Name: ___KEY_______________________________________ Period: ____ Date: ___________
Chapter 9: Nervous Tissue
I. OVERVIEW OF THE NERVOUS SYSTEM
A. Organization of the Nervous System
1. Two main subsystems of the nervous system:
a. _Central Nervous System (CNS)_: consists of the brain and spinal cord
i.
Brain contains ~ _100 billion_ neurons
ii.
Spinal cord contains ~ _100 million_ neurons and is encircled by bones of
vertebral column.
iii.
Function: _ processes different kinds of sensory information; source of
thoughts, emotions, memories_
b. _Peripheral Nervous System (PNS)_: includes all nervous tissue outside the CNS.
i.
Components of PNS:
(1) _Nerves_; bundle of hundreds to thousands of axons plus associated
connective tissue and blood vessels lying outside the brain and
spinal cord.
Cranial nerves I-XII emerge from base of the brain.
Spinal nerves emerge from spinal cord.
(2) _Ganglia_ are small masses of nervous tissue consisting mostly of neuron
cell bodies and located outside the brain and spinal cord; closely
associated with _cranial_ and _spinal_ nerves.
(3) Enteric plexuses:
Found: _walls of organs of gastrointestinal tract______________
Function: _regulate digestive system_______________________
(4) Sensory receptors:
Found: _dendrites of sensory neurons or specialized cells______
Function: _monitor changes in internal/external environment__
Recall: CNS - brain and spinal cord; integrates and correlates many different kinds of incoming
sensory information; source of thoughts, emotions, and memories.
PNS – cranial nerves and their branches, spinal nerves and their branches, ganglia, and sensory
receptors; functions divided into subdivisions….
SUBDIVISIONS OF PNS:
1. Somatic nervous system (SNS)
a. _sensory neurons_______________: convey information from somatic receptors in head,
body wall, and limbs, and from receptors for special senses of vision, hearing, taste, and
smell to CNS
b. _motor neurons_____: conduct impulses from CNS to _skeletal____muscles
only; can be consciously controlled, voluntary actions
2. Autonomic nervous system (ANS)
a. _sensory neurons____________: convey information from autonomic sensory
receptors, located in visceral organs (stomach, lungs) to CNS
b. _motor neurons_________: conduct nerve impulses from CNS to _smooth__,
_cardiac_____ muscles and glands; cannot be consciously controlled, involuntary
actions
c. Two divisions of ANS are: _sympathetic_ and _parasympathetic_; these divisions usually
perform opposite functions
i. “Fight-or-flight” responses  _sympathetic__________
ii. “Rest-and-digest” activities  _parasympathetic______
3. Enteric nervous system (ENS)
a. Known as _”brain of the gut”__________________; operation is involuntary
b. Neurons found in and extend through _gastrointestinal tract (GI)____
c. _sensory neurons____: monitor chemical changes within the GI tract and the stretching
of its walls
d. _motor neurons__: govern _contraction_ of GI tract smooth muscle, _secretions___ of
GI tract organs, and activity of GI tract endocrine cells.
Get a copy of checkpoint questions 1-3 and the applicable
critical thinking application, complete them and hand them in…
B. Functions of the Nervous System
1. Sensory functions
i. _Sensory receptors_ detect stimuli inside and outside the body.
ii. Types of neurons that carry out sensory functions:
i. _ (AFFECTORS) Sensory or afferent neurons
carry information to brain and spinal cord.
2. Integrative functions
a. Do what? _(LIKE A CONTROL CENTER) Process sensory information by analyzing and
storing some of it and by making decisions for appropriate responses________________
b. Types of neurons that carry out integrative functions: _Interneurons; have short axons
that connect with neurons in brain, spinal cord, and ganglion; are majority neurons in
the body_________________________________________________________________
3. Motor functions
a. Do what? _ (EFFECTORS) respond the integrative decisions________________________
b. Types of neurons that carry out motor functions: _Motor of efferent neurons (carry
information from brain toward spinal cord or out of brain to spinal cord into cranial or
spinal nerves) _________________________
II. HISTOLOGY OF NERVOUS TISSUE
What two types of cells make up nervous tissue? _neurons and neuroglia________
Neurons provide for what: _unique functions of the nervous system; sensing, thinking,
remembering, controlling muscle activity, and regulating glandular secretions___________________
What do neuroglia do? _support, nourish, and protect neurons and maintain homeostasis in the
intestinal fluid that baths neurons______________________________________________________
A. Neurons
Consists of three parts:
(1) _cell body_
Contains: _nucleus surrounded by cytoplasm; includes RER, lysosomes, mitochondria, Golgi_
What is synthesized here? _cellular molecules needed for a neuron’s operation___________
Processes or extensions:
(2) _dendrites_ (“little trees”)
How many? _multiple per single axon_________________________
Combined with cell body what is their function? _receiving and input parts of a neuron_____
Shape: _short, tapering, and highly branched, tree-branch array emerging from cell body___
(3) _axons_
Function: _conducts nerve impulses toward another neuron, muscle fiber, or gland cell____
Shape: _long, thin, cylindrical projection that joins cell body at a cone-shaped elevation____
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What is an axon hillock? _ cone-shaped elevation where axon joins cell body______________
What are axon collaterals? _side branches of some axons_____________________________
What are axon terminals? _many fine processes that denote the ends of axon collaterals and
axons__________________________________________
What is a synapse? _site where two neurons or a neuron and an effector cell can communicate____
What are synaptic end bulbs? _tips of most axon terminals__________________________________
What are synaptic vesicles? _tiny sacs that store chemicals__________________________________
What are neurotransmitters? _synaptic vesicle chemicals that are a means of communication at a
synapse______________________________________________
1. Classification of Neurons
STRUCTURAL CLASSIFICATION
 _multipolar neurons_: have several dendrites and one axon; most in brain and spinal
cord
 _bipolar neurons_: have one main dendrite and one axon; retina of the eye, inner
ear, olfactory area of brain
 _unipolar neurons_: dendrites and one axon fused together forming a continuous
process that emerges from cell body; begin in embryo as bipolar neurons; most
function as sensory receptors for touch, pressure, pain, or thermal stimuli. Cell
bodies of most of this type located in ganglia of spinal and cranial nerves.
FUNCTIONAL CLASSIFICATION
 _sensory or afferent neurons_: once sensory receptor activated, these form an
action potential in their axon that is conveyed into the CNS through spinal and
cranial nerves
contain sensory receptors at their distal ends or are located just after sensory
receptors that are separate cells; most unipolar in structure
 _motor or efferent neurons_: convey action potential away from CNS to effectors
(muscles and glands) in PNS through cranial and spinal nerves
Most are multipolar in structure
 _interneurons or association neurons_: integrate incoming sensory information
from sensory neurons and then elicit a motor response by activating appropriate
motor neurons Located within CNS between sensory and motor neurons; most
multipolar in structure
B. Neuroglia
Describe neuroglia: _smaller than neurons; 5-50 times more numerous_____________________
Functions: _”glue” that holds nervous tissue together; do not generate or conduct nerve
impulses; can multiply and divide in mature nervous system; in case of injury or disease multiply
to fill in spaces formerly occupied by neurons_________________________________________
What are gliomas? _brain tumors derived from glia called gliomas, very malignant and grow rapidly
C. Myelination
A myelin sheath, many-layered covering composed of lipids and protein, surround the axons of
most of our neurons.
Two Functions:
(1) _insulates the axon________________________________________
(2) _increases the speed of nerve impulse conduction_______________
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What name is given to the gaps in myelin sheath? _nodes of Ranvier_____________________
Define myelinated: _axon with a myelin sheath______________________________________
Define unmyelinated: _axon without a myelin sheath_________________________________
The amount of myelin increases from _birth_ to _maturity_
Its presence increase what? _the speed of nerve impulse conduction______________
What two diseases are known to destroy myelin sheaths? _multiple sclerosis, Tay-Sachs disease
D. Collections of Nervous Tissue
1. Clusters of Neuronal Cell Bodies
 _ganglion_: cluster of neuronal cell bodies located in PNS
 _nucleus_: cluster of neuronal cell bodies in CNS
2. Bundles of Axons
 _nerve_: bundle of axons located in PNS; cranial nerves connect brain to periphery
and spinal nerves connect spinal cord to periphery
 _tract_: bundle of axons located in CNS; tracts interconnect neurons in spinal cord
and brain
3. Gray and White Matter
 What is white matter? _myelinated and unmyelinated axons of many neurons which
is white in color; also has blood vessels__________
 What is gray matter? _neuronal cell bodies, dendrites, unmyelinated axons, axon
terminals, and neuroglia white is grayish pink in color; also has blood
vessels___________________________
obtain and complete the worksheet ‘the anatomy of the neuron’
Quiz on nervous system basics on: __________________________________
Know the components of the CNS and PNS
Know what the ANS, ENS, and SNS controls (Figure 9.1, page 254 may help)
Know the anatomy of a neuron
III. ACTION POTENTIALS
What is another name for action potentials? _nerve impulses__________________________
What two features of plasma membrane do action potentials in muscle fibers and in neurons
depend on?
1. _existence of resting membrane potential_________________________
2. _presence of specific types of ion channels________________________
_Membrane potential_, difference in the amount of electrical charge inside and outside plasma
membrane. A membrane that has potential is said to be _polarized_. When muscle fibers and
neurons are ‘at rest’; the voltage across the plasma membrane is termed the _resting membrane
potential_.
In living tissues, the flow of ions constitutes electrical currents.
A. Ion Channels
Let specific ions move from areas of high concentration to areas of low concentration, or from
positively charged areas to negatively charged areas or vice versa to equalize differences in
charges or concentration.
1. Two types of ion channels:
Leakage channels- _allow small but steady stream of ions to leak across the membrane____
Gated channels: _open and close on command_____________________________________
2. What are voltage-gated channels used for? _to generate and conduct action potentials;
open in response to a change in membrane potential________________________________
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B. Resting Membrane Potential
1. What kind of charge does the resting neuron have on the outside surface of the plasma
membrane? _positive_ on the inside? _negative_
2. Potential energy in cells is measured in _millivolts_.
3. What is the resting membrane potential in neurons? _-70_mV
4. Why is it a negative value? _inside of the membrane is negative relative to the outside_____
5. Interstitial fluid is rich in _Na+_ ions and _Cl-_ ions.
6. Cytosol is rich in _K+_ ions.
7. What offsets the small inward leak of Na+ and outward leak of K+? _sodium-potassium pump
8. The diagram on the next page will help you to understand how resting membrane potential
arises from the unequal distributions of various ions in cytosol and interstitial fluid. You
should read over this material carefully on page 260 of your textbook.
Resting membrane potential arises due to an unequal distribution of ions on either side of
the plasma membrane and a higher membrane permeability to K+ than to Na+. The level of
K+ is higher inside and the level of Na+ is higher outside, a situation that is maintained by
sodium-potassium pumps.
C. Generation of Action Potentials
what happens during an action potential (AP) or impulse? _rapidly occurring events that
decrease and increase the membrane potential and eventually restore it to its resting state___
Ability of muscle fibers and neurons to convert stimuli into action potential is called _electrical
excitability_.
What causes an action potential to arise? _stimulus in cell’s environment changes resting
membrane potential; if stimulus causes cell to depolarize to a critical level; called a threshold
(about -55mV) then an action potential arises________________________________________
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1. Two main phases:
Depolarizing phase- _rapidly occurring events that decrease and eventually reverse
polarization of membrane, makes inside more positive than outside; Na+ ions move into cell
Repolarizing phase- _membrane polarization is restored to resting state; Na+ ions move back
out cell restoring charge to original state__________________________________________
2. Explain the process of action potential from threshold state to depolarization to afterhyperpolarization phase. _Action potential depend on the existence of a resting membrane
potential and the presence of voltage-gated channels for Na+ and K+. At resting membrane
potential of -70mV, cell is polarized. Stimulus of muscle fibers or neurons convert action
potential into excitability. During an action potential, voltage-gated Na+ and K+ channels
open in sequence. Opening of voltage-gated Na+ channels results in depolarization, the loss
and then reversal of membrane polarization (from -70mV to +30 mV). Then, opening of
voltage-gated K+ channels allows repolarization, recovery of the membrane potential to the
resting level. ________________________________________________________________
3. What is the all-or none principle? _If a stimulus is strong enough to generate an action
potential; the impulse generated is of a constant size (causes depolarization to threshold,
voltage-gated Na+ and K+ channels open and action potential occurs). A very strong stimulus
cannot cause a larger action potential because the size of an action potential is always the
same, a weak stimulus that fails to cause a threshold-level depolarization does not elicit an
action potential______________________________________________________________
4. What type of stimuli elicit an action potential? _strong______________________________
5. What is a refractory period? _a period during which action potential cannot be generated__
6. Label 1-7 on the diagram below:
2. Depolarizing
phase
3.Repolarizing phase
4.Reversal of
polarization
5.Threshold
1. Stimulus
6.After-hyperpolarizing phase
7.Resting
membrane
potential
D. Conduction of Nerve Impulses
What is propagation or conduction? _the way cells communicate information from one part of
the body to another, nerve impulses travel from where they arise, usually at axon hillock, along
the axon to the axon terminal, positive feedback process________________________________
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What is continuous conduction? What type of axons does it occur in?
_Step-by-step process in which the impulse travels a relatively short distance in 10 milliseconds;
occurs in unmyelinated axons (muscle fibers) _________________________________________
What is saltatory conduction? What type of axons does it occur in?
_impulses leap from one node of Ranvier to the next on myelinated axons__________________
What type of axons have the largest diameter? _all myelinated___________________________
What type of axons have the smallest diameter? _unmyelinated__________________________
What type of factors influence the speed of nerve impulse conduction? _warmth (conducted at
higher speeds), coolness (conduct at lower speeds); large diameters impulse moves faster,
smaller diameter impulse moves slower; myelinated axons conduct impulses faster than
unmyelinated___________________________________________________________________
IV. SYNAPTIC TRANSMISSION
OBJ: Explain the events of synaptic transmission and the type of neurotransmitters used.
What is synaptic transmission? _it is how synapses neurons communicate with other neurons or
with effectors through a series of events_________________________________________________
What is the neuron sending the signal called? _presynaptic neuron________________________
What is the neuron receiving the signal called? _postsynaptic neuron______________________
A. Events at a Synapse
What separates the presynaptic and postsynaptic neurons? _synaptic cleft______________
B. Neurotransmitters
Different neurotransmitters are found in synaptic vesicles. These different neurotransmitters
have different effects.
Obtain and Complete the synaptic events worksheet…
When done with this packet you will receive packet for chapters
11 & 12…
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