Transcript nervoussystemwebquest

The Wonderful World of
THE NERVOUS SYSTEM
The Nervous
System
Provided to you by:
Jaclynn Chen
Katie Tang
Winnie Tema
An Overview of Nervous Systems
The nervous system carries out actions in three functions.
First a signal, such as flashing light, is translated through the sensory receptors .
This sensory input relays the information collected from the outside world to
integration centers.
The information is interpreted by the integration centers and sends this
interpretation to the motor output, which gives an appropriate response of the
body through effector cells.
The Central nervous system (CNS) includes the integration center.
The Peripheral nervous system (PNS) includes the sensory input and motor output.
It’s kind of like when your send a letter. When
you drop a letter you wrote to your friend in your
mailbox, your local postal carrier picks of the
letter (like a sensory receptor) and takes it to the
post office. At the office, your letter is mixed with
the rest of the mail sent that day and sorted out
to the appropriate carrier and sent out to deliver
(integration center). The carrier then sends your
letter directly to your friend’s house where he or
she can read the lovely letter your wrote just for
him or her (motor output).
What sends the signals through the nervous system?
Nerves are what do this. Nerves consist of ropelike structures in bundles of neurons tightly
wrapped in connective tissue.
Groups of neurons are what make up nerves. Neurons (aka nerve cells) carry out the structure
and function of the nerves.
Main parts of a neuron:
Cell Body contain the nucleus and organelles of cell
Dendrites receive incoming messages from other cells to the cell body (coming in)
Axons transmit signals to other cells (going out)
Neuron structure:
Axon hillock is where the axon meets the cell body
Myelin sheath wrap around axons, insulates them
Synaptic terminals are the terminal branches of axons that transmit signals by releasing
chemical signals called neurotransmitters.
Synapse is the site between a synaptic terminal and a target cell
Presynaptic cell is the transmitting cell
Postsynaptic cell is the target cell
“Nervous System Cells” http://library.thinkquest.org/2935/Natures_Best/Nat_Best_Low_Level/Nervous_page.L.html#Nervous_Sys_Cells
Can you label the structures of the neuron and the
direction of the neurotransmitter?
A.
Presynaptic Cell
B.
C.
H.
D.
E.
F.
G.
Postsynaptic Cell
D. Axon Hillock
C. Nucleus
Answers:
E. Axon
F. Myelin Sheaths
A. Dendrites
G. Synaptic Terminal
B. Cell Body
H. Synapse
Not all nervous systems are the same
you know…
The simplest animals with nervous systems have an expansive nervous system,
which are arranged in diffused nerve nets
More complex animals have nervous systems with systems of nerves.
Ever wonder what makes those knee jerking reactions?
Go ahead…Try it.
Tap the tendon connected to the quadriceps muscle
What causes this to happen?
This is a perfect example that will allow us to observe the different parts of the
nervous system.
See the movement on this site!
http://www.dushkin.com/connectext/psy/ch02/reflex.gif
http://www.bbc.co.uk/science/humanbody/body/factfiles/reflexes/reflexes.shtml
Reflexes are caused by the automatic responses of the reflex arc between the
spinal cord and brain.
There are two kinds of nerve cells involved:
Sensory neuron transmits information from a sensory receptor to a
motor neuron, which signals an effector cell to carry out the response.
The knee jerking reaction goes through the sensory neurons which relays the information
to the stretch receptor in the thigh muscle, to interneurons in the spinal cord, which finally
inhibit motor neurons to the flexor muscles.
Motor neurons and interneurons are located in the gray matter of the CNS. Motor & sensory
axons are in the white matter.
Outside the spinal cord structure is a ganglion (a cluster of nerve cell bodies) in the PNS.
Nuclei are similar to ganglion but are in the brain.
Glia – supporting cells of the nervous system
Astrocytes support the structure of the neuron and regulate the concentration of
ions and neurotransmitters.
These induces the formation of the blood brain barrier which restricts the passage of
substances into the brain.
Radial glia create and track newly formed neurons from stem cells
Oligogendrocytes and Schwann cells are glia that support the axons in the
mylein sheath.
These membranes are mostly lipids which
are poor conductors of electrical current.
Multiple Sclerosis is a disease the
degrades the myelin sheaths.
http://www.youtube.com/watch?v=qgySDmRRzxY
Explore more of the world of
the nervous system &
reflexes
http://www.bbc.co.uk/science/humanbody/body/factfiles/reflexes/reflexes.shtml
Neurotransmitters travel by electrical impulses
The membrane potential is the difference of charges across the plasma membrane
When the membrane is at resting potential, there is no transmitting of signals.
The voltage is usually around -70 mV.
This membrane potential is due to the concentration of ions on the two sides of the
membranes. Sodium (Na+) ions are usually outside making it negatively charged while
potassium (K+) are usually inside making it positively charged.
These concentrations are maintained by sodium ion pumps
K+ & Na+ have ungated ion channels that allow them to diffuse all the time at resting potential.
K+ is more permeable than Na+. When this permeability changes, the membrane
potential changes
When the electrical gradient exactly balances the concentration gradient, an equilibrium is
established.
Types of ion pumps that effect the membrane potential:
Stretch gated ion channels- cells that sense stretch and open when the membrane is
mechanically deformed
Ligand-gated ion channels- found at synapses and open or close when a specific chemical, like
a neurotransmitter, binds to the channel
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potass
ium_pump_works.html
In response to a stimuli the membrane
potential of a cell open and closes its
channels

Graded potentials

Hyperpolarization- an increase in the
magnitude of the membrane potential


May be caused by opening of gated K+
Depolarization- reduction in the
magnitude of the membrane potential.

May be caused by opening gated Na+
Production of Action Potentials



Depolarizations are graded only up to a certain
membrane voltage or a threshold
 Once a stimulus is strong enough to produce
depolarization that reaches the threshold,
action potential is then produced.
Action Potential is an all or none phenomenon
 Once it is triggered it has a magnitude that is
independent of the strength of the triggering
stimulus.
 In most neurons, the action potential is very
brief. This allows the neuron to produce them
at high frequencies.
LEARN MORE:
http://outreach.mcb.harvard.edu/animations/ac
tionpotential.swf,
http://bcs.whfreeman.com/thelifewire/content/
chp44/4402002.html.
Conduction of Action Potentials


As an action potential travels, it
regenerates itself along the axon in
order to not diminish the cell body.
The action potential is usually initiated
at the axon hillock.


Here, the Na+ influx creates an electrical
current that depolarizes the neighboring
region of the axon membrane.
Afterwards, Repolarization occurs due to
K+ efflux (Na+ channels still closed)
 Prevents action potentials from traveling
back toward the cell body
Conduction Speed

Factors that affect the speed at which action
potentials are conducted



Diameter- the larger the faster, the resistance
to the flow of electrical current is inversely
proportional to the cross-sectional area of the
conductor.
Myelin sheath- by insulating the axon
membrane, which causes the depolarizing
current associated with an action potential to
spread farther along the interior of the axon.
This brings more distant regions of the
membrane to the threshold sooner.
Saltatory Conduction- action potential appears
to jump along the axon from node to node. It
speeds it up to 120 m/sec in myelinated axons.
Action Potentials are not transmitted from
neurons to other cells, but at the synapses
information is transmitted


Electrical synapses- contains gap junctions allowing
electrical current to flow directly from cell to cell.
Chemical synapses- involves the release of chemical
neurotransmitter by the presynaptic neuron.
 Presynaptic neuron synthesizes the neurotransmitter
and packages it in synaptic vesicles.

Information transfer is more modifiable at chemical
synapses than at electrical synapses
LEARN MORE:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPag
es/S/Synapses.html,
http://faculty.washington.edu/chudler/synapse.html.


Stored in the neuron’s synaptic terminals
Direct Synaptic Transmission

The binding of the neurotransmitter to a
particular part of the channel, the receptor,
opens the channel and allows specific ions to
diffuse across the postsynaptic membrane.
 Result- postsynaptic potential- a change in the
membrane potential of the postsynaptic cell
 Synapses that cause depolarizations bring the
membrane potential toward the threshold are
called excitatory postsynaptic potentials.


Na+ and K+ diffuses here
Synapses that causes hyperpolarizations are
called inhibitory postsynaptic potentials, they
move the membrane potential farther from the
threshold.

Channels that are selective for K+ only
Summation of Postsynaptic Potentials



Postsynaptic potentials’ magnitude varies with a number of
factors
 The amount of neurotransmitter released by the
presynaptic neuron
They do not regenerate themselves as they spread along the
membrane of the cell
 Smaller with distance from the synapse
Two EPSPs are needed to trigger an action potential in a
posynaptic neuron
 Two EPSP= temporal summation
 Two EPSPs produced nearly simultaneously by different
synapses on the same postsynaptic neuron= spatial
summation
Indirect Synaptic Transmission

Here, a neurotranmitter binds to a
receptor that is not part of an ion
channel.


Activates a signal transduction pathway
involving a second messenger in the
postsynaptic cell
A variety of signal transduction
pathways play arole in indirect
synaptic transmission.

Cyclic AMP- activates protein kinase A

Phosphorylates specific channel proteins
Neurotranmitters
Acetylcholine

Biogenic Amines
One of the most
common in
vertebrates and
invertebrates

Vertebrates- it
activates a signal
transduction pathway

G proteins 1)
inhibition of
adenylyl cyclase 2)
opening of K+
channels in the
muscle cell
membrane



Derived from amino
acids
Includes: epinephrine,
norepinephrine,
dopamine, and
serotonin
Often involved in
indirect synaptic
transmission- most
common in CNS.
Amino Acids and
Peptides


Gases
Gamma Aminobutyric
Acid, Glycine,
Glutamate, and
Aspartate- all known
to function as
neurotransmitters.
Several neuropeptides
serve as
neurotranmitters.



Many produced by
post translational
modification of much
larger protein
precursors.
Substance P mediates
perception of pain
Endorphins- decreases


Nitric oxide(NO), and
Carbon
Monoxide(CO)- local
regulators
CO is synthesized by
enzyme heme
oxygenase


In brain it regulates
the release of
hypothalamic
hormones
In PNS it acts as
inhibitory
neurotransmitter that
hyperpolarizes
In vertebrates the nervous system
shows cephalization and distinct CNS
and PNS components

CNS



Brain- provides integrative power
 underling the complex behavior of
vertebrates
Spinal Cord- integrates simple responses
to certain kinds of stimuli, conveys
information to the brain
Derived form dorsal embryonic nerve cord
 In an adult- this is the narrow central
canal of the spinal cord and the four
ventricles of the brain


Called cerebrospinal fluid
Axons are often found in well-defined
bundles, or tracts
 whose myelin sheath give them a whitish
appearance
The Peripheral Nervous System





Transmits information to and from the
CNS
Plays a large role in regulating
vertebrates movement and internal
environment
Structure- left-right pairs of cranial
and spinal nerves, they are associated
with ganglia
Cranial Nerves- originate in the brain
and terminate mostly in the organs of
the head and upper body
Spinal nerves- originate in the spinal
cord and extend to parts of the body
below the head
PNS divided into two parts:


Somatic Nervous System- carries
signals to and from skeletal
muscles, mainly in response to
external stimuli
Autonomic Nervous Systemregulates the internal environment
by controlling smooth and cardiac
muscles and the organs of the
digestive, cardiovascular, excretory,
and endocrine systems.
Autonomic Nervous System Broken
into three part:



Sympathetic Division- corresponds to
arousal and energy generation
Parasympathetic Division- causes
opposite responses that promote
calming and a return to selfmaintenance functions
Enteric Division- consists of networks
of neurons in the digestive tract,
pancreas, and gallbladder

Controls these organs’ secretions as well
as activity in the smooth muscles that
produce peristalsis
Embryonic Development of the Brain

Vertebrates consist of 3 bilateral
symmetrical, anterior bulges of the
neural tube


Forebrain, midbrain and hindbrain
Fifth week of human embryonic
development, five regions have formed
from the three primary bulges



Forbrain: telencephalon( cerebrum
cerebral cortex) , diencephalon
Midbrain- mesencephalon- give rise to
brain stem
Hindbrain- metencephalon,
myelencephalon- give rise to brain stem
The Brainstem


Consists of stalk with caplike
swellings at the anterior end of the
spinal cord
Three parts: medulla oblongata,
pons, midbrain


Functioning in homeostasis,
coordination and movement, and
conduction of information to higher
brain centers
Neuron cell bodies send axons to many
areas of the cerebral cortex and


Medulla oblongata- contains centers
that control several visceral
functions
The Pons- participates in some of
the above activities
The Cerebellum



Develops from part of the
metencephalon, important for
coordination and error checking
during motor, perceptual, and
cognitive functions
Involved in learning and
remembering motor skills
Receives sensory information about
the position of the joints and the
length of the muscles
The Diencephalon



Epithalamus- includes the pineal
gland and chroid plexus
Thalamus- main input center for
sensory information going to the
cerebrum and the main output
center for motor information leaving
the cerebrum
Hypothatlumus- most important
brain regions for homeostatic
regulation
The Cerebrum


Develops from the telencephalon
Divided into right and left cerebral
hemispheres


Each consists of an outer covering of
gray matter, the cerebral cortex
Internal white matter, groups of
neurons collectively called basal nuclei
Cerebral Cotex


Sensory information is analyzed,
motor commands are issued, and
language is generated
Neocortex- forms outermost part of
mammalian cerebrum, consisting of
six parallel layers of neuron
arranged tangential to the brain
surface
ACTIVITY TIME!!!!!

On the next slide is a picture with
colors on it, only there is a catch…
the words are colors and the words
are written in different colors. Now,
try the best you can to repeat the
different colors of the words.
Instead of reading out the words
repeat what color it is written in.
Good luck because it is not an easy
task!! This game is great to
challenge your memory which is
developed by the cerebellum.
Concept 48.6 –
The cerebral cortex controls voluntary movement and
cognitive functions
Each
side of the cerebral cortex is customarily described as having four lobes,
called the frontal, temporal, occipital, and parietal lobes.
These areas include primary sensory areas, each of which receives and
processes a specific type of sensory information, and association areas, which
integrate the information from various parts of the brain.
The human cerebral
cortex. Each side of the
cerebral cortex is divided
into four lobes, and each
lobe has specialized
functions. Some of the
association areas on the
left side (shown here)
have different functions
than those on the right
side.
Information Processing in the Cerebral Cortex




Most sensory information coming into the cortex is directed via the thalamus
to primary sensory areas within the lobes:
visual information to the occipital lobe
auditory input to the temporal lobe
somatosensory information about touch, pain, pressure, temperature, and
the position of muscles and limbs to the parietal lobe
Information about taste goes to a separate sensory region of the parietal
lobe
Body representations in the
primary motor and primary
somatosensory cortices. In
these cross–sectional maps of
the cortices, the cortical surface
area devoted to each body part
is represented by the relative
size of that part in the cartoons.
(http://www.emc.maricopa.edu/faculty
/farabee/BIOBK/BioBookNERV.html)
Lateralization of Cortical Function



During brain development after birth, competing functions segregate and
displace each other in the cortex of the left and right cerebral hemispheres,
resulting in lateralization of functions.
The left hemisphere becomes more adept at language, math, logical
operations, and the serial processing of sequences of information. It has a
bias for the detailed, speed–optimized activities required for skeletal muscle
control and the processing of fine visual and auditory details.
The right hemisphere is stronger at pattern recognition, face recognition,
spatial relations, nonverbal thinking, emotional processing in general, and
the simultaneous processing of many kinds of information.
The two hemispheres normally work together harmoniously, trading information back
and forth through the fibers of the corpus callosum.
(http://www.kidshealth.org/parent/general/body_
basics/brain_nervous_system.html)
Language and Speech



The systematic mapping of higher cognitive functions to specific brain
areas began in the 19th century when physicians learned that damage to
particular regions of the cortex by injuries, strokes, or tumors can produce
distinctive changes in a person’s behavior.
The French physician Pierre Broca conducted postmortem examinations of
patients who could understand language but could not speak. He
discovered that many of these patients had defects in a small region of the
left frontal lobe.
That region, now known as Broca′s area, is located in front of the part of
the primary motor cortex that controls muscles in the face.
Mapping language
areas in the cerebral
cortex. These PET
images show regions
with different activity
levels in one person′s
brain during four
activities, all related to
speech.
(http://www.emc.maricopa.
edu/faculty/farabee/BIOBK
/BioBookNERV.html)
Emotions




Emotions are the result of a complex interplay of many regions of the brain
Prominent among these regions is the limbic system, a ring of structures
around the brainstem
The limbic system includes three parts of the cerebral cortex—the amygdala,
hippocampus, and olfactory bulb—along with some inner portions of the
cortex′s lobes and sections of the thalamus and hypothalamus
These structures interact with sensory areas of the neocortex and other
higher brain centers, mediating primary emotions that manifest themselves
in behaviors such as laughing and crying
The Limbic System: Structures
of the limbic system form early
in development and provide a
foundation for the higher
cognitive functions that appear
later, during the development of
neocortical areas.
Memory and Learning



We hold information, anticipation, or goals for a time in short–term memory
locations in the frontal lobes and then release them if they become irrelevant
Should we wish to retain knowledge of a face or a phone number, the
mechanisms of long–term memory are activated in a process that requires
the hippocampus.
The transfer of information from short–term to long–term memory is
enhanced by rehearsal (“practice makes perfect”), positive or negative
emotional states mediated by the amygdala, and the association of new data
with data previously learned and stored in long–term memory.
Consciousness



Over the past few decades, however, neuroscientists have begun studying
consciousness using brain–imaging techniques such as fMRI
It is now possible to compare activity in the human brain during different
states of consciousness
These imaging techniques can also be used to compare the conscious and
unconscious processing of sensory information
Concept 48.7 –
CNS injuries and diseases are the focus of much
research


Unlike the PNS, the mammalian CNS cannot fully repair itself when
damaged or assaulted by disease
Surviving neurons in the brain can make new connections and thus
sometimes compensate for damage
Nerve Cell Development




To reach their target cells, axons must elongate from a few micrometers
to a meter or more
An axon does not follow a straight path to its target cells; rather,
molecular signposts along the way direct and redirect the growing axon
in a series of mid–course corrections that result in a meandering, but not
random, elongation.
The responsive region at the leading edge of the growing axon is called
the growth cone
Signal molecules released by cells along the growth route bind to
receptors on the plasma membrane of the growth cone,
triggering a signal transduction pathway
Neural Stem Cells




Mice that live in stimulating environments and run on exercise wheels have
more new neurons in their hippocampus and perform better on learning
tasks than genetically identical caged mice that receive little stimulation
Mature neurons, with their extensive processes and intricate connections
with other cells, clearly are not able to undergo cell division
Therefore, the new brain neurons must have come from stem cells
Stem cells are relatively unspecialized cells that continually divide
Diseases and Disorders of the Nervous System
Schizophrenia - a severe mental disturbance characterized by psychotic
episodes in which patients lose the ability to distinguish reality
Depression - Two broad forms of depressive illness are known: bipolar
disorder and major depression. Bipolar disorder, or manic–depressive
disorder, involves swings of mood from high to low and affects about 1% of
the world′s population. In contrast, people with major depression have a
low mood most of the time; they constitute roughly 5% of the population
Alzheimer′s Disease - a mental deterioration, or dementia, characterized by
confusion, memory loss, and a variety of other symptoms. Its incidence is
age related, rising from about 10% at age 65 to about 35% at age 85
Parkinson′s Disease - a motor disorder characterized by difficulty in
initiating movements, slowness of movement, and rigidity
Activity!
The nervous system is the master controller of the body.
Each
thought, each emotion, each action- all result from the activity of
this system! Through its many parts, the nervous system monitors
conditions both within and outside the body. The nervous system
processes information and decides what the body should do in
response. When the response is needed, the nervous system will
send out electrical signals that will direct the body.
Just like the game of telephone, if one neuron (or student) confuses
the message, any neurons (or students) continuing down the chain
will receive the incorrect message.
To do this activity, you will need:
 to get into a circle with your classmates
 Choose one person to start a message by whispering the message
to the student on her right
 Continue this message until the same person who started the
message hears it from the student on his/her left
Is the message the same?
If the message isn’t the same, what do you think happened? Did one
student confuse the message? What happens in the body, if a neuron
confuses the message?
To further understand the Nervous System check out these links!



http://www.innerbody.com/image/nervov.ht
ml
http://www.argosymedical.com/medical_ani
_sys/nervous.html
http://health.howstuffworks.com/adam200011.htm
Any Questions?