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Chapter 12: Nervous Tissue
Objectives
 Describe the anatomical and functional divisions of the nervous system.
 Sketch and label the structure of a typical neuron, describe the functions of each
component, and classify neurons on the basis of their structure and function.
 Describe the locations and functions of the various types of neuroglia.
 Explain how the resting potential is created and maintained.
 Describe the events involved in the generation and propagation of an action potential.
 Discuss the factors that affect the speed with which action potentials are propagated.
 Describe the structure of a synapse, and explain the mechanism involved in synaptic
activity.
 Describe the major types of neurotransmitters and neuromodulators, and discuss their
effects on postsynaptic membranes.
 Discuss the interactions that enable information processing to occur in neural tissue.
An Introduction to the Nervous System
 Neural Tissue
o Contains two kinds of cells
 N_____________________:
 cells that send and receive signals
 N_____________________ (glial cells):
 cells that support and protect
neurons
An Introduction to the Nervous System
 Organs of the Nervous System
o Brain and spinal cord
o Sensory receptors of sense organs (eyes, ears,
etc.)
o Nerves connect nervous system with other
systems
Divisions of the Nervous System
 Anatomical Divisions of the Nervous System
o _____________________nervous system (CNS)
o Peripheral nervous system (PNS)
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Divisions of the Nervous System
 The Central Nervous System (CNS)
o Consists of the _____________________ and _____________________
o Contains neural tissue, connective tissues, and blood vessels
o Functions of the CNS
 Are to process and coordinate:
 sensory data: from inside and outside body
 motor commands: control activities of peripheral organs (e.g.,
skeletal muscles)
 higher functions of brain: intelligence, memory, learning, emotion
Divisions of the Nervous System
 The Peripheral Nervous System (PNS)
o Includes all neural tissue _____________________the CNS
o Functions of the PNS
 Deliver sensory information to the CNS
 Carry motor commands to peripheral tissues and systems

The Peripheral Nervous System (PNS)
o Nerves (also called peripheral nerves)
 Bundles of axons with connective tissues and blood vessels
 Carry sensory information and motor
commands in PNS:
 ___________________nerves—
connect to brain
 spinal nerves—attach to spinal
cord
Divisions of the Nervous System
 Functional Divisions of the PNS
o _____________________division
 Carries sensory information
 From PNS sensory receptors to CNS
o _____________________division
 Carries motor commands
 From CNS to PNS muscles and glands
Divisions of the Nervous System
 Functional Divisions of the PNS
o The efferent division
 _____________________nervous system (SNS):
 controls skeletal muscle contractions
Chapter 12: Neural Tissue
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
Autonomic nervous system (ANS):
 Controls contractions of smooth muscle, cardiac muscle and
glandular secretions
o _____________________division
o parasympathetic division
Neurons
 Neurons
o The basic functional units of the nervous system
Neurons
 The Structure of Neurons
o cell body (_____________________)
o short, branched dendrites
o long, single axon

Major Organelles of the Cell Body
o Nucleus
o Perikaryon (cytoplasm)
o Mitochondria
o RER and ribosomes (produce neurotransmitters)
o Cytoskeleton

_____________________bodies
o Dense areas of RER and ribosomes
o Make neural tissue appear gray (gray matter)

D_____________________
o Highly branched
Chapter 12: Neural Tissue
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
The _____________________
o Carries electrical signal (action potential) to target
Neurons
 Structures of the Axon
o Axon hillock
 “_____________________”
o Telodendria
 Fine extensions of distal axon
o Synaptic terminals
 Tips of telodendria
Neurons
 The Synapse
o The synaptic knob
 Contains synaptic vesicles of
_____________________
 Neurotransmitters:
 are chemical messengers
 affect receptors of postsynaptic
membrane
Neurons
 The Structure of Neurons
o The synapse
 Presynaptic cell:
 neuron that sends message
 _____________________cell:
 cell that receives message
 The synaptic cleft:
 the small gap that separates the presynaptic membrane and the
postsynaptic membrane
Neurons
 Types of Synapses
o _____________________junction
 Synapse between neuron and muscle
o Neuroglandular junction
 Synapse between neuron and gland
Neurons
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
Recycling Neurotransmitters
o Axoplasmic transport
 Neurotubules within the axon
 Transport raw materials
 Between cell body and synaptic knob
 Powered by mitochondria, kinesin, and dynein
Neurons
 Four Structural Classifications of Neurons
o Anaxonic neurons
 Found in brain and sense organs
o Bipolar neurons
 Found in special sensory organs (sight, smell,
hearing)
o Unipolar neurons
 Found in sensory neurons of PNS
o Multipolar neurons
 Common in the CNS
 Include all skeletal muscle motor neurons
Neurons
 _____________________Neurons
o Small
o All cell processes look alike
 Bipolar Neurons
o Are small
o One dendrite, one axon
 _____________________Neurons
o Have very long axons
o Fused dendrites and axon
o Cell body to one side
 Multipolar Neurons
o Have very long axons
o Multiple dendrites, one axon
Neurons
 Three Functional Classifications of Neurons
o Sensory neurons
 Afferent neurons of PNS
o _____________________neurons
 Efferent neurons of PNS
o I_____________________
 Association neurons
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Neurons
 Three Types of Sensory Receptors
o Interoceptors
 Monitor internal systems
 Internal senses
o Exteroceptors
 External senses
 Distance senses
o P_____________________
 Monitor position and movement
Neurons
 Motor Neurons
 Carry instructions from CNS to peripheral effectors
 Via efferent fibers (axons)

Two major efferent systems
o Somatic nervous system (SNS)
o Autonomic (visceral) nervous system (ANS)
Neurons
 Interneurons
o Most are located in brain, spinal cord, and autonomic ganglia
o Between sensory and motor neurons
Neuroglia
 Two types of cells of nervous tissue
o Neurons perform all communication, information processing, and control
functions of the nervous system
o _____________________preserve physical and biochemical structure of neural
tissue and are essential to survival and function of neurons
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Neuroglia
 Four Types of Neuroglia in the CNS
o Ependymal cells
o Astrocytes
o O_____________________
o Microglia
Neuroglia
 Four Types of Neuroglia in the CNS
o Ependymal cells
 Line central canal of spinal cord and ventricles of brain:
 secrete cerebrospinal fluid (CSF)
 circulate CSF
o A_____________________
 Maintain blood–brain barrier (isolates CNS)
 Control interstitial environment
o Oligodendrocytes
 Processes contact other neuron cell bodies
 Wrap around axons to form myelin sheaths
o Microglia
 Migrate through neural tissue
 Clean up cellular debris, waste products, and pathogens
Neuroglia
 Ganglia
o Masses of neuron cell bodies
o Surrounded by neuroglia
o Found in the PNS
Neuroglia
 Neuroglia of the Peripheral Nervous System
o Satellite cells
 Surround ganglia
 Regulate environment around neuron
o S_____________________ cells
 Also called neurilemmocytes
 Form myelin sheath
(neurilemma)
 many Schwann cells sheath
entire axon
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Neuroglia
 Oligodendrocytes and Schwann Cells
o Myelination
 increases speed of action potentials
 myelin insulates myelinated axons
 makes nerves appear white
o Nodes and internodes
 internodes: myelinated segments of axon
 _____________________ (also called nodes of Ranvier)
 gaps between internodes
 where axons may branch
Neuroglia
 Neural Responses to Injuries
o Wallerian degeneration
 Axon distal to injury degenerates
o Schwann cells
 Form path for _____________________growth
 Wrap new axon in myelin
Neuroglia
 Nerve Regeneration in CNS
o Limited by chemicals released by _____________________that
 Block growth
 Produce scar tissue
Disorders of Nervous Tissue
 Multiple _____________________
o Disorder of oligodendrocytes
o Weakness, incoordination, visual impairment and speech disturbances
o Most common among women 20-40
o Autoimmune disorder or viral
o No cure
 Tumors
o G_____________________
o Multiple neurofibromatosis
Transmembrane Potential
 Ion Movements and Electrical Signals
o All plasma (cell) membranes
produce electrical signals by ion
movements
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o Transmembrane potential is particularly important to neurons
Transmembrane Potential

Five Main Membrane Processes in Neural Activities
 Resting potential
o The transmembrane potential of resting cell
 Graded potential
o Temporary, localized change in
resting potential
 _____________________potential
o Is an electrical impulse
o Produced by graded potential
o Propagates along surface of axon
to synapse
 Synaptic activity
o Releases neurotransmitters at
presynaptic membrane
o Produces graded potentials in postsynaptic membrane
 Information processing
o Response (integration of stimuli) of postsynaptic cell
Transmembrane Potential
 Differing ionic concentrations between cytosol and extracellular fluid
 Selectively permeable membrane
 Transport mechanisms
Passive Forces - Gradients
 _____________________gradients
 Electrical gradients
o Potassium ions leave cytosol (ICF) more rapidly than sodium enters
o Makes interior more negative
 Electrochemical gradients
o Sum of chemical and electrical forces acting across the membrane
Active Forces
 Sodium Potassium Exchange Pump
Resting Potential
 Undisturbed cell
 High permeability of potassium
 Low permeability of Sodium
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

Sodium-potassium pump stabilization
Balanced at -70 mV
Transmembrane Potential
 Three Classes of Gated Channels
 _____________________gated channels
o Open in presence of specific chemicals
o Found on neuron cell body and dendrites

_____________________-gated channels
o Respond to changes in transmembrane potential
o Found in neural axons, skeletal muscle sarcolemma,
cardiac muscle

_____________________gated channels
o Respond to membrane distortion
o Found in sensory receptors (touch, pressure,
vibration)
Initiating a Change in the Transmembrane Potential
 Chemically regulated channels
o Acetylcholine
 Mechanically regulated channels
o Pressure (membrane distortion)
The Transmembrane Potential of an Excitable Membrane
 Voltage regulated channels
o Excitable membrane
Transmembrane Potential
 _____________________Potentials
o Also called local potentials
o Changes in transmembrane potential
 That cannot spread far from site of stimulation
o Any stimulus that opens a gated channel
 Produces a graded potential
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Transmembrane Potential
 Graded Potentials
 R_____________________
o When the stimulus is removed, transmembrane potential returns to normal
 Hyperpolarization
o Increasing the negativity of the resting potential
o Result of opening a potassium channel
o Opposite effect of opening a sodium channel
o Positive ions move out, not into cell
Graded Potential
 Transmembrane potential is most affected at point of stimulus and then diminishes with
distance
 Spreads passively
 May involve either depolarization or hyperpolarization
 The stronger the stimulus the greater the affect
Transmembrane Potential
 Graded Potentials
o Effects of graded potentials
 At cell dendrites or cell bodies
Action Potential
 Four Steps in the Generation of Action Potentials
o Step 1: Depolarization to _____________________
o Step 2: Activation of Na+ channels
 Rapid depolarization
 Na+ ions rush into cytoplasm
 Inner membrane changes from negative to positive
o Step 3: Inactivation of Na+ channels, activation of K+ channels
 At +30 mV
 Inactivation gates close (Na+ channel inactivation)
 K+ channels open
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 Repolarization begins
o Step 4: Return to normal permeability
 K+ channels begin to close:
 when membrane reaches normal resting potential (–70 mV)
+
 K channels finish closing:
 membrane is hyperpolarized to -90 mV
 transmembrane potential returns to resting level:
 action potential is over
Action Potential
 The Refractory Period
 Absolute _____________________period
o Sodium channels open or inactivated
o No action potential possible
 Relative refractory period
o Membrane potential almost normal
o Very large stimulus can initiate action potential
Action Potential
 Propagation of Action Potentials
o Two methods of propagating action potentials
 Continuous propagation: unmyelinated axons
 Saltatory propagation: myelinated axons
Axon Diameter and Speed
 Three Groups of Axons
o Type A fibers
o Type B fibers
o Type C fibers
 These groups are classified by
o Diameter
o Myelination
o Speed of action potentials
Axon Diameter and Speed
 Type A Fibers
o M_____________________
o Large diameter
o High speed (140 m/sec)
o Carry rapid information to/from CNS
o For example, position, balance, touch, and motor impulses
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

Type B Fibers
o Myelinated
o _____________________diameter
o Medium speed (18 m/sec)
o Carry intermediate signals
o For example, sensory information, peripheral effectors
Type C Fibers
o Unmyelinated
o _____________________diameter
o Slow speed (1 m/sec)
o Carry slower information
o For example, involuntary muscle, gland controls
Synapses
 Synaptic Activity
o Action potentials (nerve impulses)
 Are transmitted from presynaptic neuron
 To postsynaptic neuron (or other postsynaptic cell)
 Across a synapse
Synapses
 Two Classes of Neurotransmitters
o Excitatory neurotransmitters
 Cause depolarization of postsynaptic membranes
 Promote action potentials
o _____________________neurotransmitters
 Cause hyperpolarization of postsynaptic membranes
 Suppress action potentials
Synapses
 The Effect of a Neurotransmitter
o On a postsynaptic membrane
 Depends on the receptor
 Not on the neurotransmitter
o For example, _____________________ (ACh)
 Usually promotes action potentials
 But inhibits cardiac neuromuscular junctions
Synapses
 Cholinergic Synapses
o Any synapse that releases ACh
 All neuromuscular junctions with skeletal muscle fibers
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


Many synapses in CNS
All neuron-to-neuron synapses in PNS
All neuromuscular and neuroglandular junctions of ANS parasympathetic
division
Synapses
 Events at a _____________________Synapse
o Action potential arrives, depolarizes
synaptic knob
o Calcium ions enter synaptic knob, trigger
exocytosis of Ach
o ACh binds to receptors, depolarizes
postsynaptic membrane
o AChE breaks ACh into acetate and choline
Synapses
 Synaptic Delay
o Fewer synapses mean faster response
o Reflexes may involve only one synapse
Synapses
 Synaptic _____________________
o Occurs when neurotransmitter cannot recycle fast enough to meet demands of
intense stimuli
o Synapse inactive until ACh is replenished
Synapses
Mechanism of Drug Actions
Chemical Synapses
 The effect of a neurotransmitter on the postsynaptic membrane depends on the
properties of the receptor, not on the nature of the neurotransmitter.
Neurotransmitters and Neuromodulators
 Other Neurotransmitters
o At least 50 neurotransmitters other than ACh, including
 Some amino acids
 Peptides
 Prostaglandins
 ATP
 Some dissolved gases
Chapter 12: Neural Tissue
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Neurotransmitters and Neuromodulators
 Important Neurotransmitters
o Other than acetylcholine
 Norepinephrine (NE)
 D_____________________
 Serotonin
 Gamma aminobutyric acid (GABA)
Neurotransmitters and Neuromodulators
 Norepinephrine (NE)
o Released by adrenergic synapses
o Excitatory and depolarizing effect
o Widely distributed in brain and portions of ANS
 Dopamine
o A CNS neurotransmitter
o May be excitatory or inhibitory
o Involved in Parkinson disease, cocaine use
 S_____________________
o A CNS neurotransmitter
o Affects attention and emotional states
 Gamma Aminobutyric Acid (GABA)
o Inhibitory effect
o Functions in CNS
o Not well understood
Information Processing
 Postsynaptic Potentials
o Graded potentials developed in a postsynaptic cell
 In response to neurotransmitters
 Two Types of Postsynaptic Potentials
o Excitatory postsynaptic potential (EPSP)
 Graded depolarization of postsynaptic membrane
o Inhibitory postsynaptic potential (IPSP)
 Graded hyperpolarization of postsynaptic membrane
Information Processing
 Inhibition
o A neuron that receives many IPSPs
 Is _____________________from producing an action potential
 Because the stimulation needed to reach threshold is increased
Chapter 12: Neural Tissue
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
Summation
o To trigger an action potential
o One EPSP is not enough
o EPSPs (and IPSPs) combine through summation:
 temporal summation
 spatial summation
Information Processing
 _____________________Summation
o Multiple times
o Rapid, repeated stimuli at one synapse
 Spatial Summation
o Multiple locations
o Many stimuli, arrive at multiple synapses
Chapter 12: Neural Tissue
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