Transcript NERVOUS SYSTEM

CAMPBELL AND REECE
CHAPTER 49
 ability
to react to stimuli originated
billions of years ago with prokaryotes
• able to detect changes in environment that
enhanced survival & reproductive success….
 Hydras,
Jellies, &
other cnidarians:
• radial symmetry
• interconnected nerve
cells form a diffuse
nerve net  controls
contractions &
expansion of the
central digestive
compartment
•
Hydra
 Invertebrate
nervous systems range in
complexity from simple nerve nets to
highly centralized nervous systems
having complicated brains & ventral
nerve cords
 Central
Nervous
System: CNS
 Peripheral
 Brain
 Nerves
 Spinal
Cord
Nervous
System: PNS
 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
 automatic
protective responses to
certain stimuli thru simple nerve circuits
 http://www.sumanasinc.com/webcontent
/animations/content/reflexarcs.html
 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
 CNS
develops from a hollow dorsal nerve
cord (hallmark of chordates, with a
notochord)
• cavity of this nerve cord  central canal of
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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)
 mainly
neuron cell bodies, dendrites, &
unmyelinated axons
 outside of brain
 inside spinal cord
 mainly
bundled myelinated axons
 inside brain, outside spinal cord
 aka
neuroglia
 cells that support, nourish, regulate, &
augment functions of neurons
 Types:
• Ependymal cells
• Oligodendrocytes
• Astrocytes
• Microglia
• Schwann cells
line ventricles
 ciliated
 promote circulation
of CSF

 myelinate
axons in the CNS
 (myelination greatly increases speed of
action potentials)
 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
 Immune
cells that protect against
pathogens
 myelinate
axons in PNS
 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
 Radial
Glial cells & Astrocytes also
thought to act as stem cells for
CNS…able to generate new neurons &
glial cells…..
 plays
large role in regulating an animal’s
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
 Sympathetic
& Parasympathetic has
antagonistic effects on a diverse set of
target organs
 Efferent division: controls activity of
many digestive organs
 Brain
most complex organ of human body
 protected by thick bones of skull
 http://www.dnatube.com/video/12257/T
he-human-embryonic-braindevelopment
 rapid
expansion during 2nd & 3rd 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
 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
 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)
 part
of forebrain 
• Thalamus
• Hypothalamus
• Epithalamus
 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
 body‘s
thermostat
 central biological clock
 controls release of hormones from
pituitary
 source of posterior pituitary hormones
 includes
pineal gland
 clusters
of capillaries  produce CSF
• secretes melatonin
 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
 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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2.
3.
parts:
Midbrain
Pons
Medulla Oblongata
 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
 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
 contains
several automatic, homeostatic
functions:
• Respiratory center
• Cardiovascular center
• swallowing
• vomiting
• digestion
 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
 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
 diffuse
network of neurons in core of
brainstem
 determines which sensory information
makes it to cerebrum
 more info sent along to cerebrum…the
more aware someone is
 Pons & Medulla also contain “sleep”
centers & Midbrain has a center that
causes arousal
 all
birds & mammals
 Melatonin:
• hormone released by pineal gland
• peak secretion @ night, decrease in am
 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
a
molecular mechanism that directs
periodic gene expression & cellular
activity
 humans
removed from any light/dark
clues uniformly set a 24.2 hr cycle
 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
 their
generation & experience involve many
regions of brain but main area
 Limbic System
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Emotions
Motivation
Olfaction
Behvior
Memory
 Limbic System Parts
• Amygdala
• Hippocampus
• parts of the thalamus
 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
 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
 1800’s:
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 Broca’s area: controls muscles in
the face
• We now know this area is active during speech
generation
 Karl
Wernicke: damage to posterior
portion of temporal lobe (Wernicke’s
area) abolished ability to comprehend
speech but not the ability to speak
• We now know this area is active when speech is
heard.
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
 allows
right & left hemispheres to work
together
 If severed:
• “split-brain”
 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.
 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
 patients
w/hx of tumors removed in
same area as Gage’s injury have had
similar changes:
• intellect & memory are intact
• decision making is flawed
• emotional responses diminished
 in
humans: cerebral cortex ~80% of
total brain mass
• 5 mm thick
• ~1,000 square cm
• outermost part called the neocortex
 until
recently scientists thought a highly
convoluted neocortex required for
advanced cognition
 Primates
& Cetaceans (whales, dolphins
& porpoises) have very convoluted
neocortex
 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
 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
 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

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
 If
2 synapses on the same postsynaptic cell
are often active @ same time, the strength of
the postsynaptic response may increase @
both synapses
 relies
on temporary links in the
hippocampus
 temporary
links of short term memory
replaced by connections w/in cerebral
cortex
 transfer
of information from shortterm 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)
 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
 researchers
have identified some genes
that cause or contribute to disorders of
nervous system…so better able to
identify causes & predict outcomes
 environmental
contributions also very
significant but very difficult to identify
 1%
world’s population
 See:
• psychotic episodes in which patient has
distorted perception of reality
• hear voices
• delusional
 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
 Causes
(?):
 alteration of glutamate signaling
• Street drug PCP blocks glutamate signaling &
mimics symptoms of schizophrenia
 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
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
 aka
Manic-Depressive Disorder
 ~1% of world’s 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
 characterized
by compulsive
consumption of drug & loss of control in
limiting intake
 Drug increases activity of brain’s reward
system (normally functions in pleasure,
motivation & learning)
 Addictive Drugs
• Stimulants: cocaine, amphetamines
• Sedatives: heroin
 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
 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
 leads
to death of neurons in many areas
of the brain
• Brain shrinks
• See amyloid plaques & neurofibrillary tangles on
post-mortem
 motor
disorder, progressive disease
 more common with advancing edge (5%
by age 85)
 See:
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Muscle tremors (pill-rolling)
Poor balance
Flexed posture
Shuffling gait
Facial mask: muscles rigid, unable to vary
expression
 symptoms
result
from death of
neurons in the
midbrain that
normally release
dopamine in basal
nuclei
 no cure:
• Brain surgery
• L-dopa
 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