initial algebraic temporal and spatial summation which is used to determine excitatory or inhibitory activities of 2nd order sensory neuron
Where are 1st order sensory neurons found?
The 1st order sensory neurons enter what to synapse w/ 2nd order?
Where does the 1st order sensory neuron synapse with the 2nd order?
Spinal cord or brainstem
What occurs at the 2nd order sensory neuron?
- -initial temporal and spatial algebraic summation must take place
- -cell body decides whether or not to fire on 3rd
Where are 2nd order sensory neurons found?
throughout the NS
What do 2nd order sensory neurons form?
ascending sensory pathways (generally go to thalamus)
Where are 3rd order sensory neurons found?
Where do 3rd order sensory neurons end up?
at cortex in post central gyrus
What is the post central gyrus?
primary sensory cortex, responsible for perceiving sensation
What are the different types of synapses?
Are axosomatic synapses excitatory or inhibitory?
Are axodendritic synapses excitatory or inhibitory?
Are axoaxonic synapses excitatory or inhibitory?
Are dendrodendritic synapses excitatory or inhibitory?
What two ways is coding expressed?
What is rate of coding?
- frequency--expressed in Hz
What is pattern of coding?
variation in rate
With inhibitory synapses, rate is:
interrupted and it varies the pattern
brain's most fundamental capability
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
Inhibition v. excitation:
brain decides to be excited or not excited
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
Is inhibition the same concept as not using all of your brain?
no, it takes energy to inhibit neurons
mechanisms which prevent inhibition
Dis-inhibition is important under certain conditions to:
eliminate inhibition to increase activity of another function
What are some examples of the value of dis-inhibition?
- maximize movement
- increase awareness of special sense
What is the end result of dis-inhibition?
What type of disease is an example of dis-inhibition?
What is Parkinson's disease?
- basal ganglia inhibits activity (has been dis-inhibited pathologically b/c of shortage of dopamine)
- Causes involuntary tremors
What are the mechanisms for inhibition?
- negative feedback loop
- presynaptic inhibition
- feedback inhibition
- feed-forward inhibition
- descending supraspinal inhibitory mechanisms
Where are negative feedback loops common?
What type of cells do negative feedback loops use?
What are Renshaw cells?
- inhibitory neuron
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)
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
The lower motor neuron releases ACh onto:
Renshaw cell (an excitatory NT)
Assuming an AP occurs, Renshaw cells release:
glycine (major inhibiotry NT) at the synapse (axodendritic)
What does the release of glycine by the Renshaw cells cause?
resultant hyperpolarization, causing an inhibition (IPSP) on the NT
What does the hyperpolarizaiton, causing an inhibition on the NT make?
makes the cell fire less, therefore the skeletal muscle would contract less
The negative feedback loops allow neuron to:
keep itself under control (neuron self-regulation)
What do presynaptic inhibitions involve?
- 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
Do all neurons have presynaptic inhibition?
no, most do not
Feedback Inhibition is also called:
lateral or recurrent inhibition
Feedback inhibition utilizes:
inhibitory intra-neurons (Renshaw cells)
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
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
Feedback inhibition is particularly important where?
Feed-forward inhibition is also called?
one or more than one neuron inhibits another neuron or another group of neurons
Where do feed-forward inhibitions occur?
in brain or spinal cord
In feed-forward inhibition, there are a limited number of:
competing responses that are expressed while others are inhibited
In a feed-forward inhibition, the extensors must shut down if it is wanting to use:
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
Descending supraspinal inhibitory mechanisms occur where?
above the spinal cord, in the brain stem/brain and then descends to spinal cord
What is another name for the descending supraspinal inhibitory mechanism?
What does the descending supraspinal inhibitory mechanism involve?
more than one relay neuron
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
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
Does the descending supraspinal inhibitory mechanism wear off over time?
mechanism by which CNS channels/focuses and sorts info
- 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)
Convergence results in:
Convergence does what to information?
- means by which info from one neuron is spread to others
Divergence does what to information?
enhances spread of info
- neurons are arranged sequentially
- ascending (sensory) and descending (motor) pathways
- 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)