CH11(12)
Functions of the Nervous System
1._________ input
• Information gathered by sensory receptors about internal and
_________ changes
2.Integration
• _________ of sensory input
3.Motor output
• Activation of _________ organs (_________ and _________)
produces a response
Divisions of the Nervous System
• _________ nervous system (CNS)
• Brain and spinal cord
• Integration and command center
• _________ nervous system (PNS)
• Paired _________ and _________ nerves carry messages to and
from the CNS
Peripheral Nervous System (PNS)
• Two functional divisions
1. Sensory (_________) division
• Somatic afferent fibers—convey impulses from skin, skeletal
muscles, and joints
• _________ afferent fibers—convey impulses from visceral
organs
2. Motor (_________) division
• Transmits impulses from the CNS to effector organs
Motor Division of PNS
1.Somatic (_________) nervous system
• _________ control of skeletal muscles
Motor Division of PNS
2.Autonomic (_________) nervous system (_________)
• _________ motor nerve fibers
• Regulates _________ muscle, cardiac muscle, and glands
• _________ functional subdivisions
• _________
• Parasympathetic
Histology of Nervous Tissue
• Two principal cell types
1. _________ —excitable cells that transmit electrical signals
Histology of Nervous Tissue
2.Neuroglia (glial cells)—supporting cells:
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_________ (CNS)
Microglia (CNS)
_________ cells (CNS)
Oligodendrocytes (CNS)
_________ cells (PNS)
Schwann cells (PNS)
Astrocytes
• Most abundant, _________, and highly branched glial cells
• Cling to _________, synaptic endings, and _________
• Support and _________ neurons
Astrocytes
• Help determine capillary _________
• Guide _________ of young neurons
• Control the _________ environment
• Participate in information processing in the _________
Microglia
• Small, _________ cells with thorny processes
• _________ toward injured neurons
• Phagocytize _________ and neuronal _________
Ependymal Cells
• Range in shape from _________ to _________
• May be ciliated
• Line the central cavities of the brain and spinal column
• Separate the CNS _________ fluid from the cerebrospinal fluid in
the cavities
Oligodendrocytes
• _________ cells
• Processes wrap _________ nerve fibers, forming insulating
myelin sheaths
Satellite Cells and Schwann Cells
• _________ cells
• Surround neuron cell bodies in the PNS
• _________ cells (_________)
• Surround peripheral nerve fibers and form myelin sheaths
• Vital to _________ of damaged _________ nerve fibers
Neurons (Nerve Cells)
• Special characteristics:
• Long-lived (_________ years or more)
• _________ —with few exceptions
• _________ metabolic rate—depends on continuous supply of
oxygen and glucose
• Plasma membrane functions in:
• _________ signaling
• Cell-to-cell interactions during development
Cell Body (Perikaryon or Soma)
• _________ center of a neuron
• Spherical nucleus with nucleolus
• Well-developed _________ _________
• Rough ER called _________ bodies (chromatophilic
substance)
Cell Body (Perikaryon or Soma)
• Network of _________ (neurofilaments)
• _________ hillock—cone-shaped area from which axon arises
• Clusters of cell bodies are called nuclei in the CNS, ganglia in
the _________
Processes
• _________ and _________
• Bundles of processes are called
• Tracts in the _________
• Nerves in the _________
Dendrites
• _________, tapering, and diffusely branched
• Receptive (input) region of a _________
• Convey _________ signals toward the cell body as graded
potentials
The Axon
• _________ axon per cell arising from the axon hillock
• Long axons (nerve fibers)
• Occasional branches (_________ collaterals)
The Axon
• _________ terminal branches (_________)
• Knoblike axon terminals (synaptic knobs or boutons)
• _________ region of neuron
• Release neurotransmitters to _________ or _________ other
cells
Axons: Function
• _________ region of a neuron
• Generates and transmits nerve impulses (_________
potentials) away from the cell body
Axons: Function
• Molecules and organelles are moved along _________ by
_________ molecules in two directions:
• _________ —toward axonal terminal
• Examples: mitochondria, membrane components, enzymes
• _________ —toward the cell body
• Examples: organelles to be degraded, signal molecules,
viruses, and bacterial toxins
Myelin Sheath
• Segmented _________ -lipoid sheath around most long or
large-diameter axons
• It functions to:
• Protect and _________ insulate the axon
• _________ speed of nerve impulse transmission
Myelin Sheaths in the PNS
• _________ cells wraps many times around the axon
• Myelin sheath—concentric layers of Schwann cell membrane
• _________ —peripheral bulge of Schwann cell cytoplasm
Myelin Sheaths in the PNS
• Nodes of _________
• Myelin sheath gaps between adjacent _________ cells
• Sites where _________ collaterals can emerge
Unmyelinated Axons
• Thin nerve fibers are _________
• One Schwann cell may incompletely enclose 15 or more
_________ axons
Myelin Sheaths in the CNS
• Formed by processes of oligodendrocytes, not the whole cells
• Nodes of _________ are present
• No _________
• _________ fibers are unmyelinated
White Matter and Gray Matter
• _________ matter
• Dense collections of myelinated fibers
• _________ matter
• Mostly neuron cell bodies and unmyelinated fibers
Structural Classification of Neurons
• Three types:
1. _________ —1 axon and several dendrites
• Most abundant
• Motor neurons and _________
2. _________ —1 axon and 1 dendrite
• Rare, e.g., retinal neurons
Structural Classification of Neurons
3. Unipolar (_________)—single, short process that has two
branches:
• _________ process—more distal branch, often associated with
a sensory receptor
• _________ process—branch entering the _________
Functional Classification of Neurons
• Three types:
1. _________ (afferent)
• Transmit impulses from sensory receptors toward the CNS
2. _________ (efferent)
• Carry impulses from the CNS to effectors
Functional Classification of Neurons
3. _________ (association neurons)
• Shuttle signals through CNS pathways; most are entirely within
the CNS
Neuron Function
• Neurons are _________ irritable
• Respond to adequate _________ by generating an action
potential (nerve impulse)
• Impulse is always the _________ regardless of stimulus
Principles of Electricity
• _________ charges attract each other
• Energy is required to separate _________ charges across a
membrane
• Energy is _________ when the charges move _________ one
another
• If opposite charges are _________, the system has potential
energy
Definitions
• _________ (V): measure of potential energy generated by
separated charge
• _________ difference: voltage measured between two points
• _________ (I): the flow of electrical charge (ions) between two
points
Definitions
• _________ (R): hindrance to charge flow (provided by the
plasma membrane)
• _________: substance with high electrical resistance
• _________: substance with low electrical resistance
Role of Membrane Ion Channels
• _________ serve as membrane ion channels
• Two main types of ion channels
1. Leakage (_________) channels—always _________
Role of Membrane Ion Channels
2. _________ channels (three types):
• Chemically gated (_________ -gated) channels—open with
binding of a specific neurotransmitter
• _________ -gated channels—open and close in response to
changes in membrane potential
• _________ gated channels—open and close in response to
physical deformation of receptors
Gated Channels
• When gated channels are _________:
• Ions diffuse quickly across the membrane along their _________
gradients
• Along _________ concentration gradients from higher
concentration to _________ concentration
• Along electrical gradients toward _________ electrical charge
• Ion flow creates an electrical current and _________ changes
across the membrane
Resting Membrane Potential (Vr)
• Potential difference across the membrane of a _________ cell
• Approximately –70 mV in neurons (_________ side of membrane
is negatively charged relative to outside)
• Generated by:
• Differences in ionic makeup of _________ and _________
• Differential permeability of the plasma membrane
Resting Membrane Potential
• Differences in ionic makeup
• _________ has lower concentration of Na+ and Cl– than ECF
• _________ has higher concentration of K+ and negatively
charged proteins (A–) than ECF
Resting Membrane Potential
• Differential permeability of membrane
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_________ to A–
Slightly permeable to Na+ (through _________ channels)
75 times _________ permeable to K+ (more leakage channels)
_________ permeable to Cl–
Resting Membrane Potential
• _________ interior of the cell is due to much _________
diffusion of K+ out of the cell than Na+ diffusion into the cell
•
_________ -_________ pump stabilizes the resting membrane
potential by maintaining the concentration gradients for Na + and
K+
Membrane Potentials That Act as Signals
• Membrane _________ changes when:
• Concentrations of ions across the membrane change
• _________ of membrane to ions changes
• Changes in membrane potential are _________ used to
_________, integrate and _________ information
Membrane Potentials That Act as Signals
• Two types of signals
• _________ potentials
• Incoming short-distance signals
• _________ potentials
• Long-distance signals of axons
Changes in Membrane Potential
• Depolarization
• A _________ in membrane potential (toward zero)
• Inside of the membrane becomes less _________ than the
resting potential
• _________ the probability of producing a nerve impulse
Changes in Membrane Potential
• Hyperpolarization
• An increase in membrane potential (away from _________)
• Inside of the membrane becomes more _________ than the
resting potential
• _________ the probability of producing a nerve impulse
Graded Potentials
• _________ -lived, localized changes in membrane potential
• _________ or hyperpolarizations
• Graded potential spreads as local currents change the
membrane potential of adjacent regions
Graded Potentials
• Occur when a stimulus causes gated ion channels to open
• E.g., _________ potentials, _________ potentials, _________
potentials
• _________ varies directly (graded) with stimulus strength
• _________ in magnitude with distance as ions flow and diffuse
through leakage channels
• Short-distance signals
Action Potential (AP)
• Brief _________ of membrane potential with a total amplitude
of ~100 mV
• Occurs in _________ cells and _________ of neurons
• Does not decrease in magnitude over distance
• Principal means of _________ -distance _________
communication
Generation of an Action Potential
• _________ state
• Only leakage channels for Na+ and K+ are open
• All gated Na+ and K+ channels are closed
Properties of Gated Channels
• Properties of _________ channels
• Each _________ + channel has two voltage-sensitive gates
• _________ gates
• Closed at rest; open with depolarization
• _________ gates
• Open at rest; block channel once it is open
Properties of Gated Channels
• Each _________ + channel has one voltage-sensitive gate
• _________ at rest
• Opens _________ with depolarization
Depolarizing Phase
• _________ local currents open voltage-gated Na+ channels
• Na+ _________ causes more depolarization
• At _________ (–55 to –50 mV) _________ feedback leads to
opening of all Na+ channels, and a reversal of membrane
polarity to +30mV (spike of action potential)
Repolarizing Phase
• _________ phase
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_________ + channel slow inactivation gates close
Membrane permeability to Na+ _________ to resting levels
Slow _________ -sensitive K+ gates open
K+ exits the cell and internal _________ is restored
Hyperpolarization
• Hyperpolarization
• Some K+ channels remain _________, allowing _________ K+
efflux
• This causes after-_________ of the membrane (undershoot)
Role of the Sodium-Potassium Pump
• Repolarization
• _________ the resting electrical conditions of the neuron
• Does not restore the _________ ionic conditions
• Ionic redistribution back to resting conditions is restored by the
thousands of _________ -_________ pumps
Propagation of an Action Potential
• Na+ influx causes a patch of the axonal membrane to
depolarize
• _________ currents occur
• Na+ channels toward the point of _________ are inactivated
and not affected by the local currents
Propagation of an Action Potential
• _________ currents affect adjacent areas in the forward
direction
• _________ opens voltage-gated channels and triggers an AP
• Repolarization wave follows the depolarization wave
• (Fig. 11.12 shows the propagation process in unmyelinated
axons.)
Threshold
• At threshold:
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Membrane is _________ by 15 to 20 mV
Na+ permeability increases
Na _________ exceeds K+ efflux
The _________ feedback cycle begins
Threshold
• _________ stimulus—weak local depolarization that does not
reach threshold
• _________ stimulus—strong enough to push the membrane
potential toward and beyond threshold
• AP is an _________ phenomenon—action potentials either
happen completely, or not at all
Coding for Stimulus Intensity
• All _________ potentials are alike and are independent of
stimulus intensity
• How does the _________ tell the difference between a weak
stimulus and a strong one?
• Strong stimuli can generate action potentials _________ often
than weaker stimuli
• The CNS determines stimulus intensity by the _________ of
impulses
Absolute Refractory Period
• Time from the opening of the Na+ channels until the _________
of the channels
• Ensures that each AP is an all-or-none event
• Enforces _________ transmission of nerve impulses
Relative Refractory Period
• Follows the _________ refractory period
• Most Na+ channels have returned to their resting state
• Some K+ _________ are still open
• _________ is occurring
• _________ for AP generation is elevated
• Exceptionally _________ stimulus may generate an AP
Conduction Velocity
• _________ velocities of neurons vary widely
• Effect of axon _________
• Larger diameter fibers have less _________ to local current flow
and have faster impulse conduction
• Effect of _________
• Continuous conduction in _________ axons is slower than
saltatory conduction in myelinated axons
Conduction Velocity
• Effects of _________
• Myelin sheaths insulate and prevent leakage of charge
• _________ conduction in _________ axons is about 30 times
faster
• Voltage-gated Na+ channels are located at the nodes
• APs appear to jump rapidly from node to node
Multiple Sclerosis (MS)
• An _________ disease that mainly affects young adults
• Symptoms: visual disturbances, _________, loss of muscular control,
speech disturbances, and urinary incontinence
• Myelin sheaths in the _________ become nonfunctional scleroses
• Shunting and short-circuiting of nerve impulses occurs
• Impulse conduction _________ and eventually _________
Multiple Sclerosis: Treatment
• Some immune system–modifying drugs, including interferons
and Copazone:
• Hold symptoms at bay
• Reduce complications
• Reduce disability
Nerve Fiber Classification
• Nerve fibers are classified according to:
• Diameter
• Degree of _________
• Speed of _________
Nerve Fiber Classification
• Group _________ fibers
• Large diameter, _________ somatic sensory and motor fibers
• Group B fibers
• _________ diameter, lightly myelinated ANS fibers
• Group C fibers
• _________ diameter, unmyelinated ANS fibers
The Synapse
• A junction that mediates information transfer from one neuron:
• To another _________, or
• To an _________ cell
The Synapse
• _________ neuron—conducts impulses toward the synapse
• _________ neuron—transmits impulses away from the
synapse
Types of Synapses
• _________ —between the axon of one neuron and the dendrite
of another
• _________ —between the axon of one neuron and the soma of
another
• Less common types:
• _________ (axon to axon)
• _________ (dendrite to dendrite)
• _________ (dendrite to soma)
Electrical Synapses
• _________ common than chemical synapses
• Neurons are electrically coupled (joined by _________ junctions)
• Communication is very _________, and may be unidirectional or
bidirectional
• Are important in:
• _________ nervous tissue
• Some brain regions
Chemical Synapses
• Specialized for the release and reception of _________
• Typically composed of two parts
• Axon terminal of the _________ neuron, which contains synaptic
vesicles
• _________ region on the postsynaptic neuron
Synaptic Cleft
• Fluid-filled space separating the _________ and _________
neurons
• Prevents nerve impulses from directly passing from one neuron
to the next
Synaptic Cleft
• Transmission across the _________ cleft:
• Is a chemical event (as opposed to an electrical one)
• Involves _________, _________, and binding of
neurotransmitters
• Ensures unidirectional communication _________ neurons
Information Transfer
• AP arrives at _________ terminal of the _________ neuron
and opens voltage-gated Ca2+ channels
• _________ protein binds Ca2+ and promotes fusion of synaptic
vesicles with axon membrane
• _________ of neurotransmitter occurs
Information Transfer
• _________ diffuses and binds to receptors (often chemically
gated ion channels) on the postsynaptic neuron
• _________ channels are opened, causing an excitatory or
inhibitory event (graded potential)
Termination of Neurotransmitter Effects
• Within a few milliseconds, the neurotransmitter effect is
terminated
• Degradation by _________
• Reuptake by _________ or axon terminal
• _________ away from the synaptic cleft
Synaptic Delay
• _________ must be released, diffuse across the synapse, and
bind to receptors
• _________ delay—time needed to do this (0.3–5.0 ms)
• Synaptic delay is the rate-limiting step of _________
transmission
Postsynaptic Potentials
• Graded potentials
• _________ determined by:
• Amount of _________ released
• Time the neurotransmitter is in the area
• Types of _________ potentials
1. _________ —excitatory postsynaptic potentials
2. _________ —inhibitory postsynaptic potentials
Excitatory Synapses and EPSPs
• _________ binds to and opens chemically gated channels that
allow simultaneous flow of Na+ and K+ in opposite directions
• Na+ influx is greater that K+ _________, causing a net
depolarization
• EPSP helps trigger AP at axon _________ if EPSP is of
threshold strength and opens the voltage-gated channels
Inhibitory Synapses and IPSPs
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Neurotransmitter binds to and opens channels for K+ or Cl–
• Causes a _________ (the inner surface of membrane becomes
more negative)
• Reduces the _________ neuron’s ability to produce an action
potential
Integration: Summation
• A single _________ cannot induce an action potential
• _________ can summate to reach threshold
• _________ can also summate with _________, canceling each
other out
Integration: Summation
• _________ summation
• One or more presynaptic neurons transmit impulses in rapid-fire
order
• _________ summation
• Postsynaptic neuron is stimulated by a large number of terminals
at the same time
Integration: Synaptic Potentiation
• Repeated use _________ the efficiency of _________
• Ca2+ concentration increases in _________ terminal and ostsynaptic
neuron
• Brief _________ -frequency stimulation partially depolarizes the
postsynaptic neuron
• _________ gated channels (NMDA receptors) allow Ca2+ entry
• Ca2+ activates kinase enzymes that promote more effective responses to
subsequent stimuli
Integration: Presynaptic Inhibition
• Release of excitatory _________ by one neuron may be
inhibited by the activity of another neuron via an axoaxonic
synapse
• _________ neurotransmitter is released and _________
EPSPs are formed
Neurotransmitters
• Most neurons make _________ or more neurotransmitters,
which are released at different stimulation frequencies
• _________ or more neurotransmitters have been identified
• Classified by chemical structure and by function
Chemical Classes of Neurotransmitters
• _________ (Ach)
• Released at neuromuscular junctions and some ANS neurons
• Synthesized by enzyme choline acetyltransferase
• _________ by the enzyme _________ (AChE)
Chemical Classes of Neurotransmitters
• _________ amines include:
• Catecholamines
• _________, norepinephrine (NE), and _________
• Indolamines
• Serotonin and histamine
• _________ distributed in the brain
• Play roles in _________ behaviors and the biological clock
Chemical Classes of Neurotransmitters
• Amino acids include:
• _________ —Gamma ()-aminobutyric acid
• Glycine
• _________
• Glutamate
Chemical Classes of Neurotransmitters
• Peptides (_________) include:
• _________ P
• Mediator of pain signals
• Endorphins
• Act as natural opiates; reduce pain perception
• _________ -brain peptides
• Somatostatin and _________
Chemical Classes of Neurotransmitters
• _________ such as ATP:
• Act in both the _________ and PNS
• Produce fast or slow responses
• Induce Ca2+ influx in _________
• Provoke pain sensation
Chemical Classes of Neurotransmitters
• _________ and lipids
• _________ oxide (NO)
• Synthesized on demand
• Activates the intracellular receptor guanylyl cyclase to cyclic
_________
• Involved in learning and memory
• _________ _________ (CO) is a regulator of _________ in the
brain
Chemical Classes of Neurotransmitters
• _________ and lipids
• Endocannabinoids
• _________ soluble; synthesized on demand from membrane
lipids
• Bind with _________ protein–coupled receptors in the brain
• Involved in learning and memory
Functional Classification of Neurotransmitters
• Neurotransmitter effects may be excitatory (depolarizing) and/or inhibitory
(hyperpolarizing)
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_________ by the receptor type of the postsynaptic neuron
GABA and glycine are usually inhibitory
_________ is usually excitatory
Acetylcholine
• _________ at neuromuscular junctions in skeletal muscle
• Inhibitory in cardiac muscle
Neurotransmitter Actions
• Direct action
• _________ binds to channel-linked receptor and opens ion
channels
• Promotes _________ responses
• Examples: _________ and _________ _________
Neurotransmitter Actions
• _________ action
• Neurotransmitter binds to a _________ protein-linked receptor
and acts through an _________ second messenger
• Promotes long-lasting effects
• Examples: biogenic amines, neuropeptides, and dissolved gases
Neurotransmitter Receptors
• Types
1. Channel-linked receptors
2. G protein-linked receptors
Channel-Linked (Ionotropic) Receptors
• _________ -gated ion channels
• Action is immediate and brief
• _________ receptors are channels for small cations
• Na+ influx contributes most to depolarization
• Inhibitory receptors allow Cl– _________ or K+ efflux that
causes _________
G Protein-Linked (Metabotropic) Receptors
• _________ protein complexes
• Responses are indirect, _________, _________, and often
prolonged and widespread
• Examples: muscarinic ACh receptors and those that bind
biogenic amines and neuropeptides
G Protein-Linked Receptors: Mechanism
• Neurotransmitter binds to _________ protein–linked receptor
• G protein is activated
• _________ G protein controls production of second
messengers, e.g., _________ AMP, cyclic _________,
diacylglycerol or Ca2+
G Protein-Linked Receptors: Mechanism
• Second messengers
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_________ or close ion channels
Activate kinase enzymes
_________ channel proteins
Activate genes and induce protein synthesis
Neural Integration: Neuronal Pools
• Functional groups of _________ that:
• Integrate _________ information
• Forward the processed information to other destinations
Neural Integration: Neuronal Pools
• Simple neuronal pool
• Single _________ fiber branches and synapses with several
neurons in the pool
• _________ zone—neurons most closely associated with the
incoming fiber
• _________ zone—neurons farther away from incoming fiber
Types of Circuits in Neuronal Pools
• _________ circuit
• One incoming fiber stimulates an ever-increasing number of
fibers, often amplifying circuits
• May affect a _________ pathway or several
• Common in both sensory and motor systems
Types of Circuits in Neuronal Pools
• _________ circuit
• Opposite of diverging circuits, resulting in either strong
stimulation or inhibition
• Also common in sensory and motor systems
Types of Circuits in Neuronal Pools
• Reverberating (_________) circuit
• Chain of neurons containing collateral synapses with previous
neurons in the chain
Types of Circuits in Neuronal Pools
• _________ after-discharge circuit
• Incoming fiber stimulates _________ neurons in parallel arrays to
stimulate a common output cell
Patterns of Neural Processing
• _________ processing
• Input travels along _________ pathway to a specific destination
• Works in an all-or-none manner to produce a specific response
Patterns of Neural Processing
• _________ processing
• Example: _________ —rapid, automatic responses to stimuli that
always cause the same response
• Reflex arcs (_________) have _________ essential components:
receptor, sensory neuron, CNS integration center, motor neuron,
and effector
Patterns of Neural Processing
• Parallel processing
• Input travels along _________ pathways
• _________ stimulus promotes numerous responses
• Important for _________ -level mental functioning
• Example: a smell may remind one of the odor and associated
experiences
Developmental Aspects of Neurons
• The nervous system _________ from the neural tube and neural crest
formed from ectoderm
• The _________ tube becomes the CNS
• _________ cells of the neural tube undergo differentiation to form cells
needed for development
• Cells (neuroblasts) become amitotic and migrate
• Neuroblasts sprout axons to connect with targets and become neurons
Axonal Growth
• Growth cone at tip of axon interacts with its environment via:
• Cell surface adhesion proteins (_________, integrin, and nerve cell
adhesion molecules or N-CAMs)
• _________ that attract or repel the growth cone
• Nerve growth factor (NGF), which keeps the neuroblast alive
• _________ provide physical support and cholesterol essential for
construction of synapses
Cell Death
• About 2/3 of neurons _________ before birth
• Death results in cells that fail to make functional synaptic contacts
• Many cells also die due to _________ (programmed cell death)
during development