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Neurons and Neuronal Circuits
BMS 329 Exam 3
Terms in this set (71)
How many neurons does the human brain contain
what are nerves supported by
what are the parts of the neuron
cell body, dendrites (1 or several), axon (1)
what is the fundamental principal of neurons
-somatic and dendritic membranes sensitive to chemical and physical stimuli
If the signal is sufficiently strong, stimuli to a neuron can evoke what
where does the ap generate? how does it propagate?
junction of cell body and axon, spreads down axon quickly down to azonal terminals
what is the nature of information flow in a neuron?
polarized -- one direction (dendrite, soma, axon, axon terminals.
describe multipolar neurons, where found
several dendrites and one axon- shape of most neurons in CNS
describe bipolar neurons, where found
one dendrite and one axon (neurons in retina, inner ear and olfactory epithelium)
describe unipolar neurons, where found
one bi-furcated process
-one end of process has dendritic function, rest is an axon.
-somatosensory neurons projecting into spinal cord have this shape
what are the three main types of neuron morphologies
unipolar, bipolar, multipolar
all neurons have a _________ _________ which is actively maintained by membrane ionic pumps
the membrane potential can be ________ altered by _______________ which are released by other neurons
_________ neurotransmitters, like glutamate, __________ the membrane
___________ transmitters, like GABA, __________ the membrane
if the membrane depolarization reaches the ___________, depolarization begins
what happens once threshold potential is reached?
voltage gated sodium channels are opened
-fast spreading wave of depolarization called AP
Inhibitory neurotransmitters have what effect on an action potential
reduces chance of Ap generation.
what happens as the AP leaves the axon hillock and reaches the axon terminal of the neuron?
the arriving wave of depolarization triggers release of neurotransmitter into synapse, which binds to receptor on post synaptic cell membrane and initiates events in next neuron
what is the speed in which the neurotransmitter is release and effects the post synaptic cell?
VERY FAST- short synaptic delay
what are the two types of synapses and their descriptions?
-uncommon, cells communicate via electrical currents spreading through gap junctions
chemical-contacts between axonal terminals of one neuron and dendrites, or soma, or axon, of a nother neuron.
What are receptors classified as?
what are the two groups of neuronal receptors
inotropic (neurotransmitter activated ion channels)
-metabotropic (g-protein coupled receptors)
what does the activation of ionotropic receptors effect?
mostly effect membrane potential
ionotropic receptor is considered what type of receptor?
what can ionotropic receptors be further categorized into?
-excitatory (depolarize, Na+)
-inhibitory (hyperpolarize, Cl- or K+)
what does the term docking mean
the snare of the synaptic vesicle docks onto the membrane of the pre-synaptic cell and fuses to it to release the neurotransmitter into the synaptic cleft
why are some ionotropic receptors excitatory, and others inhibitory?
do all mammals have same number of neurons
What is the effect of excitatory input on membrane potential and generation of AP?
depolarize membrane, trigger AP (glutamate)
What is the effect of inhibitory input on membrane potential and generation of AP?
hyperpolarize membrane, prevent AP (GABA)
action potentials are typically generated where? what is the nature of the threshold here?
axon hillock; lower
What is presynaptic inhibition?
occurs when inhibitory neurotransmitter is released in an axon-axonal synapse
______________ of post-synaptic potentials in neuronal soma is required for generation of APs
what represents an elementary info processing at a single neuron?
describe an excitatory postsynaptic potential (EPSP)
release of excitatory neurotransmitter in single synapse that generates a small potential
describe an inhibitory postsynaptic potential (IPSP)
release of inhibitory neurotransmitter
what is spatial and temporal summation
simple processing of info at level of single neuron
what are the three stages of an action potential
resting, depolarization, repolarization
What is the resting membrane potential?
what triggers depolarization
the threshold is met, and NA channels rapidly open, Na enters cell
what is the series of events in an action potential
-na channels open, na floods into the cell (depolarization)
-na channels close, inactivated when the potential reaches -35mV, while K+ channels simultaneously open and K+ leaves the cell (membrane depolarizes)
how long does an ap take?
less than 1ms
what is the phenomena of sodium channels continuing to open in the axon as the ap propagates?
what speeds up the ap traveling down the axon
saltatory conduction in myelinated azons
Schwann cells wrap around what- what does this do?
around segments of ions, electrically insulate them
what forms the myelination in the CNS
how does the ap travel down the myelinated axon?
jumping from one node of ranvier to next
how much does myelination increase conduction speed?
.25m/s ---> 100m/s
what happens in the synaptic bulb when the ap arrives?
1. axonal terminals house vesicles that contain the neurotransmitter
2. some of the vesicles are docked to the membrane using a complex of several proteins
3. arriving ap depolarizes pre-synaptic membrane, which opens ca2+ channels.
4. elevated intracellular ca triggers fusion of vesicles with membrane and neurotransmitter is released in synaptic cleft
5. neurotransmitter stimulates receptors in post-syn membrane
what allows rich information processing at the neuronal circuit level
connectivity among neurons is very complex
the brain processes information in a ________ manner.
the ________ design of the brain increases what?
how do nerves converge/diverge in the visual system ?
information from many light receptors converges on 1 million axons
-which diverge to ultimately influence billions of cortical neurons.
How does information pass in the visual system
retina, optic nerve, brain
what are the examples of connectivity patterns in the brain
diverging, converging and reverberating circuits
Describe a reverberating circuit
-neurons send info to neurons and more neurons, and later neurons send axons back to perceiving neurons
aps traveling by jumping from one node of ranvier to another
which cells for myelin?
-schwann cells in peripheral nerves
-oligodendrocytes in central nervous system
excitatory and inhibitory neurotransmitters bind to what
EPSPs are mediated by opening of what?
IPSPs are mediated by opening of what?
chloride and/or potassium channels
EPSPs and IPSPs from many synapses undergo what?
spacial and temporal summation
spacial and temporal summation affects _________.
membrane potential of the neuron
if EPSPs prevail, what happens to the neuron's membrane? the neuron?
membrane is depolarized, neuron ap generated. (or mem potential dissapates if threshold not met)
if IPSPs prevail, what happens to the neuron's membrane? the neuron?
membrane is hyperpolarized, and neuron does not generate AP
neurotransmitter release is triggered by what
depolarization induced entry of calcium ions
what is a reverberating circuit helpful for?
short memory storage, thought to be responsible for intelligence
how is information processed in the converging and diverging neuronal circuits (in terms of parallel and and serial computing devices) ?
brain processes info in a serial manner, because of divergence of neuronal circuits and multiple info channels in brain, also viewed as highly parallel computational device.
what is meant by information being processed in the brain in a serial manner?
transmitted along a chain of neurons
the _________ / _______ design of the converging and diverging neuronal circuits in the brain greatly increases what?
serial/parallel, computational capacity
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