Neurophysiology (Lecture 3) Flashcards
Nervous System
- brain, spinal chord, nerves
- made up of 100’s of billions of cell (neurons and glia)
brain
- only 10% of cells (100 billion) in the brain are neurons
- rest of the brain is non-neuronal
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
cell membrane
semipermeable membrane that encloses the neuron
dendrites
the short processes emanating from the cell body which revieve most of the synaptic contacts from other neurons
axon hillock
the cone-shaped region at the junction between the axon and the cell body
axon
the long narrow process that projects from the cell body
myelin
the fatty insulation around many axons that makes the action potential move on faster
cell body
the metabolic center of the neuron also called the soma
nodes of ranvier
the gaps between sections of myelin
buttons
the buttonlike endings of the axon branches which release chemicals into synapses
synapses
the gaps between adjacent neurons across which chemical signals are transmitted
membrane of a neuron
dynamic
-protein components change and move around = critical for neuroadaptations
functional units of biology
proteins; every action in biology is carried out by a protein/ enzyme
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
cytoplasm
the clear internal fluid of the cell
ribosomes
internal cellular structures on which proteins are synthesized
-they are located on the endoplasmic recticulum
golgi complex
-connected system of membranes that packages molecules in vesicles
nucleus
the spherical DNA containing structure of the cell body
mitochondria
sites of aerobic (oxygen consuming) energy release
microtubules
tubules responsible for the rapid transport of material throughout neurons
synaptic vesicles
spherical membrane packages that store neurotransmitter molecules ready for release near synapses
neurotransmitters
molecules that are released from active neurons and influence the activity of other cells
multipolar motor neurons
- projection neurons in the brain
- more than two processes extending from its cell body
unipolar
- sensory neurons
- one process extending from its cell body
bipolar
- sensory neurons
- two processes extending from its cell body
interneurons
- in spinal cord and brain
- neurons with short axons or no axon at all
chemical neurotransmitters
amino acids, monamines, peptides
functional classifications of neurotransmitters
inhibitory, excitatory, modulatory
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
Oligodendroglia (CNS)
- myelinates many axons
- myelin attacked in MS
Schwann cell (PNS)
- only myelinates 1 axon
- myelin not vulnerable to MS
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
microglia
- respond to injured cells and infectious agents
- must be incredibly sensitive to protect precious neural tissue
- secretion of anti-inflammatory cytokines
Einstein’s Brain
- 1955 Thomas Harvey
- MC diamond= more glia in association cortex leads to higher IQ
membrane potential
difference in electrical charge between inside and ourside of the cell
At rest the cell is…….
POLARIZED
Ions
positively and negatively charged particles
K+ concentration
more concentrated inside of the cell (Na+/K+ pump)
Na+ and Ca 2+` concentration
more concentrated on the outside of the cell
selective permeability
- no ionic type is distibuted evenly across the membrane
- differential permeability due to ion channels
ration of K+ to Na+
40x
-at rest the cell membrane is 40 times more permeable to K+ than to Na+
random motion
- way that resting membrane potential is maintained
- motion down concentration gradient
electrostatic pressure
- way that resting membrane potential is maintained
- opposites attract and like repel
presynaptic cells
release neurotransmitters which diffuse across the synapse and bind to postsynaptic receptors
- depoloarize (-67mV) = EPSP
- hyperpolarize (-72mV) = IPSP
Postsynaptic Potentials
- graded
- rapid
- decremental
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)
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
absolute refrectory period
- 1 to 2 ms after initiation of AP
- AP only travels in one direction
relative refractory period
- possible to fire again but you will need more stimulation
- rate of APs relative to intensity of stimulation
Voltage Gated Channels
mediate changes in membrane permeability during the action potential
Inactivating Voltage gated Na+ channel
type of voltage-gated ion channel that mediates changes in membrane permeability during the action potential
Delayed (Rectifying) Voltage gated K+ channel
type of voltage-gated ion channel that mediates changes in membrane permeability during the action potential
At rest…
ng-K+ channel = OPEN
vg-Na + channels = CLOSED
vg-K+ channels = CLOSED
At rise….
ng-K+ channel = OPEN
vg-Na + channels = OPEN
vg-K+ channels = CLOSED
At fall….
ng-K+ channel = OPEN
vg-Na + channels = INACTIVATED
vg-K+ channels = OPEN
Action Potential Conduction
-propagation down the axon (orthodromic conduction as opposed to antidromic)
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
speed of AP depends on…
- myelination
- size
Action Potential pathway
- PSP elicted on soma and dendrites
- PSP conducted decrementally to axon
- if summated PSPs reach threshold of excitation = AP
- AP conducted down axon non-decrementally
- arrival of AP at terminal button = exocytosis of neurotransmitters
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
EPSPs (EXCITATORY POSTSYNAPTIC POTENTIALS)
POSTSYNAPTIC DEPOLARIZATIONS
IPSPs (inhibitory postsynaptic potentials)
post synaptic hyperpolarizations
-decrease the likelihood that the neuron will fire
temporal summation
- postsynaptic potential produced in rapid succession at the same synapse
- these sum to form a greater signal
spatial summation
- local EPSPs(or IPSPs) that are produced simultaneously on different parts of the receptive membrane sum
- form a larger EPSP (or IPSP)
