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Nervous
system
Ch. 9
The basics
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Divide in 2 areas
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Central Nervous system
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Brain & spinal cord
Peripheral Nervous system
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Motor & sensory nerves outside the spinal cord.
Nervous Tissue
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Cell Types
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Neuroglial cells( glial cells)
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-non-conducting
-support neurons
Produce myelin “insulation”
act as phagocytes
out number neurons 10:1
Aid in circulation of CSF
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Types
 Astrocyte: framework for brain/connects vessles
 Ependymal cells: circulate CSF
 Microglial: wandering cells/phagocytosis
 Oligodendrocyte: CNS myelin sheath
 Schwann cells: PNS myelin sheath
Structures
Neurons
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functional & Structural units of the N.S.
1. Cell Body aka: Soma
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Contains:
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Cytoplasm
Cell membrane
nucleus
neurofibrils ( thin threads extend into axon)
nissl bodies “spots”
2. Dendrites
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3. Axon
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Highly branched
Receives & conducts impulses towards cell body
single uniform cylindrical fiber
connected at axonal hillock to body
carries impulse away from body
end has a synaptic Knob that communicates to other
nerves/tissues across the synaptic cleft.
axons
Axons may be:
1. Myelinated
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Myelin Sheath gives protective covering
made of _schwann cells
increases speed of nerve impulse
impulse jumps gaps: nodes of Ranvier
“White matter”
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brain
exterior spinal cord
PNS neurons
2.Unmylenated
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“grey matter”
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brain & spinal cord
Structure cont.
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Neurilemma
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-thin outer layer of
Myelin sheath
Portion of Schwann
cell that has most of
the cytoplasm& nuclei
-role in repair
-most brain & spinal
cord neurons lack this
Structural Classification of Neurons
1. Unipolar Neurons
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Single process extending from body
2 branches function as a single axon
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peripheral process-dendrites
central process- enters CNS
may form groups called ganglia located
outside the CNS
Structural Classification of Neurons
2. Bipolar Neuron
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cell body has 2 processes
1 axon & 1 dendrite
found in specialized parts of ears, nose &
eyes
Structural Classification of Neurons
3. Multipolar Neurons
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cell body has many processes
(dendrites)
only 1 axon
most common in brain & spinal
cord
Functional Classification of Neurons
Sensory Neurons aka:
afferent
1.
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transmit impulses from receptors
toward CNS
Most are unipolar
Peripheral Nervous system (PNS)
2. Interneurons Aka:association
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links neurons to direct incoming
sensory information
most abundant
located in brain & spinal cord ( CNS)
multipolar
Functional Classification of Neurons
3. Motor Neurons Aka: effectors
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transmit impulses away from the
CNS to effector
multipolar
speed up or slow down muscle
action
voluntary or involuntary control
PNS
How they work together
Sensory neuron
CNS
Sensory
receptor
signal
Interneuron
PNS
In spinal
cord
Motor neuron
Muscle
“effector”
How they work together
How it works

http://highered.mcgrawhill.com/sites/0072437316/student_view0/
chapter45/animations.html
Nerve Impulse & Transmission
1. Nerve transmission
a.
b.
Slower than electrical current ( .5-120 m/s vs.
3x105 km/s)
Self propagating electrochemical current
Nerve Impulse & Transmission
2. Cell membrane (Axon)
a.
b.
c.
d.
Electrically charged –polarized
Polarization due to unequal distribution of
+/- ions across membrane
Inside more negatively charged
Causes electrical gradient or potential
difference
Nerve Impulse & Transmission
3. Ions
a. Intracellular
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Phosphates & sulfates (anions or – ions)
Potassium( K+) cation
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membrane very permeable to K+
K+ diffuses out of cell
b. extracellular
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Sodium ( Na+)
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membrane slightly permeable to Na+
diffuses into cell
c. ion pumps (Na-K)
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move ions in and out of cell
Nerve Impulse & Transmission
4. Resting or membrane potential
a.
b.
c.
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Nerve that is resting-is not being stimulated
K+ leaves faster than Na+ enters causing
slight + charge outside of cell.
ATP used to actively transport + ions back
into cell to maintain concentration gradient.
http://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swf
Nerve Impulse & Transmission
5. Action Potential or Nerve Impulse
a. Cell membrane becomes depolarized by
stimulus
b. Stimulus= depolarization
c. stimulus must reach threshold to create
impulse
d. axons only part capable of A.P.
e. electrical current flows short distance
triggering adjacent membrane to continue
impulse
Nerve Impulse & Transmission
6. How it works
a.
b.
c.
d.
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Threshold stimulus received by neuron
Na+ flows inward = depolarizing membrane
Causing K+= to flow outward= repolarizing
membrane
Chain reaction continues down axon
carrying impulse
http://outreach.mcb.harvard.edu/animations/actionpotential.swf
Nerve Impulse & Transmission
7. Refractory period
a.
b.
After impulse when threshold stimulus
cannot trigger another impulse: 1/2500
second= Absolute refractory
membrane is returning to resting
potential= relative refractory
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can be stimulated with high intensity stimulus
c. limits # of A.P. that can be
generated=usually 100 impulses/s
Nerve Impulse & Transmission
8. All-or – None
a. Neuron responds completely
b. Stronger impulse= more impulses /second not a
stronger impulse
Nerve Impulse & Transmission
9. Speed of impulse
a. Unmyelinated axons
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Impulse carried through entire membrane surface
b. Myelinated axons
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A.P only occurs at Nodes
Appears to jump= faster impulse
Saltitory conduction
c. diameter of axon
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diameter=
speed
thick myelinated skeletal motor nerve= 120m/s
thin umyelinated skin sensory nerve= .5 m/s
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http://www.blackwellpublishing.com/matthews/actionp.html
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Mylenation and diameter determine speed of conduction
Nerve Impulse & Transmission
10.The Synapse
a. Ca+ enters Presynaptic neuron causing it to
releases neurotransmitter into the synaptic cleft
b. Neurotransmitter will either excite or inhibit the
Postsynaptic neuron or effector
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http://www.bishopstopford.com/faculties/science/arthur/synapse.swf

http://bcs.whfreeman.com/thelifewire/content/chp44/4403s.swf
Reflexes
simple automatic responses to stimuli from inside or
outside the body (involve CNS & PNS)
simplest type of nerve pathway
carry out involuntary responses
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breathing
heart rate
blood pressure
digestion
swallowing
sneezing
blinking
coughing
vomiting……
maintain homeostasis
Types
Monosynaptic = 1 synapse
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Simple or stretch reflex
1 sensory + 1 motor neuron involved
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Patellar reflex: helps with upright posture
types
ouch
Withdrawal reflex
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protective reflex involving 3 neurons
sensory, interneuron, & motor
neurons
Interneuron initiates withdrawal then
sends impulse to brain for
interpretation
PNS
CNS
Figure 09.20
Reflex animation
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http://www.sumanasinc.com/webcontent/
animations/content/reflexarcs2.html
http://bcs.whfreeman.com/thelifewire/con
tent/chp46/46020.html
Menengies (membranes)
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3 Layers that cover the CNS
protection & contain
Cerebrospinal fluid (CSF)
Dura mater: outer most layer
- Tough, white, dense
connective tissue
- Many blood vessels &
nerves
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Arachnoid mater: Thin web like
membrane
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Lacks blood vessels
Subarachnoid space: contain CSF
Pia Mater: very thin & has many
nerves/vessels
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Nourish CNS
Attached to surface of brain & cord
Figure 09.21
Cerebrospinal fluid
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Made in the ventricles (cavities)
of brain
500mL secreted daily, only
140mL in NS, continually
reabsorbed into blood
clear, somewhat viscid
nourish & protect CNS
maintain stable ionic
concentrations
sensory feedback about internal
environment.
Spinal cord
Spinal
Cord
Structure
 Part of CNS
 foramen magnum to L1&L2
 31 pair of spinal nerves
 ends at cauda equina (horses tail) &
filum terminale (coccyx)
 Cervical enlargement: nerves to arms
 Lumbar enlargement: nerves to legs
Spinal cord
Function:
1. Conducting nerve impulses
2. Center for spinal reflexes
1. Somatic reflexes: skeletal muscle
Patellar & Withdrawal
2.
Visceral reflexes:
stimulate or inhibit visceral
organs
breathing, heart rate…
Grey matter: unmyelinated
fibers ( H)
Posterior horns: sensory
Anterior horns: motor
White matter: myelinated
fibers
Anterior, posterior & lateral
form nerve tracts
Grey Commissure:
connects horns at center of
cord
Central canal: within the
grey commissure &
contains CSF
Two tracts:
Ascending
tracts: sensory
information to
brain
Descending
tracts: motor
impulses to
muscle/glands
The
brain
Complete lab 27 &
29
Brain Structure
Cerebrum
 largest part
 2 hemispheres
 connected by corpus
callosum & seperated by
falx cerebri
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convolutions-gyri
Shallow = sulcus
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divide brain into 4 Lobes
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Frontal Lobe: voluntary skeletal muscle, higher
intellectual processes, concentration
Broca’s Area: motor speech area
Parietal lobe: Temp. touch, pressure pain of skin,
understand speech, word expression of thought &
feelings
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Temporal Lobe: hearing, interpretation of sensory info, music
patterns
Occipital lobe: vision, combine visual and sensory information
Deep =fissure
 -Longitudinal Fissure = Left & right sides
 -Transverse Fissure = cerebrum & cerebellum
Association Areas
Association areas
Hemisphere Dominance
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90 % population Left side
Dominant( Right handed)
language related activities:
reading, writing, verbal ,
analytical & computations
Non-dominant: non verbal
functions, spacial orientation,
music interpretation, visual,
emotional and intuition
Corpus callosum allows Hemi’s
to communicate/coordinate
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Diencephalon:
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located between cerebral hemi’s & above midbrain
Contains
 Thalamus & hypothalamus
 Attaches Pineal & pituitary glands
 Mammilary body
 Optic chiasma/tracts
 infandibulum
Brain Stem
Connects brain to
cord
Mostly Grey matter
3 parts
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Midbrain, pons
medulla Oblongata
Mid Brain ( reflex center)
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Between diencephalon
& pons
Visual center: moves
eyes when head turns
Auditory center: moves
head to hear sound
Red nucleus:
communicates w/
cerebellum & cord to
coordinate posture
Pons( relay station)
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-rounded bulge underside
of brain stem-bridges
cerebrum & cerebellum
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-relay impulses from
medulla/cerebrum
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-relay sensory impulses to
higher brain centers
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-assist in regulation,
depth & rate of breathing
Medulla Oblongata (vital reflexes)
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-enlargement of spinal cord at foramen
Magnum
-All ascending & descending tracts pass
through
-injury usually Fatal
Visceral reflex center
 Cardiac center: Heart Rate
 Vasomotor Canter: Blood Pressure
 Respiratory center: rate, rhythm & depth
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-non-vital reflexes
-Coughing
- vomiting
-Swallowing
- Sneezing
Cerebellum“ hind Brain”
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Mostly white matter w/ grey
matter cortex
Tree like structure posterior to
brain stem, inferior to
Cerebrum
Proprioception Center
-position of body, actual & desired
- coordination of skeletal
muscle pattern
Closed brain injury
Figure 09.27b
Figure 09.34
Cranial Nerves
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Considered part of Peripheral nervous system
12 pair
Name & Roman Numeral
Originate form Brain stem
Motor, sensory & mixed
Cranial Nerves
Cranial nerves
Nerve
function
S
Sense of smell
II. Optic
S
Sense of sight
III. Oculomotor
B
Movement of eye (pupil),
IV. Trochlear
B
Eye movement
V. Trigeminal
B
Face sensation, chewing
VI. Abducens
B
Eye movement
VII. Facial
B
Taste, facial expression, tear/salivary glands
VIII. Vestibulocochlear
S
Hearing/equilibrium
IX. Glossopharyngeal
B
Taste, pharynx, throat sensation
X. Vagus
B
Speech, swallowing, HR, peristalsis & visceral
sensation
XI. Accessory
M
Speech, swallowing, head/shoulder movement
XII> Hypoglossal
M
Tongue movement
I.
Olfactory
receptor type
(auditory)
S= sensory, M= motor B= both
mnemonics
Nerve
nerve name
nerve type
I.Olfactory
on
some
II. Optic
old
say
III. Oculomotor
olympus’
betroth
IV. Trochlear
towering
beauty
V. Trigeminal
top
but
VI. Abducens
a
big
VII. Facial
fin
brother
VIII. Vestibulocochlear
and
says
(auditory)
IX. Glossopharyngeal
german
better
X. Vagus
viewed
bet
XI. Accessory
a
marry
hop
money
XII. Hypoglossal
Cranial nerve injury
Spinal Nerves
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31 pair, all mixed
Anterior (motor) & Posterior ( sensory)
roots join outside spinal column.
Named for location
8 cervical, 12 thoracic, 5 lumbar, 5 sacral
& 1 coccygeal.
Peripheral Nervous System
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Consists of cranial & spinal nerves
2 major divisions
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Somatic (voluntary) system
Autonomic( involuntary) system
PNS
Somatic
autonomic
Somatic N.S.
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Receptors
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Sensory nerves
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Afferent fibers
Take messages to CNS/brain
Motor Nerves
Efferent fibers
 Impulses to muscles/glands
( effectors)
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Mixed nerves
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Contain both motor & sensory
fibers
Autonomic NS
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Controls homeostasis
Divided into 2 divisions
Works as antagonistic system
autonomic
sympathetic
parasympathetic
Sympathetic division
AKA thoracolumbar division
 Activates adrenaline responses “
fight or flight”
( pain/fear/anger)
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Pupil dilation
Heart rate
circulation to limbs
respiration…
Parasympathetic division
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AKA Craniosacral division
Deactivates sympathetic
responses
Returns system to “normal”
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Pupil constriction
Decrease, HR, respiration….
Nervous system
CNS
Brain
Spinal cord
somatic
“voluntary”
Cranial & spinal nerves
Motor, sensory , both
Sympathetic
PNS
Peripheral nerves
Cranial & spinal nerves
autonomic
“involuntary”
Maintains homeostasis
Antagonist system
parasympathetic
“speeds up”
“slows down”=parachute
Fight or flight
Deactivates sympathetic
division
Pain/fear/anger
Thoracolumbar division
Returns system to “normal”
Craniosacral division