Download Chapter 9 Part 3 Central Nervous System

Chapter 9
Part 3
Central Nervous System
Processing Sensory Information into Perception
(p. 315)
Once sensory information has reached its appropriate
spot in the cortex (e.g. visual information goes to
visual cortex, etc.)
Then, the information proceeds on to its association
area (e.g. visual cortex sends visual information on to
the visual association area, etc.)
Association areas integrate all of the sensory
information into perception
Perception: the brain's interpretation of sensory stimuli
In many cases, the perceived stimulus can be quite
different from the actual stimulus
– Photoreceptors in the eye receive light waves of
many different frequencies
– Brain perceives the different wavelengths as
different colors
Perception (continued)
– Pressure waves hitting the ear
– Brain translates these to sound
– Chemicals binding to chemoreceptors
– Brain translates these as taste or smell
• Taste: taste buds in mouth
• Smell: chemoreceptors in nose
Perception (continued)
Brain can often fill in missing information in order to
get a more complete picture (fig. 9-18a)
Brain can also translate a 2-dimensional (flat) drawing
into a 3-dimensional object (fig. 9-18b)
“Thus, we sometimes perceive what our brains expect
to perceive.” (p. 316)
Figure 9-18
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Perceptual translation of sensory stimuli allows the
information to be acted upon, used in voluntary motor
control or complex cognitive functions like language
Motor Output (3 parts):
– Skeletal muscle movement
• Controlled by somatic motor division
– Neuroendocrine signals
• Neurohormones secreted by hypothalamus and
adrenal medulla
– Visceral responses (see next slide)
– Visceral responses
• Governed by autonomic division
• Actions of smooth and cardiac muscle;
• Actions of endocrine and exocrine glands
Figure 8-1
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Motor Output (more details)
Skeletal muscle movement
– Can be processed in several areas:
• Simple stimulus-response pathways are
processed either in the spinal cord or in the
brain stem
• These responses do not require integration in
the cerebral cortex, but can be modified or
overridden by the cerebrum
Motor Output (more details)
Skeletal muscle movement
– Voluntary movements
• Initiated by cognitive system
• Originate in primary motor cortex and motor
association area (in frontal lobes of cerebrum)
• See fig. 9-15, p. 315
• These areas receive input from sensory areas,
cerebellum, basal ganglia
Figure 9-15
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Motor pathways
Pyramidal cells, which are long output neurons, project
axons from the motor areas down through the brain
stem to the spinal cord
Other pathways go from the cerebral cortex to the
basal ganglia and lower brain regions
Descending motor pathways cross over to the
opposite side of the body
Damage to a motor area manifests as paralysis or loss
of function on the opposite side of the body
Neuroendocrine and visceral responses
– Coordinated in the hypothalamus and medulla
– Brain Stem contains control centers for many
automatic life functions:
• Breathing
• Blood pressure
• Etc.
• Brain Stem receives sensory information from
body
• Relays motor commands to peripheral muscles
and glands
Neuroendocrine and visceral responses
– Coordinated in the hypothalamus and medulla
– Hypothalamus contains centers for:
• Temperature regulation
• Eating
• Control of body osmolarity, etc.
• Response to stimulation of these centers can be
in the form of neural or hormonal reflexes or a
behavioral response
• Hypothalamus also mediates stress,
reproduction, and growth
Sensory input not the only factor affecting motor output
The behavioral state system can modulate reflex
pathways
and
The cognitive system exerts both voluntary and
involuntary control over motor functions
Behavioral State system
– Modulates sensory and cognitive processing
– Many of the neurons of this system are located
outside the cerebral cortex:
• Some are found in the reticular formation (in the
brain stem)
• Some are found in the hypothalamus
• Some are found in the limbic system
Behavioral State system
– Diffuse modulatory systems:
• A group of neurons which originate in the
reticular formation of the brain stem
• These neurons project their axons to many brain
areas (Table 9-3; fig. 9-19)
Behavioral State system (continued)
– The diffuse modulatory system regulates brain
function by influencing:
– Attention
– Motivation
– Wakefulness
– Memory
– Motor control
– Mood
– Metabolic homeostasis
Table 9-3
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Figure 9-19: Diffuse Modulatory System
Copyright © 2010 Pearson Education, Inc.
The behavioral state system controls both levels of
consciousness and the sleep-wake cycle
Consciousness:
– Body's state of arousal or awareness of self and
the environment
Reticular Activating System
– A “diffuse collection of neurons” in the reticular
formation
– Keeps the “conscious brain” awake
– Blockage (surgical or drugs) of the ascending
pathways from the RAS up to the cerebrum can
result in unconsciousness
Reticular Activating System:
Reticular Activating System:
Sleep vs Being Awake
Can tell these apart by looking at an EEG or
electroencephalogram (fig. 9-20, p. 319)
• EEG records depolarizations of cortical neurons
When awake, lots of neurons firing, little co-ordination
among them
In awake-resting (eyes closed), electrical activity of
neurons begins to synchronize into waves with
characteristic patterns
Sleep and coma show further synchronization, etc.
Sleep vs Being Awake
As the state of arousal lessens (ie, slipping further in to
sleep), wave frequency decreases
The more synchronous the firing of cortical neurons,
the larger the amplitude of the waves
Awake-resting state has low amplitude, high frequency
waves
Deep sleep has high amplitude, low frequency waves
Figure 9-20a
Copyright © 2010 Pearson Education, Inc.
Sleep
Why we sleep:
“One of the unsolved mysteries in neurophysiology”
Very ancient, occurs in all birds and mammals
(recently found to occur in some fish also)
Most birds and mammals show the same stages of
sleep as humans (REM sleep, etc.)
Sleep is an active process, consumes as much or
more oxygen as an awake brain
Sleep
Hypotheses (why sleep?):
• To conserve energy
• To avoid predators
• To allow the body to repair itself
• To process memories
Sleep consists of 4 stages, based on somatic changes
and brain wave patterns
– REM (rapid eye movement) or stage 1
– Stage 2
– Stage 3
– Deep sleep (slow wave, non-REM) or stage 4
Sleep
Two main sleep phases are REM and Deep or slowwave
REM Sleep
EEG similar to, but not the same as, that of an awake
person (fig. 9-20a)
Has low amplitude, high frequency waves
During REM sleep, brain activity inhibits motor
neurons to skeletal muscles
This “paralyzes” most muscles, except muscles that
move the eyes and muscles that control breathing
Sleep
Two main sleep phases are REM and Deep or slowwave
REM Sleep
Most dreaming occurs during this stage
Eyes move back and forth behind closed lids (as if
following the events in the dream)
Sleepers are most likely to spontaneously wake up
from REM sleep
Sleep
Two main sleep phases are REM and Deep or slowwave
Deep sleep (slow wave, non-REM) or stage 4
Delta waves present
High amplitude, low frequency waves; waves are of
long duration
Sleepers adjust body position without conscious
commands from the brain
Typical 8-hour sleep cycle
Consists of repeating cycles (fig. 9-20b)
Hour 1:
– Person goes from wakefulness to deep sleep
(stage 4—first blue area in figure)
– Sleeper then cycles between deep sleep and REM
sleep
– Stages 2-3 occur in between these other ones
– Near end of sleep cycle, alternate between stage
2 and REM, until sleeper awakes
Figure 9-20b
Copyright © 2010 Pearson Education, Inc.
Figure 9-20a
Copyright © 2010 Pearson Education, Inc.
Next:
Chapter 10
Sensory Physiology