Exam 1 Flashcards
What is systems neuroscience?
- the study of the nervous system’s functions that emerge from the operations of systems of neurons
- consideration of how these functions emerge from cellular and molecular underpinings
- studies the emergemt properties that result form groups of neurons
The temporal portion of the right eye goes to which hemisphere?
the right hemisphere
What portion of vision crosses over?
the nasal half
Hemi-decussation
process info from the left visual field in the right visual cortex; nasal half of vision crosses over
Tactile sensation from the left side ends up on which side of the brain?
right half
Primary motor neurons on the right side of the motor cortex control which side of the body?
left side
Phrenology facts:
- structure-function relationships do exist
- size of neural circuits can be related to their importance
- size of neural circuits can be modified by experience
mass action
depends on size of lesion
equipotentiality
does not depend on which area
Karl Lashely’s observations on brain damage and learning
the size, but not the location, of the lesion is what is important to cognitive function
parallel processing
the brain often has more than one solution to a simple problem and so is resistant to damage
distributed modular processing
- complex capabilities derive from more elementary operations (modules)
- the nature of these subcomponents is often counter-intuitive, so the biological solution is not always the most logical one
saccades
- very fast, stereotyped movements of the eye
- cannot see during a saccade due to saccadic masking
dependent variable
stimulus
independent variable
response
receptive field
portion of space to which a neuron respnds
Why can PNS axons regrow?
PNS glia allow axons to regrow because they secrete neurotrophic factors
Can the brain experience phantom pain?
No
Sensation and perception are products of _____?
neural activity
Why does artifical activation work?
brain/neurons doesn’t care what starts the action potential
What is the operating range of vision?
1 - 10^14
What is the minimum # of photons we can detect?
one photon
What is the problem the nervous system must solve?
given a neural respone, it must determine what the stimulus is
modality
touch, vsison, hearing
submodality
what type of touch it is (just an example)
Our nervous system has different sensors that react to _____
different energies
adequate stimulus
each class of sensory receptors is specialized to respond to a particular form of energy
perceptive field
area from which sensation seems to arise
Is perceptive field the ame as receptive field?
basically
transduction
conversion of stimulus energy into electrical signal
Receptor types are specialized for ____
converting certain types of stimulus energies
sensory receptor
a cell or specialized portion of a neuron that transduces physical energy into a change in transmembrane potential
accessory structures
structures between the outside world and neurons; lens, pupil, ear bones, basilar membrane
Pacinian corpuscles respond to ____
vibration
With pacinian corpuscles, increasing frequency of electrical stimulation results in
increased frequency of percieved stimulation
What stimulus information does the nervous system need to encode (4W’s)?
- what is it? modality/submodaltiy/identity
- where is it? location
- how much is it? intensity
- when is it? timing/duration
Will a Pacinian corpuscle react to a crushing stimulus?
no, its the wrong submodality
What are the four major classes of receptors?
- mechanoreceptors
- chemoreceptor
- electromagneto receptors
- thermoreceptors
mechanoreceptors
mechanically couple cytoskeleton to ion channel; touch and hearing
chemoreceptor
ligand binds to receptor, causes opening of an ion channel (directly or through second messenger cascade set off by ligand binding)
electromagneto receptors
detect electromagnetic radiation, like photoreceptors
What do all receptors do?
change the electral potential of the cell in response to activation
Different receptors:
- respond to different signals
- generate different cellular reactions: depolarization vs hyperpolarization vs both
the anatomy and physiology of different receptors are well matched to their _____
function
Advantages and disadvantages of second messenger cascades:
- advantages: amplifies the signal, increasing sensitivity
- disadvantages: slow because there are so many steps
Which systems use second messenger cascades? Why?
olfaction and vision; speed isn’t important in these systems
primary afferent neurons
axons that projects into (at) the CNS; are not necessarily the receptor cell
Space constant
the distance over which signal falls to 37% of the original signal
What is the membrane resistance? Why is it so high?
1 gigaOhm; fat doesn’t conduct elecrticity well
receptor potential
- a change in transmembrane potential evoked directly by the stimulus
- often lograthimically related to stimulus intensity
a generator potential is a subclass of ____
action potentials
In sensory cells with action potentials, why are receptor potentials known as generator potentials?
because they generate action potentials
What is the net result of receptor potentials and action potentials?
action potenital firing frequencyis often related logarithmically to stimulus intensity
Which mechanoreceptors are deep?
Pacsinian corpuscles and Ruffini endings
Which mechanoreceptors are superficial?
Meissner’s corpuscles and Merkel cells
Each type of sensory axon coming form only one type of receptor results in _____?
labeled lines
RA1
rapidly adapting type 1; Meissner’s corpuscle
SA1
slowly adapting type 1; Merkel cells
RA2
rapidly adapting type 2; Pacinian corpuscle
SA2
slowly adapting type 2; Ruffini endings
What do Meissner’s corpuscles communicate?
change in pressure, rate of change matters (first derivatives)
When do Meissner’s corpuscles fire?
- during change, but not steady state
- changes in force (pressure); hand object movement
What do Merkel cells communicate?
- comunicates constant pressure
- help encode size/shape of object
- keeps from squeezing hand too hard
When do Merkel cells fire?
during change, but also during steady state
What do Pacsinian corpuscles communicate?
contact; lift-off/landing vibration; onset/offset response
When do Pacsinian corpuscles fire?
responds to how fast a change is changing; an accelerometer
Type 1 surface receptors
- resolve braille dots, firing patterns look like the braille dots
- on the surface
- have small receptive fields
Type 2 surface receptors
- deep
- large receptive fields, so not good for high resolution localization
- very sensitive
What happens to a Pacsinian corpuscle during stimulus onset?
slow redistribution of corpuslce layers, this absorbs stimulus force resulting in less stimulation of neuron
What happens to a Pacsinian corpuscle during stimulus offset?
layers return to original arrangment, neuron re-stimulated
somatotopy
the nervous system maintains an orderly representation of body surface
To be discriminable, different stimulti must activate different _____
receptive fields
Is receptive field size consistent throughout the body?
No
What is somatotopy?
the nervous system maintains an orderly representation of body surface
receptive field
the area to which a sensory neuron responds
The primary somatosensory cortex has a sesnory homonculus of which side of the body?
contralateral side
Enlargements in the somatosensory cortex reflect ____?
density of innervation (number of receptors)
What are two temporal codes?
rate codes and pattern codes
Rate codes
increased stimulus intensity results in increased firing rate
Pattern codes
bursting vs steady state firing enocde different things
What are two population codes?
which neurons fire and how many neurons fire
Contextual codes
how a given neuron fires in relationship to other neurons; synchrony among different neurons with different stimuli
How does firing encode stimulus intensity?
increasing stimulus intensity -> increasing channel opening -> increasing generator potential (receptor potential) amplitude -> cell fires faster and faster
Does increased firing rate track with perceived intensitty?
Yes
Generator potentials are often _____ related to stimulus intensity
logarithmically
Action potential frequency is often ____ related to amplitude of stimulus intensity
linearly
Action potential frequency is often ____ related to stimulus intensity
logarithmically
Weber’s law (definition)
- size of the difference threshold (JND) is often proportional to the size of the standard
- detect percentage, not absolute, differences in size
Weber’s law equation
deltaS = K x S
deltaS: just noticable difference
K: constant
S: stimulus strength
Weber-Fechner law
extends the dynamic range; I = K x log (S/S0) I: percieved intensity S: stimulus strength S0: threshold K: constant
Shift curve up (to the right)
low false positives, but high false negatives
Shift curve down (to the left)
high false positives, low false negatives
The highest probability of channels being open corresponds to what spot on a sigmoidal curve?
peak
Why can’t a simple rate code work for temperature?
firing rate maxes out at both very high and very low temps so can’t distinguish between the two temps
Population code with hot and cold neurons
lots of hot neurons fire at high temps, very few fire at low temps
Synchrony codes
neurons firing in synchrony encode something about the object
Proprioceptors of skeletal muscles
Aa, group 1, thick and heavily myelinated; rapid transduction
Mechanoreceptors of skin
AB, group II, medium diameter, thinly myelinated
Fibers that conduct pain and temperature
Ad, group III, narrow diameter, thinly myelinated
Fibers that conduct pain, itch
C, group IV, very narrow diameter, unmyelinated
dermatomes
the body area innervated by a single root
Is there overlap in dermatomes? What is the consequence of this?
Yes, so damage to a single root does not produce sensory loss in the dermatome
Why can’t we localize pain?
due to the heavy branching of axons the pain can’t be localized exactly
What is another name for the dorsal column system?
medial lemniscal system
What info does the DCML carry?
touch, pressure, flutter, vibration, proprioception from contralateral side
What info does the anterolateral system carry?
pain, temperature, minor flutter from contralateral side
General heirarchical processing pathway
primary sensory neurons -> relays -> primary sensory cortex (simple cells) -> primary sensory cortex (complex cells) -> unimodal sensory cortex (puts features together) -> multimodal sensory cortex (puts all modalities together)
Function of unimodal sensory cortex
puts features together
Function of multimodal sensory cortex
puts all modalities together
Why don’t primary sensory neurons exhibit center surround inhibition?
they do not have synapses, the only info they are getting is from the receptors
What is abstraction?
doesn’t have a physical representation; like using the word “larger” without a comparison
Where does the VPL of the thalamus project?
the primary somatosensory cortex
Columnar organization of somatosensory cortex
columns of one receptor type; each finger has a column with smaller sub-columns for sensory submodality
Inputs go into what layer of the somatosensory cortex?
layer IV
Outputs from layer I, II of somatosensory cortex go to
other cortical structures
Ouputs from layer V, VI of somatosensory cortex go to
spinal cord and subcortical strucutres, including the thalamus
