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Neural Integration
Chapter 15
Introduction
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Through the chapters covered to date we
have looked at the nervous system from
its component pieces
However, our nervous system typically
acts as an integrated whole, gathering
sensory inputs, processing information
and effecting a motor response
Integration is the process by which the
nervous system processes and interprets
sensory input and makes decisions about
what should be done at each moment
Sensory Integration
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Our survival needs depend upon
– Sensation
• Awareness of changes in our internal and
external environment
– Perception
• Conscious interpretation of stimuli
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Perception determines how we will
respond to the stimuli
Organization of Somatosensory System
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The somatosensory system receives
inputs from exteroreceptors,
proprioceptors, and interoreceptors
It transmits information about several
different sensory modalities via a system
of ascending sensory pathways between
receptors and the cerebral cortex
The pathways between receptor and
cerebral cortex follow a chain of three
neurons
Organization of Somatosensory System
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The typical chain of neurons involves
– The cell body of the afferent (1st order)
neuron in the dorsal root ganglion
– The second order neuron in the dorsal horn
of the spinal cord or medulla oblongata
– The third order neuron in the thalamus
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Although this is the basic pattern for the
upward flow of information, collateral
synapses occur along the pathway
Organization of Somatosensory System
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First order
– Cell body of the afferent
neuron in the dorsal
root ganglion
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Second order
– Neuron in the dorsal
horn of spinal cord or
medulla oblongata
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Third order
– Neuron in the thalamus
Organization of Somatosensory System
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There are three main levels of neural
integration in the somatosensory system
– Level I: The receptor level corresponding to
the sensory receptors
– Level II: The circuit level corresponding to
the ascending pathways
– Level III: The perceptual level corresponding
to the awareness of the incoming stimuli
Organization of Somatosensory System
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Receptor level
– Information about
internal and external
environment
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Circuit level
– Ascending pathways
to the brain
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Perceptual level
– Allows us to be aware
of stimuli and
discriminate about
their characteristics
Processing at the Receptor Level
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Information about the external and
internal environments presents itself as
different forms of energy (sound, light)
The sensory receptors respond to these
stimuli; the rest of the nervous system
responds chiefly to neurotransmitters
The process by which a stimulus is
transformed into an electrical response at
a receptor is called transduction
Processing at the Receptor Level
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If the receptor potential is of threshold
strength, it triggers an action potential
along the axon of the afferent neuron
Nerve impulse conduction continues as
long as a threshold stimulus is applied
The strength of the stimulus is encoded in
the frequency of the impulses sent,
stronger stimuli cause more impulses per
second to reach the CNS
Processing at the Circuit Level
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The central processes of sensory neurons,
carrying impulses from cutaneous receptors
of the skin and proprioceptors branch
diffusely as they enter the spinal cord
Some branches take part in local spinal
cord reflexes and directly initiate motor
activities
The remaining sensory afferents synapse
with second order neurons in the dorsal
horn or continue upward in the dorsal
column to synapse in medullary nuclei
Processing at the Circuit Level
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Small-diameter pain fibers synapse with
superficially located substantia gelatinosa
neurons in the dorsal horn
The large myelinated fibers from
pressure and touch receptors make
collateral synapses with interneurons in
the dorsal horns
Processing at the Circuit Level
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The somatosensory
cortex receives
sensory information
via two major
ascending routes; the
nonspecific and
specific pathways
These pathways relay
information to the
brain for three
purposes: perception,
arousal and motor
control
Nonspecific Ascending Pathways
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The nonspecific
ascending pathways
receive inputs many
different types of
sensory receptors
and make multiple
synapses in the
brain stem
These anteriolateral
pathways are
formed by the
lateral and anterior
spinothalamic tracts
Anterior
Spinothalmic
Specific Ascending Pathways
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Specific ascending
pathways (lemniscal)
are concerned with
precise, straightthrough transmission
of inputs from a
single (or related)
sensory receptor
These pathways are
formed by the dorsal
column of the spinal
cord and the medial
lemniscal tracts
Lemniscal
Processing at the Perceptual Level
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Perception is the final stage of sensory
processing which allows us to be aware of
stimuli and discriminate about their
characteristics
As sensory information reaches the
thalamus, they are perceived in a crude
sense
Full appreciation of their qualities and
sharp localization awaits the arrival of
the input at the somatosensory cortex
Processing at the Perceptual Level
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The entire sensory cortex is arranged in
columns of cortical neurons with each
column representing a building block of
sensory perception
– The thalamus projects fibers (sorted out by
sensation type) to the primary somatosensory
cortex and to sensory association areas
– First to those restricted to the same modality
and then to those considering more than one
– This allows for parallel processing of the
various inputs, and results in an internal,
conscious image of the stimulus
Processing at the Perceptual Level
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Sensory input evokes a behavioral
responses
Human decide to act or not to act on the
basis of the information
The choice we make depends, in part, on
our past experience with similar sensory
inputs
Aspects of Sensory Perception
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The main aspects of sensory perception
are
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Perceptual detection
Magnitude estimation
Spatial discrimination
Feature abstraction
Quality discrimination
Pattern recognition
Perceptual Detection
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Detecting that a stimulus has occurred is
the simplest level of perception
As a general rule, several receptor impulses
must be summated (accumulated) for
perceptual detection to occur
Magnitude Estimation
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Magnitude estimation is the ability to
detect how much of the stimulus is acting
on the body
Because of frequency coding, perception
increases as stimulus intensity increases
Spatial Discrimination
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Spatial discrimination allows us to
identify the site or pattern of stimulation
Two point discrimination test
The test is a crude map of the density of
tactile receptors in the various regions of
the skin
Feature Abstraction
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The mechanism by which a neuron or
circuit is tuned to one feature in
preference to others is called feature
abstraction
This implies that a unit of perception is
tuned to a coordinated set of several
stimulus properties called a feature
The skin integrates receptor inputs in
parallel fashion to appreciate the
“texture” of an object
Quality Discrimination
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Quality discrimination is the ability to
differentiate the submodalities of a
particular sensation
Each sensory modality has several
submodalities
– Taste (sweet, salt, bitter, sour)
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The ability to discriminate is one of the
major achievements of our sensory
system
Quality Discrimination
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Quality discrimination may be analytic
or synthetic
– Analytic / each quality retains its individual
nature (sugar and salt)
– Synthetic / our perception of the qualities
merge into a new sensation (chocolate)
– Synthetic discrimination is important in
sight as we merge red, green and blue into
the myriad of colors we see
– Vision and olfaction use only synthetic
Pattern Recognition
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Pattern recognition refers to our ability
to take in the scene around us and
recognize
– A familiar pattern
– An unfamiliar pattern
– A pattern that has special significance to us
End of Material for Test 3
Chapter 15
Motor Integration From
Intention to Effect
Levels of
Motor
Control
The Segmental Level
The Projection Level
The Programs/Instructions
Level
Homeostatic Imbalances of
Motor Integration
Higher Mental Functions
Brain Wave Patterns and the
EEG
Abnormal Electrical Activity
of the Brain: Epilepsy
Sleep and Sleep-Awake
Cycles
Types pf Sleep
Sleep Patterns
Importance of Sleep
Homeostatic Imbalances of
Sleep
Consciousness
Memory
Stages of Memory
Categories of Memory
Brain Structures Involved in
Memory
Mechanisms of Memory
Language