Lecture Human anatomy and physiology - Chapter 12: The central nervous system (part c)

PowerPoint® Lecture Slides
prepared by Vince Austin,
Bluegrass Technical
and Community College

CHAPTER

12

The Central
Nervous
System:
Part C
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Functional Brain Systems
• Networks of neurons that work together and
span wide areas of the brain
• Limbic system
• Reticular formation

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Limbic System
• Structures on the medial aspects of cerebral
hemispheres and diencephalon
• Includes parts of the diencephalon and some
cerebral structures that encircle the brain
stem

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Septum pellucidum
Diencephalic structures
of the limbic system
•Anterior thalamic
nuclei (flanking
3rd ventricle)
•Hypothalamus
•Mammillary
body

Olfactory bulb

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Corpus callosum

Fiber tracts
connecting limbic
system structures
•Fornix
•Anterior commissure
Cerebral structures of the
limbic system
•Cingulate gyrus
•Septal nuclei
•Amygdala

•Hippocampus
•Dentate gyrus
•Parahippocampal
gyrus

Figure 12.18


Limbic System
• Emotional or affective brain
• Amygdala—recognizes angry or fearful facial
expressions, assesses danger, and elicits the
fear response
• Cingulate gyrus—plays a role in expressing
emotions via gestures, and resolves mental
conflict

• Puts emotional responses to odors
• Example: skunks smell bad
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Limbic System: Emotion and Cognition
• The limbic system interacts with the prefrontal
lobes, therefore:
• We can react emotionally to things we
consciously understand to be happening
• We are consciously aware of emotional
richness in our lives

• Hippocampus and amygdala—play a role in
memory

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Reticular Formation
• Three broad columns along the length of the
brain stem
• Raphe nuclei
• Medial (large cell) group of nuclei
• Lateral (small cell) group of nuclei

• Has far-flung axonal connections with
hypothalamus, thalamus, cerebral cortex,
cerebellum, and spinal cord
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Reticular Formation: RAS and Motor Function
• RAS (reticular activating system)
• Sends impulses to the cerebral cortex to keep
it conscious and alert
• Filters out repetitive and weak stimuli (~99% of
all stimuli!)
• Severe injury results in permanent
unconsciousness (coma)

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Reticular Formation: RAS and Motor Function
• Motor function
• Helps control coarse limb movements
• Reticular autonomic centers regulate visceral
motor functions
• Vasomotor
• Cardiac
• Respiratory centers

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Radiations
to cerebral
cortex

Visual
impulses
Reticular formation
Ascending general
sensory tracts
(touch, pain, temperature)
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Auditory
impulses
Descending
motor projections
to spinal cord

Figure 12.19


Electroencephalogram (EEG)
• Records electrical activity that accompanies
brain function
• Measures electrical potential differences
between various cortical areas

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(a) Scalp electrodes are used to record brain wave
activity (EEG).
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Figure 12.20a


Brain Waves
• Patterns of neuronal electrical activity
• Generated by synaptic activity in the cortex
• Each person’s brain waves are unique
• Can be grouped into four classes based on
frequency measured as Hertz (Hz)

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Types of Brain Waves

• Alpha waves (8–13 Hz)—regular and rhythmic, lowamplitude, synchronous waves indicating an “idling”
brain
• Beta waves (14–30 Hz)—rhythmic, less regular
waves occurring when mentally alert
• Theta waves (4–7 Hz)—more irregular; common in
children and uncommon in adults
• Delta waves (4 Hz or less)—high-amplitude waves
seen in deep sleep and when reticular activating
system is damped, or during anesthesia; may
indicate brain damage
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1-second interval

Alpha waves—awake but relaxed

Beta waves—awake, alert

Theta waves—common in children

Delta waves—deep sleep
(b) Brain waves shown in EEGs fall into
four general classes.
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Figure 12.20b


Brain Waves: State of the Brain

• Change with age, sensory stimuli, brain
disease, and the chemical state of the body
• EEGs used to diagnose and localize brain
lesions, tumors, infarcts, infections,
abscesses, and epileptic lesions
• A flat EEG (no electrical activity) is clinical
evidence of death

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Epilepsy
• A victim of epilepsy may lose consciousness,
fall stiffly, and have uncontrollable jerking
• Epilepsy is not associated with intellectual
impairments
• Epilepsy occurs in 1% of the population

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Epileptic Seizures
• Absence seizures, or petit mal
• Mild seizures seen in young children where the
expression goes blank

• Tonic-clonic (grand mal) seizures
• Victim loses consciousness, bones are often
broken due to intense contractions, may
experience loss of bowel and bladder control,

and severe biting of the tongue

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Control of Epilepsy
• Anticonvulsive drugs
• Vagus nerve stimulators implanted under the
skin of the chest can keep electrical activity of
the brain from becoming chaotic

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Consciousness
• Conscious perception of sensation
• Voluntary initiation and control of movement
• Capabilities associated with higher mental
processing (memory, logic, judgment, etc.)
• Loss of consciousness (e.g., fainting or
syncopy) is a signal that brain function is
impaired

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Consciousness
• Clinically defined on a continuum that grades
behavior in response to stimuli
• Alertness

• Drowsiness (lethargy)
• Stupor
• Coma

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Sleep
• State of partial unconsciousness from which a
person can be aroused by stimulation
• Two major types of sleep (defined by EEG
patterns)
• Nonrapid eye movement (NREM)
• Rapid eye movement (REM)

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Sleep
• First two stages of NREM occur during the
first 30–45 minutes of sleep
• Fourth stage is achieved in about 90 minutes,
and then REM sleep begins abruptly

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Awake

REM: Skeletal

muscles (except
ocular muscles
and diaphragm)
are actively
inhibited; most
dreaming occurs.
NREM stage 1:
Relaxation begins;
EEG shows alpha
waves, arousal is easy.
NREM stage 2: Irregular
EEG with sleep spindles
(short high- amplitude
bursts); arousal is more
difficult.
NREM stage 3: Sleep
deepens; theta and
delta waves appear;
vital signs decline.

(a) Typical EEG patterns
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NREM stage 4: EEG is
dominated by delta
waves; arousal is difficult;
bed-wetting, night terrors,
and sleepwalking may
occur.
Figure 12.21a

Sleep Patterns
• Alternating cycles of sleep and wakefulness
reflect a natural circadian (24-hour) rhythm
• RAS activity is inhibited during, but RAS also
mediates, dreaming sleep
• The suprachiasmatic and preoptic nuclei of
the hypothalamus time the sleep cycle
• A typical sleep pattern alternates between
REM and NREM sleep
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