Transcript Unit 2: Neurobiology

Unit 2: Neurobiology
Neurons, Brain, Body Systems
Neuroscience
 How does our brain organize and
communicate with itself?
 How does our brain allow us to
remember the lyrics to dozens of
our favorite songs?
 How do we remember exactly
where we were and what we were
doing when we heard about 9/11?
Neural Communication
 The basic building block of our body’s
communication is the neuron
 The human brain has approximately 100
Billion neurons that communicate with each
other and allow us to learn, remember, feel
pain and function as human beings.
Parts of a Neuron
Dendrites
Bushy, root-like parts of a cell
Receive messages
(Neurotransmitters) from the
sending
neuron
i.e. the receiver
Soma (Cell Body) and
Nucleus
 Contains nucleus and other life sustaining
parts of the cell
 In is resting state is -70 charged
Axon
The extension of a neuron
“The sender”
When the threshold is met
an electrical charge travels
down the axon
Myelin Sheath
 Fatty covering of the axon – “the
insulator”
 Speeds up the neural impulses
 Deterioration of the myelin sheath
causes
Multiple Sclerosis
Terminal Branches/Buttons
 Branched end of the axon containing the
neurotransmitters (the chemical
messenger)
When the neuron fires, the terminal buttons
release the NT into the synapse
Synapse (Synaptic Gap/Cleft)
Space between the terminal
branches of one neuron and the
dendrite of another
The gap is less than one billionth
of an inch wide
Neurotransmitter
 The chemical messenger contained in
terminal branches that enable neurons
to communicate
 Fit into receptor
sites on dendrites
like a key to a lock
How Neurons Fire – the process
 Neural communication is an electrochemical process.
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Electricity travels within the cell (down the axon) and the
chemical (the neurotransmitter crosses the synapse to travel
between cells). Electricity does not jump between neurons.
1.) In its resting state – the neuron is just hanging out and is at
a -70 charge
2.) If enough + ions cross the cell membrane to change the
charge to +50, the neuron has met its threshold and goes into
action potential
3.) electricity travels down the axon
4.) terminal buttons release the NT
5.) the NT crosses the synapse and binds to the dendrites of the
receiving neuron
6.) the leftover NT is taken back up by the terminal buttons –
known as reuptake
Firing Neurons cont . . .
 Once a neuron fires it is in a refractory state and
cannot fire again until it pumps the + ions back out
of the cell body and returns to a -70 resting state
(i.e. it must re-load)
 Firing is an “all or none" principle – if you meet
the threshold, you fire
completely.
If you don’t, you don’t.
Neural firing takes place in
Fractions of a second
Neurotransmitters – the chemical messenger
 Dozens of NT in your body – imbalances can cause
problems
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1.) Dopamine – controls movement, alertness, emotion –
too much = schizophrenia, too little = Parkinson's
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2.) Serotonin – affects mood, hunger, sleep, arousal – too
little = depression
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3.) Acetylcholine (Ach) – affects motor movement,
learning, and memory – too little = Alzheimer's
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4.) Endorphins – body’s natural pain killers
The Nervous System
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Central Nervous System
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Brain
Spinal Chord
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Peripheral Nervous System
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Autonomic
Somatic
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Sympathetic
Parasympathetic
Afferent/Efferent Neurons
 Afferent = Sensory Neurons – run from
body to brain
 Efferent = Motor Neurons – run from brain
to body
 Ex: I put my left hand on a warm stove.
Afferent neurons in my left hand carry the
message to the sensory cortex in my right
brain. Efferent neurons from the motor
cortex in my right brain, sends a message
to move my left hand.
Peripheral Nervous System
Links the central nervous system
with all other
nerves in the body
Somatic Nervous System
Controls voluntary muscle
movement
Autonomic Nervous System
Controls autonomic functions of our
body (heart, lungs, organs, etc)
Usually
operates
on its own
Autonomic is
Automatic!
Autonomic is divided into…..
 Sympathetic NS:
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Excitatory - arouses
us for defensive
action
Alert system of the
body
Accelerates heart
rate, blood pressure,
breathing; slows
digestion
Makes you alert and
ready for action
 Parasympathetic NS
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Calming system
Returns body to
normal after stress
passes
Lowers breathing,
heart rate, constricts
pupils
Reflexes – exception to the rule….
 Message doesn’t go all the way back to the brain
 Sensory neurons carry the info to the spine and the
spine makes a motor command without the message
getting all the way to the brain first
 Ex: knee; intense heat or cold
Brain Imaging…..
 1.) Accidents and Injuries:
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If a part is damaged, we can deduce what it
controlled. – Phineus Gage
Brain Imaging
 2.) Legions:
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Removal or destruction of part of the brain (brain
tumor).
Deduces functions
Brain Imaging
 3.) EEG - Detects brain waves
Brain Imaging
 4.) CAT – Computerized Axial
Tomography
3-D x-ray of brain
Shows
Structure, not
function
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Brain Imaging
 5.) Magnetic Resonance Imaging – MRI
 Uses magnetic fields to measure the density and
location of brain material
 Structure,
not function
Brain Imaging
 6.) Positron Emission Topography - PET
 Lets researchers see what areas of the brain are most
active during certain tasks – shows function
 Measures how much of a certain chemical are used
in different parts
of the brain.
Uses radioactive glucose
Brain Imaging
 7.) Functional MRI
 Combines the MRI
and the PET scan
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Shows structure and function
Cerebral Cortex (CC)
 It’s what you think of when you picture the brain: the
gray, wrinkled surface of the brain
 It’s a thin layer of densely packed neurons
Cerebral Cortex
 Left Hemisphere
 Gets messages from
and controls the right
side of the body
 Logic
 Language
 Verbal
 Analytical
 Right Hemisphere
 Gets messages from
and controls the left
side of the body
 Spatial
 Creative
 Emotionally intuitive
The Cerebral Cortex
 The left and right hemispheres look symmetrical – but they are
biologically the “odd couple” serving complementary functions
 Complex tasks
involve both
hemispheres
Corpus Callosum - band of fibers
Connecting left and right hemispheres
Split Brain Surgery – severe corpus
callosum – rare treatment for epilepsy
Dateline NBC – Growing Hope – Is Medical Marijuana a
Viable Treatment for Epilepsy?
 http://www.nbc.com/dateline/video/dateline-
june-72015/2870103?onid=209511#vc209511=1
4 Lobes of the Brain
Frontal Lobe
 Behind the eyes/forehead
 Involved in abstract thought, emotional
control, rational judgment (Phineus Gage)
 Contains
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The Motor Cortex – sends out motor
messages via efferent neurons
Broca’s Area (left frontal) – speech center
Parietal Lobe
 Crown of the head
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Contains the Sensory cortex – where
afferent/sensory neurons carry information
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The more sensitive the body area, the greater
surface area assigned on the sensory cortex
Occipital and Temporal Lobes
 Occipital –
Back of the head
Processes vision
Temporal – sides of head
over ears
Processes hearing
Wernicke’s Area – left temporal – language
comprehension
Other Important Brain
Parts…
Three subsections of the brain
Hindbrain
Within the hindbrain…
 Hindbrain – consists of the top of the spine
and base of brain – critical life functions
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Medulla: blood pressure, heart rate, breathing
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Pons: just above medulla – critical in facial
expressions
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Cerebellum: located on the bottom, back side
of the brain. Literally means “little brain.”
Critical for balance and fine motor movements.
Midbrain
 Just above spine. Very small in humans.
 Reticular Formation:
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Finger shaped network of neurons – extends
throughout hindbrain to midbrain. Controls
arousal and ability to focus attention.
Coma when malfunctions
Forebrain
 Forebrain
 Controls thought and reason
 Most studied by psychologists
 Much bigger than the midbrain &
hindbrain
 What makes us
humans
Within the forebrain…..
 Thalamus: sensory switchboard – relays all
incoming sensory info except smell
 Hypothalamus: “pleasure center” –
regulates hunger, thirst, and sexual arousal.
Also regulates the
entire endocrine
system via the
pituitary gland
Within the forebrain….
 Amygdala: aggression and fear center.
(Legion the amygdala in a monkey and he will
be passive and docile)
 Hippocampus: critical in forming episodic
memories. Not fully formed until age 3.
Smell is routed through the hippocampus.
 Limbic System: the thalamus,
hypothalamus, amygdala, and hippocampus
all form the limbic system. Deals with
aspects of emotion and memory.
Brain Plasticity
 The brains ability to re-organize its neural
connections after some type of damage, such
that one part of the brain can develop the
capacity to carry out a function it normally
wouldn’t in a healthy brain.
 Brain plasticity is inversely correlated with the
age. The older you are the less plastic your
brain is and the more difficult it is to overcome
brain injury.
Genetics
 Every human cell
has 46
chromosomes in 23
pairs. Genetic
material that makes
up chromosomes is
DNA.
Genetics
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Dominant traits over-ride recessive
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Genotype – every gene you are a carrier of
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Phenotype – what actually manifests in your
physical characteristics
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Homozygous – having identical alleles for a single
trait (BB, bb)
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Heterozygous – having two different alleles for a
single trait (Bb)
Dominant V. Recessive
Punnett Square
Twins….
 Identical twins come
from one fertilized
egg that splits and
share DNA.
 Fraternal twins
come two separate
eggs fertilized by
two separate sperm
and are no more
genetically similar
than normal siblings.
Gender and X linked Disorders
 Gender is determined by the 23rd pair of
chromosomes. XX = girl, XY = boy
 Female eggs always carry X. Male sperm
carry X or Y and determine the gender of the
baby.
 X-linked disorders are carried on the X
chromosome. Women are often the carriers
and the disease manifests in their sons.
 Muscular Dystrophy, color blindness,
hemophilia
X Linked Disorders
Chromosomal Abnormalities
 Turner’s Syndrome - Only one single X (girls).
Cannot reproduce, short stature, webbed necks,
abnormal sexual development
 Klinefelters Syndrome – males, extra X (XXY), varied
effects – minimal sexual development, extreme
introversion, cannot reproduce
 Down’s – extra chromosome on 21st pair. Causes
mental retardation.