Download June 14_Neuroanatomy & Audition

Neuroanatomy &
Audition
June 14, 2011
Zooming In
Perspective
What is a Neuron?
http://www.nikonsmallworld.com/gallery/year/2005/37/true
Neurons
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Neurons control brain
function on a cellular
level.
There are 100 billion
neurons in human brain!
Neurons come in many
shapes and sizes.
Each neuron
communicates with
many others to
coordinate various
functions of the nervous
system.
Image courtesy of Dr. Joshua Sanes, Harvard University, 2005
“Typical” Neuron
Soma (nucleus)
Myelin Sheath
Adapted from http://www.mhhe.com/socscience/intro/ibank/ibank/0002.jpg
The Soma
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Cell body
Contains
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A nucleus with genetic
information
Ribosomes for
processing genetic
information into proteins
Endoplasmic reticulum
for transport of materials
Mitochondria for energy
Several other important
organelles
http://faculty.washington.edu/chudler/cells.html
The Axon
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Carries information AWAY from the Soma (Axons Away!)
Typically only 1 Axon per Neuron
Can be covered in a fatty conductive substance called
Myelin

Speeds the transfer of information
http://faculty.washington.edu/chudler/cells.html
Dendrites
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Bring information from other neurons to the
soma
Rough surface covered with spines
Unmyelinated
Most neurons have MANY dendrites with
extensive branching
http://www.usc.edu/programs/neuroscience/faculty/profile.php?fid=12
And Let’s Not Forget…Glia

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Glia are non-neuronal supporting cells in
the brain
Although there are many more glia than
neurons in the brain, they cannot generate
action potentials, and also don’t
communicate with neurotransmitters.
So what DO they do?
Glial Types & Functions

Astrocytes
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Microglia
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Create myelin for insulated axons
Schwann Cells
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Digest parts of dead neurons
Oligodendrocytes

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Clean up brain debris & “eat” dead neurons
Bring nutrients to neurons
Hold neurons in place
Also create myelin for insulating axons
Satellite Cells

Provide structural support for neurons
located in the periphery
http://www.psych.ndsu.nodak.edu/mccourt/Psy460/Neurophysiology%20of%20vision/
Neuronal Modeling
http://www.enchantedlearning.com/subjects/anatomy/brain/Neuron.shtml
Brief Overview of
Neuroanatomy
Parietal Lobe
Frontal Lobe
Occipital Lobe
Corpus Callosum
Temporal Lobe
Brain Stem
Cerebellum
Frontal Lobe
Found behind your
forehead
 Involved in:

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Reasoning & Planning
Some parts of speech
Movement
Emotions
Problem solving
Contains Motor
Cortex
Return to brain parts
Frontal Lobe
Parietal Lobe

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Found on the top of your head
Contains Sensory Cortex
Involved in:

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Touch
Pressure
Temperature
Pain
Spatial Orientation
Parietal Lobe
Temporal Lobe
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Found on the sides of
head above your ears
Contains Limbic
Cortex
Involved in:

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Speech perception
Hearing
Some types of memory
Emotion
Return to brain parts
Temporal Lobe
Occipital Lobe
Found at the back
of your head
 Receives input
from the eyes
 Often referred to
as the visual
cortex

Occipital Lobe
Return to brain parts
Cerebellum
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Found at the at the back
of your head under the
cerebrum.
Means “little brain”
Involved in:
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Unconscious coordination
Movement
Balance
Posture
Often takes over learned
activities
Cerebellum
Brainstem

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Most basic part of your
brain
Controls essential
functions automatically
Contains 2 parts:
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Medulla controls breathing,
heart & blood vessel activity,
digesting, eliminating waste,
sleeping, maintaining body
temperature…
Pons regulates breathing
Also responsible for
movement
Return to brain parts
Brainstem
Cerebral Cortex
Corpus Callosum
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Located centrally between
the left and right
hemispheres of your brain.
Thick bundle of nerve fibers
that connects the left and
right hemispheres.
Involved in:
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Creativity
Problem solving
Allows hemispheres to
process information together
Corpus Callosum
Create a Brain!
How Do Neurons
Communicate?
The Normal, At Rest, Condition
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When the neuron is at rest, there are several
important ions (+ or – charged chemicals) that are
carefully balanced.
Important ions
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K+ (Potassium)
Na+ (Sodium)
Cl- (Chloride)
Ca2+ (Calcium)
These ions enter and leave the neuron through
ion channels and pumps.
The Neuron At Rest
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The balance of these ions inside and
outside of the cell membrane creates a
membrane potential.
For the neuron at rest, this is -70 mV.
How does the neuron achieve this?
Electrical & Chemical Gradients
Na+
K+
Cl-
Outside
Inside
-70mV
Na+
K+
Concentration Gradient
Electrical Gradient
Cl-
At Rest

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So at rest, the inside of the neuron is
negatively charged because of the balance
of ions inside and outside the cell.
What happens when a signal comes
along??

Ions move!!
Action Potential: Na+
Na+

Outside
Inside
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-55
-70 mV
Na+
When a stimulus
occurs, Na+ channels
open and Na+ rushes
into the neuron,
making it more
positively charged.
This also passes a
negative (depolarizing)
current along to the
next section of axon.
Action Potentials: All or None
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If Na+ outflow causes the potential to reach
-55 mV, an action potential will occur and
the signal will be sent.
This is known as the threshold potential.
If the potential does not reach the
threshold, no action potential will
occur…thus it is an “All or None”
phenomenon.
Action Potential: K+
K+

Outside
Inside

+55mV
-75
mV
K+
Once the action
potential is generated,
Na+ channels close
and K+ channels
open.
K+ moves slowly
outward to bring the
potential back to -75
mV (repolarization).
Action Potential: Overshoot
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So much K+ flows out of the neuron that
the membrane potential returns to a value
lower than that of its resting state.
This is called hyperpolarization.
What effect do you think this might have on
the neuron’s ability to fire again and send a
second message?
Refractory Period
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While the neuron is hyperpolarized, it
cannot fire again.
This also prevents a signal from traveling
backwards.
Once the neuron regains its resting
membrane potential, it will be able to send
a second message.
Propagation
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Action potential in one region of axon depolarizes
the next region to pass along, or propagate, the
action potential.
This process can be sped up by myelin coating on
the axons.
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Nodes of Ranvier: Small segments of unmyelinated axon
Action potential “jumps” from Node to Node:
much speedier!
This is called saltatory conduction.
Putting it All Together
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At Rest: -70 mV (membrane potential)
Na+ enters the cell
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K+ leaves the cell
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If -55 mV threshold potential is reached, action potential
begins
Cell becomes hyperpolarized (-75 mV) and is temporarily
refractory.
Action potential is passed in one direction down
the axon.
Whew! We finally
made it down the axon!
Now What??
http://fleetfeetsportswinston-salem.blogspot.com/2010/05/moving-from-competitor-to-spectator.html
We still need to get the
message to the next neuron.
http://www.georgiapainphysicians.com/l2_edu_pharma_mod1_slides.htm
Neurons Communicate at Synapses

Neurons talk to each other
all the time, but never
actually touch.
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Two neurons meet at a
place called the synapse.
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Special chemicals called
neurotransmitters carry
the message across the
synapse.
Neurons Talk at Synapses
Photo by T. Due, Harvard University, 7/2005
These C. elegan worms contain a transgene encoding
unc-49 gene (GABA receptor) fused to its own promoter
and GFP (Harvard Medical School)
From Dr.Venkatesh N. Murthy,
Harvard University, 7/2005
Neurons Talk Through
Neurotransmitters & Receptors
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Neurotransmitters:
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Chemicals that carry messages from one neuron to another
across the synapse (messages travel really fast!)
Receptors:
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Protein molecules that receive and translate the chemical
message
Neurotransmitters
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Neurotransmitters are how
the brain passes
messages from one
neuron to the next.
Neurotransmitters can be
either:
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Inhibitory (they prevent
other neurons from firing)
Excitatory (they increase
firing in other neurons)
http://www.besttreatments.co.uk/btuk/images/epilepsy_ne
urotransmitter.gif
Neurotransmitters: GABA & Glu
GABA
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Primary inhibitory
neurotransmitter
Involved in:
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Epilepsy
Depression & Anxiety
Anesthesia
Glutamate
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Primary excitatory
neurotransmitter
Involved in:
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Epilepsy
Learning & Memory
Schizophrenia
http://www.cnsforum.com/imagebank/item/Neuro_path_GABA/default.aspxhttp://www.cnsforum.com/imagebank/item/Neuro_path_GLUT/default.aspx
Neurotransmitters: 5-HT & NE
Serotonin
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Involved in:
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Depression & Mood
Eating
Sleep & Wake
Pain
Norepinephrine
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Implicated in
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Mood & Depression
Sleep & Wake
Drug Abuse
Parkinson’s Disease
http://www.deplin.com/LifeWithDepression,Causes
Neurotransmitters: DA & ACh
Dopamine
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Involved in:
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Drug Abuse
Parkinson’s Disease
Schizophrenia
http://www.3dchem.com/molecules.asp?ID=289
Acetylcholine
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Involved in:
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Muscular movement
Nicotine Addiction
Alzheimer’s Disease
http://www.worldofmolecules.com/emotions/acetylcholine.htm
Illustrate a
Neurotransmitter
Brain Beliefs
June 14, 2011
True or False?
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The brain is static, unchanging, and set
before you start school.
True or False
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The brain contains more supporting
cells (glia) than it does neurons (cells
that send signals throughout the brain).
True or False?

Prior to birth, a baby gains 250,000
neurons per minute.
True or False?
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Some people are left-brained and some
are right-brained.
True or False?
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We use only 10 percent of our brains.
True or False?
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Rats have a broader hearing range than
humans.
True or False?
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Male and female brains are extremely
different.
True or False?
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Your brain is made up primarily of water
and fat.
Review & View a
Neuron
Review
Parts of a Neuron
 Lobes of the Brain
 Action Potentials &
Neurotransmission
 Neurotransmitters

http://students.cis.uab.edu/nkm188/project_back2.html
Neurons Galore!
Spinal Cord
Purkinje Neuron in
Cerebellum
Pyramidal
Cortical Neuron
Hippocampal
Neuron
http://faculty.washington.edu/chudler/gall1.html
Auditory System
Anatomy of the
Auditory System
http://www.hearingcarecenter.com/hearing_neural.htm
Hear Ye, Hear Ye
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Sounds waves enter the outer ear (pinna), where
they are amplified and localized.
The sound wave then vibrates the tympanic
membrane (eardrum) and passes to the ossicles.
http://sciencewithmorton.phoenix.wikispaces.net/Sound+and+Light, http://health.allrefer.com/health/ruptured-or-perforated-eardrum-eardrum-repair-series.html
Middle Ear Ossicles
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3 small bones
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Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Continue to pass
along the vibration
from the sound waves
to the cochlea
http://health.allrefer.com/health/fusion-of-the-ear-bones-earanatomy.html
The Inner Ear
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The cochlea is filled with fluid & converts air
sounds into liquid sounds
Organ of Corti
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Contains hair cells on the basilar membrane
Sound waves move the hair cells on the basilar
membrane against the tectorial membrane
Bending these hair cells causes depolarization
and neurotransmitter release
Onward to the Brain!
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Organ of Corti transmits signals
to the cochlear nerve
Medulla
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Cochlear Nucleus to Superior
Olivary Complex
Lateral Lemniscus fiber bundle
carries information to the inferior
colliculus
Proceeds to the Medial
Geniculate Nucleus of the
thalamus and on to the auditory
cortex
http://www.neuroreille.com/promenade/english/ptw/zoom1.htm
Auditory Cortex
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Tonotopic
Organization
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Different frequencies
of sound are mapped to
different regions of the
auditory cortex
Extends to the level
of the cochlea
Zhou, X. and M. M. Merzenich (2007). "Intensive
training in adults refines A1 representations
degraded in an early postnatal critical period."
Proceedings of the National Academy of Sciences
104(40): 15935-15940.
Sound Localization
Experiment
Auditory Acuity
Brainstorming
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What factors might affect hearing?
What are some possible causes of hearing
disorders?
Factors in Hearing
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One ear vs. Two ears
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Frequency of Sound
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Humans can hear sounds btw 20 to 20,000 Hz
Age
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Particularly important for localization
Frequency range narrows with age
Competing sounds
Wax or fluid build up
Why Are 2 Ears Better Than 1?
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Sound arrives at different
times to each ear (unless
its directly ahead of us).
This phase difference is
translated to the brain,
where some neurons
respond to sounds 90°
out of phase; others
respond to 180° out of
phase, etc.
McAlpine, D. (2005). "Creating a sense of
auditory space." The Journal of
Physiology 566(1): 21-28.
Hearing Disorders
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Otosclerosis
Tinnitus
Presbycusis
Auditory
Processing
Disorder
Ménière's Disease
Otosclerosis
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Abnormal growth of
the ossicles
Usually affects the
stapes
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http://www.marshfieldclinic.org/patients/?page=ent_ear_otosclerosis
Causes conductive
hearing loss
Sometimes can cause a
sensorineural hearing
loss that damages
sensory cells or nerve
fibers
Tinnitus
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Persistent ringing in
the ears
May result from the
brain’s attempt to
adapt to inner ear
damage by “turning
up” the auditory
system
Increase in unilateral
brain activity on PET
http://www.newyorker.com/reporting/2009/02/09/090209fa_fact_groopman
Presbycusis
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Age-related hearing loss
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Particularly sensitive to high-pitch
Sensorineural hearing disorder
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Damage to the sensory hair cells or cochlear
nerve
May be due to decreased blood flow to these
regions
Auditory Processing Disorder
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Difficulty paying attention to and
understanding speech
Unknown cause
Ménière's Disease
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Excess buildup of fluid on cochlea
Interferes with ability to transmit sound from
cochlea to auditory cortex
Auditory Acuity
Experiment
http://faculty.washington.edu/chudler/hearing.html