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Unit 2: Neurobiology
Neurons, Brain, Body Systems
NeuroscienceHow 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
DendritesBushy, root-like parts of a cellReceive messages
(Neurotransmitters) from the sending
neuroni.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
AxonThe 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. 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
1.) Dopamine – controls movement, alertness, emotion – too much = schizophrenia, too little = Parkinson's
2.) Serotonin – affects mood, hunger, sleep, arousal – too little = depression
3.) Acetylcholine (Ach) – affects motor movement, learning, and memory – too little = Alzheimer's
4.) Endorphins – body’s natural pain killers
The Nervous System
/
/
Central Nervous System
/ \
/ \
Brain Spinal Chord
\
\
Peripheral Nervous System
/ \
/ \
AutonomicSomatic
/ \
/ \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: 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 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: If a part is damaged, we can deduce what it
controlled. – Phineus Gage
Brain Imaging
2.) Legions: 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
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
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-7-2015/2870103?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
The Motor Cortex – sends out motor messages via efferent neurons
Broca’s Area (left frontal) – speech center
Parietal Lobe
Crown of the head
Contains the Sensory cortex – where afferent/sensory neurons carry information
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 Medulla: blood pressure, heart rate, breathing
Pons: just above medulla – critical in facial expressions
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: Finger shaped network of neurons – extends
throughout hindbrain to midbrain. Controls arousal and ability to focus attention.
Coma when malfunctions
Forebrain
ForebrainControls thought and reasonMost studied by psychologistsMuch bigger than the midbrain &
hindbrainWhat 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
Dominant traits over-ride recessive
Genotype – every gene you are a carrier of
Phenotype – what actually manifests in your physical characteristics
Homozygous – having identical alleles for a single trait (BB, bb)
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.