NRSC 428 exam 2 review questions

How is the somatosensory system organized?

Primary afferents are located in the dorsal root ganglia and send processes into the dorsal horn of the spinal cord

What is the morphology of somatosensory neurons?

-continuous peripheral and central components

-pseudounipolar so connected to the cell body by a single process

• How do stimuli evoke electrical signals in these neurons?

when the membrane is stretched, ion channels open

-encapsulation helps to tune the afferent fiber and reduce the threshold for action potential

-touch, proprioception. pain, temp, itch, non-discriminative touch

• What are the different adapting properties of these neurons?

-slowly adapting is static, will have a constant firing rate throughout the stimulus

-rapidly adapting is dynamic and will fire at the onset and offset of the stimulus

• What are the different mechanoreceptors in the skin and what are their properties?

Merkel: shape and texture; small receptive fields; slow adapting

Meissner: flutter; small receptive field; rapidly adapting

Ruffini: stretch; large receptive fields; slow adapting

Pacinian: vibration; large receptive fields; rapidly adapting

• What are dermatomes?

a dorsal root ganglion and its spinal nerve

• What are the different proprioceptors and what are their properties?

Muscle spindle: found in muscle, wrapped around intrafusal muscle fibers and respond to stretch

Group 1a= rapid

group 2 = sustained

golgi tendon organs: found in tendons, group 1B afferents

• What are the ascending pathways for somatosensory signals?

Goes through dorsal root ganglia to dorsal horn. Ascends ipsilaterally through dorsal column, synapses on dorsal column nuclei in the medulla. Decussates and synapses at the ventral posterior complex of the thalamus. goes to the somatosensory cortex

• What are the brain (central) regions that receive somatosensory signals?

ventral posterior complex in the thalamus, somatosensory cortec

What is a somatotopic map? How does this map change due to plasticity

area 1 and 3b receive cutaneous stimuli

-3a receives proprioceptive input

-2 integrates tactile and proprioceptive stimuli

-nueons form functionally distinct column

-reorganization of the somatosensory cortex happens by spreading of adjacent areas

What is nociception and what are the properties of the fibers/neurons that mediate these signals?

-pain

-involves specialized nociceptors

-Adelta and C fibers

Type 1 aD= mechanical and chemical stimuli

-type 2 AD= heat

What is first and second pain?

first: sharp immediate pain, Adelta fibers

second: long lasting, dull burning, C fibers

What are the receptors that help transmit pain?

nociceptors; free nerve endings

How does pain travel from the periphery to the brain?

enters grey matter of dorsal horn, decussate, travels through anterolateral tract to the brainstem and thalamus

What brain regions receive pain input?

somatosensory cortex, brainstem, amygdala, insular cortex, anterior cingulate cortex,

What are the mechanisms of peripheral and central sensitization?

Peripheral: due to injury, you have nociceptors producing neurotransmitter contribute more to the inflammation. immune cells can produce cutokines and growth factors HYPERALGESIA

central: due to high activity in nociceptors, which increases respones above threshold, rapid onset and activity dependent heightened sensitivity of nociceptors, lowers the threshold for action potential. Interneurons can be activated by mechanoreceptors now instead of nociceptive fibers

can also be due to LTP, dissaption of Cl- gradient, or microglia releasing cytokines, ALLODYNIA

What is neuropathic pain?

- chronic, intense pain

-can be due to damaged pathways or arise spontaneously

-constant burning sensation with shooting, stabing or shocks

How can endogenous opioids modulate pain perception

enkephalins, endorphins, dynorphins

-interneurons release them and block the nociceptive afferents from releasing their neurotransmitters

How can mechanoreceptors reduce the activation of dorsal horn projection neurons that signal pain

they can synapse onto inhibitory interneurons that will block the ascending pathway of nociceptors

• Where are opioid-releasing neurons found?

pariaqueductal gray matter

how can endogenous opioids modulate pain perception?

they are found in interneurons and inhibit nociceptors from relasing their neurotransmitters and activating the second order projections

What are the differences between allodynia and hyperalgesia

allodynia is a non-painful stimulus being perceived as painful

-hyperalgesia is a painful stimuli being perceived as more painful

How did Goldman et al. demonstrate that adenosine mediates the anti nociceptive effects of acupuncture?

adenosine gets released during acupuncture

-adenosine agonist, CCPA, mimics the analgesic effects

-adenosine receptor knockouts cause hyperalgesia

What are fEPSPs and why did Goldman et al. measure activity in the anterior cingulate cortex?

field EPSPs, anterior cingulate cortex is needed for the perception of pain

What issues with rigor can be identified in Goldman et al.

-used T test instead of anova, no blinding, no randomization, diff genders

What are the main structures of the eye?

-Scelera: whites of eyes that turn clear in front of the eye

-Uveal tract: contains the iris, choroid, and cilary body

-Retina: contains photreceptors

-vitreous humor contains phagocytic cells that clear debris and blood

-cornea and lens refract light

How does light travel through the eye and retina

goes through all layers first, then activates the retina

-ganglion cells-> amacrine cells-> bipolar cells-> horizontal cells-> photoreceptors

What are the main structural features of the retina?

-contains rods and cones

-rods have high sensitivity and low visual acuity

-cones have low sensitivy and high visual acuity

What are the cells/layers of the retina

-photoreceptors

-horizontal cells

-bipolar cells

-amacrine cells

-ganglion cells

How does the pigment epithelium support the retina?

-helps recycle the discs of the photoreceptors

-engulfs the tips

What is the response of photoreceptors to light and how is this mediated

-hyperpolarization in response to light

-light causes cis retinal to change conformation to all trans

-this causes a conformational change in rhodopsin, which activates the GPCR transducin

-this activates phosphodiesterase which breaks down cAMP so cAMP gated ion channels are shut

What are the similarities and differences between rods and cones?

rods- night, fully saturated w light, low visual acuity, high sensitivity, more plenty, convergence, detect low lever of light

What structures/cells/circuits enhance visual acuity?

horizontal cells cause lateral inhibition bc when depolarized, they release GABA back onto all the photoreceptors

-fovea high high packing of cones and no rods, so it has the highest acuity.

-also displaces the inner layers and blood vessels to reduce light scattering

How is color vision achieved in cones

respond to diff wavelengths of light, short medium and long

What are the responses of ON-center and OFF-center ganglion cells to light in the surrounding and center of receptive fields?

-On center:

lihgt hyperpolarizes center cone-> does not activate mGluR6 receptor so channels remain opened-> depolarizes bipolar cell-> depolarizes ganglion cell. Surround cones depolarized-> activate horizontal cells that release GABA to further hyperpolarize center cone

What is the circuitry (cells, neurotransmitters, receptors) that mediates ON-center and OFF-center responses

-mGluR6 vs ionotropic AMPA receptor

-bipolar cells, horizontal cells, and gnalgion cells.

-glutamate, gaba

-Na+ channels

What is lateral inhibition?

horizontal cells release GABA when activated

How does light in the surrounding receptive field change ganglion cell activity? How is this mediated

via lateral inhibtion, diffuse light slwos down firing rate

-they are better to light differences between receptive field and surrounding area

-the concentric ring outside antagonizes the response in the receptive field

-with diffuse light, surrounding cone cells are hyperpolarizaed and the horizontal cell is less active and no longer hyperpolarizes the center cone

How does light information travel from the retina to the primary visual cortex?

goes to retina, then optic nerve, optic chiasm, optic tract, visual cortex

What are the targets regions for retinal ganglion axons? What are the functions of these regions?

-visual cortex

-suprachiasmatic nucleus (circadian rhytyms)

-prectum(pupillary reflex) goes to edinger-westphal nucleus

-superior colliculus(controlling eye movemnt)

-lateral geniculate nucleus in thalamus (relay to visual cortex)

How does binocular visual information come together at the optic chiasm and where is it integrated along the visual pathway?

-integrated in the striate cortex at the ocular dominance column boundaries

-overlapping of both visual fields

-at optic chiasm, fibers from the same side of the visual field project in the same optic tract

How are visual maps organized in the LGN and striate cortex?

-visual information remains segragates in LGN

-the area of the striate cortex is divided by visual field

• What light stimuli/signals do cortical neurons respond to?

-respond to light-dark bars or edges with certain orientations

-can also be tuned to direction of motion stimulus

What are cortical layers? What are the cell types found there? How do the layers relate in a columnar fashion?

-diff layers of the striate cortex

-LGN has inputs into layer 4

-other layers have interlaminar connections

-Stellate cells are in layer 4C

-vertical penetration has the same response

What are the bands of the LGN and what information do they convey? How do these bands correspond to different types of retinal ganglion cells?

-they are segragation of of right and left eyes

-layers 1 and 2 are magnocellular layers

-layers 3-6 are koniocellular layers

-P type: small field, color sensitive

-M type: large field, sensitive to movement

-Magno-> terminates in layer 4cA

-parvo_> terminates in layer 4cB

What are the extrastriate regions and what information is transmitted via the dorsal and ventral pathways/streams?

-not in the straite cortex

-V5(MT) responds to direction of a moving edge

-V4 neurons are selective to color

-dorsal path= spatial vision, goes to MT

-ventral is for object recognition-> goes to V4

What is sound and how is it transmitted to the inner ear

-pressure waves

-amplified by pinna

-middle ear turns it from air to liquid to go to oval window and push fluid to inner ear

-tensor tympani and stapedius muscle contract to modulate energy transmission

What is the structure of the cochlea and how is "sound" perceived?

coil; its a tonotopical map

-high frequencies at basal and low frequencies at apex

-cochlear partition separats scala vestibuli and scala tympani

-scala media contains organ of corti

-cochlea trasmits sound pressure waves into neural impulses

What is the tonotopic map of the cochlea?

diff mappings of frequencies

How do sound waves initiate auditory transduction? How can outer hair cells modulate sound perception?

-hair cells sit on top of basilar membrane

-traveling waves create a shearing motion between the membrane, bending the sterocilia

-inner hair cells are the main sensory receptor

-outer hair cells when active shorten prestin and it is thought to modulate the motion of the basilar membrane

What is the structure of a hair cell and how does mechanoelectrical transduction occur?

has a hinge and sterocilia increasing in length

-bathed in scala media

-sound causes a shearing motion and stretches the tip links of hair cells opening hcMET

-causes transmitter release from the basal end

What is the polarity of a hair cell bundle? Does it respond equally to displacement in any direction?

-no, depolarizes when parallel

-hyperpolarization oppoisite way

-has to go to tallest sterocilium

How do hair cell responses encode frequency of the sound wave?

frquency is encoded in graded potential

What ions mediate depolarization and repolarization of hair cells and how?

K+ and Ca+2

-K+ is in endolymph and goes out basilar membrane for repolarization

-K+ facilitates repolarization

How is frequency encoded in the auditory nerve and how does this relate to cochlear implants?

tonotipic map helps encode frequencies about 3kHz where the biphasic response stops

-cochlear implants partially employ the tonotopic map of the cochlea

How is sound localization accomplished? What are the differences in the anatomy and qualities of sound used for localization of high and low frequency sound waves?

MSO and LSO, interaul time differences and intensity difference

-low freq=MSO

-high freq=LSO

What are the main components of the inner ear dedicated to vestibular function?

-2 otolith organs (utricle and saccule)

-3 semicircular canals

OTOLITH

-hair cells are in macula, response to tilt

SEMICIRCULA

-ampulla w cupula

What are the key anatomical and morphological structures that enable detection of the different head movements?

-movement in the direction of kinocilium

What are the typical vestibular nerve fiber responses to the different head movements (tilt, translation, and rotation)?

TIlt: sustained response, depolarization one way, hyperpolarization other way

TRanslation: transient. accelaration is depolarization, constant velocity is no firing, deaccelerating is hyperpolarization

• Where do vestibular signals go in the CNS?

-thalamus

-cortex

-cerebellum

-spinal cord

-motor nuclei

What are the circuitry and sensorimotor responses for the VOR and VCR/VSR?

VOR: bilateral connections from each side of the head enable relaxtion and contraction of antagonistic muscle pairs in the eye (aka sthe medial muscle and the lateral muscle)

-MEDial

medial vestibulat nuclei go to medial longitudianal fasciculus to reach the medial part of the ventral horn

LATERAL

-lateral vestibular nucleus sends axons via the lateral vestibular tract to contact ventral horn neurons

-superior and lateral vestibular nuclei send projection to the VPC which is important for self movmement and oritentation in space

• What is the anatomy of the human olfactory system

cilia on apical sie of olfactory neuron that projects to cribriform plate, glomerulus, mitral cells, and then to olfactory bulb

• How does olfaction compare across species

not as important in humans, our worst one

• What is the structure/morphology of olfactory receptor neurons (ORNs)?

apical end have actin protrusions, where odorant detection takes place

basal end has axons that connect to glomerulus

pcontains within an epithelial sheet

-bipolar cells with unmyelinated axons at basal end

How can stem cells regenerate the ORNs?

they accumulate on basal side and divide

How are receptor potentials generated in ORNs?

-cilia are actin protrusions to increase surface area

-scaffolding protein localize odorant receptors and signaling transduction molecules

-graded potential in the apical dendrite is converted to an action potential in the basal axon

What are the receptor proteins for odor and how are they distributed in ORNs and across the olfactory system?

odorant receptor preotins

-largest known family of genes

-7 transmembrane domains

-Golf

• What are the molecular mechanisms of odorant transduction and repolarization?

Olfactory specific G protein and olfactory specific adenylyl cyclase 2 is used

-Na+ and Ca+ depolarize

-Ca+2 induces Cl- efflux which is responsible for most of the depolarization

-Ca+2 also activates Na/Ca exhanger to repolarize the neuron

-Ca+ also activates CAMk2 and phosphodiesterase to turn GTP back to GDP and cAMP back to ATP

How is odorant information relayed to the brain?

goes from mitral cell to the rest of the brain via the lateral olfactory tract, most the pyriform cortex

What is the degree of odorant specificity and how is that maintained between the ORN, glomerulus and pyriform cortex?

ORN expreses one receptor protein transcribed from one allele

0can respond to single odorants or respond broadly to several

they have specifc mitral cells

-individual ordorants activate 1 or 2 distinct glomeruli

What is the vomeronasal system?

for pheromones and kairomones, projects to accesory olfactory bulb. not as important in humans