The
Nervous
System
2003-2004Biology
Regents
2003-2004Biology
Regents
http://inside.salve.edu/walsh/cns_pns.jpg
Structure and Function of the Neuron
• Neuron is the scientific name for a Nerve
Cell.
• Neurons consist of 3 basic structures:
 Cyton, or cell body.
 Dendrites- receive messages, impulses, and
send them to the cell body.
 Axons- send messages away from the cell
body.
• Nerve impulses travel from one neuron to
another across synapses, or spaces in
between the cells.
• The “jumping across” the synapse is
facilitated (helped) by chemicals called
Neurotransmitters.
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Parts of the Cell
• Dendrites – Branched
parts of a neuron that
receive impulses from
other neurons.
• Cyton- Contains cytoplasm
and the nucleus. Impulses
pass through here to the
axon.
• Axon- Single long fiber
that carries impulses away
from the cell body.
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• A Neuron
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Myelin coating
signal
direction
 Axon coated with insulation
made of myelin cells

speeds signal
 signal hops from node to node

330 mph vs. 11 mph
myelin coating
Multiple Sclerosis
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 immune system (T cells) attacks myelin coating
 loss of signal
Synapse
Junction between nerve cells
– 1st cell releases chemical to trigger
next cell
– where drugs affect nervous system
synapse
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Propagation of Nerve Impulses
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1
2
1
5
Depolarization and
repolarization. A, RMP results
from an excess of positive ions
on the outer surface of the
plasma membrane. More Na+
ions are on the outside of the
membrane than K+ ions are on
the inside of the membrane. B,
Depolarization of a membrane
occurs when Na+ channels
open, allowing Na+ to move to
an area of lower concentration
(and more negative charge)
inside the cell-reversing the
polarity to an inside-positive
state. C, Repolarization of a
membrane occurs when K+
channels then open, allowing K+
to move to an area of lower
concentration (and more
negative charge) outside the
cell-reversing the polarity back
to an inside-negative state. Each
voltmeter records the changing
membrane potential as a red
line.
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Role of ion channels in maintaining the resting membrane potential (RMP). Some K+ channels
are open in a "resting" membrane, allowing K+ to diffuse down its concentration gradient (out of the
cell) and thus add to the excess of positive ions on the outer surface of the plasma membrane.
Diffusion of Na+ in the opposite direction would counteract this effect but is prevented from doing so
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by closed Na+ channels.
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And the answer to how a nerve impulse
is conducted…
In the nervous system, signals are propagated by action potentials.
An action potential is initiated when the dendrites are stimulated,
and membrane potential decreases. As the signal moves down the
axon of the neuron the voltage-gated sodium channels open,
allowing an influx of positive ions. Next, the voltage-gated
potassium channels open allowing less positive ions to exit the cell,
thus restoring the cell’s negative charge behind the action
potential.
AP Biology
Continued…
The sodium-potassium pump works all the while to keep
the interior of the cell negative by pumping 3 sodium ions
out for every 2 potassium ions it pumps in. When the
action potential reaches the end of the neuron, the
neuron releases neurotransmitters into the synapse.
These tiny particles exert their effect on the target cells in
one of two ways: They can act to open voltage-gated ion
channels by binding directly to the channel, or they can
trigger a second messenger when they bind to a cell with
a receptor-mediated ion channel.
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Types of Neurons
Neurons can also be classified by the direction
that they send information:
･Sensory (or afferent) neurons: send
information from sensory receptors (e.g., in
skin, eyes, nose, tongue, ears) TOWARD the
central nervous system.
･Motor (or efferent) neurons: send information
AWAY from the central nervous system to
muscles or glands.
･Interneurons: send information BETWEEN
sensory neurons and motor neurons. Most
interneurons are located in the central
nervous system.
2003-2004Biology
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Reflexes
 Stimulus- a change
in the environment.
 Response/Reactionhow the body reacts
to a stimulus.
 Reflex Arc- the
pathway that an
impulse follows to
illicit a response to
a stimulus.
2003-2004Biology
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What is a reflex?
• A reflex is defined as an automatic,
involuntary reaction to a stimulus resulting
from a nerve impulse passing over a reflex arc.
– The reflex arc is an impulse conduction route to
and from the central nervous system; it is the
smallest part of the nervous system that can
receive a stimulus and generate a response.
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Types of Reflex Arcs
• Ipsilateral
– Reflex arc whose receptors and effectors are
located on the same side of the body.
• Contralateral
– Reflex arc whose receptors and efectors are
located on opposite sides of the body.
• Intersegmental Contralateral
– Different sensory receptors deliver stimuli at the
same time, and the motor information leaves each
segment on the opposite side of the CNS.
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With your group…
• Think up one scenario that might elicit each
type of reflex arc:
– Ipsilateral
– Contralateral
– Intersegmental contralateral
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Structure of the Nervous System
• Major division - Central
vs. Peripheral
– Central or CNS- brain and
spinal cord
– Peripheral- nerves
connecting CNS to muscles
and organs
Central Nervous System
Peripheral Nervous System
Divisions of the Peripheral Nervous
System
Peripheral Nervous System
Skeletal
(Somatic)
Autonomic
Sympathetic
Parasympathetic
Peripheral Nervous System
• Connects body to brain & spinal cord
• 12 pairs of nerves from your brain (cranial
nerves)
• 31 pairs from your spinal cord (spinal
nerves)
– Bundles of sensory and motor neurons held
together by connective tissue
• Two divisions
– Somatic
– Autonomic
2003-2004Biology
Regents
2003-2004Biology
Regents
http://www.christopherreeve.org/Research/Research.cfm?ID=178&c=21
Divisions of the PNS:
Somatic Nervous System
• Controls voluntary actions
• Made up of the cranial and spinal
nerves that go from the central nervous
system to your skeletal muscles
Autonomic Nervous System
• Controls involuntary actions-those not
under conscious control-such as your
heart rate, breathing, digestion, and
glandular functions
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Somatic System
 Nerves to/from spinal
cord
 control muscle
movements
Sensory
Neuron
 somatosensory
inputs
 Both Voluntary and
reflex movements Skin receptors
 Skeletal Reflexes
 simplest is spinal
reflex arc
Brain
Motor
Neuron
Interneuron
Muscle
Autonomic System
• Two divisions:
– sympathetic
– Parasympatheitic
• Control involuntary functions
– heartbeat
– blood pressure
– respiration
– perspiration
– digestion
• Can be influenced by thought and emotion
Sympathetic
CENTRAL NERVOUS SYSTEM SYMPATHETIC
 “ Fight or flight”
response
 Release adrenaline and
noradrenaline
 Increases heart rate and
blood pressure
 Increases blood flow to
skeletal muscles
 Inhibits digestive
functions
Brain
Dilates pupil
Stimulates salivation
Relaxes bronchi
Spinal
cord
Salivary
glands
Lungs
Accelerates heartbeat
Inhibits activity
Heart
Stomach
Pancreas
Stimulates glucose
Secretion of adrenaline,
nonadrenaline
Relaxes bladder
Sympathetic Stimulates ejaculation
ganglia
in male
Liver
Adrenal
gland
Kidney
Parasympathetic
• “ Rest and digest ”
system
• Calms body to
conserve and
maintain energy
• Lowers heartbeat,
breathing rate,
blood pressure
Sympathetic vs. Parasympathetic
Autonomic nervous system controls physiological arousal
Sympathetic
division (arousing)
Pupils dilate
Parasympathetic
division (calming)
EYES
Pupils contract
Decreases
SALVATION
Increases
Perspires
SKIN
Dries
Increases
RESPERATION
Decreases
Accelerates
HEART
Slows
Inhibits
DIGESTION
Activates
Secrete stress
hormones
ADRENAL
GLANDS
Decrease secretion
of stress hormones
Central Nervous System
AP2003-2004
Biology
Central Nervous System
Brain
• Consists of the Brain and
Spinal Cord
Spinal
Cord
Central Nervous System
• Brain
• Spinal cord
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Protections
1.
2.
3.
4.
5.
6.
Skull and Vertebrae
3 protective layers called meninges
Dura Mater (outer layer): consists of connective tissues,
blood vessels, and nerves.
Arachnoid Layer (middle layer): elastic and weblike
Pia Mater (inner layer): contains nerves and blood vessels.
Cerebrospinal fluid
–
–
–
–
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a clear watery liquid
separates the middle and inner layers
Acts as shock absorber
exchange of nutrients between blood and nervous system
The Brain
•
•
•
•
Coordinates body activities
Made up of approximately 100 billion neurons
Uses 20% of bodies oxygen and energy
Divided into three major parts– the Cerebrum
– the Cerebellum
– the Brain Stem (Medulla Oblongata, Pons)
2003-2004Biology
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Brain has 2 Hemispheres
• Left & Right sides are
separate
• Corpus Callosum : major
pathway between
hemispheres
• Some functions are
‘lateralized’
– language on left
– math, music on right
• Lateralization is never
100%
Corpus Callosum
Right
Hemisphere
Left
Hemisphere
Each hemisphere is
divided into 4 lobes
Frontal
Parietal
Occipital
Temporal
Sensory Information sent to
opposite hemisphere
• Principle is Contralateral
Organization
• Sensory data crosses over
in pathways leading to the
cortex
• Visual Crossover
Left visual Right visual
field
field
Optic
nerves
– left visual field to right hemisphere
– right field to left
• Other senses similar
Left Visual Corpus Right Visual
Cortex Callosum
Cortex
Contralateral Motor Control
 Movements
controled by motor
area
 Right hemisphere
controls left side of
body
 Left hemisphere
controls right side
 Motor nerves cross
sides in spinal cord
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Motor Cortex
Somatosensory Cortex
Corpus Callosum
 Major ( but not only)
Medial surface of right hemisphere
pathway between sides
 Connects comparable
structures on each side
 Permits data received on
one side to be processed
in both hemispheres
 Aids motor coordination
Corpus Callosum
of left and right side
Corpus Callosum
• What happens when the corpus callosum is
cut?
• Sensory inputs are still crossed
• Motor outputs are still crossed
• Hemispheres can’t exchange data
The ‘Split Brain’ studies
• Surgery for epilepsy :
cut the corpus
callosum
• Roger Sperry, 1960’s
• Special apparatus
– picture input to just one side of
brain
– screen blocks objects on table
from view
Verbal
left
hemisphere
Nonverbal
right
hemisphere
The ‘Split Brain’ studies
 Picture to right brain
“What
“Using
“What
yourdid
did
left hand,
you
see?”
Pick up
you
what
see?”
you saw.”
can’t name the object
left hand can identify
by touch
• Picture to left brain
– can name the object
– left hand cannot identify by
touch
??
I saw an
Verbal
Nonverbal
Verbal
apple.
leftleft
right
hemisphere
hemisphere hemisphere
Localization of Function
Frontal
Parietal
Occipital
Temporal
Occipital Lobe
• Input from Optic nerve
• Contains primary visual
cortex
– most is on surface
inside central fissure
• Outputs to parietal and
temporal lobes
Occipital
Lobe
Visual
Lobe
Temporal Lobe
 Contains primary
auditory cortex
 Inputs are auditory,
visual patterns
 speech recognition
 face recognition
 word recognition
 memory formation
 Outputs to limbic
System, basal Ganglia,
and brainstem
Auditory
Cortex
Temporal
Lobe
Parietal Lobe
 Receives inputs from
multiple senses
 contains primary
somatosensory cortex
 borders visual &
auditory cortex
 Outputs to Frontal lobe
 hand-eye coordination
 eye movements
 attention
Somatosensory
Parietal
Cortex
Lobe
Frontal Lobe
 Contains primary motor
cortex
 No direct sensory input
 Important planning and
sequencing areas
 Broca’s area for speech
 Prefrontal area for
working memory
Frontal
Lobe
Working
Broca’s
Memory
Area
Motor
Cortex
Parts
of the
Brain
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Functions of Different Parts of the Brain
• Brainstem
– Integration of respiratory
and cardiovascular
function
• Cerebellum
– Coordinates Movement
• Cerebral Hemispheres
– Skilled movement,
reason, learning,
memory
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• Thalamus
– Control of skeletalmuscle coordination
– Awareness
• Hypothalamus
– Hormones
– Balance
– Emotions
– Thermoregulation
• Limbic System
– Emotions
– Learning
Cerebrum
•
•
•
•
•
Largest part of the brain
Thinking
Memory is stored
Movements are controlled
Impulses from the senses are interpreted.
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Cerebrum specialization
• Regions specialized for different functions
• Lobes
frontal
– frontal
parietal
• speech,
control of emotions
– temporal
• smell, hearing
– occipital
• vision
– parietal
• speech, taste
reading
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temporal
occipital
Gray Matter vs. White Matter
• Gray Matter – Absence of myelin in
masses of neurons accounts for the gray
matter of the brain – Cerebral Cortex
• White Matter - Myelinated neurons gives
neurons a white appearance – inner
layer of cerebrum
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Cerebellum
• Responsible for the
coordination of
muscles and is the
center of balance
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Medulla
• Center of heart beat,
respiration, and other
involuntary actions
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Other Structures inside the Brain
• Thalamus – receives messages from
sensory receptors; relays information to
proper regions of cerebrum
• Hypothalamus - Regulates hunger,
thirst, fatigue, anger, etc…
– Control of pituitary for endocrine function
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Section 35-3
Cerebrum
Thalamus
Pineal
gland
Hypothalamus
Cerebellum
Pituitary gland
Pons
Medulla oblongata
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Spinal cord
The Spinal Cord
• Extension of the brain stem
• Bundles of neurons that carry impulses
from all parts of the body to the brain and
from the brain to all parts of your body
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The
Peripheral
Nervous
System
Your brain
and spinal
Somatic
cord are
and
connected
Autonomic
to the rest
Systems
of your
The
body by
peripheral
the
nervous
peripheral
system
has
nervous
two
major
system.
divisions.
The PNS
is made up
somatic
of 12 pairs
system
of nerves
controls
from your
voluntary
brain It
actions.
called
is
made up
cranial
of
the
nerves, and
cranial
and 31
spinal
pairs from
nerves
that
your
go
from
spinal
the
cord called
central
spinal
nervous
nerves. to
system
Spinal
your
nerves are
skeletal
made up of
muscles.
bundles of
The
sensory
autonomic
and motor
system
neurons
controls
bound
involuntary
together by
actionsconnective
those
not
tissue. For
under
this
conscious
Research
reason,
controla
Visit the
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Glencoe
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Science
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rate,
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to
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and
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functions.
brain at
about
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These
same
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nervous
time.
divisions,
Some
system.
nerves
along
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Make
a
contain
the
central
brochure
only
nervous
outlining
sensory
system,
recentup
neurons,
make
medical
and
your
some
advances.
contain
body's
only motor
nervous
neurons,
system.
but most
nerves
contain
both types
of neurons.
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Cranial and Facial Nerves
• How the sensory
input from the world
around us reaches
our brain…
• And how our brain
sends information to
our face and sensory
organs…
Cranial
Nerves
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