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Study Guide: Neuro Exam #2
Brain Plasticity
● Proliferation- the production of new cells/ neurons in the brain
● Migration- movement of newly formed neurons and glia (connective tissue of NS) to
their eventual locations
● Differentiation- forming of the specific shape of neurons
● Myelination- glia produce fatty sheath (myelin)
● Synaptogenesis- formation of synapses between neurons and elimination of incorrect
synapses
● Stem cells are undifferentiated, generate “daughter cells” throughout life
● Dentate gyrus ➝ hippocampal circuits
● Subventricular zone ➝ olfactory bulb circuits
● Gradient of chemicals- growing axons reach their target areas by being attracted to some
chemicals and repelled by others (Chemoaffinity Hypothesis ➝ proven by Sperry
experiment)
● An axon will “date” a lot of potential targets before it settles, genes compete for a given
area
● Axons make an excess of connections (“overproliferate”) and then eliminate (“prune”)
most of them
● Neurotrophic Hypothesis: a developing axon’s default is to die by apoptosis and a
neurotrophic factor from postsynaptic neuron can save it
● Trk receptors enhance survival and promote growth
● Nerve growth factor- canonical neurotrophic factor
● Cortical graft experiments- show that brain tissue does not retain function when moved to
a different area
● Topographic cortical plasticity- areas can expand with increased synaptic input
● Collateral sprouting- try to fill in vacant synapses as a result of a lost axon
● Bad plasticity- phantom limb

Vision
● Law of specific nerve energies- the nature of a percept is elicited by the nervous system
activating it

● Photoreceptors (Rods and Cones) - transduce photons into electrical potentials
Rods- most abundant in the sides of the eye, few in the fovea, respond to dim
light, not color sensitive
Cones- most abundant in the fovea, useful in bright light, essential for color vision
● Horizontal cells- mediate communications between photoreceptors
● Bipolar cells- receive input from photoreceptors
● Amacrine (Lateral) cells- mediate communication between bipolar and ganglion cells
● Resolution in the retina is related to the packing density of sensors/ convergence ratio of
receptors onto ganglion cells
● In temporal periphery (where cones are), there is a ​higher​ likelihood of capturing sensory
input, but ​lower​ resolution
● Cones are responsible for high resolution vision

● Cis-retinal- before light hits the retina
● Trans-retinal- conformation change once light has hit the retina
● Na+ channels are always open, unless light is entering the retina (dark current)

● Light current:

1) Light hits Rhodopsin, which produces G-protein
2) G-protein activates Phosphodiesterase
3) Phosphodiesterase inhibits the production of cGMP in the GC
4) Na+ channel closes

● The retina uses lateral inhibition to enhance contrast
● Active neurons in the dark section inhibit the neurons next to them, which are the ​first​ of
the light section (why edges are accentuated)
● Light hits the back of the light (retina) last, and only then does the activation process
start, which moves from the back of the eye to the front (retina ➝ bipolar ➝ ganglion)
● 3 types of cones, each with different spectral sensitivity (red, blue, green)

● Trichromatic theory- ratio of activity across the 3 types of cones determines color
● Opponent process theory- color is perceived in terms of paired opposites: red-green,
orange-blue, yellow-purple
● Receptive field- portion of space capable of eliciting a response in a given neuron

● Starts at the ganglion cells
● Upper pathway = retinotectal and lower pathway = retinogeniculate
● SC (superior colliculus) is in the Tectum
● LGN (lateral geniculate nucleus) is in the thalamus
● Primary Visual Cortex (V1) is in the occipital lobe
● Dorsal = localization, includes the Magnocellular ganglion cells and Area MT (motion)
● Ventral = identification, includes the Parvocellular ganglion cells, Area IT (shape), and
the fusiform face gyrus
● Visual input decussates (crosses over from left eye to right side of brain and vise versa) at
the optic chiasm

● Orientation tuning of neurons measures how a cell’s firing rate depends on the position
(orientation) of a stimulus
● This depends on the receptive field properties from the presynaptic neuron
● Simple cells = circular, center-surround organization, fixed inhibitory or excitatory zones
● Complex cells = orientation dependent, larger receptive field, bar or edge shaped, no
fixed inhibitory or excitatory zones, respond strongly to moving stimuli
● Hypercomplex cells = orientation dependent, have threshold-like boundaries in their
receptive fields that determine if it will respond
● Receptive fields become larger and more specialized from simple ​➝ complex
● In visual cortex, cells are grouped together in columns perpendicular to the surface
● Tuning properties are constant within a column of cortex
● Across columns, there is a smooth transition between properties
● Damaging either stream could produce different deficits (agnosias)
● Prosopagnosia- inability to recognize faces, occurs after damage to the fusiform gyrus

Audition
● Sound waves are a propagating, periodic disturbance of air molecules
● Alternating patterns of compression and expansion (rarefaction)
● Amplitude = intensity / volume (loudness is a property of perception)
● Frequency = pitch; number of compressions per second
● Spectral Analysis = representation of the sum of single-frequency tones

● Hair cells are auditory receptors between basilar and tectorial membrane in the cochlea
● Sound transductions occurs in the organ of corti
● Movement of hair cells causes an electrical potential
● Basilar membrane contains the hair cells and the kinocilium (special)
● Tectorial membrane moves back and forth to create impulses
● Mechanical channel:
1) K+ entering the hair cell causes a depolarization
2) Causes voltage-gated Ca+ channels to open
3) Causes neurotransmitter vesicles to bind to the membrane and go out to the receptor of
the postsynaptic cell
● Cochlear endolymph is highly concentrated in K+
● Tip links connect cilia mechanically so that the ion channels are linked
● Inner hair cells = afferent to the brain (sensation)
● Outer hair cells = efferent back out to the ears (amplification) hit the tectorial membrane
and increase the size of the action potential
● Apex- thick and floppy, low frequency sounds, inside of the spiral
● Base- thin and stiff, high frequency sounds, outside of the spiral
● Place theory- best explains high frequency sounds
● Frequency theory- best explains low frequency sounds
● Volley principle- auditory nerve as a whole produces impulses; no individual neuron hits
a particular frequency
●

Most info goes to the primary auditory cortex in the superior temporal cortex

● Cues for sound localization:
1) Sound shadow- differences in intensity in each ear (high f)
2) Time of arrival- which ear the sound reaches first
3) Phase difference- location on the wave (low f)
(ex
...

● Insula is in the primary taste cortex (emotions related to sensory input)
● No decussation (processed in ipsilateral side of brain)
● Genetic factors and hormones can account for some differences in taste sensitivity, also
related to number of fungiform papillae

Olfaction
● Olfactory cells line olfactory epithelium in rear of nasal passage
● Receptors located on cilia, which extend from cell body into mucous
● Highly responsive to some related chemicals and not others

1) G-protein (​Golf​), activates adenylate cyclase

2) Produces cyclic AMP, which
3) Opens channels that permit Na​+​ and Ca​2+​ entry (mostly Ca​2+​), thus depolarizing the
neuron​
...
extensor)
● Fast-twitch: fast contractions (ex
...
long distance running) aerobic, do not
fatigue
● Fused tetanus- twitches are so frequent that the muscle contracts smoothly
● Muscle tension is maintained by feedback (spinal cord receives input from the muscles)
● Muscle spindle- detects stretching, embedded in muscle fibers, parallel to muscle
● 2 types of proprioceptive feedback in muscles:
1) Myotactic reflex ➝ muscle spindles ➝ contraction
2) Reverse myotactic reflex ➝ golgi tendons ➝ relaxation

Cerebral Cortex
1
...
Posterior parietal cortex- keeps track of position of body relative to the environment
(external prompts)
3
...
Supplementary motor cortex - organizes rapid sequence of movements in a specific
order

(internal prompts)

- active seconds before the movement



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