Neurophysiology (Lecture 3) Flashcards Preview

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Flashcards in Neurophysiology (Lecture 3) Deck (65):
1

Nervous System

-brain, spinal chord, nerves
-made up of 100's of billions of cell (neurons and glia)

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brain

-only 10% of cells (100 billion) in the brain are neurons
-rest of the brain is non-neuronal

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neurons

-cells that are capable of sending and receiving chemical signals
-conduct information with electrical signals
-different types differ in location in the nervous system/morphology/chemicals they use to communicate

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cell membrane

semipermeable membrane that encloses the neuron

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dendrites

the short processes emanating from the cell body which revieve most of the synaptic contacts from other neurons

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axon hillock

the cone-shaped region at the junction between the axon and the cell body

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axon

the long narrow process that projects from the cell body

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myelin

the fatty insulation around many axons that makes the action potential move on faster

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cell body

the metabolic center of the neuron also called the soma

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nodes of ranvier

the gaps between sections of myelin

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buttons

the buttonlike endings of the axon branches which release chemicals into synapses

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synapses

the gaps between adjacent neurons across which chemical signals are transmitted

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membrane of a neuron

dynamic
-protein components change and move around = critical for neuroadaptations

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functional units of biology

proteins; every action in biology is carried out by a protein/ enzyme

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endoplasmic recticulum

-system of folded membranes in the cell body
-rough portions (those with ribosomes) play a role in the synthesis of proteins
-smooth portions (those without ribosomes) play a role in the synthesis of fats

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cytoplasm

the clear internal fluid of the cell

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ribosomes

internal cellular structures on which proteins are synthesized
-they are located on the endoplasmic recticulum

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golgi complex

-connected system of membranes that packages molecules in vesicles

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nucleus

the spherical DNA containing structure of the cell body

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mitochondria

sites of aerobic (oxygen consuming) energy release

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microtubules

tubules responsible for the rapid transport of material throughout neurons

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synaptic vesicles

spherical membrane packages that store neurotransmitter molecules ready for release near synapses

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neurotransmitters

molecules that are released from active neurons and influence the activity of other cells

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multipolar motor neurons

-projection neurons in the brain
-more than two processes extending from its cell body

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unipolar

-sensory neurons
-one process extending from its cell body

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bipolar

-sensory neurons
-two processes extending from its cell body

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interneurons

-in spinal cord and brain
-neurons with short axons or no axon at all

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chemical neurotransmitters

amino acids, monamines, peptides

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functional classifications of neurotransmitters

inhibitory, excitatory, modulatory

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glia

-90 % of bain
-latin for glue = support neurons
-make myelin
-regulate nutriens and waste for neurons
-response to injury, scar formation
-we now know that they are more than structural support

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Oligodendroglia (CNS)

-myelinates many axons
-myelin attacked in MS

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Schwann cell (PNS)

-only myelinates 1 axon
-myelin not vulnerable to MS

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astrocytes

-star shaped
-assist in the transfer of chemicals (nutrients, and waste products) from the nervous system to the blood (wrapped around blood vessels)
-take up and release ions and neurotransmitters

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microglia

-respond to injured cells and infectious agents
-must be incredibly sensitive to protect precious neural tissue
-secretion of anti-inflammatory cytokines

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Einstein's Brain

-1955 Thomas Harvey
-MC diamond= more glia in association cortex leads to higher IQ

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membrane potential

difference in electrical charge between inside and ourside of the cell

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At rest the cell is.......

POLARIZED

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Ions

positively and negatively charged particles

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K+ concentration

more concentrated inside of the cell (Na+/K+ pump)

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Na+ and Ca 2+` concentration

more concentrated on the outside of the cell

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selective permeability

-no ionic type is distibuted evenly across the membrane
-differential permeability due to ion channels

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ration of K+ to Na+

40x
-at rest the cell membrane is 40 times more permeable to K+ than to Na+

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random motion

-way that resting membrane potential is maintained
-motion down concentration gradient

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electrostatic pressure

-way that resting membrane potential is maintained
-opposites attract and like repel

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presynaptic cells

release neurotransmitters which diffuse across the synapse and bind to postsynaptic receptors
-depoloarize (-67mV) = EPSP
-hyperpolarize (-72mV) = IPSP

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Postsynaptic Potentials

-graded
-rapid
-decremental

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PSP integration

-whether or not a neuron fires an action potential depends on the summation of EPSPs and IPSPs over 1000s of synapses (temporal and spatial summation)
-PSP converging adjacent to the axon hillock must reach the threshold of excitation to fire (-65mV)

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Action Potential Properties

-massive but momentary reversal of membrane potential
-all or none
-action potential only involves those ions right next to the membrane
-resting potential rapidly reestablished by random movement

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absolute refrectory period

-1 to 2 ms after initiation of AP
-AP only travels in one direction

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relative refractory period

-possible to fire again but you will need more stimulation
-rate of APs relative to intensity of stimulation

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Voltage Gated Channels

mediate changes in membrane permeability during the action potential

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Inactivating Voltage gated Na+ channel

type of voltage-gated ion channel that mediates changes in membrane permeability during the action potential

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Delayed (Rectifying) Voltage gated K+ channel

type of voltage-gated ion channel that mediates changes in membrane permeability during the action potential

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At rest...

ng-K+ channel = OPEN
vg-Na + channels = CLOSED
vg-K+ channels = CLOSED

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At rise....

ng-K+ channel = OPEN
vg-Na + channels = OPEN
vg-K+ channels = CLOSED

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At fall....

ng-K+ channel = OPEN
vg-Na + channels = INACTIVATED
vg-K+ channels = OPEN

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Action Potential Conduction

-propagation down the axon (orthodromic conduction as opposed to antidromic)

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saltatory conduction

-occurs in myelinated axons
-Na+ channels concentrated at nodes of ranvier
-much faster than continuous conduction due to increased role of passive conduction down the axon and reduced leakage

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speed of AP depends on...

-myelination
-size

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Action Potential pathway

1. PSP elicted on soma and dendrites
2. PSP conducted decrementally to axon
3. if summated PSPs reach threshold of excitation = AP
4. AP conducted down axon non-decrementally
4. arrival of AP at terminal button = exocytosis of neurotransmitters

61

peptides

-large neurotransmitters
-amino acid chains that are composed of 10 or fewer amino acids
-short protein
-released gradually in response to general increases in the level of Ca+ ions

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EPSPs (EXCITATORY POSTSYNAPTIC POTENTIALS)

POSTSYNAPTIC DEPOLARIZATIONS

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IPSPs (inhibitory postsynaptic potentials)

post synaptic hyperpolarizations
-decrease the likelihood that the neuron will fire

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temporal summation

-postsynaptic potential produced in rapid succession at the same synapse
-these sum to form a greater signal

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spatial summation

-local EPSPs(or IPSPs) that are produced simultaneously on different parts of the receptive membrane sum
-form a larger EPSP (or IPSP)