CAMPBELL AND REECE CHAPTER 49. ability to react to stimuli originated billions of years ago with...
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NERVOUS SYSTEM CAMPBELL AND REECE CHAPTER 49
CAMPBELL AND REECE CHAPTER 49. ability to react to stimuli originated billions of years ago with prokaryotes able to detect changes in environment that
ability to react to stimuli originated billions of years ago
with prokaryotes able to detect changes in environment that
enhanced survival & reproductive success.
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Hydras, Jellies, & other cnidarians: radial symmetry
interconnected nerve cells form a diffuse nerve net controls
contractions & expansion of the central digestive compartment
Hydra
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Invertebrate nervous systems range in complexity from simple
nerve nets to highly centralized nervous systems having complicated
brains & ventral nerve cords
functions of brain & spinal cord tightly coordinated Brain:
integrative function Spinal Cord: conveys information to & from
the brain & generates basic patterns of locomotion; spinal
reflexes act independently of the brain Nerves: transmit sensory
& motor signals between b
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automatic protective responses to certain stimuli thru simple
nerve circuits
Invertebrates have their nerve cord on ventrally (front)
Vertebrates have spinal cord along dorsal side (back) segmental
organization in arrangement of neurons w/in spinal cord, spinal
nerves & ganglia just outside spinal cord
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CNS develops from a hollow dorsal nerve cord (hallmark of
chordates, with a notochord)
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cavity of this nerve cord central canal of spinal cord +
ventricles of brain both filled with CSF (cerebral spinal fluid) a
filtrate of arterial blood CSF flows thru these spaces then drains
into veins supplies brain with nutrients, hormones carries away
waste in mammals: cushions brain & spinal cord (layer of CSF
between these & surrounding bone)
aka neuroglia cells that support, nourish, regulate, &
augment functions of neurons Types: Ependymal cells
Oligodendrocytes Astrocytes Microglia Schwann cells
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line ventricles ciliated promote circulation of CSF
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myelinate axons in the CNS (myelination greatly increases speed
of action potentials)
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star-shaped facilitate information transfer @ synapses
sometimes release neurotransmitter can cause blood vessels near
neurons to dilate increasing oxygen & glucose delivery to
neurons regulate extracellular concentrations of ions &
neurotransmitters
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Immune cells that protect against pathogens
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myelinate axons in PNS
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Embryo: radial glia cells form tracks along which newly formed
neurons migrate from neural tube Astrocytes induce cells lining
capillaries to form tight jcts blood-brain barrier (bbb) controls
the extracellular environment of CNS by restricting entry of most
substances from blood
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Radial Glial cells & Astrocytes also thought to act as stem
cells for CNSable to generate new neurons & glial cells..
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plays large role in regulating an animals movement &
internal environment Afferent neurons: carry sensory signals CNS
Efferent neurons: carry signals to skeletal muscle & glands
& thru Autonomic Nervous system to smooth & cardiac
muscle
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Sympathetic & Parasympathetic has antagonistic effects on a
diverse set of target organs Efferent division: controls activity
of many digestive organs
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Brain most complex organ of human body protected by thick bones
of skull
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http://www.dnatube.com/video/12257/T he-human-embryonic-brain-
development http://www.dnatube.com/video/12257/T
he-human-embryonic-brain- development
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rapid expansion during 2 nd & 3 rd months of fetal
development causes the outer portion, the cortex (gray matter) to
extend over & around much of the rest of the brain Cerebral
cortex: vital for perception, voluntary actions, &
learning
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term includes cerebral cortex divided into hemispheres left
hemisphere receives information from & controls movement of
right side of body & vise versa Corpus callosum: thick band of
axons connects hemispheres
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clusters of neurons deep w/in white matter of brain serve as
centers for planning & learning movement sequences Damage
during fetal development cerebral palsy (disruption of commands to
muscles)
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part of forebrain Thalamus Hypothalamus Epithalamus
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main input center for sensory information cerebrum Sensory
tracts from spinal cord thalamus which sorts info sending it to
correct region of cerebrum for further processing
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bodys thermostat central biological clock controls release of
hormones from pituitary source of posterior pituitary hormones
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includes pineal gland secretes melatonin clusters of
capillaries produce CSF
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coordinates movement & balance helps in learning &
remembering motor skills receives info on joint position &
length of muscles + input from hearing & visual centers
integrates information on motor commands from cerebrum as it
carries out coordination & error checking during motor &
perceptual functions
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controls eye-hand coordination if damaged: Eyes can follow
moving object but eyes keep moving when object stops Hand movement
toward the object will be erratic
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3 parts: 1. Midbrain 2. Pons 3. Medulla Oblongata
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receives & integrates several types of sensory information
sends it to specific regions of forebrain all sensory axons from
hearing either terminate in midbrain or pass thru it cerebrum
coordinates visual reflexes Head turns towards object approaching
from the side w/out brain having formed image of moving object
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transfers info from PNS midbrain & forebrain coordinates
large-scale body movements (running, climbing) axon tracts cross
from 1 side to other: right side of brain controls left side of
body & vice versa
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contains several automatic, homeostatic functions: Respiratory
center Cardiovascular center swallowing vomiting digestion
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transitions from wakefulness to sleep regulated by brainstem
& cerebrum Arousal : state of awareness of external world
Sleep: state in which external stimuli are received but not
consciously perceived
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is an active state EEG (electroencephalogram): brain waves
change as go thru stages of sleep hypothesis: sleep & dreams
involved in consolidating learning & memory regions of brain
involved in learning while awake also active during sleep those
lacking sleep have more difficulty learning new task
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diffuse network of neurons in core of brainstem determines
which sensory information makes it to cerebrum more info sent along
to cerebrumthe more aware someone is Pons & Medulla also
contain sleep centers & Midbrain has a center that causes
arousal
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all birds & mammals Melatonin: hormone released by pineal
gland peak secretion @ night, decrease in am
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Bottlenose Dolphins: Swim while sleeping Rise to surface to
breathe Sleep with 1 eye open, 1 eye closed ? Does dolphin sleep
with 1 hemisphere of brain awake/ 1 asleep? Proved by using
EEG
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a molecular mechanism that directs periodic gene expression
& cellular activity humans removed from any light/dark clues
uniformly set a 24.2 hr cycle
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coordinated by a group of neurons in hypothalamus called:
suprachiasmatic nucleus or SCN acts as pacemaker: synchronizes the
biological clock in cells thru out body to natural cycles of day
length
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their generation & experience involve many regions of brain
but main area Limbic System Emotions Motivation Olfaction Behvior
Memory Limbic System Parts Amygdala Hippocampus parts of the
thalamus
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stored as memories that are recalled by similar circumstances
Fear: memory is stored separate from the memory system that
supports explicit recall of events Amygdala: stores emotional
memories
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largest structure in human brain cortex: cognitive functions:
sensory areas receive & process sensory info association areas
integrate the info motor areas transmit instructions to other parts
of the body
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1800s: Pierre Broca: autopsied brains of people that could
understand language but could not speak Discovered many of them had
defects in what is now called Brocas area: controls muscles in the
face We now know this area is active during speech generation
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Karl Wernicke: damage to posterior portion of temporal lobe
(Wernickes area) abolished ability to comprehend speech but not the
ability to speak We now know this area is active when speech is
heard.
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2 hemispheres make distinct contributions to some brain
functions: Left side: Speech Math & Logical operations Right
side: Recognition of faces & patterns Spatial relations
Nonverbal thinking
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allows right & left hemispheres to work together If
severed: split-brain
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In the somatosensory cortex (where somatosensory sensors like
touch, pressure, pain, temperature, & position of muscles &
limbs send impulses) & motor cortex (where motor commands
generated) are arranged according to the part of the body that
generates the sensory input or receives the motor commands.
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Phineas Gage: 3 meter long, 3 cm diamter pipe thru his frontal
lobe He survived but had personality changes; he became emotionally
detached, impatient, erratic in behavior
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patients w/hx of tumors removed in same area as Gages injury
have had similar changes: intellect & memory are intact
decision making is flawed emotional responses diminished
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in humans: cerebral cortex ~80% of total brain mass 5 mm thick
~1,000 square cm outermost part called the neocortex
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until recently scientists thought a highly convoluted neocortex
required for advanced cognition Primates & Cetaceans (whales,
dolphins & porpoises) have very convoluted neocortex
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have region (pallium) contains clustered nuclei that carry out
functions similar to those performed by our cerebral cortex Some
birds solve problems & understand abstractions which indicates
higher cognition
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during development more neurons and synapses form than will
exist in the adult apoptosis of neurons & elimination of
synapses in embryos establishes the basic structure of the nervous
system
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In adult, reshaping of the nervous system can involve the loss
or addition of synapses or the strengthening or weakening of
signaling at synapses This capacity for remodeling is called neural
plasticity defective remodeling of synapses is partly responsible
for the developmental abnormalities of autism
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Connections between neurons strengthened or weakened in
response to activity. High-level activity @ synapse of the
post-synaptic neuron with presynaptic neuron leads to recruitment
of more axon terminals from that neuron. Lack of activity @ synapse
with presynaptic neuron loss of functional connections with that
neuron
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If 2 synapses on the same postsynaptic cell are often active @
same time, the strength of the postsynaptic response may increase @
both synapses
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relies on temporary links in the hippocampus
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temporary links of short term memory replaced by connections
w/in cerebral cortex
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transfer of information from short- term to long-term memory is
enhanced by association of new data with that already in long-term
memory (making connections to something you already have learned
helps you learn new material)
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evidence shows they are involved in learning & memory After
damage to CNS, surviving neurons can make new connections &
sometimes compensate for lost cells. Stem cell research has long
way to go at this time
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researchers have identified some genes that cause or contribute
to disorders of nervous systemso better able to identify causes
& predict outcomes environmental contributions also very
significant but very difficult to identify
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1% worlds population See: psychotic episodes in which patient
has distorted perception of reality hear voices delusional
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Causes (?): disruption in neuronal pathways that release
dopamine Amphetamines which stimulate dopamine produce same set of
symptoms meds used to alleviate symptoms block dopamine
receptors
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Causes (?): alteration of glutamate signaling Street drug PCP
blocks glutamate signaling & mimics symptoms of
schizophrenia
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Characterized by: depressed mood alterations in sleep,
appetite, energy level Nervous disorder with best chances of
effective treatments with meds & therapy 2 broad forms: Major
Depressive Disorder Bipolar Disorder
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1 of most common nervous system disorders Patients undergo
periods of time when get no enjoyment out of things normally would
Affects ~ 1/7 adults at some time in their lives; women: men
2:1
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aka Manic-Depressive Disorder ~1% of worlds population See:
mood swings: very high to very low Highs: hi self-esteem, hi nrg,
talkativeness, & increased risk taking Lows: less ability to
feel pleasure, feel worthless, sleep disturbances
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characterized by compulsive consumption of drug & loss of
control in limiting intake Drug increases activity of brains reward
system (normally functions in pleasure, motivation & learning)
Addictive Drugs Stimulants: cocaine, amphetamines Sedatives:
heroin
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Normally: provides motivation for activities that enhance
survival & reproduction Eating in response to hunger Drinking
when thirsty In drug addict motivation is directed toward further
drug consumption
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mental deterioration or dementia characterized by confusion
& memory loss also, loss of ability to recognize people, treat
others with suspicion &/or hostility incidence age-related: ~
10% @ age 65 to ~ 35% @ age 85 No cure, drugs available that
relieve some of symptoms or slow progression
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leads to death of neurons in many areas of the brain Brain
shrinks See amyloid plaques & neurofibrillary tangles on
post-mortem
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motor disorder, progressive disease more common with advancing
edge (5% by age 85) See: Muscle tremors (pill-rolling) Poor balance
Flexed posture Shuffling gait Facial mask: muscles rigid, unable to
vary expression
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symptoms result from death of neurons in the midbrain that
normally release dopamine in basal nuclei no cure: Brain surgery
L-dopa
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most cases have no identifiable cause Except: disease that
appears in relatively young adults has a clear genetic basis Find:
disruption of genes required for certain mitochondrial
functions