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Chapter 11 Functional Organization of
Nervous Tissue 2024-2025
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9 Characteristics Responsible for Resting membrane Potential - ANS1
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plasma membrane 50-100 times more permeable to K+ because of leak channels
3
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anions trapped inside the cell
4
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small negative charge develops on inside of plasma membrane
6
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charge difference across plasma membrane at equilibrium is reflected as difference
in potential: milivolts
8
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at equilibrium, very little movement of K+ or other ions takes place across the plasma
membrane
absolute refractory period - ANS-complete insensitivity exists to another stimulus;
-from beginning of action potential until near end of repolarization;
-no matter how large the stimulus; second action potentials cannot be produced;
-has consequences for function of muscle; particularly how often a
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s
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action potentials are produced when a
graded potential reaches threshold
2
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depolarization is a result of increased membrane permeability to sodium and sodium
movement into the cell
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repolarization is a result of decreased membrane permeability to sodium and
increased membrane permeability to potassium which stops sodium movement into the
cell and increases potassium movement out of the cell
-inactivation gates of the voltage-gated Na+ channels close, and the voltage-gated K+
channels open
5
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action potentials are propagated and for a given axon or muscle fiber, the magnitude
of the action potential is constant
7
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stimulus causes ion channels to open,
increasing permeability of membrane to Na+, K+, or Cl2
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increased
permeability of membrane to k+ or Cl- results in hyperpolarization
3
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graded potentials can
also summate
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graded potentials are conducted in a decremental fashion
-magnitude decreases as they spread over plasma membrane
-graded potentails can't be measured a few milimeters from point of stimulation
5
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-if enough Na+ diffuses into postsynpatic cells, it fires
choroid plexus - ANSare within certain regions of ventricles;
They secrete cerebrospinal fluid;
-cilia help move fluid through brain cavities;
They have long processes on the basal surface that extend within brain tissue;
may have astrocyte-like functions;
Combined Summation - ANScombined spatial and temporal summation:
with both excitatory postsynaptic potentials and inhibitory postsynaptic potentials
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B
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receive sensory input
monitor internal and external stimuli
2
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control muscles and glands
4
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establish/maintain mental activity
-consciousness, thinking, memory, emotion
ganglion - ANScollection of neuron cell bodies outside CNS
gap junctions - ANSgap junctions that allow graded current; to flow between adjacent
cells
Gated Ion channels - ANSGated ion channels open and close because of some
stimulus;
when opened; permeability of cell membrane changes
Graded potentials - ANSresult from:
-ligands binding to receptors
-changes in charge across membrane
-mechanical stimulation
-temperature changes
-spontaneous change in permeability
graded:
magnitude varies from small to large depending on stimulus strength or frequency
can summate or add onto each other

spread(are conducted) over the plasma membrane in a decremental fashion: rapidly
decrease in magnitude as they spread over the surface of the plasma membrane
can cause generation of action potentials
gray matter - ANSunmyelinated axons;
cell bodies;
dendrites;
neuroglia;
Have integrative functions;
in the brain; gray matter is outer cortex and inner nuclei;
in spinal cord; gray is deeper than white;
PNS gray matter is groups of cell bodies called ganglia
hyperpolarization - ANSpotential difference becomes greater; or more polar
Inhibitory Postsynaptic Potential - ANSIPSP
-hyperpolarization and response inhibitory
-decrease action potentials by moving membrane potential farther from threshold
Interneurons and Association Neurons - ANSWITHIN CNS from one neuron to another
K+ membrane permeability changes - ANSin resting membrane;
-K+ in and out is equal because of leak channels;
also gated K+ channels in membrane;
-if opened more K+ diffuses out;
-but its opposed by negative charge
that starts to develop as K+ diffuses
out
K+concentration gradient alterations - ANS-if extracellular concentrations of K+
increases;
less gradient between inside and
outside of cell;
DEPOLARIZATION;
-if extracellular ion concentration decreases;
steeper gradient between inside and
outside of cell;

HYPERPOLARIZATION
Leak Channels - ANSalways open;
responsible for permeability when membrane is at rest;
specific for one type of ion; although not absolute;
many more leak channels for K+ and Cl-;
at rest: K+ and Cl- are moving more
than Na+;
how do they move?
-protein repels Cl- so they move out;
-K+ is higher concentration on inside then out so they move out
Ligand Gated - ANSmolecules that bind to receptors;
proteins or glycoproteins;
open or close in response to ligands;
ie ACh binds to receptor protein;
receptor proteins are usually glycoproteins;
ie acetylcholine binds to acetylcholine; receptors on a Na+ channel;
-channel opens, Na+ enters cell;
maximal stimulus - ANSjust enough to produce a maximum frequency of action
potentials
Microglia - ANSNeuroglia of the Central nervous system;
They are specialized macrophages;
They respond to inflammation;
They phagocytize necrotic tissue, microorganisms, and foreign substances that invade
the CNS
Motor Division of PNS - ANSis separated into two nervous systems;
Somatic Nervous System and
Autonomic Nervous System
Motor; efferent neurons - ANSaction potential AWAY from the CNS

Multi-polar Neurons - ANSmost neurons in CNS are multi-polar neurons;
motor neurons are multi-polar neurons;
multi-polar neurons have many dendrites and one axon;
My-elinated Axons - ANSmyelin protects/insulates axons from one another;
speeds transition;
functions in repair of axons;
not continuous;
NODES OF RANVIER;
myelin sheath development is completed at 1 year;
degeneration of myelin sheaths occurs in;
-multiple sclerosis;
-some cases of diabetes mellitus;
Nerve Fiber types - ANSType A;
Type B;
Type C;
nerves - ANSbundles of axons and sheaths;
connects CNS to sensory receptors, muscles, and glands;
cranial nerves and spinal nerves are the two types
Neuromodulators - ANSchemicals produced by neurons that facilitate action potentials
-some of these act to increase or decrease amount of neurotransmitter released by
presynaptic neuron
act in axoaxonic synapses
-axon of one neuron synapses with axon of second neuron
-second neuron is actually presynpatic
-this type of cnnection leads to release of neuromodulators in the synapse that can
alter the amt of neurotransmitter produced by the second neuron
Neuron Cell Body - ANSincludes the nucleus and nissl substance;
nissl substance is chromatophilic substance which is in the rough endoplasmic
reticulum;

the neuron cell body is the primary site of protein synthesis;
Neuronal Pathways and Circuits - ANSorganization of neurons in CNS varies in
complexity
convergent pathways
divergent pathways
oscillating circuit
Neurotransmitter Removal - ANSmethod depends on neurotransmitter/synapse
ACh: achetylcholinesterase splits ACh into acetic acid and choline
-choline recycled within presynaptic neuron
-norepinephrine: recycled within presynaptic neuron or diffuses away from synapse
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An action potential at a node of ranvier generates local
currents;
-local currents flow to the next node of ranvier bc the myelin sheath of the schwann cell
insulates the axon of the internode;
2
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Action potential propagation is rapid in myelinated axons; because the action
potentials are produced at successive nodes of Ranvier (1-5); instead of at every part of
the membrane along the axon
Satellite Cells - ANSNeuroglia of the PNS;
surround neuron cell bodies in sensory ganglia;
provide support and nutrients;
Schwann Cells - ANSNeurolemmocytes; They are the Neuroglia of the PNS;
wrap around portion of only one axon to form myelin sheath;
it wraps around many times;
during development;
-cells grow around axons;
-cytoplasm is squeezed out;
-multiple layers of cell membrane wrap around myelin sheath
Sensory Receptors - ANS-ending of neurons;

specialized cells;
detect temperature, pain, touch, pressure, light, sound, and odors;
Sensory; Afferent Neurons - ANSaction potentials TOWARDS the CNS
somatic nervous system - ANSfrom CNS to Skeletal muscle;
voluntary control;
single neuron system;
synapse;
Spacial Summation - ANSspacial summation: action potentials 1 and 2 cause the
production of graded potentials at two different dendrites
-these graded potentials summate at the trigger zone to produce a graded potential that
exceeds threshold, resulting in an action potential
speed of conduction - ANS-faster in myelinated than non-myelinated
-in myelinated axons, lipids act as insulation forcing ionic currents to jump from node to
node
-in myelinated, speed is affected by thickness of myelin sheath
-diameter of axons: large-diameter conduct more rapidly than small-diameter
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