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Coding
initial algebraic temporal and spatial summation which is used to determine excitatory or inhibitory activities of 2nd order sensory neuron
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Where are 1st order sensory neurons found?
in PNS
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The 1st order sensory neurons enter what to synapse w/ 2nd order?
enter CNS
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Where does the 1st order sensory neuron synapse with the 2nd order?
Spinal cord or brainstem
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What occurs at the 2nd order sensory neuron?
- coding
- -initial temporal and spatial algebraic summation must take place
- -cell body decides whether or not to fire on 3rd
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Where are 2nd order sensory neurons found?
throughout the NS
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What do 2nd order sensory neurons form?
ascending sensory pathways (generally go to thalamus)
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Where are 3rd order sensory neurons found?
in CNS
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Where do 3rd order sensory neurons end up?
at cortex in post central gyrus
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What is the post central gyrus?
primary sensory cortex, responsible for perceiving sensation
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What are the different types of synapses?
- axosomatic
- axodendritic
- axoaxonic
- dendrodendritic
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Are axosomatic synapses excitatory or inhibitory?
inhibitory
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Are axodendritic synapses excitatory or inhibitory?
excitatory
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Are axoaxonic synapses excitatory or inhibitory?
inhibitory
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Are dendrodendritic synapses excitatory or inhibitory?
excitatory
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What two ways is coding expressed?
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What is rate of coding?
- frequency--expressed in Hz
- rate=impulse/sec
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What is pattern of coding?
variation in rate
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With inhibitory synapses, rate is:
interrupted and it varies the pattern
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Inhibition:
brain's most fundamental capability
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Charles Sherrington described the brain's ability to choose b/w
competing alternatives --to select one and suppress the others-- as the
integrative action of the nervous system.
Regarded this decision making as the brain's most fundamental capability
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Inhibition v. excitation:
brain decides to be excited or not excited
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What would happen if inhibition did not work?
- could not have any mm contraction
- could not make sense out of special sensory input (visual or auditory), the brain would be blurry --also applies to emotions
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Is inhibition the same concept as not using all of your brain?
no, it takes energy to inhibit neurons
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Dis-inhibition:
mechanisms which prevent inhibition
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Dis-inhibition is important under certain conditions to:
eliminate inhibition to increase activity of another function
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What are some examples of the value of dis-inhibition?
- maximize movement
- increase awareness of special sense
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What is the end result of dis-inhibition?
increase activity
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What type of disease is an example of dis-inhibition?
Parkinson's disease
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What is Parkinson's disease?
- basal ganglia inhibits activity (has been dis-inhibited pathologically b/c of shortage of dopamine)
- Causes involuntary tremors
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What are the mechanisms for inhibition?
- negative feedback loop
- presynaptic inhibition
- feedback inhibition
- feed-forward inhibition
- descending supraspinal inhibitory mechanisms
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Where are negative feedback loops common?
spinal cord
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What type of cells do negative feedback loops use?
Renshaw cells
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What are Renshaw cells?
- inhibitory neuron
- interneurons
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Why do negative feedback loops use Renshaw cells?
for a means by which the neuron can influence its own activity (dampens or decreases activity--shut itself down)
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Where are Renshaw cells located?
b/w collateral branch of lower motor neuron and a dendrite and cell body region of same LMN and other LMNs
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The lower motor neuron releases ACh onto:
Renshaw cell (an excitatory NT)
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Assuming an AP occurs, Renshaw cells release:
glycine (major inhibiotry NT) at the synapse (axodendritic)
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What does the release of glycine by the Renshaw cells cause?
resultant hyperpolarization, causing an inhibition (IPSP) on the NT
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What does the hyperpolarizaiton, causing an inhibition on the NT make?
makes the cell fire less, therefore the skeletal muscle would contract less
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The negative feedback loops allow neuron to:
keep itself under control (neuron self-regulation)
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What do presynaptic inhibitions involve?
axoaxonic synapse
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Presynaptic Inhibition:
- excitatory NT released from presynaptic axon to postsynaptic axon
- graded potential occurs (due to EPSP lose vesicles; EPSP doesn't produce AP--graded)
- AP does arrive, release NT but less than normal due to pre-release, therefore, less of an EPSP which has inhibitory effect; RMP lower amplitude due to prior depol
- Since partially depoled, there is less Ca to enter postsynaptic membrane and flux inward
- W/ less Ca, there is less NT released (tendency for it not to fire b/c not released enough NT(
- axons excitatory but result of less NT, it is inhibitory
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Do all neurons have presynaptic inhibition?
no, most do not
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Feedback Inhibition is also called:
lateral or recurrent inhibition
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Feedback inhibition utilizes:
inhibitory intra-neurons (Renshaw cells)
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In feedback inhibition, the most rapidly firing 2nd order sensory neuron depresses the activity of:
- adjacent, less-active 2nd order sensory neurons
- a contrast b/w active and less-active neurons is enhanced
- results in enhancement of discrimintation of stimuli
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Feedback Inhibition alters signal to noise ratio as neurons become larger
- 25Hz:20Hz is less than 25Hz:10Hz
- 25:20 is not good, too much noise
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Feedback inhibition is particularly important where?
inner ear
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Feed-forward inhibition is also called?
reciprocal inhibition
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Feed-forward inhibition:
one or more than one neuron inhibits another neuron or another group of neurons
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Where do feed-forward inhibitions occur?
in brain or spinal cord
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In feed-forward inhibition, there are a limited number of:
competing responses that are expressed while others are inhibited
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In a feed-forward inhibition, the extensors must shut down if it is wanting to use:
flexors
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Monosynaptic reflex:
feed-forward inhibition
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What is an example of a monosynaptic reflex?
- knee jerk
- Renshaw cells send inhibitory message to knee flexors
- LMN sends an excitatory message to knee extensors
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Descending supraspinal inhibitory mechanisms occur where?
above the spinal cord, in the brain stem/brain and then descends to spinal cord
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What is another name for the descending supraspinal inhibitory mechanism?
distal inhibition
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What does the descending supraspinal inhibitory mechanism involve?
more than one relay neuron
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Descending supraspinal inhibitory mechanism:
- naturally occurring pathway that deals w/ pain must be activated
- activated via thought process that sends neurons to influence activity
- activation releases inhibitory NT (endorphins) to reduce noxious (painful) stimulation
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What are examples of descending supraspinal inhibitory mechanism?
- when you burn your hand in the kitchen, but you're not supposed to be there in the first place
- you tell yourself it doesn't hurt as bad as it really does so that you don't yell and scream as much
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Does the descending supraspinal inhibitory mechanism wear off over time?
yes
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Neural processing:
mechanism by which CNS channels/focuses and sorts info
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Convergence:
- many neurons synapse (converge) on a single neuron
- --thousands of neurons can influence a single neuron (most input is indirect --but there is still influence)
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Convergence results in:
focused input
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Convergence does what to information?
focuses information
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Divergence:
- means by which info from one neuron is spread to others
- exponential
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Divergence does what to information?
enhances spread of info
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Serial:
- neurons are arranged sequentially
- ascending (sensory) and descending (motor) pathways
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Parallel:
- info is conveyed in parallel sequences
- more than one pathway; two serial pathways that run parallel
- involved w/ rehabilitation (damage one pathway, other pathways take up the slack--neuroplasticity)
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