Regulation of smooth muscles,
heart and blood pressure, glands, digestive
system
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The Reflex Arc
•Five elements of a reflex:
•Sensory receptor–reacts to a stimulus
•Sensory neuron–carries message to the
integration center
•Integration center (CNS)–processes
information and directs motor output
•Motor neuron–carries message to an
effector
•Effector organ–is the muscle or gland to be
stimulated
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Two-Neuron Reflex Arc
•Two-neuron reflex arcs
•Simplest type
•Example: Patellar (knee-jerk) reflex
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1 Sensory (stretch) receptor
2 Sensory (afferent) neuron
3
4 Motor (efferent) neuron
5 Effector organ
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Figure 7.11b
Three-Neuron Reflex Arc
•Three-neuron reflex arcs
•Consists of five elements: receptor, sensory
neuron, interneuron, motor neuron, and
effector
•Example: Flexor (withdrawal) reflex
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1 Sensory receptor
2 Sensory (afferent) neuron
3 Interneuron
4 Motor (efferent) neuron
5 Effector organ
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Figure 7.11c, step 5
Central Nervous System (CNS)
•CNS develops from the embryonic neural tube
•The neural tube becomes the brain and
spinal cord
•The opening of the neural tube becomes the
ventricles
•Four chambers within the brain
•Filled with cerebrospinal fluid
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Cerebral
hemisphere
Outline of
diencephalon
Midbrain
Cerebellum
Brain stem
(a) 13 weeks
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Figure 7.12a
Regions of the Brain
•Cerebral hemispheres (cerebrum)
•Diencephalon
•Brain stem
•Cerebellum
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Cerebral
hemisphere
Diencephalon
Cerebellum
Brain stem
(b) Adult brain
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Figure 7.12b
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Regions of the Brain: Cerebrum
•Cerebral Hemispheres (Cerebrum)
•Paired (left and right) superior parts of the
brain
•Includes more than half of the brain mass
•The surface is made of ridges (gyri) and
grooves (sulci)
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Precentral
gyrus
Central sulcus
Postcentral gyrus
Parietal lobe
Frontal lobe
Parieto-occipital
sulcus (deep)
Lateral sulcus
Occipital lobe
Temporal lobe
Cerebellum
Pons
Medulla
oblongata
Cerebral cortex
(gray matter)
Gyrus
Spinal
cord
Sulcus
Fissure
(a deep sulcus)
(a)
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Cerebral
white
matter
Figure 7.13a
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Regions of the Brain: Cerebrum
•Lobes of the cerebrum
•Fissures (deep grooves) divide the
cerebrum into lobes
•Surface lobes of the cerebrum
•Frontal lobe
•Parietal lobe
•Occipital lobe
•Temporal lobe
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Parietal lobe
Left cerebral
hemisphere
Frontal
lobe
Occipital
lobe
Temporal
lobe
Cephalad
Caudal
(b)
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Brain
stem
Cerebellum
Figure 7.13b
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Regions of the Brain: Cerebrum
•Specialized areas of the cerebrum
•Primary somatic sensory area
•Receives impulses from the body’s
sensory receptors
•Located in parietal lobe
•Primary motor area
•Sends impulses to skeletal muscles
•Located in frontal lobe
•Broca’s area
•Involved in our ability to speak
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Primary motor area
Premotor area
Anterior
association area
• Working memory
and judgment
• Problem
solving
• Language
comprehension
Broca’s area
(motor speech)
Olfactory
area
Central sulcus
Primary somatic sensory
area
Gustatory area (taste)
Speech/language
(outlined by dashes)
Posterior association
area
Visual area
Auditory area
(c)
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Figure 7.13c
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Figure 7.14
Regions of the Brain: Cerebrum
•Cerebral areas involved in special senses
•Gustatory area (taste)
•Visual area
•Auditory area
•Olfactory area
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61
Regions of the Brain: Cerebrum
•Interpretation areas of the cerebrum
•Speech/language region
•Language comprehension region
•General interpretation area
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Primary motor area
Premotor area
Anterior
association area
• Working memory
and judgment
• Problem
solving
• Language
comprehension
Broca’s area
(motor speech)
Olfactory
area
Central sulcus
Primary somatic sensory
area
Gustatory area (taste)
Speech/language
(outlined by dashes)
Posterior association
area
Visual area
Auditory area
(c)
© 2012 Pearson Education, Inc.
Figure 7.13c
62
Regions of the Brain: Cerebrum
•Layers of the cerebrum
•Gray matter—outer layer in the cerebral
cortex composed mostly of neuron cell
bodies
•White matter—fiber tracts deep to the gray
matter
•Corpus callosum connects hemispheres
•Basal nuclei—islands of gray matter buried
within the white matter
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Longitudinal fissure
Lateral
ventricle
Basal nuclei
(basal
ganglia)
Superior
Association fibers
Commissural fibers
(corpus callosum)
Corona
radiata
Fornix
Thalamus
Internal
capsule
Third
ventricle
Pons
Projection
fibers
Medulla oblongata
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Figure 7.15
63
Regions of the Brain: Diencephalon
•Sits on top of the brain stem
•Enclosed by the cerebral hemispheres
•Made of three parts
•Thalamus
•Hypothalamus
•Epithalamus
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Cerebral
hemisphere
Diencephalon
Cerebellum
Brain stem
(b) Adult brain
© 2012 Pearson Education, Inc.
Figure 7.12b
64
Regions of the Brain: Diencephalon
•Thalamus
•Surrounds the third ventricle
•The relay station for sensory impulses
•Transfers impulses to the correct part of the
cortex for localization and interpretation
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Regions of the Brain: Diencephalon
•Hypothalamus
•Under the thalamus
•Important autonomic nervous system center
•Helps regulate body temperature
•Controls water balance
•Regulates metabolism
•Houses the limbic center for emotions
•Regulates the nearby pituitary gland
•Produces two hormones of its own
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65
Regions of the Brain: Diencephalon
•Epithalamus
•Forms the roof of the third ventricle
•Houses the pineal body (an endocrine gland)
•Includes the choroid plexus—forms
cerebrospinal fluid
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Regions of the Brain: Brain Stem
•Attaches to the spinal cord
•Parts of the brain stem
•Midbrain
•Pons
•Medulla oblongata
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66
Regions of the Brain: Brain Stem
•Midbrain
•Mostly composed of tracts of nerve fibers
•Has two bulging fiber tracts—
cerebral peduncles
•Has four rounded protrusions—
corpora quadrigemina
•Reflex centers for vision and hearing
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Regions of the Brain: Brain Stem
•Pons
•The bulging center part of the brain stem
•Mostly composed of fiber tracts
•Includes nuclei involved in the control of
breathing
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67
Regions of the Brain: Brain Stem
•Medulla oblongata
•The lowest part of the brain stem
•Merges into the spinal cord
•Includes important fiber tracts
•Contains important control centers
•Heart rate control
•Blood pressure regulation
•Breathing
•Swallowing
•Vomiting
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Regions of the Brain: Brain Stem
•Reticular Formation
•Diffuse mass of gray matter along the brain
stem
•Involved in motor control of visceral organs
•Reticular activating system (RAS) plays a
role in awake/sleep cycles and
consciousness
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68
Radiations
to cerebral
cortex
Visual impulses
Reticular formation
Ascending general sensory
tracts (touch, pain, temperature)
Auditory
impulses
Descending
motor projections
to spinal cord
(b)
© 2012 Pearson Education, Inc.
Figure 7.16b
Regions of the Brain: Cerebellum
•Two hemispheres with convoluted surfaces
•Provides involuntary coordination of body
movements
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69
Cerebral hemisphere
Corpus callosum
Choroid plexus of third
ventricle
Occipital lobe of
cerebral hemisphere
Thalamus
(encloses third ventricle)
Pineal gland
(part of epithalamus)
Corpora
quadrigemina
Midbrain
Cerebral
aqueduct
Third ventricle
Anterior
commissure
Hypothalamus
Optic chiasma
Pituitary gland
Mammillary body
Pons
Medulla oblongata
Spinal cord
Cerebral peduncle
of midbrain
Fourth ventricle
Choroid plexus
Cerebellum
(a)
© 2012 Pearson Education, Inc.
Figure 7.16a
Protection of the Central Nervous System
•Scalp and skin
•Skull and vertebral column
•Meninges
•Cerebrospinal fluid (CSF)
•Blood-brain barrier
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70
Skin of scalp
Periosteum
Bone of skull
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Periosteal
Meningeal
Dura
mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood
vessel
Falx cerebri
(in longitudinal
fissure only)
(a)
© 2012 Pearson Education, Inc.
Figure 7.17a
Meninges
•Dura mater
•Tough outermost layer
•Double-layered external covering
• Periosteum—attached to inner surface
of the skull
• Meningeal layer—outer covering of the
brain
•Folds inward in several areas
• Falx cerebri
• Tentorium cerebelli
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71
Meninges
•Arachnoid layer
•Middle layer
•Web-like extensions span the subarachnoid
space
•Arachnoid villi reabsorb cerebrospinal fluid
•Pia mater
•Internal layer
•Clings to the surface of the brain
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Occipital lobe
Tentorium
cerebelli
Cerebellum
Arachnoid mater
over medulla
oblongata
(b)
© 2012 Pearson Education, Inc.
Skull
Scalp
Superior
sagittal sinus
Dura mater
Transverse
sinus
Temporal
bone
Figure 7.17b
72
Cerebrospinal Fluid (CSF)
•Similar to blood plasma composition
•Formed by the choroid plexus
•Choroid plexuses–capillaries in the
ventricles of the brain
•Forms a watery cushion to protect the brain
•Circulated in arachnoid space, ventricles, and
central canal of the spinal cord
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Cerebrospinal Fluid (CSF) Pathway of Flow
1. CSF is produced by the choroid plexus of
each ventricle.
2. CSF flows through the ventricles and into the
subarachnoid space via the median and
lateral apertures. Some CSF flows through
the central canal of the spinal cord.
3. CSF flows through the subarachnoid space.
4. CSF is absorbed into the dural venous
sinuses via the arachnoid villi.
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73
Lateral ventricle
Anterior horn
Septum
pellucidum
Interventricular
foramen
Inferior
horn
Third ventricle
Lateral
aperture
Cerebral aqueduct
Fourth ventricle
Central canal
(a) Anterior view
Figure 7.18a
© 2012 Pearson Education, Inc.
Lateral ventricle
Anterior horn
Posterior
horn
Interventricular
foramen
Third ventricle
Inferior horn
Cerebral aqueduct
Median
aperture
Fourth ventricle
Lateral
aperture
Central canal
(b) Left lateral view
© 2012 Pearson Education, Inc.
Figure 7.18b
74
4
Superior
sagittal sinus
Arachnoid villus
Subarachnoid space
Arachnoid mater
Meningeal dura mater
Periosteal dura mater
Right lateral ventricle
(deep to cut)
Choroid plexus
Corpus
callosum
1
Interventricular
foramen
Third ventricle
3
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
of spinal cord
(c) CSF circulation
Choroid plexus
of fourth ventricle
2
1 CSF is produced by the
choroid plexus of each ventricle.
2 CSF flows through the ventricles
and into the subarachnoid space via
the median and lateral apertures.
Some CSF flows through the central
canal of the spinal cord.
3 CSF flows through the
subarachnoid space.
4 CSF is absorbed into the dural
venous sinuses via the arachnoid
villi.
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Figure 7.18c
Hydrocephalus in a Newborn
•Hydrocephalus
•CSF accumulates and exerts pressure on
the brain if not allowed to drain
•Possible in an infant because the skull
bones have not yet fused
•In adults, this situation results in brain
damage
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75
© 2012 Pearson Education, Inc.
Figure 7.19
Blood-Brain Barrier
•Includes the least permeable capillaries of the
body
•Excludes many potentially harmful substances
•Useless as a barrier against some substances
•Fats and fat soluble molecules
•Respiratory gases
•Alcohol
•Nicotine
•Anesthesia
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76
Traumatic Brain Injuries
•Concussion
•Slight brain injury
•No permanent brain damage
•Contusion
•Nervous tissue destruction occurs
•Nervous tissue does not regenerate
•Cerebral edema
•Swelling from the inflammatory response
•May compress and kill brain tissue
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Cerebrovascular Accident (CVA) or Stroke
•Result from a ruptured blood vessel supplying
a region of the brain
•Brain tissue supplied with oxygen from that
blood source dies
•Loss of some functions or death may result
•Hemiplegia–One-sided paralysis
•Aphasis–Damage to speech center in left
hemisphere
•Transischemia-attack (TIA)–temporary brain
ischemia (restriction of blood flow)
•Warning signs for more serious CVAs
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Alzheimer’s Disease
•Progressive degenerative brain disease
•Mostly seen in the elderly, but may begin in
middle age
•Structural changes in the brain include
abnormal protein deposits and twisted fibers
within neurons
•Victims experience memory loss, irritability,
confusion, and ultimately, hallucinations and
death
© 2012 Pearson Education, Inc.
Spinal Cord
•Extends from the foramen magnum of the
skull to the first or second lumbar vertebra
•Provides a two-way conduction pathway from
the brain to and from the brain
•31 pairs of spinal nerves arise from the spinal
cord
•Cauda equina is a collection of spinal nerves
at the inferior end
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78
Cervical
spinal nerves
Cervical
enlargement
C8
Dura and
arachnoid
mater
Thoracic
spinal nerves
Figure 7.20 (1 of 2)
© 2012 Pearson Education, Inc.
Lumbar
enlargement
T12
Cauda
equina
End of
meningeal
coverings
End of
spinal cord
Lumbar
spinal nerves
L5
S1
Sacral
spinal nerves
S5
© 2012 Pearson Education, Inc.
Figure 7.20 (2 of 2)
79
Spinal Cord Anatomy
•Internal gray matter is mostly cell bodies
•Dorsal (posterior) horns
•Anterior (ventral) horns
•Gray matter surrounds the central canal
•Central canal is filled with cerebrospinal
fluid
•Exterior white mater—conduction tracts
•Dorsal, lateral, ventral columns
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Dorsal root
ganglion
White matter
Central canal
Dorsal (posterior)
horn of gray matter
Lateral horn of
gray matter
Spinal nerve
Dorsal root of
spinal nerve
Ventral root
of spinal nerve
Ventral (anterior)
horn of gray matter
Pia mater
Arachnoid mater
Dura mater
© 2012 Pearson Education, Inc.
Figure 7.21
80
Spinal Cord Anatomy
•Meninges cover the spinal cord
•Spinal nerves leave at the level of each
vertebrae
•Dorsal root
•Associated with the dorsal root ganglia—
collections of cell bodies outside the
central nervous system
•Ventral root
•Contains axons
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Interneuron carrying sensory
information to cerebral cortex
Integration (processing
and interpretation of
sensory input) occurs
Cerebral cortex
(gray matter)
White matter
Interneuron carrying
response to
motor neurons
Thalamus
Cerebrum
Interneuron
carrying response
to motor neuron
Brain stem
Cell body of sensory
neuron in sensory
ganglion
Interneuron carrying
sensory information to
cerebral cortex
Nerve
Skin
Sensory
receptors
Cervical spinal cord
Muscle
© 2012 Pearson Education, Inc.
Motor output
Motor neuron
cell body
White matter
Gray matter
Interneuron
Figure 7.22
81
Peripheral Nervous System (PNS)
•Nerves and ganglia outside the central
nervous system
•Nerve = bundle of neuron fibers
•Neuron fibers are bundled by connective
tissue
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PNS: Structure of a Nerve
•Endoneurium surrounds each fiber
•Groups of fibers are bound into fascicles by
perineurium
•Fascicles are bound together by epineurium
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82
Axon
Myelin sheath
Endoneurium
Perineurium
Epineurium
Fascicle
Blood
vessels
© 2012 Pearson Education, Inc.
Figure 7.23
PNS: Classification of Nerves
•Mixed nerves
•Both sensory and motor fibers
•Sensory (afferent) nerves
•Carry impulses toward the CNS
•Motor (efferent) nerves
•Carry impulses away from the CNS
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PNS: Cranial Nerves
•Twelve pairs of nerves that mostly serve the
head and neck
•Only the pair of vagus nerves extend to
thoracic and abdominal cavities
•Most are mixed nerves, but three are sensory
only
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PNS: Cranial Nerves Device
• Oh – Olfactory
• Oh – Optic
• Oh – Oculomotor
• To – Trochlear
• Touch – Trigeminal
• And – Abducens
• Feel – Facial
• Very – Vestibulocochlear
• Green – Glossopharyngeal
• Vegetables – Vagus
• A – Accessory
• H – Hypoglossal
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PNS: Cranial Nerves
•I Olfactory nerve—sensory for smell
•II Optic nerve—sensory for vision
•III Oculomotor nerve—motor fibers to eye
muscles
•IV Trochlear—motor fiber to one eye muscle
© 2012 Pearson Education, Inc.
PNS: Cranial Nerves
•V Trigeminal nerve—sensory for the face;
motor fibers to chewing muscles
•VI Abducens nerve—motor fibers to eye
muscles
•VII Facial nerve—sensory for taste; motor
fibers to the face
•VIII Vestibulocochlear nerve—sensory for
balance and hearing
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PNS: Cranial Nerves
•IX Glossopharyngeal nerve—sensory for
taste; motor fibers to the pharynx
•X Vagus nerves—sensory and motor fibers
for pharynx, larynx, and viscera
•XI Accessory nerve—motor fibers to neck and
upper back
•XII Hypoglossal nerve—motor fibers to
tongue
© 2012 Pearson Education, Inc.
III Oculomotor
IV Trochlear
VI Abducens
I Olfactory
II Optic
V Trigeminal
V Trigeminal
VII Facial
Vestibular
branch
Cochlear
branch
VIII Vestibulocochlear
X Vagus
IX Glossopharyngeal
XII Hypoglossal
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XI Accessory
Figure 7.24
86
PNS: Spinal Nerves
•There is a pair of spinal nerves at the level of
each vertebrae for a total of 31 pairs
•Formed by the combination of the ventral and
dorsal roots of the spinal cord
•Named for the region from which they arise
© 2012 Pearson Education, Inc.
Cervical
nerves
Thoracic
nerves
Lumbar
nerves
Sacral
nerves
C1
2
3
4
5
6
7
8
T1
2
3
4
5
6
7
8
9
10
11
Ventral rami form
cervical plexus
(C1 – C5)
Ventral rami form
brachial plexus
(C5 – C8; T1)
No plexus
formed
(intercostal
nerves)
(T1 – T12)
12
L1
2
3
4
Ventral rami form
lumbar plexus
(L1 – L4)
5
(a)
© 2012 Pearson Education, Inc.
S1
2
3
4
Ventral rami form
sacral plexus
(L4 – L5; S1 – S4)
Figure 7.25a
87
PNS: Anatomy of Spinal Nerves
•Spinal nerves divide soon after leaving the
spinal cord
•Ramus—branch of a spinal nerve; contains
both motor and sensory fibers
•Dorsal rami—serve the skin and muscles of
the posterior trunk
•Ventral rami—form a complex of networks
(plexus) for the anterior
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Dorsal root
Dorsal root
ganglion
Spinal
cord
Ventral
root
Spinal nerve
(b)
© 2012 Pearson Education, Inc.
Dorsal
ramus
Ventral
ramus
Figure 7.25b
88
PNS: Spinal Nerve Plexuses
•Plexus–networks of nerves serving motor and
sensory needs of the limbs
•Form from ventral rami of spinal nerves in the
cervical, lumbar, and sacral regions
•Four plexuses:
•Cervical
•Brachial
•Lumbar
•Sacral
© 2012 Pearson Education, Inc.
PNS: Spinal Nerve Plexuses
•Cervical Plexus
•Originates from ventral rami in C1 – C5
•Important nerve is the phrenic nerve
•Areas served:
•Diaphragm
•Shoulder and neck
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PNS: Spinal Nerve Plexuses
•Brachial Plexus
•Originates from ventral rami in C5 – C8 and T1
•Important nerves:
•Axillary
•Radial
•Median
•Musculocutaneous
•Ulnar
•Areas served: shoulder, arm, forearm, and
hand
© 2012 Pearson Education, Inc.
Axillary nerve
Humerus
Radial
nerve
Musculocutaneous
nerve
Ulna
Radius
Ulnar nerve
Radial nerve
(superficial
branch)
Median nerve
(a) The major nerves
of the upper limb
© 2012 Pearson Education, Inc.
Figure 7.26a
90
PNS: Spinal Nerve Plexuses
•Lumbar Plexus
•Originates from ventral rami in L1 through L4
•Important nerves:
•Femoral
•Obturator
•Areas served:
•Lower abdomen
•Anterior and medial thighs
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Femoral
Lateral
femoral
cutaneous
Obturator
Anterior
femoral
cutaneous
Saphenous
© 2012 Pearson Education, Inc.
(b) Lumbar plexus,
anterior view
Figure 7.26b
91
PNS: Spinal Nerve Plexuses
•Sacral Plexus
•Originates from ventral rami in L4 – L5 and
S1 – S4
•Important nerves:
•Sciatic
•Superior and inferior gluteal
•Areas served:
•Lower trunk and posterior thigh
•Lateral and posterior leg and foot
•Gluteal muscles of hip area
© 2012 Pearson Education, Inc.
Superior
gluteal
Inferior
gluteal
Sciatic
Posterior
femoral
cutaneous
Common
fibular
Tibial
Sural (cut)
Deep
fibular
Superficial
fibular
Plantar
branches
© 2012 Pearson Education, Inc.
(c) Sacral plexus, posterior view
Figure 7.26c
92
PNS: Autonomic Nervous System
•Motor subdivision of the PNS
•Consists only of motor nerves
•Also known as the involuntary nervous system
•Regulates activities of cardiac and smooth
muscles and glands
•Two subdivisions
•Sympathetic division
•Parasympathetic division
© 2012 Pearson Education, Inc.
PNS: Differences Between Somatic
and Autonomic Nervous Systems
Somatic Nervous
System
Autonomic Nervous
System
Nerves
One-neuron; it
originates in the CNS
and axons extend to
the skeletal muscles
served
Two-neuron system
consisting of
preganglionic and
postganglionic
neurons
Effector organ
Skeletal muscle
Smooth muscle,
cardiac muscle,
glands
Subdivisions
None
Sympathetic and
parasympathetic
Neurotransmitter
Acetylcholine
Acetylcholine,
epinephrine,
norepinephrine
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Central
nervous system
Peripheral nervous system
Effector organs
Acetylcholine
Skeletal
muscle
Somatic nervous system
Acetylcholine
Autonomic
nervous
system
Sympathetic
division
Smooth muscle
(e.g., in stomach)
Norepinephrine
Ganglion
Acetylcholine
Epinephrine and
norepinephrine
Adrenal medulla
Acetylcholine
Blood
vessel
Glands
Cardiac
muscle
Parasympathetic
division
Ganglion
KEY:
Preganglionic
axons
(sympathetic)
Postganglionic
axons
(sympathetic)
Myelination
Preganglionic
axons
(parasympathetic)
Postganglionic
axons
(parasympathetic)
© 2012 Pearson Education, Inc.
Figure 7.27
PNS: Anatomy of the Parasympathetic
Division
•Preganglionic neurons originate from the
craniosacral regions:
•The cranial nerves III, VII, IX, and X
•S2 through S4 regions of the spinal cord
•Due to site of preganglionic neuron origination,
the parasympathetic division is also known as
the craniosacral division
•Terminal ganglia are at the effector organs
•Neurotransmitter: acetylcholine
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94
Parasympathetic
Sympathetic
Eye
Eye
Brain stem
Salivary
glands
Heart
Skin
Cranial
nerves
Sympathetic
ganglia
Salivary
glands
Cervical
Lungs
Lungs
T1
Heart
Stomach
Thoracic
Stomach
Pancreas
Pancreas
L1
Liver and
gallbladder
Lumbar
Pelvic
splanchnic
nerves
© 2012 Pearson Education, Inc.
Adrenal
gland
Bladder
Bladder
Genitals
Liver
and gallbladder
Genitals
Sacral nerves (S2 – S4)
Figure 7.28
PNS: Anatomy of the Sympathetic Division
•Preganglionic neurons originate from T1
through L2
•Ganglia are at the sympathetic trunk (near the
spinal cord)
•Short pre-ganglionic neuron and long postganglionic neuron transmit impulse from CNS
to the effector
•Neurotransmitters: norepinephrine and
epinephrine (effector organs)
© 2012 Pearson Education, Inc.
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Lateral horn of
gray matter
Dorsal ramus
of spinal nerve
Dorsal root
Sympathetic
trunk
Spinal
nerve
(a)
(b)
(c)
Ventral root
Sympathetic
trunk ganglion
Splanchnic
nerve
Ventral ramus
of spinal nerve
To effector:
blood vessels,
arrector pili
muscles, and
sweat glands
of the skin
Gray ramus
communicans
White ramus
communicans
Collateral ganglion
(such as the celiac)
Visceral effector organ
(such as small intestine)
© 2012 Pearson Education, Inc.
Figure 7.29
PNS: Autonomic Functioning
•Sympathetic—“fight or flight”
•Response to unusual stimulus
•Takes over to increase activities
•Remember as the “E” division
•Exercise, excitement, emergency, and
embarrassment
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96
PNS: Autonomic Functioning
• Parasympathetic—“housekeeping” activites
•Conserves energy
•Maintains daily necessary body functions
•Remember as the “D” division
•digestion, defecation, and diuresis
© 2012 Pearson Education, Inc.
Development Aspects of the Nervous
System
•The nervous system is formed during the first
month of embryonic development
•Any maternal infection can have extremely
harmful effects
•The hypothalamus is one of the last areas of
the brain to develop
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97
Development Aspects of the Nervous
System
•No more neurons are formed after birth, but
growth and maturation continues for several
years
•The brain reaches maximum weight as a
young adult
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98