PS100 Study Guide - Midterm Guide: Functional Magnetic Resonance Imaging, Magnetic Resonance Imaging, Auditory Cortex

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Midterm 2- Psychology
Chapter 3 Neuroscience
Wednesday, November 2, 2016
9:35 PM
3.1- How do Scientists Study the Nervous System?
Examining autopsy tissue-
o What the brain looks like, but unable to conclude how the systems work
Testing the behaviour of patients with damage to certain parts of the brain (neuropsychologists)
o Localized brain damage leads to loss of particular function (relies on inference/ patients might have
other abnormalities)
Recording electrical brain activity through multiple electrodes attached to the surface of the scalp/
Electroencephalograms (EEG)
o Non-invasive way to measure/learn about activity of the brain at different states (awake or asleep or
during behavioural tasks)
o Only provide summary of surface activity over large expanse of the scalp (general sense)
o Event related potential to time lock EEG activity
Animal studies
o Closely look at parts of functioning brains- microscopically examining specific brain regions, electrically
recording from specific brain areas or specific neurons, temporarily activating or deactivating parts of the
brain and observing outcome, or targeting specific brain areas for destruction and observing the effects
on behaviour (Lesioning)
o Temporarily impairing brain function (Transcranial magnetic stimulation)
Neuroimaging Techniques
Structure images are helpful but do not enable researcher to identify brain regions that become active under specific
conditions. Functional neuroimaging tells about activity in particular brain areas during specific behaviours.
Computerized (or computed) axial tomography (CAT or CT)
o Produce clear, detailed, two dimensional X-ray images of the brain or other organs
o Computer combination of many x-ray images taken from multiple angles result in a 3D image virtually
sliced
Magnetic resonance imaging (MRI)
o Uses strong magnetic field to produce images of the anatomy and physiology
o Creates 3D image of the brain or body, do not use radiation and much clearer
Diffusion tensor imaging (DTI)
o Newest structural imaging technique
o Measures orientation and integrity of white matter to assess damage in the brain and produce colour map
Activity Detection Methods
Position emission tomography (PET)
o Harmless radioactive substance injected into a person's blood, detectors used to scan the person's brain to
find active brain areas where more blood flow is
Functional magnetic resonance imaging (fMRI)- Preferred
o Allows for the detection of changes in blood flow, a presumed indicator changes in the activity of
neurons
o Detects the amount of oxygenated hemoglobin after a person is exposed to magnetic pulses
3.2- How does the Nervous System Work?
Neurons
The neuron or nerve cell is the fundamental building block of the nervous system (communication through
spinal cord and brain)
o Neurons are found within the peripheral nervous system too
Neurons have specialized structures that enable them to communicate with other neurons through electrical and
chemical signals
Neurons have a cell body filled with cytoplasm that contains a nucleus (residence of chromosomes), and
everything like all other cells
o Main structure is the cell body (communicate with other neurons), the axon(send info away from the cell
body), and the dendrites (receive info from other neurons)
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o A two molecules- thick neuron membrane completely covers the cell body, dendrites, and axon (have
specialized region at the end-axon terminal which contains the synapse)
o Synapse is where info is passed from one neuron to another across a very small fluid-filled space
When an electrical impulse (action potential) reaches the axon terminal, it causes fluid-filled sacs called
vesicles (filled with chemicals called neurotransmitters) to migrate and fuse with neuronal membrane and to
then release neurotransmitters into the synapse
Dendrite are highly branched, neurons have only one axon leaving the cell body, but axons are highly branched
(collaterals)-greatly increase number of neurons that the axon contacts and axons can be long
Three types of neurons:
o Sensory- specialized sensory endings in the skin that respond to external factors
o Interneuron- communicate with both sensory and motor neurons and with other interneurons
o Motor- stimulate our many muscle cells into action
Glia Cells
Same number of glial cells as neurons, but in some parts of brain glia may outnumber neurons by a factor of
about 10 to 1
Buffer the neurons from rest of the body, control nutrient supply to neurons, destroy and remove diseased and
dead neurons, and provide axons with their myelin sheath
o Categories: Atroglia (regulate blood flood-more nutrition or oxygenation)
o Oligodendroglia and Schwann cells (provide a protective fatty sheath or coating called myelin that
insulates axons which speeds up passage of electrical signals)
o Ependymal cells (specialized neuroglial cells that line the walls of the ventricles fluid filled spaces of the
brain)
o Microglia (clean up the debris of degenerating or dead neurons and glia so that brain regions can
continue with their normal functioning
3.3- How do Neurons Work?
The Action Potential (all or none principle
The ratio of negative to positive ions in the cytoplasm (intracellular fluid) is different from the ratio in the
extracellular fluid that surrounds the neuron creating a membrane potential (polarized)
An inactive polarized neuron has a stable negative resting charge, the resting potential is around -70 (mV) but
can vary (inside more negative than outside)
Four main types of ions that contribute to the resting potential: Sodium, Potassium, Chloride, and multiple
anion proteins
o Sodium and Chloride are higher concentration on the outside while Potassium and Anions are higher on
the inside (not equally distributed)
Neuron's membrane is selectively permeable to ions (specialized ion channels or pores)
o K+ and Cl- easily pass through membrane but Na+ pass with greater difficulty and anions are trapped
inside the neuron
Sodium- Potassium pump (three Na+ out and two K+ ions in)
o Action potential-> causes spike (-55 to -40) that causes an electrical signal to be propagated at high speed
down the axon (excitory input outweighs inhibitory input) potential shifted to threshold of excitation
o Neurotransmitters either depolarize (closer to zero) resting potential or they hyperpolarize (farther from
zero)
o Excitatory postsynaptic potentials vs inhibitory postsynaptic potentials
o Summation process that depicts whether neuron fires
o Sodium quickly into axon, channels close and quickly depolarize membrane (50mV), once action
potential sweeps down axon the potassium channels open allowing them to flow out and hyperpolarize
membrane (the refractory period- absolute vs relative)
Facilitating movement of action potential
The axons of many neurons are surrounded and insulated by myelin, white fatty layered coating produced by
specialized glial cells
Nodes of Ranvier
o Regularly spaced gaps in the myelin, the neuronal membrane is exposed to the extracellular fluid
o Allow action potentials to travel quickly down myelinated axons by jumping from node to node
(Saltatory conduction)
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Role of Neurotransmitters
Once action potential reaches the presynaptic axon terminal, causes the release of neurotransmitter molecules into the
synapse. It diffuses across the synapse and binds to neurotransmitter receptors on dendrite of receiving or postsynaptic
neuron.
Neurotransmitter receptors act like a lock and key model where the neurotransmitter must fit to activate the
following sequence of reactions
Postsynaptic potentials can either be excitatory (depolarized) or inhibitory (hyperpolarized)
Process of termination is essential or receptor could be blocked from receiving further input, or
neurotransmitter molecules could accumulate in synapse, obscuring future discrete chemical signals
o First process is enzymatic degradation, involves breaking down creating products that are reabsorbed by
the cell and are used to synthesize additional neurotransmitter molecules
o Reuptake where neurotransmitters are drawn back into the presynaptic neuron and recycled for future use
Neurotransmitters
Acetylcholine- Stimulating muscles and plays a key role in communicating between motor and sensory neurons
(also for attention, arousal, and memory and plays a part in REM sleep)
Dopamine- Associated with mood, control of voluntary movement, and reward mechanisms in the brain (drugs,
excess associated to schizophrenia in the frontal lobes)
Norepinephrine- excitatory involved in stimulating the sympathetic nervous system, affecting arousal,
vigilance, and mood
Serotonin- inhibitory involved in regulation of mood, appetite and sleep, also plays a role in activity level and
cognitive function such as learning and memory
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