Nervous System
Chapter 9
Introduction to the NS
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Neurons – nerve cells
Nerve impulses – electrochemical
changes which transmit information
Neurons consist of:
• Cell body – rounded area
• Dendrites – extensions that receive nerve
impulses
• Axons – extensions that send nerve impulses
(usually has only one)
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Nerves – bundles of axons
Neuroglial cells – provide physical
support, insulation, and nutrients for
neurons
Groups
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Central nervous system – consists
of brain and spinal cord
Peripheral nervous system –
consists of nerves that connect the
cns to the other body parts
Functions:
• Sensory
• Integrative
• Motor
Sensory Function
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Sensory receptors are found at the
ends of peripheral neurons gather
info. by detecting changes inside and
outside the body.
Monitor such things as light, sound,
temperature, oxygen level
Integrative Function
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Nerve impulses from sensory
receptors are transmitted to the cns
Signals are brought together,
creating sensations, adding to
memory, or helping produce
thoughts that translate sensations
into perceptions
Motor Function
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Impulses from cns to responsive
structures called effectors
• Examples: muscles that contract, glands
that secrete
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Somatic nervous system – motor
functions that are consciously
controlled
Autonomic nervous system –
motor functions that are involuntary
Dimethylmercury Poisoning
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Clings to brain
neurons,
destroying them
Neuroglial cells
overgrow
Neuroglial Cells
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Microglial – scattered throughout cns; support
neurons and phagocytize bacterial cells and
cellular debris
Oligodendrocytes – align along nerve fibers;
provide insulating layers of myelin around axons
within the cns
Astrocytes – found between neurons and blood
vessels; provide structural support; help regulate
conc. of nutrients and ions within the tissue;
form scar tissue
Ependymal cells – form an epithelia-like
membrane that covers specialized brain parts;
forms inner linings
Schwann cells – form a myelin sheath around
axons of the pns
Gliomas
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Fast-growing brain tumors
Consist of rapidly dividing neuroglia
Neurons
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Cell body
•
•
•
•
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Granular cytoplasm
Cell membrane
Organelles (mitochondria, lysosomes, neurofibrils)
Nissl bodies (similar to rough ER)
Dendrites
• Short and highly branched
• Main receptive surfaces
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Axons
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Conducts nerve impulses away from the cell body
Usually a single structure
Surrounded by Schwann cells to form a myelin sheath
Spaces in between are called nodes of Ranvier
Neural stem cells found in the hippocampus
Structural Classification of Neurons
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Multipolar – one axon; many
dendrites; lie within the brain or
spinal cord
Bipolar – one axon; one dendrite;
lie within eye, nose, and ears
Unipolar – one axon that branches
into two; one assoc. with peripheral
body part and the other enters the
brain or spinal cord
Functional Classification of
Neurons
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Sensory neurons – carry nerve
impulses from peripheral body parts
into the brain or spinal cord
Interneurons – transmit impulses
from one part of the brain or spinal
cord to another
Motor neurons – carry nerve
impulses out of the brain or spinal
cord to effectors
Cell Membrane Potential
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Surface of a cell membrane is usually
electrically charged or polarized with
respect to the inside
Polarization due to an unequal
distribution of positive and negative
ions between sides of the membrane
Distribution of Ions
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Greater conc. of Na+ outside cell
Greater conc. of K+ inside cell
Resting Potential of Neuron
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Resting membrane
more permeable to K+
than to Na+
K+ leaves faster than
Na+ enters
There exists a
potential difference of
charges in a resting
nerve cell between the
region inside the
membrane and
outside the membrane
Potential Changes
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Depolarization – resting potential
decrease (inside becomes less negative
than outside as Na ions leave)
This produces a local current
If additional stimulation arrives before the
effect of the previous stimulation
subsides, the change in potential is still
greater (summation)
Threshold potential is reached as a
result of summated potentials
Action Potential
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At the threshold potential,
permeability suddenly changes at the
trigger zone (portion of axon where
impulse begins) allowing Na+ in
Cell becomes depolarized and
repolarized as K+ enter once more
Action potential – rapid sequence
of depolarization and repolarization
Agh!
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Local anesthetic drugs
decrease membrane
permeability to
sodium ions
It interrupts impulses
from passing through
the affected region
and reaching the brain
Prevents the
sensations of touch
and pain
Impulse Conduction
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Myelinated sheath prevents almost all ion
flow through the membrane it encloses
Nodes of Ranvier between Schwann cells
interrupt the sheath
Action potentials occur at these nodes
Speed of nerve impulse conduction is
proportional to the diameter of the axon
(greater diameter=faster impulse)
All-Or-None Response
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If a neuron responds at all, it
responds completely
Conduction occurs when a stimulus
of threshold intensity or above is
applied
All impulses carried on that axon are
of the same strength
Greater intensity=more impulses per
second
Events leading to the conduction of
a nerve impulse
1.
2.
3.
4.
5.
Neuron membrane maintains
resting potential
Threshold stimulus is received
Sodium channels in the trigger zone
of the neuron open
Sodium ions diffuse inward,
depolarizing the membrane
Potassium channels in the
membrane open
6.
7.
8.
Potassium ions diffuse outward,
repolarizing the membrane
The resulting action potential
causes a local bioelectric current
that stimulates adjacent portions of
the membrane
A wave of action potentials travels
the length of the axon as a nerve
impulse
Flipbook
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Create a flipbook illustrating and
describing the events leading to the
conduction of a nerve impulse
Must be labeled, colored, and include
a short description
The Synapse
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Nerve impulses travel along nerve
pathways
The junction between any two
communicating neurons is called a
synapse
Types of Nerves
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Afferent fibers bring sensory
information into the CNS
Efferent fibers carry impulses from
the CNS to effectors (muscles or
glands)
Reflex Arc
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Type of nerve pathway
Reflexes are automatic subconscious
responses to stimuli within or outside the
body
Help maintain homeostasis by controlling
heart rate, breathing rate, blood pressure,
and digestion
Knee-jerk reflex helps maintain upright
posture
Withdrawal reflex occurs when a person
unexpectedly touches a body part to
something painful
Meninges
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Membranes that lie between bone
and soft tissues of CNS
Dura mater
• outermost layer
• composed of tough, white, fibrous
connective tissue
• contains many blood vessels and nerves
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Arachnoid mater
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•
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thin, weblike membrane
Lacks blood vessels
Lies between the dura and pia maters
Spreads over the brain and spinal cord
Pia mater
• Very thin
• Contains blood vessels that nourish underlying
cells of the brain and spinal cord
• Hugs the surfaces of organs
Spinal Cord
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Slender nerve column that passes
downward from the brain into the
vertebral column
Consists of 31 segments, each of
which gives rise to a pair of spinal
nerves
Conducts nerve impulses
Serves as a center for spinal reflexes
Brain
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Composed of about
100 billion
multipolar neurons
Weighs about 3.5
lbs.
If all the cells were
laid end-to-end,
they would cover
600 miles
Cerebrum
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Consists of left and right
hemispheres
Deep bridge of nerve fibers called
the corpus callosum connects the
cerebral hemispheres
A layer of dura mater separates
them
Gyri – ridges found on surface
Sulcus – shallow groove
Fissure – deep groove
Lobes of Cerebrum
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Frontal – forms anterior portion of
each hemisphere
Parietal – posterior to the frontal
lobe
Temporal – lies below frontal and
parietal lobes
Occipital – forms posterior portion
of each hemisphere
Cerebrum cont.
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Cerebral cortex – outermost
portion of the cerebrum composed of
a thin layer of gray matter
Just beneath the cerebral cortex is a
mass of white matter that makes up
the bulk of the cerebrum
Provides higher brain functions
Stores information that comprises
memory and utilizes it to reason
Functions of the Cerebrum
1.
2.
3.
4.
5.
6.
Motor area for voluntary muscle
control
Motor speech area
Auditory area
Cutaneous sensory area
General interpretative area
Visual area
Hemisphere Dominance
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Both hemispheres participate in basic
functions
In most persons, however, one side of the
cerebrum is the dominant hemisphere,
controlling the ability to use and
understand language
Left hemisphere is dominant in more than
90% of the population
Non-dominant hemisphere controls
emotional and intuitive thinking
Cerebrospinal Fluid
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Secreted by choroid plexuses
found in the pia mater
Completely surrounds the brain and
spinal cord
Organs float
Support and protection is provided
by absorption of forces
Diencephalon
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Located between the cerebral hemispheres
and above the midbrain
Composed largely of gray matter
Thalamus within the diencephalon relays
sensory impulses from other parts of the
nervous system to the cerebral cortex
Hypothalamus lies below the thalamus
and maintains homeostasis by regulating
a variety of visceral activities and by
linking the nervous and endocrine systems
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Brainstem – bundle of nervous tissue
that connects the cerebrum to the spinal
cord
• Midbrain – contains bundles of myelinated
axons that join lower parts of the brainstem
and spinal cord with higher parts of the brain
• Pons – rounded bulge on the underside of the
brainstem; relays impulses to and from the
medulla oblongata
• Medulla oblongata – relays impulses,
controls vital visceral activities, and reflexes
Cerebellum
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Large mass of tissue located below the
occipital lobes of the cerebrum and
posterior to the pons and medulla
oblongata
Consists of two lateral hemispheres
Reflex center for integrating sensory
information concerning the position of
body parts and for coordinating complex
skeletal muscle movements
Helps maintain posture
Peripheral Nervous System (PNS)
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Consists of nerves that branch out
from the CNS and connect it to other
body parts
Subdivided into the somatic and
autonomic nervous systems
Somatic Nervous System
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Cranial and spinal nerves
Connect the CNS to the skin and
skeletal muscles
Oversees conscious activities
Cranial Nerves
Autonomic Nervous System
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Functions independently and
continuously without conscious effort
Regulates the actions of smooth
muscles, cardiac muscles, and glands
Responds to emotional stress and
prepares the body to meet the
demands of strenuous physical
activity
Pictionary!!!
Choose a card from the deck. Draw a
picture on the board for your team
members to guess before time runs
out. You will have one minute to
complete your drawing and have
your team guess before the chance
goes to the other team. You may
not use hand motions or any sound
effects.
Disorders/Diseases
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Attention Deficit-Hyperactivity
Disorder
• affects 3-5 percent of all American
children
• interferes with a person's ability to stay
on a task and to exercise ageappropriate inhibition
• causes
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Alzheimer's disease
• age-related, non-reversible brain disorder that
develops over a period of years
• Symptoms
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behavior and personality changes
decline in cognitive abilities such as decision-making
and language skills
problems recognizing family and friends
ultimately leads to a severe loss of mental function
and death
• Cause
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Plaques caused by protein buildup
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Dementia
• impaired intellectual functioning that interferes
with normal activities and relationships
• lose their ability to solve problems and
maintain emotional control, and they may
experience personality changes and behavioral
problems, such as agitation, delusions, and
hallucinations
• Caused by Alzheimer’s disease, vascular
dementia, Lewy body dementia,
frontotemporal dementia, Huntington’s
disease, and Creutzfeldt-Jakob disease
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Coma
• profound or deep state of unconsciousness
• may occur as a complication of an underlying
illness, or as a result of injuries, such as head
trauma
• Although individuals in a persistent vegetative
state may appear somewhat normal, they do
not speak and they are unable to respond to
commands
• rarely lasts more than 2 to 4 weeks
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Meningitis and Encephalitis
• inflammatory diseases of the
membranes that surround the brain and
spinal cord and are caused by bacterial
or viral infections
• sudden fever, headache, vomiting,
heightened sensitivity to light, stiff neck
and back, confusion and impaired
judgment, drowsiness, weak muscles, a
clumsy and unsteady gait, and
irritability
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Epilepsy
• clusters of neurons in the brain
sometimes signal abnormally
• strange sensations, emotions, and
behavior or sometimes convulsions,
muscle spasms, and loss of
consciousness
• Illness, brain damage or abnormal brain
development can lead to seizures
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Parkinson's Disease
• result of the loss of dopamine-producing
brain cells
• tremor, or trembling in hands, arms,
legs, jaw, and face; rigidity, or stiffness
of the limbs and trunk; bradykinesia, or
slowness of movement; and postural
instability, or impaired balance and
coordination