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The Nervous System
3 Main Functions
• 1.) Monitors internal
and external changes
(stimuli). The gathered
information is called
sensory input
• 2.) Processes and
Interprets sensory input
and decides what to do
(integration)
• 3.) Effects a response
by activating muscles or
glands (effectors) this is
called motor output.
Vocabulary
• Stimuli: An external or internal change.
• Sensory Input: Information about stimuli that is
gathered by the nervous system.
• Integration: Sensory input is collected and
evaluated or interpreted by the nervous system
• CNS: Central Nervous System, command
center consisting of the brain and spinal cord.
• PNS: Peripheral Nervous System: Cranial and
Spinal Nerves extending from the brain and
spinal cord that carry impulses.
Divisions of the Nervous System
Central Nervous System
• Brain and Spinal
Cord
Peripheral Nervous System
• Cranial Nerves and Spinal Nerves
Afferent
or
Efferent
(Sensory)
(Motor)
• Efferent
Somatic
or
Autonomic
(Voluntary)
(Involuntary)
Skeletal Muscle
• Autonomic
Symapthetic or Parasympathetic
Fight / Flight
Rest / Digestion
Cardiac, Smooth, Glands
Nerve Tissue
Location - Brain Spinal cord, peripheral neurons
Characteristics - Neuron; cell body and tubular
processes filled with cytoplasm
Function- Sensitivity and Conduction of nerve
impulses
Two types of cells; neurons and neuroglial cells
1. Neurons
• Dendrites bring information to
the cell body and axons take
information away from the cell
body.
• Neurons communicate with
each other through an
electrochemical process.
• Neurons contain some
specialized structures (for
example, synapses) and
chemicals (for example,
neurotransmitters).
Neuron Slides
• Neurons in the
hippocampus
2. Neuroglial Cells
• About 100 billion neurons in the brain,
about 10 to 50 times that many glial
cells in the brain.
• Glia cells DO NOT carry nerve
impulses (without glia, the neurons
would not work)
• Function; 1) clean up brain "debris"; 2)
transport nutrients to neurons; 3) hold
neurons in place; 4) digest parts of
dead neurons; 5) regulate content of
extracellular space 6) insulate and
support neurons
Types of Cells
Draw Example
Name of Cell
Astrocyte
Microglia
Ependymal
Oligodenrocyte
Job
Abundant star-shaped cells that
cling to neurons, anchoring them to
a nutrient supply and act as a
barrier against harmful substances
in the blood
Spiderlike phagocytes that get rid of
debris like dead cells and bacteria
Cells that line central cavities and
have cilia that move cerebrospinal
fluid and form a protective cushion
around the CNS.
Glia that wrap their flat extensions
around nerve fibers producing a fatty
insulating substance called myelin
sheaths
Neurons
• Cell body
– Nucleus
– Large nucleolus
• Processes outside the
cell body
– Dendrites—conduct
impulses toward the
cell body
– Axons—conduct
impulses away from
the cell body toward
other neurons
Axons
• End in axonal
terminals
• Terminals contain
vesicles with
neurotransmitters
• Axonal terminals are
separated from the
next neuron by a gap
Axons
• Axon terminals with
neurotransmitter
chemicals are near,
but not touching the
dendrite of another
neuron
– Synaptic cleft - gap
between adjacent
neurons
– Synapse – a
functional junction
between nerves
Myelin Sheath
• Myelin sheath—
whitish, fatty material
covering axons
• Schwann cells—
produce myelin
sheaths in jelly roll–like
fashion
• Nodes of Ranvier—
gaps in myelin sheath
along the axon
• Insulation, speeds up
impulses.
MS – Multiple Sclerosis
• In MS the myelin
sheaths become
hardened
• The current does not
flow as well and
impulses are
disrupted
• Loss of muscle
control, speech
• Autoimmune: protein
in sheath is attacked
MS Treatments
• Corticosteroids. The
• Bee Venom is used by
most common treatment
people with many
different autoimmune
for multiple sclerosis,
disorders, including MS,
corticosteroids reduce
rheumatoid arthritis and
the inflammation
lupus.
• Beta interferons slow
• The theory is that
the rate at which multiple because the stings
sclerosis symptoms
produce inflammation, the
body mounts an antiworsen
inflammatory response
Neuron Terms
describe or tell location
• White Matter: Myelinated • Nuclei: Clusters of
regions of CNS
cell bodies found in
the CNS (well
• Gray Matter:
protected so most are
Unmyelinated regions of
here)
CNS
• Ganglia: Cell bodies
• Nerves: Nerve fibers in
in a few areas outside
the PNS
the
CNS
• Tracts: Nerve fibers in
the CNS
Neuron Classification
• Sensory (Afferent /
Toward) neurons:
– Carry impulses from
the sensory receptors
to the CNS
• Motor (efferent)
neurons
– Carry impulses from
the central nervous
system to viscera,
muscles, or glands
• Simple receptors are
found in the skin and
tendons
– Cutaneous Sense
organs
– Proprioceptors
Naked Nerve Ending
• Pain and
Temperature
• Least specialized
cutaneous
receptor
• Most numerous
• Warns of bodily
damage
Meissner’s and Pacinian
• Meissner’s Corpuscles
Touch Receptor
• Pacinian Corpuscles
Deep Pressure
Golgi Tendon Organ
• Proprioceptor –
Balance and
normal posture
sense the
amount of stretch
or tension in
skeletal muscles
Structural Classifications
Multipolar neurons—many extensions from the cell
body
Structural Classifications
Bipolar neurons—one axon and one dendrite
Structural Classification
Unipolar neurons—have a short single process
leaving the cell body
Functional Properties
• Irritability
– Ability to respond
to stimuli
• Conductivity
– Ability to transmit
an impulse
Review Questions
• 1. How does a tract differ from a nerve?
• 2. How are ganglia different from nuclei?
• 3. Which part of a neuron conducts
impulses?
• 4. Which part releases neurotransmitters?
• 5. If one neuron transmits a nerve impulse
at 1 meter per second and another on
transmits at 40 meters per second, which
one is myelinated?
Review Answers
• 1. A tract is a bundle of nerve fibers in the
CNS while a nerve is a bundle of nerve
fibers in the PNS.
• 2. A ganglion is a cluster of nerve cell
bodies in the PNS while clusters of cell
bodies in the CNS are nuclei.
• 3. Dendrites conduct nerve impulses
toward the cell body
Review Answers
• 4. Axon terminals release
neurotransmitters
• 5. The fiber that conducts at 40 meters
per second is the one that is faster, so it is
the one that is mylenated.
Physiology
• Two major
functional
properties:
Irritability:
responding to a
stimulus
Conductivity:
transmitting an
impulse to other
neurons
Irritability of a Resting Neuron
• Resting Neuron
membrane is polarized
– Fewer positive ions on
the inner surface than
on the outer surface
– Positive ions inside the
cell are mostly
Potassium (K+)
– Positive ions outside
the cell are mostly
Sodium (Na+)
Depolarization
• Action Potential: Neurons
are excited by
neurotransmitters
released by other neurons
or other stimuli
• Membrane becomes
permeable to sodium ions
through the opening of
“gates”
• Depolarization occurs and
the inside is now more
positive than the outside
Graded and Action Potential
Graded Potential:
• When the
depolarization event
is weak and remains
local.
• An “All or Nothing”
response
Action Potential:
• When the
depolarization event
is significant enough
to transmit a long
distance signal.
• A nerve impulse
Repolarization
• Action Potential is
initiated (nerve impulse)
• The membrane
immediately becomes
impermeable to sodium
but permeable to
potassium
• Potassium diffuses out,
restoring the resting
polarization
• Another impulse can now
be sent.
Sodium Potassium Pump
• The ions must now
exchange places to
restore the correct
concentrations inside
and outside the cell
• This uses ATP –
active transport
Myelinated Fibers
• Myelin Sheaths
allow for faster
conduction
• Impulse jumps
from node to
node (Nodes of
Ranvier)
• Faster
conduction is
called Saltatory
Conduction
Conductivity
• Impulse moves from
one neuron to another
• Action potential
reaches the axon
terminal
• Vesicles containing a
neurotransmitter
chemical fuse with the
membrane
• Pores form and
release the chemical
Conductivity
• Neurotransmitter diffuses
across the synapse
• Bind to receptors on the
membrane of the next
neuron
• Causes sodium entry and
depolarization of the next
neuron
• The neurotransmitter is
removed by reuptake into
the axon or enzyme
breakdown
Electrochemical Event
• The
transmission of
the impulse is
electrical
• The conduction
of the impulse to
the next neuron
is chemical
Dopamine - A Sample
Neurotransmitter
• Major role in addiction.
• Many of the concepts that apply to
dopamine apply to other neurotransmitters
• A chemical messenger, dopamine is
similar to adrenaline
• Dopamine affects brain processes that
control movement, emotional response,
and ability to experience pleasure and
pain.
Parkinson’s and Dopamine
• In Parkinson's disease, the dopaminetransmitting neurons die
• As a result, the brains of people with
Parkinson's disease contain almost no
dopamine
• To help relieve their symptoms, we give
these people L-DOPA, a drug that can be
converted in the brain to dopamine.
Reflexes
• Rapid, predictable,
involuntary
• One Way Streets –
one direction over
reflex arcs involving
CNS and PNS
• Somatic = Skeletal
Muscles
• Autonomic = Salivary
and Pupillary
5 Elements to Reflex
• 1. Sensory Receptor
Reacts to stimulus
• 2. Sensory Neuron
• 3. Integration Center
The synapse between
the sensory and
motor neurons
• 4. Motor Neuron
• 5. Effector Organ –
muscle or gland
stimulated
Review Questions
• 1. What is the difference between a
graded response and an action potential?
• 2. How is a stimulus transmitted across a
synapse?
• 3. Which portions of a neuron is(are) likely
associated with a sensory receptor or
sensory organ?
• 4. Define or describe a reflex?
Review Answers
• 1. A graded response remains local and is not
carried the length of the axon, while an action
potential is regenerated along the axon and is a
nerve impulse.
• 2. Chemically, when a neurotransmitter is
released and binds to the post synaptic
membrane.
• 3. Dendrites
• 4. A reflex is a rapid predictable response to a
stimulus.
Project
• Research Project: Choose a disease or disorder of the
Nervous System.
1. Write a research paper that will include: symptoms,
treatments, demographics of sufferers, progression of
disease, genetic influence, and current research taking
place.
2. Make a poster or provide other visual presentation like a
Model or PowerPoint.
3. Present your information to the class. (5-10 minutes)
• Due in two weeks.
Central Nervous System
The Brain
The Spinal Cord
The Cerebrum
• Cerebrum – Paired
hemispheres
(superior)
• Cerebral Cortex –
Speech, memory
logic and emotion
• Corpus Callosum –
connects the
hemispheres
The Brain Stem
• 3 Inches or 7.5
cm long
• Midbrain, pons,
medulla
oblongata
Cerebellum
• Inferior and dorsal to
cerebellum beneath
the occipital lobe
• Two hemispheres
• Provides timing for
skeletal muscles,
controls balance and
equilibrium
• Inner ear, eye and
proprioceptors
Protection
• Cerebrospinal fluid –
similar to plasma
containing vitamin C.
• Meninges – Covering
made of three
membranes, that protects
the CNS structures. The
outermost layer is called
the Dura Mater, the
middle is the arachnoid
mater and the innermost
is the Pia Mater
Spinal Cord
• 17 inches or 42 cm long
• Continuation of the brain
stem
• From foramen magnum
to the 1st or 2nd lumbar
vertebrae
• Meninges covers the
entire length extending
into the vertebral canal
• Inferior to L3 there is no
risk of damage when
removing CSF
PNS – Cranial Nerves
• 12 pair of Cranial
Nerves serve the
head and neck –
one pair the vagus
nerves extend to
thoracic and
abdominal cavities
• Numbered and
Named for the
structures they
control
Spinal Nerves
• 31 pair of
spinal
nerves
• Named for
the region
of the cord
where they
arise
Somatic and Autonomic
Somatic And Autonomic
Somatic
• Cell Bodies in CNS
• Axons extend to Skeletal
Muscles
Autonomic
• Two motor neurons
– 1st in the brain or spinal
cord
– Preganglionic axon
synapses with 2nd motor
neuron outside the CNS
– 2nd is the postganglionic
neuron goes to the organ it
serves
Q: Transmission of nerve
impulses along ANS
pathways is generally
slower than along somatic
fibers. Why?
Q: Transmission of nerve impulses
along ANS pathways is generally
slower than along somatic fibers.
Why?
• A: Postganglionic fibers of the ANS are
unmyelinated and so the conduction rate
is much slower than the myelinated fibers
found in the somatic division
Autonomic Divisions
Sympathetic
• Mobilizes the body during
extreme situations
• Thoracolumbar Division,
“Fight or Flight”
• “E” exercise, excitement,
emergency and
embarrassment
• Andrenergic:
Norepinepherine and
epinephrine
• Smooth Muscle and glands
and cardiac muscle
Parasympathetic
• Lets us “unwind” and
conserve energy
• The “Resting and
Digesting”
• “D” digestion,
defecating, and diuresis
(urination)
• Cholinergic:
Acetylcholine
• Smooth Muscle and
glands and cardiac
muscle
Homeostatic Imbalance
• Overstimulation of
the sympathetic
nervous system
can aggravate or
cause disease.
• Can you think of
some reasons
why?
Autonomic – Parasympathetic and
Sympathetic
Homeostatic Imbalance
• Type A people work
at top speed /
constantly push
themselves
• Prolonged
sympathetic nervous
system activity leads
to heart disease, high
blood pressure and
ulcers
Use Page 257 Table 7.24
260 Table 7.3 to fill out the worksheet