biological perspective
Post on 11-May-2015
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Aurelio | Lopez | Pablo |Rodas |Yao
Biological PerspectiveBiological Perspective
Nervous SystemA Network of cells that carries
information to and from all parts of the body
Neuroscience Life science concerned with the structure
and the functioning of the brain, neurons, nerves, and nerve tissues (All part of the
nervous system)Special focus on the relationship of behavior
and learning Santiago ramón y cajal (1887): Doctor who studied about brain tissue; theorized that the
nervous system is made up of individual cells
NeuronIt Receives and sends messages within the
Nervous System“Messenger of the body”
Makes up only 10% of the brain but there are millions of them!
Parts of the neuron
Dendrite (“Branch”) – receives messages from other cells
SOMA; cell body – dendrites attach to this, contains the nucleus and keeps the neuron alive and functioning
Parts of the neuronAxon – fiber attached to the soma/Cell body that carries out messages to other
cells• Does most of the travelling through the body• Coated by myelin sheaths and neurillema (aka
schwann’s membrane)
Parts of the neuronneurillema – surrounds both the axon and
the myelin sheath• Serves as a tunnel where damaged nerve
fibers can repair themselves• Axons in the brain and spinal cord don’t
have this.
Glial Cells
Gray fatty cells that compose 90% of the brain
It keeps neurons in place + lets them develop and work
Provides structural support – insulation• A Neuron’s message = electrical
Functions of the Glial Cells
Some Get nutrients to the neuronsOthers are in charge of Cleaning up dead
neurons The Communication with neurons and
other glial cells Act as insulators
Some affect the functioning of neurons and their structure, and “give birth” to
new neurons during prenatal development
What else do they do?They create myelin!
• Myelin: layer of fatty substance created by 2 types of glial cells
So, what does Myelin do?
It Creates a sheath around the axonwhich Protects it from damageMultiple sclerosis: damages the myelin sheath; leads to a loss of
function
So, what does Myelin do?
it Speeds up the neural message travelling down the axon
• HOW? Nodes of ranvier – they’re the periodic gap in the myelin sheaths of the axon; facilitate the rapid conduction of
nerve impulses
Nerves A “cable” of bundled-up myelin-coated axons
(The nerves are the ones in green)
Axon Terminal
Area at the end of the neuron where it meets another neuron
BUT ONE NEURON ALONE IS
MEANINGLESS!
Neural ImpulseElectrical and chemical transmission of
information from one neuron to another.
Neural Impulse
takes the same path all the timeProcess of conducting
information from a stimulus by the dendrite of one neuron and carrying it through the axon and
on to the next neuron.
So… What’s involved in the neural impulse?
IonsWe have both positively (+) and
negatively (-) charged particlesHowever, we’re only concerned with
the sodium (na+) and Potassium (K+) ions for the neural impulse
Ions inside are mostly negative, while ions on the outside are
mostly positive
Selectively Permeable Membrane
Outer membrane of the neuron is not impermeable
It Selectively allows some ions to pass through
HOW?It has pores that are only large
enough for small ions to pass through; the gates
Charge of the NeuronWhen the cell is at rest (not firing a neural impulse) it’s primarily negative
There are lots of positive sodium ions outside the membrane, while the ions
inside are negativeThey cluster around the membrane Difference in electrical charges =
electrical potential
Na-
Na-
Na-
Na-
Stimulus
Eventually, when the cell receives some stimulation from another cell
Dendrites activateThe particular gates are now open
which allow the sodium ions on the outside to rush into the cell
Action Potential
Causes the inside of the cell to become mostly positive; the
outside, mostly negativeThe Reversal of electrical charge
= action potential
Action Potential
When action potential gets to the end of the axon, the message is
transmitted to another cell
Repolarization
The neuron will now try to restore its charge by pumping out
the positively charged ions and bringing back the negative ones
All-or-noneNeurons are either firing at full strength, or does not fire
at allA strong message = fire more
quickly
The Synapse
End of the axon has several short fibers (axon terminals) with Calcium
ions nearbyAt the end of each terminal, there is a
synaptic knobIt has a number of saclike structures
in it called synaptic vesicles that contain neurotransmitters (chemical
inside a neuron that transmits messages)
The Synapse
Next to the synaptic knob, there’s a dendrite of another neuron
They don’t connect, but there’s a gap in between them called the synaptic
gap
The Synapse
The dendrite of the neighboring neuron contains locks called receptor
sitesShaped in a certain way that only a
particular molecule of a neurotransmitter can fit into it
The calcium stimulates the vesicles to move to the end of the knob
wherein they release neurotransmitters to the synapseThey’ll fit themselves into the
receptor sites, which activates the next cell
The Synapse
Neurons can also be turned on or off, depending on exactly what
synapse is being affectedTurn cells on (excitatory effect)Turn cells off (inhibitory effect)
Agonists
Chemical substances that can mimic/enhance the effects of a
neurotransmitter on the receptor sites of the next cell
Antagonists
Chemical substance that blocks/reduces a cell’s response
to the action of other chemicals/neurotransmitters
BETA BLOCKERS: drugs used to control blood pressure by
blocking heart contractions which lowers the blood pressure
Neurotransmitters
Acetylcholine
Found at the synapses between neurons and muscle cells
Stimulates the contraction of skeletal muscles
Also found in hippocampus (brain area responsible for new
memory)If receptor sites are blocked =
paralysisIf too much released = death
Glutamate
It’s a Major excitatory neurotransmitter of the nervous
systemImportant role in learning and
memory formation
GABA (Gamma-aminobutyric acid)
Most common inhibiting neurotransmitter of the brain
Helps calm anxiety; it’s agonized by alcohol
Causes the general inhibition of the nervous system associated
with drunkness
SerotoninFound in the lower part of the
brainCan either be excitatory or inhibitory; depends on what
synapses are affectedAssociated with sleep, mood and
appetiteLow levels of serotonin have
been linked to depression
Dopamine
Also found in the brain; like serotonin, it can have different
effects depending on the locationControl of movement, sensations
of pleasureToo little released = parkinson’s
diseaseToo much released =
schizophrenia
Endorphin (Endogenous Morphine)
–Neural regulator or neural peptide (a neurotransmitter that directly controls
the release of other neurotransmitters) that controls pain
in the body.–The body halts production of this if
people take morphine or heroin, leaving them with no protection
against pain when the drug wears off (withdrawal).
• Leads to addiction
Cleaning up the synapse
–Neurotransmitters have to get out of receptor sites before the next
stimulation occurs–Reuptake: process where
neurotransmitters are taken back into the synaptic vessels
–Acetylcholine is not taken back
Cleaning up the synapse
–SSRI (Selective serotonin reuptake inhibitors)
–Blocks the reuptake of serotonin–Leaves more in the synapse to bond
with receptor sites–Elevates mood and lifts depression
Central Nervous System
• Consists of the brain and spinal cord
- Both are composed of neurons and glial cells that control life-sustaining functions,
thought, emotion, behavior.
Brain
• Makes sense of information received from the senses, makes decisions,
sends commands out to muscles and the rest of the body
Spinal Cord
• A long bundle of neurons that serves 2 vital functions for NS.
• Divided into two areas.– Outer section is composed of axons and
nerves (which appear white). Carries messages from the body to brain and vice-
versa; a message pipeline.– Inner section is composed of somas (which appear gray). It is a primitive “brain” that is
responsible for very fast, lifesaving reflexes.
Spinal Cord
• Damage to it was once thought permanent. Healthy brain cells only took over the
damaged ones.– It is now known that they can actually be
repaired by the body systems.– Scientists can implant nerve fibers from
outside the spinal cord into a damaged area and coax the damaged spinal nerves – The brain can also change itself by
adapting neurons to serve new functions when older ones die or become damaged.– Dendrites grow and new synapses are formed in at least some areas as people
learn new things
Reflex ARC: 3 types neurons
• Afferent/Sensory Neurons (“Afferent Accesses Spinal Cord”)
– Carries messages from senses to spinal cord
• Efferent/Motor Neurons (“Efferent Exits”)– Carries messages from spinal cord to
muscles and glands• Interneurons
– Connects Sensory and Motor Neurons–Makes up the inside of the spinal cord and
brain• This all happens very quickly. It allows for
very fast response times.
Neuroplasticity
• Lifelong ability of the brain to reorganize neural pathways based on new experiences• Ability of the brain to change with learning• Has a clear age-dependent determinant (the
younger the more plastic)• Occurs in the brain under 2 conditions:– Developmental plasticity and plasticity of
learning and memory– Compensation for lost function and
maximizing what is left• Environment plays a key role in influencing
brain rewiring
Stem Cells
• Repairs brain damage/disease.• Controversial as it comes from embryos• Recently, scientists have tried turning mice bone marrow cells into stem cells. • It is possible too that adult bone
marrow can be used.
Peripheral Nervous System
• Compromised of the nerves and neurons not contained in the brain and
spinal cord• Transmits information to and from the
central nervous system
Somatic Nervous System
• Controls the voluntary muscles of the body
• Carries sensory information and controls movement of the skeletal
muscles
Autonomic Nervous System
• Controls automatic functions of the body
• Automatically regulates glands, internal organs, blood vessels, pupil dilation,
digestion, and blood pressure
Parasympathetic Division
• Maintains body functions under ordinary conditions; saves energy
Sympathetic Division
• Prepares the body to react and expand energy in times of stress
Distant Connections: The Endocrine Glands
Parasympathetic Division
• GLANDS are organs in the body that secrete chemicals, some affect
functioning of the body but not all behavior, others have widespread
influence on the body and behavior.
• ENDOCRINE GLANDS secrete chemicals called hormones into bloodstream; affect behavior and emotions by
influencing the activity of the brain and by controlling muscles and organs such
as heart, pancreas, and sex organs.
Parasympathetic Division
• pituitary gland• pineal gland• thyroid gland• Pancreas• Gonads
• adrenal glands
Peeking Inside the Brain
• It is impossible to tell the function of a brain structure if it is dead.
• A scientist can’t even be sure what the brain tissue looks like in the skull.
Clinical Studies• Study animals or people with brain
damage- Animals: May damage deliberately, then are tested. Or the area can be electrically
stimulated• Deep lesioning: insertion of a thin, insulated wire into the brain, then a
current is sent that destroys the brain cells at the tip of the wire
• ESB (Electrical Stimulation of the Brain): stimulation of brain tissue with milder current; causes neurons to react as if
they’ve received a message
EEG (Electroencephalograph)
• Record electrical activity of neurons below skull with EEG machine
• Small metal disks (electrodes) are placed on the skin covering the skull using a jelly-like substance to help
conduct. The electrodes are wired to a computer (older ones connected to
graphing machines)
EEG (Electroencephalograph)
• Output: Waves that indicate sleep, seizures, tumors, etc. It also determines
which areas of the brain are active during reading, writing, speaking, etc.• Alpha waves: Regular, slower waves -
relaxation• Beta waves: Irregular, fast waves -
waking activity• Theta waves: Drowsiness and sleep
• Delta waves: Large, slow waves - Deep stage of sleep
EEG (Electroencephalograph)
• ICA (Independent Component Analysis): Allows identification of individual
signals• ERP (Event-Related Potential): Results
of multiple presentations of a stimulus are measures and averaged; hence an
electric potential–May be used to follow Alzheimer’s, and lie
detection
CT Scan (Computed Tomography Scan)
• X-ray of the brain that maps “slices” of the brain by computer
• Can show stroke damage, tumors, injuries, abnormal structure
• Good for imaging brain structure especially if there is metal in the body
MRI Scan (Magnetic Resonance Imaging)
• Magnetic field that can create a 3D image of the brain and display “slices”
of it• More detailed than CT Scan
• Strongly not recommended if the person has metal in their body
PET Scan (Positron Emission Tomography)
• Sees brain in action• A radioactive glucose is injected in the
brain, and the computer detects which parts of the brain are using them up. It
projects it on a monitor.–Why glucose? It is the “fuel” of the brain.
• Uses colors - lighter areas are active and darker ones inactive
FMRI (Functional Magnetic Resonance Imaging)
• A form of MRI where the computer tracks changes in oxygen levels of
blood. It is placed on top of the picture of the brain
• By combining images, a “movie” can be made
• More detailed than PET Scans
Parts of the brain
Medulla
• Part of the hindbrain that relays messages between the cerebellum and
the cortex
Pons
• Part of the hindbrain that relays messages between the cerebellum and
the cortex
Reticular Formation
• A system of nerves running from the hindbrain and through the midbrain to
the cerebral cortex• Controls arousal and attention
Hippocampus
• Plays a role in our learning, memory and ability to compare sensory
information to expectations
Pituitary Gland• Regulates other endocrine glands
Hypothalamus• Part of the forebrain that regulates the amount of fear, thirst, sexual drive, and
aggression we feel.
Corpus Callosum• Connects left and right hemispheres of
the brain
Cerebral Cortex• Controls complex thought processes
Thalamus• Part of the forebrain that relays
information from sensory organs to the cerebral cortex
Paul Broca
• Case: (1861) a Man lost ability to speak after a head injury
• Later, after the post mortem autopsy, broca was able to demonstrate that the
cause of the man’s deficit lay in the damage to a specific point in the brain• Proof of this localization of function
(connecting a specific behavior to a specific brain area)
Henry Molaison
-Removal of Both Medial Temporal Lobes (Loss of hippocampus, amygdala, and perirhinal cortex)- Severe anteroggrade amnesia
Phineas Gage
The Accidental Neuroscience
Pioneer
So what happened?
John Martyn Harlow• Phineas Gage’s Doctor
• Arrived an hour after Gage was brought to the hospital
• Did all he could to find out what caused Gage’s changes in behavior.
• “No Longer Gage”
• Continued to study Gage’s skull long after he died.
Biological Perspective• The tamping iron
hit the frontal lobe of Gage’s brain causing changes in personality.
• From a mild mannered man, Gage turned into “fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom)”-Dr. John Martyn Harlow.
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