Download Central Nervous System

2/24/13
Overall Organization
The Central Nervous System
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Central nervous system
(CNS) – integration and
command center
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Keri Muma
Bio 6
Neural Tissue Organization
Types Of Tracts
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Tracts –axons running to or from
  Projection – vertical tracts, responsible for the communication
between the cerebral cortex and lower CNS
  Association (arcuate) – connect gyri within the same cerebral
hemisphere
  Commissural – connects gyri between left and right hemispheres
Protection of the CNS
Protection of CNS
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Bones of the skull and vertebral column
Meninges – three CT membranes surrounding the brain
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Dura Mater – superficial layer, consists of two layers of fibrous
CT
Arachnoid Mater – loose middle layer
Pia Mater – deepest, clings tightly to the brain following every
convolution.
Brain
Spinal cord
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Cerebrospinal fluid -found in the ventricles and the
subarachnoid space around the brain and spinal
cord
Functions
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Gives buoyancy to the brain and spinal cord – keeps it
from being damaged by its own weight
Cushions and protects
Transports materials
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Protection of the CNS
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Blood Brain Barrier - capillaries are less permeable due
to tight junctions between endothelial cells and between
astrocytes
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Helps maintain a constant environment for the brain
Very selective- fat soluble materials, glucose, and select
ions and amino acids are allowed to pass, others are not
Metabolic Requirements of the CNS
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Neurons rely on a constant supply of oxygen
and glucose to produce ATP for active transport
of ions and neurotransmitters.
Oxygen diffuses across the BBB
Under normal circumstances glucose is the only
energy source for neurons
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Regions Of CNS
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Cerebrum – integration of sensory/motor, higher functions
Diencephalon – innate drives and emotions
  Epithalamus
  Thalamus
  Hypothalamus
  Pineal gland
  Pituitary gland
Brainstem –basic functions to maintain life
  Midbrain
  Pons
  Medulla oblongata
Cerebellum – coordination
Spinal cord - reflexes
Plasticity of the Brain
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The architecture of the cortex is determined by
genetic and developmental processes but it can
be modified due to “use-dependent competition”
for cortical space
Formation of new neural pathways and
connections between existing neurons
Some cortical regions can be remodeled
throughout life while other can be for only a
limited time
Functional Areas of the Cerebral Cortex
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Sensory areas – process afferent impulses, interpret
sensations
Motor areas – involved in planning and initiating muscular
movement
Association areas – involve combining information from
multiple areas and processing them together, involved in
higher functions
Glucose is transported from the plasma into the
interstitial fluid by insulin independent membrane
transporters
Hypoglycemia leads to confusion, unconsciousness
and death
Cerebral Cortex: Sensory Areas
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Primary somatosensory area – postcentral gyrus in the
parietal lobe
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Receives impulses involved in touch, pain, pressure,
stretch
Somatosensory association – integrates sensory input
into understanding by analyzing sensory based on past
experiences
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Lies posteriorly to primary somatosensory
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Cerebral Cortex: Sensory Areas
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Cerebral Cortex: Sensory Areas
Primary visual cortex – receives sensory input
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Primary auditory – receives sensory input from
the vestibulocochlear nerve. Temporal lobe.
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Auditory association area – lies posterior to
primary, interprets sound into context
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Primary motor cortex –
controls somatic motor neuron
output
from the retina to the occipital lobe. Data only.
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Visual association area – interprets the raw data
and puts it into context. Surrounds the primary.
Cerebral Cortex: Sensory Areas
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Olfactory cortex –found on medial aspect of
temporal lobe. Sensory input from olfactory nerves.
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Gustatory cortex – perception of taste, found in the
insula
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Cerebral Cortex: Motor Areas
Linked limbic system – tied to emotions and memories
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Cerebral Cortex: Motor Areas
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Premotor cortex – anterior to the primary motor
cortex in the frontal lobe
  Responsible for coordinating learned motor skills
  Examples: typing, driving, playing the piano
Lies in the precentral gyrus of
the frontal lobe
Output is usually controlled by
higher motor areas and input
from the cerebellum
Amount of cortex devoted to
each area relates to which
regions have the most precise
control.
Control is contra lateral
Basal Nuclei
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Basal Nuclei (basal ganglia) – gray
matter
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Adjust the stopping, starting and
intensity of movements after
receiving input from cerebral cortex
and substantia nigra (midbrain)
Lesions of nuclei lead to increase
motor output leading to increased
muscle tone, difficulty initiating
movement, and involuntary muscle
movement
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Cerebral Cortex: Association Areas
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Cerebral Cortex: Language Areas
Prefrontal cortex – involved with intellect, recall,
reasoning, judgment, concern for others, personality
traits, and management of emotions
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Language areas – surrounds lateral sulcus, usually
in the left hemisphere only
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Develops later in life and is impacted by social environment
Linked to emotions (limbic system)
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Receives input from auditory and visual senses
Coordinates with the motor cortex to carry out motor skills
involved in speech and writing
Insert fig 9-23
Language Areas
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Language involves both expression and comprehension
Two cortical areas specializing in language are:
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Wernicke’s area – language comprehension and formulation of
coherent patterns of speech
Broca’s area – speech production and word formation,
associated with motor cortex
Cerebral Lateralization
Limbic System
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Limbic system – emotional brain, consists of tracts
and nuclei of the medial cerebrum, anterior
thalamus, and hypothalamus
  Functions:
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Establishes emotional state and behavioral drive
Linked to prefrontal cortex, sometimes logic overrides
emotion or vice versa
Long term memory storage and retrieval
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Functional Brain Systems
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Limbic system structures
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How Emotions Influence
Physiological Functions
Amygdala – recognizes angry or fearful expressions and assesses
danger
Cingulate gyrus – role in expressing emotion and resolving mental
conflicts
Hippocampus – role in memory along with amygdala
Memory
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Memory is the storage and retrieval of
information
The three principles of memory are:
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Storage – occurs in stages and is continually
changing (stored in regions that need them)
Processing – accomplished by the hippocampus
and surrounding structures
Memory traces – chemical or structural changes
that encode memory
Transfer from STM to LTM
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Stages of Memory
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The two stages of memory are short-term memory
and long-term memory
Short-term memory (working memory)
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STM lasts seconds to hours and is limited to 7 or 8
pieces of information
Only 5% of sensory input is transferred to STM
Long-term memory (LTM) has limitless capacity
Memory Processing
Factors that affect transfer of memory from
STM to LTM include:
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Emotional state – we learn best when we are
alert, motivated, and aroused
Rehearsal – repeating or rehearsing material
enhances memory
Association – associating new information with old
memories in LTM enhances memory
Automatic memory – subconscious information
stored in LTM
Figure 12.21
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Categories of Memory
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The two categories of memory are fact
memory and skill memory
Fact (declarative) memory:
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Skill Memory
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Entails learning explicit information (names, dates)
Is related to our conscious thoughts and our
language ability
Is stored with the context in which it was learned
Skill (procedural) memory is less conscious
than fact memory and involves motor activity
(example: riding a bike)
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How Memories are Formed
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Long-term potentiation (LTP) - prolonged
increase in synaptic strength
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It is acquired through practice or repetition
Skill memories do not retain the context in which
they were learned
Hard to unlearn
Stored in the premotor cortex
Aspects of Long-term potentiation
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Synaptic modifications that can occur as a
result of LTPs
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Repetitive stimulation results in modification of
synapses that increase the ability of pre-synaptic
neurons to stimulate post-synaptic neurons
Necessary for memory trace formation
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Aspects of Long-term potentiation
Number and size of presynaptic terminals may
increase
More neurotransmitter is released by presynaptic
neurons
Dendritic spines change shape
Extracellular proteins are deposited at synapses
Diencephalon
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Thalamus – forms lateral walls of
the 3rd ventricle
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Acts as a relay station for all
incoming sensory impulses except
olfactory
Screens sensory impulses and
decides if it should be passed
onto the cortex and where it
should be sent
Crude awareness of sensation
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Diencephalon
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Hypothalamus – slightly anterior and inferior to
the thalamus
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Hypothalamus
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Important in maintaining body homeostasis and behavioral
drives
Autonomic control center –
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Controls release of catecholamine from the adrenal medulla
Controls ANS centers in the brain stem and spinal cord, BP,
HR, digestive tract, respiration rate, pupil size
Emotions – heart of limbic system, basic primitive
drives such as fear, anger, pleasure
Regulates body temperature – thermostat, initiates
cooling or heating mechanisms
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Sleep-wake cycles – acts with pineal gland to set
cycles in response to light and dark
Hypothalamus
Brain Stem
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Midbrain – superior portion of the brain stem
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Food intake – responds to changes in levels of
nutrients and hormones. Contains satiety and
feeding centers.
Water balance and thirst – osmoreceptors that
detect concentrations of body fluids, triggers antidiuretic hormone (ADH) and thirst centers
Corpora quadrigemina – four protrusions on the dorsal surface,
contain sensory nuclei
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Superior colliculi – visual reflexes
Inferior colliculi – auditory reflexes
Substantia nigra – axons linked to cerebral basal nuclei,
release dopamine, controls motor output
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Degeneration of these neurons causes Parkinson’s disease
Hormones
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Produces releasing or inhibiting factors which controls the
release of hormones from the anterior pituitary
Produces posterior pituitary hormones, ADH and oxytocin
Brain Stem
Brain Stem
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Pons – bulging region between midbrain and medulla,
anterior to cerebellum
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Pontine nuclei – relay station for tracts between motor
cortex and cerebellum
Pneumotaxic and apneustic respiratory center – works
with medulla to maintain rhythmic breathing
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Medulla Oblongata – base of brain stem, blends
inferiorly with the spinal cord
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Pyramids – longitudinal ridges on the ventral surface
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Contains motor tracts that cross over (decussation) before
they continue down the spinal cord
Insert 9-9
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Medulla Oblongata
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Autonomic Nuclei
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Cardiovascular center – adjusts force and rate of heart
contraction and blood pressure
Respiratory center – controls rate and depth of breathing, works
with pons for rhythm
Vomiting, swallowing, coughing, sneezing, hiccups
Reticular Formation
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Reticular Activation System
(RAS) - neurons sending
constant impulses to the cortex
via the thalamus to keep the
cortex conscious and alert
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Inhibited by the hypothalamus
sleep center, adenosine, alcohol,
and tranquilizers
Damage suffered by a jolt to the
brain stem may result in
permanent unconsciousness
(coma)
Types and Stages of Sleep: REM
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Characteristics of REM sleep
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Vital signs increase
Neuronal activity is high
Skeletal muscles (except ocular muscles) are
inhibited
Most dreaming takes place
Brain Stem
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Reticular Formation – loose cluster of neurons
extending through the brain stem to the thalamus,
hypothalamus, cerebellum and spinal cord
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Responsible for the arousal (alertness) of the brain
Types of Sleep
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There are two major types of sleep:
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Non-rapid eye movement (NREM)
Rapid eye movement (REM)
One passes through four stages of NREM
during the first 30-45 minutes of sleep
REM sleep occurs after the fourth NREM
stage has been achieved
A typical sleep pattern alternates between
REM and NREM sleep
Sleep Patterns
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Alternating cycles of sleep and wakefulness
reflect a natural circadian rhythm
The suprachiasmatic and preoptic nuclei of
the hypothalamus regulate the sleep cycle
Adenosine appears to be a sleep inducing
chemical that accumulates in the brain
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Inhibits RAS neurons
Caffeine blocks adenosine receptors
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Importance of Sleep
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Sleep Disorders
NREM sleep is presumed to be the
restorative stage
REM sleep may be a reverse learning
process where superfluous information is
purged from the brain (one hypothesis)
Those deprived of REM sleep become
moody and depressed
Daily sleep requirements decline with age
Physiological Rhythms"
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Narcolepsy – lapsing abruptly into REM sleep
from the awake state
Insomnia – chronic inability to obtain the
amount or quality of sleep needed
Sleep apnea – temporary cessation of
breathing during sleep
Examples of Circadian Rhythms
Dynamic Equilibrium – variables are continuously
fluctuating within their narrow limits "
  These fluctuations tend to be in wave patterns called
biorhythms"
  If they fluctuate in a cycle every 24 hours they are
referred to as circadian rhythms!
  Controlled by the suprachiasmatic nucleus (SCN) in
the hypothalamus"
Suprachiasmatic Nucleus
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Secretes clock proteins. "
Cyclic changes in their concentration throughout the
day changes the neural output from the SCN. "
This neural output produce cyclic changes in
effector organs through the day"
Circadian Rhythms
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The SCN cycle is a little longer than 24 hours"
Internal clock must be reset daily by external cues
in order to stay in sync."
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Light and dark cycle"
Melatonin secreted from the pineal gland keeps the SCN in
tune with the environment and regulates sleep/wake cycles"
SCN
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Circadian Rhythms
Cerebellum
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Desynchronosis – internal clock is out of
synchronization with the external environment
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Jet lag, work rotations, change in sleep schedule
Effects: decreased cognitive function, depression,
foggy head, can’t sleep or wake up
Seasonal affective disorder: depression during short
winter days due to decreased sunlight
Can be treated with bright light or melatonin
Cerebellum
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Maintains posture, balance, and plays a role in learning and
executing skilled motor movements
Body map – sensory and motor maps of the body so it is
aware of what each skeletal muscle is doing
Functions of the Cerebellum
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Monitors intended movements from the motor cortex
and basal nuclei
Monitors current movements – receiving input from
proprioceptors and the vestibule (equilibrium)
Compares intended movements, sensory input, and
the actual movement and placement of muscles at
that time
Sends corrective feedback to the upper motor
centers if there is a discrepancy between the
intended movement and the actual movement
Cerebellum
Motor cortex &
Basal Nuclei
Sends intended muscle
Movement to cerebellum
Adjustments made by
Cerebellum sent back to
Motor cortex
Cerebellum
Coordinate motor intent
with sensory input
Sensory input from proprioceptors,
visual and equilibrium pathways
Cerebellum & Coordination of Muscles
Cerebellum
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Ataxia- disruption of muscle coordination
resulting in inaccurate movements
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Caused by damage to the cerebellum through
trauma or genetic disease
Abnormal walking movements, uncoordinated
speech, overshoot objects
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